Index of content:
Volume 103, Issue 6, June 1998
- SELECTED RESEARCH ARTICLE 
103(1998); http://dx.doi.org/10.1121/1.423072View Description Hide Description
The precedence effect (PE) is a perceptual phenomenon that reflects listeners’ ability to suppress echoes in reverberant environments. The PE is not present at birth and appears only several months postnatal. Recent physiological studies have demonstrated correlates of the PE in the central nucleus of the inferior colliculus (ICC) of adult animals. The present study extended the same techniques to search for similar correlates in the ICC of kittens during the first postnatal month. Stimuli consisted of pairs of clicks or noise bursts presented from different locations in free field or with different inter-aural differences in time (ITD) under headphones, with an inter-stimulus-delay (ISD) between their onsets. Results suggest that a physiological correlate of the PE, i.e. suppression of responses to the second source, is present as early as 8 days postnatal, and occurs at similar ISDs to those recorded in adult cats. Suppression in kitten neurons varies with stimulus level, duration, and azimuthal position, in a similar manner to that in adult neurons. The age at which correlates of the PE in the kitten can be found precedes the age at which kittens can localize sound sources effectively, and presumably before the age at which they would demonstrate the PE behaviorally. Thus, the neural mechanisms that might be involved in the first stages of processing PE stimuli may be in place well before the behavioral correlate develops.
103(1998); http://dx.doi.org/10.1121/1.423073View Description Hide Description
Recent studies have shown that when phonating subjects hear their voice pitch feedback shift upward or downward, they respond with a change in voice fundamental frequency output. Three experiments were performed to improve our understanding of this response and to explore the effects of different stimulus variables on voice responses to pitch-shift stimuli. In experiment 1, it was found that neither the absolute level of feedback intensity nor the presence of pink masking noise significantly affect magnitude or latency of the voice response. In experiment 2, changes in stimulus magnitude led to no systematic differences in response magnitudes or latencies. However, as stimulus magnitude was increased from 25 to 300 cents, the proportion of responses that changed in the direction opposite that of the stimulus (“opposing” response) decreased. A corresponding increase was observed in the proportion of same direction responses (“following” response). In experiment 3, increases in pitch-shift stimulus durations from 20 to 100 ms led to no differences in the response. Durations between 100 and 500 ms led to longer duration voice responses with greater response magnitude, and suggested the existence of a second response with a longer latency than the first.