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Detection of color in rotating objects by infants and its generalization over changes in velocity
JOURNAL
OF EXPERIMENTAL
CHILD
PSYCHOLOGY
28, 191-204 (1979)
Detection of Color in Rotating Objects by Infants and Its Generalization over Changes in Velocity D.K.
BURNHAM Monash
AND R. H. DAY Universit)
In three experiments, infants between 8 and 20 weeks of age were familiarized during habituation trials to either a stationary or revolving patterned cylinder (Experiment 1) or to the same object when it was revolving at one of two angular velocities (Experiments 2 and 3). In the postfamiliarization trials, anguiar velocity was changed with the color of the pattern either the same as or different from that in the familiarization trials. The results showed that the infants were not only sensitive to movement and changes in velocity but to the color of the moving pattern. Furthermore, this response to color generalized across changes in angular velocity. These findings indicate that a necessary condition for identity constancy, detection of an object property with object transformations, is present between 8 and 20 weeks, prior to the stage of manual manipulation of objects. A number of subsidiary findings concerning movement discrimination at 55 and 100 cm viewing distances by ll- and 17-week-old infants are also described.
Infants prefer movement-like sequences or displays to stationary displays. In particular, suppression of nonnutritive sucking by neonates is greater for a sequence of lights flashing from right to left than for a single, stationary light (Haith, 1966); both neonates (Carpenter, 1974) and 20- to 23-week-old babies (Wilcox & Clayton, 1968) prefer to fixate or to scan moving rather than stationary representations of human faces; 16- and 24-week-old babies prefer patterns moving vertically to stationary patterns (Silfen & Ames, Note 3); 4-, 7.5, and 12-week-old babies fixate patterns moving horizontally longer than stationary patterns (Volkmann & Dobson, 1976); and 9- and 16-week-old infants fixate rotating patterned cylinders longer than stationary cylinders (McKenzie & Day, 1976). In These experiments were undertaken when the first author was in receipt of a Commonwealth Post-Graduate Scholarship. Requests for reprints should be sent to Dr. D. K. Bumham, Department of Psychology, Monash University, Clayton, Victoria, Australia 3168. 191 0022-0%5/79/050191-14$02.00/O Copyright @ 1979 by Academic Press. Inc. All rights of reproduction in any form reserved.
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addition, Gibson, Johnston, and Owsley (1978) have shown that 5-month-old infants are capable of discriminating between different classes of motion transformation such as rigid rotation about an axis and nonrigid “squeezing” transformations. However, whether infants respond exclusively to movement in a “reflexive,” automatic manner, or whether movement is merely one of numerous, salient properties of objects, which are detected and accordingly responded to, is not yet clear. In the first case, infants presumably would respond only to the movement without identifying other properties; whereas in the second they could be expected to detect properties additional to the movement of the object. Furthermore, if infants detect and respond to properties of objects other than those of movement, then they could be expected to recognize and respond to these under changed conditions (e.g., at different velocities). With stationary objects such generalization occurs in respect of form with changes in object orientation (McGurk, 1972). Such an ability to generalize is logically necessary for identity constancy, the capacity to recognize an object as the same object despite variations in its position, orientation, or velocity. Piaget (1954) has argued that identity constancy, or the broader concept of object permanence, does not start to develop until after the age of 4% months when infants develop the ability to reach for and grasp objects and subsequently distinguish objects from the results of their own motor activity. In a more specific vein, Bower (Bower, Broughton, & Moore, 1971; Bower, 1974) has recently claimed that infants less than 20 weeks of age do not detect the properties of moving objects and, in fact, respond to a moving object simply as a path of movement and as something totally different from the same object when stationary. Bower attributes this to the limited input channels and processing capacity of young infants. However, with stationary objects, processing in the first year is certainly not limited to one channel. Infants can, for example. detect both the color and form of a stationary object (Bower. 1969; Cohen, Gelber & Lazar, 1971: Contole, Note 1; McKenzie, Note 2). More particularly, Hartlep and Forsyth ( 1977) have recently found that lo-week-old infants, operantly trained to discriminate between a stationary cube and sphere presented simultaneously, subsequently maintained this discrimination when the objects were moving. Thus, contrary to Bower’s claim, infants seem to detect the features of moving objects. However, Hartlep and Forsyth’s design could not test generalization from moving to stationary objects or across different velocities. The experiments described here were designed to establish whether infants can detect the color of stationary and moving objects and maintain this discrimination over changes in velocity. After four prefamiliarization trials, infants underwent six familiarization trials with a cylindrical object bearing a red or green pattern when it was either stationary or
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rotating (Experiment 1) or rotating at one of two velocities (Experiments 2 and 3). They then underwent four postfamiliarization trials with the pattern of the same or a different color moving at the same or a different velocity. If infants are capable of responding to the color of a moving object and generalizing this response with changes in velocity then, due to the effect of novelty, the duration of fixation with different colors should be greater. This can be determined by comparing fixation duration in postfamiliarization trials with that in the prefamiliarization trials. If such is the case then it can be concluded that infants have the perceptual potential for constancy of object identity with changes in object movement from both stationariness to movement and vice versa and from one velocity of movement to another. EXPERIMENT
1
Since it has been claimed that infants do not recognize a stationary object after having observed it when moving (Bower, Broughton, & Moore, 1971; Bower, 1974), the first experiment was concerned with responses to novel and familiar colors of stationary and moving (rotating) objects. Method
Subjects. A group of 35 healthy, full-term infants aged between 8 and 20 weeks participated. Of these, three were rejected for fussiness or crying and, of the remaining 32, 16 were in the range 8-14 weeks (x = 11 weeks 1 day) or “young” infants and 16 in the range 14-20 weeks (x = 17 weeks, 2 days) or “old” infants. All subjects were from a predominantly middleclass area. They were obtained through a local infant health center. Apparatus. The infants were supported in a commercially made baby seat modified with foam head supports on each side. The seat was mounted so that it could be moved toward and away from the stimulus object along a track on the floor of the viewing chamber, thus permitting adjustment of viewing distance. The chamber was 200 cm long, 76 cm wide, and 100 cm high. The sides of the chamber were of mid-gray curtaining but the top and end in back of the subject were open. In front of ,the subject there was a mid-gray vertical surface at the center of which a metal cylinder 20 cm long and 18 cm in diameter was mounted on an axle. The circular end of the cylinder nearest to the subject was frontoparallel. The distance between this end and the subject’s eyes was 55 cm. The cylinder could be rotated silently from 0 to 14 rpm (O-Wisec) by a motor mounted on the outside of the chamber and operating through a belt drive. The angular velocity of rotation could be adjusted by means of a voltage control. The stimulus patterns which were mounted on the cylinder (see below) were illuminated by two fluorescent tubular sources mounted vertically on either side of the chamber but screened from direct view by
