John H. Grose, Ph.D. - US grants

The long-term objective of this project is to provide a better understanding of the processes underlying sound source segregation in the normal auditory system and the effects of cochlear dysfunction on those processes. This will contribute, in particular, to an objective appreciation of the difficulties experienced by listeners with cochlear hearing loss in competitive listening situations. Four areas of study are proposed. The first area deals with the manner in which information concerning a spectrally-dispersed signal is combined across frequency to improve detection. Of interest is a comparison between conditions where the signal consists of an increment in energy across frequency and conditions where the signal consists of a decrement in energy across frequency. The second area of study is concerned with situations where a complex signal must be extracted from a background containing multiple modulation patterns. The aim is to determine the degree to which the auditory system can implement concurrent across-frequency processes to extract the complex signal and to ascertain the limitations imposed by impairments of frequency and temporal resolution on this ability. The third area of study examines the correspondence between measures of across-frequency processing and auditory grouping. One series of experiments assesses the susceptibility of comodulation masking release (CMR) and modulation detection interference (MDI) to factors which oppose the formation of auditory groupings. A second investigation implements a CMR paradigm to provide an objective measure of the fusion strength of purported auditory grouping factors. The fourth area of study quantifies the ability of cochlear-impaired listeners to segregate simultaneously-present sounds, and to segregate (or stream) sequentially-present sounds. Of primary interest is the relationship between these abilities and the functions of frequency selectivity and temporal resolution in the same listeners. A total of 15 cochlear-impaired listeners and a control group of 12 normally-hearing listeners will be recruited using strict age and audiometric criteria. Testing will take place in a sound-treated room under headphones using computer-controlled adaptive procedures. Data will be analyzed using simple descriptive statistics, correlations, and analyses of variance.

DESCRIPTION (provided by applicant): Most everyday listening environments consist of a multitude of sounds, many of which are fluctuating in level over time. The way in which the brain sifts apart this acoustic complex into its constituent sound sources is referred to as auditory perceptual organization. The root interest of this project is in understanding the role that temporal processing play in perceptual organization, and how impaired auditory systems can compromise this ability. The project pursues two lines of investigation. The first seeks to identify changes in temporal processing that may occur relatively early in the aging process, and to differentiate these from effects of cochlear hearing loss. The second line of investigation examines perceptual organization in listeners with cochlear implants. The project incorporates both psychophysical land electrophysiological paradigms. A total of 75 listeners will participate across a spectrum of experiments. Data will be analyzed using descriptive statistics, tests of correlation, and analyses of variance. The project will lead to a clearer understanding of how complex sounds are perceptually organized in both acoustic and electric hearing, and how changes in the auditory system due to age and hearing loss may affect this ability.

DESCRIPTION (provided by applicant): This research will be done in collaboration with Drs. Denise Menezes and Silvana Griz at the Universidade Federal de Pernambuco ('Federal University of Pernambuco') in Recife, Brazil, as an extension of NIH Grant No. R01DC001507, 9-20-2008 to 8-31-2013. Listeners with normal hearing usually find speech recognition easier in a modulated background than in a steady background that has the same overall level. This modulation benefit - or masking release - is typically more pronounced in younger listeners than older listeners. The purpose of this project is to assess the contribution of central deficits in temporal processing to this age-related reduction in masking release. Specific Aim 1 examines the relationship between speech recognition in modulated noise and temporal masking performance as a function of age, controlling for audibility. Masking release for both American English and Brazilian Portuguese will be measured. The goal is to assess the extent to which forward and backward masking by the masker peaks obscures speech information in the masker troughs, thereby limiting modulation benefit. The issue of age effects in forward masking is itself undeveloped, and findings are mixed as to whether older listeners exhibit exacerbated forward masking. The purpose of Specific Aim 2 is to relate psychophysical and electrophysiological measures of forward masking as a function of age in order to clarify this issue. The focus on masking effects will specifically employ speech-relevant stimuli. Jointly, these two interwoven aims will advance our understanding of how the normal aging process compromises temporal masking - particularly as it relates to speech recognition in fluctuating backgrounds. This understanding will be 'globalized'by undertaking the investigation simultaneously in two countries (U.S. and Brazil) using two languages (American English and Brazilian Portuguese). PUBLIC HEALTH RELEVANCE: The global burden of compromised communication associated with age-related hearing loss is enormous and represents a major public health challenge. This project investigates one facet of age- related hearing difficulty which is the reduced benefit exhibited by older listeners for hearing speech in an interrupted background. Understanding the role that temporal processing deficits plays in this reduced masking release will contribute to the scientific knowledge base that can address - and potentially alleviate - this public health challenge.!