Independence of frequency channels in auditory temporal gap detection

Suprathreshold auditory processes in listeners with normal audiograms but extended high-frequency hearing lossa)

Hearing loss in the extended high-frequency (EHF) range (>8 kHz) is widespread among young normal-hearing adults and could have perceptual consequences such as difficulty understanding speech in noise. However, it is unclear how EHF hearing loss might affect basic psychoacoustic processes. The hypothesis that EHF hearing loss is associated with poorer auditory resolution in the standard frequencies was tested. Temporal resolution was characterized by amplitude modulation detection thresholds (AMDTs), and spectral resolution was characterized by frequency change detection thresholds (FCDTs). AMDTs and FCDTs were measured in adults with or without EHF loss but with normal clinical audiograms. AMDTs were measured with 0.5- and 4-kHz carrier frequencies; similarly, FCDTs were measured for 0.5- and 4-kHz base frequencies. AMDTs were significantly higher with the 4 kHz than the 0.5 kHz carrier, but there was no significant effect of EHF loss. There was no significant effect of EHF loss on FCDTs at 0.5 kHz; however, FCDTs were significantly higher at 4 kHz for listeners with than without EHF loss. This suggests that some aspects of auditory resolution in the standard audiometric frequency range may be compromised in listeners with EHF hearing loss despite having a normal audiogram.

Multi-feature mismatch negativity: How can reliable data be recorded in a short time?

OBJECTIVE

The aim of the study was to conduct multi-feature mismatch negativity (MMN) implementations and identify via a test-retest study the reliability of MMN responses obtained through a 5-stimulus version of the MMN paradigm. It was also aimed to identify a reliable MMN recording number by comparing the MMN responses obtained under conditions of ten and four recordings conditions while making the recording time shorter.

METHODS

Twenty-one healthy volunteers, aged between 18 and 36 years, were included in the study. A 5-stimulus version of the multi-feature MMN paradigm was presented to participants. Ten recordings were obtained for each participant under both test and retest conditions. The MATLAB program was utilized in the evaluation of MMN amplitude and latency. The Fz was chosen for the statistical analysis. Four of the ten recordings were chosen at random, and statistical analyses were performed again for those four recordings.

RESULTS

There was no statistically significant difference in amplitudes obtained from test and retest conditions with ten recordings. With four recordings, for frequency, intensity, duration, and gap deviants, there were no statistically significant differences between amplitudes obtained under test and retest conditions. However, there was a statistically significant difference between amplitudes of the location deviant. No statistically significant difference was observed among latencies under test-retest conditions with both ten and four recordings.

CONCLUSIONS

These findings demonstrate that MMN amplitudes could be used reliably as short-time evaluations with four recordings, but more recordings are required for MMN latencies. In terms of practicality, four recordings are more advantageous and comfortable for both clinicians and patients in MMN practice.

SIGNIFICANCE

When behavioral tests are required, MMN is regarded as an objective test that can be used reliably for adults, children, and infants who cannot be evaluated using behavioral methods. It is concluded that conditions with four recordings aremore advantageous and comfortable for both clinicians and patients in MMN practice.

Within- and across-frequency temporal processing and speech perception in cochlear implant users

OBJECTIVE

Cochlear implant (CI) recipient's speech perception performance is highly variable and is influenced by temporal processing abilities. Temporal processing is commonly assessed using a behavioral task that requires the participant to detect a silent gap with the pre- and post-gap stimuli of the same frequency (within-frequency gap detection) or of different frequencies (across-frequency gap detection). The purpose of the study was to evaluate behavioral and electrophysiological measures of within- and across-frequency temporal processing and their correlations with speech perception performance in CI users.

DESIGN

Participants included 11 post-lingually deafened adult CI users (n = 15 ears; Mean Age = 50.2 yrs) and 11 age- and gender-matched normal hearing (NH) individuals (n = 15 ears; Mean Age = 49.0 yrs). Speech perception was assessed with Consonant-Nucleus-Consonant Word Recognition (CNC), Arizona Biomedical Sentence Recognition (AzBio), and Bamford-Kowal-Bench Speech-in-Noise Test (BKB-SIN) tests. Within- and across-frequency behavioral gap detection thresholds (referred to as the GDTwithin and GDTacross) were measured using an adaptive, two-alternative, forced-choice procedure. Cortical auditory evoked potentials (CAEPs) were elicited using within- and across-frequency gap stimuli under four gap duration conditions (no gap, GDT, sub-threshold GDT, and supra-threshold GDT). Correlations among speech perception, GDTs, and CAEPs were examined.

