Limits...
Extending the limits of place and temporal pitch perception in cochlear implant users.

Macherey O, Deeks JM, Carlyon RP - J. Assoc. Res. Otolaryngol. (2010)

Bottom Line: A series of experiments investigated the effects of asymmetric current waveforms on the perception of place and temporal pitch cues.For PSA pulses presented to apical electrodes, the upper limit of temporal pitch was significantly higher than that for all the other conditions, averaging 713 pps.However, a multidimensional scaling study showed that the percept associated with a rate change, even at high rates, was orthogonal to that of a place change and therefore reflected a genuine change in the temporal pattern of neural activity.

View Article: PubMed Central - PubMed

Affiliation: Medical Research Council, Cognition and Brain Sciences Unit, 15 Chaucer Road, Cambridge, UK. olivier.macherey@mrc-cbu.cam.ac.uk

ABSTRACT
A series of experiments investigated the effects of asymmetric current waveforms on the perception of place and temporal pitch cues. The asymmetric waveforms were trains of pseudomonophasic (PS) pulses consisting of a short, high-amplitude phase followed by a longer (and lower amplitude) opposite-polarity phase. When such pulses were presented in a narrow bipolar ("BP+1") mode and with the first phase anodic relative to the most apical electrode (so-called PSA pulses), pitch was lower than when the first phase was anodic re the more basal electrode. For a pulse rate of 12 pulses per second (pps), pitch was also lower than with standard symmetric biphasic pulses in either monopolar or bipolar mode. This suggests that PSA pulses can extend the range of place-pitch percepts available to cochlear implant listeners by focusing the spread of excitation in a more apical region than common stimulation techniques. Temporal pitch was studied by requiring subjects to pitch-rank single-channel pulse trains with rates ranging from 105 to 1,156 pps; this task was repeated at several intra-cochlear stimulation sites and using both symmetric and pseudomonophasic pulses. For PSA pulses presented to apical electrodes, the upper limit of temporal pitch was significantly higher than that for all the other conditions, averaging 713 pps. Measures of discriminability obtained using the method of constant stimuli indicated that this pitch percept was probably weak. However, a multidimensional scaling study showed that the percept associated with a rate change, even at high rates, was orthogonal to that of a place change and therefore reflected a genuine change in the temporal pattern of neural activity.

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A–D Results of the multidimensional scaling study of experiment 4. Dimensions 1 and 2 correspond to the type of stimulation; dimension 3 corresponds to the pulse rate. For S2, the dissimilarity judgments were well modelled by a two-dimension solution only showing the three types of stimulation. However, the three-dimension solution is shown for comparison with other subjects.
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Fig6: A–D Results of the multidimensional scaling study of experiment 4. Dimensions 1 and 2 correspond to the type of stimulation; dimension 3 corresponds to the pulse rate. For S2, the dissimilarity judgments were well modelled by a two-dimension solution only showing the three types of stimulation. However, the three-dimension solution is shown for comparison with other subjects.

Mentions: The results of the MDS analysis are illustrated in Figure 6. Each panel shows the graphical representation of the solution for individual subjects S1, S2, S3 and S6. A three-dimensional solution modelled the responses with Kruskal’s stress (formula 1) values of 0.1, 0.01, 0.13 and 0.15 for S1, S2, S3 and S6, respectively. The proportion of variance of the data accounted for by the three-dimension solutions was in every case more than 84%. The data of S4 were very variable across matrices and showed a much higher stress value for the three-dimension solution (0.23). In a further analysis, we found that his dissimilarity ratings across the whole session were negatively correlated with trial number (r = −0.44, p < 0.0001). In other words, he found all pairs of sounds to be very different at the beginning of the session and the same pairs to be very similar at the end of the session. This can be viewed as a type of contraction bias sometimes observed in magnitude estimation studies (Poulton 1979). This non-sensory bias reflects a situation where a subject tends to give ratings close to the middle of the range once he is used to the stimuli. Given this lack of consistency across repetitions, the data of S4 are not shown here.FIG. 6


Extending the limits of place and temporal pitch perception in cochlear implant users.

