This project deals with localization of multiple concurrently active sound sources. In order to localize the sources in such an environment the auditory system must correctly determine which spectral components arise from which location if the sources are to be correctly identified. The role of sound localization in this process is speculated to be great, since all components that comprise a particular source come from the same spatial location. The sound field at the two ears is said to be spectrally incoherent in that interaural differences of time and intensity, the two binaural cues for sound localization in the horizontal plane, vary across the spectrum. If binaural processing were to proceed as is suggested in the description above, it would be characterized as spectrally analytic in that the interaural differences of time associated with a particular spectral component allow it to be """"""""heard out"""""""" as separate from other components that are present. Previous work has led to the conclusion that the binaural auditory system is often spectrally synthetic when the stimulus consists of a small set of low-frequency components presented over headphones -- the system integrates interaural information across the frequency domain without regard to which components give rise to which interaural differences. One example of binaural processing that is spectrally analytic is Huggins pitch. The existence of Huggins pitch is evidence that the binaural auditory system can, in some instances, segregate targets from a background based solely on differential interaural differences across the frequency domain. This project proposes a set of studies that attempt to further examine the extent to which listeners have access to information regarding which interaural cues are associated with which spectral components.
Specific Aim 1 is an effort to ascertain the extent to which interaural information arising from different frequency components is independent. Experiments will measure the relationships between the ability of humans to detect interaural differences arising from different components of a complex and the ability to discriminate waveforms based on which component of the complex had been interaurally delayed.
Specific Aim 2 is to develop and apply a variation of the """"""""randomization technique of the general recognition theory"""""""" to further elucidate the manner in which interaural information arising from different spectral regions interacts.
Specific Aim 3 is to study the extent to which manipulating the stimulus duration and the characteristics of the spectral and temporal fringe around the target affects listeners ability to analytically """"""""hear out"""""""" targets from a background. this will be studied in stimulus configurations that lead to Huggins pitch and in conditions with small numbers of components.
Specific Aim 4 is to examine the manner in which similarities and differences in the modulation of high-frequency components interact with interaural differences between targets and distractors to support segregation/fusion of targets with background components.
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