Kourosh Saberi, Ph.D. - US grants

The long-term objective of the proposed research is to improve our understanding of how the binaural system facilitates the detection and recognition of complex sounds (i.e, sounds that have a bandwidth) in the presence of masking sounds. To date, few studies have provided an in depth investigation of binaural unmasking of complex signals and none has modeled the relevant results. The proposal has three specific goals: 1) to improve our understanding of how complex binaural objects are formed and localized, particularly when multiple images are detected, 2) to determine the degree to which the unmasking of a complex signal is dependent on the perceived spatial separation of the signal and masker, and 3) to develop, improve, and evaluate binaural- based models of unmasking capable of predicting the benefits to complex-signal detection. Two experimental paradigms are used. First, a complex signal (narrowband noise, or a multi-tone complex) is alternated with an acoustic pointer which the observer adjusts to match the perceived spatial position of the signal. In the second experimental paradigm, the degree to which spatial position affects unmasking is examined. Here, a complex sound (either a narrowband of noise, an AM or FM carrier, a two-tone complex, or a sequence of tone bursts defined by the pattern of intertone times) is presented in a background of a complex masker. The subject is required to indicate in which of two observation intervals the signal was presented. Both energetic and informational masking will be examined. The magnitude of binaural unmasking is usually very large, as great as 30 dB for narrowband maskers, and therefore has strong influences on auditory perception in natural environments. The results of the current experiments are expected to have further benefits for multi-channel hearing-aid design, and for basic theory and models of binaural interaction.

DESCRIPTION (provided by applicant): The functional anatomy of the planum temporale (PT) has been of great theoretical interest for decades, and a focus of recent clinical studies of a number of disorders ranging from autism to schizophrenia. Although the (left) PT was initially thought to subserve language functions, recent basic research has shown that it is multifunctional, being implicated in such diverse processing domains as speech perception and production, tonal processing, auditory-motor integration, spatial hearing, and multi-sensory integration. Given the potential importance of the PT in both theoretical models of cortical function for a range of abilities as well as its widespread clinical implications, a more thorough understanding of the functional organization of the PT is sorely needed. The present proposal seeks to fill this gap through a series of fMRI studies using within subject designs, and organized around four specific aims. Aim 1 is to assess activation patterns for several functions known to activate the PT, including speech perception/production, tonal/melodic perception, sensory-motor integration, visual speech perception, and spatial hearing. Aim 2 seeks to understand the functional basis for sensory-motor activations in the PT. Sensory-motor behaviors have been strongly associated with the PT (particular on the left) both clinically and functionally. This aim examines whether PT sensory-motor activations are more strongly aligned with the auditory system (as is typically thought) or to the vocal tract articulator system (as we have recently hypothesized). In addition, we examine this system's role in temporal sequence processing, which we believe is connected to sensory-motor function. Aim 3 is to identify neural networks supporting the interaction of spatial hearing and speech processing. Both speech-related and spatial hearing- related functions have been associated with PT function. We examine a possible interaction of these two functions in connection with auditory stream segmentation, in particular whether activation in the PT reflects the use of spatial cues to segment auditory information into distinct objects. Finally, Aim 4 is to map the relation between spatial-speech integration and visual-speech integration. It is well known that auditory stream segregation processes can make use not only of spatial cues, but also of visual speech cues. Interestingly, processing both of these cues involves the PT suggesting a possible connection. PUBLIC HEALTH RELEVANCE The proposed research is of importance from a public-health standpoint because in recent clinical studies the planum temporale has been implicated in a number of disorders ranging from autism to schizophrenia. This brain region appears to be involved in several critical functions from language processing to integration of auditory, visual, and motor functions. In spite of its central role in sensory/cognitive functions, very little is known about how this brain area is organized, and given its widespread clinical importance, a more thorough understanding of the functional organization of this region may lead to more effective treatment strategies for cognitive dysfunctions.