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A new response-time measure of object persistence in the tunnel effect
Acta Psychologica 123 (2006) 73–90 www.elsevier.com/locate/actpsy
A new response-time measure of object persistence in the tunnel eVect Yousuke Kawachi ¤, Jiro Gyoba Department of Psychology, Graduate School of Arts and Letters, Tohoku University, 27-1 Kawauchi, Aoba-ku, Sendai 980-8576, Japan Received 18 October 2005; received in revised form 22 January 2006; accepted 18 April 2006 Available online 14 June 2006
Abstract The recognition of information about an object is facilitated by a preview of the information concerning that object. This facilitation is regarded as evidence for the representational persistence of the object. It is not known, however, if such facilitation is obtained even under the tunnel eVect, in which a moving object is temporarily occluded. This facilitation may be a new way to measure the representational persistence of a moving object in the tunnel eVect. We addressed this question by a “samediVerent” judgment task of a target symbol (“ⴰ” or “+”), drawn within the moving object, before and after encountering the occluder. Response times (RTs) were shorter when the object reappeared with spatial continuity at the proper place than it reappeared at the improper place, as in Experiments 1 and 3. Thus, facilitation was obtained even in the tunnel eVect. When the occluder was invisible and deletion/accretion cues along the contour of the occluder were either removed (Experiment 2) or given improperly (Experiment 4), no facilitation was found. These results clearly indicate that the facilitated recognition was caused by amodal integration of the persisting representation from the unoccluded and modal phases. The present study demonstrates that the facilitated recognition (RT measurement) can be used to investigate the representational persistence in the tunnel eVect. © 2006 Elsevier B.V. All rights reserved. PsycINFO classiWcation: 2323 Keywords: Moving object; Spatial continuity; Representational persistence; Tunnel eVect; Response time
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1. Introduction When objects move in the real world, visual inputs from the moving objects change constantly. Moving objects are often occluded, leading to temporary disruption of the inputs. Despite these input gaps, representations of the moving objects must be maintained to perceive the apparent continuity of the visual environment. Several studies have focused on the factors underlying the representation of moving objects (e.g., Noles, Scholl, & MitroV, 2005). Little research, however, has examined situations in which the moving objects are temporarily concealed behind an occluder. 1.1. The tunnel eVect An object moves and gradually disappears behind an occluder. Then, the object reappears on the other side of the occluder. In this situation, the object is temporarily invisible. Nonetheless, humans perceive that the object that reappeared is identical to the object that disappeared previously, suggesting that the representation of the object is maintained during its disappearance. This phenomenon, Wrst reported by Michotte and Burke, is called the tunnel eVect (Burke, 1952; Michotte, 1946/1963, 1950; Michotte, Thinès, & Crabbé, 1964/1991). Previous behavioral studies of the tunnel eVect have relied primarily on verbal reports by subjects. These verbal reports appear to indicate that this eVect is phenomenologically robust. Moreover, if the use of the verbal reports can be optimized and used rigorously, it would be helpful to measure the tunnel eVect (Thinès, 1991). However, the verbal reports have some shortcomings such as higher-level biases and the inability to measure quantitatively (Flombaum, Kundey, Santos, & Scholl, 2004; Flombaum & Scholl, in press). In this study, we used the indirect measure of the response time (RT) to examine the information required to promote the representational persistence of an object moving behind an occluder. As far as we know, this is the Wrst attempt to quantify the persistence of an object representation in the tunnel eVect with an objective response-time measure (but see Wagemans & d’Ydewalle, 1989, for related work with the RT measure). We describe the measurement of response time in detail below. 1.2. The index of the persistence of object representation In an experiment conducted by Kahneman, Treisman, and Gibbs (1992), two objects that each contained a letter within them were presented. The letters were then removed, and the objects moved brieXy. Once the objects stopped moving, a target letter appeared within one of the objects. The participant’s task was to name that target letter as quickly and accurately as possible. The response times were shorter when the initially presented letter was re-presented within the same object than when the letter was shown within a diVerent object. This facilitated recognition of information about an object is regarded as an indication that the object representation persists (e.g., Gordon & Irwin, 1996; Henderson, 1994; MitroV, Scholl, & Wynn, 2005; Noles et al., 2005). Kahneman et al. (1992) proposed that the representation of a moving object persists in the tunnel eVect. If the tunnel eVect is perceived, preview of information on an object may facilitate the recognition of that information. They did not, however, examine this suggestion experimentally. In this study, we used a similar measurement to investigate persistence of the representation of a moving object that is temporarily occluded, instead of the traditional verbal methods.
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1.3. Spatiotemporal continuity and the surface features of the moving object Previous work (reviewed in Scholl, 2001) has demonstrated that the maintenance of a persisting object representation relies upon spatiotemporal continuity in an object’s trajectory. This study addressed whether spatiotemporal continuity in an object’s trajectory through an occluder facilitates the recognition of previewed information associated with the object. Meanwhile, the eVect of non-spatiotemporal properties, such as surface features, has not been previously explored in detail. Previous research has reported that representational persistence is perceived even if the surface features of an object, such as color or size, diVered before and after an occlusion, as long as the constraints of spatiotemporal continuity were met (Burke, 1952). Furthermore, previous research on apparent motion conWrmed that changes in surface features did not aVect the persistence of object representation when all spatiotemporal factors are completely balanced; two Wgures with diVerent surface features, such as colors or shapes, represented the same object (Kolers & Pomerantz, 1971; Navon, 1976; Ramachandran & Anstis, 1983). These Wndings imply that an object representation is created and maintained, based primarily on spatiotemporal continuity, not on surface feature congruity. Surface feature information may be added to the representation later (Leslie, Xu, Tremoulet, & Scholl, 1998). In this study, we also investigated the eVect of surface feature changes by RT measurement. 1.4. The role of deletion and accretion in the tunnel eVect Deletion of surface elements occurs when a moving object gradually disappears behind an occluder, while accretion occurs when it gradually appears. Deletion/accretion cues along the boundaries of an occluder are necessary for the tunnel eVect (Gibson, Kaplan, Reynolds, & Wheeler, 1969; Scholl, 2001; Scholl & Pylyshyn, 1999). Gibson et al. (1969) suggested that it is diYcult to perceive an occluding edge without deletion/accretion cues along the contour of the occluder. When deletion/accretion cues are removed or are improper and the occluder is invisible, the tunnel eVect is barely perceived; the persisting representation of the moving object is not amodally integrated from the unoccluded and modal phases (Yantis, 1995). Therefore, the facilitated recognition of information associated with an object may attenuate under these conditions. Investigation of the eVect of deletion/accretion cues may help us to better understand the role of these cues in representational persistence in the tunnel eVect. 1.5. Purposes of the present study This study sought to examine if the visual system can maintain the representation of a moving object that becomes temporarily occluded using indirect, but psychophysical performance measures, that is, RT measurements, instead of verbal reports. In Experiments 1 and 3, we examined the eVects of spatial continuity on the representation of a moving object and the update of the representation from surface feature changes. We manipulated the spatial continuity of the object (if the object reappeared at the proper place after being occluded) and the congruity of the surface features before and after occlusion. We then asked the participants to judge whether a target pattern depicted inside the object was the same or diVerent after the object was occluded as before occlusion. We expected that the “same” response would be faster when the object maintained spatial continuity than when
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it did not. We also anticipated that the “same” response would be signiWcantly faster when the object maintained feature congruency as well as spatial continuity. In Experiments 2 and 4, we conducted the same task with the tunnel eVect barely perceivable due to either a lack of accretion/deletion cues along the occluder’s contour (Experiment 2) or improper accretion/deletion cues (Experiment 4). If facilitated recognition of information about a temporarily occluded object was not observed in the absence of these cues, it would provide evidence that the representational persistence of the object occurs by amodal persistence of the moving object behind the occluder. 2. Experiment 1: The tunnel eVect with a visible occluder In Experiment 1, we examined the dependence of the facilitated recognition of information for an object on the constraint of spatial continuity. This experiment provided evidence for representational persistence in the tunnel eVect and a new behavioral demonstration of the tunnel eVect, which is independent of verbal reports. In addition, we examined if recognition was facilitated by the observation of identical surface features. 2.1. Method 2.1.1. Participants Sixteen students from Tohoku University participated in Experiment 1. The data from two participants were eliminated because their rates of correct responses were lower than 90%. All participants had either normal or corrected-to-normal vision. 2.1.2. Stimuli The target object, a moving square (0.43 £ 0.43 deg), was generated by a computer (SHARP X68030) and presented on a CRT display (SHARP CZ-621Z). The participants sat approximately 172 cm away from the display, with their heads resting on a chin rest. A grey vertical occluder (5.8 £ 1.3 deg) was located at the center of the display. The square moved 5.64 deg/s horizontally from the right or left side of the display. As it passed behind the occluder, the object temporarily disappeared. After 230.50 ms, it reappeared on the opposite side of the occluder (Fig. 1). A white Wxation dot was presented 0.27 deg from the left or right of the occluder. To investigate the eVects of spatial continuity information on representational persistence, we manipulated the place of reappearance of the occluded object. The object reappeared at the correct place (with continuity) on half of the trials and at a wrong place on the remaining trials (with discontinuity of a 1.5 deg vertical spatial gap). The surface features (color or size) of the object were also manipulated. In the color condition, participants were presented with a moving square that was colored either red (48.70 cd/m2) or green (49.11 cd/m2). In the size condition, individuals saw a large square (0.43 £ 0.43 deg) or a small square (0.3 £ 0.3 deg). DiVerentially sized squares were always colored green. On half of the trials, the surface features were the same before and after the occlusion, while on the remaining trials, the object reappeared after the occlusion with diVerent surface features. The symbols (“ⴰ” or “+”) were used as the target pattern drawn at the center of the object. The target pattern was approximately 0.23 deg in size and colored white. On half of the trials, the target pattern did not change from before to after the occlusion. On the
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TIME
Spatial continuity Same Target Pattern
Spatial continuity Different Target Pattern
Spatial discontinuity (1.5 deg) Same Target Pattern
Spatial discontinuity (1.5 deg) Different Target Pattern
Fig. 1. Schematic presentation of the tunnel event stimuli used in Experiment 1. In half of the trials, the surface features changed after occlusion (red to green or green to red under color changing condition; small to large or large to small under size changing condition). Dotted lines indicate the virtual trajectories of the object movements. These lines did not appear on the display.
remaining trials, the depicted target pattern changed after the object reappeared on the other side of the occlusion. 2.1.3. Procedure We asked the participants to judge whether the target pattern was the same or diVerent before and after the moving object was occluded. The participants were asked to push either the “same” or “diVerent” response keys as rapidly and accurately as possible. Throughout each trial, the participants were asked to focus on the Wxation dot as much as possible. The participants were also asked to ignore the spatial continuity and surface features of the object, paying sole attention to the target patterns. Each participant performed at least 20 practice trials prior to the experimental trials. Each block of 128 trials, consisting of blocks of color-leftward motion, color-rightward motion, size-leftward motion, and size-rightward motion, was counterbalanced for each participant. Half of the participants performed the color change blocks Wrst, while the other half conducted the size change blocks Wrst. Within each block, the spatial continuity, surface features, and target patterns were randomly manipulated. The positions of the response keys were also counterbalanced for each participant. 2.1.4. Measurement Response times were measured from the appearance of the leading edge of the moving object on the opposite side of the occluder until the participant pressed a response key.
