Envelope Cues Research Articles

Mandarin tone recognition in acoustic and electric hearing

Mandarin tone recognition can be achieved using either spectral cues or temporal cues. Although the pitch contour is the most salient cue for voice pitch perception × Liang, 1963; Abramson, 1978), temporal envelope cues such as amplitude contour, periodicity and duration also contribute significantly to Mandarin tone recognition (Liang, 1963; Fu et al., 1998; Fu and Zeng, 2000). Fu and colleagues (1998, 2000) showed that normalhearing listeners performed approximately 80% tone identification with only temporal envelope cues. However, no studies have been done on whether reliable Mandarin tone recognition could be achieved in the presence of noise. The purpose of this study was to investigate the relative contribution of envelope and fine-structure cues in normalhearing and cochlear-implanted listeners to Mandarin tone recognition in quiet and in noise. We hypothesized that while the temporal envelope can support tone recognition in quiet, it is not adequate in noisy conditions. We further hypothesized that the temporal fine structure is required for tone recognition in noise.

Auditory processing skills and phonological representation in dyslexic children.

It is now well-established that there is a causal connection between children's phonological skills and their acquisition of reading and spelling. Here we study low-level auditory processes that may underpin the development of phonological representations in children. Dyslexic and control children were given a battery of phonological tasks, reading and spelling tasks and auditory processing tasks. Potential relations between deficits in dyslexic performance in the auditory processing tasks and phonological awareness were explored. It was found that individual differences in auditory tasks requiring amplitude envelope rise time processing explained significant variance in phonological processing. It is argued that developmentally, amplitude envelope cues may be primary in establishing well-specified phonological representations, as these cues should yield important rhythmic and syllable-level information about speech.

Exploring the Benefits of Bilateral Cochlear Implants

Several recent reports indicate that both localization and speech intelligibility in spatially separated noise are substantially improved by using cochlear implants (CIs) in both ears rather than in just one. Benefits appear to be largely derived from the effects of level variations at the two ears due to the head shadow whereas contributions from interaural time differences (ITDs) seem smaller than in normal hearing listeners. The effect of binaural unmasking estimated from speech studies to date varies from study to study and is possibly confounded by issues such as listening experience, bias or loudness effects when comparing the performance for the better ear with that using both ears. To improve the contribution from timing information at the two ears, it may be necessary to change present clinical sound-processing schemes that currently preserve only envelope cues so that they also preserve fine-timing information. However, recently published data show that basic psychophysical sensitivity to fine-timing ITDs in CI patients is very poor for rates beyond a few hundred hertz, suggesting that subjects do not actually hear ITD cues at those rates anyway. Data from a number of new studies are presented to discuss these and other issues related to the potential to benefit from bilateral implantation.

Temporal streaming based on fine structure cues

Alternating sequence of two A and B bursts of sound tends to be perceptually organized in different auditory streams when introducing either a spectral or a temporal difference between A and B. In general, the channeling theory of streaming predicts that any salient difference between the excitation patterns evoked by A and B sounds would lead to a segregated percept. Some previous studies have, however, evidenced that a sequence of sounds with similar spectral properties but with different temporal properties can be heard as segregated. In particular, temporal cues are probably responsible for the segregated percept when hearing a sequence of bursts of noises that are amplitude-modulated at different rates. All previous streaming experiments involved stimuli that had frequency components below 5000 Hz. As a consequence, the individual contribution of temporal fine structure cues and envelope cues could not be dissociated and remains largely undetermined. The current experiment is dedicated to test further the relative importance of both envelope and fine structure cues to segregate sequences of unresolved complex tones with different fundamental frequencies. Two high-frequency regions above and below 5000 Hz and several phase relationships leading to several temporal peak factors have been used in a subjective streaming task.

Differentiating speech and nonspeech sounds via amplitude envelope cues

Recent evidence from neuroscience and behavioral speech science suggests that the temporal modulation pattern of the speech signal plays a distinctive role in speech perception. As a first step in exploring the nature of the perceptually relevant information in the temporal pattern of speech, this experiment examined whether speech versus nonspeech environmental sounds could be differentiated on the basis of their amplitude envelopes. Conversational speech was recorded from native speakers of six different languages (French, German, Hebrew, Hindi, Japanese, and Russian) along with samples of their English. Nonspeech sounds included animal vocalizations, water sounds, and other environmental sounds (e.g., thunder). The stimulus set included 30 2-s speech segments and 30 2-s nonspeech events. Frequency information was removed from all stimuli using a technique described by Dorman et al. [J. Acoust. Soc. Am. 102 (1997)]. Nine normal-hearing adult listeners participated in the experiment. Subjects decided whether each sound was (originally) speech or nonspeech and rated their confidence (7-point Likert scale). Overall, subjects differentiated speech from nonspeech very accurately (84% correct). Only 12 stimuli were not correctly categorized at greater than chance levels. Acoustical analysis is underway to determine what parameters of the amplitude envelope differentiate speech from nonspeech sounds.

