Deficits In Temporal Resolution Research Articles

Investigating Auditory Spectral and Temporal Resolution Deficits in Children with Reading Difficulties.

The types of reading difficulties experienced by children are highly heterogeneous in nature, which makes diagnosis and intervention difficult. Over the past 30 years, there has been much debate over the cause of dyslexia. The two most popular theories for phonological deficits in dyslexia are the rate-processing constraint hypothesis, which relates to short timescale processing, and the temporal sampling framework hypothesis, which relates to longer timescale processing. To investigate the relationship between sublexical (i.e., nonword) reading skills and auditory spectral and temporal resolution patterns in children with reading difficulties using the Phoneme Identification Test (PIT) and the Parsing Syllable Envelopes Test (ParSE). These tests were developed to assess the rate-processing constraint and the temporal sampling framework hypotheses, respectively. We hypothesized that a proportion of children who have sublexical reading difficulties may have an underlying auditory-resolution deficit which may impact their ability to form letter-sound correspondences. We predicted that children's sublexical reading difficulties may not be explained by one theory, but instead that both theories may describe different types of reading difficulties found in different children. We also hypothesized that children with lexical (i.e., irregular word) reading difficulties but intact sublexical reading skills would not show atypical results on PIT or ParSE. Behavioral experimental clinical study with children who have reading difficulties. Sixteen children with nonword, irregular word, or mixed reading difficulties diagnosed by the Castles and Coltheart Test 2. Children completed a test battery consisting of a hearing screen and tests of reading, auditory resolution, phonological awareness, attention, spatial auditory processing, auditory memory, and intelligence. Categorization and correlational analyses were conducted. All four children with a pure sublexical reading deficit also had an auditory-resolution deficit. Four of seven children with a mixed reading deficit had an auditory-resolution deficit. Only one of five children with a lexical reading deficit had an auditory-resolution deficit. Individual children's specific deficits were related to either rate processing (n = 5) or temporal sampling (n = 4), but never both. Children's nonword reading scores were strongly correlated with their performance on the PIT in noise, but not with the PIT in quiet or the ParSE. Children's irregular word scores were not significantly correlated with their performance on the PIT in quiet or in noise, or the ParSE, as hypothesized. Strong correlations were also found between children's nonword scores and their phonological awareness scores. The results of this study suggest that neither the rate-processing hypothesis nor the temporal sampling framework is the single cause of reading difficulties in children. Instead, both of these hypotheses are likely to account for different types of reading deficits found in children. This is an important finding as the specific mechanisms driving different reading impairments must be identified to create tools to better diagnose and treat different types of reading difficulties. Further investigation of the PIT and ParSE as potential diagnostic tools for specific auditory-resolution-based reading difficulties in a larger group of children is currently underway.

Detection of Gap and Modulations: Auditory Temporal Resolution Deficits in Adults Who Stutter

Background: Recent models of speech production suggest a link between speech production and perception. Persons with stuttering are known to have deficits in sensorimotor timing and exhibit auditory processing problems. Most of the earlier studies have focused on assessing temporal ordering in adults who stutter (AWS), but limited attempts have been made to document temporal resolution abilities in AWS. Methods: A group of 16 AWS and 16 age- and gender-matched adults who do not stutter (AWNS) were recruited for the study. Temporal resolution abilities were assessed using the Gap Detection Test and temporal modulation transfer function (TMTF). Results: The results revealed significant differences in TMTF between AWS and AWNS, but no differences were found in the gap detection thresholds. Conclusions: Results suggest that the sensory representations of the temporal modulations are compromised in AWS, which may contribute to the programming of rhythmic movements during speech planning.

The Influence of Hearing Aid Gain on Gap-Detection Thresholds for Children and Adults With Hearing Loss.

