Effects of hair cell lesions on responses of cochlear nerve fibers. I. Lesions, tuning curves, two-tone inhibition, and responses to trapezoidal-wave patterns.
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Animals↗
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Effects of hair cell lesions on responses of cochlear nerve fibers. II. Single- and two-tone intensity functions in relation to tuning curves.
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Acoustic Stimulation↗
Characteristics of neurons in auditory cortex of monkeys performing a simple auditory task.
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Animals↗
Auditory nerve representation of vowels in background noise.
Responses of auditory nerve fibers to steady-state vowels presented alone and in the presence of background noise were obtained from anesthetized cats. Representation of vowels based on average discharge rate and representation based primarily on phase-locked properties of responses are considered. Profiles of average discharge rate versus characteristic frequency (CF) ("rate-place" representation) can show peaks of discharge rate in the vicinity of formant frequencies when vowels are presented alone. These profiles change drastically in the presence of background noise, however. At moderate vowel and noise levels and signal/noise ratios of +9 dB, there are not peaks of rate near the second and third formant frequencies. In fact, because of two-tone suppression, rate to vowels plus noise is less than rate to noise alone for fibers with CFs above the first formant. Rate profiles measured over 5-ms intervals near stimulus onset show clear formant-related peaks at higher sound levels than do profiles measured over intervals later in the stimulus (i.e., in the steady state). However, in background noise, rate profiles at onset are similar to those in the steady state. Specifically, for fibers with CFs above the first formant, response rates to the noise are suppressed by the addition of the vowel at both vowel onset and steady state. When rate profiles are plotted for low spontaneous rate fibers, formant-related peaks appear at stimulus levels higher than those at which peaks disappear for high spontaneous fibers. In the presence of background noise, however, the low spontaneous fibers do not preserve formant peaks better than do the high spontaneous fibers. In fact, the suppression of noise-evoked rate mentioned above is greater for the low spontaneous fibers than for high. Representations that reflect phase-locked properties as well as discharge rate ("temporal-place" representations) are much less affected by background noise. We have used synchronized discharge rate averaged over fibers with CFs near (+/- 0.25 octave) a stimulus component as a measure of the population temporal response to that component. Plots of this average localized synchronized rate (ALSR) versus frequency show clear first and second formant peaks at all vowel and noise levels used. Except at the highest level (vowel at 85 dB sound pressure level (SPL), signal/noise = +9 dB), there is also a clear third formant peak. At signal-to-noise ratios where there are no second formant peaks in rate profiles, human observers are able to discriminate second formant shifts of less than 112 Hz. ALSR plots show clear second formant peaks at these signal/noise ratios.
Animals↗
Effects of ear plugging on single-unit azimuth sensitivity in cat primary auditory cortex. I. Evidence for monaural directional cues.
1. Single-unit recordings were carried out in primary auditory cortex (AI) of barbiturate-anesthetized cats. Neurons, sensitive to sound direction in the horizontal plane (azimuth), were identified by their responses to noise bursts, presented in the free field, that varied in azimuth and sound pressure level (SPL). SPLs typically varied between 0 and 80 dB and were presented at each azimuth that was tested. Each azimuth-sensitive neuron responded well to some SPLs at certain azimuths and did not respond well to any SPL at other azimuths. This report describes AI neurons that were sensitive to the azimuth of monaurally presented noise bursts. 2. Unilateral ear plugging was used to test each azimuth-sensitive neuron's response to monaural stimulation. Ear plugs, produced by injecting a plastic ear mold compound into the concha and ear canal, attenuated sound reaching the tympanic membrane by 25-70 dB. Binaural interactions were inferred by comparing responses obtained under binaural (no plug) and monaural (ear plug) conditions. 3. Of the total sample of 131 azimuth-sensitive cells whose responses to ear plugging were studied, 27 were sensitive to the azimuth of monaurally presented noise bursts. We refer to these as monaural directional (MD) cells, and this report describes their properties. The remainder of the sample consisted of cells that either required binaural stimulation for azimuth sensitivity (63/131), because they were insensitive to azimuth under unilateral ear plug conditions or responded too unreliably to permit detailed conclusions regarding the effect of ear plugging (41/131). 4. Most (25/27) MD cells received either monaural input (MD-E0) or binaural excitatory/inhibitory input (MD-EI), as inferred from ear plugging. Two MD cells showed other characteristics. The contralateral ear was excitatory for 25/27 MD cells. 5. MD-E0 cells (22%, 6/27) were monaural. They were unaffected by unilateral ear plugging, showing that they received excitatory input from one ear, and that stimulation of the other ear was without apparent effect. On the other hand, some monaural cells in AI were insensitive to the azimuth of noise bursts, showing that sensitivity to monaural directional cues is not a property of all monaural cells in AI. 6. MD-EI cells (70%, 19/27) exhibited an increase in responsiveness on the side of the plugged ear, showing that they received excitatory drive from one ear and inhibitory drive from the other. MD-EI cells remained azimuth sensitive with the inhibitory ear plugged, showing that they were sensitive to monaural directional cues at the excitatory ear.(ABSTRACT TRUNCATED AT 400 WORDS)
Animals↗
Influence of phenomenal time on perceived space.