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2.2. Results Error trials were removed (6.17% of all trials) from analysis. RTs that exceeded the corresponding cell means for each participant by greater than two standard deviation units were also excluded (3.15% of all trials). The mean RTs of the combined data regarding the size and color conditions are shown in Fig. 2. A 2 (spatial continuity: continuity or discontinuity) £ 2 (feature type: size or color) £ 2 (feature congruency: same or diVerent) £ 2 (target congruency: same or diVerent) ANOVA was used to analyze the participants’ mean RTs. Overviews of the results of ANOVA are presented in the Appendix as Table 1. As can be seen in Table 1, the main eVect of the spatial continuity was signiWcant, while the other main eVects were not signiWcant. There was a signiWcant interaction between spatial continuity and target congruency. Most importantly, we observed a signiWcant three-way interaction between spatial continuity, feature congruency, and target congruency. Post hoc analysis of the spatial congruity £ feature congruency £ target congruency interaction revealed the following results. First, responses were facilitated when spatial continuity was maintained, despite feature and target congruency. For all combinations of feature and target congruency, RTs were shorter under conditions of continuity than discontinuity (F(1, 52) D 61.21, p < .001, for the combination of the same feature and the same target; F(1, 52) D 35.14, p < .001, for the same feature and a diVerent target; F(1, 52) D 108.62, p < .001, for a diVerent feature and the same target; and F(1, 52) D 34.64, p < .001, for a diVerent feature and a diVerent target, respectively). Second, responses were facilitated by the combination of the same features and targets, or by the combination of diVerent features and targets. When the target was the same under 580 560
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Response time (ms)
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500 496.45 ms 487.92 ms
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481.16 ms 474.35 ms
460 440 spatial continuitysame surface feature
spatial continuitydifferent surface feature
spatial discontinuitysame surface feature
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Fig. 2. Mean response times for each condition in Experiment 1. Neither the main nor the interaction eVects of feature type (size/color) were signiWcant. Therefore, the mean RTs of the combined data of size and color conditions are shown. The error bars display the standard errors of the means.
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continuity conditions, the mean RT was shorter for the same feature than for a diVerent feature [F(1, 52) D 4.60, p < .05]. For a diVerent target under continuity conditions, the mean RT was shorter for diVerent features than for the same features [F(1, 52) D 8.26, p < .01]. When the target pattern was same under discontinuity conditions, the mean RT was shorter for the same surface features than for diVerent surface features [F(1, 52) D 53.69, p < .001]. For a diVerent target under discontinuity conditions, the responses were faster for the diVerent surface features than for the same surface features [F(1, 52) D 8.75, p < .005]. Third, a response of “same” was made signiWcantly faster under the combined condition of spatial continuity and unchanged features, but was made slower by the combined condition of spatial discontinuity and diVerent features. When the surface features were held constant under continuity conditions, the same target prompted a faster response than did a diVerent target [F(1, 52) D 8.30, p < .01]. For a diVerent surface feature under continuity conditions, there was no signiWcance diVerence between the same target and a diVerent target [F(1, 52) D 0.61, p D .439]. When the feature was changed under discontinuity conditions, a diVerent target prompted a faster response than did the same target [F(1, 52) D 9.04, p < .005]. For the same surface under discontinuity conditions, there was no signiWcance diVerence between the same target and a diVerent target [F(1, 52) D 1.68, p D .200]. 2.3. Discussion For all combinations of surface features and target patterns, the responses were facilitated in the continuity, but not the discontinuity, conditions. These results demonstrate that when spatial continuity of the moving object was maintained, the representation of the object persisted in the tunnel eVect, even when the surface features or target pattern diVered following the occlusion. This result supports the Wndings that spatiotemporal properties play an important role in the perception of persisting objects even following surface feature transformation (Burke, 1952; Michotte et al., 1964/1991). Moreover, when surface features were the same under continuity conditions, the “same” response was facilitated (the mean RT was the shortest) more than all of the other conditions. This result indicates that the representation of a moving object persists in accordance with spatial continuity in the tunnel eVect. At the same time, it also provides evidence that facilitated recognition is obtained even under the tunnel eVect and validates the use of RT measurements to examine the tunnel eVect. In the present experiment, surface features were also found to have a small but signiWcant eVect on recognition of the same target (the “same” response). When the spatial continuity of an object was maintained, responses were facilitated by the combination of unchanged surface features and an unchanged target. Accordingly, these results seem to indicate that surface feature information does not have a decisive eVect; instead, this information has a supplementary inXuence on the persistence of object representation. However, changes in the surface features under spatial discontinuity conditions lead to ‘diVerent’ responses that are faster than the ‘same’ responses. Therefore, there is also the possibility that these results can be explained by a possible response bias eVect, which means that the observers may need to suppress the responses to the surface features when the surface features do not match but the target was the same. In short, it is unclear whether the surface feature eVect is due to surface features per se or to the response bias. We also discuss this problem in Experiment 3 and in the General discussion.
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3. Experiment 2: An invisible occluder and the removal of accretion/deletion cues In Experiment 1, we examined whether the facilitated recognition of information associated with an object depends upon spatiotemporal continuity in the object’s motion. We conducted Experiment 2 to conWrm whether facilitation resulted from the persistence of the object representation in the tunnel eVect. This experiment may also strengthen the behavioral demonstration of the tunnel eVect provided by the results of Experiment 1. Experiment 2, therefore, was a repeat of Experiment 1 with the exception that deletion/ accretion cues were removed and the occluder was made invisible, rendering the tunnel eVect imperceptible. An occluding edge is not perceived without the presence of deletion/ accretion cues along the contour of the occluder (Gibson et al., 1969; Scholl & Pylyshyn, 1999). We expected that these alterations made in Experiment 2 would disrupt the persistence of object representation under spatial continuity conditions, reducing the facilitation seen in Experiment 1. 3.1. Method 3.1.1. Participants Sixteen new students from Tohoku University participated in Experiment 2. The data from two participants were discarded, because their rates of correct responses were lower than 90%. All participants had either normal or corrected-to-normal vision. 3.1.2. Stimuli The stimuli were identical to those in Experiment 1, with the two following exceptions. First, when the leading edge of a moving object touched the proximal edge of an occluder, the object disappeared instantly. Then, when the trailing edge of the moving object touched the distal edge of the occluder, the object reappeared instantly. Second, the occluder was invisible (the occluder had the same luminance value as the background). Fig. 3 displays an example of the stimulus sequences used in Experiment 2.
No deletion/accretion cues and an invisible occluder (Experiment 2) An invisible occluder (Experiment 3) Reversed virtual occlusion and an invisible occluder (Experiment 4)
TIME Fig. 3. Schematic presentation of the stimuli used in Experiments 2–4. Dotted lines indicate the invisible virtual occluder. These lines did not appear on the display.
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3.1.3. Procedure and measurement The procedure was identical to that described for Experiment 1, except that we asked the participants to judge whether the target pattern was the same or diVerent before the disappearance as after the reappearance of the object. Measurements were performed as described in Experiment 1. 3.2. Results Error trials were removed (7.28% of all trials) from analysis. RTs that exceeded the corresponding cell means for each participant by greater than two standard deviation units were also excluded (3.10% of all trials). The mean RTs for the size and color conditions are shown in Figs. 4a and 4b. The results demonstrated that the same/diVerence responses were not modulated by spatial continuity. A 2 (spatial continuity: continuity or discontinuity) £ 2 (feature type: size or color) £ 2 (feature congruency: same or diVerent) £ 2 (target congruency: same or diVerent) ANOVA was used to analyze the participants’ mean RTs. Overviews of the results of ANOVA are presented in Appendix as Table 1. As can be seen in Table 1, the main eVect of feature type was signiWcant. While the RTs were shorter for the size condition than for the color condition, the main eVects of spatial continuity were marginally signiWcant. There was a marginally signiWcant interaction between spatial continuity and target congruency.1 Moreover, there were no signiWcant three-way interactions. 3.3. Discussion Although the main eVect of feature type was signiWcant, neither the main nor the interaction eVects of spatial continuity were signiWcant. This result suggests that the slower response times found in the discontinuous (compared to the continuous) motion condition of Experiment 1 were not simply due to the greater distance that the objects in this condition traversed while occluded. Accordingly, we did not observe any facilitation similar to that obtained in Experiment 1. This lack of facilitation may result from the removal of deletion/accretion cues and the invisible occluder because no amodal integration of the object’s representation was produced in this case. Therefore, it is likely that the reappearing object in Experiment 2 was perceived as a new object under condition in which the tunnel eVect was barely perceptible. These results support the possibility that the persistence of object representation behind the occluder produced the facilitated recognition seen in Experiment 1. 4. Experiment 3: The tunnel eVect with an invisible occluder While facilitated recognition of information on the same object was found in Experiment 1, no facilitated recognition was observed in Experiment 2. In Experiment 3, we examined the dependence of this diVerence in the results of Experiments 1 and 2 on the
1
Although this marginal eVect could reach signiWcance with greater statistical power, it is clear that this marginal eVect is far weaker than the eVect for the same conditions in Experiment 1.
