Synthetic Speech Stimuli Research Articles

No influence of regular rhythmic priming on grammaticality judgment and sentence comprehension in English-speaking children

A growing body of research has demonstrated the association between music and language, particularly between rhythm and grammar skills in children. A compelling piece of evidence for the influence of music on language comes from findings that a brief exposure to regular musical rhythm improved subsequent syntactic language performance in children. Nevertheless, those observations were made on one particular task, i.e., grammaticality judgment, mostly with French-speaking children. Here, we sought to corroborate and extend the rhythmic priming effect with English-speaking children aged 7 to 12 years who underwent two different syntactic tasks on spoken sentences: one involving judgment on morphosyntactic well-formedness (grammaticality judgment) and the other requiring noun–verb relation analysis (sentence comprehension), both following either regular or irregular rhythmic priming. Half of the children were administered synthetic speech stimuli (Experiment 1), and the other half were presented with natural speech (Experiment 2). Across the two experiments, we did not find any rhythmic priming effect; children’s performance on both the grammaticality judgment and sentence comprehension tasks was comparable irrespective of the regularity in prior rhythms. These results imply that the positive influence of regular rhythmic priming on syntactic processing may be confined to specific language or age populations, warranting further investigation.

Aided Cortical Auditory Evoked Potentials in Infants With Frequency-Specific Synthetic Speech Stimuli: Sensitivity, Repeatability, and Feasibility.

The cortical auditory evoked potential (CAEP) test is a candidate for supplementing clinical practice for infant hearing aid users and others who are not developmentally ready for behavioral testing. Sensitivity of the test for given sensation levels (SLs) has been reported to some degree, but further data are needed from large numbers of infants within the target age range, including repeat data where CAEPs were not detected initially. This study aims to assess sensitivity, repeatability, acceptability, and feasibility of CAEPs as a clinical measure of aided audibility in infants. One hundred and three infant hearing aid users were recruited from 53 pediatric audiology centers across the UK. Infants underwent aided CAEP testing at age 3 to 7 months to a mid-frequency (MF) and (mid-)high-frequency (HF) synthetic speech stimulus. CAEP testing was repeated within 7 days. When developmentally ready (aged 7-21 months), the infants underwent aided behavioral hearing testing using the same stimuli, to estimate the decibel (dB) SL (i.e., level above threshold) of those stimuli when presented at the CAEP test sessions. Percentage of CAEP detections for different dB SLs are reported using an objective detection method (Hotellings T 2 ). Acceptability was assessed using caregiver interviews and a questionnaire, and feasibility by recording test duration and completion rate. The overall sensitivity for a single CAEP test when the stimuli were ≥0 dB SL (i.e., audible) was 70% for the MF stimulus and 54% for the HF stimulus. After repeat testing, this increased to 84% and 72%, respectively. For SL >10 dB, the respective MF and HF test sensitivities were 80% and 60% for a single test, increasing to 94% and 79% for the two tests combined. Clinical feasibility was demonstrated by an excellent >99% completion rate, and acceptable median test duration of 24 minutes, including preparation time. Caregivers reported overall positive experiences of the test. By addressing the clinical need to provide data in the target age group at different SLs, we have demonstrated that aided CAEP testing can supplement existing clinical practice when infants with hearing loss are not developmentally ready for traditional behavioral assessment. Repeat testing is valuable to increase test sensitivity. For clinical application, it is important to be aware of CAEP response variability in this age group.