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the subject. Mid-gray, draw-string curtains could be drawn across the chamber between subject and cylinder thus occluding the latter from view. The curtains were 14 cm from the end of the cylinder. A 0.7-cm aperture through which the infant’s head and eyes could be viewed was located in the end of the chamber I7 cm to the right of the cylinder axle. A small light was mounted on the back of the seat above and slightly in back of the baby’s head. This could be turned on by means of a foot-pedal at the beginning of a trial and off automatically by a preset timer, thus signalling the end of a trial. Stimulus patterns. The stimulus patterns were two cylindrical sleeves made of white cardboard, which fitted closely over the metal cylinder. On the end of one sleeve was a red cross extending across the full 18 cm diameter of the sleeve and on the end of the other a similar green cross. The center of each cross coincided with the center of the cylinder so that when the cylinder rotated, the cross rotated about its center. The luminance of the white surface between the arms of the cross was 423.8 cd/m2. That of the midgray surround was 13 1.5 cd/m2. Procedure. Babies were tested at the center at a time when mothers judged them to be fully alert. Mothers were present throughout the experimental sessions but did not participate. With the curtains closed the appropriate sleeve was placed over the cylinder and the angular velocity set on the voltage control. The curtains were then opened and the experimenter, observing the cornea1 reflection of the stimulus pattern, switched on the light above the infant’s head when the pattern was first fixated as described below. The light then remained on for 20 sec. The duration of each fixation was recorded by means of a switch on a chart recorder. (In the subsequent analyses, only the duration of the first fixations were used). At the end of the 20-set trial the curtains were closed. If no fixation occurred within 30 set of the curtains being opened the duration of fixation was scored as zero. Each subject underwent 14 trials with intertrial intervals of about 10 sec. The duration of each session was about 10 min. Testing involved three phases: four prefamiliarization (pre-F) trials, six familiarization (F) trials, and four postfamiliarization (post-F) trials. In pre-F trials the subjects were presented successively with the four possible combinations of stimulus conditions: green stationary, red stationary, green moving, and red moving. The order of the four pre-F trials was determined by a 4 x 4 Latin square with the same order for the four subgroups (see experimental design below). In the F trials a particular color was presented either when it was stationary (stationary F group) or moving (moving F group) for six consecutive trials. In the four post-F trials the subjects were again presented with the four combinations of stimulus conditions in the same order as in the pre-F trials. For convenience, the pre-F and post-F trials are referred to as novel or familiar
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relative to the color of the stimulus pattern presented during the familiarization trials. In summary, each subject was presented with the four combinations of movement and color (stationary familiar, stationary novel, moving familiar, and moving novel) over four pre-F trials, then the familiar stimulus pattern over six F trials, either stationary or moving depending on the F group, and, finally, the four combinations of movement and color over four post-F trials, a total of 14 trials. Scoring. Infants were judged to be fixating the stimulus pattern when the major part of its cornea1 reflection fell over the pupil. Earlier data (McKenzie & Day, 1971) have shown that the reliability coefficient for this method is of the order of .92. The score throughout was the duration of the first fixation for each trial. The duration of the first fixation rather than that of all fixations was used since there is evidence to indicate that this score is a sensitive measure of attention to different patterns (Lewis, Kagan, & Kalafat, 1966). Experimental design. The within subject independent variables were stage (pre-F and post-F trials), stationariness and rotation of the stimulus pattern, and color of the pattern (red and green). The between subject variables were age (young and old) and familiarization condition (stationary and moving pattern). The 32 infants were allocated to these latter two groups with 16 in the stationary F trials group and 16 in the moving F trials group. In each group half the subjects were young and half were old. Sex and color of stimulus pattern in F trials were balanced across the four age and F trials subgroups. Results
A comparison of mean and median first fixations revealed that these were quite similar, indicating that the distribution of scores was approximately normal and that parametric analyses were appropriate. (This was also the case in Experiments 2 and 3.) The results are shown graphically in Fig. 1. Separate analyses of variance were carried out on the scores for the pre-F and post-F trials and on those for the F trials. Pre-F and post-F scores. AnF group x age x stage x movement x color analysis of variance with repeated measures on the last three factors was carried out on the pre- and post-F scores. There was a significant effect of stage with subjects looking at the stimulus patterns longer in pre-F (X = 8.98 set) than in post-F (2 = 6.63 set) [F( 1,28) = 9.73; p < .Ol]. Subjects also looked significantly longer at moving (X = 12.15 set) than at stationary (X = 3.46 set) patterns [F(1,28) = 154.82; p < .OOl]. There was also a stage x movement interaction [F(1’28) = 10.54;~ < .Ol]. A posteriori Newman-Keuls tests showed that this interaction was due to a reduction in duration of fixation of moving (p < .Ol) but not stationary Cp > .05) patterns between the pre-F and post-F stage.
196
FM . NM.
I St FG MFG PRE- FAM. TRIALS
1
2
3 4 FAMILIARIZATION TRIALS
5
6
StFG MFG POST - FAM. TRIALS
FIG. 1. Mean duration of first fixation in prefamiliarization, familiarization, and postfamiliarization trials in Experiment 1. F St: familiar color, stationary pattern; N St: novel color, stationary pattern; FM: familiar color, moving pattern: NM: novel color, moving pattern. Stationary Familiarization Group (StFG): 0 O--O. Moving Familiarization Group (MFG): 0 0’.
The main aim of the experiment was to establish whether infants respond differentially to novel and familiar colors following familiarization. A significant stage x color interaction [F( 1,28) = 5.09; p < .05] indicated that this was so. Newman-Keuls tests also showed that there was no significant decrease in the length of fixation of novel patterns from the pre-F to the post-F stage but that infants looked significantly less at familiar colors in the post-F stage than in the pre-F stage Cp < .05). The analysis also showed that the younger infants fixated the patterns longer (2 = 9.39 set) than the older infants (2 = 6.22 set) [F( 1,28) = 7.50; p < .05], There was also a significant age x movement interaction [F( 1,28) = 9.37; p < .Ol]. Newman-Keuls tests showed that this was due to the young and old subjects looking at the stationary patterns for similar periods but younger infants looking significantly longer at moving patterns (p < .Ol). F trials scores. The F trials data were analysed in a group x age x trials analysis of variance with repeated measures on the last factor. There was a significant F group effect [F(1,28) = 24.30; p < .OOll with subjects fixating the pattern for longer when it was moving (x = 10.15 set) than when it was stationary (2 = 2.75 set). There was also a significant effect for age with the younger infants looking longer (2 = 8.38 set) at the patterns than older subjects (2 = 4.52 set) [F(1,28) = 6.62; p < .Ol]. The main effect for trials also proved to be significant [F(5,140) = 2.62; p <
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.05]. This effect was investigated in more detail by means of orthogonal comparisons which showed that the significance was attributable to longer fixations in Trial 1 compared with the remaining trials [F( 1,140) = 5.69; p < .05] and longer fixations in Trial 3 compared with subsequent trials [F(1,140) = 6.82; p < .Ol]. In summary, the infants looked for a shorter time at patterns during the post-F stage than in the pre-F stage and looked at the patterns less towards the end than the beginning of the six F trials. They also looked longer at moving than at stationary patterns with the younger subjects looking longer than the older at all stages. The duration of fixation of patterns of a familiar color decreased from the pre-F to the post-F stage while the duration for those of a novel color remained the same, indicating that infants can detect a pattern of a familiar color even when it changes from stationary to moving and vice versa. EXPERIMENT
2
The main outcomes of Experiment 1 were that infants aged between 8 and 20 weeks are capable of discriminating between moving and stationary patterns and, at the same time, of detecting and generalizing the color of a pattern from stationariness to rotary movement and vice versa. The aim of the second experiment was to establish whether these capacities are manifest for different angular velocities of rotation (i.e., whether infants can discriminate between different angular velocities and, at the same time, detect and generalize the color of a pattern across velocities). Method Subjects. A group of 18 infants between 8 and 20 weeks of age participated in the experiment. Of these, two were rejected for crying. Of the remaining 16, 8 were between 8 and 14 weeks old (3 = 12 weeks 1 day) and 8 between 14 and 20 weeks (x = 17 weeks 2 days). Apparatus. The apparatus was the same as that used in the first experiment. Stimulus patterns. The patterns again consisted of cylindrical, white, cardboard sleeves which fitted over the metal cylinder. In order to render the patterns more prominent, they were in the form of red and green Maltese crosses with the colored and white areas between them equal in area. Procedure, scoring, and design. With two exceptions the procedure, scoring and design of the experiment were the same as for Experiment 1. First, since there were only 16 subjects the two F groups each consisted of 8 subjects; and second, the patterns were rotated at two angular velocities, 42 and 84”/sec (7 and 14 rpm). These are referred to henceforth as slow and fast movement.