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Response time (ms)
560
different target
same target
540 542.71 ms 535.32 ms
520
523.81 ms 515.64 ms
517.28 ms
533.68 ms 523.82 ms
520.09 ms
500 480 460 440 spatial continuitysame surface feature
spatial continuitydifferent surface feature
spatial discontinuitysame surface feature
spatial discontinuitydifferent surface feature
Fig. 4a. Mean response times for each size condition in Experiment 2. The error bars show the standard errors of the means.
580 560
different target
same target
Response time (ms)
540
548.69 ms
552.04 ms
541.44 ms
537.22 ms
520
564.67 ms
533.76 ms 527.67 ms
523.77 ms
500 480 460 440 spatial continuitysame surface feature
spatial continuitydifferent surface feature
spatial discontinuitysame surface feature
spatial discontinuitydifferent surface feature
Fig. 4b. Mean response times for each color condition in Experiment 2. The error bars indicate the standard errors of the means.
visibility of an occluder. This experiment may generalize the behavioral demonstration of the tunnel eVect using the RT measure.
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Previous studies reported that the tunnel eVect occurs even when an occluder is invisible (Michotte et al., 1964/1991). Thus, if deletion and accretion cues were given properly despite the use of an invisible occluder, we would expect that the tunnel eVect would still occur, and recognition would be facilitated. 4.1. Method 4.1.1. Participants Sixteen new students from Tohoku University participated in Experiment 3. The data from two participants were discarded because their rates of correct responses were lower than 90%. All participants had either normal or corrected-to-normal vision. 4.1.2. Stimuli The stimuli were identical to those described in Experiment 1, with the exception that the occluder was invisible (the occluder had the same luminance value as the background). Fig. 3 displays an example of the stimulus sequences used in Experiment 3. 4.1.3. Procedure and measurement The procedure and measurement were identical to that of Experiment 2. 4.2. Results Error trials were removed (6.34% of all trials) from analysis. RTs that exceeded the corresponding cell means for each participant by greater than two standard deviation units were also excluded (2.66% of all trials). The mean RTs of the combined data regarding the size and color conditions are shown in Fig. 5. A 2 (spatial continuity: continuity or discontinuity) £ 2 (feature type: size or color) £ 2 (feature congruency: same or diVerent) £ 2 (target congruency: same or diVerent) ANOVA was used to analyze the participants’ mean RTs. Overviews of the results of ANOVA are presented in Appendix as Table 2. The main eVects of both spatial continuity and target congruency were signiWcant. SigniWcant interactions were found between spatial continuity and target congruency. Post hoc analysis revealed that facilitated responses for the same target were obtained only under spatial continuity conditions. Under these conditions, the same target gave a faster response than a diVerent target [F(1, 26) D 19.71, p < .001]. For conditions of spatial discontinuity, there was marginally signiWcant diVerence between the same target and a diVerent target [F(1, 26) D 3.23, p D .084].2 For both the same and diVerent targets, the responses under spatial continuity conditions were faster than those under spatial discontinuity conditions (F(1, 26) D 41.00, p < .001; F(1, 26) D 16.97, p < .001, respectively). However, in Experiment 3, diVerent from in Experiment 1, there was no signiWcant three-way interaction between spatial continuity, feature congruency, and target congruency (see Table 2 in Appendix).
2
The ‘same’ responses tend to be facilitated under conditions of spatial discontinuity. However, under conditions of spatial continuity, the ‘same’ responses are more robustly facilitated.
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Response time (ms)
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different target
same target 553.06 ms
540
549.13 ms
547.27 ms
537.62 ms
520 500
529.11 ms
527.21 ms 509.97 ms 503.63 ms
480 460 440
spatial continuitysame surface feature
spatial continuitydifferent surface feature
spatial discontinuitysame surface feature
spatial discontinuitydifferent surface feature
Fig. 5. Mean response times for each condition in Experiment 3. Neither the main nor the interaction eVects of feature type (size/color) were signiWcant. Therefore, the mean RTs of the combined data of size and color conditions are shown. The error bars display the standard errors of the means.
4.3. Discussion As in Experiment 1, these results demonstrate that the ‘same’ response was facilitated according to the constraint of spatial continuity. This result indicates that the representation of a moving object persists in the tunnel eVect, regardless of the visibility of the occluder. Therefore, the diVerence in the results between Experiments 1 and 2 may not depend on the visibility of the occluder. Although the mean RT was the shortest under the spatial continuity – feature congruency – same target conditions, the surface feature eVect on the recognition of the same target under spatial continuity conditions, were not observed in Experiment 3, which is inconsistent with the results of Experiment 1. Moreover, the eVect of the surface features was not observed on the recognition of a diVerent target under spatial discontinuity conditions. Hence, we did not Wnd conclusive evidence, which excluded the involvement of a response bias in the surface feature eVect observed in Experiment 1. 5. Experiment 4: Reversed virtual occlusion Experiment 2 demonstrated that a lack of deletion/accretion cues along the contour of occluder resulted in a large decline in facilitated recognition of information within the same object. These results are evidence that this facilitation can only be obtained in stimulus conWgurations in which the participants can perceive the tunnel eVect; thus, deletion/ accretion cues contribute to representational persistence in the tunnel eVect. The possibility remains, however, that the results in Experiment 2 may have been produced by other factors, such as abrupt onsets/oVsets and visual memory decline. Abrupt
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onsets and oVsets of an object are reported to capture attention independent of the participants’ goals or beliefs (Yantis, 1993), momentarily distracting the observers from their task performance. Previous research has also suggested that abrupt onsets/oVsets discard an object representation (Yantis & Jonides, 1984). In addition, the invisible times of the moving object in Experiments 1 and 3 were shorter than that in Experiment 2 (76.24 ms at the maximum). This diVerence might contribute to a decline in visual memory of the object, resulting in the lack of facilitation recognition in Experiment 2. Experiment 4 was conducted to control these factors by using reversed virtual occlusion (Scholl & Pylyshyn, 1999). This experiment may show the strong dependence of the facilitated recognition on the perception of the tunnel eVect. As other experiments cited above, this experiment should support the validity of using the RT measure to analyze the tunnel eVect. 5.1. Method 5.1.1. Participants Eight new students from Tohoku University participated in Experiment 4. All participants had either normal or corrected-to-normal vision. 5.1.2. Stimuli In Experiment 4, we used reversed virtual occlusion (Scholl & Pylyshyn, 1999), in which deletion/accretion cues are improperly given. Fig. 3 displays an example of the stimulus sequences used in Experiment 4. When the leading edge of the moving object touched the proximal edge of the virtual occluder, the trailing edge of the object stopped, while the leading edge moved in the opposite direction of object motion. When the trailing edge of the object touched the distal edge of the occluder, the leading edge of the object reappeared and stopped, while the trailing edge moved contrary to the direction of motion of the object. Using this stimulus conWguration, the objects disappear and reappear gradually at the same rates as those seen in both Experiments 1 and 3. In this experiment, the moving object is visible for the same duration as Experiments 1 and 3. 5.1.3. Procedure and measurement The procedure and measurements were identical to those of Experiments 2 and 3. 5.2. Results Error trials were removed (7.37% of all trials) from analysis. RTs that exceeded the corresponding cell means for each participant by greater than two standard deviation units were also excluded (2.51% of all trials). The mean RTs of the combined data regarding the size and color conditions are shown in Fig. 6. A 2 (spatial continuity: continuity or discontinuity) £ 2 (feature type: size or color) £ 2 (feature congruency: same or diVerent) £ 2 (target congruency: same or diVerent) ANOVA was used to analyze the participants’ mean RTs. Overviews of the results of ANOVA are presented in Appendix as Table 2. This analysis revealed that no facilitated responses were obtained under spatial continuity conditions. All of the main eVects were not signiWcant. No other interactions were observed between spatial continuity and target congruency. Furthermore, there were no three-way signiWcant interactions.
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Response time (ms)
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spatial continuitysame surface feature
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spatial discontinuitysame surface feature
spatial discontinuitydifferent surface feature
Fig. 6. Mean response times for each condition in Experiment 4. Neither the main nor the interaction eVects of feature type (size/color) were signiWcant. Therefore, the mean RTs of the combined data of size and color conditions are shown. The error bars indicate the standard errors of the means.
5.3. Discussion In Experiment 4, we used improper deletion/accretion cues (reversed virtual occlusion) to control for the potential eVects of abrupt onsets/oVsets and visual memory decline in Experiment 2. Reversed virtual occlusion minimizes the perception of the tunnel eVect by the participants. The results of Experiment 4 showed none of the facilitation eVects obtained in Experiments 1 and 3. Therefore, we can rule out the potential confounding eVects of abrupt onsets/oVsets and visual memory decline, allowing us to conclude that the reappearing object is likely to be perceived as a new object in both Experiments 2 and 4, in which the tunnel eVect was barely perceivable. Also, the results of Experiment 4 indicate that the facilitated response seen for spatial continuity in Experiments 1 and 3 cannot be explained by the spatial distance diVerence between the places in which the object reappears alone.3 6. General discussion The purpose of this study was to develop a new RT measure, which could replace subjective verbal reports, by examining whether facilitated recognition of information associated with a previewed object is obtained under the tunnel eVect. In Experiment 1, we found 3
The results of Experiment 4 indicate that the facilitated response under spatial continuity conditions in Experiments 1 and 3 cannot be explained by the diVerence in the spatial distance between the places where the object reappears by itself. However, it still seems to be possible that a larger diVerence in the spatial distance leads to a diVerent pattern of results in Experiment 4, which decreases the eVect of the deletion/accretion cues.
