Release from interference in auditory working memory for pitch

The purpose of this study was to quantify the effect of interpolated tones upon a pitch standard held within auditory working memory through measurement of the difference limen (just noticeable difference) for frequency and the usefulness of “Where” cues to ameliorate the interference produced by these intervening stimuli. To this end, we measured the degree to which tones, containing identical and disparate localization cues, presented within the retention interval altered differential sensitivity for frequency via the method of constant stimuli. The difference limen for frequency nearly tripled when tones were presented within the retention interval and sound localization cues produced a significant partial release from interference within the short-term pitch store. Interference produced by “Where” cues ranged from 4.0 to 5.2 Hz. These findings indicate that there is a possible integrative use of the “What” and “Where” pathways in forming and maintaining pitch information within the pitch array within auditory working memory.     

Effects of recurrent tonal information on auditory working memory for pitch

This study ascertained the influence of repeating pitch information within an intervening tonal sequence upon the extent of interference for a pitch standard held within auditory working memory as measured by the difference limen for frequency (DLF). Standard and comparison tones were presented to subjects and same/different responses were obtained using a touch screen monitor and the DLF was measured using single interval adjustment matrix (SIAM) procedure [Kaernbach, C., 1990. A single-interval adjustment-matrix (SIAM) procedure for unbiased adaptive testing. J. Acoust. Soc. Am. 88, 2645–2655]. Estimates of the DLF were obtained in a control condition with a silent inter-comparison interval and three conditions containing intervening tones within the temporal gap between the standard and comparison stimuli. The presence of intervening stimuli produced a significant increase in the DLF when the intervening tonal sequence contained tones with pitches that differed from that of the standard (Int condition) as well as when the sequence contained a tone with a pitch identical to that of the comparison (RptCmp condition). Further, the DLFs obtained for RptCmp condition were significantly higher than those measured in the Int condition. The DLFs measured in the condition where the pitch of an intervening tone was identical to the standard were significantly lower than those for the Int and RptCmp condition, but did not differ from the DLFs for the control condition. These results indicate that either a release from or an increase in interference in auditory working memory for pitch can occur dependent upon the frequency relationships between of the standard, comparison, and intervening tones.     

Temporal (phase and time) disparities in lateralization

The topic of this paper concerns the judgement of just noticeable differences (JND) and of complete lateral position for dichotic 1 000-Hz stimuli with phase or onset time or delay differences and for a click. The 1 000-Hz sinusoids had 30 ms steady state with 10 or 50 ms rise/decay time and were presented at 50 dB HL in listeners with normal hearing. For every value of delta phi, delta onset or delay, the presentation consisted of blocks of 20 trials and the JND was determined as the phase or onset time or delay differences producing 80% of correct responses (forced choice). The intracranial 1 000-Hz tone image with long disparities was evaluated for 90, 180 and 270 degrees delta phi, for 250, 500 and 750 microseconds delta onset and for 250, 500 and 750 microseconds delay. Our results demonstrate that the interaural time differences with suitable headphone onset cues have a negligible effect on JND in pure-tone lateralization tests; the JND for a 1 000-Hz tone is based on phase cues only. With 180 and 270 degrees phase shifts, the interaural onset time differences, with 10 ms rise-fall time, become critical and override phase information. The JND for clicks on the contrary is based on time cue only. The intracranial click image with long disparities and duality threshold was evaluated.     

Temporal (Phase and Time) Disparities in Lateralization

The topic of this paper concerns the judgement of just noticeable differences (JND) and of complete lateral position for dichotic 1 000-Hz stimuli with phase or onset time or delay differences and for a click. The 1 000-Hz sinusoids had 30 ms steady state with 10 or 50 ms rise/decay time and were presented at 50 dB HL in listeners with normal hearing. For every value of Δ, Δ_onset or delay, the presentation consisted of blocks of 20 trials and the JND was determined as the phase or onset time or delay differences producing 80% of correct responses (forced choice). The intracranial 1 000-Hz tone image with long disparities was evaluated for 90, 180 and 270° Δ, for 250, 500 and 750 μs Δ_onset and for 250, 500 and 750 μs delay.

