1. Multiple microelectrode maps of the hand representation within and across the borders of cortical area 3b were obtained before, immediately after, or several weeks after a period of behaviorally controlled hand use. Owl monkeys were conditioned in a task that produced cutaneous stimulation of a limited sector of skin on the distal phalanges of one or more fingers. 2. Analysis of microelectrode mapping experiment data revealed that 1) stimulated skin surfaces were represented over expanded cortical areas. 2) Most of the cutaneous receptive fields recorded within these expanded cortical representational zones were unusually small. 3) The internal topography of representation of the stimulated and immediately surrounding skin surfaces differed greatly from that recorded in control experiments. Representational discontinuities emerged in this map region, and "hypercolumn" distances in this map sector were grossly abnormal. 4) Borders between the representations of individual digits and digit segments commonly shifted. 5) The functionally defined rostral border of area 3b shifted farther rostralward, manifesting either an expansion of the cutaneous area 3b fingertip representation into cortical field 3a or an emergence of a cutaneous input zone in the caudal aspect of this normally predominantly deep-receptor representational field. 6) Significant lateralward translocations of the borders between the representations of the hand and face were recorded in all cases. 7) The absolute locations--and in some cases the areas or magnifications--of representations of many skin surfaces not directly involved in the trained behavior also changed significantly. However, the most striking areal, positional, and topographic changes were related to the representations of the behaviorally stimulated skin in every studied monkey. 3. These experiments demonstrate that functional cortical remodeling of the S1 koniocortical field, area 3b, results from behavioral manipulations in normal adult owl monkeys. We hypothesize that these studies manifest operation of the basic adaptive cortical process(es) underlying cortical contributions to perception and learning.

It has been hypothesized that the acoustic properties within a temporal domain of 10 to 30 ms of boundaries between speech sounds contain significant information on the phonetic features of segments, and that these cues are perceptually integrated by the auditory system [Stevens, Phonetic Linguistics: Essays in Honor of Peter Ladefoged (Academic, London, 1985)]. The purpose of the current research was to examine the effects of stimulus duration adjacent to speech sound boundaries on the perceptual integration of place of articulation of nasals before and after disruption of the abrupt changes in spectra between the murmur and transition. In experiment I, three children, aged 3, 5, and 7 years, and an adult female and male produced consonant-vowel (CV) syllables consisting of [m] and [n] in four vowel contexts, [i ae u a]. Approximately 25-ms segments of the murmur and vowel transition adjacent to the speech sound boundary were digitally removed from these productions. Intervals of silence ranging from 0 to 2000 ms, which can potentially perturb integration processes, were inserted between these segments. The stimuli were then presented to adult listeners for the identification of the nasal. The main findings revealed a consistent decline in identification with gap durations up to 150 ms across speakers and vowel context. However, the adult labial feature was resistant to perceptual change as a function of gap duration. This result appeared to relate to formant transition duration, and not to response bias. In experiment II, stimuli with durations shorter than those in experiment I were further analyzed for adult speakers. The main finding was a quantification of the acoustic segment duration needed for perceptual integration of the murmur and vowel transition. Across both experiments, the results reveal a decline in the identification of both alveolar and labial nasals within a time interval mediated by short-term auditory memory, and that the duration of the acoustic segment needed for perceptual integration is longer for [n] than [m].

Computer-synthesized vowels were used to examine methods for controlling and measuring the perceptions elicited during electrical stimulation of the human cochlea. In the first experiment, we measured the importance of the second formant (F2) in the identification of vowels, matched for duration, in a single subject with a multichannel cochlear implant. The subject never confused vowels having a "low" frequency F2 with those having a "high" frequency F2. In the second experiment, identification functions were generated for a series of vowels varying only in F2. When the pattern of F2 stimulation at the basilar membrane was manipulated, vowel identification functions were altered. For the categorization of vowels, the data indicate that the relative cochlear position of F2 stimulation was more important than fine-grain temporal waveform cues. The data are supportive of cochlear implant coding strategies that make use of cochlear place information. In the later experiments, we manipulated filter passbands and channel gains to explore their effect on these classifications. These preliminary studies indicate that it is possible to "fine-tune" such classifications.

Amplification technology has changed considerably in the last decade, particularly with the introduction of more advanced adaptive signal processing approaches and digital/hybrid hearing aids. Because difficulty understanding speech in the presence of background noise is the most common complaint of hearing-impaired patients, an increasing number of these new products are being marketed as "noise reduction" hearing aids. There remain, however, many unanswered questions regarding patient candidacy for these instruments, and the relative benefit that can be expected from the new technology. This article discusses issues and assumptions underlying noise reduction strategies, reviews categories of hearing aids on the market that are meant to alleviate listening difficulty in noise, and outlines future needs in research and development in this area. 800Hz 1600Hz Volume Control , 7 y , High pass filter Gain Control 6 PC Control I Flnal Ampllfier Low pass filter ASP Threshold ControlFigure 3. Block diagram of the Siemens model 283 ASP, a two-channel behind the ear hearing aid that uses compression for high-level inputs only in the low-frequency channel.