Macherey O, Deeks JM, Carlyon RP - J. Assoc. Res. Otolaryngol. (2010)

A–D Results of the multidimensional scaling study of experiment 4. Dimensions 1 and 2 correspond to the type of stimulation; dimension 3 corresponds to the pulse rate. For S2, the dissimilarity judgments were well modelled by a two-dimension solution only showing the three types of stimulation. However, the three-dimension solution is shown for comparison with other subjects.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3046333&req=5

Fig6: A–D Results of the multidimensional scaling study of experiment 4. Dimensions 1 and 2 correspond to the type of stimulation; dimension 3 corresponds to the pulse rate. For S2, the dissimilarity judgments were well modelled by a two-dimension solution only showing the three types of stimulation. However, the three-dimension solution is shown for comparison with other subjects.
Mentions: The results of the MDS analysis are illustrated in Figure 6. Each panel shows the graphical representation of the solution for individual subjects S1, S2, S3 and S6. A three-dimensional solution modelled the responses with Kruskal’s stress (formula 1) values of 0.1, 0.01, 0.13 and 0.15 for S1, S2, S3 and S6, respectively. The proportion of variance of the data accounted for by the three-dimension solutions was in every case more than 84%. The data of S4 were very variable across matrices and showed a much higher stress value for the three-dimension solution (0.23). In a further analysis, we found that his dissimilarity ratings across the whole session were negatively correlated with trial number (r = −0.44, p < 0.0001). In other words, he found all pairs of sounds to be very different at the beginning of the session and the same pairs to be very similar at the end of the session. This can be viewed as a type of contraction bias sometimes observed in magnitude estimation studies (Poulton 1979). This non-sensory bias reflects a situation where a subject tends to give ratings close to the middle of the range once he is used to the stimuli. Given this lack of consistency across repetitions, the data of S4 are not shown here.FIG. 6

Bottom Line: A series of experiments investigated the effects of asymmetric current waveforms on the perception of place and temporal pitch cues.For PSA pulses presented to apical electrodes, the upper limit of temporal pitch was significantly higher than that for all the other conditions, averaging 713 pps.However, a multidimensional scaling study showed that the percept associated with a rate change, even at high rates, was orthogonal to that of a place change and therefore reflected a genuine change in the temporal pattern of neural activity.

View Article: PubMed Central - PubMed

Affiliation: Medical Research Council, Cognition and Brain Sciences Unit, 15 Chaucer Road, Cambridge, UK. olivier.macherey@mrc-cbu.cam.ac.uk

ABSTRACT
A series of experiments investigated the effects of asymmetric current waveforms on the perception of place and temporal pitch cues. The asymmetric waveforms were trains of pseudomonophasic (PS) pulses consisting of a short, high-amplitude phase followed by a longer (and lower amplitude) opposite-polarity phase. When such pulses were presented in a narrow bipolar ("BP+1") mode and with the first phase anodic relative to the most apical electrode (so-called PSA pulses), pitch was lower than when the first phase was anodic re the more basal electrode. For a pulse rate of 12 pulses per second (pps), pitch was also lower than with standard symmetric biphasic pulses in either monopolar or bipolar mode. This suggests that PSA pulses can extend the range of place-pitch percepts available to cochlear implant listeners by focusing the spread of excitation in a more apical region than common stimulation techniques. Temporal pitch was studied by requiring subjects to pitch-rank single-channel pulse trains with rates ranging from 105 to 1,156 pps; this task was repeated at several intra-cochlear stimulation sites and using both symmetric and pseudomonophasic pulses. For PSA pulses presented to apical electrodes, the upper limit of temporal pitch was significantly higher than that for all the other conditions, averaging 713 pps. Measures of discriminability obtained using the method of constant stimuli indicated that this pitch percept was probably weak. However, a multidimensional scaling study showed that the percept associated with a rate change, even at high rates, was orthogonal to that of a place change and therefore reflected a genuine change in the temporal pattern of neural activity.

Show MeSH