Informational Masking in Normal-hearing and Hearing-impaired Listeners

The present study aimed to test whether central, across-channel, informational auditory processing abilities are altered by hearing loss. The informational masking effect exerted on a 1 kHz tone-pip by a simultaneous four-tone masker, whose spectral content changed within as well as across trials, was measured in the left and right ears of normal-hearing subjects and hearing-impaired subjects with either symmetrical or asymmetrical hearing loss between the two ears. In the subjects with normal-hearing or symmetrical hearing loss, the level of the masker was set to 40 dB SL in each ear, in the subjects with asymmetrical hearing loss, the masker was set to 40 dB SL in the best ear and loudness-balanced in the other ear. The results failed to reveal significant differences in informational masking between normal-hearing and hearing-impaired subjects. However, in subjects with asymmetric hearing loss, less informational masking was observed in the ear with the more elevated absolute thresholds than in the opposite ear. Since the latter finding can be explained in terms of across-ear differences in loudness recruitment, it is suggested that central, across-channel, informational processing abilities are not substantially different in hearing-impaired than in normal-hearing ears.     

Temporal Pitch Sensitivity in an Animal Model: Psychophysics and Scalp Recordings: Temporal Pitch Sensitivity in Cat

Cochlear implant (CI) users show limited sensitivity to the temporal pitch conveyed by electric stimulation, contributing to impaired perception of music and of speech in noise. Neurophysiological studies in cats suggest that this limitation is due, in part, to poor transmission of the temporal fine structure (TFS) by the brainstem pathways that are activated by electrical cochlear stimulation. It remains unknown, however, how that neural limit might influence perception in the same animal model. For that reason, we developed non-invasive psychophysical and electrophysiological measures of temporal (i.e., non-spectral) pitch processing in the cat. Normal-hearing (NH) cats were presented with acoustic pulse trains consisting of band-limited harmonic complexes that simulated CI stimulation of the basal cochlea while removing cochlear place-of-excitation cues. In the psychophysical procedure, trained cats detected changes from a base pulse rate to a higher pulse rate. In the scalp-recording procedure, the cortical-evoked acoustic change complex (ACC) and brainstem-generated frequency following response (FFR) were recorded simultaneously in sedated cats for pulse trains that alternated between the base and higher rates. The range of perceptual sensitivity to temporal pitch broadly resembled that of humans but was shifted to somewhat higher rates. The ACC largely paralleled these perceptual patterns, validating its use as an objective measure of temporal pitch sensitivity. The phase-locked FFR, in contrast, showed strong brainstem encoding for all tested pulse rates. These measures demonstrate the cat’s perceptual sensitivity to pitch in the absence of cochlear-place cues and may be valuable for evaluating neural mechanisms of temporal pitch perception in the feline animal model of stimulation by a CI or novel auditory prostheses.     

Evaluating Psychophysical Polarity Sensitivity as an Indirect Estimate of Neural Status in Cochlear Implant Listeners

The physiological integrity of spiral ganglion neurons is presumed to influence cochlear implant (CI) outcomes, but it is difficult to measure neural health in CI listeners. Modeling data suggest that, when peripheral processes have degenerated, anodic stimulation may be a more effective neural stimulus than cathodic stimulation. The primary goal of the present study was to evaluate the emerging theory that polarity sensitivity reflects neural health in CI listeners. An ideal in vivo estimate of neural integrity should vary independently of other factors known to influence the CI electrode-neuron interface, such as electrode position and tissue impedances. Thus, the present analyses quantified the relationships between polarity sensitivity and (1) electrode position estimated via computed tomography imaging, (2) intracochlear resistance estimated via electrical field imaging, and (3) focused (steered quadrupolar) behavioral thresholds, which are believed to reflect a combination of local neural health, electrode position, and intracochlear resistance. Eleven adults with Advanced Bionics devices participated. To estimate polarity sensitivity, electrode-specific behavioral thresholds in response to monopolar, triphasic pulses where the central high-amplitude phase was either anodic (CAC) or cathodic (ACA) were measured. The polarity effect was defined as the difference in threshold response to the ACA compared to the CAC stimulus. Results indicated that the polarity effect was not related to electrode-to-modiolus distance, electrode scalar location, or intracochlear resistance. Large, positive polarity effects, which may indicate SGN degeneration, were associated with relatively high focused behavioral thresholds. The polarity effect explained a significant portion of the variation in focused thresholds, even after controlling for electrode position and intracochlear resistance. Overall, these results provide support for the theory that the polarity effect may reflect neural integrity in CI listeners. Evidence from this study supports further investigation into the use of polarity sensitivity for optimizing individual CI programming parameters.

