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Influence of visual contextual cues on haptic discrimination of orientations in 5-month-old infants
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a v a i l a b l e a t w w w. s c i e n c e d i r e c t . c o m
w w w. e l s e v i e r. c o m / l o c a t e / b r a i n r e s
Research Report
Influence of visual contextual cues on haptic discrimination of orientations in 5-month-old infants Stéphanie Kerzerho a , Edouard Gentaz b,c,⁎, Arlette Streri a a
Paris Descartes University, L.P.P. CNRS, France CNRS, France c University of Grenoble, France b
A R T I C LE I N FO
AB S T R A C T
Article history:
The present research addressed the question of the influence of visual contextual cues on
Accepted 16 June 2008
the manual discrimination of spatial orientations in 5-month-old infants. Different types of
Available online 24 June 2008
visual contextual cues were proposed during the haptic discrimination task: congruent– informative, non congruent–informative or noninformative. A familiarisation (with a 60-s
Keywords:
fixed-duration)/reaction to novelty procedure was used in three experiments. In Experiment
Multisensory integration
1, a congruent–informative visual context (a visual context composed of alternate black and
Perception
white stripes tilted to 20°-left) was present and a haptic discrimination between a 20°-left
Hand
rod and a 30°-left rod was observed (this discrimination was absent without visual context
Infancy
in Gentaz and Streri's study, 2004). In Experiment 2, the visual context cues (composed of
Oblique effect
black dots) were noninformative, and infants could not discriminate these two oblique rods.
Orientation
In Experiment 3, the presence of a non congruent visual context (a visual context composed of alternate black and white stripes tilted to 20°-left, as in Experiment 1) disturbed the gravitational vertical perception usually observed: infants could not discriminate the vertical rod from the 10°-left rod. These results showed that only the informative (congruent and non congruent) visual contextual cues influenced the haptic discrimination of spatial orientations in 5-month-old infants. These results are discussed in relation with data observed in adults and with the current models of the multisensorial integration and attentional level. © 2008 Elsevier B.V. All rights reserved.
1.
Introduction
This study addresses the question whether different types of visual contextual cues (congruent–informative, non congruent–informative or noninformative) influenced the manual discrimination of the spatial orientations in 5-month-old infants. In vision, a vast literature has demonstrated in adults that the visual directional cues strongly influenced the perception of orientations (Beh et al., 1971; Groen et al., 2002;
Howard and Hu, 2001; Luyat et al. 2005a,b). In haptics, only two studies showed in blindfolded adults that the tactile contextual cues influenced the perception of orientations (Luyat et al. 2005a,b; Walker, 1972). Recent studies investigated in adults the effect of visual cues during the exploration phase of a haptic parallel and mirror tasks. In these tasks, participants were asked to rotate a test bar in such a way that it felt as being parallel (in physical space) or “in mirror” to a reference bar. First, Newport et al. (2002) observed that these tasks were
⁎ Corresponding author. Laboratoire Psychologie et NeuroCognition (UMR 5105), Université Pierre Mendès France, Bâtiment des Sciences de L'homme et des Mathématiques, BP 47, 38040 Grenoble Cedex 9, France. E-mail address: [email protected] (E. Gentaz). 0006-8993/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.brainres.2008.06.055
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differentially affected by noninformative visual cues from the surrounding room. The term “noninformative vision” indicates that the visual cues were not explicitly relevant to the task solving. Whereas parallel matching improved when participants could freely view the region above the haptic workspace, mirror matching was unaffected or even deteriorated. This finding was interpreted as evidence for a preferential use of extrinsic, visual coordinates in the parallel task, and intrinsic, limb-based coordinates in the mirror task. The beneficial effects in Newport et al.'s study (2002) might be partly explained by gaze orienting towards the site of haptic stimulation, which has been shown to improve parallel matching (Zuidhoek et al. 2004). However, over and above the effect of gaze orienting, an effect of noninformative vision remained in Zuidhoek et al.'s study (2004). In the noninformative vision studies by Newport et al. (2002) and Zuidhoek et al. (2004), the visual surroundings offered a profusion of vertical and horizontal cues. These contextual oriented spatial cues, together with the presence of a fixed haptic start orientation parallel to the midsagittal plane in Newport et al.'s study (2002), might have helped participants to build a stable visuo-haptic spatial reference frame. Hence, the availability of visual input might have changed the strategies used for parallel and mirror matching in the visual condition. Recently, in the study of Kaas et al. (2007), mirror matching error increased during runs with congruent visual input and was unaffected in runs with incongruent visual input. By contrast, in the parallel task, no general beneficial effect of visual input was observed on matching error, neither for congruent visual cues, nor for positively incongruent visual cues as compared to purely haptic parallel matching. Parallel matching error varied as a function of the deviation size and direction of incongruent visual orientation cues. Negatively incongruent visual cues significantly improved parallel matching accuracy. That is, parallel matching error was smallest when visual orientation slightly counteracted the typical positive bias in haptic parallel matching. Taken together, these results suggest that the effects of visual cues on haptic tasks varied according to the parameter of experimental tasks. For example, the cross-modal influence of the distracter in the parallel matching task could be either deleterious when it carried incongruent information or beneficial when the information was congruent. The main question of the current study was to determine whether this cross-modal effect of visual contextual cues on the haptic perception of orientation is present early in age, i.e. in infancy. Several studies investigated the haptic perception of spatial orientations in infancy. At about 5 months of age, infants are able to discriminate between several spatial orientations (Gentaz and Streri, 2002, 2004; Kerzerho et al., 2005). Gentaz and Streri's (2002) experiments revealed that 5-month-old infants in upright body position were manually able to discriminate (without visual control) a vertical (defined gravitationally) rod from a 45°-left oblique rod positioned in the fronto-parallel plane. For example, after familiarisation with a vertical rod, infants held a longer time the 45° oblique rod (novel orientation). In another experiment examining whether an anisotropic perception (i.e., which differed according to the value of angular orientation) in the haptic mode was present in 5-month-old infants (Gentaz and Streri, 2004), infants had to discriminate a vertical oriented rod
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from a 10°-left oriented rod and a 55°-left oblique vs. 45°-left oblique orientation. For the same angular value, infants were able to discriminate between a vertical rod and a 10° oriented rod but not between 55° vs. 45° oriented rods. These results showed that the manual discrimination of spatial orientations is anisotropic. In the same vein, Kerzerho et al. (2005) showed that infants could discriminate a vertical from a 10°-left oblique orientation but could not discriminate a 20°-left oblique from a 30°-left oblique orientation. In all these studies, no visual context cues were provided to infants: the vertical and horizontal cues of the experimental room were consistently reduced by using large white clothes on the lateral sides and a bubble roof on the top. Consequently the effect of visual contextual cues on the haptic perception of orientations has not been investigated yet in infancy. Nevertheless several studies in connected fields suggested that this influence was possible. They showed the influence of visual context on infants' proprioceptive adjustments to maintain their postural stability by using the movable room. Infants adjusted their position in relation with the forward, backward (Lee and Aronson, 1974) and lateral movements (Butterworth and Hicks, 1977) of the visual field. Thus vision plays an important proprioceptive function, like vestibular receptors, in sitting position support (Butterworth and Hicks, 1977; Butterworth and Cicchetti, 1978), in vertical position support (Lee and Aronson, 1974; Brandt et al., 1976) or in the tonic control of head's position (Butterworth and Pope, 1983). These comments show that tactile and visual modalities are intimately linked in the first year of life to apprehend the properties of the environmental objects (cf. Streri and Gentaz, 2003, 2004). In this present research, we investigated the influence of different visual contextual cues (congruent-informative: Exp 1; noninformative: Exp 2 or non congruent–informative: Exp 3) on haptic discrimination of orientations in 5-month-old infants. Visual contextual effects may specify whether the mechanisms implied in orientation perception are modality specific or, by opposition, whether they can have a reciprocal influence on the other modality. They also permit to know if the results observed in infants are comparable to adults' results, suggesting precocious common mechanisms. An oriented visual context (20° on the left side) composed of alternate black and white stripes (Experiments 1 and 3) or a non oriented visual context composed of black dots (Experiment 2), were presented to infants while holding a rod with their hand without the possibility of seeing it. In the familiarisation phase, the rod orientation was either the 20°left oblique (Exp 1: congruent visual context condition) or vertical (0°) (Exp 3: non congruent visual context condition). In Experiment 2 (noninformative visual context) infants held the 20°-left oblique with a black dot visual context. The main hypotheses were the following. If infants are not influenced by the different visual context conditions, results should be the same as those observed by Gentaz and Streri (2002, 2004) in upright body position without visual context. Both in Experiments 1 and 2, after a familiarisation with the 20°-left oblique rod, no discrimination should be observed between the 20°-left rod and the 30°-left rod. In Experiment 3, after a vertical familiarisation, a significant discrimination between the vertical rod and the 10°-left rod should be obtained. By contrast, if infants are influenced by the presence of the visual context, several
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results are possible. If the informative visual context alone plays a role, we should observe a visual effect on haptic performances only in Experiments 1 (congruent visual context) and 3 (non congruent visual context), but not in Experiment 2 (noninformative visual context). If both the informative and the noninformative contexts play a role, each visual context condition should modify haptic performances. Finally, we proposed that the visual context could have a differential effect according to the rod orientation (vertical or oblique).
