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PubMedDate not supplied

Effects of intermodulation distortion on speech intelligibility.

This investigation was designed (1) to investigate further intermodulation distortion in hearing aids, and (2) to determine the effect of this type of distortion on speech intelligibility. After four hearing aids were analyzed for intermodulation distortion, 10 CID sentences were recorded through each instrument and presented to both normally hearing and sensorineurally impaired listeners. Results indicated an inverse relationship between levels of intermodulation distortion and frequency, with the highest distortion levels found below 1 kHz. This low-frequency distortion significantly interfered with speech intelligibility for sensorineurally impaired subjects listening to sentences in quite. For both the normally hearing group and the sensorineural group listening in noise, no significant differences were found. The results were interpreted to suggest that the low-frequency intermodulation distortion resulted in an upward spread of masking which interfered with perception of high-frequency acoustic cues in sensorineural impaired listeners; however, with the addition of a competing signal, the subtle masking effect of intermodulation distortion were obscured. Implications for additional research are discussed.

Adult↗
PubMed1979

Multiplicative effects on sentence comprehension for combined acoustic distortions.

This study was designed to explore the effect on speech comprehension of combining two types of signal distortion. A tape of clearly-enunciated sentences in quiet was distorted in each of four ways: low-pass (LP) filtering, time compression, interruption, and noise masking. Data are reported on a population of normal-hearing young men for multiple-choice answer tests of colloquial sentences of either LP filtered at 1, 2, 3, or 4 kHz, time compressed by computer at 250 words/min, interrupted (50 msec on--50 msec off), masked by speech-spectrum noise at +2 dB S/N, or given each of the 12 possible combinations of LP filtering plus the other three distortions. Individual distortion conditions were adjusted to reduce speech comprehension performance to about 90% accuracy, Low-pass filtering above 1 kHz reduced comprehension by no more than five to 10 percentage points, but when LP filtering was added to the other distortions in turn, latent effects were uncovered. The reduction in comprehension with the combined distortions was much greater than the simple additive effects of the distortion and LP filtering by themselves. For example, LP filtering above 2 kHz produced no measurable effect on sentence comprehension but this same distortion in combination with noise masking reduced performance from 89.4 to 59.7% correct (where 25% was chance). This study further validates the multiply-compounded nature of simultaneous types of distortion. The use of LP filtering extends the multiplicative principle to the simulated case of high-frequency hearing losses.

Adult↗
PubMed2004

Estimation of the level and phase of the simple distortion tone the modulation domain.

These experiments were designed to test the idea that nonlinearities in the auditory system can introduce a distortion component into the internal representation of the envelope of a sound, and to estimate the phase of the hypothetical distortion component. In experiment 1, a two-alternative forced-choice (2AFC) task with feedback was used to measure psychometric functions for detecting 5-Hz probe modulation of a 4-kHz sinusoidal carrier in the presence of a masker modulator with components at 50 and 55 Hz (m=0.3 for each component). Performance was measured as a function of the relative phase, delta[symbol see text], of the probe relative to the "venelope" (envelope of the envelope) of the masker. Performance was poorest for delta[symbol see text]= 135 degrees. In experiment 2, delta[symbol see text] was fixed at 135 degrees, m was set to 0.48 for each masker component, and psychometric functions for detecting probe modulation were measured using a 2AFC task without feedback. For small probe modulation depths (m approximately 0.03), the detectability index, d', was consistently negative, consistent with the existence of a weak distortion product which can "cancel" the probe modulation. The distortion component for the conditions of the experiment was estimated to have a phase of about -25 degrees relative to the venelope.

Acoustic Stimulation↗
PubMed2005

Modulation masking produced by second-order modulators.

Recent studies suggest that an auditory nonlinearity converts second-order sinusoidal amplitude modulation (SAM) (i.e., modulation of SAM depth) into a first-order SAM component, which contributes to the perception of second-order SAM. However, conversion may also occur in other ways such as cochlear filtering. The present experiments explored the source of the first-order SAM component by investigating the ability to detect a 5-Hz, first-order SAM probe in the presence of a second-order SAM masker beating at the probe frequency. Detection performance was measured as a function of masker-carrier modulation frequency, phase relationship between the probe and masker modulator, and probe modulation depth. In experiment 1, the carrier was a 5-kHz sinusoid presented either alone or within a notched-noise masker in order to restrict off-frequency listening. In experiment 2, the carrier was a white noise. The data obtained in both carrier conditions are consistent with the existence of a modulation distortion component. However, the phase yielding poorest detection performance varied across experimental conditions between 0 degrees and 180 degrees, confirming that, in addition to nonlinear mechanisms, cochlear filtering and off-frequency listening play a role in second-order SAM perception. The estimated magnitude of the modulation distortion component ranges from 5%-12%.

