While deficits in social communication are among the most salient symptoms of autism, the underlying source of these deficits may arise from lower-level deficits in perception and/or attention. For example, a child with autism that effectively neglects social interactions could have established such a pattern of social response over the course of development, as a downstream consequence of an early developmental failure to detect and orient to important changes in the sensory environment. While prior studies have established evidence for abnormal orienting responses to novel stimuli in persons with autism, the current study was designed to investigate whether the neural response to a visual, sensory-level change, occurring outside of the focus of attention, differs between children with autism and their typically developing peers. Such a difference would suggest a perceptual-level deficit in the sensory encoding of environmental change.
Objectives:
To determine whether the neural response to the sensory registration of change and/or attentional orienting differs between typically developing children and children diagnosed with autism. We hypothesized that children diagnosed with autism would not readily detect unattended visual environmental changes, and further, that orienting to such changes would be slowed or might not occur at all.
Methods:
Visual sensory-level discrimination was tested passively while the typically developing children (TD) or high-functioning children with autism (HFA) watched a video of their choice. The video was surrounded by a rapidly presented pattern of line gratings of different standard and deviant orientations (45 degree tilt to the right or left of center), appearing in the visual periphery. The visual mismatch event-related brain potential (ERP) was measured as an index of sensory-level stimulus discrimination and elicited by presenting the line patterns, in a randomized manner, in both standard (frequent: 80%) and deviant (infrequent: 20%) orientations. The resulting difference in the ERP response between deviant and standard line orientations was calculated.
Results:
Both the TD and HFA groups elicited a differential response to the deviantly oriented lines. The mismatch ERP response in the TD group occurred as early as the P1 ERP component, becoming statistically significant by 110 ms. In contrast, the mismatch response in the HFA group occurred much later, by 160 ms. These results suggest that the TD group distributed their attention as a gradient on and around the video, resulting in an early, sensory-level discrimination of the lines, while the difference in the HFA group was manifested in a later, orienting response to the unattended stimuli with larger responses to the lines of a deviant orientation.
Conclusions:
Both TD and HFA groups of children discriminate changes in the environment, but the timing differed between the two groups with early sensory-level discrimination occurring in the TD group, but not the HFA group. This observation may help to explain why autistic children often do not respond quickly to commands, and may also provide one explanation for their difficulty with transitions— the additional time required to process sensory information may contribute to a strong stress reaction in situations that require rapid processing of changing information.