Armando Bertone

Motion Perception in Autism: A Complex Issue

We present the first assessment of motion sensitivity for persons with autism and normal intelligence using motion patterns that require neural processing mechanisms of varying complexity. Compared to matched controls, our results demonstrate that the motion sensitivity of observers with autism is similar to that of nonautistic observers for different types of first-order (luminance-defined) motion stimuli, but significantly decreased for the same types of second-order (texture-defined) stimuli. The latter class of motion stimuli has been demonstrated to require additional neural computation to be processed adequately. This finding may reflect less efficient integrative functioning of the neural mechanisms that mediate visuoperceptual processing in autism. The contribution of this finding with regards to abnormal perceptual integration in autism, its effect on cognitive operations, and possible behavioral implications are discussed.

Enhanced Pure-Tone Pitch Discrimination among Persons with Autism but not Asperger Syndrome.

Persons with Autism spectrum disorders (ASD) display atypical perceptual processing in visual and auditory tasks. In vision, Bertone, Mottron, Jelenic, and Faubert (2005) found that enhanced and diminished visual processing is linked to the level of neural complexity required to process stimuli, as proposed in the neural complexity hypothesis. Based on these findings, Samson, Mottron, Jemel, Belin, and Ciocca (2006) proposed to extend the neural complexity hypothesis to the auditory modality. They hypothesized that persons with ASD should display enhanced performance for simple tones that are processed in primary auditory cortical regions, but diminished performance for complex tones that require additional processing in associative auditory regions, in comparison to typically developing individuals. To assess this hypothesis, we designed four auditory discrimination experiments targeting pitch, non-vocal and vocal timbre, and loudness. Stimuli consisted of spectro-temporally simple and complex tones. The participants were adolescents and young adults with autism, Asperger syndrome, and typical developmental histories, all with IQs in the normal range. Consistent with the neural complexity hypothesis and enhanced perceptual functioning model of ASD (Mottron, Dawson, Soulières, Hubert, & Burack, 2006), the participants with autism, but not with Asperger syndrome, displayed enhanced pitch discrimination for simple tones. However, no discrimination-thresholds differences were found between the participants with ASD and the typically developing persons across spectrally and temporally complex conditions. These findings indicate that enhanced pure-tone pitch discrimination may be a cognitive correlate of speech-delay among persons with ASD. However, auditory discrimination among this group does not appear to be directly contingent on the spectro-temporal complexity of the stimuli.

Reduced multisensory facilitation in persons with autism

Although the literature concerning auditory and visual perceptual capabilities in the autism spectrum is growing, our understanding of multisensory integration (MSI) is rather limited. In the present study, we assessed MSI in autism by measuring whether participants benefited from an auditory cue presented in synchrony with the color change of a target during a complex visual search task. The synchronous auditory pip typically increases search efficacy (pip and pop effect), indicative of the beneficial use of sensory input from both modalities. We found that for conditions without auditory information, autistic participants were better at visual search compared to neurotypical participants. Importantly, search efficiency was increased by the presence of auditory pip for neurotypical participants only. The simultaneous occurrence of superior unimodal performance with altered audio-visual integration in autism suggests autonomous sensory processing in this population.

Far visual acuity is unremarkable in autism: do we need to focus on crowding?

Although autism presents a unique perceptual phenotype defined in part by atypical (often enhanced) analysis of spatial information, few biologically plausible hypotheses have been advanced to explain its neural underpinnings. One plausible explanation is functional but altered lateral connectivity mediating early or local mechanisms selectively responsive to different stimulus attributes, including spatial frequency and contrast. The goal of the present study was first to assess far visual acuity in autism using Landolt‐C optotypes defined by different local stimulus attributes. Second, we investigated whether acuity is differentially affected in autism when target optotypes are simultaneously presented with flanking stimuli at different distances. This typical detrimental “crowding effect” of flanking stimuli on target optotype discrimination is attributed to lateral inhibitory interaction of neurons encoding for visual properties of distracters close to the target. Results failed to demonstrate a between‐group difference in acuity to Landolt‐C optotypes, whether defined by luminance‐ or texture‐contrast. However, the expected crowding effect at one gap‐size opening distance was evidenced for the control group only; a small effect was observed for the autism group at two gap‐size opening. These results suggest that although far visual acuity is unremarkable in autism, altered local lateral connectivity within early perceptual areas underlying spatial information processing in autism is atypical. Altered local lateral connectivity in autism might originate from an imbalance in excitatory/inhibitory neural signaling, resulting in changes regarding elementary feature extraction and subsequent downstream visual integration and visuo‐spatial analysis. This notion is discussed within the context of characteristic lower‐ and higher‐level perceptual processing in autism.