Our results demonstrate that the interaural time differences with suitable headphone onset cues have a negligible effect on JND in pure-tone lateralization tests; the JND for a 1 000-Hz tone is based on phase cues only. With 180 and 270° phase shifts, the interaural onset time differences, with 10 ms rise-fall time, become critical and override phase information.

The JND for clicks on the contrary is based on time cue only. The intracranial click image with long disparities and duality threshold was evaluated.     

The auditory spatial acuity of the domestic cat in the inter aural horizontal and median vertical planes

The auditory spatial acuity of the domestic cat in the interaural horizontal plane was examined using broadband noise and nine pure-tone stimuli ranging in frequency from 0.5 to 32 kHz. Acuity in the median vertical plane was also examined using broadband noise and three pure tones of frequencies 2, 8 and 16 kHz. Minimum audible angles (MAAs) for a reference source directly in front of an animal were measured in the horizontal plane for five cats and in the vertical plane for four. The smallest MAAs measured were those for the noise stimulus, for which MAAs in the horizontal and vertical planes were similar in magnitude. Horizontal plane MAAs for low-frequency tones were smaller than those for high, and the pattern of MAA change with frequency was consistent with the use of interaural phase and sound pressure level difference cues to localize low- and high-frequency tones, respectively. Three of the four cats trained on the vertical plane MAA task did not achieve criterion performance for any of the three pure tones, and the MAAs obtained from the fourth cat at each frequency were relatively large. Vertical plane performance was consistent with the use of spectral transformation cues to discern the elevation of a complex stimulus.     

Auditory Processing Deficits in Reading Disabled Adults

The nature of the auditory processing deficit of disabled readers is still an unresolved issue. The quest for a fundamental, nonlinguistic, perceptual impairment has been dominated by the hypothesis that the difficulty lies in processing sequences of stimuli at presentation rates of tens of milliseconds. The present study examined this hypothesis using tasks that require processing of a wide range of stimulus time constants. About a third of the sampled population of disabled readers (classified as "poor auditory processors") had difficulties in most of the tasks tested: detection of frequency differences, detection of tones in narrowband noise, detection of amplitude modulation, detection of the direction of sound sources moving in virtual space, and perception of the lateralized position of tones based on their interaural phase differences. Nevertheless, across-channel integration was intact in these poor auditory processors since comodulation masking release was not reduced. Furthermore, phase locking was presumably intact since binaural masking level differences were normal. In a further examination of temporal processing, participants were asked to discriminate two tones at various intervals where the frequency difference was ten times each individual's frequency just noticeable difference (JND). Under these conditions, poor auditory processors showed no specific difficulty at brief intervals, contrary to predictions under a fast temporal processing deficit assumption. The complementary subgroup of disabled readers who were not poor auditory processors showed some difficulty in this condition when compared with their direct controls. However, they had no difficulty on auditory tasks such as amplitude modulation detection, which presumably taps processing of similar time scales. These two subgroups of disabled readers had similar reading performance but those with a generally poor auditory performance scored lower on some cognitive tests. Taken together, these results suggest that a large portion of disabled readers suffer from diverse difficulties in auditory processing. No parsimonious explanation based on current models of low-level auditory processing can account simultaneously for all these results, though increased within-channel noise is consistent with the majority of the deficits found in the subgroup of poorer auditory processors.     