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facilitated recognition of target patterns and surface features when an object emerged from behind an occluder by following a spatiotemporally continuous path. SpeciWcally, the condition in which the surface features were congruent both before and after the occlusion according to the constraint of spatiotemporal continuity strongly facilitated the “same” response. In Experiment 3, the “same” response was facilitated when the spatial continuity of a moving object was maintained, while no clear eVect of surface feature was observed. Such facilitation indicates that the representation of a moving object persists according to the spatial continuity in the tunnel eVect. In contrast, Experiments 2 and 4 utilized conditions in which the deletion/accretion cues were removed. The participants could barely perceive the tunnel eVect. No such facilitation was observed in these experiments. Therefore, the facilitation seen in Experiments 1 and 3 was caused by amodal integration of the object representation followed by perception of the tunnel eVect. The present study clearly indicates that instead of verbal reports, indirect, but psychophysical RT measurements are valid to measure the tunnel eVect. The results of the present study demonstrate that the RT is shorter when the spatiotemporal continuity of the occluded object is maintained and the tunnel eVect occurs compared to when the continuity is not maintained and the tunnel eVect does not occur. The method used in the present study becomes a new method to measure the tunnel eVect, together with other psychophysical methods such as multiple object tracking task through occlusion (Scholl & Pylyshyn, 1999) and change detection task (Flombaum & Scholl, in press). The present results can be interpreted according to the object Wle theory (Kahneman & Treisman, 1984; Kahneman et al., 1992). An object Wle is an episodic representation of the object that persists on the basis of spatiotemporal continuity. If an object moves continuously, its object Wle is maintained. If the motion of the object is discontinuous, the object Wle is discarded, and a new object Wle is formed. In this study, when the motion path of the object was discontinuous before and after the occluder, the object Wle would have been destroyed, requiring the formation of a new object Wle. Therefore, the responses would have been delayed under spatial discontinuity conditions. In contrast, when the motion path of the object was continuous, the object Wle persists. The participants would utilize the previously processed information about the object without creating a new object Wle, resulting in facilitated responses under conditions of spatial continuity. Recent fMRI experiments have begun to specify the neural correlates, which are involved in the tunnel eVect, and provide converging evidence for the Wndings reported here. Olson, Gatenby, Leung, Skudlarski, and Gore (2003) compared the brain activations in the tunnel conditions in the absence or presence of deletion/accretion cues. They demonstrated that the intraparietal sulcus (IPS) as well as the middle temporal (MT) regions are activated in the presence of the cues, suggesting that neurons in the IPS maintain a representation of the brieXy occluded object. The new psychophysical methods developed in the present research would provide more powerful tools to isolate the neural basis of the tunnel eVect. Finally, the eVect of surface features on the representational persistence remains unclear. The results of Experiment 1 suggest the possibility that the feature congruent information may facilitate recognition, but do not exclude a response bias eVect. In addition, the results in Experiment 3 are inconsistent with the results in Experiment 1. Hence, the results of our experiments are not conclusive regarding the role of surface features in visual object persistence. However, together with a number of recent studies using other paradigms like multiple object tracking, object substitution masking, and apparent motion
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(e.g., Flombaum & Scholl, in press; Moore & Lleras, 2005; Saiki, 2003a, 2003b), they seem to converge on the conclusion that surface features do not matter much. 7. Conclusion This study introduces a new RT measure, which analyzes the representational persistence in the tunnel eVect. Using this new measure, instead of the verbal reports, the present research also presents two Wndings. First, the representation of a moving object can be maintained even through occlusion; spatiotemporal information aVects the representational persistence. Second, deletion and accretion cues at the boundaries of the occluder leading to the tunnel eVect contribute signiWcantly to the persistence of object representation during occlusion. Both traditional phenomenological methods and recent neuroimaging studies require exploration of new methods, which do not rely on verbal reports to analyze the representational persistence of occluded moving objects. The psychophysical approach proposed in this study meets the requirements and would contribute to clarify the underlying mechanism of the representational persistence in the tunnel eVect. Acknowledgements We wish to thank Johan Wagemans, Jonathan Flombaum, Brian Scholl, and Rob van Lier for their useful comments, suggestions, and criticism on early versions of this manuscript. We are also grateful for helpful suggestions from an anonymous reviewer. Appendix See Tables 1 and 2. Table 1 ANOVA summaries for each condition in Experiments 1 and 2 Factor
Experiment 1
Experiment 2
SigniWcance
2
SigniWcance
2
Spatial continuity (SC) Feature type (FT) Feature congruency (FC) Target congruency (TC)
F(1, 13) D 80.57, p < .001 F(1, 13) < 0.01, p D .929 F(1, 13) D 3.62, p D .079 F(1, 13) D 0.30, p D .592
.861 .001 .218 .023
F(1, 13) D 4.52, p D .053 F(1, 13) D 5.01, p < .05 F(1, 13) D 2.24, p D .158 F(1, 13) D 1.04, p D .326
.258 .278 .147 .074
SC £ FT SC £ FC SC £ TC FT £ FC FT £ TC FC £ TC
F(1, 13) < 0.01, p D .942 F(1, 13) D 5.02, p < .05 F(1, 13) D 13.54, p < .005 F(1, 13) D 0.80, p D .389 F(1, 13) D 0.37, p D .555 F(1, 13) D 42.88, p < .001
.001 .278 .510 .058 .028 .767
F(1, 13) D 0.31, p D .586 F(1, 13) D 4.04, p D .066 F(1, 13) D 3.71, p D .076 F(1, 13) D 3.81, p D .073 F(1, 13) D 9.33, p < .01 F(1, 13) D 39.40, p < .001
.233 .237 .222 .227 .418 .752
SC £ FT £ FC SC £ FT £ TC SC £ FC £ TC FT £ FC £ TC
F(1, 13) D 0.02, p D .905 F(1, 13) D 0.56, p D .466 F(1, 13) D 16.34, p < .005 F(1, 13) D 0.02, p D .882
.001 .042 .557 .002
F(1, 13) D 1.07, p D .320 F(1, 13) D 1.17, p D .300 F(1, 13) D 0.40, p D .537 F(1, 13) D 2.64, p D .128
.076 .082 .030 .169
SC £ FT £ FC £ TC
F(1, 13) D 0.16, p D .697
.001
F(1, 13) D 0.35, p D .563
.026
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Table 2 ANOVA summaries for each condition in Experiments 3 and 4 Factor
Experiment 3
Experiment 4
SigniWcance
2
SigniWcance
2
Spatial continuity (SC) Feature type (FT) Feature congruency (FC) Target congruency (TC)
F(1, 13) D 32.46, p < .001 F(1, 13) < 0.01, p D .943 F(1, 13) D 2.27, p D .156 F(1, 13) D 12.11, p < .005
.714 .001 .149 .482
F(1, 7) D 3.29, p D .113 F(1, 7) D 0.16, p D .700 F(1, 7) D 0.04, p D .841 F(1, 7) D 4.89, p D .063
.320 .022 .006 .411
SC £ FT SC £ FC SC £ TC FT £ FC FT £ TC FC £ TC
F(1, 13) D 0.55, p D .473 F(1, 13) D 0.05, p D .825 F(1, 13) D 8.86, p < .05 F(1, 13) D 0.18, p D .682 F (1, 13) D 1.20, p D .294 F(1, 13) D 18.83, p < .001
.040 .004 .405 .013 .084 .592
F(1, 7) D 0.51, p D .497 F(1, 7) D 0.40, p D .546 F(1, 7) D 1.01, p D .349 F(1, 7) D 4.85, p D .064 F(1, 7) D 0.69, p D .432 F(1, 7) D 17.81, p < .005
.068 .054 .126 .409 .090 .718
SC £ FT £ FC SC £ FT £ TC SC £ FC £ TC FT £ FC £ TC
F(1, 13) D 0.61, p D .448 F(1, 13) D 3.88, p D .071 F(1, 13) D 0.92, p D .354 F(1, 13) D 0.20, p D .661
.045 .230 .066 .015
F(1, 7) D 1.63, p D .242 F(1, 7) D 0.34, p D .576 F(1, 7) < 0.01, p D .977 F(1, 7) D 0.17, p D .694
.189 .047 .001 .024
SC £ FT £ FC £ TC
F(1, 13) D 0.47, p D .507
.035
F(1, 7) D 0.43, p D .534
.058
References Burke, L. (1952). On the tunnel eVect. Quarterly Journal of Experimental Psychology, 4, 121–138. Flombaum, J. I., Kundey, S. M., Santos, L. R., & Scholl, B. J. (2004). Dynamic object individuation in rhesus macaques: A study of the tunnel eVect. Psychological Science, 15(12), 795–800. Flombaum, J. I., & Scholl, B. J. (in press). A temporal same-object advantage in the tunnel eVect: Facilitated change detection for persisting objects. Journal of Experimental Psychology: Human Perception & Performance. Gibson, J. J., Kaplan, G., Reynolds, H. N., & Wheeler, K. (1969). The change from visible to invisible: A study of optical transitions. Perception & Psychophysics, 5, 113–116. Gordon, R. D., & Irwin, D. E. (1996). What’s in an object Wle? Evidence from priming studies. Perception & Psychophysics, 58(8), 1260–1277. Henderson, J. M. (1994). Two representational systems in dynamic visual identiWcation. Journal of Experimental Psychology: General, 123, 410–426. Kahneman, D., & Treisman, A. (1984). Changing views of attention and automaticity. In R. Parasuraman & D. R. Davies (Eds.), Varieties of attention (pp. 29–61). New York: Academic Press. Kahneman, D., Treisman, A., & Gibbs, B. J. (1992). The reviewing of object Wles: Object-speciWc integration of information. Cognitive Psychology, 24, 175–219. Kolers, P. A., & Pomerantz, J. R. (1971). Figural change in apparent motion. Journal of Experimental Psychology, 87, 99–108. Leslie, A. M., Xu, F., Tremoulet, P., & Scholl, B. J. (1998). Indexing the object concept: Developing “what” and “where” systems. Trends in Cognitive Sciences, 2, 10–18. Michotte, A. (1946/1963). La perception de la causalité. Louvain, Belgique: Institut Supérieur de Philosophie, 1946. English translation of updated edition by Miles, T., & Miles, E. The perception of causality, Basic Books, 1963. Michotte, A. (1950). On phenomenal permanence: Facts and theories. Acta Psychologica, 7, 293–322. Michotte, A., Thinès, G., & Crabbé, G. (1964/1991). Les compléments amodaux des structures perceptives. Louvain, Belgique: Publications Universitaires. Excerpted in: Thinés, G., Costall, A., Butterworth, G. (Eds.), Michotte’s experimental phenomenology of perception (pp. 140–167). Hillsdale, NJ: Erlbaum. MitroV, S. R., Scholl, B. J., & Wynn, K. (2005). The relationship between object Wles and conscious perception. Cognition, 96(1), 67–92. Moore, C. M., & Lleras, A. (2005). On the role of object representations in substitution masking. Journal of Experimental Psychology: Human Perception and Performance, 31, 1171–1180.
