Differences in Neural Mechanisms for Auditory and Visual Rhythm Processing

Only humans and a few other species of animals share the ability to reliably entrain and synchronize to rhythms. Accurately synchronizing to rhythms, as in tapping a foot to a metronome, requires the ability to precisely predict the onset of each rhythmic event. Curiously, humans have much greater difficulty synchronizing to flashing visual rhythms compared to auditory rhythms, even when both stimuli contain exactly the same timing information. While it is known that the auditory system works in conjunction with the motor system for the timing processing needed for rhythm perception, it has not been clear how the visual system processes rhythm timing. In collaboration with my co- authors, I present evidence to explain this discrepancy by showing the visual system has its own internal timing capabilities, which are separate than those utilized in auditory rhythms. I show that the visual system is able to detect perturbations of visual rhythms, but that error detection is not able to be translated into effective error correction in a synchronization task as is the case with auditory rhythms (Chapter 2). From an experiment in passive rhythm perception, I show evidence of visual timing activity arising from the visual system, as well as evidence of separate timing networks for auditory and visual rhythm processing (Chapter 3). I also show evidence that visual system timing information, in the form of neural entrainment, is present in the motor system at similar levels as auditory neural entrainment. Although visual timing information is present in the motor system, it is not able to be utilized in the same capacity as auditory rhythm timing in the motor system (Chapter 4). Taken together, these results suggest the visual system is processing rhythm timing through a visual modality specific mechanism. This mechanism is not as capable for rhythm processing as the motor system utilized in auditory rhythm processing, which results in poorer visual rhythm timing capabilities for visual rhythms compared to auditory rhythms.This dissertation, Differences in Neural Mechanisms for Auditory and Visual Rhythm Processing, is submitted by Daniel C. Comstock in the summer of 2021 in partial fulfillment of the degree Doctor of Philosophy in Cognitive and Information Sciences at the University of California, Merced, under the guidance of Ramesh Balasubramaniam