     

Temporal Pitch Sensitivity in an Animal Model: Psychophysics and Scalp Recordings

Journal of the Association for Research in Otolaryngology - Cochlear implant (CI) users show limited sensitivity to the temporal pitch conveyed by electric stimulation, contributing to impaired...     

Temporal Acuity in Normal and Hearing-Impaired Listeners

Temporal acuity, defined as the minimum detectable gap in an otherwise continuous noise, was measured with an adaptive version of the two-alternative forced-choice task. For 6 normal listeners, the minimum duration detectable decreased from an average of 20.3 ms at a noise level of 30 dB SPL to 3.2 ms at 80 dB SPL. By comparison, the temporal acuity of 4 listeners with conductive hearing losses, 2 with otosclerosis, and 7 with sensorineural hearing losses, was poorer than that for normal listeners at equal sound pressure levels. At higher sound pressure levels, the acuity of those with conductive hearing losses or otosclerosis approached normal values, but the acuity for listeners with sensorineural hearing losses did not.

Nous avons mesuré l'acuité temporelle, définie comme la durée minimale d'une interruption d'un bruit par ailleurs continu pour qu'elle soit décelable, en appliquant une version particulière de la méthode des choix forcés entre deux alternatives. Chez 6 sujets jouissant d'une audition normale, ce temps passait en moyenne de 20,3 ms pour un bruit de 30 dB SPL à 3,2 ms pour un bruit de 80 dB SPL. Dans 4 cas de surdité de transmission, 2 cas d'otospongiose et 7 cas d'atteinte de l'oreille interne, nous avons trouvé une acuité temporelle moins bonne aux měmes intensités de bruit. Dans les cas de surdité de transmission et d'otospongiose, les valeurs se rapprochaient de la normale à des intensités de son plus élevées, mais il n'en était pas de měme pour les malades souffrant d'atteintes de l'oreille interne.     

Temporal Regularity Detection and Rate Discrimination in Cochlear-Implant Listeners

Cochlear implants (CIs) convey fundamental-frequency information using primarily temporal cues. However, temporal pitch perception in CI users is weak and, when measured using rate discrimination tasks, deteriorates markedly as the rate increases beyond 300 pulses-per-second. Rate pitch may be weak because the electrical stimulation of the surviving neural population of the implant recipient may not allow accurate coding of inter-pulse time intervals. If so, this phenomenon should prevent listeners from detecting when a pulse train is physically temporally jittered. Performance in a jitter detection task was compared to that in a rate-pitch discrimination task. Stimuli were delivered using direct stimulation in cochlear implants, on a mid-array and an apical electrode, and at two different rates (100 and 300 pps). Average performance on both tasks was worse at the higher pulse rate and did not depend on electrode. However, there was a large variability across and within listeners that did not correlate between the two tasks, suggesting that rate-pitch judgement and regularity detection are to some extent limited by task-specific processes. Simulations with filtered pulse trains presented to NH listeners yielded broadly similar results, except that, for the rate discrimination task, the difference between performance with 100- and 300-pps base rates was smaller than observed for CI users.     

Detection and Identification of Monaural and Binaural Pitch Contours in Dyslexic Listeners

The use of binaural pitch stimuli to test for the presence of binaural auditory impairment in reading-disabled subjects has so far led to contradictory outcomes. While some studies found that a majority of dyslexic subjects was unable to perceive binaural pitch, others obtained a clear response of dyslexic listeners to Huggins’ pitch (HP). The present study clarified whether impaired binaural pitch perception is found in dyslexia. Results from a pitch contour identification test, performed in 31 dyslexic listeners and 31 matched controls, clearly showed that dyslexics perceived HP as well as the controls. Both groups also showed comparable results with a similar-sounding, but monaurally detectable, pitch-evoking stimulus. However, nine of the dyslexic subjects were found to have difficulty identifying pitch contours both in the binaural and the monaural conditions. The ability of subjects to correctly identify pitch contours was found to be significantly correlated to measures of frequency discrimination. This correlation may be attributed to the similarity of the experimental tasks and probably reflects impaired cognitive mechanisms related to auditory memory or auditory attention rather than impaired low-level auditory processing per se.     

