FURTHER EVIDENCE OF TOP-DOWN GAIN CONTROL IN THE AUDITORY SYSTEM
We have repeatedly proposed that a non-linear gain-control system under top-down governance regulates the encoding of auditory intensity. Here we examine the effects of individual differences and continued training on the identification of tones differing only in intensity. In a baseline condition, participants were asked to identify which one of four 1-kHztones (25, 30, 35, or 40 dB) was presented on a trial. In two other conditions an additional tone(50 or 80 dB) was added to the baseline set. Each of the three conditions was tested over the course of 20 sessions, each stimulus occurring 50 times per session. Performance improved over sessions with large individual differences among participants. However, in all cases, the pattern of change across conditions was consistent with the notion that the encoding of intensity along the decision axis is regulated by a non-linear gain control mechanism.