[Show abstract][Hide abstract] ABSTRACT: Cochlear implant (CI) users usually exhibit marked across-electrode differences in detection thresholds with Bfocused^ modes of stimulation, such as partial-tripolar (pTP) mode. This may reflect differences either in local neural survival or in the distance of the electrodes from the modiolus. To shed light on these two explanations, we compared stimulus-detection thresholds and gap-detection thresholds (GDTs) at comfortably loud levels for at least four electrodes in each of ten Advanced Bionics CI users, using 1031-pps pulse trains. The electrodes selected for each user had a wide range of stimulus-detection thresholds in pTP mode. We also measured across-electrode variations in both stimulus-detection and gap-detection tasks in monopolar (MP) mode. Both stimulus-detection and gap-detection thresholds correlated across modes. However, there was no significant correlation between stimulus-detection and gap-detection thresholds in either mode. Hence, gap-detection thresholds likely tap a source of across-electrode variation additional to, or different from, that revealed by stimulus-detection thresholds. Stimulus-detection thresholds were significantly lower for apical than for basal electrodes in both modes; this was only true for gap detection in pTP mode. Finally, although the across-electrode standard deviation in stimulus-detection thresholds was greater in pTP than in MP mode, the reliability of these differences—assessed by dividing the across-electrode standard deviation by the stan-dard deviation across adaptive runs for each electrode—was similar for the two modes; this metric was also similar across modes for gap detection. Hence across-electrode differences can be revealed using clinically available MP stimula-tion, with a reliability comparable to that observed with focused stimulation.
Journal of the Association for Research in Otolaryngology 02/2015; · 2.95 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Five normally hearing listeners pitch-ranked harmonic complexes of different fundamental frequencies (F0s) filtered in three different frequency regions. Harmonics were summed either in sine, alternating sine-cosine (ALT), or pulse-spreading (PSHC) phase. The envelopes of ALT and PSHC complexes repeated at rates of 2F0 and 4F0. Pitch corresponded to those rates at low F0s, but, as F0 increased, there was a range of F0s over which pitch remained constant or dropped. Gammatone-filterbank simulations showed that, as F0 increased and the number of harmonics interacting in a filter dropped, the output of that filter switched from repeating at 2F0 or 4F0 to repeating at F0. A model incorporating this phenomenon accounted well for the data, except for complexes filtered into the highest frequency region (7800-10 800 Hz). To account for the data in that region it was necessary to assume either that auditory filters at very high frequencies are sharper than traditionally believed, and/or that the auditory system applies smaller weights to filters whose outputs repeat at high rates. The results also provide evidence on the highest pitch that can be derived from purely temporal cues, and corroborate recent reports that a complex pitch can be derived from very-high-frequency resolved harmonics.
The Journal of the Acoustical Society of America 12/2014; 136(6):3186. · 1.65 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Objective: To evaluate a speech-processing strategy in which the lowest frequency channel is conveyed using an asymmetric pulse shape and “phantom stimulation”, where current is injected into one intra-cochlear electrode and where the return current is shared between an intra-cochlear and an extra-cochlear electrode. This strategy is expected to provide more selective excitation of the cochlear apex, compared to a standard strategy where the lowest-frequency channel is conveyed by symmetric pulses in monopolar mode. In both strategies all other channels were conveyed by monopolar stimulation. Design: Within-subjects comparison between the two strategies. Four experiments: (1) discrimination between the strategies, controlling for loudness differences, (2) consonant identification, (3) recognition of lowpass-filtered sentences in quiet, (4) sentence recognition in the presence of a competing speaker. Study sample: Eight users of the Advanced Bionics CII/Hi-Res 90k cochlear implant. Results: Listeners could easily discriminate between the two strategies but no consistent differences in performance were observed. Conclusions: The proposed method does not improve speech perception, at least in the short term.
International Journal of Audiology 10/2014; · 1.43 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Cochlear implants are the first example of a neural prosthesis that can substitute a sensory organ: they bypass the malfunctioning auditory periphery of profoundly-deaf people to electrically stimulate their auditory nerve. The history of cochlear implants dates back to 1957, when Djourno and Eyriès managed, for the first time, to elicit sound sensations in a deaf listener using an electrode implanted in his inner ear. Since then, considerable technological and scientific advances have been made. Worldwide, more than 300,000 deaf people have been fitted with a cochlear implant; it has become a standard clinical procedure for born-deaf children and its success has led over the years to relaxed patient selection criteria; for example, it is now not uncommon to see people with significant residual hearing undergoing implantation. Although the ability to make sense of sounds varies widely among the implanted population, many cochlear implant listeners can use the telephone and follow auditory-only conversations in quiet environments.
