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PubMed1999

Auditory temporal integration in the rhesus macaque (Macaca mulatta).

Temporal integration for pure tones was examined in two rhesus macaques. The subjects were required to respond to a brief sound (a tone burst) that deviated from a previous series of sounds (noise bursts) on a trial (a deviant-stimulus detection paradigm). Psychometric functions and thresholds were determined from correct detections (hit proportions) alone, and from d' scores. Two models describing the decline in threshold as a function of stimulus duration, one a power function the other an exponential, were tested against the data. When the decline (slope) in threshold per log stimulus duration is used as a rate measure, our results yield a lower estimate of temporal integration rate in rhesus than did a previous study [Clack, J. Acoust. Soc. Am. 40, 1140-1146 (1966)]. Both studies, however, gave slope estimates of integration rate that were higher than in most other species. Comparison of the models using data from several species, revealed that the exponential, but not the power model, could account for two sources of variation in threshold measurement. One source is due to the range across threshold as a function of duration (the linear rate component), and is described by the constant of proportionality Ik in the model. The other source of variation arises from the rate of decline within this range (the nonlinear rate component), and is described by the time constant tau. In terms of this model, differences in rate estimates between Clack's study and ours (and between rhesus and other species) are primarily due to the linear component. The nonlinear rate component was about equal for our study and Clack's (tau = approximately 150 ms): a time constant that is just slightly larger (indicating a rate of temporal integration slightly slower) than for most other species examined.

Animals↗
PubMed2000

Effects of ipsilateral and contralateral precursors on the temporal effect in simultaneous masking with pure tones.

In tone-on-tone masking, thresholds often decrease as the onset of the signal is delayed relative to the onset of the masker, especially when the frequency of the masker is higher than the frequency of the signal. This temporal effect was studied here by using a tonal "precursor," whose offset preceded the onset of the tonal masker (and signal). Under the right conditions, the precursor can reduce or eliminate the temporal effect by decreasing the threshold for a signal at masker onset, presumably for the same reason that the threshold decreases as a signal is delayed relative to the onset of a masker. In the present study, the frequency of the signal was 4000 Hz, and the frequency of the masker and precursor was typically 5000 Hz. In experiment 1, the precursor was presented to the ear receiving the masker and signal (ipsilateral precursor); in experiment 2, it was presented to the opposite ear (contralateral precursor). The results from experiment 1 can be summarized as follows: the ipsilateral precursor (a) reaches its maximum effectiveness (in reducing the temporal effect) for precursor durations of 200-400 ms; (b) is ineffective once the delay between its offset and the onset of the masker reaches about 50-100 ms; (c) is generally ineffective when its level is 10 or more dB lower than the level of the masker, but is effective when its level is equal to or greater than the level of the masker; and (d) becomes progressively less effective as its frequency is either increased or decreased relative to the frequency of the masker. The results from experiment 2 can be summarized simply by stating that the contralateral precursor is ineffective in reducing the temporal effect. These results suggest that the effect of the precursor may be mediated peripherally.

Adult↗
PubMed1984

Derived acoustically evoked brainstem responses by means of narrow-band and notched-noise masking in normal-hearing subjects.

Derived acoustically evoked brainstem responses determined by narrow-band and notched-noise masking at 2000 Hz frequencies and below were investigated and compared with those obtained in the use of the common high-pass masking technique. With all three masking methods a dominant late wave Wa could be detected at less than or equal to 1 600 Hz centre frequencies of the derived band and this wave is typical of the excitation of the apical section of the cochlea. The latency of this wave increases when the centre frequency is decreased at a constant stimulation level. For a constant centre frequency of the derived band the latency of wave Wa increases when the stimulation level of the click and in parallel to that the masking level is decreased. Wave Wa could be found near the hearing threshold in all three masking methods. The notched-noise masking method offers major advantages provided that full masking of the frequency regions above and below the notch frequency range is carried out. A direct frequency-specific stimulation takes place and there is no need for subtracting one response from a second one. This reduces the investigation time and the memory capacity of the measuring device. The advantages and applicability of the notched-noise masking method have to be re-checked in patients with different frequency-dependent loss of hearing.