The perception of synthetic speech versus natural speech stimuli in adult listeners

The majority of speech perception research investigates interpersonal perception through presentation of two types of stimuli: synthetic speech and/or natural speech. Synthetically created speech stimuli allows for precisely controlled manipulation of individual acoustic variables, but can sound unnatural calling into questions its ecological validity. Alternatively, natural speech preserves the full complement of redundant acoustic cues yet limits control of specific acoustic parameters. In this study, we investigate speech discrimination comparing perception of specified acoustic parameters (formant transition duration, F3 onset frequency, F3-F2 distance) across three types of speech stimuli: synthetic speech stimuli, natural speech of a standard adult speaker, and each participant’s own voice. We use the Wide Range Acoustic Accuracy Scale (WRAAS), a computer-based perceptual assessment that uses a parameter estimation by sequential testing (PEST) adaptive-tracking algorithm to rapidly identify a listener’s ability to discriminate sounds. Most trials are presented near the Just-Noticeable-Difference (JND) of a stimulus continuum; thus, few trials are “wasted” with obviously same or different sounds. This study of typical adult listeners (n = 20, enrollment is ongoing) will provide baseline data for future work investigating perception of these same stimuli in children.

Audiovisual high variability phonetic training promotes second language lexical tone learning: An event-related potential study

This study investigated the efficacy of a modified high variability phonetic training (HVPT) protocol in second language learning. The target Mandarin lexical tones in the training stimuli were acoustically exaggerated at four levels in terms of duration, pitch range, and pitch contour. Seven audiovisual perceptual training sessions were designed to deliver the training stimuli adaptively based on the listener's identification score. Pre- and post-tests used behavioral identification and discrimination tasks with natural speech, synthetic speech, and non-speech control stimuli. ERP experiments were also conducted with synthetic speech stimuli in a passive listening oddball paradigm. A total of 24 adult monolingual American English speakers were randomly assigned to the training group and control group. Behavioral data showed significant improvement in identifying the four lexical tones in the trainees but not in the controls. There was also training-induced enhancement of categorical perception of the lexical tones for the synthetic speech stimuli. Posttest versus pretest comparison in the trainees showed an increased mismatch negativity (MMN) response with decreased MMN peak latency for the across-category lexical tone stimuli. Collectively, the results demonstrate fundamental neural sensitivity changes at the pre-attentive level underlying training-induced behavioral identification and discrimination changes in second language learners.

Auditory Sensory Gating of Speech and Nonspeech Stimuli.

Purpose Auditory sensory gating is a neural measure of inhibition and is typically measured with a click or tonal stimulus. This electrophysiological study examined if stimulus characteristics and the use of speech stimuli affected auditory sensory gating indices. Method Auditory event-related potentials were elicited using natural speech, synthetic speech, and nonspeech stimuli in a traditional auditory gating paradigm in 15 adult listeners with normal hearing. Cortical responses were recorded at 64 electrode sites, and peak amplitudes and latencies to the different stimuli were extracted. Individual data were analyzed using repeated-measures analysis of variance. Results Significant gating of P1-N1-P2 peaks was observed for all stimulus types. N1-P2 cortical responses were affected by stimulus type, with significantly less neural inhibition of the P2 response observed for natural speech compared to nonspeech and synthetic speech. Conclusions Auditory sensory gating responses can be measured using speech and nonspeech stimuli in listeners with normal hearing. The results of the study indicate the amount of gating and neural inhibition observed is affected by the spectrotemporal characteristics of the stimuli used to evoke the neural responses.

Bimodal Benefits Revealed by Categorical Perception of Lexical Tones in Mandarin-Speaking Kindergarteners With a Cochlear Implant and a Contralateral Hearing Aid.

