Semester

Fall

Date of Graduation

2020

Document Type

Dissertation

Degree Type

PhD

College

School of Medicine

Department

Not Listed

Committee Chair

Marc W. Haut

Committee Member

James W. Lewis

Committee Member

Mary Beth Mandich

Committee Member

Carla Mazefsky

Committee Member

Bernard G. Schreurs

Abstract

Sensory processing differences are a prevalent aspect of autism spectrum disorder (ASD) that may contribute to core deficits of ASD such as repetitive behaviors as well as comorbidities including anxiety disorders. The ability to integrate information among our senses is required to comprehend the world around us and is crucial for the development of language, motor skills, and social communication. Prior studies have shown that individuals with autism differ from individuals without autism when presented with simple, non-natural audio-visual stimuli such as basic shapes accompanied by pure tones. Because the human brain processes non-natural and natural stimuli differently, more recent studies have used real-world images paired with a sound. However, the stimuli used in many of these studies were static photos paired with a congruent sound and do not reflect the dynamic nature of a real-world environment. The bulk of studies using dynamic real-world stimuli have investigated language processing by pairing human vocalizations with a human face. However, because face and vocalization stimuli are processed in distinct areas of the brain, dynamic stimuli that contain faces and vocalizations confound investigations of multisensory integration. The remaining studies that used dynamic real-world videos to investigate multisensory integration, have primarily used very short video clips of only a few seconds in length. While these stimuli do represent the natural environment, the short length of these videos lacks the continuous nature of what we see and hear in our environment. Only two studies have used dynamic, real-world stimuli that are continuous to investigate multisensory integration in autism. Unfortunately, the stimuli used in both of these studies contained confounding facial and or language processing. Therefore, we currently do not have a good understanding of how individuals with autism integrate multiple real-world sensory inputs that reflect dynamic natural stimuli encountered in the environment outside of our understanding of language and face processing.

Considering the gap in the current literature regarding processing of real-world, dynamic stimuli, the goal of this research was to use functional magnetic resonance imaging (fMRI) to investigate how individuals with autism integrate auditory and visual information of a real-world, dynamic scene. We hypothesized that individuals with high-functioning autism would show different levels of brain activation in regions known to process auditory and visual information as well as in brain areas known to integrate audio-visual information. While undergoing an MRI, participants (ASD n=20 and typically developed controls [TD] n=21) watched a video of a person bouncing a basketball. The person was filmed from the neck down to avoid engaging face processing brain regions while viewing the video. To ensure engagement, a simple attention task was used and was easily accomplished by both groups. Analysis of the fMRI data showed that the ASD group had significantly less brain activation in left-lateralized intraparietal sulcus and putamen/globus pallidus. These brain regions are known to be involved in processing human biological motion and regulating motor movements respectively. The hypoactivation seen in the ASD group may reflect underconnectivity between and within the hemispheres for processing this dynamic audio-visual stimulus. These data support the Underconnectivity Theory of Autism which posits long-distance networks are underconnected in individuals with autism contributing to global processing deficits.

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