1.1.
Note regarding the three experiments
All infants came from middle class backgrounds, and were observed at our laboratory. Informed consent was obtained from all parents. The present study was conducted in accordance with the Declaration of Helsinki: It was conducted with the understanding and the written consent of each parent and was approved by the local ethic committee of the LPNC (CNRS and University of Grenoble 2).
2.
Results
2.1.
Experiment 1
The data were carried out on the holding times (in seconds) of the rod during the test phase for each experimental condition. Holding times were verified a posteriori from the videorecordings by the two observers. The interobserver reliability in all sessions was very high (Pearson correlation; r = .90). The means and standard deviations of the holding times in the test phase for each experimental condition are shown in Table 1. A preliminary ANOVA on the holding times in seconds showed that the factors “order of test trial pair” and “gender” had no effect. Thus we conducted a 2 (test trial pair) × 2 (test rod) ANOVA on the holding times in seconds with the trials pair and test stimulus as within-subjects factors. We obtained a significant effect of the test stimulus (F(1,19) = 5.13, p b .05), with longer holding time for the novel orientation (30°-left oblique orientation) (M = 18.96) than for the familiar orientation (20°-left oblique orientation) (M = 13.36). The main effect of the test trial pair was not significant (F(1,19) = 1.75, p N .20). The test and test trial pair interaction was significant (F(1,19) = 4.75, p b .05). This means that in the first test trial pair the holding time was longer for the 30°-left oblique orientation (M = 23.87) than for the 20°-left oblique orientation (M= 13.33) whereas in the second test trial
Table 1 – Mean holding time (M) in seconds and standard deviations (σ) in the test phase as a function of test trial pair and test stimulus in the Experiment 1 Visual contextual cues: congruentinformative
Haptic familiarised orientation: 20°-left oblique rod
Test trial pair × test stimulus Test trial pair 1
Test trial pair 2
20° M (σ)
30° M (σ)
20° M (σ)
30° M (σ)
13.33 (17.75)
23.87 (13.67)
13.38 (4.23)
14.05 (8.67)
Table 2 – Mean holding time (M) in seconds and standard deviations (σ) in the test phase as a function of test trial pair and test stimulus in the Experiment 2 Visual contextual cues: non informative
Haptic familiarised orientation: 20°-left oblique rod
Test trial pair × test stimulus Test trial pair 1
Test trial pair 2
20° M (σ)
30° M (σ)
20° M (σ)
30° M (σ)
24.89 (35.34)
21.78 (21.87)
19.90 (21.34)
11.47 (7.49)
pair there was no significant difference between the 20°-left oblique orientation (M = 13.38) and the 30°-left oblique orientation (M = 14.05). Taken together, the results showed that 5-month-old infants preferred the novel orientation in the test phase after a 20°-left oblique orientation familiarisation in the presence of a congruent oblique visual context. Thus, the presence of a congruent visual context improved oblique rod discrimination. But what would happen if a noninformative visual context was present? To make sure that the oriented visual context really played a role, we tested in the second experiment infants with a non oriented context composed of black dots. Indeed the presence of the visual oriented cues could attract the infant's attention on the haptic task.
2.2.
Experiment 2
The data were carried out on the holding times (in seconds) of the rod during the test phase for each experimental condition. Holding times were verified a posteriori from the videorecordings by the two observers. The interobserver reliability in all sessions was very high (Pearson correlation; r = .97). The means and standard deviations of the holding times in the test phase for each experimental condition are shown in Table 2. A preliminary ANOVA on the holding times in seconds showed that the factors “order of test trial pair” and “gender” had no effect. Thus we conducted a 2 (test trial pair) × 2 (test rod) ANOVA on the holding times in seconds with the trials pair and test stimulus as within-subjects factors. We obtained a significant effect of the test trial pair (F(1,19) = 6.53, p b .05) with longer holding time in the first test trial pair (M = 23.33) than in the second test trial pair (M = 15.69). This effect underlines the habituation phenomenon commonly found in infants' habituation tasks. The main effect of the test stimulus was not significant (F(1,19) = .85, p N .25). The test and test trial pair interaction was not significant too (F(1,19) = .89, p N .25). Taken together, the results showed that 5-month-old infants could not discriminate the 20°-left oblique orientation from the 30°-left oblique orientation in the test phase after a 20°-left oblique familiarisation in the presence of a non oriented context. This result confirms those previously observed without informative visual context (Gentaz and Streri, 2004; Kerzerho et al., 2005).
2.3.
Experiment 3
The data were carried out on the holding times (in seconds) of the rod during the test phase for each experimental condition.
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Table 3 – Mean holding time (M) in seconds and standard deviations (σ) in the test phase as a function of test trial pair and test stimulus in the Experiment 3 Visual contextual cues: non congruentinformative
Haptic familiarised orientation: vertical rod
Test trial pair × test stimulus Test trial pair 1
Test trial pair 2
0° M (σ)
10° M (σ)
0° M (σ)
10° M (σ)
19.37 (22.81)
15.03 (15.65)
12.17 (9.11)
13.45 (14.83)
Holding times were verified a posteriori from the videorecordings by the two observers. The interobserver reliability in all sessions was very high (Pearson correlation; r = .98). The means and standard deviations of the holding times in the test phase for each experimental condition are shown in Table 3. A preliminary ANOVA on the holding times in seconds showed that the factors “order of test trial pair” and “gender” had no effect. Thus we conducted a 2 (test trial pair) × 2 (test rod) ANOVA on the holding times in seconds with the trials pair and test stimulus as within-subjects factors. We obtained no significant effect of the test stimulus (F(1,19) = .23, p N .25) and of the test trial pair (F(1,19) = 1.64, p N .20). The test and test trial pair interaction was not significant too (F(1,19)= 1.23, p N .25). Taken together, the results showed that 5-month-old infants could not discriminate the vertical from the 10°-left oblique orientation in the test phase after a vertical familiarisation in the presence of a non congruent oblique visual context. Thus the presence of a non congruent visual context disturbed the haptic perception of vertical orientation.
