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Relation of sound intensity and accuracy of localization.

Tests were carried out on 17 subjects to determine the accuracy of monaural sound localization when the head is not free to turn toward the sound source. Maximum accuracy of localization for a constant-volume sound source coincided with the position for maximum perceived intensity of the sound in the front quadrant. There was a tendency for sounds to be perceived more often as coming from a position directly toward the ear. That is, for sounds in the front quadrant, errors of localization tended to be predominantly clockwise (i.e., biased toward a line directly facing the ear). Errors for sounds occurring in the rear quadrant tended to be anticlockwise. The pinna's differential effect on sound intensity between front and rear quadrants would assist in identifying the direction of movement of objects, for example an insect, passing the ear.

Adolescent↗

Effects of randomizing signal level and duration on temporal gap detection.

Although discriminable changes in stimulus energy or overall duration may accompany the silent temporal gap, there is little evidence that these extraneous cues confound the measurement of temporal gap detection threshold. In this report we show that (1) under conditions where gap detection thresholds are large in relation to the duration of the standard, extraneous cues may confound gap detection leading to underestimates of the true threshold, and (2) randomization of overall stimulus level and duration can successfully remove confounding energy and duration cues without distracting the listener's attention from the temporal-gap cue.

Adult↗

Binaural phase differences and binaural auditory adaptation.

In order to determine the relationship between binaural phase localization and auditory adaptation, subjects were asked to perform a series of phase-based localization tasks, as well as an SDLB adaptation task. A binaurally presented 400 Hz tone was used for midplane localization tasks, and adaptation balances. The tone was presented monaurally during adaptation after binaural localization and the SDLB pre-test. Following 7 min exposure, subjects readjusted phase to centre the binaural stimulus in the midline, and then adjusted intensity to determine dB of adaptation. No consistent or statistically significant change in phase settings occurred. There was a significant decline in the balance intensity as a function of adaptation. A further re-establishment of the midline by phase manipulation also showed no localization effect. For the stimulus values used in the present study, there was no inter-effect of binaural phase localization, and SDLB auditory adaptation.

Adaptation, Physiological↗

Conjoining auditory and visual features during high-rate serial presentation: processing and conjoining two features can be faster than processing one.

The time required to conjoin stimulus features in high-rate serial presentation tasks was estimated in auditory and visual modalities. In the visual experiment, targets were defined by color, orientation, or the conjunction of color and orientation features. Responses were fastest in color conditions, intermediate in orientation conditions, and slowest in conjunction conditions. Estimates of feature conjunction time (FCT) were derived on the basis of a model in which features were processed in parallel and then conjoined, permitting FCTs to be estimated from the difference in reaction times between conjunction and the slowest single-feature condition. Visual FCTs averaged 17 msec, but were negative for certain stimuli and subjects. In the auditory experiment, targets were defined by frequency, location, or the conjunction of frequency and location features. Responses were fastest in frequency conditions, but were faster in conjunction than in location conditions, yielding negative FCTs. The results from both experiments suggest that the processing of stimulus features occurs interactively during early stages of feature conjunction.

Adolescent↗

Perception of the relative distances of nearby sound sources.

The pressure of a sound varies systematically with a listener's distance from a sound source, providing a useful cue for perceiving changes in the distance between a listener and a sound-producing object. The pressure-discrimination hypothesis predicts that thresholds for discriminating changes in distance are constrained by the underlying ability to discriminate the resulting changes in sound pressure--specifically, that the smallest discriminable change in distance should be about 5% of the reference distance. Previous studies reported thresholds of about 5% for reference distances greater than a few meters but surprisingly worse thresholds for closer reference distances. In the present study, thresholds at two close distances, 1 and 2 m, were within the 5% range predicted from the pressure-discrimination hypothesis. Moreover, thresholds were significantly worse in a control condition in which the pressure cue was removed. Results of previous studies were adjusted to take into account the possibility of conservative response tendencies by the subjects. These adjusted findings agree well with the results of the present study and the pressure-discrimination hypothesis. It is concluded that variations in sound pressure are very useful for perceiving changes in listener-source distances, even at close distances.

Adult↗

[Reaction time and temporal serial judgment: corroboration or dissociation?].

Dissociations between a motor response and the subject's verbal report have been reported from various experiments that investigated special experimental effects (e.g., metacontrast or induced motion). To examine whether similar dissociations can also be observed under standard experimental conditions, we compared reaction times (RT) and temporal order judgments (TOJ) to visual and auditory stimuli of three intensity levels. Data were collected from six subjects, each of which served for nine sessions. The results showed a strong, highly significant modality dissociation: While RTs to auditory stimuli were shorter than RTs to visual stimuli, the TOJ data indicated longer processing times for auditory than for visual stimuli. This pattern was found over the whole range of intensities investigated. Light intensity had similar effects on RT and TOJ, while there was a marginally significant tendency of tone intensity to affect RT more strongly than TOJ. It is concluded that modality dissociation is an example of "direct parameter specification", where the pathway from stimulus to response in the simple RT experiment is (at least partially) separate from the pathway that leads to a conscious, reportable representation. Two variants of this notion and alternatives to it are discussed.