Discrimination of the fundamental frequency of complex tones with fixed and shifting spectral envelopes by normally hearing and hearing-impaired subjects

Difference limens for the fundamental frequency (F0) of complex tones (DLCs) were measured for four normally hearing subjects and three subjects with cochlear hearing loss. The nominal F0 was 100, 200 or 400 Hz. The two tones to be compared contained either low resolved harmonics (RES), harmonics with intermediate resolvability (INT) or high unresolved harmonics (UNRES). For one set of stimuli (fixed harmonics, FH), the tones to be compared contained three harmonics of fixed number, so the changes in F0 were associated with spectral cues. For a second set of stimuli (Shaped), spectral cues were minimized by filtering stimuli through a fixed passband. For the INT and UNRES conditions, the excitation patterns evoked by the Shaped stimuli hardly changed when F0 was altered. To prevent subjects from comparing the frequencies of individual harmonics in the RES condition, subjects were required to detect F0 differences between two tones with non-overlapping harmonics. It was not possible to obtain repeatable results for the hearing-impaired subjects in this condition. The normally hearing subjects had smaller DLCs for the FH than for the Shaped stimuli for the RES condition, and the UNRES condition at the two higher F0s. However, DLCs were similar for the FH and Shaped stimuli for the INT condition and the UNRES condition at the 100-Hz F0, suggesting that spectral cues were not used in these conditions. Except for one subject with F0=400 Hz, the hearing-impaired subjects had smaller DLCs for the FH than for the Shaped stimuli, for both INT and UNRES conditions (although the difference was small for F0=200 Hz in the UNRES condition), suggesting that they used spectral cues for the FH stimuli. For the Shaped stimuli, DLCs were similar in the INT and UNRES conditions for the hearing-impaired subjects, but were smaller in the INT than the RES condition for the normally hearing subjects. We suggest that, in the INT condition with Shaped stimuli, normally hearing subjects used temporal fine structure cues to perform the task. The hearing-impaired subjects appeared to use only temporal envelope cues.

Modulation rate discrimination for unresolved components: temporal cues related to fine structure and envelope.

The present study investigated the hypothesis that the cues for modulation rate discrimination for unresolved spectral components differ as a function of the spectral region occupied by the stimuli. Specifically, it was hypothesized that when components occupy relatively low spectral regions, phase locking both to the fine structure and to the envelope are useful cues. However, as the spectral region occupied by the components increases, phase locking to the fine structure becomes less robust, whereas phase locking to the envelope remains as a potentially strong cue. Observers were asked to detect a decrease in modulation rate for carrier frequencies between 1500 and 6000 Hz. Both amplitude-modulated (AM) and quasifrequency-modulated (QFM) tones were used in order to produce stimuli having strong and weak envelope cues, respectively. Although there were marked individual differences, the results showed an interaction between modulation type and spectral region, with AM and QFM performance being relatively similar at low spectral region, but with QFM showing a steeper reduction in performance as the spectral region of the carrier frequency increased. Overall, the data are consistent with an interpretation that pitch perception for unresolved components depends upon both fine structure and envelope cues, and that the relative importance of these cues depends upon the spectral region occupied by the stimuli.

Spectral and temporal cues to pitch in noise-excited vocoder simulations of continuous-interleaved-sampling cochlear implants.