It is known from work by Helson and King that the apparent spatial distance between stimuli presented in succession depends on the time interval between those stimuli ("tau effect"). It is also known that the apparent time (i.e., the interval of time perceived between stimuli presented in succession) depends on the spatial distance between the stimuli defining the time interval (called "kappa effect" by Cohen, Hansel, and Sylvester). For the "kappa effect," apparent time between lights and stimuli on the skin of the forearm undergoes modification depending on the apparent spatial distance, as presented in Suto's work beginning in the early 1940s. The present work is complementary to Suto's. Its purpose is to test whether apparent spatial distance depends on the objective or subjective (apparent, phenomenal) time interval. To achieve this, our crucial (third) experiment was preceded by two exploratory experiments: the first to verify the illusion in which a subdivided interval appears longer than an empty interval of the same length (Oppel-Kundt temporal illusion); the second to verify the presence of the "tau effect" with simultaneous tactual and auditory stimuli for time intervals between 1500 and 2500 msec. In the third experiment subjects received successive tactual stimuli defining two spatial distance and two time intervals. They also received auditory stimuli that produced the Oppel-Kundt illusion by making the time intervals phenomenally different. The results fill a small experimental gap by showing it is subjective (phenomenal) and not objective (physical) time that influences perceived spatial distances.
Adolescent↗
Monaural and binaural intensity discrimination in normal and cochlear-impaired listeners.
Monaural and binaural intensity difference limens for 75-dB SPL pure tones were determined for 6 normal subjects and for 6 subjects with cochlear hearing loss. The magnitude of binaural masking level difference (BMLD) was also determined. Both normal and hearing-impaired subjects showed a 0.45-dB binaural advantage for intensity discrimination. In contrast, the BMLD was appreciably reduced with hearing impairment. Results are discussed in terms of specific effects of hearing loss on binaural hearing.
Adult↗
Compound action potentials recorded from the intracranial portion of the auditory nerve in man: effects of stimulus intensity and polarity.
Compound action potentials (CAP) were recorded from the intracranial portion of the eighth nerve in patients with normal hearing who were undergoing neurosurgical operations for cranial nerve disorders (trigeminal neuralgia and hemifacial spasm). Brain-stem auditory-evoked potentials were recorded intraoperatively to ensure that no noticeable changes occurred in conduction in the auditory nerve as a result of surgical dissections. The CAP recorded from the middle portion of the exposed intracranial portion of the eighth nerve in response to clicks of high intensity (100-110 dB peak equivalent SPL, or pe SPL) had a triphasic shape, as is commonly seen in monopolar recordings from long nerves. A second negative peak (N2) could be identified in some patients. There was little difference in the waveform of the CAP in response to condensation and rarefaction clicks, and in some patients the waveform of the CAP remained the same over a range of stimulus intensities (from 105 to 75 dB pe SPL), whereas in others the negative peak of the CAP became much broader in response to stimuli with intensities of less than 85 dB. In some patients the N2 peak became dominant as the stimulus intensity was decreased. At low stimulus intensities, the response consisted of a single, broad negativity. The latency-intensity curves for the N1 peak had different slopes in different patients. In those individuals in whom there was a noticeable difference between the latency of the N1 peak in response to clicks of opposite polarity, the latency-intensity curves of the responses to rarefaction clicks were steeper than those of the responses to condensation clicks, and the latency of the N1 peak to condensation clicks became shorter than that to rarefaction clicks at intensities below 85-90 dB pe SPL. The latency-intensity curves for the N2 peak were usually less steep than those of the N1 peak, but in some patients the curves for these two peaks had similar slopes. The amplitude of the N1 peaks showed a steep increase in click intensities at 95 and 105 dB, and a much less steep course for intensities below 95 dB. The amplitudes of the N2 peak reached a plateau in the range 95-105 dB, and decreased more rapidly than the N1 peak below 95 dB.