The localisation of spectrally restricted sounds by human listeners

The two principal binaural cues to sound location are interaural time differences (ITDs), which are thought to be dominant at low frequencies, and interaural level differences (ILDs), which are thought to dominate at mid to high frequencies. The outer ear also filters the sound in a location dependent manner and provides spectral cues to location. In these experiments we have examined the relative contribution of these cues to the auditory localisation performance by humans. Six subjects localised sounds by pointing their face toward the perceived location of stimuli presented in complete darkness in an anechoic chamber. Control stimuli were spectrally flat (400 Hz to 16 kHz), while the relative contribution of location cues in the low frequency channels was determined using noise high passed at 2 kHz and in the high frequency channels using stimuli low passed at 2 kHz. The removal of frequencies below 2 kHz had little effect on either the pattern of systematic errors or the distribution of localisation estimates with the exception of an increase in the size of the standard deviations associated with a few rear locations. This suggests considerable redundancy in the auditory localisation information contained within a broadband sound. In contrast, restricting the target spectrum to frequencies below 2 kHz resulted in a large increase in the cone-of-confusion errors as well as a subject dependent biasing of the front-to-back or back-to-front confusions. These biases and the reduction in localisation accuracy for high pass stimuli at some posterior locations are consistent with a contribution of spectral information at low frequencies.     

Time-intensity trading functions for selected pure tones.

A substantial number of investigations have examined the ability of the auditory system to trade time for intensity on a lateralization task. Most of these investigations, however, have employed clicks and noise bursts as stimuli with interaural disparities between onset times. Consequently, there is a lack of quantitative data for time-intensity trades where pure tones that had identical onset times but disparate phase were employed as signals. For this reason we employed sinusoids ranging from 200 to 2000 Hz and determined the extent to which the intensity of one signal must be decreased to achieve a midline image when interaural phase disparities of 0 degrees to 360 degrees were imposed between the binaural signals in 30 degree increments. The time-intensity trading functions yielded in this experiment demonstrate that (1) not unexpectedly, the largest time-intensity trades were accomplished for the lower frequencies; (2) the maximum time-intensity trade for each frequency occurred at interaural phase disparities of 90 degrees and 270 degrees; and (3) when the low-frequency tones were 180 degrees out of phase, essentially the same intraaural intensity relationship was required to achieve midline as was needed for the 0 degree interaural phase condition.     

Sound localization in chinchillas. I: Left/right discriminations

The ability of chinchillas to localize sound was examined behaviorally using a conditioned avoidance procedure in which the animals were trained to discriminate left from right sound sources. Their minimum audible angle was 15.6° for 100-ms broadband noise making them one of the more accurate rodents, although they are not as accurate as primates and carnivores. Thresholds obtained for filtered noise stimuli demonstrated that chinchillas are equally accurate in localizing either low- or high-frequency noise. Further, they are able to use both interaural phase-difference and interaural intensity-difference cues as demonstrated by their ability to localize both low- and high-frequency pure tones. Finally, analysis of the chinchilla retina supports the hypothesis that the role of auditory localization in directing the eyes to sound sources played a role in the evolution of auditory spatial perception.     

The influence of externalization and spatial cues on the generation of auditory brainstem responses and middle latency responses

The effect of externalization and spatial cues on the generation of auditory brainstem responses (ABRs) and middle latency responses (MLRs) was investigated in this study. Most previous evoked potential studies used click stimuli with variations of interaural time (ITDs) and interaural level differences (ILDs) which merely led to a lateralization of sound inside the subject's head. In contrast, in the present study potentials were elicited by a virtual acoustics stimulus paradigm with 'natural' spatial cues and compared to responses to a diotic, non-externalized reference stimulus. Spatial sound directions were situated on the horizontal plane (corresponding to variations in ITD, ILD, and spectral cues) or the midsagittal plane (variation of spectral cues only). An optimized chirp was used which had proven to be advantageous over the click since it compensates for basilar membrane dispersion. ABRs and MLRs were recorded from 32 scalp electrodes and both binaural potentials (B) and binaural difference potentials (BD, i.e., the difference between binaural and summed monaural responses) were investigated. The amplitudes of B and BD to spatial stimuli were not higher than those to the diotic reference. ABR amplitudes decreased and latencies increased with increasing laterality of the sound source. A rotating dipole source exhibited characteristic patterns in dependence on the stimulus laterality. For the MLR data, stimulus laterality was reflected in the latency of component N(a). In addition, dipole source analysis revealed a systematic magnitude increase for the dipole contralateral to the azimuthal position of the sound source. For the variation of elevation, the right dipole source showed a stronger activation for stimuli away from the horizontal plane. The results indicate that at the level of the brainstem and primary auditory cortex binaural interaction is mostly affected by interaural cues (ITD, ILD). Potentials evoked by stimuli with natural combinations of ITD, ILD, and spectral cues were not larger than those elicited by diotic chirps.     

