Frequency discrimination in regions of normal and impaired sensitivity.

Psychometric functions for frequency discrimination were obtained from both normal-hearing and hearing-impaired listeners at 300, 1200, and 3000 Hz. Difference limens for frequency (DLFs) were derived from those psychometric functions after repeated practice sessions, ensuring that all listener's results represented levels of optimum performance. Practice effects were found to be considerable in many listeners. The psychometric functions for all listeners, both normal-hearing and hearing-impaired, were well described by linear functions of performance level (d') and frequency difference (Hz), which passed through the zero origin. Those listeners with normal sensitivity thresholds at all frequencies exhibited the most acute frequency discriminations. Listeners with sensitivity losses at high frequencies exhibited larger DLFs, even at lower test frequencies where sensitivity thresholds were normal.