Acoustic Stimulation↗
Auditory streaming and vertical localization: interdependence of "what" and "where" decisions in audition.
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Acoustic Stimulation↗
Duplex perception with musical stimuli: a further investigation.
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Auditory Perception↗
Modality effects in the coding and reproduction of rhythms.
The temporal coding assumption is that time of presentation is coded more accurately for auditory events than for visual events. This assumption has been used to explain the modality effect, in which recall of recent auditory events is superior to recall of recent visual events. We tested the temporal coding assumption by examining the coding and reproduction of quintessentially temporal stimuli-rhythms. The rhythms were produced by sequences of short and long auditory stimuli or short and long visual stimuli; in either case, the task was to reproduce the temporal sequence. The results from four experiments demonstrated reproduction of auditory rhythms superior to that of visual rhythms. We conclude that speech-based explanations of modality effects cannot accommodate these findings, whereas the findings are consistent with explanations based on the temporal coding assumption.
Adult↗
Time estimation and expectancies.
The purpose of this research was to examine the influence of different types of expectancies on time estimation behavior. In Experiment 1, subjects were led to expect that a given number of trials would occur in a music perception task. In Experiment 2, expectancies concerning the duration of a given waiting period were varied. Results of both experiments indicated that the confirmation/violation of expectancies exerted a significant impact on duration judgments. When subjects received more/fewer trials than expected or waited for a duration that was longer/shorter than expected, the total duration of these time spans was over- and underestimated, respectively. Conversely, time estimates were relatively accurate when subjects' expectancies were confirmed. The results of Experiment 1 further revealed that reaction time responses within the music perception task were also systematically influenced by the expected amount of activity. Results are discussed in terms of a framework that emphasizes the role of anticipatory attending on time estimation behavior.
Acoustic Stimulation↗
Infants' responsiveness to the auditory and visual attributes of a sounding/moving stimulus.
Responses to unimodal and multimodal attributes of a compound auditory/visual stimulus were investigated in 4-, 6-, 8-, and 10-month-old infants. First, infants were habituated to a compound stimulus consisting of a visual stimulus that moved up and down on a video monitor and a sound that occurred each time the visual stimulus reversed direction at the bottom. Once each infant met a habituation criterion, a series of test trials was administered to assess responsiveness to the components of the compound stimulus. Response was defined as the total duration of visual fixation in each trial. In the two unimodal test trials, the rate at which the component was presented was changed while the rate of the other component remained the same, whereas in the bimodal test trial the rate of both components was changed simultaneously. Results indicated that infants at each age successfully discriminated the bimodal and the two unimodal changes and that regression to the mean did not account for the results. Results also showed that disruption of the temporal relationship that accompanied the change in rate in the two unimodal test trials was also discriminable, but rate changes appeared to play a greater role in responsiveness than did synchrony changes. Considered together with results from similar prior studies, the current results are consistent with the modality appropriateness hypothesis in showing that discrimination of temporal changes in the auditory and visual modalities is dependent on the specialization of the sensory modalities.
Arousal↗
Perceptual organization of auditory temporal patterns in European starlings (Sturnus vulgaris).
The perception of continuously repeating auditory patterns by European starlings was explored in seven experiments. In Experiment 1, 4 starlings learned to discriminate between two continuously repeating, eight-element, auditory patterns. Each eight-element pattern was constructed from different temporal organizations of two elements differing in timbre. In Experiments 2-7, the repeating patterns were transformed in ways designed to identify the starlings' perceptual organization of the patterns. In Experiment 2, the starlings identified patterns beginning with novel starting points. In Experiment 3, discrimination performance was adversely affected by reorganizing the elements in the patterns. In Experiments 4 and 5, the pattern elements were altered. In Experiment 4, the patterns were constructed from two novel elements. In Experiment 5, the temporal location of the two pattern elements was reversed. The transformations of the patterns in Experiments 4 and 5 affected discrimination performance for some, but not all, of the starlings. In Experiments 6 and 7, replacing either of the two elements with silent intervals had no effect on discrimination performance. The results of these experiments identify basic grouping principles that starlings use when they perceive auditory patterns.
