PERCEPTUAL DISTORTIONS OF VISUAL ILLUSIONS IN CHILDREN WITH HIGH-FUNCTIONING AUTISM SPECTRUM DISORDER

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1 Psychologia, 2009, 52, PERCEPTUAL DISTORTIONS OF VISUAL ILLUSIONS IN CHILDREN WITH HIGH-FUNCTIONING AUTISM SPECTRUM DISORDER Rie ISHIDA 1), Yoko KAMIO 2) 1) Kyushu University, Japan 2) National Institute of Mental Health, National Center of Neurology and Psychiatry, Japan and Sachio NAKAMIZO 3) 3) The University of Kitakyushu, Japan This study examined perceptual distortion of visual illusions in children with autism spectrum disorder (ASD) and age-, sex- and IQ-matched typically developing children to determine whether local bias exists in low-level visual processing in ASD as the weak central coherence (WCC) theoretical account predicts. To explore whether higher-level contextual information can be integrated with low-level information in ASD, the perception with and without perspective cues was also examined. The children with ASD succumbed to illusions to a lesser degree than did the comparison group, and the degree of perceptual distortion was negatively correlated with Block Design score, a marker of WCC. The presence of perspective cues did not increase perceptual distortion among both groups to a statistically significant degree. The results support the WCC account suggesting abnormalities in integrating visual information in low-level processing in individuals with ASD when they perceived illusory figures. Key words: autism spectrum disorder, visual illusion, weak central coherence, lowlevel perceptual processing Sensory abnormalities strongly affect the daily lives of individuals with autism spectrum disorder (ASD), and no single theory has been found that can unitarily explain the multi-modal sensory abnormalities seen in such individuals (Dakin & Frith, 2005). While research into ASD is relatively advanced in the social domain, comparatively little research has been conducted in the sensory domain. Studies over the past few decades have demonstrated some unique assets and deficits in the higher-level visual processing of individuals with ASD (Dakin & Frith, 2005). For instance, individuals with ASD generally perform well on the WISC Block Design test Correspondence concerning this article should be addressed to Yoko Kamio, Department of Child and Adolescent Mental Health, National Institute of Mental Health, National Center of Neurology and Psychiatry, Japan ( kamio@ncnp.go.jp). This research was partly supported by a grant from RISTEX of Japan (Japan Science and Technology Agency) to the second author, and by a grant from the COE program provided by the Japanese Ministry of Education, Culture, Sports, Science, and Technology to the third author. The authors thank all participants and their families for their cooperation and Mr. Daiichiro Kuroki and Dr. Yasuyuki Okumura for help with statistical analysis. This paper is especially dedicated to Rie Ishida, who planned, executed, analyzed and wrote the manuscript to its completion, but passed away from injuries suffered in a traffic accident. 175

2 176 ISHIDA, KAMIO, & NAKAMIZO (Shah & Frith, 1983, 1993), the embedded figures test (Jolliffe & Baron-Cohen, 1997), visual search (Plaisted, O Riordan, & Baron-Cohen, 1998), and copying impossible figures (Mottron, Belleville, & Menard, 1999), while their performance tends to be poor for detecting biological motion (Blake, Tumer, Smoski, Pozdol, & Stone, 2003), integrating rapid visual motion (Gepner & Mestre, 2002), and perceiving coherent motion (Spencer et al., 2000). These findings have often been argued from the viewpoint of local vs. global processing (Frith, 1989; Happé, 1996; Mottron & Burack, 2001; Plaisted, 2001). One persuasive theoretical account to explain these assets and deficits characterizing ASD is that of weak central coherence (WCC); it addresses the bias toward detail-focused, local processing over global processing resulting in failure to extract global form/meaning (Happé & Frith, 2006). However, it still remains unclear at what level such an imbalance between local and global processing occurs in ASD, and the corresponding neural substrate for WCC has not been postulated. Visual phenomena can sometimes provide us with a distorted and illusory view of our physical environment. Such phenomena are referred to as visual illusions, and are considered to involve adaptation of our visual processing rather than its malfunction. Therefore, exploration of the processing of these illusions should advance our understanding of visual processing in general as well as in ASD. The research findings regarding visual illusions in ASD are so far mixed. Happé (1996) was the first to report perception of visual illusory figures (Ponzo, Kanizsa, Titchener, Müller-Lyer, Hering, and Poggendorf illusions) in children with autism. She compared the number of incorrect verbal judgments made by autistic children with those made by children with moderate learning difficulties (MLD) and typically developing young children. Significantly fewer autistic children, proportionately, succumbed to illusions, and the autistic children succumbed to significantly fewer numbers of illusions than those in the two comparison groups (except in the case of Müller-Lyer illusions). However, by artificially disembedding the induced components from the inducing context using color and depth, the group differences disappeared, indicating that the perception of the autistic children was less influenced by contextual cues. On the basis of these findings, Happé suggested that children with autism may ignore the inducing context and perceive the figures more accurately, thereby avoiding the typical illusory effects. Thus, she linked the WCC at low perceptual level with atypical illusory effects in individuals with autism. By contrast, Ropar and Mitchell (1999) demonstrated that children with autism and Asperger s syndrome were susceptible to visual illusions such as the Ponzo, Müller-Lyer, and Titchener (except the Hat) illusions on both a computer task and a verbal response task to a similar degree as were children with MLD and typically developing children of three different age groups (8 years, 11 years, adolescents). In a later study by Ropar and Mitchell (2001), they replicated their earlier findings for a similar but not identical subject population. Moreover, they demonstrated that children with autism and Asperger s syndrome who performed better on the WCC-related visuospatial tasks (embedded figures, block design, and Rey complex figure tests) were more susceptible to certain illusions, contradicting Happé s (1996) predictions. They concluded that alternatives to the WCC