The objective of this experiment was to examine the contributions of audibility to the ability to perceive a gap in noise for children and adults. Sensorineural hearing loss (SNHL) in adulthood is associated with a deficit in gap detection. It is well known that reduced audibility in adult listeners with SNHL contributes to this deficit; however, it is unclear the extent to which hearing aid amplification can restore gap-detection thresholds, and the effect of childhood SNHL on gap-detection thresholds have not been described. For adults, it was hypothesized that restoring the dynamic range of hearing for listeners with SNHL would lead to approximately normal gap-detection thresholds. Children with normal hearing (NH) exhibit poorer gap-detection thresholds than adults. Because of their hearing loss, children with SNHL have less auditory experience than their peers with NH. Yet, it is unknown the extent to which auditory experience impacts their ability to perceive gaps in noise. Even with the provision of amplification, it was hypothesized that children with SNHL would show a deficit in gap detection, relative to their peers with normal hearing, because of reduced auditory experience. The ability to detect a silent interval in noise was tested by adapting the stimulus level required for detection of gap durations between 3 and 20 ms for adults and children with and without SNHL. Stimulus-level thresholds were measured for participants with SNHL without amplification and with two prescriptive procedures-the adult and child versions of the desired sensation level i/o program-using a hearing aid simulator. The child version better restored the normal dynamic range than the adult version. Adults and children with NH were tested without amplification. When fitted using the procedure that best restored the dynamic range, adults with SNHL had stimulus-level thresholds similar to those of adults with normal hearing. Compared to the children with NH, the children with SNHL required a higher stimulus level to detect a 5-ms gap, despite having used the procedure that better restored the normal dynamic range of hearing. Otherwise, the two groups of children had similar stimulus-level thresholds. These findings suggest that apparent deficits in temporal resolution, as measured using stimulus-level thresholds for the detection of gaps, are dependent on age and audibility. These novel results indicate that childhood SNHL may impair temporal resolution as measured by stimulus-level thresholds for the detection of a gap in noise. This work has implications for understanding the effects of amplification on the ability to perceive temporal cues in speech.

The Relative Contributions of Temporal Envelope and Fine Structure to Mandarin Lexical Tone Perception in Auditory Neuropathy Spectrum Disorder.

Previous studies have demonstrated that temporal envelope (E) is sufficient for speech perception, while fine structure (FS) is important for pitch perception for normal-hearing (NH) listeners. Listeners with sensorineural hearing loss (SNHL) have an impaired ability to use FS in lexical tone perception due to the reduced frequency resolution. Listeners with auditory neuropathy spectrum disorder (ANSD) may have deficits in temporal resolution. Little is known about how such deficits may impact their ability to use E and FS to perceive lexical tone, and whether it is the deficit in temporal resolution or frequency resolution that may lead to more detrimental effects on FS processing in pitch perception. Three experiments were conducted in the present study. Experiment I used the "auditory chimera" technique to investigate how SNHL and ANSD listeners would achieve lexical tone recognition using either the E or the FS cues. Experiment II tested their frequency resolution as measured with their psychophysical tuning curves (PTCs). Experiment III tested their temporal resolution as measured with the temporal gap detection (TGD) threshold. The results showed that the SNHL listeners had reduced frequency selectivity, but intact temporal resolution ability, while the ANSD listeners had degraded temporal resolution ability, but intact frequency selectivity. In comparison with the SNHL listeners, the ANSD listeners had severely degraded ability to process the FS cues and thus their ability to perceive lexical tone mainly depended on the ability to use the E cues. These results suggested that, in comparison with the detrimental impact of the reduced frequency selectivity, the impaired temporal resolution may lead to more degraded FS processing in pitch perception.

The Role of Temporal Envelope and Fine Structure in Mandarin Lexical Tone Perception in Auditory Neuropathy Spectrum Disorder.

Temporal information in a signal can be partitioned into temporal envelope (E) and fine structure (FS). Fine structure is important for lexical tone perception for normal-hearing (NH) listeners, and listeners with sensorineural hearing loss (SNHL) have an impaired ability to use FS in lexical tone perception due to the reduced frequency resolution. The present study was aimed to assess which of the acoustic aspects (E or FS) played a more important role in lexical tone perception in subjects with auditory neuropathy spectrum disorder (ANSD) and to determine whether it was the deficit in temporal resolution or frequency resolution that might lead to more detrimental effects on FS processing in pitch perception. Fifty-eight native Mandarin Chinese-speaking subjects (27 with ANSD, 16 with SNHL, and 15 with NH) were assessed for (1) their ability to recognize lexical tones using acoustic E or FS cues with the “auditory chimera” technique, (2) temporal resolution as measured with temporal gap detection (TGD) threshold, and (3) frequency resolution as measured with the Q10dB values of the psychophysical tuning curves. Overall, 26.5%, 60.2%, and 92.1% of lexical tone responses were consistent with FS cues for tone perception for listeners with ANSD, SNHL, and NH, respectively. The mean TGD threshold was significantly higher for listeners with ANSD (11.9 ms) than for SNHL (4.0 ms; p < 0.001) and NH (3.9 ms; p < 0.001) listeners, with no significant difference between SNHL and NH listeners. In contrast, the mean Q10dB for listeners with SNHL (1.8±0.4) was significantly lower than that for ANSD (3.5±1.0; p < 0.001) and NH (3.4±0.9; p < 0.001) listeners, with no significant difference between ANSD and NH listeners. These results suggest that reduced temporal resolution, as opposed to reduced frequency selectivity, in ANSD subjects leads to greater degradation of FS processing for pitch perception.