Behavioral Sensitivity to Broadband Binaural Localization Cues in the Ferret

Although the ferret has become an important model species for studying both fundamental and clinical aspects of spatial hearing, previous behavioral work has focused on studies of sound localization and spatial release from masking in the free field. This makes it difficult to tease apart the role played by different spatial cues. In humans and other species, interaural time differences (ITDs) and interaural level differences (ILDs) play a critical role in sound localization in the azimuthal plane and also facilitate sound source separation in noisy environments. In this study, we used a range of broadband noise stimuli presented via customized earphones to measure ITD and ILD sensitivity in the ferret. Our behavioral data show that ferrets are extremely sensitive to changes in either binaural cue, with levels of performance approximating that found in humans. The measured thresholds were relatively stable despite extensive and prolonged (>16 weeks) testing on ITD and ILD tasks with broadband stimuli. For both cues, sensitivity was reduced at shorter durations. In addition, subtle effects of changing the stimulus envelope were observed on ITD, but not ILD, thresholds. Sensitivity to these cues also differed in other ways. Whereas ILD sensitivity was unaffected by changes in average binaural level or interaural correlation, the same manipulations produced much larger effects on ITD sensitivity, with thresholds declining when either of these parameters was reduced. The binaural sensitivity measured in this study can largely account for the ability of ferrets to localize broadband stimuli in the azimuthal plane. Our results are also broadly consistent with data from humans and confirm the ferret as an excellent experimental model for studying spatial hearing.     

Effects of randomizing phase on the discrimination between amplitude-modulated and quasi-frequency-modulated tones

This study investigated the bandwidth of phase sensitivity. Subjects discriminated amplitude-modulated tones (AM), and quasi-frequency-modulated tones (QFM) in a two-interval, forced-choice task. An adaptive threshold procedure was used to estimate the modulation depth needed to discriminate the stimuli as a function of carrier and modulation frequency. Non-monotonicities in threshold-bandwidth functions were often observed at higher modulation frequencies. The results are discussed in terms of two potential cues: (1) waveform envelope, (2) cubic distortion products. In order to degrade the information obtained from auditory distortions, the phase for the carrier frequency was randomly sampled from a uniform distribution, which diminished the non-monotonicities with minimal effect at lower modulation frequencies. Model simulations demonstrated that phase randomization degrades distortion product cues with only a modest effect on temporal cues. Final results show that maximum bandwidths for phase sensitivity (BW(max)) were not proportional to carrier frequencies.     

Perceptual Sensitivity to High-Frequency Interaural Time Differences Created by Rustling Sounds