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Results
The results are shown graphically in Fig. 2. As for the results in the first experiment, two separate analyses of variance were carried out, one on the data from the pre-F and post-F trials and the other on those from the F trials. Both analyses were essentially the same as before. Be-F andpost-F scores. The F group x age x stage x velocity x color analysis showed that the subjects looked longer at the stimulus patterns in pre-F trials (x = 12.89 set) than in post-F trials (J$?= 7.71 set) [F( 1,12) = 28.25;~ < .OOl], and longer at fast (x = 12.47 set) than at slow movement (2 = 8.14) [F(1,12) = 42.16; p < .OOl]. Novel colors were looked at for significantly longer than familiar colors (x = 11.34 and 9.26 set, respectively) [F(1,12) = 7.15; p < .051. Newman-Keuls tests on the significant stage x color interaction [F(1,12) = 6.07; p < .051 revealed no difference in fixation times between novel and familiar colors in the pre-F stage, a significant decrement in fixation times from the pre-F to post-F stage with familiar colors (p < .Ol) but not for novel colors, and significantly longer fixations of novel than of familiar colors in the post-F stage @ < .05). There was no significant main effect of age, possibly due to the decreased sample size in this experiment, but the age x color interaction proved to be significant [F(1,12) = 8.03; p < .05]. Newman-Keuls tests showed that this was due to young infants failing to look for significantly different times at novel and familiar colors over both stages and old
FS . t
.
,sFG
FFG,
PRE - FAM TRIALS
1
2
3 4 FAMILIARIZATION TRIALS
5
6
?FG FFG, POST - FAM TRIALS
FIG. 2. Mean duration of first fixation in prefamiliarization, familiarization, and postfamiliarization trials in Experiment 2. FS: familiar color, slow movement; NS: novel color, slow movement; FF: familiar color, fast movement; NF: novel color, fast movement. Slow Movement Familiarization Group (SF@: 0 u. Fast Movement Familiarization Group (FFG): A A-A.
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infants looking longer at novel than at familiar colors over both stages (p < .05). However as indicated above, the stage x color interaction (p < .05) shows that all subjects looked longer at novel than familiar colors in the post-F but not in the pre-F stage. F trials scores. Analysis of the F trials data in an F group x age x trials analysis of variance showed a main effect of trials [F(5,60) = 2.55; p < .05]. Orthogonal comparisons revealed that this was due to subjects looking longer in Trial 1 than in subsequent trials [F( 1,60) = 4.69; p < .05], and longer in Trial 2 than in subsequent trials [F(1,60) = 6.35; p < .05]. There was no main effect due to age, again possibly due to the decreased sample size compared to the first experiment. There were no significant interactions involving age and none due to F group. In summary, the fixation scores decreased from the pre-F to the post-F stage and decreased over trials, subjects looked longer at fast- than at slow-moving patterns in both the pre-F and post-F stages, and novel colors were looked at for longer than familiar colors in the post-F stage after exposure to a familiar color. This last result was obtained for both age groups as is shown by the stage x color interaction but the age x color interaction suggests that the older subjects contributed more towards this result than the younger subjects. EXPERIMENT
3
The third experiment was subsidiary to the second. Its purpose was to establish whether the outcomes of Experiment 2 obtain for a greater viewing distance. McKenzie and Day (1972) showed that duration of fixation of stationary objects by infants between 6 and 20 weeks of age declines markedly with distance regardless of visual angle; at 90 cm the object is hardly looked at. However, a pilot experiment in this series indicated that a rotating object is fixated by infants for prolonged periods even when it is 100 cm away. It was considered worthwhile to establish whether the basis for identity constancy which had emerged from the first two experiments occurs with moving objects viewed from a greater distance. The experiment described below was the same in all essential respects as the second with the exception that the viewing distance was 100 cm. Method Subjects. Of a group of 38 healthy, full-term infants 8-20 weeks old, four were rejected for fussiness or crying and two for drowsiness or for sleeping. Of the remaining 32, 16 were in the age range 8-14 weeks (z = 11 weeks 4 days) and 16 in the range 14-20 weeks (x = 17 weeks 3 days). Apparatus, procedure, scoring, and design. The apparatus, procedure, scoring, and design of the experiment were essentially the same as in the
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second experiment with the exception that there were 32 subjects in two F groups of 16 and the viewing distance was increased to 100 cm. Results
The mean fixation times are shown in Fig. 3. Two analyses similar to those in the earlier experiments were carried out on the scores. Pre-F and post-F scores. An F group x age x stage x velocity x color analysis of variance revealed a significant effect for stage [F(1,28) = 37.25; p < .OOl], with subjects fixating the rotating stimulus pattern for longer in the pre-F (x = 14.30 set) stage than in the post-F (2 = 9.84 set) stage. Subjects also looked longer at the fast-moving (2 = 12.88 set) than at the slow-moving (x = 11.26 set) pattern [F(1,28) = 4.84, p < .051. Newman-Keuls tests directed at the significant stage x velocity interaction [F( 1,28) = 7.78; p < .Ol)] showed that it was attributable mainly to subjects looking longer at the fast-moving than at the slow moving pattern during the post-F stage (p < .05) but not during the pre-F stage. The stage x color interaction was not significant [F( 1,28) = 3.16; p > .051, but since babies looked longer at novel (12.89 set) than at familiar (I 1.24 set) colors overall [F(1,28) = 12.47; p < .005], and since the main purpose of the experiment was to compare the duration of fixation of novel and familiar colors in the post-F stage, Newman-Keuls tests were nevertheless carried out. These showed that the differences between novel and familiar colors
NF.
SFG PRE-FAM. TRIALS
FFG
1
2
3
4
FAMILIARIZATION TRIALS
5
6
H.
SFG
FFG
POSTTRIALS
FIG. 3. Mean duration of first fixation in prefamiliarization, familiarization, and postfamiliarization trials in Experiment 3. FS: familiar color, slow movement: NS: novel color. slow movement; FF: familiar color, fast movement: NF: novel color, fast movement. Slow Movement Familiarization Group (SFG): 0 04. Fast Movement Familiarization Group (FFG): A A--A.