RESULTS

CI users had poorer speech perception scores compared to NH listeners (p < 0.05), but the GDTs were not different between groups (p > 0.05). Compared to NH peers, CI users showed increased N1 latency in the CAEPs evoked by the across-frequency gap stimuli (p < 0.05). No group difference was observed for the CAEPs evoked by the within-frequency gap (p > 0.05). Three CI ears showing the longest GDTwithin also showed the poorest performance in speech in noise. The within-frequency CAEP increased in amplitude with the increase of gap duration; while the across-frequency CAEP displayed a similar amplitude for all gap durations. There was a significant correlation between speech scores and within-frequency CAEP measures for the supra-threshold GDT condition, with CI users with poorer speech performance having a smaller N1-P2 amplitude and longer N1 latency. No correlations were found among GDTacross, speech perception, and across-frequency CAEP measures.

CONCLUSIONS

Within- and across-frequency gap detection may involve different neural mechanisms. The within-frequency gap detection task can help identify CI users with poor speech performance for rehabilitation. The within-frequency CAEP is a better predictor for speech perception performance than the across-frequency CAEP.

Auditory gap-in-noise detection behavior in ferrets and humans

The precise encoding of temporal features of auditory stimuli by the mammalian auditory system is critical to the perception of biologically important sounds, including vocalizations, speech, and music. In this study, auditory gap-detection behavior was evaluated in adult pigmented ferrets (Mustelid putorius furo) using bandpassed stimuli designed to widely sample the ferret's behavioral and physiological audiogram. Animals were tested under positive operant conditioning, with psychometric functions constructed in response to gap-in-noise lengths ranging from 3 to 270 ms. Using a modified version of this gap-detection task, with the same stimulus frequency parameters, we also tested a cohort of normal-hearing human subjects. Gap-detection thresholds were computed from psychometric curves transformed according to signal detection theory, revealing that for both ferrets and humans, detection sensitivity was worse for silent gaps embedded within low-frequency noise compared with high-frequency or broadband stimuli. Additional psychometric function analysis of ferret behavior indicated effects of stimulus spectral content on aspects of behavioral performance related to decision-making processes, with animals displaying improved sensitivity for broadband gap-in-noise detection. Reaction times derived from unconditioned head-orienting data and the time from stimulus onset to reward spout activation varied with the stimulus frequency content and gap length, as well as the approach-to-target choice and reward location. The present study represents a comprehensive evaluation of gap-detection behavior in ferrets, while similarities in performance with our human subjects confirm the use of the ferret as an appropriate model of temporal processing.

Performance at different stimulus intensities with the within- and across-channel adaptive tests of temporal resolution

OBJECTIVE

The Adaptive Tests of Temporal Resolution (ATTR©) software provides within-channel (WC) and across-channel (AC) adaptive measures of temporal resolution that are feasible for clinical applications. The purpose of the present study was to obtain normative values for young adults on two of the ATTR tests: the narrow-band noise within-channel (NBN-WC) test and the narrow-band noise across-channel (NBN-AC) test, at different stimulus intensities.

DESIGN

Gap detection thresholds were measured at five sensation levels. A Latin square design was used to control for practice effects.

STUDY SAMPLE

The NBN-WC group and the NBN-AC group each consisted of 25 young adults with normal hearing.

RESULTS

Gap detection thresholds for both conditions decreased with increasing stimulus intensity, and stimulus intensities above 20 dB SL were not associated with large improvements in performance. Variability was larger in the NBN-AC condition. Values obtained for the NBC-WC condition were very similar to previously reported ATTR results despite equipment and design differences.

CONCLUSION

Results provide normative values for NBN-WC and NBN-AC performance on the ATTR and suggest that the ATTR is a robust test for clinical use.