Purpose Pitch reception poses challenges for individuals with cochlear implants (CIs), and adding a hearing aid (HA) in the nonimplanted ear is potentially beneficial. The current study used fine-scale synthetic speech stimuli to investigate the bimodal benefit for lexical tone categorization in Mandarin-speaking kindergarteners using a CI and an HA in opposite ears. Method The data were collected from 16 participants who were required to complete two classical tasks for speech categorical perception (CP) with CI + HA device condition and CI alone condition. Linear mixed-effects models were constructed to evaluate the identification and discrimination scores across different device conditions. Results The bimodal kindergarteners showed CP for the continuum varying from Mandarin Tone 1 and Tone 2. Moreover, the additional acoustic information from the contralateral HA contributes to improved lexical tone categorization, with a steeper slope, a higher discrimination score of between-category stimuli pair, and an improved peakedness score (i.e., an increased benefit magnitude for discriminations of between-category over within-category pairs) for the CI + HA condition than the CI alone condition. The bimodal kindergarteners with better residual hearing thresholds at 250 Hz level in the nonimplanted ear could perceive lexical tones more categorically. Conclusion The enhanced CP results with bimodal listening provide clear evidence for the clinical practice to fit a contralateral HA in the nonimplanted ear in kindergarteners with unilateral CIs with direct benefits from the low-frequency acoustic hearing.

Measuring Speech Perception Using the Wide-Range Acoustic Accuracy Scale: Preliminary Findings

Purpose Speech perception requires individuals to hear and differentiate acoustic signals integral to effective communication. Measuring speech perception in children is challenging because speech perception methodology typically requires lengthy experiments that may fatigue children, resulting in limited knowledge of developmental perceptual skills. In this study, we used an adaptive tracking measure along with a wide range of acoustic stimuli to explore how adults, typically developing (TD) children, and children with speech sound disorder (SSD) perceive small acoustic differences in synthetic speech stimuli. Method Twenty-four adults, 15 TD children, and 15 children with SSD between the ages of 7;0–14;0 (years;months) were administered a newly developed perceptual assessment, the Wide-Range Acoustic Accuracy Scale, to determine the just-noticeable difference in discrimination for three separate syllable contrasts. Each syllable contrast varied along a single acoustic parameter: formant transition duration for /bɑ/–/wɑ/, F3 onset frequency for /dɑ/–/ɡɑ/, and F3–F2 distance for /rɑ/–/wɑ/. Results Findings revealed that adults and TD children did not differ in their discrimination of any syllable contrast, but adults significantly differed from SSD children on all syllable contrasts. TD children and children with SSD differed only on the /rɑ/–/wɑ/ contrast. Conclusions Children with SSD demonstrate less accurate and more variable perception skills relative to adults and TD children for /bɑ/–/wɑ/, /dɑ/–/ɡɑ/, and /rɑ/–/wɑ/ syllable contrasts. Clinical implications of the utility of the Wide-Range Acoustic Accuracy Scale are discussed.

Lexical processing depends on sublexical processing: Evidence from the visual world paradigm and aphasia.

Some early studies of people with aphasia reported strikingly better performance on lexical than on sublexical speech perception tasks. These findings challenged the claim that lexical processing depends on sublexical processing and suggested that acoustic information could be mapped directly to lexical representations. However, Dial and Martin (Neuropsychologia 96: 192-212, 2017) argued that these studies failed to match the discriminability of targets and distractors for the sublexical and lexical stimuli and showed that when using closely matched tasks with natural speech tokens, no patient performed substantially better at the lexical than at the sublexical processing task. In the current study, we sought to provide converging evidence for the dependence of lexical on sublexical processing by examining the perception of synthetic speech stimuli varied on a voice-onset time continuum using eye-tracking methodology, which is sensitive to online speech perception processes. Eight individuals with aphasia and ten age-matched controls completed two visual world paradigm tasks: phoneme (sublexical) and word (lexical) identification. For both identification and eye-movement data, strong correlations were observed between the sublexical and lexical tasks. Critically, no patient within the control range on the lexical task was impaired on the sublexical task. Overall, the current study supports the claim that lexical processing depends on sublexical processing. Implications for inferring deficits in people with aphasia and the use of sublexical tasks to assess sublexical processing are also discussed.