Adolescent↗
PubMed2001

Effects of degradation of intensity, time, or frequency content on speech intelligibility for normal-hearing and hearing-impaired listeners.

Many hearing-impaired listeners suffer from distorted auditory processing capabilities. This study examines which aspects of auditory coding (i.e., intensity, time, or frequency) are distorted and how this affects speech perception. The distortion-sensitivity model is used: The effect of distorted auditory coding of a speech signal is simulated by an artificial distortion, and the sensitivity of speech intelligibility to this artificial distortion is compared for normal-hearing and hearing-impaired listeners. Stimuli (speech plus noise) are wavelet coded using a complex sinusoidal carrier with a Gaussian envelope (1/4 octave bandwidth). Intensity information is distorted by multiplying the modulus of each wavelet coefficient by a random factor. Temporal and spectral information are distorted by randomly shifting the wavelet positions along the temporal or spectral axis, respectively. Measured were (1) detection thresholds for each type of distortion, and (2) speech-reception thresholds for various degrees of distortion. For spectral distortion, hearing-impaired listeners showed increased detection thresholds and were also less sensitive to the distortion with respect to speech perception. For intensity and temporal distortion, this was not observed. Results indicate that a distorted coding of spectral information may be an important factor underlying reduced speech intelligibility for the hearing impaired.

Adult↗
PubMed2003

Spatial distortions induced by multiple visual landmarks: how local distortions combine to produce complex distortion patterns.

Visual landmarks introduce systematic distortions into spatial short-term memory for single target positions, the exact form of the distortion depending on the spatial layout of the landmarks. In two experiments, we investigated how the combined effect of two landmarks can be predicted from the effects of individual landmarks. Participants used a mouse cursor to reproduce the positions of briefly presented targets in the context of one, the other, or both landmarks. We found that distortions near a landmark are independent of whether another landmark is present, so that remembered space is partitioned into regions dominated by single landmarks. Interestingly, the display midpoint behaves like a "virtual landmark," with its own pattern of distortion. Results are inconsistent with current models of spatial memory distortions but suggest that attentional processes can lead to enhanced fidelity of salient regions in topographical neural networks while also introducing some spatial biases.

Adult↗
PubMed2002

Is the middle between both halves?: midpoint location and segment size estimation in neglect.

BACKGROUND: Line bisection errors in neglect are attributed to perceptual size distortions. In order to compare the two segments of the line to determine if they are equal, one might first estimate the location of a midpoint that defines the two line segments to be compared. OBJECTIVES: The authors attempted to determine whether estimating a line's midpoint can be dissociated from comparing the two segments of this line, and if so, what the relative contribution of each of these tasks is to the perceptual bias in neglect. METHODS: The authors studied two patients with hemispatial neglect from right hemisphere lesions by asking them where bisection marks were placed on prebisected lines and whether the two adjacent line segments were equal. RESULTS: There was a stronger bias judging the position of the bisecting marks ("where" determination) than comparing the size of two adjacent line segments. CONCLUSIONS: These results suggest that perceptual size distortion of line segments alone cannot explain the subjects' line bisection bias, but postperceptual deficits in "where" computations may better account for their errors locating the midpoint. "Where" determinations might require more attentional capacity, depend more heavily on viewer-centered allocation of attention, and be mediated by the right hemisphere's "where" dorsal stream. In contrast, comparing the length of two segments might be mediated by the left hemisphere's "what" ventral stream.

Aged↗
PubMed1982

Different patterns of harmonics in frequency-following responses.