Psychophysical Tuning Curves as a Correlate of Electrode Position in Cochlear Implant Listeners

Speech understanding abilities vary widely among cochlear implant (CI) listeners. A potential source of this variability is the electrode-neuron interface (ENI), which includes peripheral factors such as electrode position and integrity of remaining spiral ganglion neurons. Suboptimal positioning of the electrode array has been associated with poorer speech outcomes; however, postoperative computerized tomography (CT) scans are often not available to clinicians. CT-estimated electrode-to-modiolus distance (distance from the inner wall of the cochlea) has been shown to account for some variability in behavioral thresholds. However, psychophysical tuning curves (PTCs) may provide additional insight into site-specific variation in channel interaction. Thirteen unilaterally implanted adults with the Advanced Bionics HiRes90K device participated. Behavioral thresholds and PTCs were collected for all available electrodes with steered quadrupolar (sQP) configuration, using a modified threshold sweep procedure, used in Bierer et al. (Trends Hear 19:1–12, 2015). PTC bandwidths were quantified to characterize channel interaction across the electrode array, and tip shifts were assessed to identify possible contributions of neural dead regions. Broader PTC bandwidths were correlated with electrodes farther from the modiolus, but not correlated with sQP threshold, though a trend was observed. Both measures were affected by scalar location, and PTC tip shifts were observed for electrodes farther from the modiolus. sQP threshold was the only variable correlated with word recognition. These results suggest PTCs may be used as a site-specific measure of channel interaction that correlates with electrode position in some CI listeners.     

Interaction Between Pitch and Timbre Perception in Normal-Hearing Listeners and Cochlear Implant Users

Journal of the Association for Research in Otolaryngology - Despite their mutually exclusive definitions, pitch and timbre perception interact with each other in normal-hearing (NH) listeners....     

Pitch Discrimination Learning: Specificity for Pitch and Harmonic Resolvability,and Electrophysiological Correlates

Multiple-hour training on a pitch discrimination task dramatically decreases the threshold for detecting a pitch difference between two harmonic complexes. Here, we investigated the specificity of this perceptual learning with respect to the pitch and the resolvability of the trained harmonic complex, as well as its cortical electrophysiological correlates. We trained 24 participants for 12 h on a pitch discrimination task using one of four different harmonic complexes. The complexes differed in pitch and/or spectral resolvability of their components by the cochlea, but were filtered into the same spectral region. Cortical-evoked potentials and a behavioral measure of pitch discrimination were assessed before and after training for all the four complexes. The change in these measures was compared to that of two control groups: one trained on a level discrimination task and one without any training. The behavioral results showed that learning was partly specific to both pitch and resolvability. Training with a resolved-harmonic complex improved pitch discrimination for resolved complexes more than training with an unresolved complex. However, we did not find evidence that training with an unresolved complex leads to specific learning for unresolved complexes. Training affected the P2 component of the cortical-evoked potentials, as well as a later component (250–400 ms). No significant changes were found on the mismatch negativity (MMN) component, although a separate experiment showed that this measure was sensitive to pitch changes equivalent to the pitch discriminability changes induced by training. This result suggests that pitch discrimination training affects processes not measured by the MMN, for example, processes higher in level or parallel to those involved in MMN generation.     

Limitations on Monaural and Binaural Temporal Processing in Bilateral Cochlear Implant Listeners

Monaural rate discrimination and binaural interaural time difference (ITD) discrimination were studied as functions of pulse rate in a group of bilaterally implanted cochlear implant users. Stimuli for the rate discrimination task were pulse trains presented to one electrode, which could be in the apical, middle, or basal part of the array, and in either the left or the right ear. In each two-interval trial, the standard stimulus had a rate of 100, 200, 300, or 500 pulses per second and the signal stimulus had a rate 35 % higher. ITD discrimination between pitch-matched electrode pairs was measured for the same standard rates as in the rate discrimination task and with an ITD of +/− 500 μs. Sensitivity (d′) on both tasks decreased with increasing rate, as has been reported previously. This study tested the hypothesis that deterioration in performance at high rates occurs for the two tasks due to a common neural basis, specific to the stimulation of each electrode. Results show that ITD scores for different pairs of electrodes correlated with the lower rate discrimination scores for those two electrodes. Statistical analysis, which partialed out overall differences between listeners, electrodes, and rates, supports the hypothesis that monaural and binaural temporal processing limitations are at least partly due to a common mechanism.     