Stimulus, task, and learning effects on measures of temporal resolution: implications for predictors of language outcome

PURPOSE

Some studies find that temporal processing ability predicts language outcome whereas other studies do not. Resolution of this debate is hindered by the variety of temporal measures used, nonsensory loading of the tasks, and differential amounts of practice across studies. The goal of this study was to examine the effects of stimulus properties, experimental task, and perceptual learning on listeners' gap detection performance.

METHOD

Gap detection thresholds were obtained from adults with normal hearing and language ability. The effects of marker frequency similarity and marker duration on thresholds were examined in yes-no, two-interval forced-choice (2IFC), and dual-pair comparison tasks (which vary in nonsensory loading) over 4 days of testing.

RESULTS

Thresholds were highest for gaps defined by markers with disparate frequencies (1000 and 4000 Hz; i.e., between-channel gap detection), and with longer (300 ms) trailing markers, obtained using yes-no and 2IFC tasks. However, these effects were attenuated with training or the initial use of the dual-pair comparison task.

CONCLUSIONS

These results suggest that gap detection thresholds reflect a variety of sensory and nonsensory factors. Understanding these underlying factors is critical to any evaluation of the relation between temporal processing and language outcome.

Ear and contralateral masker effects on auditory temporal gap detection thresholds

A temporal processing advantage is thought to underlie the left hemisphere dominance for language. One measure of a temporal processing advantage is temporal acuity or resolution. A standard paradigm for measuring auditory temporal resolution is gap detection in its "within-channel" and "between-channel" forms. Previous experiments investigating a right ear advantage for within-channel gap detection have yielded conflicting results, and between-channel gap detection has not previously been studied for ear differences. In the present study, the two types of gap detection task were employed, under each of three contralateral masking conditions (no noise, continuous noise and interrupted noise). An adaptive tracking procedure was used to measure the minimal detectable gap at each ear (and therefore, the temporal acuity of the contralateral hemisphere). A significant effect of masking noise was observed in both of the gap detection tasks. Within-channel gap threshold durations were longer in the interrupted noise condition for both ears. Between-channel gap threshold durations were shorter in the interrupted noise condition at the left ear, with a trend in the same direction at the right ear. The study found no significant difference between the ears in thresholds in either gap detection task in any of the masking conditions. This suggests that if the left cerebral hemisphere has a temporal processing advantage, then it is not in the form of acuity for temporal gap detection.

The development of temporal resolution: between-channel gap detection in infants and adults

PURPOSE

Infants have a good ability to detect brief silent gaps between 2 short identical sound markers (within-channel gap detection), with thresholds between 2 and 11 ms. The present experiment traces the development of temporal resolution for between-channel gaps (i.e., gaps delineated by spectrally disparate markers). This ability appears crucial for the perception of complex stimuli such as speech and is thought to reflect more central auditory processing.

METHOD

Infants age 6-7.5 months and adults were tested in a between-channel gap detection task using a conditioned head-turn procedure. Gaps were marked by 1- and 4-kHz Gaussian-enveloped sine-tone markers.

RESULTS

Infant gap thresholds were between 30 and 40 ms under conditions in which adult thresholds were between 10 and 20 ms.

CONCLUSIONS

Unlike within-channel gap detection, the central temporal processing required for between-channel gap detection is still immature at 6 months of age.

The relation between auditory temporal interval processing and sequential stream segregation examined with stimulus laterality differences

In this study, we examine the effects of laterality differences between noise bursts on two objective measures of temporal interval processing (gap detection and temporal asymmetry detection) and one subjective measure of temporal organization (stream segregation). Noise bursts were lateralized by presentation to different ears or dichotic presentation with oppositely signed interaural level (ILD) or time (ITD) differences. Objective thresholds were strongly affected by ear-of-entry differences, were moderately affected by ILD differences, but were unaffected by ITD differences. Subjectively, A and B streams segregated well on the basis of ear-of-entry or ILD differences but segregated poorly on the basis of ITD differences. These results suggest that perceptual segregation may be driven more effectively by differential activation of the two ears (peripheral channeling) than by differences in perceived laterality.