3.
Discussion
Our objective was to investigate the effect of visual cues on the haptic orientations discrimination in infants. In previous
279
studies (Gentaz and Streri, 2004; Kerzerho et al., 2005), a haptic oblique effect (better discrimination of the vertical orientation than the oblique orientations) was revealed when 5-monthold infants were upright without visual contextual cues. This effect was observed by the presence of a discrimination between vertical and 10°-left oblique rods and a failure between 20°-left oblique and 30°-left oblique rods. What did we obtain in the presence of oriented or non oriented visual cues and comparatively to adults results in visuo-haptic tasks (see Table 4; Kaas et al., 2007)? With the presence of oriented (20°-left oblique) visual context, the pattern of results is reversed: indeed, no discrimination between vertical orientation and 10°-left oblique rods was observed after a vertical familiarisation, but there was a discrimination between 20°left oblique and 30°-left oblique rods after a 20°-left familiarisation. Thus, congruent oblique visual context improved oblique discrimination (Exp 1) whereas a non congruent oblique visual context (Exp 3) disturbed vertical perception. Both vertical and oblique perceptions in haptic modality seem to integrate multisensorial information. These results invalidate therefore the hypothesis of differential effects of the visual context according to the tested haptic orientation. These results confirm once more that tactile and visual modalities are intimately linked in the first year of life to apprehend the properties of environmental objects. Taken together, the results also suggest that a cross-modal influence of informative visual contextual cues on the haptic perception of orientation is at work in 5-month-old infants as it is in adults (see Table 4; Kaas et al., 2007). This supports the idea of a mixed-reference frame defining spatial orientations. A classic difference is made between egocentric (referred to the participant's body) and allocentric (referred to environmental cues) to define manually an orientation. The egocentric reference frame may be divided into a head, or a trunk, or a hand–shoulder centered reference frames, and the allocentric reference frame into a gravitational frame and visual or haptic contextual cues. The results proved that the
Table 4 – Comparison of 5-month-old infants results in visuo-haptic tasks which measure influence of visual cues on haptic spatial tasks Informative visual context
Congruent Adults
Non congruent
Non informative visual context
Effect on parallel matching haptic task Effect on mirror haptic task 5-month-old 20°-left oblique visual context, congruent with rod orientation Effect on oblique infants (Experiment 1) discrimination haptic task Adults Non congruent visual orientation cues (Kaas et al., 2007) Effect on parallel matching haptic task No effect on mirror haptic task 5-month-old 20°-left oblique visual context, non congruent with rod orientation Effect on vertical infants (Experiment 3) discrimination haptic task
Adults
Congruent visual orientation cues (Kaas et al., 2007)
Subjects could see freely the region above the haptic space (Newport et al., 2002, Zuidhoek et al., 2004)
5-month-old Irrelevant visual cues for the task resolution (Experiment 2) infants No orientated visual cues (Gentaz et al., 2004; Kerzerho et al., 2005)
Effect on parallel matching haptic task No effect on mirror haptic task No effect on oblique discrimination haptic task Haptic oblique effect in discrimination task
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Fig. 1 – Experimental design. visual system could work in relation with the shoulder–arm– hand system in infants. Therefore, the gravitational cues provided by the haptic system are not always sufficient to perceive haptically spatial orientations. The coding of the orientation (oblique effect) is defined in a multimodal reference frame which integrates proprioceptive and visual information. This suggests that both egocentric and allocentric (gravitational and visual) information would be combined to form a coherent representation of the spatial orientation when the context is congruent. This coordination of visual and haptic modalities is really representative of the different integration mechanisms involved in space perception (cf. Gentaz, 2000; Gentaz and Ballaz, 2000; Gentaz et al., 2002, 2008). As indicated in the Introduction section, the influence of noninformative vision on haptic tasks is task-dependant (Newport et al., 2002) in adults. Newport et al.'s (2002) and Zuidhoek et al. (2004) observed a beneficial effect of noninformative vision in parallel matching task resolution whereas no advantage was observed in mirror task. According to Zuidhoek et al. (2004), orienting towards the position of the haptic stimulation would improve parallel matching performance. According to Honoré et al. (1989) and Driver and Grossenbacher (1996), it may also be that orienting enhances the attentional spatial resources. Nevertheless, contrary to the findings of Newport et al. (2002) and Zuidhoek et al. (2004) in parallel matching, we did not observe in the second experiment any advantage nor any effect of noninformative vision on the haptic orientation discrimination in 5-month-old infants. Indeed, the noninformative visual cues provided by the non oriented visual context did not ameliorate the oblique discrimination. As in the no visual context cues condition (Kerzerho et al., 2005), infants could not discriminate the 20°-left oblique orientation from the 30°left oblique orientation after a 20°-left oblique familiarisation. This result is consistent with the mirror matching performance observed in adults (Newport et al., 2002). It seems likely that the presentation of a non oriented visual context would produce the same effect on vertical discrimination in comparison with the condition without visual context used in
Gentaz and Streri (2004) and Kerzerho et al. (2005) studies. Five-month-old infants should discriminate a vertical rod from a 10°-left oblique rod. In sum, the classical oblique effect should be recovered with a non oriented visual context. More recently (Kerzerho et al., in press) we addressed the question of the factors affecting the manual discrimination of spatial orientations and the orientation preferences in 5month-old infants in the fronto-parallel plane. It seems that when both gravitational vertical and body axis are aligned, the intrinsic “vertical preference” exists when the angular difference between the two orientations tested in the test phase is 10°. When the angular deviation to the vertical is greater than 10°, the novel orientation is preferred. This novelty preference is in accordance with results usually obtained in experiments using familiarisation vs. reaction to novelty procedure. This modification of orientation preference in the manual discrimination of orientation by 5-monthold infants was discussed in relation to the magnitude of the angular deviation to the gravitational vertical and the spatial reference cues available in each condition. When infants were tested with orientations which were close to both the gravitational vertical and their body axis, these reference cues may have acted as “attractors” and thus, reinforced the “vertical preference”. Finally, the presence of the visual context during the familiarisation and the test phases could have increased the attention and arousal state of the infants in the haptic task. But if such an increase actually occurred, our results showed that it is effective only when visual information is relevant for this specific haptic spatial task. Similarly, no advantage was observed in the haptic mirror task in adults (Zuidhoek et al., 2004). In the same vein, Millar and Al-Attar (2005) found no beneficial effect on a tactile landmark task when the visual stimulation consisted of diffuse light eliminating all spatial cues. They argued that spatial and non-spatial aspects have to be distinguished when considering the effect of vision on haptics: vision improves haptic spatial performance to the extent that it adds cues with potential relevance to spatial discrimination and reference. It seems that this remark is useful in orientation haptic discrimination in infants.
