DISCRIMINATION OF FREQUENCY GLIDES WITH SUPERIMPOSED RANDOM GLIDES INLEVEL

These experiments were designed to test the hypothesis that glides in frequency are detected and discriminated by monitoring changes in exci tation level on the low-frequency side of the excitation pattern. Thre sholds were measured for detecting an increase in the extent of a freq uency glide, for various standard extents (transition spans). The cent er frequency of each stimulus was roved, to prevent subjects from usin g the start or endpoint frequencies of the stimuli as cues. The level was either fixed at 70 dB SPL, or changed linearly in dB/s by an amoun t that varied randomly in extent and direction, keeping the level at t he midpoint of the glide at 70 dB SPL. These random changes in level w ere intended to disrupt cues based on monitoring changes in excitation level on one side of the excitation pattern. For some conditions, per formance was too good to be explained by subjects monitoring the start or endpoint frequencies of the stimuli. Performance was also too good to be explained in terms of the discrimination of changes in excitati on level on one side of the excitation pattern. Thresholds, expressed as a proportion of the equivalent rectangular bandwidth (ERB) of the a uditory filter, did not vary greatly with center frequency (0.5, 2, or 6 kHz), suggesting that discrimination did not depend strongly on inf ormation derived from phase locking. Glide duration (50 or 400 ms) and glide direction (upward or downward) also had little effect. Threshol ds increased with increasing standard transition span, when that span was increased beyond 0.5 ERB. It is concluded that changes in glide ex tent per se can be discriminated, but this is not done by monitoring j ust one side of the excitation pattern. (C) 1998 Acoustical Society of America.