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PubMed1989

Long-term habituation and sensitization of the acoustic startle response in the normal adult human.

The development and independence of short-term and long-term habituation (and short-term sensitization) of the acoustic startle response to repetitive stimuli has been repeatedly demonstrated in the experimental animal. Although short-term habituation (and sensitization) of acoustic startle has been studied in humans, neither long-term habituation nor sensitization has been demonstrated. In this study, long-term habituation (response amplitude decrement) of the blink component of the acoustic startle response occurred in normal men across five consecutive daily sessions of repetitive acoustic stimulation. Long-term sensitization (onset latency shortening) developed after the third day. Both the long-term habituation and sensitization were independent of the day. Both the long-term habituation and sensitization were independent of the short-term habituation, which developed within each daily session.

Adolescent↗
PubMed1987

Cochlear or nerve stimulation.

To stimulate through electrical stimulation the auditory nerve excitation patterns produced by a normal ear, it is necessary to control both the spatial and the timing aspects of the neural firing pattern. While the spatial localization, the "place" aspect of stimulation can probably be achieved adequately with either scala tympani or direct eighth nerve electrodes, only the eighth nerve electrodes have the potential to reproduce the detailed timing patterns of the normal nerve. While such complete control of the stimulation pattern is probably necessary to produce "natural" auditory percepts, it may well not be necessary for the conveying of the information in speech because of the plasticity and pattern recognition capabilities of the brain. Present encouraging results as open speech comprehension with scala tympani electrode arrays suggest that, in many cases at least, the cruder stimulation pattern control will suffice.

Cochlear Implants↗
PubMed1975

Auditory thresholds and the effect of reduced auditory feedback of suttering.

The effects of reduced auditory feedback were investigated using an accurately calibrated binaudal pure tone producer on 27 stuttering children and 68 non-stuttering controls. A comparison was made of both auditory hearing and discomfort thresholds in the two groups; the hearing thresholds did not differ between the groups. The results did however replicate an earlier finding which suggested that stutters have a lower threshold for auditory discomfort than do normal speakers, and showed that fluency is inversely related to auditory feedback. The discussion suggests that a necessary cause of stuttering is a physiological abnormality in side-tone conduction and central processing.

Adolescent↗
PubMed1995

Four weeks inhalation exposure to n-heptane causes loss of auditory sensitivity in rats.

The effects of exposure to 800 or 4000 p.p.m. of n-heptane, CAS No. [142-82-5]) 6 hr per day during a period of 28 days, on the function of the auditory system were examined by measurements of auditory brain stem response (ABR) in Long Evans rats. The ABR was measured simultaneously with both needle electrodes and implanted electrodes. The wave forms recorded with the two types of electrodes were similar, but the amplitudes were largest on the recordings with implanted electrodes. The overall ratio between the amplitudes obtained with implanted electrodes and with needle electrodes was 1.4 for peak Ia and 2.5 for peak IV of the ABR. The exposure to n-heptane (4000 p.p.m.) reduced the amplitudes of components Ia and IV of the ABR. The reduction was most consistent for component IV and most pronounced at higher frequencies and intensities. The reduction in ABR corresponds to an increase in the auditory threshold of approximately 10 dB at all frequencies. Neither the latencies nor the interpeak latencies of components Ia and IV were changed. No significant changes in ABR were observed in the group exposed to 800 p.p.m. The mechanism behind the ototoxicity of organic solvents is discussed.

Administration, Inhalation↗
PubMed1976

Slow evoked cortical responses to linear frequency ramps of a continuous pure tone.

Slow evoked cortical potentials from ten young normal-hearing subjects have been recorded as responses to linear frequency ramps of a continuous pure tone. Frequency changes from 10 to 500 Hz were studied; the rate of frequency change was varied from 0.02 to 50 kHz/s while the duration of the change was varied from 10 to 500 ms. The rate of frequency change was shown to have the greatest bearing on the responses except for frequency ramp durations below 50 ms and frequency changes below 50 Hz. The base frequencies (250-4000 Hz) and sound levels (20-80 dB HL) exerted an influence on the evoked responses that was qualitatively similar to their influence on behavioral thresholds. The direction of the frequency sweep had no significant influence on the evoked responses. A functional model is proposed in which the time derivate of the signal frequency is integrated with an adaptable integration time that is controlled by the rate of the frequency change.