Animals↗
Speech recognition abilities of adults using cochlear implants with FM systems.
Speech recognition was evaluated for ten adults with normal hearing and eight adults with Nucleus cochlear implants (CIs) at several different signal-to-noise ratios (SNRs) and with three frequency modulated (FM) system arrangements: desktop, body worn, and miniature direct connect. Participants were asked to repeat Hearing in Noise Test (HINT) sentences presented with speech noise in a classroom setting and percent correct word repetition was determined. Performance was evaluated for both normal-hearing and CI participants with the desktop soundfield system. In addition, speech recognition for the CI participants was evaluated using two FM systems electrically coupled to their speech processors. When comparing the desktop sound field and the No-FM condition, only the listeners with normal hearing made significant improvements in speech recognition in noise. When comparing the performance across the three FM conditions for the CI listeners, the two electrically coupled FM systems resulted in significantly greater improvements in speech recognition in noise relative to the desktop soundfield system.
Adult↗
Spectral frequency and the modulation of the acoustic startle reflex by background noise.
The rat's (Long-Evans) acoustic startle reflex to a high-frequency tone burst (10.5 kHz) was depressed by intense high-frequency band-pass noise (8-16 kHz) but enhanced by low frequency noise (1-2 kHz). However, contrary to the hypothesis that the depression of startle in intense background noise is produced by sensory masking, the reflex to a low-frequency tone burst (at 1 kHz) was depressed by both high- and low-frequency band-pass noise. Two additional hypotheses are offered to supplement sensory masking in order to explain the asymmetry in these data. The first is that the intratympanic reflex, which acts as a high pass filter on acoustic input, is elicited in intense backgrounds. The second is that acoustic startle reflexes elicited by intense low-frequency tones are in part elicited by their high-frequency distortion products and that these distortion products are then masked by high-frequency background noise.
Animals↗
Two-state compression of spectral tilt: individual differences and psychoacoustical limitations to the benefit from compression.
A psychoacoustic rationale was developed for a hearing aid design in which compression of spectral tilt was incorporated without any instantaneous nonlinear distortion. This involved switching between a 'flat' and a 'rising' frequency response; the switching was done slowly to avoid audible transients and was controlled by feedback derived from comparison of output levels in low- and high-frequency channels, approximating voiced/unvoiced detection. The effect of this switching process was to narrow the distribution of spectral tilt values compared with the input. Asynchrony between the switching and the triggering speech structures was avoided by also delaying the signal path. Unfortunately, hearing-impaired listeners performed more poorly on the switching system than on either of the control 'flat' or 'rising' frequency-responses. An explanation is offered (on the basis of growing evidence from perceptual experiments) of the perceptual importance of temporal envelope contours within individual frequency bands. It was possible, in part, to predict individuals' results in the switching condition from age and audiometric or psychoacoustic characteristics. The results suggest a modification to the switching design, and they point to an intrinsic limit to the ability of all hearing aids of the compression type to enhance intelligibility.
Adult↗
Hearing in two cricetid rodents: wood rat (Neotoma floridana) and grasshopper mouse (Onychomys leucogaster).
The audiograms of two wood rats and three grasshopper mice were determined with a conditioned avoidance procedure. The wood rats were able to hear tones from 940 Hz to 56 kHz at a level of 60 dB (SPL), with their best sensitivity of -3 dB occurring at 8 kHz. The hearing of the grasshopper mice ranged from 1.85 kHz to 69 kHz at 60 dB (SPL), with their best sensitivity of 9 dB also occurring at 8 kHz. These results support the relation between interaural distance and high-frequency hearing and between high- and low-frequency hearing. The inability of the grasshopper mouse to hear low frequencies as well as other desert rodents such as kangaroo rats and gerbils demonstrates that not all rodents found in deserts have developed good low-frequency hearing. The degree to which general and specific selective pressures have played a role in the evolution of rodent hearing is discussed.
Animals↗