Objectives: We examined whether people with ASD could individuate as many objects as typically developing people, and whether they were as sensitive as controls to grouping information in an individuation task.
Methods: We tested 38 high functioning individuals with ASD (9 to 29 years old) and 38 typically developing individuals matched on IQ, age and sex using two well-established tasks that examine parallel individuation of multiple elements: rapid enumeration of 1 to 4 objects and multiple object tracking (MOT) of 4 objects. In separate ‘grouping’ conditions, the arrangement of elements varied, influencing the difficulty of the task. We hypothesized that individuals with autism would be less sensitive to the grouping of objects regardless of whether it helped or hurt typical adults.
Results: Individuals with autism exhibited poorer performance than typically developing individuals on the rapid enumeration and MOT task across age on both tasks with 4 objects. However, the developmental pattern differed when enumerating 1 to 3 objects. With these smaller numbers, the performance differences emerged with age, reflecting that developmental improvements evident in typical adolescents were not present in the group with autism.
We then examined the effect of grouping on performance. When the elements were in a dice pattern in the enumeration task, performance improved in both groups but this improvement was more striking in the group with autism. Similarly, when common motion was used to link two targets together in the MOT task, the common motion helped everyone but helped people with autism more than typically developing people. A slightly different pattern was evident when the elements were grouped together in a way that typically hurts performance (enumerating concentric squares, tracking targets that are linked to distracters by common motion). In this case, the groups were affected similarly by the grouping manipulation in both tasks.
Conclusions: Individuation of multiple elements is impaired in autism, indicating that it utilizes a distinct process from visual search tasks that are relatively strong in ASD. The results suggest there is a lack of late development in autism in the parallel processing of small numbers of elements. Additionally, attentional processes supporting the serial individuation of larger numbers of elements appeared abnormal throughout development. In contrast to our hypothesis, we found that individuals with autism are as sensitive as controls to grouping information – in fact, grouping that helps performance typically actually helped people with autism more than controls, providing the support needed to elevate performance to a more typical level. This indicates that grouping information is perceived and utilized by individuals with autism on tasks that measure sensitivity to the individual elements. Together these findings indicate that the visual processing of objects, and its developmental course, is unique in autism.