Processing of Complex Acoustic Signals in the Central Auditory System; Echolocation; Aging Effects on Temporal and Spatial Processing in the Central Auditory System.
Acoustic communication, including human speech, is mediated by dynamic sounds that vary in both time and frequency. Recent research focuses on the neuronal mechanisms in the auditory midbrain involved in the encoding of complex biologically-relevant acoustic signals. In particular, we are interested in the neural basis for the perception of brief frequency modulations (FM), which are nearly ubiquitous in the communication sounds used by most vertebrates, including consonant-vowel transitions in human speech. Our studies have been carried out in echolocating mustached bats that emit biosonar signals with prominent FM sweeps. Neurons in the bat auditory midbrain, thalamus and cortex are often selective for the direction of frequency change in FM sweeps, with some preferring upward sweeps, and others preferring downward sweeps. We have shown that directional preference depends on the velocity of frequency change in the sweep that is correlated with a time dependent interaction between excitation and inhibition driving these cells. By using pseudorandom tone sequences to mimic the dynamic acoustic microstructure of FM sweeps, we have developed a novel way to describe auditory receptive fields that captures the dynamic non-linear interactions underlying the encoding of these signals. Techniques include digital sound synthesis, neurophysiological recording of single-unit activity, anatomical tract tracing, and immunocytochemistry.
A second area of investigation is aimed at a common complaint of elderly listeners, who report having no trouble understanding speech in quiet, but suffer significant loss of intelligibility in noisy environments, even though they have minimal peripheral hearing loss. This effort is carried out by a team of investigators at the UR and Rochester Inst. of Technology. Our working hypothesis is that this problem is caused by deterioration of temporal processing in the central auditory system. To address this question, young and old human and animal subjects (inbred mice, gerbils, guinea pigs) are tested in parallel at functionally comparable life stages, with the intention of ultimately understanding which central auditory processes deteriorate with age, and what strategies might be developed to ameliorate this problem.
A third project, done in collaboration with NBA Department chair Dr. Gary Paige, also has an aging component. We are investigating in human subjects how spatial information, separately encoded in visual, auditory and vestibular coordinate space, is combined to create a unified sense of personal space, and how this concordance of spatial information processing changes with age. Current experiments being carried out by graduate and undergraduate students revolve around 1) the effect of distraction on auditory localization in the elderly, and 2) the effect of displaced eye or ear position on auditory localization.
Zettel, M.L., X. Zhu, W.E. O'Neill, and R.D. Frisina. Age-related Decline in Kv3.1b Expression in the Mouse Auditory Brainstem Correlates with Functional Deficits in the Medial Olivocochlear Efferent System. J. Assoc. Res. Otolaryngol. 8(2): 280 – 293, 2007.
Razavi B., W.E. O'Neill, and G.D. Paige. Auditory spatial perception dynamically realigns with changing eye position. J. Neuroscience 27(38): 10,249 – 10,258, 2007.
Ison, J.R., P.D. Allen, and W.E. O'Neill. Age-related hearing loss in C57BL/6J mice has both frequency specific and non-frequency specific components that produce a hyperacusis-like exaggeration of the startle reflex. J. Assoc. Res. Otolaryngol. 8(4): 539-550, 2007.