BME PhD Dissertation Defense - Lenny Varghese

3:00 pm on Monday, March 25, 2013
5:00 pm on Monday, March 25, 2013
677 Beacon Street, room B02 (CompNet Auditorium)
Committee Members:
Barbara G. Shinn-Cunningham (BME, advisor)
H. Steven Colburn (BME) *Chair*
Nancy Kopell (Math)
David Somers (Psychology)
Virginia Best (Sargent College)

Title: Psychophysical and electrophysiological investigations into the mechanisms supporting everyday communication

Abstract: Humans solve the so-called “cocktail party problem” with relative ease, and are generally able to direct selective auditory attention to process and recall acoustic information from one sound source in the presence of other irrelevant stimuli competing for cognitive resources. This ability depends on a variety of factors, including volitional control of selective attention, the ability to store information in memory for recall at a later time, and the ability to integrate information across multiple sensory modalities. Here, psychophysical and electroencephalography (EEG) experiments were conducted to study these three factors. The effects of selective attention on cortical and subcortical structures were examined using EEG recorded during a dichotic listening task. Cortical potentials showed robust effects of attention (demonstrated by the ability to classify responses to attended and ignored speech based on short segments of EEG responses); however, potentials originating in the brainstem did not, even though stimuli were engineered to maximize the separability of the neural representation of the competing sources in the auditory periphery and thus the possibility of seeing attention-specific modulation of subcortical responses. In another study, the relationship between object formation and memory processing was explored in a psychophysical experiment examining how sequences of nonverbal auditory stimuli are stored and recalled from short-term memory. The results of this study support the notion that auditory short-term memory, like visual short-term memory, can be explained in terms of object formation. In particular, storage and recall of auditory stimuli in memory depends on stream formation and the perceptual costs involved in switching attention between multiple streams. Finally, effects of audiovisual integration were studied in a psychophysical experiment using complex speech-like stimuli (zebra finch songs). Results show visual cues improve performance differently depending on whether target identification is limited by energetic masking or whether it is limited by object formation difficulties and uncertainty about when a target occurs. Together, these studies support the idea that everyday communication depends on an interplay of many mechanisms including attention, memory, and multisensory integration, each of which is influenced by perceptual organization.