Adult↗

[Responses of auditory neurons of the medulla oblongata of the frog to presentation of tones with sinusoidal amplitude modulation].

The responses of single units in the medullary auditory regions of the frog Rana ridibunda to sinusoidally amplitude-modulated tones of characteristic frequencies were studied. The reproduction of the sound modulation in the discharge frequency of the units was determined from cycle histograms of the discharges locked to the modulation period. In dorsal nucleus units the amplitude modulation was preserved in the discharge modulation over a wide modulation frequency and sound intensity ranges. In many superior olivary neurons an enhancement of small amplitude changes within the range of modulation frequencies 70-150 Hz was observed. The reaction phase was linear-dependent on the modulation frequency. The best enhancement of amplitude changes took place for small modulation indices.

Animals↗

Infants' coordination of auditory and visual depth information.

Using the preferential-looking procedure infants 5, 7, and 9 months of age were presented two videoimages side by side on separate monitors accompanied by a soundtrack that matched one of the images. Each infant was presented: (1) a stationary drum-beating toy paired with the same toy approaching and receding in depth, to assess infants' recognition both that changing sound amplitude is a property of an object that is moving in space and that constancy in amplitude is a property of a stationary object; (2) a drum-beating toy moving horizontally paired with one approaching and receding in depth, to assess infants' recognition that systematic increases and decreases in amplitude accompany object movement in a particular dimension, namely depth; and (3) two identical toys alternately approaching and receding in depth but out of phase (i.e., one approaching while the other is receding), to assess infants' recognition that increases and decreases in amplitude accompany a particular type of object movement in depth. Measures of mean duration of looking time indicated that the 5-month-olds looked reliably to the correct videoimage only for the stationary toy paired with the constant amplitude sound. The 7-month-olds recognized that changes in amplitude accompany object movement in depth but did not coordinate auditory with visual depth information as well as older infants. The 9-month-olds looked reliably to the correct videoimages in all conditions. Possible contributing factors to these developmental trends in performance are discussed.

Attention↗

Ontogeny of neural discharge patterns in the ventral cochlear nucleus of the mongolian gerbil.

Discharge patterns were recorded extracellularly from single neurons in the ventral cochlear nucleus (VCN) of Mongolian gerbils ranging in age from 10 days after birth (DAB) to adult, a period which includes the onset of responsiveness to acoustic stimulation. At 10 DAB none of the neurons encountered within the VCN responded to acoustic stimulation. At 12 DAB approximately 15% of the neurons isolated in VCN were responsive. This coincided with the earliest cochlear microphonic potentials and preceded the appearance of the cochlear compound action potential (AP) by two days. At 14 DAB, or older, the great majority of neurons isolated in VCN responded to acoustic stimulation. Most parameters of VCN neural function exhibited significant changes between 12 and 18 DAB: neural thresholds improved approximately 100 dB; mean spontaneous discharge rate increased; the high-frequency range of characteristic frequency (CF) values increased from 10.0 to 24.0 kHz; the upper limit for phase locking increased from 0.8 kHz to 3.0 kHz; dynamic range increased from 16 dB to 44 dB, and the proportion of units with well-defined initial onset peaks in their post-stimulus-time (PST) response patterns increased from 40% to 100% of units. Most of the neural parameters examined achieved adult characteristics by 18 DAB. Frequency tuning (Q10dB) matured earlier for high-CF units. The most sharply tuned neurons with high CFs (greater than 4 kHz) at 12 DAB had Q10dB values equal to those for adults. None of the neurons with low CFs (less than 4 kHz) had Q10dB values greater than 1.2 at this age. Classical 'on' PST response patterns were not seen at 12 and 14 DAB. A unique PST response type, characterized by very long latency phasic discharge, was observed only at 12 DAB. None of the VCN neurons recorded from 12 DAB subjects displayed rhythmic 'bursting' or 'pulsing' PST response patterns, as has been reported at the earliest stages of functional development in the VCN of the cat. Most units were capable of sustained discharge, even with long stimulus durations. Units with 'primary-like' PST response patterns at 12 exhibited greater variability in first spike latency and less pronounced initial rates of firing than was characteristic in adults, resulting in poorly defined onset peaks. In contrast, units with chopper PST response patterns showed well-defined onset peaks.

Animals↗

Dynamic effects in the input/output relationship of auditory nerve.