Four-band and single-band noise-excited vocoders were used in acoustic simulations to investigate spectral and temporal cues to melodic pitch in the output of a cochlear implant speech processor. Noise carriers were modulated by amplitude envelopes extracted by half-wave rectification and low-pass filtering at 32 or 400 Hz. The four-band, but not the single-band processors, may preserve spectral correlates of fundamental frequency (F0). Envelope smoothing at 400 Hz preserves temporal correlates of F0, which are eliminated with 32-Hz smoothing. Inputs to the processors were sawtooth frequency glides, in which spectral variation is completely determined by F0, or synthetic diphthongal vowel glides, whose spectral shape is dominated by varying formant resonances. Normal listeners labeled the direction of pitch movement of the processed stimuli. For processed sawtooth waves, purely temporal cues led to decreasing performance with increasing F0. With purely spectral cues, performance was above chance despite the limited spectral resolution of the processors. For processed diphthongs, performance with purely spectral cues was at chance, showing that spectral envelope changes due to formant movement obscured spectral cues to F0. Performance with temporal cues was poorer for diphthongs than for sawtooths, with very limited discrimination at higher F0. These data suggest that, for speech signals through a typical cochlear implant processor, spectral cues to pitch are likely to have limited utility, while temporal envelope cues may be useful only at low F0.

Temporal envelope perception in dyslexic children.

Speech intelligibility depends heavily on the accurate perception of auditory temporal envelope cues, that is the slower amplitude modulations present in the speech waveform. In a previous study, McAnally and Stein demonstrated that dyslexics may show impaired audibility (i.e. detectability) of these envelope cues. In the present psychophysical study, the ability to process temporal envelope cues was further investigated in dyslexic children by measuring detection thresholds of sinusoidal amplitude-modulation (SAM) and discrimination thresholds of SAM depth and SAM rate. Each threshold was measured at slow and fast SAM rates of 4 and 128 Hz, respectively. Overall, SAM thresholds were higher in dyslexics than in controls at both rates. The strongest deficit was observed at 4 Hz in the SAM detection task, but a deficit was also apparent at 128 Hz in the SAM discrimination tasks. Therefore, these results reveal that, in addition to reduced audibility of slow and fast envelope cues, some dyslexic children show poor encoding fidelity for these cues (as measured by the discrimination tasks). Overall, these findings are consistent with Tallal's hypothesis according to which the speech and reading deficits in some dyslexics may be caused by impaired temporal processes.

A physiological model for comodulation masking release based on cross-frequency coincidence detection

Detection thresholds for tones in noise can be significantly improved when the masker is amplitude modulated, or when its various components are comodulated [e.g., Hall et al., J. Acoust. Soc. Am. 76, 50–56 (1984)]. Several stimulus-based signal-processing models have been proposed to explain this phenomenon, referred to as comodulation masking release (CMR); however, no physiologically based models have successfully described the psychophysical data. These models have tested hypotheses that CMR involves either cross-frequency processing strategies or within channel envelope-based processing strategies. Cross-frequency coincidence detection is a physiologically realistic, nonlinear processing mechanism that is consistent with suggestions that information from different frequency channels is combined to explain CMR. Furthermore, cross-frequency coincidence detectors are sensitive to envelope cues, thus this mechanism is also consistent with within-channel envelope-based models for CMR. The sensitivity of coincidence detectors to envelope cues is due to the nonlinear timing of low-frequency auditory-nerve (AN) fibers—changes in amplitude of the stimulus result in systematic changes in the relative times of phase-locked AN fibers tuned to different frequencies [Heinz et al., J. Acoust. Soc. Am. 110, 2065–2084 (2001)]. A cross-frequency coincidence-detection model can explain the psychophysical results for the basic CMR paradigm described in Hall et al. (1984). [Work supported by NIH-NIDCD.]

Use of temporal envelope cues by children with developmental dyslexia.

This study evaluates the ability to process auditory temporal-envelope cues in a group of 6 children with dyslexia (mean age: 10;10 years;months). To address this issue, we measured (a) temporal modulation transfer functions (TMTFs), that is, the detection thresholds of sinusoidal amplitude modulation (SAM) applied to a white noise carrier, as a function of modulation frequency, fm (fm was 4, 16, 64, 256, and 1,024 Hz) and (b) identification performance for vowel-consonant-vowel (VCV) stimuli over 5 sessions. VCV stimuli were either unprocessed or digitally processed to remove the original spectral information, resulting in a time-varying speech envelope amplitude modulating a noise carrier. The same tests were conducted in 6 normal control children (mean age: 11;6 years;months) and 6 normal control adults (mean age: 24;8 years;months). SAM thresholds were similar in normal children and adults. For both normal groups, TMTFs were low pass in shape and showed low between-listener variability. TMTFs measured in children with dyslexia showed higher between-listener variability: TMTFs were band pass in 2 children, flat in 1 child, and low pass in the 3 others. Overall, SAM thresholds were higher in children with dyslexia than in normal children at fm = 4 and 1,024 Hz. Unprocessed-speech identification performance was nearly perfect in normal children and adults, and impaired in children with dyslexia. "Speech-envelope noise" identification performance was poorer in normal children and children with dyslexia than in normal adults. Performance improved across sessions in normal children and adults, but remained constant in children with dyslexia. Compared to normal children, children with dyslexia showed poorer reception of voicing, manner, and place of articulation for unprocessed speech and poorer reception of voicing for "speech-envelope noise." Taken together, these results support the hypothesis that some children with dyslexia may show abnormal auditory temporal-envelope processing. Such a deficit, in turn, may explain the difficulties of children with dyslexia with speech perception.