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in the pre-F stage were not significant, decrements from the pre-F to post-F stage were significant for both novel and familiar colors @ < .05 and p < .Ol , respectively), and that the differences between familiar and novel colors in the post-F stage were significant @ < .OS>. The younger subjects looked longer (x = 15.56 set) than the older subjects (2 = 8.57 set) [F(1,28) = 37.25;~ < .Oll. Newman-Keuls tests on the significant age x velocity interaction [F( 1,28) = 5.72; p < .05] showed that whereas the younger subjects looked longer at the fastmoving than at the slow-moving patterns @ < .Ol), the older subjects did not. F trials scores. Data from the F trials were again analyzed in an F group x age x trials analysis of variance. This showed that there was a significant effect for age [F( 1,28) = 16.61; p < .OOll, with younger subjects looking longer than older subjects, x = 12.20 and 4.92 set, respectively. Neither the effects of F group, trials, or the interactions between them achieved significance. In summary, subjects looked longer during the pre-F than during the post-F stage, the younger subjects looked longer than the older subjects at all patterns, the younger but not the older subjects looked longer at fastthan slow-moving patterns, and all subjects looked longer at novel than at familiar colors in the post-F trials. DISCUSSION
AND CONCLUSIONS
The outcomes of the three experiments show that infants 8 to 20 weeks of age are sensitive to the movement of a revolving pattern and to at least one other feature, that of color, and respond to this feature when the pattern changes from movement to stationariness or vice versa and from slow to fast rotation or vice versa. From these results it can be concluded that the response to movement by young infants does not exclude detection of another property as has been suggested by Bower, Broughton, and Moore (1971) and Bower (1974). However, it can be argued that rotary movement with the object remaining in the same position, as in the experiments described here, and lateral movement with change in the position of the object, as in Bower’s experiments, are the basis of the different outcomes. Nevertheless, the fact remains that infants are capable of detecting at least one other object property of a moving object. Additional experiments are necessary to establish whether under otherwise similar conditions different outcomes obtain for rotary movement and lateral displacement. At the most general level the results from the three experiments demonstrate that in infancy it is possible that recognition of object identity over gross object transformations may occur without the ability to handle objects. While this finding is contrary to the view of object permanence proposed by Piaget (1954) it agrees with results reported recently by Field
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(1976). Field found that babies 15 weeks of age look longer at, but do not reach more often for, three-dimensional than they do for two-dimensional objects which are otherwise similar. By the age of 24 weeks, the same subjects also reached for the three-dimensional objects more than the two-dimensional. This observation suggests that visual discriminations can be made ontogenetically prior to manual discriminations and opens the possibility that motor activities may be partially directed by visual discriminations first made at an earlier age. The data also show that infants between 8 and 20 weeks of age can discriminate between stationariness and rotary movement and between changes in angular velocity for distances up to 100 cm. It is emphasized, however, that the infants do not look longer at novel velocities of movement but at the faster of two velocities (i.e., at 84”/sec longer than 42”/sec, and at 42Vsec longer than O”/sec). These results thus confirm the earlier observations cited above, which show that infants prefer to look at movement and movement-like sequences rather than static displays. It can be noted also that the data reported here are broadly in agreement with those which show that young infants in the range 8-14 weeks tend to look at patterns longer than older infants in the range 14-20 weeks and that, in particular, the younger infants look at revolving rather than stationary and fast moving rather than slow moving objects for longer (McKenzie & Day, 1976). Three issues from the experiments warrant further comment. First, the infants looked longer at fast moving patterns in both the pre-F and post-F stages when the pattern was 55 cm away but in only the post-F stage when it was 100 cm away. This result suggests that either both fast and slow rotation were highly interesting to these subjects in pre-F trials for a viewing distance of 100 cm or, simply, that differences in velocity were not discriminable in pre-F trials for this distance and that some degree of sensitization to movement was necessary before the discrimination could be made in the post-F trials. Clearly it is not at present possible to choose between these two possibilities. To be able to do so would be of some interest in regard to the possible role of “priming” or sensitization in velocity discrimination. Second, when the stimulus patterns were moving, all subjects looked longer at novel than at familiar patterns at 100 cm, but at 55 cm, although all subjects again looked longer at novel than familiar patterns, this was mainly due to the older babies. Therefore the novel-familiar difference was discriminated by the younger subjects at both 100 cm and 55 cm but at 55 cm the objects tended to be fixated more equally, possibly due to the high degree of interest in moving patterns. Third, mainly younger babies discriminated between fast- and slowmoving patterns when the objects were at 100 cm. This suggests that older infants could make the discrimination but that at 100 cm the difference was not of marked salience.
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Visual angle was not controlled between the two distances. If the existence of sustained and transient cells, and furthermore the equivocal evidence regarding their differential dispersion over the retina (De Monasterio & Gouras, 1975; Schiller & Malpeli, 1977) can be generalized from monkeys to humans, then it might be argued that at 55 cm more movement sensitive transient cells would be stimulated than at 100 cm. Even if this were the case it is not clear how such could have resulted in the differences between the two distances. The experiments described here were not designed to distinguish between interpretations based on changes in distance itself or in the visual angle subtended at the eye by the patterned object. However, McKenzie and Day (1972) found that fixations by infants of stationary objects are determined by distance, not by visual subtense. It seems reasonable to suppose that the same applies with moving objects, although this supposition must in due course be checked experimentally. It can be concluded that infants between 8 and 20 weeks generalize the color of a pattern from a stationary to a rotating mode and vice versa at a viewing distance of 55 cm. When all patterns rotate and are viewed from 55 cm all babies in this age range respond to a change in color despite changes in velocity but this is less evident for the younger babies. With an increase in the viewing distance to 100 cm differences in velocity are either less discriminable or less salient. Nevertheless the perceptual capacity to discriminate between a familiar and a novel color and to generalize this discrimination over velocity changes, continues to be evident at both ages. REFERENCES Bower, T. G. R. Object permanence and short term memory in the human infant (Manuscript, 1966). Reported in E. J. Gibson (Ed.), Principles of perceptual learning and development. New York: Appleton-Century-Crofts, 1969. Bower, T. G. R. Development in infancy. San Francisco: W. H. Freeman & Company, 1974. Bower, T. G. R., Broughton, J., & Moore, M. K. Development of the object concept as manifested in changes in the tracking behaviour of infants between 7 and 20 weeks of age. Journal of Experimental Child Psychology, 1971, 11, 182-193. Carpenter, G. C. Visual regard of moving and stationary faces in early infancy. MerrillPalmer Quarterly, 1974, 20, 181-194. Cohen, L. B., Gelber, E. R., & Lazar. M. A. Infant habituation and generalization to differing degrees of stimulus novelty. Journal of Experimental Child Psychology, 1971, 11, 379-389.
De Monasterio, F. M., & Gouras, P. Functional properties of ganglion cells of the rhesus monkey retina. Journa/ of Physiology, 1975, 251, 167-195. Field, J. Relation of young infants’ reaching behaviour to stimulus distance and solidity. Developmental Psychology, 1976, 12, 444-448. Gibson, E., Johnston, J., & Owsley, C. Perception of invariance by five-month-old infants: Differentiation of two types of motion. Developmental Psychology. 1978. 14,407-415. Haith, M. M. The response of the human newborn to visual movement. Journal of Experimental Child Psychology, 1966, 3, 235-243.
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Hartlep, K. L.. & Forsyth, G. A. Infants’ discrimination Perceptual
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of moving and stationary objects.
1977, 45, 27-33.
Lewis, M., Kagan, J., & Kalafat, J. Patterns of fixation in the young infant. Child Developmen?, 1966, 37, 331-341. McGurk, H. Infant discrimination of orientation. Journal of Experimental Child Psychology, 1972, 14, 151-164. McKenzie, B. E., & Day, R. H. Orientation discrimination in infants: A comparison of visual fixation and operant training methods. Journal of Experimenfnl Child Psychology, 1971, 11, 366-375. McKenzie, B. E., & Day. R. H. Object distance as a determinant of visual fixation in early infancy. Science, 1972, 178, 1108-I 110. McKenzie, B. E., & Day, R. H. Infants’ attention to stationary and moving objects at different distances. Australian Journal of Psychology, 1976, 28, 45-51. Piaget, J. The construction of reality in the child. London: Routledge & Kegan Paul, 1954. Schiller, P. H.. & Malpeli, J. G. Properties and tectal projections of monkey retinal ganglion cells. Journal of Neurophysiology. 1977, 40, 428-445. Volkmann. F. C., & Dobson, M. V. Infant responses of ocular fixation to moving visual stimuli. Journal of Experimental Child Psychology, 1976, 22, 86-99. Wilcox, B. M., & Clayton, F. L. Infant visual fixation of the human face. Journal of Experimental
Child
Psychology,
1968. 6, 22-32.
REFERENCE
NOTES
1. Contole, J. Young infants’ responses to color undform stimulus-attribute change. Paper presented at the Australian Psychological Society Conference, Melbourne, September 1975. 2. McKenzie, B. E. Comparison ofJixation times and looking styles forfamiliar and novel stimuli in day-care and home-reared babies. Paper presented at the Australian Psychological Society Conference, Melbourne, September 1975. 3. Silfen, C. K., & Ames, E. W. Visual movement preferences in the human infant. Paper presented at the Eastern Psychology Association. Philadelphia, April 1964. RECEIVED:
May
9, 1978;
REVISED:
August 22, 1978.
