Disruptions in the spatial filtering and temporal processing of low-level unisensory and multisensory stimuli in autism spectrum disorders
Kwakye, Leslie Ellen Dowell
Autism spectrum disorders (ASD) are characterized by disrupted social interactions, disordered language and communication, and restrictive interests and repetitive behaviors. Although not part of the main diagnostic criteria, alterations in sensory responsiveness and perception are also prevalent in autistic individuals. Neurobiologically based theories as to the underlying mechanisms of autism, such as increased excitation/inhibition ratio, minicolumnopathy, and temporal binding deficit suggest that several fundamental aspects of sensory processing may be disrupted in ASD. At the core of these ideas is the concept that neurons in the autistic brain may have a reduced capacity for filtering sensory information as compared to neurons in a typically developing brain, and that timing-related aspects of sensory processes may be altered. To test these filtering- and temporal-based aspects of sensory processing in ASD, we have employed a battery of tasks to contrast performance in ASD and typically developing (TD) individuals. We established that autism is associated with disruptions in sensory filtering by investigating differences in the critical bandwidth (the range of frequencies which are able to mask a pure tone or gabor target) for both the auditory and visual modalities. We were also able to demonstrate that children with ASD show differences in auditory, but not visual, temporal acuity by measuring thresholds on visual and auditory temporal order judgment (TOJ) tasks. Finally, we demonstrated that autism is associated with disrupted multisensory temporal processing by determining the temporal window of multisensory integration (the duration in which the integration of information from multiple modalities is likely) for three distinct multisensory tasks: (the flash beep illusion, the multisensory TOJ, and the detection of multisensory targets). In each of these tasks, children with ASD showed a dramatic enlargement in the size of the multisensory temporal window, thus establishing disrupted temporal multisensory processing as an integral factor in the sensory abnormalities that characterize autism. These changes in filtering and temporal processing of individuals with ASD represent a unique way of looking at the nature of the sensory disturbances seen in autism, and may represent an important window into the etiology of autistic symptomology and its relationship to the core disrupted domains including communication and social interactions. Furthermore, these results are likely to provide important insights for the development of better interventional strategies for those living with autism.