Acoustic Stimulation↗
PubMed1972

On the existence in human auditory pathways of channels selectively tuned to the modulation present in frequency-modulated tones.

1. The sensitivity of detecting modulation in a test tone sinusoidally frequency-modulated at a rate varphi(test) is diminished after exposure to a conditioning tone more deeply frequency-modulated at a rate varphi(cond) provided that varphi(cond) is not very different from varphi(test), the sound amplitude being kept constant for each tone at a comfortable hearing level 40-45 dB above threshold.2. When varphi(cond) = varphi(test) the frequency deviation in the modulated test tone must be increased to about three times the unconditioned threshold magnitude to be detectable immediately after exposure to the conditioning tone. Detection sensitivity returns to normal in about one minute.3. At low modulation frequencies the conditioning effects are tuned, being much diminished when varphi(cond) differs from varphi(test) by a few cycles per second.4. Comparing monaural with contra-aural conditioning demonstrates a considerable interaural transfer of about 60-80% of the effect, indicating that the conditioning and its selectivity are predominantly central phenomena.5. The magnitude of the deterioration in detection sensitivity after conditioning is about 3 x at modulation frequencies between about 3/sec and 30/sec. It diminishes at lower and higher modulation frequencies and is effectively absent at 100/sec modulation. The bandwidth of the effect increases from a few cycles per second at the lower end of this range, to some tens of cycles per second at the upper end.6. For the same modulation frequency, the conditioning is relatively insensitive to the mean ;carrier' audiofrequency, f(0). The band width in terms of carrier frequency is at least as wide as ;critical bands'. With a test signal f(0) = 250 Hz, varphi(test) = 8/sec, conditioning is still appreciable for a conditioning tone of varphi(cond) = 8/sec but centred upon f(0) = 150 Hz or = 350 Hz. Conditioning is thus not explicable in terms of coincidences between particular spectral components in the conditioning and test tones.7. Whereas the sensitivity of detecting 8/sec amplitude modulation in a tone is conditioned by prior exposure to either amplitude- or frequency-modulated tones, in contrast the detectability of 8/sec frequency-modulated signals is conditioned only by prior exposure to frequency-modulated tones and not by amplitude-modulated conditioning tones. This underlines the special place of frequency modulation in human audition and emphasizes that the operative stimulus cannot be some aspect common to amplitude modulation and frequency modulation, like identical periodicity or coincident positioning of bands in the integrated spectra of the tones, but points to the instantaneous frequency-modulated wave form as the adequate stimulus.8. These findings strongly suggest that the human auditory pathways contain ;channels' in their organization which determine a final response selectively tuned to particular frequency-modulations. Periodicity coding alone cannot adequately explain this effect which may well only be understood in terms of a ;place' theory of frequency selectivity.9. This organization is well suited to subserve the recognition of frequency-modulation patterns in acoustic signals rather independently of the mean audiofrequency that carries the frequency modulation.

Acoustic Stimulation↗
PubMed2000

Failure to unlearn the precedence effect.

Studies of the precedence effect using two binaural clicks have shown that listeners' ability to discriminate changes in the interaural time difference (ITD) of the lagging click is much poorer than that for the leading click [e.g., Zurek, J. Acoust. Soc. Am. 67, 952-964 (1980)]. This difference is thought to reflect an auditory process that suppresses directional information from the lagging sound and attributes greater perceptual weight to directional information contained in the leading one. A report by Saberi and Perrott [J. Acoust. Soc. Am. 87, 1732-1737 (1990)] suggested that listeners can "unlearn" this suppression of the lag's directional information after training with an adaptive psychophysical procedure involving 100 reversals and extremely small step sizes. Here, an attempt was made to find a similar effect using psychophysical procedures that are more common to precedence studies. Eight subjects were rigorously trained on the precedence task using either a blocked procedure or an adaptive procedure to vary ITD. Listeners showed no sign of unlearning. After 9-31 h of participating in the task, all subjects maintained high lag just-noticeable differences (jnd's) and low single source jnd's. This failure to train away the precedence effect (as manifested in discrimination suppression) suggests that directional information contained in the lagging source is not easily accessed. Several possible explanations for the discrepancies between the present study and Saberi and Perrott's finding are discussed.

Auditory Perception↗
PubMed2001

A consideration of the normalization that is typically included in correlation-based models of binaural detection.

