Temporal integration in the gerbil: the effects of age, hearing loss and temporally unmodulated and modulated speech-like masker noises.

We characterized temporal integration for 2k Hz pure tones with durations between 10 and 1000 ms in young, normal hearing old and old gerbils with a small hearing loss. Thresholds determined in silence increased for durations below 300 ms and were on average more than 10 dB higher for the 10 ms signal than asymptotic thresholds for the long signals. The amount of temporal integration tended to be less in gerbils with hearing loss. Threshold determination was repeated in the same individuals in the presence of speech-like unmodulated and modulated masking noises. Threshold shift due to the maskers was inversely related to the threshold in silence resulting in a reduced inter-individual variability of thresholds in both masking conditions. Thresholds differed systematically between both masker types in a duration dependent fashion. For long signal durations (300 and 1000 ms) thresholds were on average 2dB lower and for the 10 ms signal 1.9 dB higher in the presence of the modulated masker. These differences in threshold obtained with the two maskers were significant. One hypothesis is that long signals can be detected in the troughs of the modulated masker, while peaks interfere with the detection of short signals.