Conjunctive Visual Processing Appears Abnormal in Autism

Abstract

Face processing in autism spectrum disorder (ASD) is thought to be atypical, but it is unclear whether differences in visual conjunctive processing are specific to faces. To address this, we adapted a previously established eye-tracking paradigm which modulates the need for conjunctive processing by varying the degree of feature ambiguity in faces and objects. Typically-developed (TD) participants showed a canonical pattern of conjunctive processing: High-ambiguity objects were processed more conjunctively than low-ambiguity objects, and faces were processed in an equally conjunctive manner regardless of ambiguity level. In contrast, autistic individuals did not show differences in conjunctive processing based on stimulus category, providing evidence that atypical visual conjunctive processing in ASD is the result of a domain general lack of perceptual specialization.

Keywords: autism spectrum disorder; face processing; holistic; object recognition; sensory; vision; visual processing.

FIGURE 1

Visual discrimination tasks and processing strategies. Participants indicated whether stimuli were a match or a non-match. Stimuli consisted of abstract objects (A,B) and faces (C,D) manipulated to be low ambiguity (A,C) or high ambiguity (B,D). All examples depict non-match trials; match trials comprised two identical, but rotated, stimuli. Conjunctive versus feature-based strategies were assessed by comparing the number of saccades an individual made within an object/face versus the number of saccades between objects/faces in non-match trials. If participants viewed the objects as a unified conjunction of features, we would expect more saccades within an individual object relative to saccades across the two objects (blue lines). If participants treated the objects as three separate individual features, we would expect to see more comparisons of features across the two objects than within an individual object (red lines). Each fixation is shown by a numbered circle indicating the order of the fixation; lines connecting the fixations indicate saccades.

FIGURE 2

Hypotheses and results. Measurements of within:between saccade ratios were used to measure visual conjunctive processing, where higher ratios are indicative of a more conjunctive processing strategy, and lower ratios of a more feature-based strategy. (A) We predicted that typically-developed individuals would show greater conjunctive processing for high- relative to low-ambiguity objects, as well as high levels of conjunctive processing for both high- and low-ambiguity faces across ambiguity. (B) If the autism spectrum disorder (ASD) group shows a face-specific difficulty in conjunctive processing, conjunctive processing would be typical for objects, but decreased for faces. (C) If the ASD group exhibits a domain-general difficulty in conjunctive processing such that visual conjunctive processing is decreased overall, the within:between ratios would be reduced relative to TD, but their overall pattern would remain consistent across groups. (D) If the ASD group exhibits a domain-general difficulty in conjunctive processing through a lack of perceptual specialization, the pattern of within:between saccades would change such that the level conjunctive processing would not vary between any conditions and would be reduced overall relative to TD. For all panels, TD individuals are shown in black/gray and ASD individuals in red/pink. Panel (E) shows data for within versus between item saccades in the TD group and ASD group. Significant statistical effects are denoted with ^∗ indicating a 3-way interaction, # indicating 2-way interactions, and ¥ indicating simple main effects. Results support a domain general difficulty with visual conjunctive processing in ASD. Error bars represent standard error. Panel (G) depicts the relationship between autistic traits and conjunctive processing. Higher levels of autistic traits were associated with lower levels of conjunctive processing. For all bar graphs, TD individuals are shown in black/gray and ASD individuals in red/pink. Low-ambiguity conditions (LA) are presented in red/black, and high-ambiguity conditions (HA) are presented in pink/gray. Outliers are indicated with +, but in each case inclusion of outliers did not change the significance of results.