OF EXPERIMENTAL
CHILD
PSYCHOLOGY
28, 191-204 (1979)
Detection of Color in Rotating Objects by Infants and Its Generalization over Changes in Velocity D.K.
BURNHAM Monash
AND R. H. DAY Universit)
In three experiments, infants between 8 and 20 weeks of age were familiarized during habituation trials to either a stationary or revolving patterned cylinder (Experiment 1) or to the same object when it was revolving at one of two angular velocities (Experiments 2 and 3). In the postfamiliarization trials, anguiar velocity was changed with the color of the pattern either the same as or different from that in the familiarization trials. The results showed that the infants were not only sensitive to movement and changes in velocity but to the color of the moving pattern. Furthermore, this response to color generalized across changes in angular velocity. These findings indicate that a necessary condition for identity constancy, detection of an object property with object transformations, is present between 8 and 20 weeks, prior to the stage of manual manipulation of objects. A number of subsidiary findings concerning movement discrimination at 55 and 100 cm viewing distances by ll- and 17-week-old infants are also described.
Infants prefer movement-like sequences or displays to stationary displays. In particular, suppression of nonnutritive sucking by neonates is greater for a sequence of lights flashing from right to left than for a single, stationary light (Haith, 1966); both neonates (Carpenter, 1974) and 20- to 23-week-old babies (Wilcox & Clayton, 1968) prefer to fixate or to scan moving rather than stationary representations of human faces; 16- and 24-week-old babies prefer patterns moving vertically to stationary patterns (Silfen & Ames, Note 3); 4-, 7.5, and 12-week-old babies fixate patterns moving horizontally longer than stationary patterns (Volkmann & Dobson, 1976); and 9- and 16-week-old infants fixate rotating patterned cylinders longer than stationary cylinders (McKenzie & Day, 1976). In These experiments were undertaken when the first author was in receipt of a Commonwealth Post-Graduate Scholarship. Requests for reprints should be sent to Dr. D. K. Bumham, Department of Psychology, Monash University, Clayton, Victoria, Australia 3168. 191 0022-0%5/79/050191-14$02.00/O Copyright @ 1979 by Academic Press. Inc. All rights of reproduction in any form reserved.
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addition, Gibson, Johnston, and Owsley (1978) have shown that 5-month-old infants are capable of discriminating between different classes of motion transformation such as rigid rotation about an axis and nonrigid “squeezing” transformations. However, whether infants respond exclusively to movement in a “reflexive,” automatic manner, or whether movement is merely one of numerous, salient properties of objects, which are detected and accordingly responded to, is not yet clear. In the first case, infants presumably would respond only to the movement without identifying other properties; whereas in the second they could be expected to detect properties additional to the movement of the object. Furthermore, if infants detect and respond to properties of objects other than those of movement, then they could be expected to recognize and respond to these under changed conditions (e.g., at different velocities). With stationary objects such generalization occurs in respect of form with changes in object orientation (McGurk, 1972). Such an ability to generalize is logically necessary for identity constancy, the capacity to recognize an object as the same object despite variations in its position, orientation, or velocity. Piaget (1954) has argued that identity constancy, or the broader concept of object permanence, does not start to develop until after the age of 4% months when infants develop the ability to reach for and grasp objects and subsequently distinguish objects from the results of their own motor activity. In a more specific vein, Bower (Bower, Broughton, & Moore, 1971; Bower, 1974) has recently claimed that infants less than 20 weeks of age do not detect the properties of moving objects and, in fact, respond to a moving object simply as a path of movement and as something totally different from the same object when stationary. Bower attributes this to the limited input channels and processing capacity of young infants. However, with stationary objects, processing in the first year is certainly not limited to one channel. Infants can, for example. detect both the color and form of a stationary object (Bower. 1969; Cohen, Gelber & Lazar, 1971: Contole, Note 1; McKenzie, Note 2). More particularly, Hartlep and Forsyth ( 1977) have recently found that lo-week-old infants, operantly trained to discriminate between a stationary cube and sphere presented simultaneously, subsequently maintained this discrimination when the objects were moving. Thus, contrary to Bower’s claim, infants seem to detect the features of moving objects. However, Hartlep and Forsyth’s design could not test generalization from moving to stationary objects or across different velocities. The experiments described here were designed to establish whether infants can detect the color of stationary and moving objects and maintain this discrimination over changes in velocity. After four prefamiliarization trials, infants underwent six familiarization trials with a cylindrical object bearing a red or green pattern when it was either stationary or
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rotating (Experiment 1) or rotating at one of two velocities (Experiments 2 and 3). They then underwent four postfamiliarization trials with the pattern of the same or a different color moving at the same or a different velocity. If infants are capable of responding to the color of a moving object and generalizing this response with changes in velocity then, due to the effect of novelty, the duration of fixation with different colors should be greater. This can be determined by comparing fixation duration in postfamiliarization trials with that in the prefamiliarization trials. If such is the case then it can be concluded that infants have the perceptual potential for constancy of object identity with changes in object movement from both stationariness to movement and vice versa and from one velocity of movement to another. EXPERIMENT
1
Since it has been claimed that infants do not recognize a stationary object after having observed it when moving (Bower, Broughton, & Moore, 1971; Bower, 1974), the first experiment was concerned with responses to novel and familiar colors of stationary and moving (rotating) objects. Method
Subjects. A group of 35 healthy, full-term infants aged between 8 and 20 weeks participated. Of these, three were rejected for fussiness or crying and, of the remaining 32, 16 were in the range 8-14 weeks (x = 11 weeks 1 day) or “young” infants and 16 in the range 14-20 weeks (x = 17 weeks, 2 days) or “old” infants. All subjects were from a predominantly middleclass area. They were obtained through a local infant health center. Apparatus. The infants were supported in a commercially made baby seat modified with foam head supports on each side. The seat was mounted so that it could be moved toward and away from the stimulus object along a track on the floor of the viewing chamber, thus permitting adjustment of viewing distance. The chamber was 200 cm long, 76 cm wide, and 100 cm high. The sides of the chamber were of mid-gray curtaining but the top and end in back of the subject were open. In front of ,the subject there was a mid-gray vertical surface at the center of which a metal cylinder 20 cm long and 18 cm in diameter was mounted on an axle. The circular end of the cylinder nearest to the subject was frontoparallel. The distance between this end and the subject’s eyes was 55 cm. The cylinder could be rotated silently from 0 to 14 rpm (O-Wisec) by a motor mounted on the outside of the chamber and operating through a belt drive. The angular velocity of rotation could be adjusted by means of a voltage control. The stimulus patterns which were mounted on the cylinder (see below) were illuminated by two fluorescent tubular sources mounted vertically on either side of the chamber but screened from direct view by