Current Biology 09/2014; 24(18):R878–R884. · 9.92 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Under binaural listening conditions, the detection of target signals within background masking noise is substantially improved when the interaural phase of the target differs from that of the masker. Neural correlates of this 'Binaural masking level difference' (BMLD) have been observed in the inferior colliculus and temporal cortex, but it is not known whether degeneration of the inferior colliculus would result in a reduction of the BMLD in humans. We used magnetoencephalography to examine the BMLD in 13 healthy adults and 13 patients with progressive supranuclear palsy (PSP). PSP is associated with severe atrophy of the upper brain stem, including the inferior colliculus, confirmed by voxel-based morphometry of structural MRI. Stimuli comprised in-phase sinusoidal tones presented to both ears at three levels (high, medium and low) masked by in-phase noise which rendered the low-level tone inaudible. Critically, the BMLD was measured using a low-level tone presented in opposite phase across ears, making it audible against the noise. The cortical waveforms from bilateral auditory sources revealed significantly larger N1m peaks for the out-of-phase low-level tone compared to the in-phase low-level tone, for both groups, indicating preservation of early cortical correlates of the BMLD in PSP. In PSP a significant delay was observed in the onset of the N1m deflection and the amplitude of the P2m was reduced, but these differences were not restricted to the BMLD condition. The results demonstrate that although PSP causes subtle auditory deficits, binaural processing can survive the presence of significant damage to the upper brain stem.
Journal of Neurophysiology 09/2014; · 3.04 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The Gold Medal is presented in the spring to a member of the Society, without age limitation, for contributions to acoustics. The first Gold Medal was presented in 1954 on the occasion of the Society's Twenty-Fifth Anniversary Celebration and biennially until 1981. It is now an annual award.
The Journal of the Acoustical Society of America 04/2014; 135(4):2327. · 1.65 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Roy Patterson and Brian Moore, perhaps more than any other psychoacousticians, have succeeded in applying their research for the common good. Those who have benefited from this translation of basic research include users of hearing aids and of auditory warnings. I will describe the results of recent experiments aimed at improving hearing by another group, namely users of cochlear and auditory brainstem implants. These include attempts to exploit the polarity sensitivity of the electrically stimulated auditory system in order to extend the ranges of pitch that can be conveyed by each type of implant.
The Journal of the Acoustical Society of America 04/2014; 135(4):2346. · 1.65 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: There is evidence that the contribution of a given harmonic in a complex tone to residue pitch is influenced by the accuracy with which the frequency of that harmonic is encoded. We investigated whether listeners adjust the weights assigned to individual harmonics based on acquired knowledge of the reliability of the frequency estimates of those harmonics. In a two-interval forced-choice task, seven listeners indicated which of two 12-harmonic complex tones had the higher overall pitch. In context trials (60% of all trials), the fundamental frequency (F0) was 200 Hz in one interval and 200+ΔF0 Hz in the other. In different blocks, either the third or the fourth harmonic, plus (always) the seventh, ninth, and 12th harmonics were replaced by narrowband noises that were identical in the two intervals. Feedback was provided. In test trials (40% of all trials), the fundamental frequency was 200+ΔF0/2 Hz in both intervals and either the third or the fourth harmonic was shifted slightly up or down in frequency. There were no narrowband noises. Feedback was not provided. The results showed that substitution of a harmonic by noise in context trials significantly reduced the contribution of that harmonic to pitch judgments in the test trials.
The Journal of the Acoustical Society of America 04/2014; 135(4):2161. · 1.65 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We studied the effect of voice familiarity on the ability to segregate one voice from a competing speaker. Specifically, we examine the utility of arguably the most familiar voice of all-the mother's voice-in facilitating segregation, and compared it to the effect of a voice that listeners had been familiarized with in the laboratory. We tested 19 older adolescents (still living at home) on a version of the coordinate-response-measure procedure (CRM; Bolia et al., 2001), with mixtures of two voices, at three signal-to-noise ratios (Ő3 dB, 0 dB, + 3 dB). Performance was better when the mother's voice was the target, compared both to novel and lab-familiar targets. At the most disadvantageous target-to-masker ratio (Ő3 dB), listeners were also better able to ignore their mother's voice so as to comprehend a stranger's voice more effectively, demonstrating that extremely familiar voice information facilitates segregation. This pattern of results is similar to that observed with older people (aged 44-59) when their spouse's voice was present in a two-voice CRM mixture (Johnsrude et al., 2013). The new results demonstrate the importance of long-term (rather than short-term) familiarity and show that it aids sound segregation for adolescents as well as older adults.
