Sound and noise

Sound and noise problems in space environment and human tolerance criteria at varying frequencies and intensitie

Theories of developmental dyslexia: Insights from a multiple case study of dyslexic adults

A multiple case study was conducted in order to assess three leading theories of developmental dyslexia: the phonological, the magnocellular (auditory and visual) and the cerebellar theories. Sixteen dyslexic and 16 control university students were administered a full battery of psychometric, phonological, auditory, visual and cerebellar tests. Individual data reveal that all 16 dyslexics suffer from a phonological deficit, 10 from an auditory deficit, 4 from a motor deficit, and 2 from a visual magnocellular deficit. Results suggest that a phonological deficit can appear in the absence of any other sensory or motor disorder, and is sufficient to cause a literacy impairment, as demonstrated by 5 of the dyslexics. Auditory disorders, when present, aggravate the phonological deficit, hence the literacy impairment. However, auditory deficits cannot be characterised simply as rapid auditory processing problems, as would be predicted by the magnocellular theory. Nor are they restricted to speech. Contrary to the cerebellar theory, we find little support for the notion that motor impairments, when found, have a cerebellar origin, or reflect an automaticity deficit. Overall, the present data support the phonological theory of dyslexia, while acknowledging the presence of additional sensory and motor disorders in certain individuals

Effects of noise suppression and envelope dynamic range compression on the intelligibility of vocoded sentences for a tonal language

Vocoder simulation studies have suggested that the carrier signal type employed affects the intelligibility of vocoded speech. The present work further assessed how carrier signal type interacts with additional signal processing, namely, single-channel noise suppression and envelope dynamic range compression, in determining the intelligibility of vocoder simulations. In Experiment 1, Mandarin sentences that had been corrupted by speech spectrum-shaped noise (SSN) or two-talker babble (2TB) were processed by one of four single-channel noise-suppression algorithms before undergoing tone-vocoded (TV) or noise-vocoded (NV) processing. In Experiment 2, dynamic ranges of multiband envelope waveforms were compressed by scaling of the mean-removed envelope waveforms with a compression factor before undergoing TV or NV processing. TV Mandarin sentences yielded higher intelligibility scores with normal-hearing (NH) listeners than did noise-vocoded sentences. The intelligibility advantage of noise-suppressed vocoded speech depended on the masker type (SSN vs 2TB). NV speech was more negatively influenced by envelope dynamic range compression than was TV speech. These findings suggest that an interactional effect exists between the carrier signal type employed in the vocoding process and envelope distortion caused by signal processing

Backward detection and discrimination unmasking : suppression or cueing?

Previous research has shown the threshold for a masked signal may decrease if another auditory stimulus, a suppressor, is added to the masker. This improvement in signal threshold is called unmasking. The experiments outlined in this paper were designed to examine possible underlying mechanisms responsible for unmasking. In particular, the experiments attempted to eliminate cueing effects which have plagued previous detection unmasking experiments. The rationale was that if cueing effects could be eliminated, the presence or absence of underlying physiological suppressive mechanisms could be inferred. Because the same set of cues exists in each observation interval of a discrimination task, it was reasoned that a backward discrimination unmasking task would not be susceptible to the cueing effects found in detection unmasking experiments. Backward discrimination unmasking was measured separately for both pitch and intensity discrimination. There were no observed unmasking effects in the backward pitch discrimination unmasking experiment. The magnitude of the unmasking effects observed in the backward intensity discrimination unmasking experiment were far less than in the corresponding detection unmasking study. The intensity discrimination experiment yielded a maximum unmasking value of approximately 5 dB as compared to the 26 dB observed in the detection experiment

Neural Mechanisms of Selective Auditory Attention in Rats (Dissertation)

How does attention modulate sensory representations? In order to probe the underlying neural mechanisms, we established a simple rodent model of modality-specific attention. Rats were trained to perform distinct auditory two-tone discrimination and olfactory odor discrimination in a two alternative choice (2AC) paradigm. 
To determine auditory cortex’s role in this frequency discrimination task, we used GABA-A receptor agonist muscimol to transiently and reversibly inactivate auditory cortexes bilaterally in rats performing simple interleaved auditory and olfactory discrimination. With olfactory discrimination performance serving as internal control for motivation and decision making capability, we found only auditory two-tone discrimination was selectively impaired in these rats. This shows the auditory cortex is involved in this two-tone discrimination task.
To investigate the neural correlate of modality-specific attention in the auditory cortex, we trained rats to perform interleaved auditory and olfactory blocks (of 50~70 trials each) in a single session. In auditory blocks, pure tones were either presented with or without a neutral odor (caproic acid, n=2 and 3 respectively), and subjects were rewarded for discriminating auditory stimuli. In olfactory blocks, both task odors and pure tones were presented simultaneously, and subjects were rewarded for discriminating olfactory stimuli. We recorded neural responses in primary auditory cortex (area A1) in freely moving rats while subjects performed this behavior. Single unit responses to tones were heterogeneous, and included transient, sustained, and suppressed. We found 205 of 802 units recorded responsive to the stimuli we used. Of these 205 units, 18.5% showed modality-specific attentional modulation of the anticipatory activity before tone onset. In addition, we also observed in smaller proportion of units (11.2%) modality-specific attentional modulation of the tone-evoked responses; in most cases, the responses to a particular auditory stimulus was enhanced in the auditory block (or, equivalently, suppressed in the olfactory block). Attention increased choice probability of the population in the auditory block. We have also observed significant behavior choice probability in small proportions of units. 
Our results suggest that shifting attention between audition to olfaction tasks can modulate the activity of single neurons in primary auditory cortex

