A Systematic Examination of Early Perceptual Influences on Low-, Mid- and Higher-Level Visual Abilities in Autism Spectrum Disorder

Background: It is now well accepted that perceptual alterations are a key characteristic of the autistic behavioral phenotype (Mottron 2006, Bertone et al 2010a). Studies investigating visual perception in Autism Spectrum Disorder (ASD) have identified atypical abilities mediated by low- (primary visual areas), mid- (extra-striate areas) and higher-levels (large-scale neural functioning) of processing. The bulk of this research, however, has focused on individual levels of processing in isolation (i.e. low or high). It is therefore unknown if a functional relationship exists between levels of information processing in ASD, and more so, if alterations in early levels of visual analysis influence mid- and higher-level perception.  The answer to this question is critical in understanding the origins of the autistic perceptual phenotype and ultimately, the effect of early encoding on subsequent perceptual, cognitive and social abilities.

Objectives:  The goal of this set of studies was to systematically assess whether manipulating either (i) the type (luminance vs texture), or (ii) access to early, local information differentially affects autistic performance on tasks targeting low-level (spatial frequency perception), mid-level (global form perception) and higher-level (visuo-spatial and face identity perception) perceptual processes.

Methods:  Four separate studies examining the effect of manipulating physical stimulus properties on progressively complex visuo-spatial tasks were conducted: (i) low-level perception was assessed using vertically oriented, sine-wave luminance- and texture-defined gratings over a range of low to high spatial frequencies; (ii) mid-level perception was examined using luminance and texture-defined radial-frequency patterns (RFPs): closed-contour spatial stimuli manipulated to create “bumps” or radial frequencies along their quasi-circular contours to optimize global (i.e. few bumps) and local (i.e. many bumps) processing; (iii) higher-level, non-social perception was assessed using a reversed block design task where the physical attributes of the block stimuli were manipulated (luminance vs texture); (iv) higher-level, social perception was assessed with a face-identification task incorporating four view conditions (front-view, side-view, inverted and view-change conditions) where access to local and global cues was manipulated.

Results:  For the low-level task, results revealed an increased sensitivity of the ASD group for high-spatial frequency information for the luminance-defined condition alone. For the mid-level task, individuals with ASD were significantly worse at discriminating texture-defined RFPs across all modulation conditions. However, the ASD group performed as well as the control group for the luminance-defined RFPs with many modulations along their contour: a condition that biases local information processing. For the higher-level, non-social block design task, individuals with ASD outperformed the control group when blocks were luminance-defined; however, this “cognitive peak” disappeared when blocks were texture-defined. For the higher-level, social task, individuals with ASD were significantly worse in identifying faces in the view-change condition only, which limited local information cues.

Conclusions: Our findings indicate that visual abilities mediated by low-, mid- and higher-level mechanisms in autism are differentially affected by the nature and access to early visual information during task completion. These results provide compelling evidence to suggest that early perceptual alterations in autism are at least in part responsible for autism’s perceptual phenotype, irrespective of the level at which it is defined.