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the subject. Mid-gray, draw-string curtains could be drawn across the chamber between subject and cylinder thus occluding the latter from view. The curtains were 14 cm from the end of the cylinder. A 0.7-cm aperture through which the infant’s head and eyes could be viewed was located in the end of the chamber I7 cm to the right of the cylinder axle. A small light was mounted on the back of the seat above and slightly in back of the baby’s head. This could be turned on by means of a foot-pedal at the beginning of a trial and off automatically by a preset timer, thus signalling the end of a trial. Stimulus patterns. The stimulus patterns were two cylindrical sleeves made of white cardboard, which fitted closely over the metal cylinder. On the end of one sleeve was a red cross extending across the full 18 cm diameter of the sleeve and on the end of the other a similar green cross. The center of each cross coincided with the center of the cylinder so that when the cylinder rotated, the cross rotated about its center. The luminance of the white surface between the arms of the cross was 423.8 cd/m2. That of the midgray surround was 13 1.5 cd/m2. Procedure. Babies were tested at the center at a time when mothers judged them to be fully alert. Mothers were present throughout the experimental sessions but did not participate. With the curtains closed the appropriate sleeve was placed over the cylinder and the angular velocity set on the voltage control. The curtains were then opened and the experimenter, observing the cornea1 reflection of the stimulus pattern, switched on the light above the infant’s head when the pattern was first fixated as described below. The light then remained on for 20 sec. The duration of each fixation was recorded by means of a switch on a chart recorder. (In the subsequent analyses, only the duration of the first fixations were used). At the end of the 20-set trial the curtains were closed. If no fixation occurred within 30 set of the curtains being opened the duration of fixation was scored as zero. Each subject underwent 14 trials with intertrial intervals of about 10 sec. The duration of each session was about 10 min. Testing involved three phases: four prefamiliarization (pre-F) trials, six familiarization (F) trials, and four postfamiliarization (post-F) trials. In pre-F trials the subjects were presented successively with the four possible combinations of stimulus conditions: green stationary, red stationary, green moving, and red moving. The order of the four pre-F trials was determined by a 4 x 4 Latin square with the same order for the four subgroups (see experimental design below). In the F trials a particular color was presented either when it was stationary (stationary F group) or moving (moving F group) for six consecutive trials. In the four post-F trials the subjects were again presented with the four combinations of stimulus conditions in the same order as in the pre-F trials. For convenience, the pre-F and post-F trials are referred to as novel or familiar
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relative to the color of the stimulus pattern presented during the familiarization trials. In summary, each subject was presented with the four combinations of movement and color (stationary familiar, stationary novel, moving familiar, and moving novel) over four pre-F trials, then the familiar stimulus pattern over six F trials, either stationary or moving depending on the F group, and, finally, the four combinations of movement and color over four post-F trials, a total of 14 trials. Scoring. Infants were judged to be fixating the stimulus pattern when the major part of its cornea1 reflection fell over the pupil. Earlier data (McKenzie & Day, 1971) have shown that the reliability coefficient for this method is of the order of .92. The score throughout was the duration of the first fixation for each trial. The duration of the first fixation rather than that of all fixations was used since there is evidence to indicate that this score is a sensitive measure of attention to different patterns (Lewis, Kagan, & Kalafat, 1966). Experimental design. The within subject independent variables were stage (pre-F and post-F trials), stationariness and rotation of the stimulus pattern, and color of the pattern (red and green). The between subject variables were age (young and old) and familiarization condition (stationary and moving pattern). The 32 infants were allocated to these latter two groups with 16 in the stationary F trials group and 16 in the moving F trials group. In each group half the subjects were young and half were old. Sex and color of stimulus pattern in F trials were balanced across the four age and F trials subgroups. Results
A comparison of mean and median first fixations revealed that these were quite similar, indicating that the distribution of scores was approximately normal and that parametric analyses were appropriate. (This was also the case in Experiments 2 and 3.) The results are shown graphically in Fig. 1. Separate analyses of variance were carried out on the scores for the pre-F and post-F trials and on those for the F trials. Pre-F and post-F scores. AnF group x age x stage x movement x color analysis of variance with repeated measures on the last three factors was carried out on the pre- and post-F scores. There was a significant effect of stage with subjects looking at the stimulus patterns longer in pre-F (X = 8.98 set) than in post-F (2 = 6.63 set) [F( 1,28) = 9.73; p < .Ol]. Subjects also looked significantly longer at moving (X = 12.15 set) than at stationary (X = 3.46 set) patterns [F(1,28) = 154.82; p < .OOl]. There was also a stage x movement interaction [F(1’28) = 10.54;~ < .Ol]. A posteriori Newman-Keuls tests showed that this interaction was due to a reduction in duration of fixation of moving (p < .Ol) but not stationary Cp > .05) patterns between the pre-F and post-F stage.
196
FM . NM.
I St FG MFG PRE- FAM. TRIALS
1
2
3 4 FAMILIARIZATION TRIALS
5
6
StFG MFG POST - FAM. TRIALS
FIG. 1. Mean duration of first fixation in prefamiliarization, familiarization, and postfamiliarization trials in Experiment 1. F St: familiar color, stationary pattern; N St: novel color, stationary pattern; FM: familiar color, moving pattern: NM: novel color, moving pattern. Stationary Familiarization Group (StFG): 0 O--O. Moving Familiarization Group (MFG): 0 0’.
The main aim of the experiment was to establish whether infants respond differentially to novel and familiar colors following familiarization. A significant stage x color interaction [F( 1,28) = 5.09; p < .05] indicated that this was so. Newman-Keuls tests also showed that there was no significant decrease in the length of fixation of novel patterns from the pre-F to the post-F stage but that infants looked significantly less at familiar colors in the post-F stage than in the pre-F stage Cp < .05). The analysis also showed that the younger infants fixated the patterns longer (2 = 9.39 set) than the older infants (2 = 6.22 set) [F( 1,28) = 7.50; p < .05], There was also a significant age x movement interaction [F( 1,28) = 9.37; p < .Ol]. Newman-Keuls tests showed that this was due to the young and old subjects looking at the stationary patterns for similar periods but younger infants looking significantly longer at moving patterns (p < .Ol). F trials scores. The F trials data were analysed in a group x age x trials analysis of variance with repeated measures on the last factor. There was a significant F group effect [F(1,28) = 24.30; p < .OOll with subjects fixating the pattern for longer when it was moving (x = 10.15 set) than when it was stationary (2 = 2.75 set). There was also a significant effect for age with the younger infants looking longer (2 = 8.38 set) at the patterns than older subjects (2 = 4.52 set) [F(1,28) = 6.62; p < .Ol]. The main effect for trials also proved to be significant [F(5,140) = 2.62; p <
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.05]. This effect was investigated in more detail by means of orthogonal comparisons which showed that the significance was attributable to longer fixations in Trial 1 compared with the remaining trials [F( 1,140) = 5.69; p < .05] and longer fixations in Trial 3 compared with subsequent trials [F(1,140) = 6.82; p < .Ol]. In summary, the infants looked for a shorter time at patterns during the post-F stage than in the pre-F stage and looked at the patterns less towards the end than the beginning of the six F trials. They also looked longer at moving than at stationary patterns with the younger subjects looking longer than the older at all stages. The duration of fixation of patterns of a familiar color decreased from the pre-F to the post-F stage while the duration for those of a novel color remained the same, indicating that infants can detect a pattern of a familiar color even when it changes from stationary to moving and vice versa. EXPERIMENT
2
The main outcomes of Experiment 1 were that infants aged between 8 and 20 weeks are capable of discriminating between moving and stationary patterns and, at the same time, of detecting and generalizing the color of a pattern from stationariness to rotary movement and vice versa. The aim of the second experiment was to establish whether these capacities are manifest for different angular velocities of rotation (i.e., whether infants can discriminate between different angular velocities and, at the same time, detect and generalize the color of a pattern across velocities). Method Subjects. A group of 18 infants between 8 and 20 weeks of age participated in the experiment. Of these, two were rejected for crying. Of the remaining 16, 8 were between 8 and 14 weeks old (3 = 12 weeks 1 day) and 8 between 14 and 20 weeks (x = 17 weeks 2 days). Apparatus. The apparatus was the same as that used in the first experiment. Stimulus patterns. The patterns again consisted of cylindrical, white, cardboard sleeves which fitted over the metal cylinder. In order to render the patterns more prominent, they were in the form of red and green Maltese crosses with the colored and white areas between them equal in area. Procedure, scoring, and design. With two exceptions the procedure, scoring and design of the experiment were the same as for Experiment 1. First, since there were only 16 subjects the two F groups each consisted of 8 subjects; and second, the patterns were rotated at two angular velocities, 42 and 84”/sec (7 and 14 rpm). These are referred to henceforth as slow and fast movement.
