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PubMed1989

Auditory and visual effects on solutions to computerized mathematics problems as a function of rate of digit presentation.

This exploratory investigation concerned the effects of both auditory and visual stimulus variations on the accuracy of mental solutions to addition problems presented on a computer screen (CRT). 5 intensities of background noise and 5 background hues were presented randomly to 123 undergraduate volunteers as they mentally summed 25 numerals ranging from 1 to 5 at rates of either 1 sec. or 3 sec. per numeral timed from the onset of the previous numeral. A 2 x 2 x 5 mixed splitplot factorial analysis of variance gave a significant difference in errors between rates of digit presentation with greater accuracy associated with the 3-sec. rate. There was no significant difference in mean errors for auditory vs color modalities, yet a post hoc Newman-Keuls paired-comparison test of decibel levels at the 1-sec. rate of digit presentation gave a significant difference in mean errors between 60-dB and 70-dB sound-pressure levels (SPLs) of white masking noise. Also, a post hoc F test on differences between successive stages indicated significant differences suggesting a "learning set." Comparisons between 'everyday' instances of these noise levels are made with implications for optimal computational environments.

Adult↗
PubMed1980

Effect of signal bandwidth upon threshold of the acoustic reflex and upon loudness.

The effect of activating-signal bandwidth upon the threshold of the acoustic reflex (TAR) was measured. Subsequently, loudness measurements were made for the same signals at the same intensity levels that were required to elicit an acoustic-reflex response. When loudness and TAR are compared at comparable levels, similar trends emerged. Results from this experiment provide evidence for both qualitative and quantitative similarities between acoustic reflex and the perception of loudness. This, in turn, suggest that signals at TAR may be equally loud for listeners with normal hearing.

Acoustic Stimulation↗
PubMed1992

Hearing aid saturation, coherence, and aided loudness discomfort.

Real-ear measurements of the aided Loudness Discomfort Level (LDL) were obtained from five hearing-impaired listeners who were fit with two Class A and two Class D linear hearing aids, each with a different saturation sound pressure level (HFA SSPL90). These measurements were obtained with 75 dB SPL continuous discourse to determine whether saturation-induced distortion contributes to the sensation of loudness. Real-ear coherence measurements made at LDL were used to determine the extent of saturation, and sound quality judgments were used to determine whether the distortion present at LDL affected sound quality. Results indicated that the SPL, coherence, and sound quality ratings obtained at LDL were all higher for Class D hearing aids with relatively high HFA SSPL90 than for Class A hearing aids with relatively low HFA SSPL90. Overall results were generally consistent with the hypothesis that distortion affects both sound quality and the perception of loudness.

Adult↗
PubMed2003

[Contralateral electrically evoked reflex of the musculus stapedius in patients with cochlear implant].

Registration of electrically evoked reflex is widely applied in rehabilitation of patients by cochlear implantation. As a rule, visual assessment of the ipsilateral reflex is made intraoperatively for functional evaluation of surgical results. Of interest is use of contralateral electrically evoked reflex of the musculus stapedius in the course of adjustment of the speech processor. We studied the latter reflex in 20 patients with cochlear implants Cl24M and Cl22 made by 'Cochlear'. 13 patients used Sprint processors, 7 patients - Spectra ones. Zodiak impedansometer registered the reflex which was recorded in 12 patients. The threshold of the reflex registration correlated well with comfortable perception of loudness. Most of the patients evaluated threshold (for the reflex) sound perception as the sound of moderate loudness. The conclusion is made that registration and analysis of the contralateral electrically evoked reflex can assess a comfortable stimulation level in adjustment of speech processors in patients with cochlear implants.

Adolescent↗
PubMed1982

Auditory distortion.