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4.2.1.1. Participants. Twenty infants aged from 4 months 20 days to 5 months 10 days (11 females and 9 males; mean age: 154.9 days) participated in this experiment.
tioned above the haptic display. The visual panel orientation was congruent with the haptic familiarised orientation (20° on the left side). 4.2.1.2.1. Familiarisation phase. In the familiarisation phase, a fixed-duration procedure was adopted in which the stimulus was presented until each infant accumulated a 60-second amount of holding time. The infant's right hand was put on the rod fixed upon the apparatus. When the infant let go of the rod more than 2 s before the 60-second time was up and did not self-re-grasp the rod, the experimenter put her/ his hand on the rod again until she/he accumulated 60-s duration of familiarisation. The familiarised rod orientation was the 20°-left oblique (same orientation than the visual panel orientation). The parents could see their child on a television screen during the experiment. 4.2.1.2.2. Test phase. The test phase began immediately after the familiarisation phase. For each trial, an infant-controlled procedure was used: the trial began when infants held the rod with their right hand and finished when they let it go. During this phase, two orientations were presented successively: the familiar orientation (previously used in the familiarisation: −20°) and the novel orientation (differing from the familiar orientation by 10° on infant's left side: −30°). The 10° difference choice between the familiar and the novel orientations could allow us to make comparisons with Gentaz and Streri's results (2002). Those two orientations were presented alternately during 4 trials (two test trial pairs) in a counterbalanced order between subjects. The test phase was: 20°/30°/20°/30° (order 1) or 30°/20°/30°/20° (order 2). Consequently, there were 10 infants in the 2 experimental groups.
4.2.1.2. Apparatus.
4.3.
Experiment 2: noninformative visual contextual cues
4.3.1.
Method
4.
Experimental procedures
4.1. General experimental conditions and procedures in the three experiments Each infant was seated in the baby car seat which was lightly backward tilted to maintain infant in seated position. A large white cloth bib was attached around the baby's neck at one side and to the screen at the other. The bib prevented infants from seeing their shoulder–hand systems, even laterally, but left them free to move. It also allowed the infant's right hands to be video-recorded with a TV camera the lens of which was located in a hole in the screen under the bib level. The visual panel was presented during the whole experience, from the beginning of the familiarisation phase until the end of the test phase (cf. Fig. 1: experimental design). During this procedure, the first experimenter, located behind the screen, controlled the video-recording. The second experimenter sat under the bib and to the right of the infant. Her tasks included putting the rod in the infant's hand and recording holding times. The infants' right hands were used in all experimental conditions as in Gentaz and Streri (2002).
4.2.
Experiment 1: congruent visual contextual cues
4.2.1.
Method
The baby car seat: The baby car seat was put on a solid plinth (37 cm deep, 35 cm wide and 10.5 cm high) to keep the center of the rod at the same level to that in the previous experiences. Moreover, a cushion was placed around the neck of the infant in order to maintain the head in a vertical position and in line with the trunk. The haptic display: The haptic display was composed of Plexiglas disk (diameter, 30 cm) equipped with a handleshaped rod (18 cm × 15 cm). This rod (.5 cm in diameter) was chosen because it was easily handled and explored by the 5month-old infants. The rod, mounted on the center of the disk, could be rotated 360° around its central axis. The rod could be maintained in the desired orientation in order to prevent involuntary deviation from its position during haptic scanning. The disk was graduated in degrees (the sensitivity threshold of this display was equal to .5°) and was taped on a wooden plank which upheld the device. The rod and the disk were positioned in the frontal plane and were centered on the midline of the infant's body. The height of the disk was adjusted so that the center of the rod was at the level of the infant's right shoulder, to a 52 cm height. The haptic display was the same as that used by Gentaz and Streri (2002). The visual panel: The visual panel (82 cm × 57 cm) was composed of alternate black and white stripes, inclined by 20° on the left side. Each line was 2 cm wide (equivalent to 2.12 cpd). The panel was positioned 55 cm away from the baby's face and was slightly tilted to be parallel with the baby's face (in upright body position). The visual panel was posi-
4.3.1.1. Participants. Twenty infants aged from 4 months 20 days to 5 months 10 days (10 females and 10 males; mean age: 154.7 days) participated in this experiment. 4.3.1.2. Apparatus, experimental conditions and procedure. The haptic display and the baby car seat were exactly the same as in the first experiment. By contrast, the visual panel (82 cm × 57 cm) was composed of 3 cm radius black dots. The black/white ratio was exactly the same than in the visual oriented context. The panel was positioned 55 cm away from the baby face and was slightly tilted to be parallel with the baby's face. Finally, experimental conditions and procedure were the same as in the first experiment.
4.4.
Experiment 3: non congruent visual contextual cues
4.4.1.
Method
4.4.1.1. Participants. Twenty infants aged from 4 months 20 days to 5 months 10 days (12 females and 8 males; mean age: 155.6 days) participated in this experiment. 4.4.1.2. Apparatus, experimental conditions and procedure. The haptic and the visual displays, the baby car seat, the
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experimental conditions (except for rod orientations) and procedure were the same as in the first experiment. 4.4.1.2.1. Familiarisation phase. In the familiarisation phase, a fixed-duration procedure was adopted in which the stimulus was presented until each infant accumulated a 60-second amount of holding time. In this present research, the infant's right hand was put on the rod fixed upon the apparatus. When the infant let go of the rod more than 2 s before the 60-second time was up and did not self-re-grasp the rod, the experimenter put her/his hand on the rod again until she/he accumulated 60-s duration of familiarisation. The familiarised rod orientation was the vertical (0°) defined gravitationally. The parents could see their child on a television screen during the experiment. 4.4.1.2.2. Test phase. The test phase began immediately after the familiarisation phase. For each trial, an infantcontrolled procedure was used: the trial began when infants held the rod with their right hand and finished when they let it go. During this phase, two orientations were presented successively: the familiar orientation (previously used in the familiarisation: 0°) and the novel orientation (differing from the familiar orientation by 10° on infant's left side: 10°). The 10° difference between the familiar and the novel orientations will allow comparisons with Gentaz and Streri's results (2002). These two orientations were presented alternately during 4 trials (two test trial pairs) in a counterbalanced order between subjects. The test phase was: 0°/10°/0°/10° (order 1) or 10°/0°/ 10°/0° (order 2). Consequently, there were 10 infants in the 2 experimental groups.
Acknowledgments We thank all the infants and their parents who participated in the experiments. This work was supported by grants from the University Institute of France.