3 VISUAL ILLUSIONS IN ASD 177 account should be considered in order to explain perceptual abnormalities in ASD. In line with these studies, Mottron and Belleville (1993) reported a high-functioning ASD (HFASD) adult case (E.C.) with exceptional graphic abilities. Extensive examination revealed that E.C. s perception at the initial representation level, including visual illusions (Hering, Ponzo, Jastraw, Müller-Lyer, Poggendorf, Zollner), was comparable with that of the control adults, despite a selective deficit in the part/whole hierarchization of visual stimuli. The question of whether individuals with ASD are in fact susceptible to visual illusions remains controversial even now (Best, Moffat, Power, Owen, & Johnstone, 2008; Bölte, Holtmann, Poustka, Scheurich, & Schmidt, 2007; Hoy, Hatton, & Hare, 2004). Phillips, Chapman & Berry (2004) urge caution in interpreting the research findings concerning visual illusion perception in ASD since context sensitivity of size perception may be lower in males than in females and the earlier findings might be attributable to male predominance in the sample. In the previous studies of Happé (1996) and Ropar and Mitchell (1999, 2001), the sex ratio of the participants was not addressed. Thus, when interpreting the findings of visual illusion perception in ASD, we need to take into consideration the sex ratio of participants. This preliminary study was intended to examine whether children with ASD are susceptible to visual illusions and to compare their performance with typically developing children matched for age, sex and IQ. The study proceeded on the premise that the existence of WCC in low-level perceptual processing in ASD would mean that these children would be unlikely to be susceptible to visual illusions. Furthermore, since it is reported that perceptual distortion may be increased with perspective cues in adults (Mitchell, Ropar, Ackroyd, & Rajendran, 2005), we explored the effect of higher-level contextual information by adding perspective cues such as scenery pictures to the meaningless illusory figures. Our predictions were as follows: (i) if WCC exists in lowlevel perceptual processing, perceptual distortion of visual illusions would be reduced or even absent in children with ASD compared with the comparison children; (ii) if WCC exists only in higher-level processing and not in low-level perceptual processing, children with ASD would be susceptible to visual illusions similarly to the comparison children; and (iii) if the presence of perspective cues increases perceptual distortion in children as well as adults, the augmentative effect would be observed in the comparison children but it would be reduced or absent in children with ASD. METHOD Participants Six boys with autism and three boys with Asperger s disorder participated in this study and were assigned to the high-functioning autism spectrum disorder (HFASD) group. All had been diagnosed by experienced clinicians using DSM-IV (APA, 1994) and the Childhood Autism Rating Scale-Tokyo version (CARS-TV, Kurita Miyake, & Katsuno, 1989) with a score of 30 serving as the cutoff for a diagnosis of autism. Nine comparison participants recruited from the local community were assigned to the control group. Through parental interviews they were confirmed to have no history of neurological disorders, or social,