The auditory system responds to pulsatile energy flow from the environment. Compression and rarefaction of gaseous molecular mass is transduced into electromechanical forms, in order to produce an effect at the cortical level. For energy input to have consistent meaning, transduction must preserve information coded within the pattern of energy flow. Distortion, or alteration of the original form, occurs in many ways throughout the chain of generation/transmission/reception/interpretation. Parameters of energy flow are discussed, and distortion of each parameter is presented in a context which permits the development of a distortion-based analysis of common clinical problems in otolaryngology.

Acoustics↗
PubMed1991

Effects of subchronic d-amphetamine on prepulse and gap inhibition of the acoustic startle reflex in rats.

Prepulse inhibition of the startle reflex has been used as an animal model for information processing deficits found in some types of schizophrenia. These deficits may be mediated by hypersensitive dopaminergic systems. In the present study, the effects of subchronic d-amphetamine administration [2 mg/kg intraperitoneally (IP)] on prepulse and gap inhibition of the startle reflex were compared to the effects of acute amphetamine and saline administration on startle inhibition. Results of three experiments are reported. The first two experiments were used to select prestimulus parameters sensitive to changes in stimulus intensity on the one hand, and prestimulus parameters sensitive to temporal aspects of stimulus processing on the other hand. Because schizophrenics have problems with the temporal sequencing of information, prestimulus inhibition of the startle reflex was expected to be more pronounced when prestimulus processing depended predominantly upon temporal factors. Results supported this hypothesis, although the effects of d-amphetamine were found at near detection threshold duration only. Subchronic amphetamine had no effect on the neuronal mechanisms underlying inhibition of the startle reflex by prestimuli. The results also suggested that a careful selection of duration and intensity of the prestimulus may increase the sensitivity of the prestimulus-startle paradigm for the effects of drugs, for example.

Acoustic Stimulation↗
PubMed1987

Stimulus properties influencing the responses of inferior colliculus neurons to amplitude-modulated sounds.

The temporal pattern of the responses of neurons in the inferior colliculus of the anesthetized rat were studied using continuous tone or noise carrier signals, amplitude modulated by pseudorandom noise. Period histograms of the responses, cross-correlated with the pseudorandom noise, gave an estimate of the unit's impulse responses to modulation. The amplitude-modulation rate transfer function (MTF) was obtained by Fourier transforming the correlograms. At sound levels within approximately 15 dB of the unit threshold, the MTFs were near lowpass functions between 6 and 200 Hz but became more bandpass-like as the intensity was increased. There was a steep decline in the response to modulation at modulation frequencies above 200 Hz for all stimulus intensities. For the bandpass-type MTFs the greatest modulation of the discharge pattern occurred at modulation frequencies between 10 and 200 Hz with a maximum in the distribution of MTF peak values between 100 and 120 Hz. There was no consistent relationship with characteristic frequency of either the position of the MTF peak or the high-frequency cutoff of the MTF. The cross-correlograms obtained at high stimulus intensities (30-60 dB above threshold) often showed a negative peak, representing a decrease in the probability of firing in response to intensity increments in the stimulus, and denoting a nonmonotonic rate-intensity function. The MTFs for units responding to amplitude-modulated broadband noise were often flatter in the low frequency region than those generated with tone carriers at corresponding intensities. For some units addition of a broadband noise background to the modulated tone changed the response characteristic of the MTF from bandpass to lowpass and shifted the MTF peak to a lower modulation frequency. The results demonstrate that although neurons in the inferior colliculus are selectively sensitive to the modulation frequency of dynamic stimuli, the response characteristics are not invariant, but instead are closely dependent on the conditions under which the modulation is presented.

Acoustic Stimulation↗
PubMed1992

Musical duplex perception: perception of figurally good chords with subliminal distinguishing tones.

