Detection and discrimination of gliding tones as a function of frequency transition and center frequency

Two experiments were performed to investigate subjects' ability to detect and discriminate 50-ms up-glides in frequency in several different conditions. In the first experiment, the subjects indicated which of two signals increased more in pitch. The comparison, or standard signal, was a sinusoid which increased in frequency by either 0, 250, or 500 Hz. Center frequencies were 0.5, 1, 2, 4, and 6 kHz. Discrimination thresholds were obtained in both nonroved and roved conditions. In the roved condition, the actual center frequencies of the signals were varied randomly over a range equal to 0.1 times the nominal center frequency. The second experiment was the same as the first, except that the standard signals were swept over a frequency range equal to 0.5, 1, and 2 times the equivalent rectangular bandwidth (ERB) of the auditory filter at the nominal center frequency. Discrimination thresholds expressed as delta Hz/ERB varied little as a function of center frequency as long as the frequency transition of the standard was a constant proportion of ERB. In addition, discrimination thresholds did not vary significantly as a function of the frequency extent of the standard when the extent was one ERB or less, but doubled when the extent was two ERBs. The relatively small amount of variation in threshold across center frequency and the pattern of variation across different standard transitions supports a place mechanism of frequency coding for these signals based on the detection of changes in the excitation pattern.