The Journal of the Acoustical Society of America 04/2014; 135(4):2423. · 1.65 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Many natural sounds fluctuate over time. The detectability of sounds in a sequence can be reduced by prior stimulation in a process known as forward masking. Forward masking is thought to reflect neural adaptation or neural persistence in the auditory nervous system, but it has been unclear where in the auditory pathway this processing occurs. To address this issue, the present study used a "Huggins pitch" stimulus, the perceptual effects of which depend on central auditory processing. Huggins pitch is an illusory tonal sensation produced when the same noise is presented to the two ears except for a narrow frequency band that is different (decorrelated) between the ears. The pitch sensation depends on the combination of the inputs to the two ears, a process that first occurs at the level of the superior olivary complex in the brainstem. Here it is shown that a Huggins pitch stimulus produces more forward masking in the frequency region of the decorrelation than a noise stimulus identical to the Huggins-pitch stimulus except with perfect correlation between the ears. This stimulus has a peripheral neural representation that is identical to that of the Huggins-pitch stimulus. The results show that processing in, or central to, the superior olivary complex can contribute to forward masking in human listeners.
PLoS ONE 09/2013; 8(9):e75822. · 3.53 Impact Factor
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[Show abstract][Hide abstract] ABSTRACT: People often have to listen to someone speak in the presence of competing voices. Much is known about the acoustic cues used to overcome this challenge, but almost nothing is known about the utility of cues derived from experience with particular voices-cues that may be particularly important for older people and others with impaired hearing. Here, we use a version of the coordinate-response-measure procedure to show that people can exploit knowledge of a highly familiar voice (their spouse's) not only to track it better in the presence of an interfering stranger's voice, but also, crucially, to ignore it so as to comprehend a stranger's voice more effectively. Although performance declines with increasing age when the target voice is novel, there is no decline when the target voice belongs to the listener's spouse. This finding indicates that older listeners can exploit their familiarity with a speaker's voice to mitigate the effects of sensory and cognitive decline.
[Show abstract][Hide abstract] ABSTRACT: Biologically salient sounds, including speech, are rarely heard in isolation. Our brains must therefore organize the input arising from multiple sources into separate "streams" and, in the case of speech, map the acoustic components of the target signal onto meaning. These auditory and linguistic processes have traditionally been considered to occur sequentially and are typically studied independently [1, 2]. However, evidence that streaming is modified or reset by attention , and that lexical knowledge can affect reports of speech sound identity [4, 5], suggests that higher-level factors may influence perceptual organization. In two experiments, listeners heard sequences of repeated words or acoustically matched nonwords. After several presentations, they reported that the initial /s/ sound in each syllable formed a separate stream; the percept then fluctuated between the streamed and fused states in a bistable manner. In addition to measuring these verbal transformations, we assessed streaming objectively by requiring listeners to detect occasional targets-syllables containing a gap after the initial /s/. Performance was better when streaming caused the syllables preceding the target to transform from words into nonwords, rather than from nonwords into words. Our results show that auditory stream formation is influenced not only by the acoustic properties of speech sounds, but also by higher-level processes involved in recognizing familiar words.
Current biology: CB 07/2013; · 10.99 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Users of Advanced Bionics, MedEl, and Cochlear Corp. implants balanced the loudness of trains of asymmetric pulses of opposite polarities presented in monopolar mode. For the Advanced Bionics and MedEl users the pulses were triphasic and consisted of a 32-μs central phase flanked by two 32-μs phases of opposite polarity and half the amplitude. The central phase was either anodic (TP-A) or cathodic (TP-C). For the Cochlear Corp. users, pulses consisted of two 32-μs phases of the same polarity separated by an 8-μs gap, flanked by two 32-μs phases of the opposite polarity, each of which was separated from the central portion by a 58-μs gap. The central portion of these quadraphasic pulses was either anodic (QP-A) or cathodic (QP-C), and all phases had the same amplitude. The current needed to achieve matched loudness was lower for the anodic than for the cathodic stimuli. This polarity effect was similar across all electrode locations studied, including the most apical electrode of the MedEl device which stimulates the very apex of the cochlea. In addition, when quadraphasic pulses were presented in bipolar mode, listeners reported hearing a lower pitch when the central portion was anodic at the more apical, than at the more basal, electrode. The results replicate previous reports that, unlike the results of most animal studies, human cochlear implant listeners are more sensitive to anodic than to cathodic currents, and extend those findings to a wider range of cochlear sites, implant types, and pulse shapes.
