Temporal integration of trains of tone pulses by normal and by cochlearly impaired listeners

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Abstract
Two experiments investigated the temporal integration of trains of tone pulses by normal and by cochlearly impaired listeners. In the first experiment, thresholds were measured for a single 5-ms, 4-kHz tone pulse, and for ten such tone pulses as a function of interpulse interval (.DELTA.t). For normal listeners, temporal integration, defined as the threshold difference between one and ten pulses, was about 8 dB for .DELTA.t < 20 ms, and about 5 dB at longer .DELTA.t''s. For impaired listeners, temporal integration was only about 2-3 dB across the range of .DELTA.t''s (5-160 ms) studied. A second experiment measured psychometric functions (log d'' versus log signal power) for a single pulse and for ten pulses with .DELTA.t''s of 5 ms and 80 ms. The normal listeners'' functions had slopes close to unity in all three conditions, with a few exceptions. The impaired listeners'' functions had slopes close to unity for ten pulses with .DELTA.t = 5 ms, but had slopes significantly greater than unity for .DELTA.t = 80 ms, and for a single pulse. At .DELTA.t = 80 ms, the increase in d'' relative to the condition with a single tone was similar (a factor of .sqroot. 10) for both impaired and normal listeners, but the threshold difference was smaller for the impaired listeners due to their steeper psychometric functions. For impaired listeners, then, temporal integration at .DELTA.t = 80 ms was normal in terms of a change in d'', but abnormal when measured as a threshold difference. Impaired listeners'' functions for ten pulses at .DELTA.t = 5 m were shallower than for a single pulse, so temporal integration at this .DELTA.t depended on the point on the psychometric function at which it was measured. The results of both experiments are discussed in relation to various hypotheses proposed to account for the reduced temporal integration in impaired ears.

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