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A new response-time measure of object persistence in the tunnel eVect Yousuke Kawachi ¤, Jiro Gyoba Department of Psychology, Graduate School of Arts and Letters, Tohoku University, 27-1 Kawauchi, Aoba-ku, Sendai 980-8576, Japan Received 18 October 2005; received in revised form 22 January 2006; accepted 18 April 2006 Available online 14 June 2006
Abstract The recognition of information about an object is facilitated by a preview of the information concerning that object. This facilitation is regarded as evidence for the representational persistence of the object. It is not known, however, if such facilitation is obtained even under the tunnel eVect, in which a moving object is temporarily occluded. This facilitation may be a new way to measure the representational persistence of a moving object in the tunnel eVect. We addressed this question by a “samediVerent” judgment task of a target symbol (“ⴰ” or “+”), drawn within the moving object, before and after encountering the occluder. Response times (RTs) were shorter when the object reappeared with spatial continuity at the proper place than it reappeared at the improper place, as in Experiments 1 and 3. Thus, facilitation was obtained even in the tunnel eVect. When the occluder was invisible and deletion/accretion cues along the contour of the occluder were either removed (Experiment 2) or given improperly (Experiment 4), no facilitation was found. These results clearly indicate that the facilitated recognition was caused by amodal integration of the persisting representation from the unoccluded and modal phases. The present study demonstrates that the facilitated recognition (RT measurement) can be used to investigate the representational persistence in the tunnel eVect. © 2006 Elsevier B.V. All rights reserved. PsycINFO classiWcation: 2323 Keywords: Moving object; Spatial continuity; Representational persistence; Tunnel eVect; Response time
*
Corresponding author. Tel.: +81 22 795 6048; fax: +81 22 795 3703. E-mail address: [email protected] (Y. Kawachi).
0001-6918/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.actpsy.2006.04.003
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1. Introduction When objects move in the real world, visual inputs from the moving objects change constantly. Moving objects are often occluded, leading to temporary disruption of the inputs. Despite these input gaps, representations of the moving objects must be maintained to perceive the apparent continuity of the visual environment. Several studies have focused on the factors underlying the representation of moving objects (e.g., Noles, Scholl, & MitroV, 2005). Little research, however, has examined situations in which the moving objects are temporarily concealed behind an occluder. 1.1. The tunnel eVect An object moves and gradually disappears behind an occluder. Then, the object reappears on the other side of the occluder. In this situation, the object is temporarily invisible. Nonetheless, humans perceive that the object that reappeared is identical to the object that disappeared previously, suggesting that the representation of the object is maintained during its disappearance. This phenomenon, Wrst reported by Michotte and Burke, is called the tunnel eVect (Burke, 1952; Michotte, 1946/1963, 1950; Michotte, Thinès, & Crabbé, 1964/1991). Previous behavioral studies of the tunnel eVect have relied primarily on verbal reports by subjects. These verbal reports appear to indicate that this eVect is phenomenologically robust. Moreover, if the use of the verbal reports can be optimized and used rigorously, it would be helpful to measure the tunnel eVect (Thinès, 1991). However, the verbal reports have some shortcomings such as higher-level biases and the inability to measure quantitatively (Flombaum, Kundey, Santos, & Scholl, 2004; Flombaum & Scholl, in press). In this study, we used the indirect measure of the response time (RT) to examine the information required to promote the representational persistence of an object moving behind an occluder. As far as we know, this is the Wrst attempt to quantify the persistence of an object representation in the tunnel eVect with an objective response-time measure (but see Wagemans & d’Ydewalle, 1989, for related work with the RT measure). We describe the measurement of response time in detail below. 1.2. The index of the persistence of object representation In an experiment conducted by Kahneman, Treisman, and Gibbs (1992), two objects that each contained a letter within them were presented. The letters were then removed, and the objects moved brieXy. Once the objects stopped moving, a target letter appeared within one of the objects. The participant’s task was to name that target letter as quickly and accurately as possible. The response times were shorter when the initially presented letter was re-presented within the same object than when the letter was shown within a diVerent object. This facilitated recognition of information about an object is regarded as an indication that the object representation persists (e.g., Gordon & Irwin, 1996; Henderson, 1994; MitroV, Scholl, & Wynn, 2005; Noles et al., 2005). Kahneman et al. (1992) proposed that the representation of a moving object persists in the tunnel eVect. If the tunnel eVect is perceived, preview of information on an object may facilitate the recognition of that information. They did not, however, examine this suggestion experimentally. In this study, we used a similar measurement to investigate persistence of the representation of a moving object that is temporarily occluded, instead of the traditional verbal methods.
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1.3. Spatiotemporal continuity and the surface features of the moving object Previous work (reviewed in Scholl, 2001) has demonstrated that the maintenance of a persisting object representation relies upon spatiotemporal continuity in an object’s trajectory. This study addressed whether spatiotemporal continuity in an object’s trajectory through an occluder facilitates the recognition of previewed information associated with the object. Meanwhile, the eVect of non-spatiotemporal properties, such as surface features, has not been previously explored in detail. Previous research has reported that representational persistence is perceived even if the surface features of an object, such as color or size, diVered before and after an occlusion, as long as the constraints of spatiotemporal continuity were met (Burke, 1952). Furthermore, previous research on apparent motion conWrmed that changes in surface features did not aVect the persistence of object representation when all spatiotemporal factors are completely balanced; two Wgures with diVerent surface features, such as colors or shapes, represented the same object (Kolers & Pomerantz, 1971; Navon, 1976; Ramachandran & Anstis, 1983). These Wndings imply that an object representation is created and maintained, based primarily on spatiotemporal continuity, not on surface feature congruity. Surface feature information may be added to the representation later (Leslie, Xu, Tremoulet, & Scholl, 1998). In this study, we also investigated the eVect of surface feature changes by RT measurement. 1.4. The role of deletion and accretion in the tunnel eVect Deletion of surface elements occurs when a moving object gradually disappears behind an occluder, while accretion occurs when it gradually appears. Deletion/accretion cues along the boundaries of an occluder are necessary for the tunnel eVect (Gibson, Kaplan, Reynolds, & Wheeler, 1969; Scholl, 2001; Scholl & Pylyshyn, 1999). Gibson et al. (1969) suggested that it is diYcult to perceive an occluding edge without deletion/accretion cues along the contour of the occluder. When deletion/accretion cues are removed or are improper and the occluder is invisible, the tunnel eVect is barely perceived; the persisting representation of the moving object is not amodally integrated from the unoccluded and modal phases (Yantis, 1995). Therefore, the facilitated recognition of information associated with an object may attenuate under these conditions. Investigation of the eVect of deletion/accretion cues may help us to better understand the role of these cues in representational persistence in the tunnel eVect. 1.5. Purposes of the present study This study sought to examine if the visual system can maintain the representation of a moving object that becomes temporarily occluded using indirect, but psychophysical performance measures, that is, RT measurements, instead of verbal reports. In Experiments 1 and 3, we examined the eVects of spatial continuity on the representation of a moving object and the update of the representation from surface feature changes. We manipulated the spatial continuity of the object (if the object reappeared at the proper place after being occluded) and the congruity of the surface features before and after occlusion. We then asked the participants to judge whether a target pattern depicted inside the object was the same or diVerent after the object was occluded as before occlusion. We expected that the “same” response would be faster when the object maintained spatial continuity than when
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it did not. We also anticipated that the “same” response would be signiWcantly faster when the object maintained feature congruency as well as spatial continuity. In Experiments 2 and 4, we conducted the same task with the tunnel eVect barely perceivable due to either a lack of accretion/deletion cues along the occluder’s contour (Experiment 2) or improper accretion/deletion cues (Experiment 4). If facilitated recognition of information about a temporarily occluded object was not observed in the absence of these cues, it would provide evidence that the representational persistence of the object occurs by amodal persistence of the moving object behind the occluder. 2. Experiment 1: The tunnel eVect with a visible occluder In Experiment 1, we examined the dependence of the facilitated recognition of information for an object on the constraint of spatial continuity. This experiment provided evidence for representational persistence in the tunnel eVect and a new behavioral demonstration of the tunnel eVect, which is independent of verbal reports. In addition, we examined if recognition was facilitated by the observation of identical surface features. 2.1. Method 2.1.1. Participants Sixteen students from Tohoku University participated in Experiment 1. The data from two participants were eliminated because their rates of correct responses were lower than 90%. All participants had either normal or corrected-to-normal vision. 2.1.2. Stimuli The target object, a moving square (0.43 £ 0.43 deg), was generated by a computer (SHARP X68030) and presented on a CRT display (SHARP CZ-621Z). The participants sat approximately 172 cm away from the display, with their heads resting on a chin rest. A grey vertical occluder (5.8 £ 1.3 deg) was located at the center of the display. The square moved 5.64 deg/s horizontally from the right or left side of the display. As it passed behind the occluder, the object temporarily disappeared. After 230.50 ms, it reappeared on the opposite side of the occluder (Fig. 1). A white Wxation dot was presented 0.27 deg from the left or right of the occluder. To investigate the eVects of spatial continuity information on representational persistence, we manipulated the place of reappearance of the occluded object. The object reappeared at the correct place (with continuity) on half of the trials and at a wrong place on the remaining trials (with discontinuity of a 1.5 deg vertical spatial gap). The surface features (color or size) of the object were also manipulated. In the color condition, participants were presented with a moving square that was colored either red (48.70 cd/m2) or green (49.11 cd/m2). In the size condition, individuals saw a large square (0.43 £ 0.43 deg) or a small square (0.3 £ 0.3 deg). DiVerentially sized squares were always colored green. On half of the trials, the surface features were the same before and after the occlusion, while on the remaining trials, the object reappeared after the occlusion with diVerent surface features. The symbols (“ⴰ” or “+”) were used as the target pattern drawn at the center of the object. The target pattern was approximately 0.23 deg in size and colored white. On half of the trials, the target pattern did not change from before to after the occlusion. On the
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TIME
Spatial continuity Same Target Pattern
Spatial continuity Different Target Pattern
Spatial discontinuity (1.5 deg) Same Target Pattern
Spatial discontinuity (1.5 deg) Different Target Pattern
Fig. 1. Schematic presentation of the tunnel event stimuli used in Experiment 1. In half of the trials, the surface features changed after occlusion (red to green or green to red under color changing condition; small to large or large to small under size changing condition). Dotted lines indicate the virtual trajectories of the object movements. These lines did not appear on the display.