Interaural time differences (ITDs) can be used to localize sounds in the horizontal plane. ITDs can be extracted from either the fine structure of low-frequency sounds or from the envelopes of high-frequency sounds. Studies of the latter have included stimuli with periodic envelopes like amplitude-modulated tones or transposed stimuli, and high-pass filtered Gaussian noises. Here, four experiments are presented investigating the perceptual relevance of ITD cues in synthetic and recorded “rustling” sounds. Both share the broad long-term power spectrum with Gaussian noise but provide more pronounced envelope fluctuations than Gaussian noise, quantified by an increased waveform fourth moment, W. The current data show that the JNDs in ITD for band-pass rustling sounds tended to improve with increasing W and with increasing bandwidth when the sounds were band limited. In contrast, no influence of W on JND was observed for broadband sounds, apparently because of listeners' sensitivity to ITD in low-frequency fine structure, present in the broadband sounds. Second, it is shown that for high-frequency rustling sounds ITD JNDs can be as low as 30 μs. The third result was that the amount of dominance for ITD extraction of low frequencies decreases systematically with increasing amount of envelope fluctuations. Finally, it is shown that despite the exceptionally good envelope ITD sensitivity evident with high-frequency rustling sounds, minimum audible angles of both synthetic and recorded high-frequency rustling sounds in virtual acoustic space are still best when the angular information is mediated by interaural level differences.     

Lateralization of high-frequency pure tones with interaural phase difference and bone conduction

This study tested the prediction that interaural phase differences (IPDs) are converted to interaural level differences (ILDs) with bilateral bone-conduction stimulation due to the effects of acoustic interference arising from transcranial transmission. Seven normal-hearing listeners judged the lateral position of 3000-6000-Hz pure tones, presented via bone vibrators on the mastoids, as a function of IPD. Evidence for lateralization was obtained in five listeners despite humans being insensitive to IPD in pure tones at these frequencies. The direction of lateralization depended on frequency, as well as IPD, for three listeners. It is argued that these findings are consistent with the conversion of external IPD to internal ILD during transcranial transmission. Inter-individual variation in lateralization was apparent and no evidence of lateralization was found in two listeners at the frequency tested, which may reflect, at least in part, inter-individual variation in transcranial transmission properties. The notion that external IPD within the waveform fine-structure at high-frequencies does not influence localization with air conduction may not apply to bone conduction due to the acoustic interference effects.     

Human frequency-following responses to binaural masking level difference stimuli

Binaural masking level difference is the behavioral threshold difference between a diotic condition (SoNo) and a dichotic condition with a 180 degrees interaural phase delay of either the signal (SpiNo) or the masker (SoNpi). Threshold disparity is partially related to coincidence-detecting units in the medial superior olive that are sensitive to low-frequency binaural stimuli with interaural phase differences. Previous surface evoked potential studies report significant latency and amplitude differences to SpiNo stimuli with respect to SoNo stimuli in the P1-N1 auditory event related potential, but no study has reported physiologic masking level differences in a brain stem evoked potential. The human frequency-following response (FFR) represents activity from low-frequency, phase locking neural units in the upper brainstem. Unmasked FFRs to 500 Hz tone bursts and masked FFRs using a 1.5 kHz low-pass masker were recorded from nine normal-hearing adult subjects. Significant reduction in FFR amplitude occurred in the SoNo condition, re the So condition, with masker intensities near the psychoacoustic SoNo masking level. Significant FFR amplitude recovery was observed for both the SoNpi and SpiNo conditions. These results support the role of phase-locked neural activity in brainstem mechanisms involved in perceptual masking release.     

Binaural interactions in cortical area AI of cats reared with unilateral atresia of the external ear canal

Binaural interactions were recorded in auditory cortical (AI) neurons of anesthetized adult cats that had unilateral atresias created shortly after birth by surgically ligating and cutting one external ear canal. At the time of the recording experiment, the atresia and associated debris were removed and tones were delivered to both tympanic membranes via a sealed and calibrated acoustic system. The majority of neurons recorded were in the cortex ipsilateral to the previously occluded ear. Thresholds for monaural stimulation of either the operated or unoperated ear were within normal range although thresholds to stimulation of the previously operated ear tended to occupy the upper end of the normal distribution. Monotonie and nonmonotonic spike count-vs-intensity functions derived from responses to monaural stimulation of the atretic ear were indistinguishable in their shape from those recorded in normal cats. All binaural classes were represented in our sample in proportions similar to those reported in cats with two normal ears. The forms of the functions relating spike count to interaural intensity differences and interaural phase differences were essentially the same as those seen in normal animals. The main binaural deficit observed under these conditions was a shift in the interaural intensity difference to which an AI neuron was most sensitive. The intensity needed for a stimulus to the atretic ear to participate in the binaural response was as much as 50 dB higher than that at the opposite normal ear in contrast to the nearly equal SPLs required for binaural interactions in cats with two ears intact. It was suggested that elevated thresholds at the previously operated ear could account for much of the shift observed.     