In a variant of duplex perception with speech, phoneme perception is maintained when distinguishing components are presented below intensities required for separate detection, forming the basis for the claim that a phonetic module takes precedence over nonspeech processing. This finding is replicated with music chords (C major and minor) created by mixing a piano fifth with a sinusoidal distinguishing tone (E or E flat). Individual threshold intensities for detecting E or E flat in the context of the fixed piano tones are established. Chord discrimination thresholds defined by distinguishing tone intensity were determined. Experiment 2 verified masked detection thresholds and subliminal chord identification for experienced musicians. Accurate chord perception was maintained at distinguishing tone intensities nearly 20 dB below the threshold for separate detection. Speech and music findings are argued to demonstrate general perceptual principles.

Adult↗
PubMed1993

Tracking of "moving" fused auditory images by children.

Recent investigations (Cranford, Boose, & Moore, 1990a,b; Moore, Cranford, & Rahn, 1990) studied the ability of normal adult subjects to localize sounds under conditions that elicit the Precedence Effect. In different tests, subjects were required either to report the perceived location of a stationary fused auditory image (FAI) or track the apparent motion of a "moving" FAI. Movement of the FAI was simulated by incrementally varying the delay between pairs of clicks presented, one each, from two matched loudspeakers placed on opposite sides of the listener. In the present study, groups of normally developing children, ranging in age from 6 to 12 years of age, were tested with these two procedures. Although subjects performed at normal adult levels with the stationary FAI test, a significant age-related trend was observed with the moving FAI test. The younger children exhibited poorer tracking performances than did the older children. These results provide evidence that significant changes in binaural temporal processing abilities may occur in the early childhood years.

Acoustic Stimulation↗
PubMed1987

Relative effectiveness of three stimulus variables for locating a moving sound source.

A study is reported in which it is shown that observers can use at least three types of acoustic variables that indicate reliably when a moving sound source is passing: interaural temporal differences, the Doppler effect, and amplitude change. Each of these variables was presented in isolation and each was successful in indicating when a (stimulated) moving sound source passed an observer. These three variables were put into competition (with each indicating that closest passage occurred at a different time) in an effort to determine their relative importance. It was found that amplitude change dominated interaural temporal differences which, in turn, dominated the Doppler effect stimulus variable. The results are discussed in terms of two interpretations. First, it is possible that subjects based their judgements on the potential discriminability of each stimulus variable. However, because the stimuli used involved easily discriminable changes, subjects may instead have based their judgements on the independence of a stimulus variable from different environmental situation conditions. The dominance ordering obtained supports the second interpretation.

Attention↗
PubMed2004

Infinite-impulse-response models of the head-related transfer function.

Head-related transfer functions (HRTFs) measured from human subjects were approximated using infinite-impulse-response (IIR) filter models. Models were restricted to rational transfer functions (plus simple delays) so that specific models are characterized by the locations of poles and zeros in the complex plane. The all-pole case (with no nontrivial zeros) is treated first using the theory of linear prediction. Then the general pole-zero model is derived using a weighted-least-squares (WLS) formulation of the modified least-squares problem proposed by Kalman (1958). Both estimation algorithms are based on solutions of sets of linear equations and result in efficient computational schemes to find low-order model HRTFs. The validity of each of these two low-order models was assessed in psychophysical experiments. Specifically, a four-interval, two-alternative, forced-choice paradigm was used to test the discriminability of virtual stimuli constructed from empirical and model HRTFs for corresponding locations. For these experiments, the stimuli were 80 ms, noise tokens generated from a wideband noise generator. Results show that sounds synthesized through model HRTFs were indistinguishable from sounds synthesized from original HRTF measurements for the majority of positions tested. The advantages of the techniques described here are the computational efficiencies achieved for low-order IIR models. Properties of the all-pole and pole-zero estimators are discussed in the context of low-order HRTF representations, and implications for basic and applied contexts are considered.

Acoustics↗
PubMed2004

Robustness of spatial average equalization: a statistical reverberation model approach.