A setup for simultaneous measurement of electrophysiological and psychometric temporal encoding in the auditory system

BackgroundSimultaneous assessment of psychometric tasks and electrophysiological recordings is challenging because each requires specific technical and physiological preconditions.Electrophysiological recordings require a comparatively long test time duration to gain sufficient signal-to-noise ratios, whereas test duration of psychometric measurements should be limited to prevent challenges to the attention of the subject. In order to investigate immediate correlation between both measurements a method is described, which combines electrophysiological and psychometrical measurements in a single test procedure. The test may be applied to subjects with deficits in temporal resolution (e.g. auditory neuropathy spectrum disorder, ANSD). New methodAuditory steady state responses (ASSR) and a pitch discrimination task were combined in a single procedure. The setup employed two short-time ASSR sub-stimuli with different fixed modulation frequencies but same carrier frequencies (signal 1 and 2). Simultaneously to the recording of ASSR, the test subject had to determine the signal interval which generated the perception of higher pitch. ResultsThe developed setup was successfully tested by means of an artificial EEG signal and in one human subject. ASSR signal as well as pitch discrimination performance. Comparison with existing methodsTo our knowledge the presented method has not yet been described elsewhere. ConclusionsThe feasibility of a setup to simultaneously perform a pitch discrimination task and electrophysiological measurements was demonstrated for the first time. The method provides the facility to apply sinusoidal amplitude modulated stimuli (SAM) with jittered modulation period lengths.

No Evidence for Prolonged Visible Persistence in Patients with Schizophrenia

BackgroundTemporal visual processing is strongly deteriorated in patients with schizophrenia. For example, the interval required between a visual stimulus and a subsequent mask has to be much longer in schizophrenic patients than in healthy controls. We investigated whether this deficit in temporal resolution is accompanied by prolonged visual persistence and/or deficient temporal precision (temporal asynchrony perception).Methodology/Principal FindingsWe investigated visual persistence in three experiments. In the first, measuring temporal processing by so-called backward masking, prolonged visible persistence is supposed to decrease performance. In the second experiment, requiring temporal integration, prolonged persistence is supposed to improve performance. In the third experiment, we investigated asynchrony detection, as another measure of temporal resolution. Eighteen patients with schizophrenia and 15 healthy controls participated. Asynchrony detection was intact in the patients. However, patients' performance was inferior compared to healthy controls in the first two experiments. Hence, temporal processing in schizophrenic patients is indeed significantly impaired but this impairment is not caused by prolonged temporal integration.Conclusions/SignificanceOur results argue against a generally prolonged visual persistence in patients with schizophrenia. Together with the preserved ability of patients, to detect temporal asynchronies in permanently presented stimuli, the results indicate a more specific deficit in temporal processing of schizophrenic patients.

The Potential Role of the cABR in Assessment and Management of Hearing Impairment

Hearing aid technology has improved dramatically in the last decade, especially in the ability to adaptively respond to dynamic aspects of background noise. Despite these advancements, however, hearing aid users continue to report difficulty hearing in background noise and having trouble adjusting to amplified sound quality. These difficulties may arise in part from current approaches to hearing aid fittings, which largely focus on increased audibility and management of environmental noise. These approaches do not take into account the fact that sound is processed all along the auditory system from the cochlea to the auditory cortex. Older adults represent the largest group of hearing aid wearers; yet older adults are known to have deficits in temporal resolution in the central auditory system. Here we review evidence that supports the use of the auditory brainstem response to complex sounds (cABR) in the assessment of hearing-in-noise difficulties and auditory training efficacy in older adults.