remaining trials, the depicted target pattern changed after the object reappeared on the other side of the occlusion. 2.1.3. Procedure We asked the participants to judge whether the target pattern was the same or diVerent before and after the moving object was occluded. The participants were asked to push either the “same” or “diVerent” response keys as rapidly and accurately as possible. Throughout each trial, the participants were asked to focus on the Wxation dot as much as possible. The participants were also asked to ignore the spatial continuity and surface features of the object, paying sole attention to the target patterns. Each participant performed at least 20 practice trials prior to the experimental trials. Each block of 128 trials, consisting of blocks of color-leftward motion, color-rightward motion, size-leftward motion, and size-rightward motion, was counterbalanced for each participant. Half of the participants performed the color change blocks Wrst, while the other half conducted the size change blocks Wrst. Within each block, the spatial continuity, surface features, and target patterns were randomly manipulated. The positions of the response keys were also counterbalanced for each participant. 2.1.4. Measurement Response times were measured from the appearance of the leading edge of the moving object on the opposite side of the occluder until the participant pressed a response key.
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2.2. Results Error trials were removed (6.17% of all trials) from analysis. RTs that exceeded the corresponding cell means for each participant by greater than two standard deviation units were also excluded (3.15% of all trials). The mean RTs of the combined data regarding the size and color conditions are shown in Fig. 2. A 2 (spatial continuity: continuity or discontinuity) £ 2 (feature type: size or color) £ 2 (feature congruency: same or diVerent) £ 2 (target congruency: same or diVerent) ANOVA was used to analyze the participants’ mean RTs. Overviews of the results of ANOVA are presented in the Appendix as Table 1. As can be seen in Table 1, the main eVect of the spatial continuity was signiWcant, while the other main eVects were not signiWcant. There was a signiWcant interaction between spatial continuity and target congruency. Most importantly, we observed a signiWcant three-way interaction between spatial continuity, feature congruency, and target congruency. Post hoc analysis of the spatial congruity £ feature congruency £ target congruency interaction revealed the following results. First, responses were facilitated when spatial continuity was maintained, despite feature and target congruency. For all combinations of feature and target congruency, RTs were shorter under conditions of continuity than discontinuity (F(1, 52) D 61.21, p < .001, for the combination of the same feature and the same target; F(1, 52) D 35.14, p < .001, for the same feature and a diVerent target; F(1, 52) D 108.62, p < .001, for a diVerent feature and the same target; and F(1, 52) D 34.64, p < .001, for a diVerent feature and a diVerent target, respectively). Second, responses were facilitated by the combination of the same features and targets, or by the combination of diVerent features and targets. When the target was the same under 580 560
different target
same target
Response time (ms)
540 538.39 ms 528.74 ms
520
517.67 ms
520.66 ms
500 496.45 ms 487.92 ms
480
481.16 ms 474.35 ms
460 440 spatial continuitysame surface feature
spatial continuitydifferent surface feature
spatial discontinuitysame surface feature
spatial discontinuitydifferent surface feature
Fig. 2. Mean response times for each condition in Experiment 1. Neither the main nor the interaction eVects of feature type (size/color) were signiWcant. Therefore, the mean RTs of the combined data of size and color conditions are shown. The error bars display the standard errors of the means.
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continuity conditions, the mean RT was shorter for the same feature than for a diVerent feature [F(1, 52) D 4.60, p < .05]. For a diVerent target under continuity conditions, the mean RT was shorter for diVerent features than for the same features [F(1, 52) D 8.26, p < .01]. When the target pattern was same under discontinuity conditions, the mean RT was shorter for the same surface features than for diVerent surface features [F(1, 52) D 53.69, p < .001]. For a diVerent target under discontinuity conditions, the responses were faster for the diVerent surface features than for the same surface features [F(1, 52) D 8.75, p < .005]. Third, a response of “same” was made signiWcantly faster under the combined condition of spatial continuity and unchanged features, but was made slower by the combined condition of spatial discontinuity and diVerent features. When the surface features were held constant under continuity conditions, the same target prompted a faster response than did a diVerent target [F(1, 52) D 8.30, p < .01]. For a diVerent surface feature under continuity conditions, there was no signiWcance diVerence between the same target and a diVerent target [F(1, 52) D 0.61, p D .439]. When the feature was changed under discontinuity conditions, a diVerent target prompted a faster response than did the same target [F(1, 52) D 9.04, p < .005]. For the same surface under discontinuity conditions, there was no signiWcance diVerence between the same target and a diVerent target [F(1, 52) D 1.68, p D .200]. 2.3. Discussion For all combinations of surface features and target patterns, the responses were facilitated in the continuity, but not the discontinuity, conditions. These results demonstrate that when spatial continuity of the moving object was maintained, the representation of the object persisted in the tunnel eVect, even when the surface features or target pattern diVered following the occlusion. This result supports the Wndings that spatiotemporal properties play an important role in the perception of persisting objects even following surface feature transformation (Burke, 1952; Michotte et al., 1964/1991). Moreover, when surface features were the same under continuity conditions, the “same” response was facilitated (the mean RT was the shortest) more than all of the other conditions. This result indicates that the representation of a moving object persists in accordance with spatial continuity in the tunnel eVect. At the same time, it also provides evidence that facilitated recognition is obtained even under the tunnel eVect and validates the use of RT measurements to examine the tunnel eVect. In the present experiment, surface features were also found to have a small but signiWcant eVect on recognition of the same target (the “same” response). When the spatial continuity of an object was maintained, responses were facilitated by the combination of unchanged surface features and an unchanged target. Accordingly, these results seem to indicate that surface feature information does not have a decisive eVect; instead, this information has a supplementary inXuence on the persistence of object representation. However, changes in the surface features under spatial discontinuity conditions lead to ‘diVerent’ responses that are faster than the ‘same’ responses. Therefore, there is also the possibility that these results can be explained by a possible response bias eVect, which means that the observers may need to suppress the responses to the surface features when the surface features do not match but the target was the same. In short, it is unclear whether the surface feature eVect is due to surface features per se or to the response bias. We also discuss this problem in Experiment 3 and in the General discussion.
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3. Experiment 2: An invisible occluder and the removal of accretion/deletion cues In Experiment 1, we examined whether the facilitated recognition of information associated with an object depends upon spatiotemporal continuity in the object’s motion. We conducted Experiment 2 to conWrm whether facilitation resulted from the persistence of the object representation in the tunnel eVect. This experiment may also strengthen the behavioral demonstration of the tunnel eVect provided by the results of Experiment 1. Experiment 2, therefore, was a repeat of Experiment 1 with the exception that deletion/ accretion cues were removed and the occluder was made invisible, rendering the tunnel eVect imperceptible. An occluding edge is not perceived without the presence of deletion/ accretion cues along the contour of the occluder (Gibson et al., 1969; Scholl & Pylyshyn, 1999). We expected that these alterations made in Experiment 2 would disrupt the persistence of object representation under spatial continuity conditions, reducing the facilitation seen in Experiment 1. 3.1. Method 3.1.1. Participants Sixteen new students from Tohoku University participated in Experiment 2. The data from two participants were discarded, because their rates of correct responses were lower than 90%. All participants had either normal or corrected-to-normal vision. 3.1.2. Stimuli The stimuli were identical to those in Experiment 1, with the two following exceptions. First, when the leading edge of a moving object touched the proximal edge of an occluder, the object disappeared instantly. Then, when the trailing edge of the moving object touched the distal edge of the occluder, the object reappeared instantly. Second, the occluder was invisible (the occluder had the same luminance value as the background). Fig. 3 displays an example of the stimulus sequences used in Experiment 2.
No deletion/accretion cues and an invisible occluder (Experiment 2) An invisible occluder (Experiment 3) Reversed virtual occlusion and an invisible occluder (Experiment 4)
TIME Fig. 3. Schematic presentation of the stimuli used in Experiments 2–4. Dotted lines indicate the invisible virtual occluder. These lines did not appear on the display.