An analysis of binaural detection and new data that elucidate the nature and precision of normalization that must be assumed if binaural detection is accomplished via mechanisms that effectively compute the coefficient of cross correlation is presented. Based on that analysis, it is argued that the precision of normalization required to remove deleterious effects resulting from variations in the levels of the stimuli is so great that it is highly unlikely that normalization, per se, actually occurs as part of binarual processing. Instead, it appears more likely that binaural processing is accomplished via "subtractive" mechanisms, such as the one originally described by Durlach [J. Acoust. Soc. Am. 35, 1206-1218 (1963)]. Within that framework, deleterious effects that could result from variations in the levels of the stimuli simply do not arise.

Auditory Perception↗
PubMed2001

Forward masking: adaptation or integration?

The aim of this study was to attempt to distinguish between neural adaptation and persistence (or temporal integration) as possible explanations of forward masking. Thresholds were measured for a sinusoidal signal as a function of signal duration for conditions where the delay between the masker offset and the signal offset (the offset-offset interval) was fixed. The masker was a 200-ms broadband noise, presented at a spectrum level of 40 dB (re: 20 microPa), and the signal was a 4-kHz sinusoid, gated with 2-ms ramps. The offset-offset interval was fixed at various durations between 4 and 102 ms and signal thresholds were measured for a range of signal durations at each interval. A substantial decrease in thresholds was observed with increasing duration for signal durations up to about 20 ms. At short offset-offset intervals, the amount of temporal integration exceeded that normally found in quiet. The results were simulated using models of temporal integration (the temporal-window model) and adaptation. For both models, the inclusion of a peripheral nonlinearity, similar to that observed physiologically in studies of the basilar membrane, was essential in producing a good fit to the data. Both models were about equally successful in accounting for the present data. However, the temporal-window model provided a somewhat better account of similar data from a simultaneous-masking experiment, using the same parameters. This suggests that the linear, time-invariant properties of the temporal-window approach are appropriate for modeling forward masking. Overall the results confirm that forward masking can be described in terms of peripheral nonlinearity followed by linear temporal integration at higher levels in the auditory system. However, the difference in predictions between the adaptation and integration models is relatively small, meaning that influence of adaptation cannot be ruled out.

Adaptation, Physiological↗
PubMed2001

A comparison of threshold estimation methods in children 6-11 years of age.

Estimating detection threshold for auditory stimuli in children can be problematic because of lapses in attention and the time limits usually imposed by scheduling restrictions or fatigue. Data reported here were collected to compare the stability of threshold estimation procedures in testing children ages 6 to 11 in a three-alternative, forced-choice paradigm. Stimuli consisted of a 1-kHz tonal signal and a Gaussian noise masker, bandpass filtered between 500-2,000 Hz and presented at 25-dB spectrum level. The signal was either presented for 400 ms in the presence of a continuous masker (simultaneous masking) or for 10 ms just prior to a 400-ms masker (backward masking). For each masking paradigm the 79% correct threshold was assessed via each of three procedures: 3-down, 1-up adaptive staircase (Levitt), maximum likelihood estimation (MLE), and method of constant stimuli. Percent correct was measured at the end of the study for a signal 10 dB above the previously determined threshold in order to estimate the most appropriate psychometric function asymptote for fitting data collected via the method of constant stimuli. Both the MLE and Levitt procedures produced equally stable threshold estimates for both conditions and age groups. This was the case despite considerable variability in backward-masking thresholds.

Adult↗
PubMed2001

Auditory backward recognition masking in children with a specific language impairment and children with a specific reading disability.

The auditory backward recognition masking (ABRM) and intensity discrimination (ID) thresholds of children with a specific language impairment and poor reading (SLI-poor readers), children with an SLI and average reading (SLI-average readers), children with a specific reading disability and average spoken language skills (SRD-average language), and children with normal spoken and written language (controls) were estimated with "child-friendly" psychophysical tasks. The pattern of ABRM and ID scores suggests that a subset of children with concomitant oral language and reading impairments has poor ABRM thresholds, and that a subgroup of children with an SLI or SRD has poorer ID thresholds than controls. The latter result warns against using rapid auditory processing tasks that do not actively control for auditory discrimination ability. Further, some unusually poor ABRM scores and ID scores question the validity of extreme scores produced by children on psychophysical tasks. Finally, the poor oral language scores of many of the children who had impaired reading highlight the need to test the oral language skills of SRD samples to ascertain how homogeneous and specifically disabled they really are.

Adolescent↗