Temporal resolution deficits in patients with refractory complex partial seizures and mesial temporal sclerosis (MTS)

We studied the temporal resolution ability in patients with refractory complex partial seizures and mesial temporal sclerosis (MTS) using Gaps-In-Noise (GIN) test in a prospective cross-sectional study. Thirteen patients with right MTS (age: 31±7.67years; M:F=8:5) and 13 patients with left MTS (age: 25.76±8.26years; M:F=9:4) having normal hearing and mini-mental state examination (MMSE) score of >23/30 were recruited. Fifty healthy volunteers (26.3±5.17years; M:F=28:22) formed the control group. Gaps-In-Noise test demonstrated impaired temporal resolution: 69.2% of patients with right MTS (RMTS) and 76.9% of patients with left MTS (LMTS) had abnormal scores in the right ear for gap detection threshold (GDT) measure. Similarly, 53.8% of patients in the RMTS group and 76.9% of patients in the LMTS group had abnormal scores in the left ear. In percentage of correct identification (PCI), 46.1% of patients with RMTS and 69.2% of patients with LMTS had poorer scores in the right ear, whereas 46.1% of patients with RMTS and 61.5% of patients with LMTS had poorer scores in the left ear. Both patient groups, viz., RMTS and LMTS, demonstrated bilateral temporal resolution deficits.

Emotional cues enhance the attentional effects on spatial and temporal resolution

In the present study, we demonstrated that the emotional significance of a spatial cue enhances the effect of covert attention on spatial and temporal resolution (i.e., our ability to discriminate small spatial details and fast temporal flicker). Our results indicated that fearful face cues, as compared with neutral face cues, enhanced the attentional benefits in spatial resolution but also enhanced the attentional deficits in temporal resolution. Furthermore, we observed that the overall magnitudes of individuals’ attentional effects correlated strongly with the magnitude of the emotion × attention interaction effect. Combined, these findings provide strong support for the idea that emotion enhances the strength of a cue’s attentional response.

GIN (Gaps-In-Noise) Performance in the Pediatric Population

The recently developed Gaps-In-Noise (GIN) test has provided a new diagnostic tool for the detection of temporal resolution deficits. Previous reports indicate that the GIN is a relatively sensitive tool for the diagnosis of central auditory processing disorder ([C]APD) in adult populations. The purpose of the present study was to determine the feasibility of the GIN test in the pediatric population. This was a prospective pseudorandomized investigation. This investigation involved administration of the GIN to 72 participants divided into six groups of normal children ranging from 7 through 18 years of age. The approximate GIN threshold (the shortest gap duration for which at least four of six gaps were correctly identified) served as the dependent variable. Results were analyzed using an ANOVA to examine between- and within-group differences. No statistically significant differences were seen in GIN thresholds among age groups. In addition, within group analysis yielded no statistically significant differences between ears within each age group. No developmental effect was seen in GIN thresholds between the ages of 7 and 18 years. Children as young as age 7 are able to complete the GIN with no significant difficulty and perform at levels commensurate with normal adults. The absence of ear differences suggests that temporal resolution as measured by the GIN is an auditory process that develops relatively early and symmetrically (i.e., no laterality or ear dominance effects). The GIN procedure appears to be a feasible measure of temporal resolution in both pediatric and adult populations.

Auditory Brainstem Correlates of Perceptual Timing Deficits

Children with language-based learning problems often exhibit pronounced speech perception difficulties. Specifically, these children have increased difficulty separating brief sounds occurring in rapid succession (temporal resolution). The purpose of this study was to better understand the consequences of auditory temporal resolution deficits from the perspective of the neural encoding of speech. The findings provide evidence that sensory processes relevant to cognition take place at much earlier levels than traditionally believed. Thresholds from a psychophysical backward masking task were used to divide children into groups with good and poor temporal resolution. Speech-evoked brainstem responses were analyzed across groups to measure the neural integrity of stimulus-time mechanisms. Results suggest that children with poor temporal resolution do not have an overall neural processing deficit, but rather a deficit specific to the encoding of certain acoustic cues in speech. Speech understanding relies on the ability to attach meaning to rapidly fluctuating changes of both the temporal and spectral information found in consonants and vowels. For this to happen properly, the auditory system must first accurately encode these time-varying acoustic cues. Speech perception difficulties that often co-occur in children with poor temporal resolution may originate as a neural encoding deficit in structures as early as the auditory brainstem. Thus, speech-evoked brainstem responses are a biological marker for auditory temporal processing ability.