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3.1.3. Procedure and measurement The procedure was identical to that described for Experiment 1, except that we asked the participants to judge whether the target pattern was the same or diVerent before the disappearance as after the reappearance of the object. Measurements were performed as described in Experiment 1. 3.2. Results Error trials were removed (7.28% of all trials) from analysis. RTs that exceeded the corresponding cell means for each participant by greater than two standard deviation units were also excluded (3.10% of all trials). The mean RTs for the size and color conditions are shown in Figs. 4a and 4b. The results demonstrated that the same/diVerence responses were not modulated by spatial continuity. A 2 (spatial continuity: continuity or discontinuity) £ 2 (feature type: size or color) £ 2 (feature congruency: same or diVerent) £ 2 (target congruency: same or diVerent) ANOVA was used to analyze the participants’ mean RTs. Overviews of the results of ANOVA are presented in Appendix as Table 1. As can be seen in Table 1, the main eVect of feature type was signiWcant. While the RTs were shorter for the size condition than for the color condition, the main eVects of spatial continuity were marginally signiWcant. There was a marginally signiWcant interaction between spatial continuity and target congruency.1 Moreover, there were no signiWcant three-way interactions. 3.3. Discussion Although the main eVect of feature type was signiWcant, neither the main nor the interaction eVects of spatial continuity were signiWcant. This result suggests that the slower response times found in the discontinuous (compared to the continuous) motion condition of Experiment 1 were not simply due to the greater distance that the objects in this condition traversed while occluded. Accordingly, we did not observe any facilitation similar to that obtained in Experiment 1. This lack of facilitation may result from the removal of deletion/accretion cues and the invisible occluder because no amodal integration of the object’s representation was produced in this case. Therefore, it is likely that the reappearing object in Experiment 2 was perceived as a new object under condition in which the tunnel eVect was barely perceptible. These results support the possibility that the persistence of object representation behind the occluder produced the facilitated recognition seen in Experiment 1. 4. Experiment 3: The tunnel eVect with an invisible occluder While facilitated recognition of information on the same object was found in Experiment 1, no facilitated recognition was observed in Experiment 2. In Experiment 3, we examined the dependence of this diVerence in the results of Experiments 1 and 2 on the
1
Although this marginal eVect could reach signiWcance with greater statistical power, it is clear that this marginal eVect is far weaker than the eVect for the same conditions in Experiment 1.
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Response time (ms)
560
different target
same target
540 542.71 ms 535.32 ms
520
523.81 ms 515.64 ms
517.28 ms
533.68 ms 523.82 ms
520.09 ms
500 480 460 440 spatial continuitysame surface feature
spatial continuitydifferent surface feature
spatial discontinuitysame surface feature
spatial discontinuitydifferent surface feature
Fig. 4a. Mean response times for each size condition in Experiment 2. The error bars show the standard errors of the means.
580 560
different target
same target
Response time (ms)
540
548.69 ms
552.04 ms
541.44 ms
537.22 ms
520
564.67 ms
533.76 ms 527.67 ms
523.77 ms
500 480 460 440 spatial continuitysame surface feature
spatial continuitydifferent surface feature
spatial discontinuitysame surface feature
spatial discontinuitydifferent surface feature
Fig. 4b. Mean response times for each color condition in Experiment 2. The error bars indicate the standard errors of the means.
visibility of an occluder. This experiment may generalize the behavioral demonstration of the tunnel eVect using the RT measure.
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Previous studies reported that the tunnel eVect occurs even when an occluder is invisible (Michotte et al., 1964/1991). Thus, if deletion and accretion cues were given properly despite the use of an invisible occluder, we would expect that the tunnel eVect would still occur, and recognition would be facilitated. 4.1. Method 4.1.1. Participants Sixteen new students from Tohoku University participated in Experiment 3. The data from two participants were discarded because their rates of correct responses were lower than 90%. All participants had either normal or corrected-to-normal vision. 4.1.2. Stimuli The stimuli were identical to those described in Experiment 1, with the exception that the occluder was invisible (the occluder had the same luminance value as the background). Fig. 3 displays an example of the stimulus sequences used in Experiment 3. 4.1.3. Procedure and measurement The procedure and measurement were identical to that of Experiment 2. 4.2. Results Error trials were removed (6.34% of all trials) from analysis. RTs that exceeded the corresponding cell means for each participant by greater than two standard deviation units were also excluded (2.66% of all trials). The mean RTs of the combined data regarding the size and color conditions are shown in Fig. 5. A 2 (spatial continuity: continuity or discontinuity) £ 2 (feature type: size or color) £ 2 (feature congruency: same or diVerent) £ 2 (target congruency: same or diVerent) ANOVA was used to analyze the participants’ mean RTs. Overviews of the results of ANOVA are presented in Appendix as Table 2. The main eVects of both spatial continuity and target congruency were signiWcant. SigniWcant interactions were found between spatial continuity and target congruency. Post hoc analysis revealed that facilitated responses for the same target were obtained only under spatial continuity conditions. Under these conditions, the same target gave a faster response than a diVerent target [F(1, 26) D 19.71, p < .001]. For conditions of spatial discontinuity, there was marginally signiWcant diVerence between the same target and a diVerent target [F(1, 26) D 3.23, p D .084].2 For both the same and diVerent targets, the responses under spatial continuity conditions were faster than those under spatial discontinuity conditions (F(1, 26) D 41.00, p < .001; F(1, 26) D 16.97, p < .001, respectively). However, in Experiment 3, diVerent from in Experiment 1, there was no signiWcant three-way interaction between spatial continuity, feature congruency, and target congruency (see Table 2 in Appendix).
2
The ‘same’ responses tend to be facilitated under conditions of spatial discontinuity. However, under conditions of spatial continuity, the ‘same’ responses are more robustly facilitated.
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Response time (ms)
560
different target
same target 553.06 ms
540
549.13 ms
547.27 ms
537.62 ms
520 500
529.11 ms
527.21 ms 509.97 ms 503.63 ms
480 460 440
spatial continuitysame surface feature
spatial continuitydifferent surface feature
spatial discontinuitysame surface feature
spatial discontinuitydifferent surface feature
Fig. 5. Mean response times for each condition in Experiment 3. Neither the main nor the interaction eVects of feature type (size/color) were signiWcant. Therefore, the mean RTs of the combined data of size and color conditions are shown. The error bars display the standard errors of the means.
4.3. Discussion As in Experiment 1, these results demonstrate that the ‘same’ response was facilitated according to the constraint of spatial continuity. This result indicates that the representation of a moving object persists in the tunnel eVect, regardless of the visibility of the occluder. Therefore, the diVerence in the results between Experiments 1 and 2 may not depend on the visibility of the occluder. Although the mean RT was the shortest under the spatial continuity – feature congruency – same target conditions, the surface feature eVect on the recognition of the same target under spatial continuity conditions, were not observed in Experiment 3, which is inconsistent with the results of Experiment 1. Moreover, the eVect of the surface features was not observed on the recognition of a diVerent target under spatial discontinuity conditions. Hence, we did not Wnd conclusive evidence, which excluded the involvement of a response bias in the surface feature eVect observed in Experiment 1. 5. Experiment 4: Reversed virtual occlusion Experiment 2 demonstrated that a lack of deletion/accretion cues along the contour of occluder resulted in a large decline in facilitated recognition of information within the same object. These results are evidence that this facilitation can only be obtained in stimulus conWgurations in which the participants can perceive the tunnel eVect; thus, deletion/ accretion cues contribute to representational persistence in the tunnel eVect. The possibility remains, however, that the results in Experiment 2 may have been produced by other factors, such as abrupt onsets/oVsets and visual memory decline. Abrupt
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onsets and oVsets of an object are reported to capture attention independent of the participants’ goals or beliefs (Yantis, 1993), momentarily distracting the observers from their task performance. Previous research has also suggested that abrupt onsets/oVsets discard an object representation (Yantis & Jonides, 1984). In addition, the invisible times of the moving object in Experiments 1 and 3 were shorter than that in Experiment 2 (76.24 ms at the maximum). This diVerence might contribute to a decline in visual memory of the object, resulting in the lack of facilitation recognition in Experiment 2. Experiment 4 was conducted to control these factors by using reversed virtual occlusion (Scholl & Pylyshyn, 1999). This experiment may show the strong dependence of the facilitated recognition on the perception of the tunnel eVect. As other experiments cited above, this experiment should support the validity of using the RT measure to analyze the tunnel eVect. 5.1. Method 5.1.1. Participants Eight new students from Tohoku University participated in Experiment 4. All participants had either normal or corrected-to-normal vision. 5.1.2. Stimuli In Experiment 4, we used reversed virtual occlusion (Scholl & Pylyshyn, 1999), in which deletion/accretion cues are improperly given. Fig. 3 displays an example of the stimulus sequences used in Experiment 4. When the leading edge of the moving object touched the proximal edge of the virtual occluder, the trailing edge of the object stopped, while the leading edge moved in the opposite direction of object motion. When the trailing edge of the object touched the distal edge of the occluder, the leading edge of the object reappeared and stopped, while the trailing edge moved contrary to the direction of motion of the object. Using this stimulus conWguration, the objects disappear and reappear gradually at the same rates as those seen in both Experiments 1 and 3. In this experiment, the moving object is visible for the same duration as Experiments 1 and 3. 5.1.3. Procedure and measurement The procedure and measurements were identical to those of Experiments 2 and 3. 5.2. Results Error trials were removed (7.37% of all trials) from analysis. RTs that exceeded the corresponding cell means for each participant by greater than two standard deviation units were also excluded (2.51% of all trials). The mean RTs of the combined data regarding the size and color conditions are shown in Fig. 6. A 2 (spatial continuity: continuity or discontinuity) £ 2 (feature type: size or color) £ 2 (feature congruency: same or diVerent) £ 2 (target congruency: same or diVerent) ANOVA was used to analyze the participants’ mean RTs. Overviews of the results of ANOVA are presented in Appendix as Table 2. This analysis revealed that no facilitated responses were obtained under spatial continuity conditions. All of the main eVects were not signiWcant. No other interactions were observed between spatial continuity and target congruency. Furthermore, there were no three-way signiWcant interactions.
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Y. Kawachi, J. Gyoba / Acta Psychologica 123 (2006) 73–90 580 different target
Response time (ms)
560
same target
551.02 ms
540
544.12 ms
540.62 ms
520
531.95 ms
531.44 ms 525.87 ms
523.93ms
519.71 ms
500 480 460 440
spatial continuitysame surface feature
spatial continuitydifferent surface feature
spatial discontinuitysame surface feature
spatial discontinuitydifferent surface feature
Fig. 6. Mean response times for each condition in Experiment 4. Neither the main nor the interaction eVects of feature type (size/color) were signiWcant. Therefore, the mean RTs of the combined data of size and color conditions are shown. The error bars indicate the standard errors of the means.