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Results
The results are shown graphically in Fig. 2. As for the results in the first experiment, two separate analyses of variance were carried out, one on the data from the pre-F and post-F trials and the other on those from the F trials. Both analyses were essentially the same as before. Be-F andpost-F scores. The F group x age x stage x velocity x color analysis showed that the subjects looked longer at the stimulus patterns in pre-F trials (x = 12.89 set) than in post-F trials (J$?= 7.71 set) [F( 1,12) = 28.25;~ < .OOl], and longer at fast (x = 12.47 set) than at slow movement (2 = 8.14) [F(1,12) = 42.16; p < .OOl]. Novel colors were looked at for significantly longer than familiar colors (x = 11.34 and 9.26 set, respectively) [F(1,12) = 7.15; p < .051. Newman-Keuls tests on the significant stage x color interaction [F(1,12) = 6.07; p < .051 revealed no difference in fixation times between novel and familiar colors in the pre-F stage, a significant decrement in fixation times from the pre-F to post-F stage with familiar colors (p < .Ol) but not for novel colors, and significantly longer fixations of novel than of familiar colors in the post-F stage @ < .05). There was no significant main effect of age, possibly due to the decreased sample size in this experiment, but the age x color interaction proved to be significant [F(1,12) = 8.03; p < .05]. Newman-Keuls tests showed that this was due to young infants failing to look for significantly different times at novel and familiar colors over both stages and old
FS . t
.
,sFG
FFG,
PRE - FAM TRIALS
1
2
3 4 FAMILIARIZATION TRIALS
5
6
?FG FFG, POST - FAM TRIALS
FIG. 2. Mean duration of first fixation in prefamiliarization, familiarization, and postfamiliarization trials in Experiment 2. FS: familiar color, slow movement; NS: novel color, slow movement; FF: familiar color, fast movement; NF: novel color, fast movement. Slow Movement Familiarization Group (SF@: 0 u. Fast Movement Familiarization Group (FFG): A A-A.
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infants looking longer at novel than at familiar colors over both stages (p < .05). However as indicated above, the stage x color interaction (p < .05) shows that all subjects looked longer at novel than familiar colors in the post-F but not in the pre-F stage. F trials scores. Analysis of the F trials data in an F group x age x trials analysis of variance showed a main effect of trials [F(5,60) = 2.55; p < .05]. Orthogonal comparisons revealed that this was due to subjects looking longer in Trial 1 than in subsequent trials [F( 1,60) = 4.69; p < .05], and longer in Trial 2 than in subsequent trials [F(1,60) = 6.35; p < .05]. There was no main effect due to age, again possibly due to the decreased sample size compared to the first experiment. There were no significant interactions involving age and none due to F group. In summary, the fixation scores decreased from the pre-F to the post-F stage and decreased over trials, subjects looked longer at fast- than at slow-moving patterns in both the pre-F and post-F stages, and novel colors were looked at for longer than familiar colors in the post-F stage after exposure to a familiar color. This last result was obtained for both age groups as is shown by the stage x color interaction but the age x color interaction suggests that the older subjects contributed more towards this result than the younger subjects. EXPERIMENT
3
The third experiment was subsidiary to the second. Its purpose was to establish whether the outcomes of Experiment 2 obtain for a greater viewing distance. McKenzie and Day (1972) showed that duration of fixation of stationary objects by infants between 6 and 20 weeks of age declines markedly with distance regardless of visual angle; at 90 cm the object is hardly looked at. However, a pilot experiment in this series indicated that a rotating object is fixated by infants for prolonged periods even when it is 100 cm away. It was considered worthwhile to establish whether the basis for identity constancy which had emerged from the first two experiments occurs with moving objects viewed from a greater distance. The experiment described below was the same in all essential respects as the second with the exception that the viewing distance was 100 cm. Method Subjects. Of a group of 38 healthy, full-term infants 8-20 weeks old, four were rejected for fussiness or crying and two for drowsiness or for sleeping. Of the remaining 32, 16 were in the age range 8-14 weeks (z = 11 weeks 4 days) and 16 in the range 14-20 weeks (x = 17 weeks 3 days). Apparatus, procedure, scoring, and design. The apparatus, procedure, scoring, and design of the experiment were essentially the same as in the
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second experiment with the exception that there were 32 subjects in two F groups of 16 and the viewing distance was increased to 100 cm. Results
The mean fixation times are shown in Fig. 3. Two analyses similar to those in the earlier experiments were carried out on the scores. Pre-F and post-F scores. An F group x age x stage x velocity x color analysis of variance revealed a significant effect for stage [F(1,28) = 37.25; p < .OOl], with subjects fixating the rotating stimulus pattern for longer in the pre-F (x = 14.30 set) stage than in the post-F (2 = 9.84 set) stage. Subjects also looked longer at the fast-moving (2 = 12.88 set) than at the slow-moving (x = 11.26 set) pattern [F(1,28) = 4.84, p < .051. Newman-Keuls tests directed at the significant stage x velocity interaction [F( 1,28) = 7.78; p < .Ol)] showed that it was attributable mainly to subjects looking longer at the fast-moving than at the slow moving pattern during the post-F stage (p < .05) but not during the pre-F stage. The stage x color interaction was not significant [F( 1,28) = 3.16; p > .051, but since babies looked longer at novel (12.89 set) than at familiar (I 1.24 set) colors overall [F(1,28) = 12.47; p < .005], and since the main purpose of the experiment was to compare the duration of fixation of novel and familiar colors in the post-F stage, Newman-Keuls tests were nevertheless carried out. These showed that the differences between novel and familiar colors
NF.
SFG PRE-FAM. TRIALS
FFG
1
2
3
4
FAMILIARIZATION TRIALS
5
6
H.
SFG
FFG
POSTTRIALS
FIG. 3. Mean duration of first fixation in prefamiliarization, familiarization, and postfamiliarization trials in Experiment 3. FS: familiar color, slow movement: NS: novel color. slow movement; FF: familiar color, fast movement: NF: novel color, fast movement. Slow Movement Familiarization Group (SFG): 0 04. Fast Movement Familiarization Group (FFG): A A--A.