Responses elicited from medial superior olivary neurons by stimuli associated with binaural masking and unmasking

The responses of binaural neurons of the medial superior olive were measured as a function of interaural temporal differences for tones and as a function of signal-to-noise ratio under homophasic and antiphasic masking conditions. The degree of neural response synchrony to the frequency of the signal was related to the degree of behavioral detectability of the signal in the homophasic, but not the antiphasic masking condition. For the antiphasic condition, a decrease in discharge rate resulted from the addition of the signal to the noise, similar to the decrease which occurred when interaural temporal differences were introduced in the tonal stimuli. The results are compatible with a model in which interaural temporal-difference information arriving over monaural afferents in the form of synchronized impulses is mapped into a place code by a neural coincidence-detection device. Several differences were noted between the responses to tones found in the present experiment and those reported by others. These differences were attributed mainly to differences among the experimental procedures in use among the various reporting laboratories.     

Normal ipsilateral/contralateral asymmetries in infant multiple auditory steady-state responses to air- and bone-conduction stimuli

OBJECTIVES: Two-channel recordings of infants' air- and bone-conduction auditory brainstem responses to brief tones show ipsilateral and contralateral (to the stimulated ear) asymmetries which may be used to isolate which cochlea is the primary contributor to the response. The objective of this study was to determine whether similar ipsilateral/contralateral asymmetries are also present in the air- and bone-conduction "brainstem" (77 to 101 Hz) auditory steady-state responses (ASSRs) of infants. DESIGN: Two-channel ASSRs were recorded in infants (2 to 11 mo) and adults (18 to 40 yr) with normal hearing. Multiple stimuli (carrier frequencies: 500 to 4000 Hz; amplitude/frequency modulated) were presented using a B-71 oscillator on the temporal bone or an ER3-A insert earphone. Bone-conduction ASSR amplitudes, phase delays, and thresholds were obtained for the electroencephalographic (EEG) channels ipsilateral and contralateral to the oscillator temporal-bone placement. Bone-conduction ASSRs were also obtained to the stimulus presented to the opposite temporal bone (at 40 dB HL only). Air-conduction ASSR amplitudes and phase delays were obtained at 60 dB HL in each ear for the EEG channels ipsilateral and contralateral to the transducer. RESULTS: Infants showed more ipsilateral/contralateral asymmetries in both air- and bone-conduction ASSRs compared with adults. Mean bone-conduction ASSR thresholds in infants were 13 to 15 dB higher (i.e., poorer) in the contralateral EEG channel compared with the ipsilateral EEG channel for 500 to 4000 Hz. In adults, there were no large differences (i.e., within 1 dB) between ipsilateral and contralateral ASSR thresholds. Based on ipsilateral/ contralateral threshold differences in infants, interaural attenuation for bone-conducted stimuli was estimated to be at least 10 to 30 dB for most infants. In contrast, most adults showed little interaural attenuation for bone-conducted stimuli. ASSR amplitudes are larger and phase delays are shorter in the ipsilateral EEG channel. For infants, the difference in air-conduction ASSR amplitude between EEG channels was twice that observed for adults. Infants also had greater ASSR amplitude differences between EEG channels for bone-conduction stimuli compared with adults, but the difference was less than that seen for air-conduction stimuli. For air-conduction stimuli, infants had significantly longer phase delays in the contralateral EEG channel compared with the ipsilateral EEG channel. Adults showed no significant differences in air-conduction ASSR phase delay between EEG channels. For bone-conduction stimuli, both infants and adults had significantly longer phase delays in the contralateral EEG channel compared with the ipsilateral EEG channel; the differences in ASSR phase delays between EEG channels were much smaller in infants compared with adults and fewer adults had absent responses in the contralateral EEG channels compared with infants (12% versus 34%). When the transducers were switched to the opposite ear/mastoid, the infant and adult ipsilateral/contralateral asymmetries also switched. CONCLUSIONS: Ipsilateral/contralateral asymmetries in air- and bone-conduction ASSRs are clearly present more often and are larger in infants compared with adults. Our findings also suggest that most infants have at least 10 to 30 dB of interaural attenuation to bone-conducted stimuli. These asymmetries in the bone-conduction ASSR have potential as a clinical tool for isolating the cochlea that is contributing to the response in infants.     