Atypical Lateral Connectivity: A Neural Basis for Altered Visuospatial Processing in Autism

BACKGROUND Autistic perception encompasses both inferior and superior performance on different types of visuospatial tasks. Influential neurocognitive models relevant to atypical perception (i.e., weak central coherence, enhanced perceptual functioning) can, to differing degrees, account for these findings. However, the neural underpinnings mediating atypical visuospatial autistic perception have yet to be elucidated. METHODS In the present study, we used a lateral masking paradigm to assess the functional integrity of lateral interactions mediating visuospatial information processing within early visual areas of autistic (n = 18) and nonautistic (n = 15) observers. Detection thresholds were measured for centrally presented Gabor targets flanked collinearly at different distances (experiment 1) and flanked orthogonally at different contrasts (experiment 2). RESULTS Autistic and nonautistic groups showed increased target sensitivity when the distance between collinear targets and flankers was small (3 lambda) but not large (6 lambda). However, the effect of small-distance facilitation was significantly greater for the autistic group. In addition, we observed a group-specific effect of contrast: in the autistic group, target sensitivity was enhanced by low flanker contrasts of both 5% and 10% luminance difference, whereas for the nonautistic group, this effect occurred at 10% contrast only. CONCLUSIONS These findings support the idea that atypical visuospatial perception in autism may originate from altered lateral connectivity within primary visual areas, differentially affecting perception at the earliest levels of feature extraction.

The impact of blurred vision on cognitive assessment

The purpose of this study was to systematically assess the effect of blurred vision on several nonverbal neuropsychological measures commonly used as part of test batteries to assess the cognitive status of different patient populations. A total of 30 highly educated and healthy participants aged between 21 and 33 years were placed in one of three blurred vision groups, defined by their maximal visual acuity (20/20 or control group, 20/40, and 20/60). Blurred vision was simulated using positive diopters at a distance of 40 cm, the same distance as that at which tests were administered. Each participant was then assessed on a predetermined battery of nonverbal and verbal neuropsychological tests demanding different levels of acuity for optimal performance (i.e., tests whose items varied in terms of size and spatial frequency characteristics). In general, blurred vision significantly affected performance on nonverbal tests defined by small-sized/high-spatial-frequency items to a greater extent than on tests defined by larger sized/lower spatial-frequency items. As expected, blurred vision did not affect verbal test performance (Similarities, Information, and Arithmetic WAIS subtests).Our results are a clear indication of how even a “minimal” loss of visual acuity (20/40) can have a significant effect on the performance for certain nonverbal tests. In conclusion, such inferior performance is hypothetically interpretable as reflecting impaired cognitive functioning (i.e., attentional) targeted by a specific task (i.e., visual search) and suggests that the precision of the cognitive assessment and subsequent diagnosis are significantly biased when visuo-sensory abilities are not optimal, particularly for older patient populations where blurred vision resulting from correctable visual impairment is quite common.

Increased sensitivity to mirror symmetry in autism.

Can autistic people see the forest for the trees? Ongoing uncertainty about the integrity and role of global processing in autism gives special importance to the question of how autistic individuals group local stimulus attributes into meaningful spatial patterns. We investigated visual grouping in autism by measuring sensitivity to mirror symmetry, a highly-salient perceptual image attribute preceding object recognition. Autistic and non-autistic individuals were asked to detect mirror symmetry oriented along vertical, oblique, and horizontal axes. Both groups performed best when the axis was vertical, but across all randomly-presented axis orientations, autistics were significantly more sensitive to symmetry than non-autistics. We suggest that under some circumstances, autistic individuals can take advantage of parallel access to local and global information. In other words, autistics may sometimes see the forest and the trees, and may therefore extract from noisy environments genuine regularities which elude non-autistic observers.