Adolescent↗
PubMed2004

Mechanisms of tinnitus generation.

PURPOSE OF REVIEW: The current understanding of mechanisms of tinnitus generation is continuing to advance. This review is intended to outline new knowledge in the areas of neuroanatomy, physiology, psychophysics, and brain imaging that are revealing novel mechanisms of tinnitus development. Advances in these areas will open new avenues for effective treatment of tinnitus. RECENT FINDINGS: Application of high-pulse train electrical stimulation to the cochlea may be effective in restoring the normal pattern of spontaneous activity from the periphery that is interpreted by the auditory brainstem as coding for silence. Clinical and laboratory evidence for a significant interaction between the somatosensory and auditory systems has important implications for understanding and treating tinnitus. Application of principles of neuroplasticity and novel imaging techniques has expanded our understanding of tinnitus through analogous approaches to phantom limb pain. Finally, a novel receptor type recently located in auditory neurovascular structures has opened a new field of study of inflammatory mechanisms contributing to tinnitus. SUMMARY: Our understanding of the mechanisms that lead to a phantom auditory perception, and the associated debilitating consequences of this sensory experience, is continuing to improve. Tinnitus appears to be significantly affected in complex ways by somatosensory, limbic, and motor influences. Effective treatments will certainly emerge from these new areas of research.

Acoustic Stimulation↗
PubMed2006

Perceptual interaction between carrier periodicity and amplitude-modulation in the gerbil (Meriones unguiculatus).

Due to its extended low-frequency hearing, the Mongolian gerbil (Meriones unguiculatus) has become a well-established animal model for human auditory processing. Here, two experiments are presented which quantify the gerbil's sensitivity to amplitude modulation (AM) and carrier periodicity (CP) in broad-band stimuli. Two additional experiments investigate a possible interaction of the two types of periodicity. The results show that overall sensitivity to AM and CP is considerably less than in humans (by at least 10 dB). The gerbil's amplitude-modulation sensitivity is almost independent of modulation frequency up to a modulation frequency of 1 kHz. Above, amplitude-modulation sensitivity deteriorates dramatically. On the basis of individual animals, carrier-periodicity detection may improve with increasing fundamental frequency up to about 500 Hz or may be independent of fundamental frequency. Amplitude-modulation thresholds are consistent with the hypothesis that intensity difference limens in the gerbil may be considerably worse than in humans, leading to the relative insensitivity for low modulation frequencies. Unlike in humans, inner-ear filtering appears not to limit amplitude-modulation sensitivity in the gerbil. Carrier-periodicity sensitivity changes with fundamental frequency similar to humans. Unlike in humans, there is no systematic interaction between AM and CP in the gerbil. This points to a relatively independent processing of the perceptual cues associated with AM and CP.

Acoustic Stimulation↗
PubMed1979

Evoked potential correlates of human information processing.

The late positive component (P3) of the feedback evoked potential was investigated in two tasks: the detection of near-threshold auditory stimuli, and the estimation of 1 s time intervals. When the intensity or probability of the threshold stimuli was varied in the detection task, it became apparent that the feedback P3 was related to the 'contingent probability' of confirming or disconfirming feedback given a particular response. In the time-estimation task the relative probabiliti-s of confirming and disconfirming feedback were altered by changing the time-window wherein a response was judged correct. In these experiments it was found that the feedback P3 component was highly dependent upon the probability of the feedback, and relatively independent of its confirming or disconfirming meaning. With decreasing probability of the feedback stimuli, the P3 component became larger, later, and somewhat more frontal.

Auditory Perception↗
PubMed1983

Responses from AVCN units in the cat before and after inducement of an acute noise trauma.