Effects of Age and Hearing Loss on Gap Detection and the Precedence Effect

Deficits in temporal resolution and/or the precedence effect may underlie part of the speech understanding difficulties experienced by older listeners in degraded acoustic environments. In a previous investigation, R. Roberts and J. Lister (2004) identified a positive correlation between measures of temporal resolution and the precedence effect, specifically across-channel gap detection (as measured dichotically) and fusion. Across-channel gap detection may also be measured using frequency-disparate markers. Thus, the present investigation was designed to determine if the relation is specific to dichotic gap detection or may generalize to all types of across-channel gap detection. Gap-detection thresholds (GDTs) for fixed-frequency and frequency-disparate markers and lag-burst thresholds (LBTs) were measured for 3 groups of listeners: young with normal hearing sensitivity (YNH), older with normal hearing sensitivity (ONH), and older with sensorineural hearing loss (OIH). Also included were conditions of diotic and dichotic GDT. Largest GDTs were measured for the frequency-disparate markers, whereas largest LBTs were measured for the fixed-frequency markers. ONH and OIH listeners exhibited larger frequency-disparate and dichotic GDTs than YNH listeners. Listener age and hearing loss appeared to influence temporal resolution for frequency-disparate and dichotic stimuli, which is potentially important for the resolution of timing cues in speech. Age and hearing loss did not significantly influence fusion as measured by LBTs. Within each participant group, most GDTs and LBTs were positively, but not significantly, correlated. For all participants combined, across-channel GDTs and LBTs were positively and significantly correlated. This suggests that the 2 tasks may rely on a common across-channel temporal mechanism.

Effects of Age and Hearing Loss on Gap Detection and the Precedence Effect

Older listeners with normal-hearing sensitivity and impaired-hearing sensitivity often demonstrate poorer-than-normal performance on tasks of speech understanding in noise and reverberation. Deficits in temporal resolution and in the precedence effect may underlie this difficulty. Temporal resolution is often studied by means of a gap-detection paradigm. This task is similar to binaural fusion paradigms used to measure the precedence effect. The purpose of this investigation was to determine if within-channel (measured with monotic and diotic gap detection) or across-channel (measured with dichotic gap detection) temporal resolution is related to fusion (measured with lag-burst thresholds; LBTs) under dichotic, anechoic, and reverberant conditions. Gap-detection thresholds (GDTs) and LBTs were measured by means of noise-burst stimuli for 3 groups of listeners: young adults with normal-hearing sensitivity (YNH), older adults with normal-hearing sensitivity (ONH), and older adults with impaired-hearing sensitivity (OIH). The GDTs indicated that across-channel temporal resolution is poorer than within-channel temporal resolution and that the effects of age and hearing loss are dependent on condition. Results for the fusion task indicated higher LBTs in reverberation than for the dichotic and anechoic conditions, regardless of group, and no effect of age or hearing loss for the nonreverberant conditions. However, higher LBTs were observed in the reverberant condition for the ONH listeners. Further, there was a correlation between across-channel temporal resolution and fusion in reverberation. Gap detection and fusion may not necessarily reflect the same underlying processes; however, across-channel gap detection may influence fusion under certain conditions (i.e., in reverberation).

The auditory basis of language impairments: temporal processing versus processing efficiency hypotheses

Claims have been made that language-impaired children have deficits processing rapidly presented or brief sensory information. These claims, known as the ‘temporal processing hypothesis’, are supported by demonstrations that language-impaired children have excess backward masking (BM). One explanation for these results is that BM is developmentally delayed in these children. However, little was known about how BM normally develops. Recently, we assessed BM in normally developing 6- and 8-year-old children and adults. Results showed that BM thresholds continue to improve over a comparatively protracted period (>10 years old). We also analysed reported deficits in BM in language-impaired and younger children in terms of a model of temporal resolution. This analysis suggests that poor processing efficiency, rather than deficits in temporal resolution, can account for these results. This ‘processing efficiency hypothesis’ was recently tested in our laboratory. This experiment measured BM as a function of delays between the tone and the noise in children and adults. Results supported the processing efficiency hypothesis, and suggested that reduced processing efficiency alone could account for differences between adults and children. These findings provide a new perspective on the mechanisms underlying communication disorders, and imply that remediation strategies should be directed towards improving processing efficiency, not temporal resolution.