4 178 ISHIDA, KAMIO, & NAKAMIZO Table 1. Participant Characteristics Characteristics HFASD group (n = 9) Control group (n =9) CA M (SD) (y:m) 12:3 (2:0) 11:7 (1:0) Range (10:6 16:3) (10:11 13:4) IQ M (SD) 98.2 (14.1) 98.4 (13.3) a Range (86 129) (84 122) VIQ M (SD) 98.6 (18.4) Range (72 123) PIQ M (SD) 99.9 (17.4) Range (83 131) Block Design M (SD) 13.6 (3.8) 8.8 (4.2) Range (9 19) (4 18) CARS-TV M (SD) 35.6 (3.9) Range ( ) Note. HFASD = High-functioning Autism Spectrum Disorders; CA = chronological age; VIQ = Verbal IQ; PIQ = Performance IQ; CARS-TV = Childhood Autism Rating Scale-Tokyo version. a IQ for the HFASD group was calculated based on the full version of the WISC-III, and IQ for the control group was estimated using the short version (Vocabulary, Information, Block Design, and Picture Completion). academic, behavioral, and emotional difficulties. The IQs of the HFASD group participants were assessed using the full version of the Japanese version of the Wechsler Intelligence Scale for Children-Third Edition (WISC-III), while those of the control group participants were estimated based on the short version consisting of four subtests (Vocabulary, Information, Block Design, and Picture Completion) of the WISC-III using a formula by Sattler (1998). IQ estimates using this formula have been reported to correlate closely with full scale IQ (γ 0.90) (Sattler, 1998). Both groups were matched for age, sex (all boys) and IQ (paired t-test: t(8) = 0.92, n.s. for age; t(8) = 0.03, n.s. for IQ) (Table 1). As predicted, the average score on the Block Design subscale of WISC-III was significantly higher for the HFASD group than for the control group (t(8) = 2.58, p < 0.05; Table 1). Verbal consent was obtained from the participants and written informed consent was obtained from their parents prior to participation in the study. Materials Ponzo and Müller-Lyer illusions were selected from Gregory (1968) as materials for this study (see Fig. 1). The stimuli were drawn with black ink in a booklet of white paper measuring 37.5 cm 26.5 cm. Each stimulus was presented in two conditions: without and with perspective cues. The Ponzo illusion was 9.5 cm 7.0 cm without perspective cues, and 13.5 cm 8.0 cm with perspective cues. The target lines were presented horizontally, their length was 3.5 cm, and the intersectional angle of outer lines was 53. The Müller-Lyer illusion was 8.0 cm 7.5 cm (inward arrowheads) and 8.0 cm 11.5 cm (outward arrowheads) without perspective cues, and 11.0 cm 11.0 cm (inward arrowheads) and 9.0 cm 11.5 cm (outward arrowheads) with perspective cues. The target lines were presented vertically, their length was 7.5 cm, and the intersectional angle of the inward arrowheads was 127 and that of the outward arrowheads was 233.

5 VISUAL ILLUSIONS IN ASD 179 Fig. 1. Examples of the stimulus figures used in this study: (a) Ponzo illusion and (b) Müller-Lyer illusion. The illusion without perspective cues is presented in the left column; that with perspective cues is presented in the right column. Procedure Prior to the experimental trials, a practice trial using single lines was conducted so that the participants could familiarize themselves to the task. Participants were tested individually in a quiet, secluded room. Stimuli were presented at approximately 50 cm from the eyes of the participant. Participants were instructed to re-create the lengths of two target lines per stimulus, using a device similar to a slide rule. Scales in millimeters were located on the reverse side of the device so the participants were not able to see them. The experimenter recorded the length by checking the scale on a trial-by-trial basis. All the participants were naïve to our purpose and were not informed that the stimuli could cause visual illusions. Each participant performed six trials per stimulus type, that is, 24 trials in total, and the presentation order of the 24 illusory figures and the measurement order of two target lines for each illusory figure were randomized. For each trial, there was no time limit.

6 180 ISHIDA, KAMIO, & NAKAMIZO RESULTS Analyses of variance (ANOVAs) with repeated measures were carried out on the participant s lengths of the two target lines for each stimulus separately for each figure in order to delineate its unique features. As an index of illusory effect, we used the ratio calculated from the lengths of each stimulus for t-tests. A ratio over 1.0 reflects that the top line was perceived longer than the bottom one for the Ponzo illusion and that the outward arrowhead line was perceived longer than the inward one for the Müller-Lyer illusion. Ponzo (Figure 2) A repeated measures ANOVA was conducted with two withinsubject factors of Condition (2: with perspective cues or without perspective cues) and Position of lines (2: top or bottom), and one between-subject factor of Group (2: HFASD or Control). Although the main effect of Position of lines was significant [F = 27.43, p < 0.001], neither the main effect of Condition [F =2.41, n.s.] nor that of Group was significant [F =0.38, n.s.]. The interaction between Group and Position of lines was significant [F =5.43, p < 0.05] but neither the interaction between Group and Condition Table 2. Participant s Perceived Length of the Illusory Figures by Group Illusory figure HFASD group (n = 9) Control group (n =9) Ponzo mean ± SD (cm) without perspective cues top 4.84 ± ± 1.15 bottom 4.60 ± ± 0.61 illusory effect 1.05 ± ± 0.11 with perspective cues top 4.99 ± ± 1.15 bottom 4.57 ± ± 0.64 illusory effect 1.09 ± ± 0.12 Müller-Lyer mean ± SD (cm) without perspective cues inward 6.87 ± ± 1.06 outward 7.62 ± ± 1.29 illusory effect 1.10 ± ± 0.06 with perspective cues inward 7.11 ± ± 1.20 outward 7.72 ± ± 1.17 illusory effect 1.09 ± ± 0.03