Binaural listening in young and middle-aged adults: Interaural phase differences and speech-in-noise measures

Difficulty understanding speech in the presence of noise is a common complaint of middle-aged and older adults with and without hearing loss. There is an incomplete picture of what contributes to difficulties understanding speech-in-noise in adults who have normal audiograms. As humans we listen binaurally, so declines in binaural processing may contribute to speech-in-noise difficulties. We examined the effects of age on the upper frequency limit of interaural phase difference (IPD) detection and IPD detection at fixed frequencies. We also examined a speech-in-noise measure of spatial separation across young and middle-aged, normal-hearing individuals. Participants were young (n=12) and middle-aged (n=8) adults with normal and symmetrical hearing from 250-8000 Hz. Two interaural phase difference tasks were undertaken. The first assessed interaural phase difference discrimination across frequencies and the second assessed interaural phase difference discrimination at fixed frequencies (500, 750, 1000, 1125 Hz). In addition, the speech-in-noise measure of benefit from spatial separation was assessed by having subjects complete the words-in-noise test with speech and noise at 0° and again with speech at 0° and noise at 90°. The young group had significantly higher (better) upper frequency limits for interaural phase difference discrimination. There was no statistically significant difference between the IPD discrimination at fixed frequencies for the young and middle-aged group, contrary to what was hypothesized. The young group also did not have a greater benefit from spatial separation compared to the middle-aged group. The outcomes from this study add to a growing body of literature suggesting a decline in the upper frequency limit of IPD discrimination with advancing age. This negative effect of aging begins in middle-aged, normal-hearing listeners. The results from this study also suggest that factors other than age and IPD discrimination affect spatial processing in middle-aged adults with clinically normal audiograms. Knowing what contributes to difficulty understanding speech-in-noise will aid in counseling patients and will improve approaches to aural rehabilitation

Engineering data compendium. Human perception and performance. User's guide

The concept underlying the Engineering Data Compendium was the product of a research and development program (Integrated Perceptual Information for Designers project) aimed at facilitating the application of basic research findings in human performance to the design and military crew systems. The principal objective was to develop a workable strategy for: (1) identifying and distilling information of potential value to system design from the existing research literature, and (2) presenting this technical information in a way that would aid its accessibility, interpretability, and applicability by systems designers. The present four volumes of the Engineering Data Compendium represent the first implementation of this strategy. This is the first volume, the User's Guide, containing a description of the program and instructions for its use

Effects on orientation perception of manipulating the spatio–temporal prior probability of stimuli

Spatial and temporal regularities commonly exist in natural visual scenes. The knowledge of the probability structure of these regularities is likely to be informative for an efficient visual system. Here we explored how manipulating the spatio–temporal prior probability of stimuli affects human orientation perception. Stimulus sequences comprised four collinear bars (predictors) which appeared successively towards the foveal region, followed by a target bar with the same or different orientation. Subjects' orientation perception of the foveal target was biased towards the orientation of the predictors when presented in a highly ordered and predictable sequence. The discrimination thresholds were significantly elevated in proportion to increasing prior probabilities of the predictors. Breaking this sequence, by randomising presentation order or presentation duration, decreased the thresholds. These psychophysical observations are consistent with a Bayesian model, suggesting that a predictable spatio–temporal stimulus structure and an increased probability of collinear trials are associated with the increasing prior expectation of collinear events. Our results suggest that statistical spatio–temporal stimulus regularities are effectively integrated by human visual cortex over a range of spatial and temporal positions, thereby systematically affecting perception

Changes in the Perception of Stop Consonants Through Enhanced Cue Training as Reflected by Categorical Boundaries and Late Auditory Evoked Potentials

Hearing-impaired listeners have difficulty in discriminating between voiced stop consonants. An important acoustic cue in this discrimination is the transition from the frequency of the consonant to the frequency of the vowel. The main purpose of this study was to investigate the effect of auditory training on the perception of the formant transition cue in the discrimination of the place of articulation of voiced stop consonants in synthetic CV stimuli of hearing-impaired listeners. Changes in perception were represented by behavioral and electrophysiological measures. Generalization effects after training and correlations between behavioral and electrophysiological measures were also measured. Eight male and three female hearing-impaired subjects (23 - 72 years of age) participated in this study. The behavioral measures involved the participants performing categorization of stimuli as either /b/ and /d/ in a 2AFC task. Stimuli varied in onset frequency of the second formant. Electrophysiological measures, including P100, N100, P200, N200 latencies and P100-N100, N100-P200, P200-N200 peak-to-peak amplitudes, were recorded as participants sat quietly while watching a video in silence as stimuli was presented in one ear. Subjects participated in auditory training on the formant transition cue over the period of four days. Stimuli used in auditory training were consistent with stimuli used in behavioral and electrophysiological measures, except that the formant transition cue was enhanced during training. This enhancement resulted from amplification of the transition portion of the stimulus to ensure audibility of the cue for the listener. Behavioral measures involved identifying the category (/b/ or /d/) to which the stimulus belonged. Visual feedback was given after each correct response. Results were consistent with previous studies. Behavioral measures indicated improvement from before training to after training in the perception of the formant transition cue by some listeners. However, analysis of variance (ANOVA) and correlation procedures failed to reflect any pre versus post training change. Age and severity of hearing were not correlated with improvement due to training. However, ability to categorize prior to training correlated with improvement after training. Statistical results for electrophysiological measures did not find significant changes between pre and post training