Effect of age on detection of gaps in speech and nonspeech markers varying in duration and spectral symmetry

Gap detection thresholds for speech and analogous nonspeech stimuli were determined in younger and older adults with clinically normal hearing in the speech range. Gap detection thresholds were larger for older than for younger listeners in all conditions, with the size of the age difference increasing with stimulus complexity. For both ages, gap detection thresholds were far smaller when the markers before and after the gap were the same (spectrally symmetrical) compared to when they were different (spectrally asymmetrical) for both speech and nonspeech stimuli. Moreover, gap detection thresholds were smaller for nonspeech than for speech stimuli when the markers were spectrally symmetrical but the opposite was observed when the markers were spectrally asymmetrical. This pattern of results may reflect the benefit of activating well-learned gap-dependent phonemic contrasts. The stimulus-dependent age effects were interpreted as reflecting the differential effects of age-dependent losses in temporal processing ability on within- and between-channel gap detection.

GIN (Gaps-In-Noise) Test Performance in Subjects with Confirmed Central Auditory Nervous System Involvement

OBJECTIVE

The purpose of the present study was to investigate the value of a new gap detection procedure called Gaps-In-Noise (GIN) for assessment of temporal resolution in a clinical population.

DESIGN

The test consists of 0 to 3 silent intervals ranging from 2 to 20 msec embedded in 6-sec segments of white noise. The location, number, and duration of the gaps per noise segment vary throughout the test for a total of 60 gaps presented in each of four lists. The GIN procedure was administered to 50 normal-hearing listeners (group I) and 18 subjects with confirmed neurological involvement of the central auditory nervous system (group II).

RESULTS

Results showed mean approximated gap detection thresholds of 4.8 msec for the left ear and 4.9 msec for the right ear for group I. In comparison, results for group II demonstrated a statistically significant increase in gap detection thresholds, with approximated thresholds of 7.8 msec and 8.5 msec being noted for the left and right ears, respectively. Significant mean differences were also observed in the overall performance scores (i.e., the identification of the presence of the gaps within the noise segments) of the two groups of subjects. Finally, psychometric functions, although similar for short and long duration gaps, were highly different for gaps in the 4- to 10-msec range for the two groups.

CONCLUSIONS

A variety of psychoacoustic procedures are available to assess temporal resolution; however, the clinical use of these procedures is minimal at best. Results of the present study show that the GIN test holds promise as a clinically useful tool in the assessment of temporal resolution in the clinical arena.

Within- and between-channel gap detection in the human auditory cortex

We examined the neural correlates associated with a short gap between two identical pure tones (within-channel) and between two different tones (between-channel) in an odd-ball paradigm. Gap durations were selected such that a gap between identical tones was as discriminable as a gap between two different tones. Spatio-temporal dipole source modeling of electrophysiological data revealed a significant difference between standard and deviant gap stimuli, with mismatch negativity responses that were comparable in amplitude and latency for within- and between-channel conditions. Therefore, the ability to automatically register discontinuity (i.e., gap) within and between channels is comparable despite significant differences in gap size. The dipole source modeling suggests that both within- and between-gap signals are represented in or near the primary auditory cortex.

Auditory temporal gap detection for noise markers with partially overlapping and non-overlapping spectra

Temporal gap detection thresholds were obtained from six listeners using an adaptive tracking method and constant spectrum-level noises. In separate blocks of trials, the markers bounding the gap were systematically varied in their spectral overlap or separation (expressed in equivalent rectangular bandwidths, ERBs). In the same listeners, gap thresholds were also obtained for noises of the same bandwidths as those constituting the overlap in the overlap conditions (in the presence of a wideband notched noise masker: 'mask' conditions). For the spectral overlap/separation conditions, gap thresholds were a systematic, linear function of spectral dissimilarity in four of six listeners. In the mask conditions, gap thresholds were inversely related to bandwidth in all listeners. For the three-, four- and five-ERB conditions, gap thresholds in the same listeners for the spectral overlap conditions were higher than those for mask stimuli with the same available within-channel bandwidth and spectrum levels. These data suggest that the spectral dissimilarity between the markers over-rode the availability of within-channel information in the recovery of the temporal gap.