7 VISUAL ILLUSIONS IN ASD 181 Fig. 2. Perceived length of the target lines in the Ponzo illusion without cues (upper) and with cues (lower) by the HFASD and the Control children. The slope of lines reflects the magnitude of illusory effect. [F = 0.48, n.s.] nor that between Position of lines and Condition [F =1.21, n.s.] was significant. The interaction between Group, Position of lines and Condition was not significant [F = 1.32, n.s.]. These results indicate that children of both the HFASD and control groups were susceptible to the Ponzo, which occurred irrespective of the presence of cues. Further comparisons demonstrated that the magnitude of illusory effect differed by group: the illusory effect was significantly greater on the without cues condition [t = 3.34, p < 0.01] and tended to be significantly greater on the with cues condition [t = 1.76, p = 0.1] in the control group than in the HFASD group. On closer inspection of individual response, it was found that all the participants were susceptible to the Ponzo except two boys with HFASD on the with cues condition. However, the distribution of the participants who succumbed to the illusion on the with cues condition did not significantly differ between groups [χ 2 = 0.13, n.s.]. Müller-Lyer (Figure 3). A repeated measures ANOVA was conducted with two within-subject factors of Condition (2: with perspective cues or without perspective cues) and Direction of arrowheads (2: inward or outward), and one between-subject factor of

8 182 ISHIDA, KAMIO, & NAKAMIZO Fig. 3. Perceived length of the target lines in the Müller-Lyer illusion without cues (upper) and with cues (lower) by the HFASD and the Control children. The slope of lines reflects the magnitude of illusory effect. Group (2: HFASD or Control). All the main effects were statistically significant for Condition, Direction of arrowheads, and Group [F = 10.20, p < 0.01; F = 68.03, p <0.01; F = 4.64, p < 0.05, respectively], although no interactions were statistically significant [F = 0.07, n.s. between Condition and Group; F =0.60, n.s. between Direction of arrowheads and Group; F =2.29, n.s. between Condition and Direction of arrowheads; F = 0.01, n.s. between Condition, Direction of arrowheads, and Group]. That is, both groups subjectively perceived the outward lines longer than the inward ones, and did the target lines longer with the cues than without the cues. And children of the control group subjectively perceived the target lines longer than children of the HFASD group. On closer inspection of individual response, it was found that all the participants were susceptible to the illusion except one boy with HFASD on the with cues condition. The distribution of the participants who succumbed to the illusion on the with cues condition did not differ significantly between groups [χ 2 = 0.30, n.s.]. Relationship between the illusory effect and Block Design For the Ponzo illusion, there was a tendency toward negative correlation between the illusory effect and the

9 VISUAL ILLUSIONS IN ASD 183 Fig. 4a. Illusory effect for the Ponzo without cues by the HFASD and the Control children. Each figure presents data for two linear relationships for both groups and their regression lines (the thick line for the Control, the dotted one for the HFASD). Fig. 4b. Illusory effect for the Ponzo with cues by the HFASD and the Control children. Each figure presents data for two linear relationships for both groups and their regression lines (the thick line for the Control, the dotted one for the HFASD).