REFERENCES
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Le Développement Dans La Première Année. Presses Universitaires de France, Paris, pp. 107–128. Driver, J., Grossenbacher, P.G., 1996. Multimodal spatial constraints on tactile selective attention. In: Inui, T., McClelland, J. (Eds.), Information Integration in Perception and Communication. Attention and Performance 16. MIT Press, Cambridge MA, pp. 209–235. Gentaz, E., 2000. Existe-t-il un “effet de l'oblique” dans la perception tactile des orientations? Annee Psychol. 100, 111–140. Gentaz, E., Badan, M., Luyat, M., Touil, N., 2002. The manual haptic perception of orientations and the oblique effect in patients with left visuo-spatial neglect. NeuroReport 13, 327–331. Gentaz, E., Ballaz, C., 2000. La perception visuelle des orientations et l'effet de l'oblique. Annee Psychol. 100, 715–744. Gentaz, E., Baud-Bovy, G., Luyat, M., 2008. The haptic perception of spatial orientations. Exp. Brain Res. 187, 331–348. Gentaz, E., Streri, A., 2002. Infant's haptic discrimination of spatial orientations. Curr. Psychol. Lett. 9, 61–71. Gentaz, E., Streri, A., 2004. An “oblique effect” in infant's haptic perception of spatial orientations. J. Cogn. Neurosci. 16, 1–7. Groen, E.L., Jenkin, H.L., Howard, I.P., 2002. Perception of self-tilt in a true and illusory vertical plane. Perception 31, 1477–1490. Honoré, J., Bourdeaud'hui, M., Sparrow, L., 1989. Reduction of cutaneous reaction time by directing eyes towards the source of stimulation. Neuropsychologia 27, 367–371. Howard, I.P., Hu, G., 2001. Visually induced reorientation illusions. Perception 30, 583–600. Kaas, A.L., Van Mier, H.I., Lataster, J., fingal, M., Sack, A.T., 2007. The effect of visuo-haptic congruency on haptic spatial matching. Exp. Brain Res. 183, 75–85. Kerzerho, S., Streri, A., Gentaz, E., 2005. Reference frame and haptic discrimination of orientations in infants. Neuroreport 16, 1833–1837. Kerzerho, S., Gentaz, E., Streri, A. in press. Factors influencing the manual discrimination of orientations in 5 month-old infants, Perception. Lee, D.N., Aronson, E., 1974. Visual proprioceptive control of standing in human infants. Percept. Psychophys. 15, 529–532. Luyat, M., Mobarek, S., Leconte, C., Gentaz, E., 2005a. The plasticity of gravitational reference frame and the subjective vertical: peripheral visual information affects the oblique effect. Neurosci. Lett. 385, 215–219. Luyat, M., Moroni, C., Gentaz, E., 2005b. The role of contextual cues in the haptic perception of orientations and the oblique effect. Psychon. Bull. Rev. 12, 760–766. Millar, S., Al-Attar, Z., 2005. What aspects of vision facilitate haptic processing? Brain Cogn. 59, 258–268. Newport, R., Rabb, B., Jackson, S.R., 2002. Noninformative vision improves haptic spatial perception. Curr. Biol. 12, 1166–1661. Streri, A., Gentaz, E., 2004. Cross-modal recognition of shape from hand to eyes and handedness in human newborns. Neuropsychologia 42, 1365–1369. Streri, A., Gentaz, E., 2003. Cross-modal recognition of shape from hand to eyes in human newborns. Somatosens. Motor Res. 20, 11–16. Walker, J.T., 1972. Tactual field dependence. Psychon. Sci. 26, 311–313. Zuidhoek, S., Visser, A., Bredemero, M.E., Postma, A., 2004. Multisensory integration mechanisms in haptic space perception. Exp. Brain Res. 157, 265–268.
a v a i l a b l e a t w w w. s c i e n c e d i r e c t . c o m
w w w. e l s e v i e r. c o m / l o c a t e / b r a i n r e s
Research Report
Influence of visual contextual cues on haptic discrimination of orientations in 5-month-old infants Stéphanie Kerzerho a , Edouard Gentaz b,c,⁎, Arlette Streri a a
Paris Descartes University, L.P.P. CNRS, France CNRS, France c University of Grenoble, France b
A R T I C LE I N FO
AB S T R A C T
Article history:
The present research addressed the question of the influence of visual contextual cues on
Accepted 16 June 2008
the manual discrimination of spatial orientations in 5-month-old infants. Different types of
Available online 24 June 2008
visual contextual cues were proposed during the haptic discrimination task: congruent– informative, non congruent–informative or noninformative. A familiarisation (with a 60-s
Keywords:
fixed-duration)/reaction to novelty procedure was used in three experiments. In Experiment
Multisensory integration
1, a congruent–informative visual context (a visual context composed of alternate black and
Perception
white stripes tilted to 20°-left) was present and a haptic discrimination between a 20°-left
Hand
rod and a 30°-left rod was observed (this discrimination was absent without visual context
Infancy
in Gentaz and Streri's study, 2004). In Experiment 2, the visual context cues (composed of
Oblique effect
black dots) were noninformative, and infants could not discriminate these two oblique rods.
Orientation
In Experiment 3, the presence of a non congruent visual context (a visual context composed of alternate black and white stripes tilted to 20°-left, as in Experiment 1) disturbed the gravitational vertical perception usually observed: infants could not discriminate the vertical rod from the 10°-left rod. These results showed that only the informative (congruent and non congruent) visual contextual cues influenced the haptic discrimination of spatial orientations in 5-month-old infants. These results are discussed in relation with data observed in adults and with the current models of the multisensorial integration and attentional level. © 2008 Elsevier B.V. All rights reserved.
1.
Introduction
This study addresses the question whether different types of visual contextual cues (congruent–informative, non congruent–informative or noninformative) influenced the manual discrimination of the spatial orientations in 5-month-old infants. In vision, a vast literature has demonstrated in adults that the visual directional cues strongly influenced the perception of orientations (Beh et al., 1971; Groen et al., 2002;
Howard and Hu, 2001; Luyat et al. 2005a,b). In haptics, only two studies showed in blindfolded adults that the tactile contextual cues influenced the perception of orientations (Luyat et al. 2005a,b; Walker, 1972). Recent studies investigated in adults the effect of visual cues during the exploration phase of a haptic parallel and mirror tasks. In these tasks, participants were asked to rotate a test bar in such a way that it felt as being parallel (in physical space) or “in mirror” to a reference bar. First, Newport et al. (2002) observed that these tasks were
⁎ Corresponding author. Laboratoire Psychologie et NeuroCognition (UMR 5105), Université Pierre Mendès France, Bâtiment des Sciences de L'homme et des Mathématiques, BP 47, 38040 Grenoble Cedex 9, France. E-mail address: [email protected] (E. Gentaz). 0006-8993/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.brainres.2008.06.055
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differentially affected by noninformative visual cues from the surrounding room. The term “noninformative vision” indicates that the visual cues were not explicitly relevant to the task solving. Whereas parallel matching improved when participants could freely view the region above the haptic workspace, mirror matching was unaffected or even deteriorated. This finding was interpreted as evidence for a preferential use of extrinsic, visual coordinates in the parallel task, and intrinsic, limb-based coordinates in the mirror task. The beneficial effects in Newport et al.'s study (2002) might be partly explained by gaze orienting towards the site of haptic stimulation, which has been shown to improve parallel matching (Zuidhoek et al. 2004). However, over and above the effect of gaze orienting, an effect of noninformative vision remained in Zuidhoek et al.'s study (2004). In the noninformative vision studies by Newport et al. (2002) and Zuidhoek et al. (2004), the visual surroundings offered a profusion of vertical and horizontal cues. These contextual oriented spatial cues, together with the presence of a fixed haptic start orientation parallel to the midsagittal plane in Newport et al.'s study (2002), might have helped participants to build a stable visuo-haptic spatial reference frame. Hence, the availability of visual input might have changed the strategies used for parallel and mirror matching in the visual condition. Recently, in the study of Kaas et al. (2007), mirror matching error increased during runs with congruent visual input and was unaffected in runs with incongruent visual input. By contrast, in the parallel task, no general beneficial effect of visual input was observed on matching error, neither for congruent visual cues, nor for positively incongruent visual cues as compared to purely haptic parallel matching. Parallel matching error varied as a function of the deviation size and direction of incongruent visual orientation cues. Negatively incongruent visual cues significantly improved parallel matching accuracy. That is, parallel matching error was smallest when visual orientation slightly counteracted the typical positive bias in haptic parallel matching. Taken together, these results suggest that the effects of visual cues on haptic tasks varied according to the parameter of experimental tasks. For example, the cross-modal influence of the distracter in the parallel matching task could be either deleterious when it carried incongruent information or beneficial when the information was congruent. The main question of the current study was to determine whether this cross-modal effect of visual contextual cues on the haptic perception of orientation is present early in age, i.e. in infancy. Several studies investigated the haptic perception of spatial orientations in infancy. At about 5 months of age, infants are able to discriminate between several spatial orientations (Gentaz and Streri, 2002, 2004; Kerzerho et al., 2005). Gentaz and Streri's (2002) experiments revealed that 5-month-old infants in upright body position were manually able to discriminate (without visual control) a vertical (defined gravitationally) rod from a 45°-left oblique rod positioned in the fronto-parallel plane. For example, after familiarisation with a vertical rod, infants held a longer time the 45° oblique rod (novel orientation). In another experiment examining whether an anisotropic perception (i.e., which differed according to the value of angular orientation) in the haptic mode was present in 5-month-old infants (Gentaz and Streri, 2004), infants had to discriminate a vertical oriented rod