5.3. Discussion In Experiment 4, we used improper deletion/accretion cues (reversed virtual occlusion) to control for the potential eVects of abrupt onsets/oVsets and visual memory decline in Experiment 2. Reversed virtual occlusion minimizes the perception of the tunnel eVect by the participants. The results of Experiment 4 showed none of the facilitation eVects obtained in Experiments 1 and 3. Therefore, we can rule out the potential confounding eVects of abrupt onsets/oVsets and visual memory decline, allowing us to conclude that the reappearing object is likely to be perceived as a new object in both Experiments 2 and 4, in which the tunnel eVect was barely perceivable. Also, the results of Experiment 4 indicate that the facilitated response seen for spatial continuity in Experiments 1 and 3 cannot be explained by the spatial distance diVerence between the places in which the object reappears alone.3 6. General discussion The purpose of this study was to develop a new RT measure, which could replace subjective verbal reports, by examining whether facilitated recognition of information associated with a previewed object is obtained under the tunnel eVect. In Experiment 1, we found 3
The results of Experiment 4 indicate that the facilitated response under spatial continuity conditions in Experiments 1 and 3 cannot be explained by the diVerence in the spatial distance between the places where the object reappears by itself. However, it still seems to be possible that a larger diVerence in the spatial distance leads to a diVerent pattern of results in Experiment 4, which decreases the eVect of the deletion/accretion cues.
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facilitated recognition of target patterns and surface features when an object emerged from behind an occluder by following a spatiotemporally continuous path. SpeciWcally, the condition in which the surface features were congruent both before and after the occlusion according to the constraint of spatiotemporal continuity strongly facilitated the “same” response. In Experiment 3, the “same” response was facilitated when the spatial continuity of a moving object was maintained, while no clear eVect of surface feature was observed. Such facilitation indicates that the representation of a moving object persists according to the spatial continuity in the tunnel eVect. In contrast, Experiments 2 and 4 utilized conditions in which the deletion/accretion cues were removed. The participants could barely perceive the tunnel eVect. No such facilitation was observed in these experiments. Therefore, the facilitation seen in Experiments 1 and 3 was caused by amodal integration of the object representation followed by perception of the tunnel eVect. The present study clearly indicates that instead of verbal reports, indirect, but psychophysical RT measurements are valid to measure the tunnel eVect. The results of the present study demonstrate that the RT is shorter when the spatiotemporal continuity of the occluded object is maintained and the tunnel eVect occurs compared to when the continuity is not maintained and the tunnel eVect does not occur. The method used in the present study becomes a new method to measure the tunnel eVect, together with other psychophysical methods such as multiple object tracking task through occlusion (Scholl & Pylyshyn, 1999) and change detection task (Flombaum & Scholl, in press). The present results can be interpreted according to the object Wle theory (Kahneman & Treisman, 1984; Kahneman et al., 1992). An object Wle is an episodic representation of the object that persists on the basis of spatiotemporal continuity. If an object moves continuously, its object Wle is maintained. If the motion of the object is discontinuous, the object Wle is discarded, and a new object Wle is formed. In this study, when the motion path of the object was discontinuous before and after the occluder, the object Wle would have been destroyed, requiring the formation of a new object Wle. Therefore, the responses would have been delayed under spatial discontinuity conditions. In contrast, when the motion path of the object was continuous, the object Wle persists. The participants would utilize the previously processed information about the object without creating a new object Wle, resulting in facilitated responses under conditions of spatial continuity. Recent fMRI experiments have begun to specify the neural correlates, which are involved in the tunnel eVect, and provide converging evidence for the Wndings reported here. Olson, Gatenby, Leung, Skudlarski, and Gore (2003) compared the brain activations in the tunnel conditions in the absence or presence of deletion/accretion cues. They demonstrated that the intraparietal sulcus (IPS) as well as the middle temporal (MT) regions are activated in the presence of the cues, suggesting that neurons in the IPS maintain a representation of the brieXy occluded object. The new psychophysical methods developed in the present research would provide more powerful tools to isolate the neural basis of the tunnel eVect. Finally, the eVect of surface features on the representational persistence remains unclear. The results of Experiment 1 suggest the possibility that the feature congruent information may facilitate recognition, but do not exclude a response bias eVect. In addition, the results in Experiment 3 are inconsistent with the results in Experiment 1. Hence, the results of our experiments are not conclusive regarding the role of surface features in visual object persistence. However, together with a number of recent studies using other paradigms like multiple object tracking, object substitution masking, and apparent motion
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(e.g., Flombaum & Scholl, in press; Moore & Lleras, 2005; Saiki, 2003a, 2003b), they seem to converge on the conclusion that surface features do not matter much. 7. Conclusion This study introduces a new RT measure, which analyzes the representational persistence in the tunnel eVect. Using this new measure, instead of the verbal reports, the present research also presents two Wndings. First, the representation of a moving object can be maintained even through occlusion; spatiotemporal information aVects the representational persistence. Second, deletion and accretion cues at the boundaries of the occluder leading to the tunnel eVect contribute signiWcantly to the persistence of object representation during occlusion. Both traditional phenomenological methods and recent neuroimaging studies require exploration of new methods, which do not rely on verbal reports to analyze the representational persistence of occluded moving objects. The psychophysical approach proposed in this study meets the requirements and would contribute to clarify the underlying mechanism of the representational persistence in the tunnel eVect. Acknowledgements We wish to thank Johan Wagemans, Jonathan Flombaum, Brian Scholl, and Rob van Lier for their useful comments, suggestions, and criticism on early versions of this manuscript. We are also grateful for helpful suggestions from an anonymous reviewer. Appendix See Tables 1 and 2. Table 1 ANOVA summaries for each condition in Experiments 1 and 2 Factor
Experiment 1
Experiment 2
SigniWcance
2
SigniWcance
2
Spatial continuity (SC) Feature type (FT) Feature congruency (FC) Target congruency (TC)
F(1, 13) D 80.57, p < .001 F(1, 13) < 0.01, p D .929 F(1, 13) D 3.62, p D .079 F(1, 13) D 0.30, p D .592
.861 .001 .218 .023
F(1, 13) D 4.52, p D .053 F(1, 13) D 5.01, p < .05 F(1, 13) D 2.24, p D .158 F(1, 13) D 1.04, p D .326
.258 .278 .147 .074
SC £ FT SC £ FC SC £ TC FT £ FC FT £ TC FC £ TC
F(1, 13) < 0.01, p D .942 F(1, 13) D 5.02, p < .05 F(1, 13) D 13.54, p < .005 F(1, 13) D 0.80, p D .389 F(1, 13) D 0.37, p D .555 F(1, 13) D 42.88, p < .001
.001 .278 .510 .058 .028 .767
F(1, 13) D 0.31, p D .586 F(1, 13) D 4.04, p D .066 F(1, 13) D 3.71, p D .076 F(1, 13) D 3.81, p D .073 F(1, 13) D 9.33, p < .01 F(1, 13) D 39.40, p < .001
.233 .237 .222 .227 .418 .752
SC £ FT £ FC SC £ FT £ TC SC £ FC £ TC FT £ FC £ TC
F(1, 13) D 0.02, p D .905 F(1, 13) D 0.56, p D .466 F(1, 13) D 16.34, p < .005 F(1, 13) D 0.02, p D .882
.001 .042 .557 .002
F(1, 13) D 1.07, p D .320 F(1, 13) D 1.17, p D .300 F(1, 13) D 0.40, p D .537 F(1, 13) D 2.64, p D .128
.076 .082 .030 .169
SC £ FT £ FC £ TC
F(1, 13) D 0.16, p D .697
.001
F(1, 13) D 0.35, p D .563
.026
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Table 2 ANOVA summaries for each condition in Experiments 3 and 4 Factor
Experiment 3
Experiment 4
SigniWcance
2
SigniWcance
2
Spatial continuity (SC) Feature type (FT) Feature congruency (FC) Target congruency (TC)
F(1, 13) D 32.46, p < .001 F(1, 13) < 0.01, p D .943 F(1, 13) D 2.27, p D .156 F(1, 13) D 12.11, p < .005
.714 .001 .149 .482
F(1, 7) D 3.29, p D .113 F(1, 7) D 0.16, p D .700 F(1, 7) D 0.04, p D .841 F(1, 7) D 4.89, p D .063
.320 .022 .006 .411
SC £ FT SC £ FC SC £ TC FT £ FC FT £ TC FC £ TC
F(1, 13) D 0.55, p D .473 F(1, 13) D 0.05, p D .825 F(1, 13) D 8.86, p < .05 F(1, 13) D 0.18, p D .682 F (1, 13) D 1.20, p D .294 F(1, 13) D 18.83, p < .001
.040 .004 .405 .013 .084 .592
F(1, 7) D 0.51, p D .497 F(1, 7) D 0.40, p D .546 F(1, 7) D 1.01, p D .349 F(1, 7) D 4.85, p D .064 F(1, 7) D 0.69, p D .432 F(1, 7) D 17.81, p < .005
.068 .054 .126 .409 .090 .718
SC £ FT £ FC SC £ FT £ TC SC £ FC £ TC FT £ FC £ TC
F(1, 13) D 0.61, p D .448 F(1, 13) D 3.88, p D .071 F(1, 13) D 0.92, p D .354 F(1, 13) D 0.20, p D .661
.045 .230 .066 .015
F(1, 7) D 1.63, p D .242 F(1, 7) D 0.34, p D .576 F(1, 7) < 0.01, p D .977 F(1, 7) D 0.17, p D .694
.189 .047 .001 .024
SC £ FT £ FC £ TC
F(1, 13) D 0.47, p D .507
.035
F(1, 7) D 0.43, p D .534
.058
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