Temporal Resolution of the Normal Ear in Listeners with Unilateral Hearing Impairment

Unilateral hearing loss (UHL) leads to an imbalanced input to the brain and results in cortical reorganization. In listeners with unilateral impairments, while the perceptual deficits associated with the impaired ear are well documented, less is known regarding the auditory processing in the unimpaired, clinically normal ear. It is commonly accepted that perceptual consequences are unlikely to occur in the normal ear for listeners with UHL. This study investigated whether the temporal resolution in the normal-hearing (NH) ear of listeners with long-standing UHL is similar to those in listeners with NH. Temporal resolution was assayed via measuring gap detection thresholds (GDTs) in within- and between-channel paradigms. GDTs were assessed in the normal ear of adults with long-standing, severe-to-profound UHL (N = 13) and age-matched, NH listeners (N = 22) at two presentation levels (30 and 55 dB sensation level). Analysis indicated that within-channel GDTs for listeners with UHL were not significantly different than those for the NH subject group, but the between-channel GDTs for listeners with UHL were poorer (by greater than a factor of 2) than those for the listeners with NH. The hearing thresholds in the normal or impaired ears were not associated with the elevated between-channel GDTs for listeners with UHL. Contrary to the common assumption that auditory processing capabilities are preserved for the normal ear in listeners with UHL, the current study demonstrated that a long-standing unilateral hearing impairment may adversely affect auditory perception—temporal resolution—in the clinically normal ear. From a translational perspective, these findings imply that the temporal processing deficits in the unimpaired ear of listeners with unilateral hearing impairments may contribute to their overall auditory perceptual difficulties.     

Multichannel Place Pitch Sensitivity in Cochlear Implant Recipients

Cochlear implant recipients perceive a rise in pitch when the site of stimulation is moved from the apex toward the base. The place pitch sensitivity is typically measured using the stimulation of single channels. However, all current cochlear implant devices stimulate multiple channels simultaneously or with pulses temporally interleaved. The primary goal of the present study is to test whether the sensitivity of a cochlear implant recipient to changes in perceived pitch associated with changes of place of excitation improves or deteriorates when the number of active channels is increased, compared with stimulation with only one active channel. Place pitch sensitivity was recorded in four Nucleus CI24 subjects as a function of number of active channels (from 1 to 8). Just noticeable differences were estimated from a constant stimuli 2AFC pitch-ranking experiment with roving loudness. Reference and comparison stimuli contained the same number of active channels but were shifted one or two electrodes toward the base or toward the apex. The place pitch sensitivity was measured using monopolar stimulation at two locations along the electrode array. To minimize cues related to loudness, the multichannel stimuli were loudness balanced relative to the single-channel stimuli presented at C-level. The number of active channels did not affect place pitch sensitivity. This is consistent with a model that compares the edges of the excitation pattern irrespective of the overlap between excitation patterns. There was a significant difference in sensitivity to place pitch among subjects. The average just noticeable differences of place pitch, extrapolated from a fitting procedure, for the subjects ranged from 0.25 mm to 0.46 mm.     

Pitch Comparisons between Electrical Stimulation of a Cochlear Implant and Acoustic Stimuli Presented to a Normal-hearing Contralateral Ear

Four cochlear implant users, having normal hearing in the unimplanted ear, compared the pitches of electrical and acoustic stimuli presented to the two ears. Comparisons were between 1,031-pps pulse trains and pure tones or between 12 and 25-pps electric pulse trains and bandpass-filtered acoustic pulse trains of the same rate. Three methods—pitch adjustment, constant stimuli, and interleaved adaptive procedures—were used. For all methods, we showed that the results can be strongly influenced by non-sensory biases arising from the range of acoustic stimuli presented, and proposed a series of checks that should be made to alert the experimenter to those biases. We then showed that the results of comparisons that survived these checks do not deviate consistently from the predictions of a widely-used cochlear frequency-to-place formula or of a computational cochlear model. We also demonstrate that substantial range effects occur with other widely used experimental methods, even for normal-hearing listeners.     