Cyclic histograms of the responses of single auditory ganglion cells in the guinea pig were recorded during stimulation with amplitude modulated tones. Modulation frequencies ranged from 10 Hz to 800 Hz. The response histograms, phase-locked to the modulation signals, were analysed for mean action potential rate and for the amplitude of the fundamental component at the modulation frequency. Expected values for the amplitude of the modulation responses were calculated using the variation of mean firing rate with intensity. The observed responses differed from the expected responses in several ways. First, the amplitudes of the modulation responses were larger than expected. Second, the stimulus intensities at which the observed modulation responses peaked was greater by about 7-10 dB than the expected intensity for maximum response. Third, both the magnitude of the response at a given intensity and the intensity at which the response peaked increased with modulation frequency. Fourth, the responses extended to higher stimulus intensities than expected. The observed modulation responses were compared with predictions from the Schroeder and Hall model of adaptation and were found to agree with good quantitative precision. These results suggest that the observed modulation responses are another manifestation of the very rapid (less than 20 ms) adaptation seen in the onset responses of nerve fibres [(1985) Hear. Res. 17, 1-12]. It is concluded that the static input-output responses of auditory nerve are not a good predictor of the dynamic responses to fluctuating stimuli.

Adaptation, Physiological↗

Aftereffect arising from unidirectional change of sound level in a tone: frequency specificity with a complex adaptor.

Subjects adapted to square-wave adaptors, stimuli containing odd harmonics of the fundamental, and, to provide baseline data, sinusoidal adaptors matching the square-wave's fundamental. Nulls were obtained for various frequencies of the test stimulus. At any given frequency, the baseline null was subtracted from the null for square-wave adaptation. These corrected nulls indicated frequency-specific aftereffects at the third and fifth harmonics. The evidence is consistent with previous attempts to link the aftereffect of changing sound level in a tone with the auditory movement aftereffect because the latter may also show frequency specificity.

Adult↗

A correction for converting 2 cm3 coupler responses to insertion responses for custom in-the-ear nondirectional hearing aids.

A correction for custom in-the-ear nondirectional hearing aids is obtained for converting a frequency response measured using a 2 cm3 coupler to an insertion response, approximating that measured using a manikin and ear simulator. The results are compared to those of a previous published study. The methods used for obtaining the responses make use of a signal analyzer with discrete Fourier transform capabilities.

Acoustics↗

Hands help hearing: facilitatory audiotactile interaction at low sound-intensity levels.

Auditory and vibrotactile stimuli share similar temporal patterns. A psychophysical experiment was performed to test whether this similarity would lead into an intermodal bias in perception of sound intensity. Nine normal-hearing subjects performed a loudness-matching task of faint tones, adjusting the probe tone to sound equally loud as a reference tone. The task was performed both when the subjects were touching and when they were not touching a tube that vibrated simultaneously with the probe tone. The subjects chose on average 12% lower intensities (p < 0.01) for the probe tone when they touched the tube, suggesting facilitatory interaction between auditory and tactile senses in normal-hearing subjects.

Adult↗

Frequency and intensity difference limens for harmonics within complex tones.

A two-interval, two-alternative forced choice task was used to estimate frequency difference limens (DLs) for individual harmonics within complex tones, and DLs for the periodicity (i.e., number of periods per s) of the whole complexes. For complex tones with equal-amplitude harmonics, the DLs for the lowest harmonics were small (less than one percent). The DLs increased rather abruptly around the fifth to seventh harmonic. The highest harmonic in each complex was also well discriminated, and the discriminability of a single high harmonic was markedly improved by increasing its level relative to the other components. The DL for a complex tone was generally smaller than the frequency DL of its most discriminable component. The DL for a complex was found to be predictable from the DLs of the harmonics comprising the complex, using a formula derived by Goldstein [J. Acoust. Soc. Am. 54, 1496-1516 (1973)] from his optimum processor theory for the formation of the pitch of complex tones. The DL for a complex is sometimes primarily determined by high harmonics, such as the highest harmonic, or a harmonic whose level exceeds that of adjacent harmonics. We also measured intensity DLs for individual harmonics within complex tones. The intensity DLs were smallest for low harmonic numbers, and for the highest harmonic in a complex. An excitation-pattern model was used to determine whether the frequency DLs of harmonics within complex tones could be explained in terms of place mechanisms, i.e., in terms of changes in the amount of excitation at appropriate frequency places. We conclude that place mechanisms are not adequate, and that information about the frequencies of individual harmonics is probably carried in the time patterning of neural impulses.

Auditory Perception↗

The relations among critical ratios, critical bands, and intensity difference limens in man.

Band-narrowing estimates of the critical bandwidth (CB) are consistently larger than critical-ratio (CR) estimates for the same signal frequency. Bilger [in Hearing and Davis: Essays Honoring Hallowell Davis, edited by S.K. Hirsh et al. (Washington U.P., St. Louis, 1976), p. 191] proposed that this difference could be accounted for by reference to intensity-discrimination performance [CR(Hz)/CB(Hz) = delta I/I]. To test this hypothesis, band-narrowing, critical-ratio, and intensity-discrimination data were collected for four normally hearing, well-trained listeners. Signal frequency was 2000 Hz and two noise levels were used: 20 and 50 dB N0. The relations proposed by Bilger among critical-bandwidth estimates from band-narrowing experiments, critical-ratio estimates from pure-tone detection in wideband noise, and intensity discrimination for a critical-band-wide noise in wideband noise are not supported by the results of individual listeners, or results averaged across listeners.

Adult↗