277
from a 10°-left oriented rod and a 55°-left oblique vs. 45°-left oblique orientation. For the same angular value, infants were able to discriminate between a vertical rod and a 10° oriented rod but not between 55° vs. 45° oriented rods. These results showed that the manual discrimination of spatial orientations is anisotropic. In the same vein, Kerzerho et al. (2005) showed that infants could discriminate a vertical from a 10°-left oblique orientation but could not discriminate a 20°-left oblique from a 30°-left oblique orientation. In all these studies, no visual context cues were provided to infants: the vertical and horizontal cues of the experimental room were consistently reduced by using large white clothes on the lateral sides and a bubble roof on the top. Consequently the effect of visual contextual cues on the haptic perception of orientations has not been investigated yet in infancy. Nevertheless several studies in connected fields suggested that this influence was possible. They showed the influence of visual context on infants' proprioceptive adjustments to maintain their postural stability by using the movable room. Infants adjusted their position in relation with the forward, backward (Lee and Aronson, 1974) and lateral movements (Butterworth and Hicks, 1977) of the visual field. Thus vision plays an important proprioceptive function, like vestibular receptors, in sitting position support (Butterworth and Hicks, 1977; Butterworth and Cicchetti, 1978), in vertical position support (Lee and Aronson, 1974; Brandt et al., 1976) or in the tonic control of head's position (Butterworth and Pope, 1983). These comments show that tactile and visual modalities are intimately linked in the first year of life to apprehend the properties of the environmental objects (cf. Streri and Gentaz, 2003, 2004). In this present research, we investigated the influence of different visual contextual cues (congruent-informative: Exp 1; noninformative: Exp 2 or non congruent–informative: Exp 3) on haptic discrimination of orientations in 5-month-old infants. Visual contextual effects may specify whether the mechanisms implied in orientation perception are modality specific or, by opposition, whether they can have a reciprocal influence on the other modality. They also permit to know if the results observed in infants are comparable to adults' results, suggesting precocious common mechanisms. An oriented visual context (20° on the left side) composed of alternate black and white stripes (Experiments 1 and 3) or a non oriented visual context composed of black dots (Experiment 2), were presented to infants while holding a rod with their hand without the possibility of seeing it. In the familiarisation phase, the rod orientation was either the 20°left oblique (Exp 1: congruent visual context condition) or vertical (0°) (Exp 3: non congruent visual context condition). In Experiment 2 (noninformative visual context) infants held the 20°-left oblique with a black dot visual context. The main hypotheses were the following. If infants are not influenced by the different visual context conditions, results should be the same as those observed by Gentaz and Streri (2002, 2004) in upright body position without visual context. Both in Experiments 1 and 2, after a familiarisation with the 20°-left oblique rod, no discrimination should be observed between the 20°-left rod and the 30°-left rod. In Experiment 3, after a vertical familiarisation, a significant discrimination between the vertical rod and the 10°-left rod should be obtained. By contrast, if infants are influenced by the presence of the visual context, several
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results are possible. If the informative visual context alone plays a role, we should observe a visual effect on haptic performances only in Experiments 1 (congruent visual context) and 3 (non congruent visual context), but not in Experiment 2 (noninformative visual context). If both the informative and the noninformative contexts play a role, each visual context condition should modify haptic performances. Finally, we proposed that the visual context could have a differential effect according to the rod orientation (vertical or oblique).
1.1.
Note regarding the three experiments
All infants came from middle class backgrounds, and were observed at our laboratory. Informed consent was obtained from all parents. The present study was conducted in accordance with the Declaration of Helsinki: It was conducted with the understanding and the written consent of each parent and was approved by the local ethic committee of the LPNC (CNRS and University of Grenoble 2).
2.
Results
2.1.
Experiment 1
The data were carried out on the holding times (in seconds) of the rod during the test phase for each experimental condition. Holding times were verified a posteriori from the videorecordings by the two observers. The interobserver reliability in all sessions was very high (Pearson correlation; r = .90). The means and standard deviations of the holding times in the test phase for each experimental condition are shown in Table 1. A preliminary ANOVA on the holding times in seconds showed that the factors “order of test trial pair” and “gender” had no effect. Thus we conducted a 2 (test trial pair) × 2 (test rod) ANOVA on the holding times in seconds with the trials pair and test stimulus as within-subjects factors. We obtained a significant effect of the test stimulus (F(1,19) = 5.13, p b .05), with longer holding time for the novel orientation (30°-left oblique orientation) (M = 18.96) than for the familiar orientation (20°-left oblique orientation) (M = 13.36). The main effect of the test trial pair was not significant (F(1,19) = 1.75, p N .20). The test and test trial pair interaction was significant (F(1,19) = 4.75, p b .05). This means that in the first test trial pair the holding time was longer for the 30°-left oblique orientation (M = 23.87) than for the 20°-left oblique orientation (M= 13.33) whereas in the second test trial
Table 1 – Mean holding time (M) in seconds and standard deviations (σ) in the test phase as a function of test trial pair and test stimulus in the Experiment 1 Visual contextual cues: congruentinformative
Haptic familiarised orientation: 20°-left oblique rod
Test trial pair × test stimulus Test trial pair 1
Test trial pair 2
20° M (σ)
30° M (σ)
20° M (σ)
30° M (σ)
13.33 (17.75)
23.87 (13.67)
13.38 (4.23)
14.05 (8.67)
Table 2 – Mean holding time (M) in seconds and standard deviations (σ) in the test phase as a function of test trial pair and test stimulus in the Experiment 2 Visual contextual cues: non informative
Haptic familiarised orientation: 20°-left oblique rod
Test trial pair × test stimulus Test trial pair 1
Test trial pair 2
20° M (σ)
30° M (σ)
20° M (σ)
30° M (σ)
24.89 (35.34)
21.78 (21.87)
19.90 (21.34)
11.47 (7.49)
pair there was no significant difference between the 20°-left oblique orientation (M = 13.38) and the 30°-left oblique orientation (M = 14.05). Taken together, the results showed that 5-month-old infants preferred the novel orientation in the test phase after a 20°-left oblique orientation familiarisation in the presence of a congruent oblique visual context. Thus, the presence of a congruent visual context improved oblique rod discrimination. But what would happen if a noninformative visual context was present? To make sure that the oriented visual context really played a role, we tested in the second experiment infants with a non oriented context composed of black dots. Indeed the presence of the visual oriented cues could attract the infant's attention on the haptic task.
2.2.
Experiment 2
The data were carried out on the holding times (in seconds) of the rod during the test phase for each experimental condition. Holding times were verified a posteriori from the videorecordings by the two observers. The interobserver reliability in all sessions was very high (Pearson correlation; r = .97). The means and standard deviations of the holding times in the test phase for each experimental condition are shown in Table 2. A preliminary ANOVA on the holding times in seconds showed that the factors “order of test trial pair” and “gender” had no effect. Thus we conducted a 2 (test trial pair) × 2 (test rod) ANOVA on the holding times in seconds with the trials pair and test stimulus as within-subjects factors. We obtained a significant effect of the test trial pair (F(1,19) = 6.53, p b .05) with longer holding time in the first test trial pair (M = 23.33) than in the second test trial pair (M = 15.69). This effect underlines the habituation phenomenon commonly found in infants' habituation tasks. The main effect of the test stimulus was not significant (F(1,19) = .85, p N .25). The test and test trial pair interaction was not significant too (F(1,19) = .89, p N .25). Taken together, the results showed that 5-month-old infants could not discriminate the 20°-left oblique orientation from the 30°-left oblique orientation in the test phase after a 20°-left oblique familiarisation in the presence of a non oriented context. This result confirms those previously observed without informative visual context (Gentaz and Streri, 2004; Kerzerho et al., 2005).