Absence of P300 Amplitude Laterality in Persons Who Stutter

Objective: This study investigated differences in P300 auditory-evoked potentials between Persons Who Stutter (PWS) and Persons Who Do Not Stutter (PWNS). Methods: Responses to tonal and synthetic speech stimuli were recorded from electrodes over the right and left parietal locations and amplitude and latency measures were analyzed. The speech stimuli /bA/-/pA/ and /bA/-/dA/ were two sets of syllables contrasting across and within categorical boundaries on the first phoneme. Results: PWS demonstrated different inter-hemispheric activity in response to the stimuli than PWNS. Whereas PWNS had significantly greater P300 amplitudes over the left than the right parietal location, PWS did not demonstrate significantly greater P300 amplitudes over either location. Conclusion: This lack of laterality for PWS is discussed in the light of cerebral dominance theories and speech development.

The role of voice onset time in the perception of English voicing contrasts in children’s speech

The perception of phonemic voicing distinctions is typically attributed mainly to voice onset time (VOT). Most previous research focusing on voicing discrimination used synthetic speech stimuli varying in VOT. Results of this work suggest that adult listeners show stable crossover boundaries in the 20-35 ms range. However, no research has evaluated how VOT values correspond to adult labeling regardless of whether the intended target is voiced or voiceless. The present study obtained adult labeling data for natural productions of bilabial and alveolar pairs produced by 2-3-year-old monolingual, English-speaking children. Randomized stimuli were presented twice to 20 listeners resulting in 5,760 rated stimuli. Stimuli were categorized as short VOT ( 35 ms). The findings show that listeners demonstrated the greatest accuracy for bilabials (>99%) and alveolars (>92%) when the target matched the expected VOT duration (i.e., doe → short lag and toe → long lag). As...

Acoustic Cue Weighting by Adults with Cochlear Implants: A Mismatch Negativity Study.

Formant rise time (FRT) and amplitude rise time (ART) are acoustic cues that inform phonetic identity. FRT represents the rate of transition of the formant(s) to a steady state, while ART represents the rate at which the sound reaches its peak amplitude. Normal-hearing (NH) native English speakers weight FRT more than ART during the perceptual labeling of the /ba/-/wa/ contrast. This weighting strategy is reflected neurophysiologically in the magnitude of the mismatch negativity (MMN)-MMN is larger during the FRT than the ART distinction. The present study examined the neurophysiological basis of acoustic cue weighting in adult cochlear implant (CI) listeners using the MMN design. It was hypothesized that individuals with CIs who weight ART more in behavioral labeling (ART users) would show larger MMNs during the ART than the FRT contrast, and the opposite would be seen for FRT users. Electroencephalography was recorded while 20 adults with CIs listened passively to combinations of 3 synthetic speech stimuli: a /ba/ with /ba/-like FRT and ART; a /wa/ with /wa/-like FRT and ART; and a /ba/ stimulus with /ba/-like FRT and /wa/-like ART. The MMN response was elicited during the FRT contrast by having participants passively listen to a train of /wa/ stimuli interrupted occasionally by /ba/ stimuli, and vice versa. For the ART contrast, the same procedure was implemented using the /ba/ and /ba/ stimuli. Both ART and FRT users with CIs elicited MMNs that were equal in magnitudes during FRT and ART contrasts, with the exception that FRT users exhibited MMNs for ART and FRT contrasts that were temporally segregated. That is, their MMNs occurred significantly earlier during the ART contrast (~100 msec following sound onset) than during the FRT contrast (~200 msec). In contrast, the MMNs for ART users of both contrasts occurred later and were not significantly separable in time (~230 msec). Interestingly, this temporal segregation observed in FRT users is consistent with the MMN behavior in NH listeners. Results suggest that listeners with CIs who learn to classify phonemes based on formant dynamics, consistent with NH listeners, develop a strategy similar to NH listeners, in which the organization of the amplitude and spectral representations of phonemes in auditory memory are temporally segregated.