10 184 ISHIDA, KAMIO, & NAKAMIZO performance on Block Design for each group on the without cues condition [r = 0.65, p = 0.06 for the HFASD group; r = 0.64, p = 0.06 for the control group], while on the with cues condition, there were no significant correlations [r = 0.45, n.s. for the HFASD group; r = 0.59, n.s. for the control group]. When the data of the both groups (n = 18) were combined, a negative correlation was found between them [r = 0.74, p <0.001 without cues; r = 0.62, p < 0.01 with cues] (Figure 4a, 4b). For the Müller-Lyer illusion, there were no correlations between the illusory effects and the performance of Block Design [without cues, r =0.11, n.s. for the HFASD group; r = 0.35, n.s. for the control group; r = 0.03, n.s. for the combined data; with cues, r = 0.13, n.s. for the HFASD group; r = 0.23, n.s. for the control group; r =0.27, n.s. for the combined data]. DISCUSSION This preliminary study has provided some clues toward answering our questions. First, the children with HFASD were found to be susceptible to visual illusions, which was partly opposed to the argument by Happé (1996) and partly in line with that by Ropar and Mitchell (1999, 2001). By comparing them with the typically developing children matched on age, sex and IQ, they were susceptible to the Ponzo less than the typically developing children, although they were so to the Müller-Lyer to the same degree as the typically developing children were. The finding for the Ponzo partly supports the hypothesis (i) that WCC begins from a preattentive stage and the susceptibility to visual illusions is associated with WCC in lowlevel visual processing, which was addressed by Happé (1996). Along this hypothesis, the integration of visual information would be diminished in the low-level visual processing in children with ASD. Furthermore, the hypothesis is also supported by a negative correlation found between the illusory effect of the Ponzo and the Block Design score as a marker of WCC (Happé & Frith, 2006), both of which are suggested to share a common processing by Bölte et al. (2007). Our finding regarding the Müller-Lyer is in contrast to that found for the Ponzo but consistent with that of previous studies (Happé, 1996; Ropar & Mitchell, 1999, 2001) in that children with ASD as well as the comparison children could not avoid distorted perception to almost the same degree. Our finding that the susceptibility to the Müller- Lyer was not related with either WCC or the presence of cues also supported neither of our hypothesis (i) nor (ii). This WCC-insensitive property may be attributed to the structure; its components are tightly connected so that even individuals with ASD automatically integrate the figure s visual information. The inconsistency of results reported by previous studies of visual illusion in ASD might be partly attributable to variations in methodology. First, the illusory figures used varied among the studies; for example, the Ponzo illusions used by Happé and us are railway-like with two converging lines and two horizontal lines, whereas that used by Ropar and Mitchell contains two circles instead of horizontal lines. In addition, the upper

11 VISUAL ILLUSIONS IN ASD 185 horizontal line is connected with two converging lines in our Ponzo, while the lines of Happé s are separated. Since multiple mechanisms are inferred to be involved in the illusory effect, some components would likely activate a particular mechanism more so than other components (Ropar and Mitchell, 2001), which may influence the illusory effect to some degree. Second, the evaluative method of perceptual distortion used in the previous studies was either a yes/no verbal judgment or a length measurement. Most studies except Ropar and Mitchell s (1999, 2001) and the present study adopted a verbal dichotomous judgment. If we had adopted the verbal one instead of length measurement, we would not have detected the quantitative differences in the susceptibility between groups and would have concluded that children with HFASD were susceptible to visual illusions in the same manner as were the typically developing children. Third, considering sex differences in the visual illusion susceptibility suggested by Phillips et al. (2004), our two groups were matched on sex and all were boys, while other studies except Hoy et al. (2004) and Bölte et al. (2007) did not explicitly mention it. Another question we sought to answer was whether the presence of meaningful perspective cues (e.g., railway, building, room) would influence length perception and increase the illusory effect. Contrary to our prediction (iii), the presence of the perspective cues did not enhance the illusory effects for children of both groups for both the figures. However, cue effect was found only for the Ponzo in the typically developing children but not the children with HFASD, although it was not statistically significant. The Ponzo was again more sensitive to the cue effect than the Müller-Lyer. It could be possible that while higher-level semantic information such as the cues may influence low-level visual processing in a top-down manner in typically developing children, such context-sensitive information processing may be diminished in children with HFASD, which was not proved in this study. With a larger sample size, the cues might sufficiently augment the illusory effect in typically developing children, which would not be the case in children with HFASD. In terms of WCC, our results suggest that the Happé (1996) s WCC hypothesis can be applied to general population including non-clinical individuals by the finding that children who performed better on the WCC-related task were less susceptible to visual illusion. Taken together, children with HFASD are suggested to be impaired in integrating visual information in low-level processing with various degrees. Although we have discussed from a viewpoint of WCC account, it should be noted that these results do not contradict the alternative account by Mottron et al. (2001) and Plaisted (2001). Discussion about low-level visual processing based on empirical data in autism has just begun (see Bertone & Faubert, 2006; Milne et al., 2006). Further systematic investigations are necessary to explore the low-level perceptual processing characteristic of autism, using psychophysiological and neurophysiological approaches (Brown, Gruber, Boucher, Rippon, & Brock, 2005; Stroganova et al., 2007). We recognize that the present study has methodological limitations: the sample size was small, and the range of illusory figures and the tasks studied was limited. Despite these limitations, this preliminary study

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