Older listeners' use of temporal cues altered by compression amplification.

This study compared the ability of younger and older listeners to use temporal information in speech when that information was altered by compression amplification. Recognition of vowel-consonant-vowel syllables was measured for four groups of adult listeners (younger normal hearing, older normal hearing, younger hearing impaired, older hearing impaired). There were four conditions. Syllables were processed with wide-dynamic range compression (WDRC) amplification and with linear amplification. In each of those conditions, recognition was measured for syllables containing only temporal information and for syllables containing spectral and temporal information. Recognition of WDRC-amplified speech provided an estimate of the ability to use altered amplitude envelope cues. Syllables were presented with a high-frequency masker to minimize confounding differences in high-frequency sensitivity between the younger and older groups. Scores were lower for WDRC-amplified speech than for linearly amplified speech, and older listeners performed more poorly than younger listeners. When spectral information was unrestricted, the age-related decrement was similar for both amplification types. When spectral information was restricted for listeners with normal hearing, the age-related decrement was greater for WDRC-amplified speech than for linearly amplified speech. When spectral information was restricted for listeners with hearing loss, the age-related decrement was similar for both amplification types. Clinically, these results imply that when spectral cues are available (i.e., when the listener has adequate spectral resolution) older listeners can use WDRC hearing aids to the same extent as younger listeners. For older listeners without hearing loss, poorer scores for compression-amplified speech suggest an age-related deficit in temporal resolution.

Auditory Temporal Envelope Processing in a Patient with Left-hemisphere Damage

Abstract Auditory temporal envelope processing was investigated in a patient showing a mild speech identification impairment following left-hemisphere damage. Three tasks evaluated the patient's ability to: (1) detect a sinusoidal amplitude modulation (SAM) applied to a white noise, as a function of modulation rate (i.e. her ‘temporal modulation transfer function’ or TMTF); (2) discriminate between two white noises amplitude modulated by time-reversed temporally asymmetric envelopes; and (3) identify white noises amplitude modulated by the temporal envelope of speech stimuli. Measurements of intensity discrimination thresholds were performed as a control task. Compared to normal data, the results obtained with the brain-damaged patient showed: (1) increased thresholds for the detection of SAM; (2) increased thresholds for the discrimination of temporal asymmetry; and (3) a deficit in the identification of speechenvelope noise stimuli. In contrast, intensity discrimination thresholds were within the normal range. Taken together, the results indicate a general impairment in auditory temporal acuity, which is now specified as a deficit in the coding of envelope rate and shape, and a deficit in the ability to use temporal envelope cues in speech processing. These results support the hypothesis that left-hemisphere damage is associated with an impairment in time analysis, which may cause, in turn, speech intelligibility disorders.

Auditory temporal envelope processing in a patient with left-hemisphere damage

Auditory temporal envelope processing was investigated in a patient showing a mild speech identification impairment following left-hemisphere damage. Three tasks evaluated the patient's ability to: (1) detect a sinusoidal amplitude modulation (SAM) applied to a white noise, as a function of modulation rate (i.e. her ‘temporal modulation transfer function’ or TMTF); (2) discriminate between two white noises amplitude modulated by time-reversed temporally asymmetric envelopes; and (3) identify white noises amplitude modulated by the temporal envelope of speech stimuli. Measurements of intensity discrimination thresholds were performed as a control task. Compared to normal data, the results obtained with the brain-damaged patient showed: (1) increased thresholds for the detection of SAM; (2) increased thresholds for the discrimination of temporal asymmetry; and (3) a deficit in the identification of speechenvelope noise stimuli. In contrast, intensity discrimination thresholds were within the normal range. Taken together, the results indicate a general impairment in auditory temporal acuity, which is now specified as a deficit in the coding of envelope rate and shape, and a deficit in the ability to use temporal envelope cues in speech processing. These results support the hypothesis that left-hemisphere damage is associated with an impairment in time analysis, which may cause, in turn, speech intelligibility disorders.

