Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Perceptual Distortion”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 271 records · Page 15Linked to original sources
PubMed1980

Cochlear models: evidence in support of mechanical nonlinearity and a second filter (a review).

We have studied properties of a nonlinear one-dimensional model for motion of the basilar membrane. The model is able to reproduce a variety of physiological and psychophysical effects, and in some instances predictions of the model have been subssequently confirmed. We regard the agreement between model and nature as evidence that the major features of the model are qualitatively correct. Areas of agreement include generation and propagation of two-toine distortion products, two-tone suppression, and Zwicker's psychophysical masking period patterns. In order to reproduce all of the above effects, the model must contain the following major features: (1) A mechanical nonlinearity. This nonlinearity is asymmetric, with membrane damping increasing during the same phase of membrane motion that elicits response activity in primary auditory fibers. (2) An additional stage of sharpening, a 'second filter', between the physical variable controlling mechanical nonlinearity and the physical variable controlling neural excitation.

Basilar Membrane↗
PubMed1982

A model for the speech-reception threshold in noise without and with a hearing aid.

This paper presents a summary of the main results of our current research programme on the speech-reception threshold for sentences as a function of the sound-pressure level of interfering noise. The experimental results agree with a simple quantitative model in which every hearing loss for speech is interpreted as the sum of a class-A loss (attenuation), characterized by a reduction in the levels of both speech signal and noise, and a class-D loss (distortion), comparable to a reduction in S/N ratio. The experiments confirm the model's prediction that a hearing aid can compensate for class-A hearing losses but, generally, not for class-D hearing losses. The implies that the problem of having difficulties in understanding speech in a noisy environment, which is the primary handicap of hearing-impaired subjects, is not solved by the hearing aid.

Audiometry, Speech↗
PubMed1983

Discrimination of envelope frequency.

Discrimination of envelope frequency was measured as the just noticeable increase in envelope frequency of monotic, 60-dB two-tone complexes at geometric center frequencies (CFs) of 500, 1000, 2000, and 4000 Hz. (The envelope frequency is equal to the frequency separation, delta F, between the two components.) At a given CF the jnds were approximately constant up to a critical envelope frequency between 10% and 20% of the CF, roughly equivalent to the critical band, beyond which they increased to a maximum at about 40% of the CF. Below the critical envelope frequency, the jnd increased with CF. Measurements at 40 dB SPL with and without masking of the aural distortion products showed that the influence of aural distortion is minimal. Additional measurements showed that at narrow frequency separations, discrimination was better for monotic two-tone complexes than for pure tones, three-tone complexes, and dichotic two-tone complexes. The results indicate that envelope frequency may serve as a cue for discrimination up to a frequency between 30% and 40% of the CF, although its effectiveness at high envelope frequencies is severely diminished by the auditory filter. A comparison with other data on envelope frequency discrimination indicates that the jnds' dependence on the envelope frequency may depend on how the slope of the temporal envelope varies with envelope frequency.

Adult↗
PubMed1996

Olivocochlear reflex assays: effects of contralateral sound on compound action potentials versus ear-canal distortion products.

The strength of the olivocochlear reflex has been assayed by comparing ipsilateral cochlear responses with and without contralateral sound. In humans, ipsilateral cochlear responses have usually been inferred by measuring otoacoustic emissions (OAEs), whereas, in animal work, they have been assessed by measuring compound action potentials (CAPs). Thus reports that the reflex strength is smaller in humans than in animals cannot be interpreted until the differences between the two tests are better understood. The present study directly compares reflex assays using distortion-product (DP) OAE and CAP measures in the same animals. For ipsilateral frequencies of 2-8 kHz and levels from 25 to 80 dB SPL, efferent reflex strength was computed from the CAP or DPOAE amplitude-versus-level curves measured with and without contralateral noise. The "effective attenuation" produced by efferent activation was, with few exceptions, greater when measured with the CAP than with the DPOAE assay. Differences between the two measures increased as frequency increased, with differences as large as 10 dB observed. These results, coupled with previous measurements on humans and animals, suggest that the efferent reflex is at least as strong in humans as has been shown in animal experiments.

Acoustic Stimulation↗
PubMed2003

Effect of a noise modulation masker on the detection of second-order amplitude modulation.