Adults' perceptual voicing boundaries of 2-year-olds' citation form speech

One way that speakers distinguish between phonemic categories is through voicing, frequently measured using voice onset time (VOT). Much perceptual research on voicing identification and discrimination has used synthetic speech stimuli varying in VOT. Results from adult listeners typically show stable crossover regions in the 20–35 ms range. Subsequent work, however, reveals that listeners' VOT boundaries vary with speech rate; further, an extensive history of research into vowel perception indicates that listeners normalize across vocal tract sizes. These considerations lead to the possibility that adult voicing boundaries may differ between the speech of adults vs. children, since children have slower speech rates and smaller vocal tracts. The present study obtained adult discrimination data for natural productions of bilabial and alveolar cognate pairs produced by 2–3-year-old monolingual, English-speaking children. Randomized stimuli were presented twice to 20 listeners resulting in 4,000 rated stimuli per category. The findings show 50% crossover points for VOT values at 28 ms for bilabials and 32 ms for alveolar phonemes. Such outcomes are consistent with past work based on adult data and suggest that mature listeners do not use substantially different perceptual criteria for judging voicing in children’s speech. Declaration of Interest Statement The authors have no financial or nonfinancial disclosures to report.

Evaluation of non-linear frequency compression hearing aids using speech P1-cortical auditory evoked potential

Objective: To investigate the potential effects of frequency lowering technology on outcome measures of hearing aid efficacy. The detection of mid- and high-frequency syllables in children with sensorineural hearing loss (SNHL) fitted with non-linear frequency compression (NLFC) hearing aids was studied using speech P1 cortical auditory evoked potentials (CAEP). Study design: Thirty Arabic speaking children with bilateral high frequency SNH and with a history of regular binaural hearing aid use were included. All children were fitted with binaural Phonak Naida III UP with a NLFC feature. Verification of NLFC was achieved through aided sound field testing and aided speech P1-CAEP recordings. Aided P1-CAEPs were elicited using synthetic speech stimuli ‘da’ and ‘ga’. Fifteen age-matched normal hearing children served as a control group to provide a reference of typically maturing CAEPs without the influence of hearing impairment. Results: NLFC improved aided thresholds in the mid and high frequencies. No statistically significant difference existed between the control and study group in their CAEP responses to the ‘ga’ stimulus in both NLFC-disabled/enabled conditions. The ‘da’ stimulus elicited P1-CAEP in only 27% of the study group with the NLFC disabled condition; this increased to 83% with activation of NLFC. The P1-CAEP latency of the study group was prolonged compared to children of the control group for both stimuli. The presence of P1-CAEP to both ‘ga’ and ‘da’ stimuli was significantly negatively correlated with the age of the child, duration of hearing loss, and duration of hearing aid use. Conclusion: The NLFC significantly improved the audibility of high frequency sounds for children with severe high frequency SNHL. Speech P1-CAEP can be used as an objective validation tool in children to evaluate the benefit from NLFC especially when behavioural aided thresholds are difficult to obtain.

Speech experience and cue trading in budgerigars

The current project investigates how experience with human speech can influence speech perception in budgerigars. Budgerigars are vocal mimics and speech exposure can be tightly controlled in a laboratory setting. The data collected include behavioral responses from 30 budgerigars, tested using a cue-trading paradigm with synthetic speech stimuli. Prior to testing, the birds were divided into three exposure groups: Passive speech exposure (regular exposure to human speech), no speech exposure (completely isolated), and speech-trained (using the Model-Rival Method). After the exposure period, all budgerigars were tested using operant conditioning procedures. Birds were trained to peck keys in response to hearing different synthetic speech sounds that began with either “d” or “t.” Sounds varied in VOT and in the frequency of the first formant. Once training performance reached 80% on the series endpoints, budgerigars were presented with the entire series, including ambiguous sounds. The responses on these trials were used to determine which speech cues the birds use, if cue trading behavior was present, and whether speech exposure had an influence on perception. Preliminary data suggest experience with speech sounds is not necessary for cue trading by budgerigars.