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in the pre-F stage were not significant, decrements from the pre-F to post-F stage were significant for both novel and familiar colors @ < .05 and p < .Ol , respectively), and that the differences between familiar and novel colors in the post-F stage were significant @ < .OS>. The younger subjects looked longer (x = 15.56 set) than the older subjects (2 = 8.57 set) [F(1,28) = 37.25;~ < .Oll. Newman-Keuls tests on the significant age x velocity interaction [F( 1,28) = 5.72; p < .05] showed that whereas the younger subjects looked longer at the fastmoving than at the slow-moving patterns @ < .Ol), the older subjects did not. F trials scores. Data from the F trials were again analyzed in an F group x age x trials analysis of variance. This showed that there was a significant effect for age [F( 1,28) = 16.61; p < .OOll, with younger subjects looking longer than older subjects, x = 12.20 and 4.92 set, respectively. Neither the effects of F group, trials, or the interactions between them achieved significance. In summary, subjects looked longer during the pre-F than during the post-F stage, the younger subjects looked longer than the older subjects at all patterns, the younger but not the older subjects looked longer at fastthan slow-moving patterns, and all subjects looked longer at novel than at familiar colors in the post-F trials. DISCUSSION
AND CONCLUSIONS
The outcomes of the three experiments show that infants 8 to 20 weeks of age are sensitive to the movement of a revolving pattern and to at least one other feature, that of color, and respond to this feature when the pattern changes from movement to stationariness or vice versa and from slow to fast rotation or vice versa. From these results it can be concluded that the response to movement by young infants does not exclude detection of another property as has been suggested by Bower, Broughton, and Moore (1971) and Bower (1974). However, it can be argued that rotary movement with the object remaining in the same position, as in the experiments described here, and lateral movement with change in the position of the object, as in Bower’s experiments, are the basis of the different outcomes. Nevertheless, the fact remains that infants are capable of detecting at least one other object property of a moving object. Additional experiments are necessary to establish whether under otherwise similar conditions different outcomes obtain for rotary movement and lateral displacement. At the most general level the results from the three experiments demonstrate that in infancy it is possible that recognition of object identity over gross object transformations may occur without the ability to handle objects. While this finding is contrary to the view of object permanence proposed by Piaget (1954) it agrees with results reported recently by Field
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(1976). Field found that babies 15 weeks of age look longer at, but do not reach more often for, three-dimensional than they do for two-dimensional objects which are otherwise similar. By the age of 24 weeks, the same subjects also reached for the three-dimensional objects more than the two-dimensional. This observation suggests that visual discriminations can be made ontogenetically prior to manual discriminations and opens the possibility that motor activities may be partially directed by visual discriminations first made at an earlier age. The data also show that infants between 8 and 20 weeks of age can discriminate between stationariness and rotary movement and between changes in angular velocity for distances up to 100 cm. It is emphasized, however, that the infants do not look longer at novel velocities of movement but at the faster of two velocities (i.e., at 84”/sec longer than 42”/sec, and at 42Vsec longer than O”/sec). These results thus confirm the earlier observations cited above, which show that infants prefer to look at movement and movement-like sequences rather than static displays. It can be noted also that the data reported here are broadly in agreement with those which show that young infants in the range 8-14 weeks tend to look at patterns longer than older infants in the range 14-20 weeks and that, in particular, the younger infants look at revolving rather than stationary and fast moving rather than slow moving objects for longer (McKenzie & Day, 1976). Three issues from the experiments warrant further comment. First, the infants looked longer at fast moving patterns in both the pre-F and post-F stages when the pattern was 55 cm away but in only the post-F stage when it was 100 cm away. This result suggests that either both fast and slow rotation were highly interesting to these subjects in pre-F trials for a viewing distance of 100 cm or, simply, that differences in velocity were not discriminable in pre-F trials for this distance and that some degree of sensitization to movement was necessary before the discrimination could be made in the post-F trials. Clearly it is not at present possible to choose between these two possibilities. To be able to do so would be of some interest in regard to the possible role of “priming” or sensitization in velocity discrimination. Second, when the stimulus patterns were moving, all subjects looked longer at novel than at familiar patterns at 100 cm, but at 55 cm, although all subjects again looked longer at novel than familiar patterns, this was mainly due to the older babies. Therefore the novel-familiar difference was discriminated by the younger subjects at both 100 cm and 55 cm but at 55 cm the objects tended to be fixated more equally, possibly due to the high degree of interest in moving patterns. Third, mainly younger babies discriminated between fast- and slowmoving patterns when the objects were at 100 cm. This suggests that older infants could make the discrimination but that at 100 cm the difference was not of marked salience.
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Visual angle was not controlled between the two distances. If the existence of sustained and transient cells, and furthermore the equivocal evidence regarding their differential dispersion over the retina (De Monasterio & Gouras, 1975; Schiller & Malpeli, 1977) can be generalized from monkeys to humans, then it might be argued that at 55 cm more movement sensitive transient cells would be stimulated than at 100 cm. Even if this were the case it is not clear how such could have resulted in the differences between the two distances. The experiments described here were not designed to distinguish between interpretations based on changes in distance itself or in the visual angle subtended at the eye by the patterned object. However, McKenzie and Day (1972) found that fixations by infants of stationary objects are determined by distance, not by visual subtense. It seems reasonable to suppose that the same applies with moving objects, although this supposition must in due course be checked experimentally. It can be concluded that infants between 8 and 20 weeks generalize the color of a pattern from a stationary to a rotating mode and vice versa at a viewing distance of 55 cm. When all patterns rotate and are viewed from 55 cm all babies in this age range respond to a change in color despite changes in velocity but this is less evident for the younger babies. With an increase in the viewing distance to 100 cm differences in velocity are either less discriminable or less salient. Nevertheless the perceptual capacity to discriminate between a familiar and a novel color and to generalize this discrimination over velocity changes, continues to be evident at both ages. REFERENCES Bower, T. G. R. Object permanence and short term memory in the human infant (Manuscript, 1966). Reported in E. J. Gibson (Ed.), Principles of perceptual learning and development. New York: Appleton-Century-Crofts, 1969. Bower, T. G. R. Development in infancy. San Francisco: W. H. Freeman & Company, 1974. Bower, T. G. R., Broughton, J., & Moore, M. K. Development of the object concept as manifested in changes in the tracking behaviour of infants between 7 and 20 weeks of age. Journal of Experimental Child Psychology, 1971, 11, 182-193. Carpenter, G. C. Visual regard of moving and stationary faces in early infancy. MerrillPalmer Quarterly, 1974, 20, 181-194. Cohen, L. B., Gelber, E. R., & Lazar. M. A. Infant habituation and generalization to differing degrees of stimulus novelty. Journal of Experimental Child Psychology, 1971, 11, 379-389.
De Monasterio, F. M., & Gouras, P. Functional properties of ganglion cells of the rhesus monkey retina. Journa/ of Physiology, 1975, 251, 167-195. Field, J. Relation of young infants’ reaching behaviour to stimulus distance and solidity. Developmental Psychology, 1976, 12, 444-448. Gibson, E., Johnston, J., & Owsley, C. Perception of invariance by five-month-old infants: Differentiation of two types of motion. Developmental Psychology. 1978. 14,407-415. Haith, M. M. The response of the human newborn to visual movement. Journal of Experimental Child Psychology, 1966, 3, 235-243.
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Lewis, M., Kagan, J., & Kalafat, J. Patterns of fixation in the young infant. Child Developmen?, 1966, 37, 331-341. McGurk, H. Infant discrimination of orientation. Journal of Experimental Child Psychology, 1972, 14, 151-164. McKenzie, B. E., & Day, R. H. Orientation discrimination in infants: A comparison of visual fixation and operant training methods. Journal of Experimenfnl Child Psychology, 1971, 11, 366-375. McKenzie, B. E., & Day. R. H. Object distance as a determinant of visual fixation in early infancy. Science, 1972, 178, 1108-I 110. McKenzie, B. E., & Day, R. H. Infants’ attention to stationary and moving objects at different distances. Australian Journal of Psychology, 1976, 28, 45-51. Piaget, J. The construction of reality in the child. London: Routledge & Kegan Paul, 1954. Schiller, P. H.. & Malpeli, J. G. Properties and tectal projections of monkey retinal ganglion cells. Journal of Neurophysiology. 1977, 40, 428-445. Volkmann. F. C., & Dobson, M. V. Infant responses of ocular fixation to moving visual stimuli. Journal of Experimental Child Psychology, 1976, 22, 86-99. Wilcox, B. M., & Clayton, F. L. Infant visual fixation of the human face. Journal of Experimental
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REFERENCE
NOTES
1. Contole, J. Young infants’ responses to color undform stimulus-attribute change. Paper presented at the Australian Psychological Society Conference, Melbourne, September 1975. 2. McKenzie, B. E. Comparison ofJixation times and looking styles forfamiliar and novel stimuli in day-care and home-reared babies. Paper presented at the Australian Psychological Society Conference, Melbourne, September 1975. 3. Silfen, C. K., & Ames, E. W. Visual movement preferences in the human infant. Paper presented at the Eastern Psychology Association. Philadelphia, April 1964. RECEIVED:
May
9, 1978;
REVISED:
August 22, 1978.