Forward Masking in Cochlear Implant Users: Electrophysiological and Psychophysical Data Using Pulse Train Maskers

Electrical stimulation of auditory nerve fibers using cochlear implants (CI) shows psychophysical forward masking (pFM) up to several hundreds of milliseconds. By contrast, recovery of electrically evoked compound action potentials (eCAPs) from forward masking (eFM) was shown to be more rapid, with time constants no greater than a few milliseconds. These discrepancies suggested two main contributors to pFM: a rapid-recovery process due to refractory properties of the auditory nerve and a slow-recovery process arising from more central structures. In the present study, we investigate whether the use of different maskers between eCAP and psychophysical measures, specifically single-pulse versus pulse train maskers, may have been a source of confound.In experiment 1, we measured eFM using the following: a single-pulse masker, a 300-ms low-rate pulse train masker (LTM, 250 pps), and a 300-ms high-rate pulse train masker (HTM, 5000 pps). The maskers were presented either at same physical current (Φ) or at same perceptual (Ψ) level corresponding to comfortable loudness. Responses to a single-pulse probe were measured for masker-probe intervals ranging from 1 to 512 ms. Recovery from masking was much slower for pulse trains than for the single-pulse masker. When presented at Φ level, HTM produced more and longer-lasting masking than LTM. However, results were inconsistent when LTM and HTM were compared at Ψ level. In experiment 2, masked detection thresholds of single-pulse probes were measured using the same pulse train masker conditions. In line with our eFM findings, masked thresholds for HTM were higher than those for LTM at Φ level. However, the opposite result was found when the pulse trains were presented at Ψ level.Our results confirm the presence of slow-recovery phenomena at the level of the auditory nerve in CI users, as previously shown in animal studies. Inconsistencies between eFM and pFM results, despite using the same masking conditions, further underline the importance of comparing electrophysiological and psychophysical measures with identical stimulation paradigms.     

Effect of Chronic Stimulation and Stimulus Level on Temporal Processing by Cochlear Implant Listeners

A series of experiments investigated potential changes in temporal processing during the months following activation of a cochlear implant (CI) and as a function of stimulus level. Experiment 1 tested patients on the day of implant activation and 2 and 6 months later. All stimuli were presented using direct stimulation of a single apical electrode. The dependent variables were rate discrimination ratios (RDRs) for pulse trains with rates centred on 120 pulses per second (pps), obtained using an adaptive procedure, and a measure of the upper limit of temporal pitch, obtained using a pitch-ranking procedure. All stimuli were presented at their most comfortable level (MCL). RDRs decreased from 1.23 to 1.16 and the upper limit increased from 357 to 485 pps from 0 to 2 months post-activation, with no overall change from 2 to 6 months. Because MCLs and hence the testing level increased across sessions, two further experiments investigated whether the performance changes observed across sessions could be due to level differences. Experiment 2 re-tested a subset of subjects at 9 months post-activation, using current levels similar to those used at 0 months. Although the stimuli sounded softer, some subjects showed lower RDRs and/or higher upper limits at this re-test. Experiment 3 measured RDRs and the upper limit for a separate group of subjects at levels equal to 60 %, 80 % and 100 % of the dynamic range. RDRs decreased with increasing level. The upper limit increased with increasing level for most subjects, with two notable exceptions. Implications of the results for temporal plasticity are discussed, along with possible influences of the effects of level and of across-session learning.

     

Objective and Subjective Psychophysical Measures of Auditory Stream Integration and Segregation

The perceptual organization of sound sequences into auditory streams involves the integration of sounds into one stream and the segregation of sounds into separate streams. “Objective” psychophysical measures of auditory streaming can be obtained using behavioral tasks where performance is facilitated by segregation and hampered by integration, or vice versa. Traditionally, these two types of tasks have been tested in separate studies involving different listeners, procedures, and stimuli. Here, we tested subjects in two complementary temporal-gap discrimination tasks involving similar stimuli and procedures. One task was designed so that performance in it would be facilitated by perceptual integration; the other, so that performance would be facilitated by perceptual segregation. Thresholds were measured in both tasks under a wide range of conditions produced by varying three stimulus parameters known to influence stream formation: frequency separation, tone-presentation rate, and sequence length. In addition to these performance-based measures, subjective judgments of perceived segregation were collected in the same listeners under corresponding stimulus conditions. The patterns of results obtained in the two temporal-discrimination tasks, and the relationships between thresholds and perceived-segregation judgments, were mostly consistent with the hypothesis that stream segregation helped performance in one task and impaired performance in the other task. The tasks and stimuli described here may prove useful in future behavioral or neurophysiological experiments, which seek to manipulate and measure neural correlates of auditory streaming while minimizing differences between the physical stimuli.     