Consonant recognition in noise with temporal cues: II. Effects of temporal envelope enhancement on response times

In an effort to evaluate the importance of envelope cues in speech recognition, response times and percentages of correct responses were measured simultaneously in normal-hearing and hearing-impaired listeners, using a forced-choice identification paradigm. Naturally produced /aCa/ disyllables presented in a white noise background (+6 dB signal-to-noise ratio) were used to create temporal-only stimuli having instantaneous amplitudes identical to the natural speech stimuli, but flat spectra. The temporal envelope of the /aCa/ disyllables was either left intact or enhanced by raising it to the power 2. In the first experiment, 13 young normal-hearing listeners (24–27 years) were tested. The results show that envelope enhancement yields a general improvement in both percent correct identification (4.75%) and response times (63 ms). In the second experiment, nine hearing-impaired listeners (53–71 years) were tested at a comfortable listening level. Overall, temporal expansion fails to show better consonant identification in terms of percentage of correct responses, but yields a significant improvement (66 ms) in terms of response time. These results suggest that: (1) the perceptual effects of speech-envelope enhancement cannot be completely accounted for by percent correct-responses measurements, and (2) response times seem to be more sensitive to the effects of envelope enhancement.

Identification of temporal envelope cues in Chinese tone recognition

For tonal languages such as Mandarin Chinese, tone recognition is important for understanding the meaning of words, phrases or sentences. While fundamental frequency carries the most distinctive information for tone recognition, waveform temporal envelope cues can also produce a high level of tone recognition. This study attempts to identify what types of temporal envelope cues contribute to tone recognition and whether these temporal envelope cues are dependent on speakers and vowel contexts. Several signal-correlated-noise stimuli were generated to separate the contribution of three major temporal envelope cues – duration, amplitude contour, and periodicity – to tone recognition. Perceptual results show that the duration cue contributed mostly to discrimination of Tone-3, the amplitude cue contributed mostly to Tone-3 and Tone-4 discrimination, and the periodicity cue contributed to recognition of all tones. However, tone recognition based on temporal envelope cues was highly variable across speakers and vowel contexts. Acoustic analysis of these temporal envelope cues revealed that this variability in tone recognition is directly related to the acoustic variability between the amplitude contour and fundamental frequency contour.

Effects of envelope expansion on speech recognition

This study investigated the effects of expanding the gross time-amplitude variations of ‘speech-envelope noise’ stimuli on speech recognition. The initial stimuli were VCV logatomes presented in quiet or against a steady white noise with a 0-dB signal-to-noise ratio. Their low-frequency temporal modulations (<500 Hz) were extracted in broad frequency bands, and raised to the power 2. The resulting envelopes were then used to modulate a white noise, and combined to produce the ‘speech-envelope noise’ stimuli. As a consequence, listeners were forced to identify speech using primarily temporal envelope cues. The results obtained with four normal-hearing listeners show small decrements in recognition performance of 1–15% when expanding the envelope of the speech stimuli presented in quiet. The results also show a small but consistent improvement in performance of 6–14% when expanding the envelope of the speech stimuli presented in noise. These results are consistent with those obtained by Fu and Shannon (J. Acoust. Soc. Am. 104 (1998) 2570–2577) with speech presented in quiet. They also suggest that the reduction in the modulation depth of the speech envelope caused by noise or reverberation could be compensated by expanding low-frequency temporal modulations.

Leaky integrators, Fletcher curves, and period histograms: A new link

Fletcher curves, thresholds from tone-in-noise detection tasks plotted as a function of masker bandwidth, are thought to reflect characteristics of peripheral filters. This notion, however, is compromised by the finding that a roving level procedure affects thresholds only for very narrow bandwidths [Kidd et al., J. Acoust. Soc. Am. 86, 1310–1317 (1989)]. Alternatively, a three-stage, leaky integrator (i.e., initial, relatively broad bandpass filter, followed by half-wave rectification and low-pass filtering) yields frequency-dependent, level-invariant Fletcher curves, thus entertaining the possibility that sensitivity to envelope cues underlies detection at all masker bandwidths. The decision statistic is a measure of similarity (Mahalanobis distance) between the observed amplitude spectrum of the leaky integrator output and expected spectra with and without a signal. Regarding physiological plausibility, the model also describes the temporal response of auditory nerve fibers to complex stimuli. Horst et al. [J. Acoust. Soc. Am. 85, 1898–1901 (1985)] used multicomponent, periodic stimuli to obtain period histograms from auditory nerve recordings. Fourier transforms of the histograms were used to assess temporal responses of fibers. For various stimulus configurations, the spectra of the period histogram and leaky integrator output are nearly identical. Theoretical implications are discussed. [Work supported by ONR.]