2.3.
Experiment 3
The data were carried out on the holding times (in seconds) of the rod during the test phase for each experimental condition.
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Table 3 – Mean holding time (M) in seconds and standard deviations (σ) in the test phase as a function of test trial pair and test stimulus in the Experiment 3 Visual contextual cues: non congruentinformative
Haptic familiarised orientation: vertical rod
Test trial pair × test stimulus Test trial pair 1
Test trial pair 2
0° M (σ)
10° M (σ)
0° M (σ)
10° M (σ)
19.37 (22.81)
15.03 (15.65)
12.17 (9.11)
13.45 (14.83)
Holding times were verified a posteriori from the videorecordings by the two observers. The interobserver reliability in all sessions was very high (Pearson correlation; r = .98). The means and standard deviations of the holding times in the test phase for each experimental condition are shown in Table 3. A preliminary ANOVA on the holding times in seconds showed that the factors “order of test trial pair” and “gender” had no effect. Thus we conducted a 2 (test trial pair) × 2 (test rod) ANOVA on the holding times in seconds with the trials pair and test stimulus as within-subjects factors. We obtained no significant effect of the test stimulus (F(1,19) = .23, p N .25) and of the test trial pair (F(1,19) = 1.64, p N .20). The test and test trial pair interaction was not significant too (F(1,19)= 1.23, p N .25). Taken together, the results showed that 5-month-old infants could not discriminate the vertical from the 10°-left oblique orientation in the test phase after a vertical familiarisation in the presence of a non congruent oblique visual context. Thus the presence of a non congruent visual context disturbed the haptic perception of vertical orientation.
3.
Discussion
Our objective was to investigate the effect of visual cues on the haptic orientations discrimination in infants. In previous
279
studies (Gentaz and Streri, 2004; Kerzerho et al., 2005), a haptic oblique effect (better discrimination of the vertical orientation than the oblique orientations) was revealed when 5-monthold infants were upright without visual contextual cues. This effect was observed by the presence of a discrimination between vertical and 10°-left oblique rods and a failure between 20°-left oblique and 30°-left oblique rods. What did we obtain in the presence of oriented or non oriented visual cues and comparatively to adults results in visuo-haptic tasks (see Table 4; Kaas et al., 2007)? With the presence of oriented (20°-left oblique) visual context, the pattern of results is reversed: indeed, no discrimination between vertical orientation and 10°-left oblique rods was observed after a vertical familiarisation, but there was a discrimination between 20°left oblique and 30°-left oblique rods after a 20°-left familiarisation. Thus, congruent oblique visual context improved oblique discrimination (Exp 1) whereas a non congruent oblique visual context (Exp 3) disturbed vertical perception. Both vertical and oblique perceptions in haptic modality seem to integrate multisensorial information. These results invalidate therefore the hypothesis of differential effects of the visual context according to the tested haptic orientation. These results confirm once more that tactile and visual modalities are intimately linked in the first year of life to apprehend the properties of environmental objects. Taken together, the results also suggest that a cross-modal influence of informative visual contextual cues on the haptic perception of orientation is at work in 5-month-old infants as it is in adults (see Table 4; Kaas et al., 2007). This supports the idea of a mixed-reference frame defining spatial orientations. A classic difference is made between egocentric (referred to the participant's body) and allocentric (referred to environmental cues) to define manually an orientation. The egocentric reference frame may be divided into a head, or a trunk, or a hand–shoulder centered reference frames, and the allocentric reference frame into a gravitational frame and visual or haptic contextual cues. The results proved that the
Table 4 – Comparison of 5-month-old infants results in visuo-haptic tasks which measure influence of visual cues on haptic spatial tasks Informative visual context
Congruent Adults
Non congruent
Non informative visual context
Effect on parallel matching haptic task Effect on mirror haptic task 5-month-old 20°-left oblique visual context, congruent with rod orientation Effect on oblique infants (Experiment 1) discrimination haptic task Adults Non congruent visual orientation cues (Kaas et al., 2007) Effect on parallel matching haptic task No effect on mirror haptic task 5-month-old 20°-left oblique visual context, non congruent with rod orientation Effect on vertical infants (Experiment 3) discrimination haptic task
Adults
Congruent visual orientation cues (Kaas et al., 2007)
Subjects could see freely the region above the haptic space (Newport et al., 2002, Zuidhoek et al., 2004)
5-month-old Irrelevant visual cues for the task resolution (Experiment 2) infants No orientated visual cues (Gentaz et al., 2004; Kerzerho et al., 2005)
Effect on parallel matching haptic task No effect on mirror haptic task No effect on oblique discrimination haptic task Haptic oblique effect in discrimination task
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Fig. 1 – Experimental design. visual system could work in relation with the shoulder–arm– hand system in infants. Therefore, the gravitational cues provided by the haptic system are not always sufficient to perceive haptically spatial orientations. The coding of the orientation (oblique effect) is defined in a multimodal reference frame which integrates proprioceptive and visual information. This suggests that both egocentric and allocentric (gravitational and visual) information would be combined to form a coherent representation of the spatial orientation when the context is congruent. This coordination of visual and haptic modalities is really representative of the different integration mechanisms involved in space perception (cf. Gentaz, 2000; Gentaz and Ballaz, 2000; Gentaz et al., 2002, 2008). As indicated in the Introduction section, the influence of noninformative vision on haptic tasks is task-dependant (Newport et al., 2002) in adults. Newport et al.'s (2002) and Zuidhoek et al. (2004) observed a beneficial effect of noninformative vision in parallel matching task resolution whereas no advantage was observed in mirror task. According to Zuidhoek et al. (2004), orienting towards the position of the haptic stimulation would improve parallel matching performance. According to Honoré et al. (1989) and Driver and Grossenbacher (1996), it may also be that orienting enhances the attentional spatial resources. Nevertheless, contrary to the findings of Newport et al. (2002) and Zuidhoek et al. (2004) in parallel matching, we did not observe in the second experiment any advantage nor any effect of noninformative vision on the haptic orientation discrimination in 5-month-old infants. Indeed, the noninformative visual cues provided by the non oriented visual context did not ameliorate the oblique discrimination. As in the no visual context cues condition (Kerzerho et al., 2005), infants could not discriminate the 20°-left oblique orientation from the 30°left oblique orientation after a 20°-left oblique familiarisation. This result is consistent with the mirror matching performance observed in adults (Newport et al., 2002). It seems likely that the presentation of a non oriented visual context would produce the same effect on vertical discrimination in comparison with the condition without visual context used in
Gentaz and Streri (2004) and Kerzerho et al. (2005) studies. Five-month-old infants should discriminate a vertical rod from a 10°-left oblique rod. In sum, the classical oblique effect should be recovered with a non oriented visual context. More recently (Kerzerho et al., in press) we addressed the question of the factors affecting the manual discrimination of spatial orientations and the orientation preferences in 5month-old infants in the fronto-parallel plane. It seems that when both gravitational vertical and body axis are aligned, the intrinsic “vertical preference” exists when the angular difference between the two orientations tested in the test phase is 10°. When the angular deviation to the vertical is greater than 10°, the novel orientation is preferred. This novelty preference is in accordance with results usually obtained in experiments using familiarisation vs. reaction to novelty procedure. This modification of orientation preference in the manual discrimination of orientation by 5-monthold infants was discussed in relation to the magnitude of the angular deviation to the gravitational vertical and the spatial reference cues available in each condition. When infants were tested with orientations which were close to both the gravitational vertical and their body axis, these reference cues may have acted as “attractors” and thus, reinforced the “vertical preference”. Finally, the presence of the visual context during the familiarisation and the test phases could have increased the attention and arousal state of the infants in the haptic task. But if such an increase actually occurred, our results showed that it is effective only when visual information is relevant for this specific haptic spatial task. Similarly, no advantage was observed in the haptic mirror task in adults (Zuidhoek et al., 2004). In the same vein, Millar and Al-Attar (2005) found no beneficial effect on a tactile landmark task when the visual stimulation consisted of diffuse light eliminating all spatial cues. They argued that spatial and non-spatial aspects have to be distinguished when considering the effect of vision on haptics: vision improves haptic spatial performance to the extent that it adds cues with potential relevance to spatial discrimination and reference. It seems that this remark is useful in orientation haptic discrimination in infants.