Preliminary studies (Krogh et al., 1977) indicated pronounced intersubject differences with respect to harmonic distortion in the frequency-following responses (FFRs) elicited by high intensity, low frequency stimuli and recorded by means of surface electrodes from man. In the present investigation it was confirmed that the responses from 10 test subjects could be divided into three significantly different patterns on the basis of the relative amplitudes of the fundamental (first harmonic) and the second harmonic response component as measured by spectral analyses. In three of the subjects the ratio of the fundamental to the second harmonic was greater than 10 dB (which were termed a type I response). In five, the ratio was between 0 and 10 dB (type II response) and in two the second harmonic was equal to or greater than the fundamental (type III response). The possible causes of harmonic distortion if FFRs are discussed, but not definite explanation of the interindividual differences can be given. A psychoacoustical evaluation of the second harmonic distortion using a tone-on-tone octave masking technique (TOM) showed no correlation between TOM results and FFR type in 10 subjects.

Acoustic Stimulation↗
PubMed1980

Distortion products f1 + fh and 2f1 + fh in the inner ear.

The ear introduces spectral components which are not present in the stimulating sound. These components are commonly attributed to nonlinearities in the inner ear. In this paper it is shown that the sum product of f1 + fh and cubic sum product 2f1 + fh, perceptively measured, do behave as predicte d by the conventional distortion theory of a power series nonlinearity and that they are most likely masked by the d.c. component generated by the same nonlinearity. We present a model in an attempt to explain the data.

Ear, Inner↗
PubMed1989

Perceptual and conceptual factors in distortions in memory for graphs and maps.

We propose that representations of visual stimuli are a consequence of both perceptual and conceptual factors that may be revealed in systematic errors in memory. Three experiments demonstrated increased (horizontal or vertical) symmetry in perception and memory of nearly symmetric curves in graphs and rivers in maps. Next, a conceptual factor, an accompanying description biasing toward symmetry or asymmetry, also distorted memory in the expected direction for the symmetric descriptions. In the two final experiments, we investigated conceptual factors in selection of a frame of reference. Subjects remembered lines in graphs, but not in maps, as closer to the imaginary 45 degrees line. Combined with earlier research, this suggests that the reference frame for map lines is the canonical axes and for graph lines, the imaginary 45 degrees line.

Adult↗
PubMed1999

Scotopic sensitivity/Irlen syndrome and the use of coloured filters: a long-term placebo controlled and masked study of reading achievement and perception of ability.

This study investigated the effects of using coloured filters on reading speed, accuracy, and comprehension as well as on perception of academic ability. A double-masked, placebo-controlled crossover design was used, with subjects being assessed over a period of 20 mo. There were three treatment groups (Placebo filters, Blue filters, and Optimal filters) involving 113 subjects with "reading difficulties", ranging in age from 9.2 yr. to 13.1 yr. and with an average discrepancy between chronological age and reading age of 1.8 yr. The 35 controls (who did not use coloured filters) ranged in age from 9.4 yr. to 12.9 yr., with an average discrepancy between chronological age and reading age of 2.1 yr. The treatment groups increased at a significantly greater rate than the control group in reading accuracy and reading comprehension but not for speed of reading. For self-reported perception of academic ability, two of the three treatment groups showed significantly greater increases than the control group. The larger improvements for treatment groups in reading comprehension may be related to a reduction in print and background distortions allowing attention to be directed to the processing of continuous text rather than to the identification of individual words. A reduction in print distortion, however, may not be sufficient to generate improved word-identification skills without additional remedial support, and this may be indicated by the nonsignificant increase in rate of reading.

Achievement↗
PubMed1983

Psychophysical measures of two-tone suppression and distortion products (2f1-f2) and (f2-f1).

Psychophysical two-tone suppression and the growth of the (2f1-f2) and (f2-f1) distortion products were measured in four normal-hearing young adults using a forward-masking paradigm. The stimulus parameters investigated were: (1) f1 = 750 and 3000 Hz; (2) f2/f1 = 1.11, 1.26, and 1.41; (3) L1 = 50, 65, 80, and 90 dB SPL; and (4) L2 - L1 varied from -20 to +20 dB in 10-dB increments. It appears that the p-law class of nonlinearity, which maintains that suppression and growth functions for the distortion products are directly related, is not supported by the data. Of existing models of aural nonlinearity, Goldstein's [J. Acoust. Soc. Am. 41, 458-479 (1967)] normalized power series appears to provide the most accurate description of the data, especially when modifications brought about by suppression are incorporated into the model.

Adult↗
PubMed2004

Immediate spatial distortions of pointing movements induced by visual landmarks.