Relative Contributions of Temporal Envelope and Fine Structure Cues to Lexical Tone Recognition in Hearing-Impaired Listeners

It has been reported that normal-hearing Chinese speakers base their lexical tone recognition on fine structure regardless of temporal envelope cues. However, a few psychoacoustic and perceptual studies have demonstrated that listeners with sensorineural hearing impairment may have an impaired ability to use fine structure information, whereas their ability to use temporal envelope information is close to normal. The purpose of this study is to investigate the relative contributions of temporal envelope and fine structure cues to lexical tone recognition in normal-hearing and hearing-impaired native Mandarin Chinese speakers. Twenty-two normal-hearing subjects and 31 subjects with various degrees of sensorineural hearing loss participated in the study. Sixteen sets of Mandarin monosyllables with four tone patterns for each were processed through a “chimeric synthesizer” in which temporal envelope from a monosyllabic word of one tone was paired with fine structure from the same monosyllable of other tones. The chimeric tokens were generated in the three channel conditions (4, 8, and 16 channels). Results showed that differences in tone responses among the three channel conditions were minor. On average, 90.9%, 70.9%, 57.5%, and 38.2% of tone responses were consistent with fine structure for normal-hearing, moderate, moderate to severe, and severely hearing-impaired groups respectively, whereas 6.8%, 21.1%, 31.4%, and 44.7% of tone responses were consistent with temporal envelope cues for the above-mentioned groups. Tone responses that were consistent neither with temporal envelope nor fine structure had averages of 2.3%, 8.0%, 11.1%, and 17.1% for the above-mentioned groups of subjects. Pure-tone average thresholds were negatively correlated with tone responses that were consistent with fine structure, but were positively correlated with tone responses that were based on the temporal envelope cues. Consistent with the idea that the spectral resolvability is responsible for fine structure coding, these results demonstrated that, as hearing loss becomes more severe, lexical tone recognition relies increasingly on temporal envelope rather than fine structure cues due to the widened auditory filters.     

Acoustic Temporal Modulation Detection in Normal-Hearing and Cochlear Implanted Listeners: Effects of Hearing Mechanism and Development

Temporal modulation detection ability matures over many years after birth and may be particularly sensitive to experience during this period. Profound hearing loss during early childhood might result in greater perceptual deficits than a similar loss beginning in adulthood. We tested this idea by measuring performance in temporal modulation detection in profoundly deaf children and adults fitted with cochlear implants (CIs). At least two independent variables could constrain temporal modulation detection performance in children with CIs: altered encoding of modulation information due to the CI-auditory nerve interface, and atypical development of central processing of sound information provided by CIs. The effect of altered encoding was investigated by testing subjects with one of two different hearing mechanisms (normal hearing vs. CI) and the effect of atypical development was studied by testing two different age groups. All subjects were tested for their ability to detect acoustic temporal modulations of sound amplitude. A comparison of the slope, or cutoff frequency, of the temporal modulation transfer functions (TMTFs) among the four subject groups revealed that temporal resolution was mainly constrained by hearing mechanism: normal-hearing listeners could detect smaller amplitude modulations at high modulation frequencies than CI users. In contrast, a comparison of the height of the TMTFs revealed a significant interaction between hearing mechanism and age group on overall sensitivity to temporal modulation: sensitivity was significantly poorer in children with CIs, relative to the other three groups. Results suggest that there is an age-specific vulnerability of intensity discrimination or non-sensory factors, which subsequently affects sensitivity to temporal modulation in prelingually deaf children who use CIs.     

The Role of Spectral and Temporal Cues in Voice Gender Discrimination by Normal-Hearing Listeners and Cochlear Implant Users

The present study investigated the relative importance of temporal and spectral cues in voice gender discrimination and vowel recognition by normal-hearing subjects listening to an acoustic simulation of cochlear implant speech processing and by cochlear implant users. In the simulation, the number of speech processing channels ranged from 4 to 32, thereby varying the spectral resolution; the cutoff frequencies of the channels envelope filters ranged from 20 to 320 Hz, thereby manipulating the available temporal cues. For normal-hearing subjects, results showed that both voice gender discrimination and vowel recognition scores improved as the number of spectral channels was increased. When only 4 spectral channels were available, voice gender discrimination significantly improved as the envelope filter cutoff frequency was increased from 20 to 320 Hz. For all spectral conditions, increasing the amount of temporal information had no significant effect on vowel recognition. Both voice gender discrimination and vowel recognition scores were highly variable among implant users. The performance of cochlear implant listeners was similar to that of normal-hearing subjects listening to comparable speech processing (4–8 spectral channels). The results suggest that both spectral and temporal cues contribute to voice gender discrimination and that temporal cues are especially important for cochlear implant users to identify the voice gender when there is reduced spectral resolution.