The perception of phonologically significant contrasts using speech envelope cues.

The observation that many cochlear implantees demonstrate high levels of speech recognition, despite limited or distorted spectral information, has motivated research on the importance of temporal information for the perception of speech. The purpose of this study was to measure the recognition of speech contrasts via only the speech envelope before and after training. Test stimuli consisted of eight segmental and two suprasegmental contrasts of the Hebrew Speech Pattern Contrast test using a binary forced-choice paradigm. Multiplying the speech waveform with white noise eliminated spectral information. Results show that stress, intonation and manner of articulation were very well perceived using only temporal information, whereas voicing and place of articulation were perceived above chance levels. Results also show that vowels were more susceptible to the removal of spectral information than consonants. These findings help to better understand speech perception performance of hearing-impaired individuals, including cochlear implant users. They may also have practical implications for aural rehabilitation and sensory aids design for the Hebrew speaking population.

Effects of electrode location and spacing on phoneme recognition with the Nucleus-22 cochlear implant.

The objective of this paper was to determine how phoneme identification was affected by the cochlear location and spacing of the electrodes in cochlear implant listeners. Subjects were initially programmed with the full complement of 20 active electrodes, in which each electrode was assigned to represent the output of one filter in the normal SPEAK processor. In the present study several four-electrode processors were constructed by assigning the output of more than one filter to a single electrode. In all conditions speech sounds were still analyzed into 20 frequency bands and processed according to the usual SPEAK processing strategy, but the location and spacing of the four stimulated electrode pairs were varied systematically. In Experiment I, the spacing between stimulated electrodes was fixed at 3.75 mm and the cochlear location of the four electrode pairs was shifted from the most-apical position up to 3.0 mm toward the base in 0.75 mm steps. In Experiment II, the spatial separation between the four electrode pairs (each bipolar-plus-one) was systematically changed from 1.5 mm to 4.5 mm while holding the most apical active electrode fixed. In Experiment III, the spacing of active electrodes was varied to represent equal tonotopic spacing to equal linear frequency intervals between pairs. Recognition of medial vowels and consonants was measured in three subjects with these custom four-electrode speech processors. In Experiment I, results showed that both vowel and consonant recognition were best when the electrodes were in the most apical locations. In Experiment II, best speech recognition occurred when electrode pairs were separated by 3 to 3.75 mm. In Experiment III, both vowel and consonant recognition scores decreased when the spacing of electrode pairs was changed from equal tonotopic spacing to equal linear frequency intervals. Overall, vowel and consonant recognition were best at the most apical electrode locations and when the spacing of electrodes matched the frequency intervals of the analysis filters. Consonant recognition was relatively robust to alterations in electrode location and spacing. The best vowel scores with four-electrode speech processors were about 10 percentage lower than scores obtained with the full 20-electrode speech processors. However, the best consonant scores with four-electrode speech processors were similar to those obtained with the full 20-electrode speech processors. Information transmission analysis revealed that temporal envelope cues (voicing and manner) were not strongly affected by changes in electrode location and spacing, whereas spectral cues, as represented by vowel recognition and consonantal place of articulation, were strongly affected. Both spectral and temporal phoneme cues were strongly affected by the degree of tonotopic warping, created by altering both the location and spacing of the activated electrodes. The cochlear location and spacing of the activated electrodes had a clear effect on phoneme recognition. Temporal cues were less affected by tonotopic shifts or linear tonotopic stretching or shrinking, but were susceptible to nonlinear tonotopic warping. Spectral cues were sensitive to all tonotopic manipulations: shifting, linear stretching, and nonlinear warping. However, the present experiments could not differentiate whether the optimal mapping between analysis frequency bands and stimulation electrodes was determined by the normal acoustic tonotopic pattern or by the pattern learned from experience with the 20-electrode implant.