Acoustically evoked responses of single units in the anteroventral part of the cochlear nucleus (AVCN) in the cat were studied together with compound eighth-nerve action potentials (AP). Halfway through the experiments the cats were exposed for half an hour to pink noise at 105 dB SPL, producing an average threshold shift of 30 dB (maximum 50 dB) in the 2-6 kHz region. The effect of noise exposure was studied in two ways. On the one hand we compared the results for one population of units measured before the noise exposure with those found for another population measured afterwards. On the other hand we compared the results before and after the noise exposure for one unit that could be kept under observation during the noise exposure. After the noise exposure spontaneous activity and phase-locking of the responses of the units to the stimulus waveform were not significantly different from the pre-exposure findings. Response latency tended to increase. Therefore, the decrease of latency found for APs must be due to a shift to higher frequencies of the population of units contributing to the AP. The sharply tuned tip segments of tuning curves shift to higher levels whereas the low-frequency tails remain at about the same level. Q10 decreases by at most 50%, which was also found for AP tuning curves. Response spectra for clicks and noise (reverse correlation function) did not show a significant decrease of frequency selectivity. Units with CF less than 3 kHz may show a shift of CF to a lower frequency by 10-20%. After inducement of the noise trauma the sharply tuned tip segment of a tuning curve may not be found and CF may be assigned to a local minimum in the low-frequency tail of the tuning curve.

Animals↗
PubMed1987

The auditory spatial acuity of the domestic cat in the interaural 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.

Animals↗
PubMed2005

Is poor frequency modulation detection linked to literacy problems? A comparison of specific reading disability and mild to moderate sensorineural hearing loss.

Specific reading disability (SRD) is now widely recognised as often being caused by phonological processing problems, affecting analysis of spoken as well as written language. According to one theoretical account, these phonological problems are due to low-level problems in auditory perception of dynamic acoustic cues. Evidence for this has come from studies showing poor discrimination of frequency-modulated from unmodulated tones. We measured frequency modulation detection limens (FMDLs) in 16 children with specific reading disability (SRD group), 16 children with mild to moderate hearing loss (SNH group) and 16 age-matched controls (CA group) aged 8-14. To obtain information about possible mechanisms used in frequency modulation detection, FMDLs were measured at modulation rates of 2 and 20 Hz, both in the absence and the presence of amplitude modulation, intended to force listeners to rely, if possible, upon phase-locking cues. Although both the SNH and SRD groups showed a trend for elevated FMDLs at both 2 and 20 Hz, these differences reached statistical significance for the SNH group alone. However, the SNH group had no evidence of literacy impairments. This study thus shows that impairments in perceiving dynamically modulated auditory stimuli do not necessarily lead to difficulty in learning to read.

Adolescent↗
PubMed2002

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.

Adult↗
PubMed1997

Deficits in auditory temporal and spectral resolution in language-impaired children.

Between 3 and 6 per cent of children who are otherwise unimpaired have extreme difficulties producing and understanding spoken language. This disorder is typically labelled specific language impairment. Children diagnosed with specific language impairment often have accompanying reading difficulties (dyslexia), but not all children with reading difficulties have specific language impairment. Some researchers claim that language impairment arises from failures specific to language or cognitive processing. Others hold that language impairment results from a more elemental problem that makes affected children unable to hear the acoustic distinctions among successive brief sounds in speech. Here we report the results of psychophysical tests employing simple tones and noises showing that children with specific language impairment have severe auditory perceptual deficits for brief but not long tones in particular sound contexts. Our data support the view that language difficulties result from problems in auditory perception, and provide further information about the nature of these perceptual problems that should contribute to improving the diagnosis and treatment of language impairment and related disorders.

Analysis of Variance↗
PubMedDate not supplied

Temporal specificity of perceptual learning in an auditory discrimination task.

Although temporal processing is used in a wide range of sensory and motor tasks, there is little evidence as to whether a single centralized clock or a distributed system underlies timing in the range of tens to hundreds of milliseconds. We investigated this question by studying whether learning on an auditory interval discrimination task generalizes across stimulus types, intervals, and frequencies. The degree to which improvements in timing carry over to different stimulus features constrains the neural mechanisms underlying timing. Human subjects trained on a 100- or 200-msec interval discrimination task showed an improvement in temporal resolution. This learning generalized to a perceptually distinct duration stimulus, as well as to the trained interval presented with tones at untrained spectral frequencies. The improvement in performance did not generalize to untrained intervals. To determine if spectral generalization was dependent on the importance of frequency information in the task, subjects were simultaneously trained on two different intervals identified by frequency. As a whole, our results indicate that the brain uses circuits that are dedicated to specific time spans, and that each circuit processes stimuli across nontemporal stimulus features. The patterns of generalization additionally indicate that temporal learning does not rely on changes in early, subcortical processing, because the nontemporal features are encoded by different channels at early stages.