Development of visually driven postural reactivity: A fully immersive virtual reality study

The objective of this study was to investigate the development of visually driven postural regulation in typically developing children of different ages. Thirty-two typically developing participants from 5 age groups (5-7 years, 8-11 years, 12-15 years, 16-19 years, or 20-25 years) were asked to stand within a virtual tunnel that oscillated in an anterior-posterior fashion at three different frequencies (0.125, 0.25, and 0.5 Hz). Body sway (BS) and postural perturbations (as measured by velocity root mean squared or vRMS) were measured. Most of the 5- to 7-year-old participants (67%) were unable to remain standing during the dynamic conditions. For older participants, BS decreased significantly with age for all frequencies. Moreover, vRMS decreased significantly from the 8- to 11- through 16- to 19-years age groups (greatest decreases for 0.5 Hz, followed by 0.25-Hz and 0.125-Hz conditions). No difference of frequency or instability was found between the 16- to 19- and 20- to 25-year-old groups for most conditions. Results suggest an over-reliance on visual input relative to proprioceptive and vestibular inputs on postural regulation at young ages (5-7 years). The finding that vRMS decreased significantly with age before stabilizing between 16 and 19 years suggests an important transitory period for sensorimotor development within this age range.

Development of static and dynamic perception for luminance-defined and texture-defined information.

The development of static and dynamic perception for stimuli requiring different levels of neural analysis was assessed by measuring orientation-identification and direction-identification thresholds for both lower-level [or first-order (FO)] and higher-level [or second-order (SO)] stimuli as a function of age. Results demonstrate that both lower-level and higher-level perception continue to develop during school-age years in both dynamic and static domains. When compared with adult levels, dynamic performance for 5–6-year-olds is significantly decreased for SO, but not for the FO perception; however, type of stimulus (FO vs. SO) did not affect the development of static perception. We therefore suggest that levels of stimulus complexity should be considered an important variable when assessing and making inferences regarding the typical and atypical development of static and dynamic perception.

Autism-specific covariation in perceptual performances: "g" or "p" factor?

Background Autistic perception is characterized by atypical and sometimes exceptional performance in several low- (e.g., discrimination) and mid-level (e.g., pattern matching) tasks in both visual and auditory domains. A factor that specifically affects perceptive abilities in autistic individuals should manifest as an autism-specific association between perceptual tasks. The first purpose of this study was to explore how perceptual performances are associated within or across processing levels and/or modalities. The second purpose was to determine if general intelligence, the major factor that accounts for covariation in task performances in non-autistic individuals, equally controls perceptual abilities in autistic individuals. Methods We asked 46 autistic individuals and 46 typically developing controls to perform four tasks measuring low- or mid-level visual or auditory processing. Intelligence was measured with the Wechslers Intelligence Scale (FSIQ) and Raven Progressive Matrices (RPM). We conducted linear regression models to compare task performances between groups and patterns of covariation between tasks. The addition of either Wechslers FSIQ or RPM in the regression models controlled for the effects of intelligence. Results In typically developing individuals, most perceptual tasks were associated with intelligence measured either by RPM or Wechsler FSIQ. The residual covariation between unimodal tasks, i.e. covariation not explained by intelligence, could be explained by a modality-specific factor. In the autistic group, residual covariation revealed the presence of a plurimodal factor specific to autism. Conclusions Autistic individuals show exceptional performance in some perceptual tasks. Here, we demonstrate the existence of specific, plurimodal covariation that does not dependent on general intelligence (or “g” factor). Instead, this residual covariation is accounted for by a common perceptual process (or “p” factor), which may drive perceptual abilities differently in autistic and non-autistic individuals.