The auditory basis of language impairments: temporal processing versus processing efficiency hypotheses

Claims have been made that language-impaired children have deficits processing rapidly presented or brief sensory information. These claims, known as the ‘temporal processing hypothesis’, are supported by demonstrations that language-impaired children have excess backward masking (BM). One explanation for these results is that BM is developmentally delayed in these children. However, little was known about how BM normally develops. Recently, we assessed BM in normally developing 6- and 8-year-old children and adults. Results showed that BM thresholds continue to improve over a comparatively protracted period (>10 years old). We also analysed reported deficits in BM in language-impaired and younger children, in terms of a model of temporal resolution. This analysis suggests that poor processing efficiency, rather than deficits in temporal resolution, can account for these results. This ‘processing efficiency hypothesis’ was recently tested in our laboratory. This experiment measured BM as a function of delays between the tone and the noise in children and adults. Results supported the processing efficiency hypothesis, and suggested that reduced processing efficiency alone could account for differences between adults and children. These findings provide a new perspective on the mechanisms underlying communication disorders, and imply that remediation strategies should be directed towards improving processing efficiency, not temporal resolution.

Age-related improvements in auditory temporal resolution in reading-impaired children.

Individuals with developmental dyslexia show impairments in processing that require precise timing of sensory events. Here, we show that in a test of auditory temporal acuity (a gap-detection task) children ages 6-9 years with dyslexia exhibited a significant deficit relative to age-matched controls. In contrast, this deficit was not observed in groups of older reading-impaired individuals (ages 10-11 years; 12-13 years) or in adults (ages 23-25 years). It appears, therefore, that early temporal resolution deficits in those with reading impairments may significantly ameliorate over time. However, the occurrence of an early deficit in temporal acuity may be antecedent to other language-related perceptual problems (particularly those related to phonological processing) that persist after the primary deficit has resolved. This result suggests that if remedial interventions targeted at temporal resolution deficits are to be effective, the early detection of the deficit and early application of the remedial programme is especially critical.

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.

Frequency and temporal resolution in elderly listeners with good and poor word recognition.

There is a subgroup of elderly listeners with hearing loss who can be characterized by exceptionally poor speech understanding. This study examined the hypothesis that the poor speech-understanding performance of some elderly listeners is associated with disproportionate deficits in temporal resolution and frequency resolution, especially for complex signals. Temporal resolution, as measured by gap detection, and frequency resolution, as measured by the critical ratio, were examined in older listeners with normal hearing, older listeners with hearing loss and good speech-recognition performance, and older listeners with hearing loss and poor speech-recognition performance. Listener performance was evaluated for simple and complex stimuli and for tasks of added complexity. In addition, syllable recognition was assessed in quiet and noise. The principal findings were that older listeners with hearing loss and poor word-recognition performance did not perform differently from older listeners with hearing loss and good word recognition on the temporal resolution measures nor on the spectral resolution measures for relatively simple stimuli. However, frequency resolution was compromised for listeners with poor word-recognition abilities when targets were presented in the context of complex signals. Group differences observed for syllable recognition in quiet were eliminated in the noise condition. Taken together, the findings support the hypothesis that unusual deficits in word-recognition performance among elderly listeners were associated with poor spectral resolution for complex signals.

Masking by harmonic complexes with different phase spectra in hearing-impaired listeners

At the last meeting, we showed that in normal-hearing listeners, masking effectiveness of harmonic complexes depends on the maskers’ phase spectra. Such masking differences are thought to partially reflect an interaction between the input waveform and phase characteristics of the normal auditory system. We have extended that work to explore masking by harmonic complexes in listeners with hearing impairment. The masker was a harmonic complex with equal-amplitude components, with phases selected according to scaled modifications of the Schroeder algorithm. Masking was measured for several different signal frequencies and levels. In contrast to normal-hearing listeners, most hearing-impaired listeners showed little change in masking for different phase selections. Some listeners did demonstrate masking differences, but the greatest reduction in masking occurred when the components had nearly equal phases (i.e., a highly modulated masker waveform). Apparently, in those listeners, the within-channel phase characteristic did not substantially alter the phase structure of the input stimulus, as is thought to occur in normal ears. In aggregate, these data suggest that sensorineural hearing loss is accompanied by deficits in temporal resolution, possibly involving changes in the phase characteristics of auditory channels. [Work supported by NIH DC00626.]