We tested the influence of two horizontally aligned visual landmarks on pointing movements to memorized targets, to investigate whether the visuomotor system can make use of an egocentric representation unaffected by visual context. The endpoints of pointing movements were systematically distorted toward the nearest visual landmark, indicating that spatial representations included both target and nontarget information. These distortions were not due to the presence of the landmarks during the movement but, rather, to their presence in the encoding phase. Qualitatively similar distortions were present even with the shortest possible retention phase, when the target was extinguished at movement onset. Finally, we found the same pattern of distortion when participants were forced to remember the target within an allocentric frame of reference. We argue that even early memory representations for pointing movements are influenced by visual information in the surrounding visual field.

Adolescent↗
PubMed1994

A proposed classification scheme for Rorschach autisms.

Exner's WSUM6 score includes only a select few of the Rorschach "autisms" (i.e., perceptual-cognitive distortions) observed by various authors over the years. A logical and clinically relevant classification scheme was presented which is inclusive enough to capture most types of Rorschach autisms. These include relationship errors (RELERs), hyperattentional errors (HYPERs), and errors of underattention (HYPOs). Empirical comparisons among diagnostic groups on these three categories of autisms were recommended.

Attention↗
PubMed1980

Aural distortion product fl + fh: growth rate and phase characteristics at different frequencies.

This paper addresses the question of whether the nonlinear amplitude response of the ear depends only on stimulus level or on both level and frequency. The level of the quadratic distortion product fh + fl was estimated using the tone-on-tone masking paradigm under a 2AFC transformed UP-DOWN procedure. The higher frequency tone (fh) was maintained at 1.2 times the lower (fl = 250, 500, 1000, or 2000 HZ). Changes in the maximum and minimum threshold as maskee phase changes, [the monaural phase effect (MPE) amplitude], changes in the phase of the aural distortion product, and changes in the growth of the combination tone amplitude were examined as functions of primary frequency and level. The results indicate that MPE amplitude is simply a function of S/N ratio between the combination tone and the masking at that frequency. Distortion product phase varies over 360 degrees with respect to the primary tones and is unrelated to primary frequency or intensity. Within listeners the range of distortion product phase is more narrow (70-90 deg) at a single frequency. The absolute level of the summation tone does not correlate well with primary frequency and the growth rate of the combination tone varies with frequency and observers over a range of 1.1-2.3 dB/dB. The results suggest frequency independent nonlinearity when the ratio of primary frequencies is constant.

Adult↗
PubMed2005

Coherence and the speech intelligibility index.

The speech intelligibility index (SII) (ANSI S3.5-1997) provides a means for estimating speech intelligibility under conditions of additive stationary noise or bandwidth reduction. The SII concept for estimating intelligibility is extended in this paper to include broadband peak-clipping and center-clipping distortion, with the coherence between the input and output signals used to estimate the noise and distortion effects. The speech intelligibility predictions using the new procedure are compared with intelligibility scores obtained from normal-hearing and hearing-impaired subjects for conditions of additive noise and peak-clipping and center-clipping distortion. The most effective procedure divides the speech signal into low-, mid-, and high-level regions, computes the coherence SII separately for the signal segments in each region, and then estimates intelligibility from a weighted combination of the three coherence SII values.

Adolescent↗
PubMed1992

The effect of olivocochlear bundle transection on tuning curves and acoustic distortion products.

A growing body of research suggests that the efferent innervation to the cochlea, the olivocochlear bundle (OCB), may modulate the mechanical function of the cochlea. However, the role of tonic OCB input in cochlear function remains poorly understood. The purpose of this study was to determine the influence of tonic efferent input on cochlear mechanics, by transecting the entire OCB in guinea pigs, and observing changes in tuning curves and acoustic distortion products. The OCB was transected by avulsing the inferior vestibular nerve as it enters the internal auditory canal of the right bulla. Auditory brainstem response (ABR) thresholds, ABR tuning curves, and acoustic distortion products were measured before and after surgery. Successful transection of the OCB was verified histochemically. Results revealed no consistent changes in tuning curves or in the growth functions of the distortion products. To the extent that these measures reflect cochlear mechanical nonlinearities, it is concluded that tonic OCB input is not necessary for grossly normal cochlear mechanical function in the 10-kHz region of the guinea pig cochlea. It thus seems unlikely that the efferents are involved in establishing a "set point" for cochlear operation.

Animals↗