The Journal of the Acoustical Society of America 07/2013; 134(1):503-9. · 1.65 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The neural mechanisms of pitch coding have been debated for more than a century. The two main mechanisms are coding based on the profiles of neural firing rates across auditory nerve fibers with different characteristic frequencies (place-rate coding), and coding based on the phase-locked temporal pattern of neural firing (temporal coding). Phase locking precision can be partly assessed by recording the frequency-following response (FFR), a scalp-recorded electrophysiological response that reflects synchronous activity in subcortical neurons. Although features of the FFR have been widely used as indices of pitch coding acuity, only a handful of studies have directly investigated the relation between the FFR and behavioral pitch judgments. Furthermore, the contribution of degraded neural synchrony (as indexed by the FFR) to the pitch perception impairments of older listeners and those with hearing loss is not well known. Here, the relation between the FFR and pure-tone frequency discrimination was investigated in listeners with a wide range of ages and absolute thresholds, to assess the respective contributions of subcortical neural synchrony and other age-related and hearing loss-related mechanisms to frequency discrimination performance. FFR measures of neural synchrony and absolute thresholds independently contributed to frequency discrimination performance. Age alone, i.e., once the effect of subcortical neural synchrony measures or absolute thresholds had been partialed out, did not contribute to frequency discrimination. Overall, the results suggest that frequency discrimination of pure tones may depend both on phase locking precision and on separate mechanisms affected in hearing loss.
Journal of the Association for Research in Otolaryngology 06/2013; 14(5). · 2.95 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: An unresolved question is how the reported clarity of degraded speech is enhanced when listeners have prior knowledge of speech content. One account of this phenomenon proposes top-down modulation of early acoustic processing by higher-level linguistic knowledge. Alternative, strictly bottom-up accounts argue that acoustic information and higher-level knowledge are combined at a late decision stage without modulating early acoustic processing. Here we tested top-down and bottom-up accounts using written text to manipulate listeners' knowledge of speech content. The effect of written text on the reported clarity of noise-vocoded speech was most pronounced when text was presented before (rather than after) speech (Experiment 1). Fine-grained manipulation of the onset asynchrony between text and speech revealed that this effect declined when text was presented more than 120 ms after speech onset (Experiment 2). Finally, the influence of written text was found to arise from phonological (rather than lexical) correspondence between text and speech (Experiment 3). These results suggest that prior knowledge effects are time-limited by the duration of auditory echoic memory for degraded speech, consistent with top-down modulation of early acoustic processing by linguistic knowledge. (PsycINFO Database Record (c) 2013 APA, all rights reserved).
Journal of Experimental Psychology Human Perception & Performance 06/2013; · 3.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We used an adaptation paradigm to investigate whether the frequency following response (FFR) would show evidence for neurons tuned to modulation rate in humans, as has been previously shown in the inferior colliculus of the macaque using fMRI [Baumann et al. Nat. Neurosci. 14, 423-425 (2011)]. The FFR to a 100-ms, 75-dB SPL, target complex tone with an envelope rate of 213 Hz was measured for ten subjects. The target was preceded by a 200-ms, 75-dB SPL, adaptor complex with an envelope rate of 90, 213, or 504 Hz. All complexes contained alternating-phase harmonics from approximately 3.9 to 5.4 kHz. A "vertical" montage (+ Fz, - C7, ground = mid-forehead) was used, for which the FFR is assumed to reflect phase-locked neural activity from generators in the rostral brainstem. The results showed significant adaptation effects in the spectral magnitude of the 213-Hz envelope-related component of the FFR. However, the identical-rate adaptor did not generally produce more adaptation than the different-rate adaptors. Hence, the present results do not provide evidence for neurons tuned to modulation rate in the human brainstem. [Work supported by Wellcome Trust Grant 088263.].
The Journal of the Acoustical Society of America 05/2013; 133(5):3429. · 1.65 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Recent behavioral studies have suggested that the human auditory nerve of cochlear implant (CI) users is mainly excited by the positive (anodic) polarity. Those findings were only obtained using asymmetric pseudomonophasic (PS) pulses where the effect of one phase was measured in the presence of a counteracting phase of opposite polarity, longer duration, and lower amplitude than the former phase. It was assumed that only the short high-amplitude phase was responsible for the excitation. Similarly, it has been shown that electrically evoked compound action potentials could only be obtained in response to the anodic phases of asymmetric pulses. Here, experiment 1 measured electrically evoked auditory brainstem responses to standard symmetric, PS, reversed pseudomonophasic, and reversed pseudomonophasic with inter-phase gap (6 ms) pulses presented for both polarities. Responses were time locked to the short high-amplitude phase of asymmetric pulses and were smaller, but still measurable, when that phase was cathodic than when it was anodic. This provides the first evidence that cathodic stimulation can excite the auditory system of human CI listeners and confirms that this stimulation is nevertheless less effective than for the anodic polarity. A second experiment studied the polarity sensitivity at different intensities by means of a loudness balancing task between pseudomonophasic anodic (PSA) and pseudomonophasic cathodic (PSC) stimuli. Previous studies had demonstrated greater sensitivity to anodic stimulation only for stimuli producing loud percepts. The results showed that PSC stimuli required higher amplitudes than PSA stimuli to reach the same loudness and that this held for current levels ranging from 10 to 100 % of the dynamic range.
