Effect of stimulus level and place of stimulation on temporal pitch perception by cochlear implant users

Abstract

Three experiments studied the effect of pulse rate on temporal pitch perception by cochlear implant users. Experiment 1 measured rate discrimination for pulse trains presented in bipolar mode to either an apical, middle, or basal electrode and for standard rates of 100 and 200 pps. In each block of trials the signals could have a level of -0.35, 0, or +0.35 dB re the standard, and performance for each signal level was recorded separately. Signal level affected performance for just over half of the combinations of subject, electrode, and standard rate studied. Performance was usually, but not always, better at the higher signal level. Experiment 2 showed that, for a given subject and condition, the direction of the effect was similar in monopolar and bipolar mode. Experiment 3 employed a pitch comparison procedure without feedback, and showed that the signal levels in experiment 1 that produced the best performance for a given subject and condition also led to the signal having a higher pitch. It is concluded that small level differences can have a robust and substantial effect on pitch judgments and argue that these effects are not entirely due to response biases or to co-variation of place-of-excitation with level.

Pitch matching in bimodal cochlear implant patients: Effects of frequency, spectral envelope, and level

“…Shannon (1983) and Allen and Oxenham (2014) reported that pitch increased with increasing level while Townshend et al (1987) and Pijl (1997) reported a significant decrease in pitch with increase in level. Carlyon et al (2010a) showed both increase and decrease in pitch with level which varied from one electrode to another, which was in line with the results of the pitch matching experiment of Green et al (2012) in bimodal CI users.…”

“…Intensity has a small effect on perceived pitch for people with normal hearing: less than 1% for pure tones below 1 kHz and less than 5% between 1 and 2 kHz (Verschuure and Meeteren, 1975). In contrast to NH, Carlyon et al (2010a) reported a large pitch perception change with increase in level (2.3 semitones or 16%). Shannon (1983) and Allen and Oxenham (2014) reported that pitch increased with increasing level while Townshend et al (1987) and Pijl (1997) reported a significant decrease in pitch with increase in level.…”

Extending the Limits of Place and Temporal Pitch Perception in Cochlear Implant Users

“…The particularity of this measure was that the different rate stimuli had the same current level per pulse. It has been shown that loudness can have an effect on pitch and that it is more often the case that louder stimuli are associated with higher pitches (Carlyon et al 2010b). If the good performance obtained with PSA-Apex was solely due to residual loudness cues, we would have expected most subjects to perform better when the level is kept constant (because loudness cues should be even more salient).…”

“…If this result applies to human CI listeners, we would expect temporal pitch perception, which relies on phase locking, to be better when stimulating apical rather than basal electrodes. However, previous studies comparing the upper limits of temporal pitch at different cochlear locations did not show any superiority of apical stimulation (Zeng 2002; Baumann and Nobbe 2004; Carlyon et al 2010b). One possible reason for this is that the electrode currents did not stimulate the apex selectively enough and that the temporal information coming from apical fibres was blurred by more basal fibres projecting to IC neurons with a lower limiting rate.…”

Temporal Regularity Detection and Rate Discrimination in Cochlear-Implant Listeners

“…In this regard, it is worth noting that large effects of a level rove have been observed for CI users in an odd-man-out task; Baumann and Nobbe (2004) found that rate DLs for a 200-pps pulse train increased from about 15 % to about 40 % as the amount of roving increased from zero to 10 % of the dynamic range. This may have been due to a “distracting” effect of the level rove and the effects of level on pitch in CI users (Carlyon et al 2010). Note that, in the present study, the same level rove was applied in all tasks and conditions, and so although the rove may have decreased performance overall, it is unlikely to have affected the pattern of results.…”