At the perceptual level speech perception is determined by the audibility of the speech signal and by the clarity of its internal representation. Age-related losses in threshold audibility can be attributed most readily to changes in the sensori-neural receptive machinery in the inner ear or the eye. To some extent, the loss of clarity in the signal may similarly result from degenerative changes in the receptor apparatus that widen sensory filters and thus diminish frequency discrimination. But a very significant decrement in auditory processing in the aged, that is observed also in some children who have language-learning problems, is the loss of temporal acuity. The theoretical principle that motivates the research is that the clarity of the internal representation is not given in the acoustic input but, rather, results as a product of central image enhancement. The guiding hypothesis is that the developing central representations of stimulus frequencies and amplitudes as they vary in time are derived from the operations of excitatory and, especially, inhibitory neural networks, that induce sharp neural transitions in potentially interfering and slowly decaying afferent signals. These neural networks are understood as being responsive to experience and a major challenge is to understand the extent to which neuroplasticity in central mechanisms can compensate for peripheral loss.

• Ison, J.R., & Agrawal, P. (1998). The effect of spatial separation of signal and noise on masking in the free field, as a function of signal frequency and age in the mouse. Journal of the Acoustical Society of America, 104, 1689-1695.
• Ison,J.R., Agrawal, P., Pak, J., & Vaughn, W.J. (1998). Changes in temporal acuity with age and with hearing impairment in the mouse: A study of the acoustic startle reflex and its inhibition by brief decrements in noise level. Journal of the Acoustical Society of America, 104, 1696-1704.
• Ison, J.R., Bowen, G.P., & del Cerro, M. (1998). A behavioral study of temporal processing and visual persistence in young and aged rats. Journal of the Acoustical Society of America, 112, 1273-1279.
• Ison, J. R., Payman, G. H., Palmer, M. J., & Walton, J. P. (1997). Nimodipine at a dose that slows ABR latencies does not protect the ear against noise. Hearing Research, 106, 179-183.
• Ison, J. R., Taylor, M. K., Bowen, G. P., & Schwarzkopf, S. B. (1997). Facilitation and inhibition of the acoustic startle reflex in the rat after a momentary increase in background noise level. Behavioral Neuroscience, 111, 1335-1352.
• Walton, J. P., Frisina, R. D., Ison, J. R., & O'Neill, W.E. (1997). Neural correlates of behavioral gap detection in the inferior colliculus of the young CBA mouse. Journal of Comparative Physiology, 181, 161-176.
• Schwarzkopf, S. B., Bruno, J. P., Mitra, T., & Ison, J. R. (1996). Effects of haloperidol and SCH 23390 on acoustic startle in animals depleted of dopamine as neonates: Implications for neuropsychiatric syndromes. Psychopharmacology, 12, 258-266.
• Taylor, M. K., Ison, J. R., & Schwarzkopf, S. B. (1995). Effects of single and repeated exposure to apomorphine on the acoustic startle reflex and its inhibition by a visual prepulse. Psychopharmacology, 120, 117-127.
• Snell, K. B., Ison, J. R., & Frisina, D. R. (1994). The effects of signal frequency and absolute bandwidth on gap detection in noise. Journal of the Acoustical Society of America, 96, 1458-1464.