Adult↗
PubMed1993

Interaural temporal discrimination using two sinusoidally amplitude-modulated, high-frequency tones: conditions of summation and interference.

This paper concerns sensitivity to interaural temporal delays (ITD) in the envelopes of two, sometimes simultaneously presented, sinusoidally amplitude-modulated (SAM) tones. The SAM tones were fully modulated (typically at a rate of 250 Hz) and had carrier frequencies of either 2 or 4 kHz. Of particular interest were cases in which the delay to be detected (target ITD) occurred in only one spectral region or in both. The reference ITD, to which the target ITD was added, was either 0, 300, or 600 microseconds. There were three general outcomes: (1) When both regions contained a target ITD, there was an improvement in sensitivity that was quantitatively consistent with an optimal use of independent information. This type of summation was seen even when the target ITDs were added to a pair of SAM tones with two different reference ITDs; (2) when the target ITD was restricted to the higher spectral region, sensitivity was reduced, indicating interference. Interference occurred when the two spectral regions had the same or different reference ITDs and the same or different rates of modulation; (3) sensitivity was unaffected (i.e., no interference occurred) when the target ITD was restricted to the lower spectral region of the pair of SAM tones. These results supplement the observations of Buell and Hafter [J. Acoust. Soc. Am. 90, 1894-1900 (1991)], who used low-frequency tones.

Acoustic Stimulation↗
PubMed1993

The combination of interaural information across frequencies: the effects of number and spacing of components, onset asynchrony, and harmonicity.

Threshold interaural delays were measured for a single interaurally delayed low-frequency target component presented against a background of two, four, six, or eight diotic "distractor" components. In the first experiment, a 753-Hz target and the flanking distractor components were gated on and off simultaneously. In subsequent experiments, the distractors were gated on 25-200 ms prior to the target. In addition, the target and distractor components were given various harmonic configurations. In general, threshold interaural delays were higher in all conditions in which distractors were present relative to thresholds obtained for the target component in isolation. Subjects reported that the pitch of the target component was more salient when an onset asynchrony between the target and distractors was present, but the components were perceived as occupying a single intracranial position in spite of the various interaural delays across the frequency domain. These results suggest that binaural processing of stimuli consisting of a small number of low-frequency temporally overlapping components occurs in a spectrally synthetic manner in which interaural information is combined across the spectrum, even in situations in which the segregation of pitch information occurs.

Auditory Perception↗
PubMed2000

Observer weighting of monaural level information in a pair of tone pulses.

A correlational analysis was used to assess the relative weight given to the levels of two monaurally presented tone pulses for interpulse intervals (IPIs) ranging from 2-256 ms. In three different experimental conditions, listeners were instructed to discriminate the level of the first pulse, the level of the second pulse, or the difference between the levels of the two pulses. The level of the target pulse was chosen randomly and independently from trial to trial from a Gaussian distribution. The level of the nontarget pulse was either fixed at 75 dB SPL or varied in the same manner as the level of the target. In the tasks in which one pulse was to be ignored, listeners gave increasing weight to the nontarget component as IPI decreased. Listeners weighted the level information in the pulses appropriately only when the IPI approached 256 ms. When the listeners were instructed to compare the pulse levels to one another, two of three listeners weighted the levels optimally at all IPIs, while the third listener did so only at the longest IPI. For the two listeners who weighted the pulses optimally, a minimum in performance was achieved at IPIs around 16-32 ms. Intensity discrimination thresholds were also measured for one pulse in the presence of a second fixed pulse for IPIs of 2-256 ms. Thresholds were higher in all the two-pulse conditions relative to a one-pulse condition, and were dependent on the level of the nontarget pulse but not on IPI. The results indicate that level information is integrated to some extent over fairly long durations, but not in a manner that is consistent with simple temporal integration.

Auditory Perception↗