Testing the reliability of Grade, Roughness and Breathiness scores by means of synthetic speech stimuli

This article describes a synthesizer of disordered voices and reports a test of the reliability of Grade, Roughness, and Breathiness scores assigned to synthetic stimuli by eight expert listeners in two sessions. Speech stimuli [a], [i], [u], [ai], and [ia] were synthesized with three values of vocal frequency and four levels of vocal jitter and pulsatile additive noise each. The agreement and correlation of scores assigned by the same rater in different sessions, or by different raters in the same session, accord with published data. Only a small part of the variance of the arithmetic differences between the scores that are assigned to the same stimulus is explained by the stimuli properties. The conclusion is that differences between scores that are assigned to the same stimulus are not attributable to biases of individual raters; such biases would shift all the scores assigned on a scale, and the shift would be interpretable in terms of the properties of the stimuli.

Amplitude Rise Time Does Not Cue the /bɑ/–/wɑ/ Contrast for Adults or Children

Previous research has demonstrated that children weight the acoustic cues to many phonemic decisions differently than do adults and gradually shift those strategies as they gain language experience. However, that research has focused on spectral and duration cues rather than on amplitude cues. In the current study, the authors examined amplitude rise time (ART; an amplitude cue) and formant rise time (FRT; a spectral cue) in the /b/-/w/ manner contrast for adults and children, and related those speech decisions to outcomes of nonspeech discrimination tasks. Twenty adults and 30 children (ages 4-5 years) labeled natural and synthetic speech stimuli manipulated to vary ARTs and FRTs, and discriminated nonspeech analogs that varied only by ART in an AX paradigm. Three primary results were obtained. First, listeners in both age groups based speech labeling judgments on FRT, not on ART. Second, the fundamental frequency of the natural speech samples did not influence labeling judgments. Third, discrimination performance for the nonspeech stimuli did not predict how listeners would perform with the speech stimuli. Even though both adults and children are sensitive to ART, it was not weighted in phonemic judgments by these typical listeners.

Functional ear (a)symmetry in brainstem neural activity relevant to encoding of voice pitch: A precursor for hemispheric specialization?

Pitch processing is lateralized to the right hemisphere; linguistic pitch is further mediated by left cortical areas. This experiment investigates whether ear asymmetries vary in brainstem representation of pitch depending on linguistic status. Brainstem frequency-following responses (FFRs) were elicited by monaural stimulation of the left and right ear of 15 native speakers of Mandarin Chinese using two synthetic speech stimuli that differ in linguistic status of tone. One represented a native lexical tone (Tone 2: T2); the other, T2′, a nonnative variant in which the pitch contour was a mirror image of T2 with the same starting and ending frequencies. Two 40-ms portions of f 0 contours were selected in order to compare two regions (R1, early; R2 late) differing in pitch acceleration rate and perceptual saliency. In R2, linguistic status effects revealed that T2 exhibited a larger degree of FFR rightward ear asymmetry as reflected in f 0 amplitude relative to T2′. Relative to midline (ear asymmetry = 0), the only ear asymmetry reaching significance was that favoring left ear stimulation elicited by T2′. By left- and right-ear stimulation separately, FFRs elicited by T2 were larger than T2′ in the right ear only. Within T2′, FFRs elicited by the earlier region were larger than the later in both ears. Within T2, no significant differences in FFRS were observed between regions in either ear. Collectively, these findings support the idea that origins of cortical processing preferences for perceptually-salient portions of pitch are rooted in early, preattentive stages of processing in the brainstem.