Lateralization of high-frequency pure tones with interaural phase difference and bone conduction

This study tested the prediction that interaural phase differences (IPDs) are converted to interaural level differences (ILDs) with bilateral bone-conduction stimulation due to the effects of acoustic interference arising from transcranial transmission. Seven normal-hearing listeners judged the lateral position of 3000–6000-Hz pure tones, presented via bone vibrators on the mastoids, as a function of IPD. Evidence for lateralization was obtained in five listeners despite humans being insensitive to IPD in pure tones at these frequencies. The direction of lateralization depended on frequency, as well as IPD, for three listeners. It is argued that these findings are consistent with the conversion of external IPD to internal ILD during transcranial transmission. Inter-individual variation in lateralization was apparent and no evidence of lateralization was found in two listeners at the frequency tested, which may reflect, at least in part, inter-individual variation in transcranial transmission properties. The notion that external IPD within the waveform fine-structure at high-frequencies does not influence localization with air conduction may not apply to bone conduction due to the acoustic interference effects.     

Some measures of verbal and spatial working memory in eight- and nine-year-old hearing-impaired children with cochlear implants

OBJECTIVE: The purpose of this study was to examine working memory for sequences of auditory and visual stimuli in prelingually deafened pediatric cochlear implant users with at least 4 yr of device experience. DESIGN: Two groups of 8- and 9-yr-old children, 45 normal-hearing and 45 hearing-impaired users of cochlear implants, completed a novel working memory task requiring memory for sequences of either visual-spatial cues or visual-spatial cues paired with auditory signals. In each sequence, colored response buttons were illuminated either with or without simultaneous auditory presentation of verbal labels (color-names or digit-names). The child was required to reproduce each sequence by pressing the appropriate buttons on the response box. Sequence length was varied and a measure of memory span corresponding to the longest list length correctly reproduced under each set of presentation conditions was recorded. Additional children completed a modified task that eliminated the visual-spatial light cues but that still required reproduction of auditory color-name sequences using the same response box. Data from 37 pediatric cochlear implant users were collected using this modified task. RESULTS: The cochlear implant group obtained shorter span scores on average than the normal-hearing group, regardless of presentation format. The normal-hearing children also demonstrated a larger "redundancy gain" than children in the cochlear implant group-that is, the normal-hearing group displayed better memory for auditory-plus-lights sequences than for the lights-only sequences. Although the children with cochlear implants did not use the auditory signals as effectively as normal-hearing children when visual-spatial cues were also available, their performance on the modified memory task using only auditory cues showed that some of the children were capable of encoding auditory-only sequences at a level comparable with normal-hearing children. CONCLUSIONS: The finding of smaller redundancy gains from the addition of auditory cues to visual-spatial sequences in the cochlear implant group as compared with the normal-hearing group demonstrates differences in encoding or rehearsal strategies between these two groups of children. Differences in memory span between the two groups even on a visual-spatial memory task suggests that atypical working memory development irrespective of input modality may be present in this clinical population.