Journal of the Association for Research in Otolaryngology 03/2013; 14(3). · 2.95 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Previous studies have suggested that cochlear implant users may have particular difficulties exploiting opportunities to glimpse clear segments of a target speech signal in the presence of a fluctuating masker. Although it has been proposed that this difficulty is associated with a deficit in linking the glimpsed segments across time, the details of this mechanism are yet to be explained. The present study introduces a method called Zebra-speech developed to investigate the relative contribution of simultaneous and sequential segregation mechanisms in concurrent speech perception, using a noise-band vocoder to simulate cochlear implants. One experiment showed that the saliency of the difference between the target and the masker is a key factor for Zebra-speech perception, as it is for sequential segregation. Furthermore, forward masking played little or no role, confirming that intelligibility was not limited by energetic masking but by across-time linkage abilities. In another experiment, a binaural cue was used to distinguish the target and the masker. It showed that the relative contribution of simultaneous and sequential segregation depended on the spectral resolution, with listeners relying more on sequential segregation when the spectral resolution was reduced. The potential of Zebra-speech as a segregation enhancement strategy for cochlear implants is discussed.
The Journal of the Acoustical Society of America 01/2013; 133(1):502-18. · 1.65 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Cochlear implant (CI) users can derive a musical pitch from the temporal pattern of pulses delivered to one electrode. However, pitch perception deteriorates with increasing pulse rate, and most listeners cannot detect increases in pulse rate beyond about 300 pps. In addition, previous studies using irregular pulse trains suggest that pitch can be substantially influenced by neural refractory effects. We presented electric pulse trains to one CI electrode and measured rate discrimination, pitch perception, and auditory nerve (AN) activity in the same subjects and with the same stimuli. The measures of AN activity, obtained using the electrically evoked compound action potential (ECAP), replicated the well-known finding that the neural response to isochronous pulse trains at rates above about 200-300 pps is modulated, with the ECAP being larger to odd-numbered than to even-numbered pulses. This finding has been attributed to refractoriness. Behavioural results replicated the deterioration in rate discrimination at rates above 200-300 pps and the finding that pulse trains whose inter-pulse intervals (IPIs) alternate between a shorter and a longer value (e.g. 4 and 6 ms) have a pitch lower than that corresponding to the mean IPI. To link ECAP modulation to pitch, we physically modulated a 200-pps pulse train by attenuating every other pulse and measured both ECAPs and pitch as a function of modulation depth. Our results show that important aspects of temporal pitch perception cannot be explained in terms of the AN response, at least as measured by ECAPs, and suggest that pitch is influenced by refractory effects occurring central to the AN.
Advances in Experimental Medicine and Biology 01/2013; 787:363-371. · 2.01 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Oxenham et al. [Proc. Nat. Acad. Sci. 101, 1421-1425 (2004)] reported that listeners cannot derive a "missing fundamental" from three transposed tones having high carrier frequencies and harmonically related low-frequency modulators. This finding was attributed to complex pitch perception requiring correct tonotopic representation but could have been due to the very high modulator rate difference limens (DLs) observed for individual transposed tones. Experiments 1 and 2 showed that much lower DLs could be obtained for bandpass-filtered pulse trains than for transposed tones with repetition rates of 100 or 300 pps; however, DLs were still larger than for low-frequency pure tones. Experiment 3 presented three pulse trains filtered between 1375 and 1875, 3900 and 5400, and 7800 and 10 800 Hz simultaneously with a pink-noise background. Listeners could not compare the "missing fundamental" of a stimulus in which the pulse rates were, respectively, 150, 225, and 300 pps, to one where all pulse trains had a rate of 75 pps, even though they could compare a 150 + 225 + 300 Hz complex tone to a 75-Hz pure tone. Hence although filtered pulse trains can produce fairly good pitch perception of simple stimuli having low repetition rates and high-frequency spectral content, no evidence that such stimuli enable complex pitch perception in the absence of a place-rate match was found.
The Journal of the Acoustical Society of America 01/2013; 133(1):377-88. · 1.65 Impact Factor