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4.2.1.1. Participants. Twenty infants aged from 4 months 20 days to 5 months 10 days (11 females and 9 males; mean age: 154.9 days) participated in this experiment.
tioned above the haptic display. The visual panel orientation was congruent with the haptic familiarised orientation (20° on the left side). 4.2.1.2.1. Familiarisation phase. In the familiarisation phase, a fixed-duration procedure was adopted in which the stimulus was presented until each infant accumulated a 60-second amount of holding time. The infant's right hand was put on the rod fixed upon the apparatus. When the infant let go of the rod more than 2 s before the 60-second time was up and did not self-re-grasp the rod, the experimenter put her/ his hand on the rod again until she/he accumulated 60-s duration of familiarisation. The familiarised rod orientation was the 20°-left oblique (same orientation than the visual panel orientation). The parents could see their child on a television screen during the experiment. 4.2.1.2.2. Test phase. The test phase began immediately after the familiarisation phase. For each trial, an infant-controlled procedure was used: the trial began when infants held the rod with their right hand and finished when they let it go. During this phase, two orientations were presented successively: the familiar orientation (previously used in the familiarisation: −20°) and the novel orientation (differing from the familiar orientation by 10° on infant's left side: −30°). The 10° difference choice between the familiar and the novel orientations could allow us to make comparisons with Gentaz and Streri's results (2002). Those two orientations were presented alternately during 4 trials (two test trial pairs) in a counterbalanced order between subjects. The test phase was: 20°/30°/20°/30° (order 1) or 30°/20°/30°/20° (order 2). Consequently, there were 10 infants in the 2 experimental groups.
4.2.1.2. Apparatus.
4.3.
Experiment 2: noninformative visual contextual cues
4.3.1.
Method
4.
Experimental procedures
4.1. General experimental conditions and procedures in the three experiments Each infant was seated in the baby car seat which was lightly backward tilted to maintain infant in seated position. A large white cloth bib was attached around the baby's neck at one side and to the screen at the other. The bib prevented infants from seeing their shoulder–hand systems, even laterally, but left them free to move. It also allowed the infant's right hands to be video-recorded with a TV camera the lens of which was located in a hole in the screen under the bib level. The visual panel was presented during the whole experience, from the beginning of the familiarisation phase until the end of the test phase (cf. Fig. 1: experimental design). During this procedure, the first experimenter, located behind the screen, controlled the video-recording. The second experimenter sat under the bib and to the right of the infant. Her tasks included putting the rod in the infant's hand and recording holding times. The infants' right hands were used in all experimental conditions as in Gentaz and Streri (2002).
4.2.
Experiment 1: congruent visual contextual cues
4.2.1.
Method
The baby car seat: The baby car seat was put on a solid plinth (37 cm deep, 35 cm wide and 10.5 cm high) to keep the center of the rod at the same level to that in the previous experiences. Moreover, a cushion was placed around the neck of the infant in order to maintain the head in a vertical position and in line with the trunk. The haptic display: The haptic display was composed of Plexiglas disk (diameter, 30 cm) equipped with a handleshaped rod (18 cm × 15 cm). This rod (.5 cm in diameter) was chosen because it was easily handled and explored by the 5month-old infants. The rod, mounted on the center of the disk, could be rotated 360° around its central axis. The rod could be maintained in the desired orientation in order to prevent involuntary deviation from its position during haptic scanning. The disk was graduated in degrees (the sensitivity threshold of this display was equal to .5°) and was taped on a wooden plank which upheld the device. The rod and the disk were positioned in the frontal plane and were centered on the midline of the infant's body. The height of the disk was adjusted so that the center of the rod was at the level of the infant's right shoulder, to a 52 cm height. The haptic display was the same as that used by Gentaz and Streri (2002). The visual panel: The visual panel (82 cm × 57 cm) was composed of alternate black and white stripes, inclined by 20° on the left side. Each line was 2 cm wide (equivalent to 2.12 cpd). The panel was positioned 55 cm away from the baby's face and was slightly tilted to be parallel with the baby's face (in upright body position). The visual panel was posi-
4.3.1.1. Participants. Twenty infants aged from 4 months 20 days to 5 months 10 days (10 females and 10 males; mean age: 154.7 days) participated in this experiment. 4.3.1.2. Apparatus, experimental conditions and procedure. The haptic display and the baby car seat were exactly the same as in the first experiment. By contrast, the visual panel (82 cm × 57 cm) was composed of 3 cm radius black dots. The black/white ratio was exactly the same than in the visual oriented context. The panel was positioned 55 cm away from the baby face and was slightly tilted to be parallel with the baby's face. Finally, experimental conditions and procedure were the same as in the first experiment.
4.4.
Experiment 3: non congruent visual contextual cues
4.4.1.
Method
4.4.1.1. Participants. Twenty infants aged from 4 months 20 days to 5 months 10 days (12 females and 8 males; mean age: 155.6 days) participated in this experiment. 4.4.1.2. Apparatus, experimental conditions and procedure. The haptic and the visual displays, the baby car seat, the
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experimental conditions (except for rod orientations) and procedure were the same as in the first experiment. 4.4.1.2.1. Familiarisation phase. In the familiarisation phase, a fixed-duration procedure was adopted in which the stimulus was presented until each infant accumulated a 60-second amount of holding time. In this present research, the infant's right hand was put on the rod fixed upon the apparatus. When the infant let go of the rod more than 2 s before the 60-second time was up and did not self-re-grasp the rod, the experimenter put her/his hand on the rod again until she/he accumulated 60-s duration of familiarisation. The familiarised rod orientation was the vertical (0°) defined gravitationally. The parents could see their child on a television screen during the experiment. 4.4.1.2.2. Test phase. The test phase began immediately after the familiarisation phase. For each trial, an infantcontrolled procedure was used: the trial began when infants held the rod with their right hand and finished when they let it go. During this phase, two orientations were presented successively: the familiar orientation (previously used in the familiarisation: 0°) and the novel orientation (differing from the familiar orientation by 10° on infant's left side: 10°). The 10° difference between the familiar and the novel orientations will allow comparisons with Gentaz and Streri's results (2002). These two orientations were presented alternately during 4 trials (two test trial pairs) in a counterbalanced order between subjects. The test phase was: 0°/10°/0°/10° (order 1) or 10°/0°/ 10°/0° (order 2). Consequently, there were 10 infants in the 2 experimental groups.
Acknowledgments We thank all the infants and their parents who participated in the experiments. This work was supported by grants from the University Institute of France.
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