The Perception of Voice Onset Time: An fMRI Investigation of Phonetic Category Structure

This study explored the neural systems underlying the perception of phonetic category structure by investigating the perception of a voice onset time (VOT) continuum in a phonetic categorization task. Stimuli consisted of five synthetic speech stimuli which ranged in VOT from 0 msec ([da]) to 40 msec ([ta]). Results from 12 subjects showed that the neural system is sensitive to VOT differences of 10 msec and that details of phonetic category structure are retained throughout the phonetic processing stream. Both the left inferior frontal gyrus (IFG) and cingulate showed graded activation as a function of category membership with increasing activation as stimuli approached the phonetic category boundary. These results are consistent with the view that the left IFG is involved in phonetic decision processes, with the extent of activation influenced by increased resources devoted to resolving phonetic category membership and/or selecting between competing phonetic categories. Activation patterns in the cingulate suggest that it is sensitive to stimulus difficulty and resolving response conflict. In contrast, activation in the posterior left middle temporal gyrus and the left angular gyrus showed modulation of activation only to the "best fit" of the phonetic category, suggesting that these areas are involved in mapping sound structure to its phonetic representation. The superior temporal gyrus (STG) bilaterally showed weaker sensitivity to the differences in phonetic category structure, providing further evidence that the STG is involved in the early analysis of the sensory properties of speech.

Effects of vocalic duration and first formant offset on final voicing judgments by children and adults (L)

Developmental research into relative weighting of vocalic duration and spectral properties in final voicing perception has produced different results, depending on whether natural or synthetic speech stimuli have been used and how spectral properties have been manipulated. This paper reports developmental data for final voicing using natural stimuli waveform edited for vocalic duration and resynthesized for first formant offset. Results indicate that in perception of final voicing there are adult-child differences in weighting of vocalic duration and first formant offset, consistent with previous findings for vocalic duration and spectral properties more generally [S. Nittrouer, J. Acoust. Soc. Am. 115, 1777–1790 (2004)].

Effect of age on silent gap discrimination in synthetic speech stimuli.

The difficulty that older listeners experience understanding conversational speech may be related to their limited ability to use information present in the silent intervals (i.e., temporal gaps) between dynamic speech sounds. When temporal gaps are present between nonspeech stimuli that are spectrally invariant (e.g., noise bands or sinusoids), older listeners are less able to resolve temporal gaps than are younger listeners. It has also been demonstrated that temporal gap perception deteriorates as the frequency difference between the sounds bordering the silent gap increases, and this effect becomes more pronounced with age (J. Lister, J. Besing, and J. Koehnke, 2002; J. Lister, J. Koehnke, and J. Besing, 2000). In this study, the effect of age on the ability to discriminate temporal gaps in dynamic stimuli (i.e., changing in frequency and duration over time) was measured in a gap duration discrimination (GDD) task. The participants were two groups of listeners with normal hearing sensitivity through at least 4000 Hz: (a) ages 21-38 years and (b) ages 50-72 years. Stimuli simulated the frequency characteristics of 1 consonant (/s/), a steady-state vowel (/a/), a weak diphthong (/eI/), and a voiced bilabial plosive (/burst/) in 6 combinations: (a) /s-a/, (b) /s-eI/, (c) /a-a/, (d) /eI-eI/, (e) /burst-a/, and (f) /burst-eI/. For each of the 6 phoneme combinations, 2 conditions of stimulus duration were used: (a) fixed, meaning that the durations of leading and trailing noises were fixed at values typical for the speech sounds being simulated, and (b) random, meaning that duration varied randomly within a range acceptable for accurate perception of the speech contrasts. Gap duration difference limens (GDDLs) were significantly larger for the older listeners than for younger listeners. For both groups, GDDLs were poorer for the spectrally dynamic marker pairs (e.g., /burst-eI/) than for the marker pairs that were relatively stable in frequency over time (/a-a/). GDD performance also was poorer for the random conditionthan for the fixed condition. Listener age and hearing sensitivity were significantly correlated, and age was not significantly correlated with GDD when controlling for hearing sensitivity. The authors conclude that temporal resolution (as measured by gap discrimination) is affected by age, stimulus complexity, and, perhaps, by hearing sensitivity in a speech context.