Traditionally, multiple listener room equalization is performed to improve sound quality at all listeners, during audio playback, in a multiple listener environment (e.g., movie theaters, automobiles, etc.). A typical way of doing multiple listener equalization is through spatial averaging, where the room responses are averaged spatially between positions and an inverse equalization filter is found from the spatially averaged result. However, the equalization performance, will be affected if there is a mismatch between the position of the microphones (which are used for measuring the room responses for designing the equalization filter) and the actual center of listener head position (during playback). In this paper, we will present results on the effects of microphone-listener mismatch on spatial average equalization performance. The results indicate that, for the analyzed rectangular configuration, the region of effective equalization depends on (i) the distance of a listener from the source, (ii) the amount of mismatch between the responses, and (iii) the frequency of the audio signal. We also present some convergence analysis to interpret the results.

Architecture↗
PubMed1985

The comparative effects of signal sensation level and sound-pressure level on interaural time discrimination.

A series of experiments was performed to examine the extent to which precision of interaural time discrimination depends on the sound-pressure level (SPL) and/or sensation level (SL) of the signal. All experiments used a tone burst signal and a continuous white noise masker, which was either diotic or interaurally phase reversed. Results of the first experiment indicate that (1) at equal signal SLs, interaural time and intensity discrimination is more precise when measured with the added diotic noise, and (2) addition of the phase reversed noise, previously shown to cause less precise interaural time discrimination, has a similar effect on interaural intensity discrimination. In the second experiment, interaural time JNDs for a signal of constant SPL were measured as a function of noise level. Results show that a low-level diotic noise can benefit interaural time discrimination, particularly at 500 Hz. The third and fourth experiments were performed to measure interaural time discrimination as a function of increasing signal SPL but constant signal-to-noise ratio. The data show the JND decreasing with increasing signal SPL at nearly the same rate with or without the added noise, indicating that an increase in signal-to-noise ratio is not necessary for improved discrimination.

Auditory Perception↗
PubMed1985

Sensitivity to amplitude modulated sounds in the anuran auditory nervous system.

Auditory responses were recorded from single units in the eighth nerve and in the midbrain torus semicircularis of the leopard frog (Rana pipiens). Acoustic stimuli included sinusoidally amplitude-modulated (AM) tones and noise, as well as pure tones. Mean spike rates were measured at various rates of AM, and the degree to which a unit's spikes were restricted to a particular phase of the modulation cycle was described by a synchronization coefficient. The firing rate of eighth-nerve fibers was largely independent of the rate of AM over the modulation range 10 to 150 Hz. Further, the general shape of the spike rate vs. AM-rate function was invariant with either depth of modulation or sound-pressure level (SPL). Although virtually all eighth-nerve fibers exhibited significant synchronization to the envelope of AM, the shape of the synchronization function depended on the unit's best-excitatory frequency (BEF). Fibers with highest BEF's, presumed to innervate the basilar papilla, generally showed greater synchronization as the AM rate was increased (up to 100-150 Hz). Fibers tuned to the low-and midfrequency region, which innervate the amphibian papilla, exhibited low-pass synchronization characteristics. As the depth of modulation was reduced, the degree of synchronization of eighth-nerve fibers decreased. For a given depth of modulation an increase in sound level tended to decrease the degree of synchronization, but significant synchronization could still be observed at stimulus intensities at least 65 dB above threshold. On the basis of the spike rate vs. AM-rate functions, the temporal selectivity of single cells in the torus could be characterized by five response types: AM nonselective (spike rate was largely independent of the AM rate); AM high-pass (activity increased as the AM rate was increased); AM low-pass (response was greatest for slow AM rates and decreased at high rates); AM band-suppression (these neurons responded well to low and high AM rates, but responded weakly to intermediate rates); and AM-tuned (spike rate was greatest over a narrow range of modulation rates). In these measurements the depth of modulation was held constant at 100%. The five response categories are not discrete, but rather reflect representative examples along a continuum with regard to temporal selectivity. The temporal selectivity exhibited by toral units in their firing rates was not evident in their AM-synchronization functions.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