THE PERCEPTION OF TEMPORAL MODULATIONS BY COCHLEAR IMPLANT PATIENTS

The perception of temporal modulations of pulsatile electric stimuli w as measured in seven cochlear implant patients using the Cochlear Pty. Limited prosthesis. Four patients were postlingually deafened adults and three patients were young adults who were deafened very early in l ife. The first study measured detection thresholds for modulated pulse duration for a series of modulation frequencies and pulse rates. The shape of the detection thresholds as a function of modulation frequenc y, the temporal modulation transfer function, often resembled a low-pa ss filter with a 50-100-Hz cut-off frequency. Thresholds did not marke dly vary across the different pulse rates for most patients. Threshold s were less than 10%-20% of the range of usable hearing for most patie nts. The second study compared detection thresholds for modulated puls e durations around different reference pulse durations: 50, 100, and 3 00 mus. Detection thresholds were generally proportional to the differ ent reference pulse durations. The third study measured difference lim ens for the discrimination of modulation depth. The difference limens were similar to the detection thresholds for the same reference pulse duration and pulse rate. The three patients deafened very early in lif e showed more within-group variation in performance, and their overall levels of performance were poorer than those of the postlingually dea fened adults.