Amplitude modulation waveforms can contain complex patterns of modulation frequency and depth that are characteristic of many biologically relevant sounds. To investigate the mechanisms involved in the processing of such patterns, we measured detection thresholds for second-order amplitude modulation (AM), a sinusoidal AM in which AM depth varies with time at frequency f(m)'. Second-order AM generates sidebands in the modulation spectrum on either side of the frequency components introduced by the first-order AM. Previous masking studies suggested that a distortion product located at f(m)' contributes to the detection of second-order AM. This hypothesis was tested by masking the putative distortion product using a noise modulation masker centred on (1) the second-order modulation frequency (f(m)'=2 Hz) and (2) the first-order modulation frequency (f(m)=16 Hz). The second-order AM was applied to a 5-kHz pure-tone carrier. Increasing the depth of a 2-Hz-wide noise modulator masker centred on 2 Hz had little effect on detection thresholds for second-order AM, but increased detection thresholds for 2-Hz first-order AM six-fold. Increasing the depth of an 8-Hz-wide noise modulator masker centred on 16 Hz increased detection thresholds for both first- and second-order AM three-fold. These results show that the detection of the second-order AM, when f(m)' is 2 Hz, is not dependent on the detection of modulation at f(m)' but is dependent on the detection of modulation components centred on f(m).

Adult↗
PubMed1992

Looking at pictures but remembering scenes.

Ss tend to remember close-up photographs as having had extended boundaries (Intraub & Richardson, 1989). Three alternate explanations were tested: object completion, distortion toward a perceptual schema, and normalization toward a prototypic view. In three experiments, 55-130 undergraduates viewed 16 close-up, prototypic, or wide-angle views of objects for 15 s each. Immediately or 48 hr later, they rated test pictures on a 5-point scale as "same", "closer up", or "father away." Results ruled out object completion because boundary extension occurred when the picture contained no incomplete objects. Immediate tests supported the perceptual schema hypothesis because all unidirectional distortions involved boundary extension. Delayed tests were more suggestive of a memory schema effect because wide-angle pictures yielded boundary restriction. A two-component model of picture processing is proposed.

Adult↗
PubMed2004

Distortion product otoacoustic emission (2f1-f2) suppression in 3-month-old infants: evidence for postnatal maturation of human cochlear function?

The complete timeline for maturation of human cochlear function has not been defined. Distortion product otoacoustic emission (DPOAE)-based measures of cochlear function show non-adult-like responses from premature and term-born neonates at high f2 frequencies; however, older infants were not included in these studies. In the present experiment, previously collected DPOAE ipsilateral suppression data from premature neonates were combined with new data collected from adults, term-born neonates, and 3-month-old infants to further examine the time course for maturation of cochlear function. DPOAE suppression tuning curves (STC) and suppression growth patterns were measured in the three age groups at f2 = 6000 Hz, L1 = 65, L2 = 55 dB SPL, with an f2/f1 of 1.2. Results indicate that term-born neonates and 3-month-old infants have non-adult-like STC width, slope on the low-frequency flank, and tip features. However, the two infant groups are not significantly different from one another. Suppression growth patterns for low-frequency suppressor tones show a clear developmental progression. In general, the younger the infant, the more shallow and compressive the suppression growth for the lowest suppressor frequencies. These findings suggest a high-frequency postnatal immaturity in cochlear function as measured by DPOAE suppression. Results may have been influenced by noncochlear factors, such as middle-ear immaturity. These factors are reviewed and considered.

Acoustic Stimulation↗
PubMed1995

[Distortion product otoacoustic emissions (DPOAE) in chronic noise-induced hearing loss--recommendations for expert assessment].

The German guidelines for evaluation of chronic noise-induced hearing loss (NHL) require two special auditory tests besides pure tone and speech audiometry tests as proof of damage to the organum spirale. This requirement is the subject of controversy because of the subjective nature of the tests as well as the secondary ascending degeneration of neurons in cases of long-term NIHL. The application of otoacoustic emissions (OAE) could be a new starting point, independent of recruitment. DPOAE are preferable to TEOAE because they are frequency specific. For this reason, we carried out measurements of DPOAE in addition to the required tests on 33 patients (= 66 ears). The results are collected in four groups according to the pure-tone audiogram: a) slight b) typical, c) severe, d) no NIHL. The respective DP-Gram curves had typical features similar to the course of the pure-tone audiogram. The following conclusions are possible: a) in the frequency range up to 1 kHz, ambient noise often causes interference to the DP, b) in the frequency range from 1 kHz to the frequency of the steep pure-tone threshold decay clear DP amplitudes are seen, c) from a inner ear caused hearing loss of appr. 50 dB no DP are detectable, d) DP amplitudes are approximately inversely proportional to hearing loss, e) in severe NIHL (group C) or even slight conductive hearing loss (group D) no DP are found. Based on these results, we recommend including DPOAE as a further differential diagnostic test in the evaluation of NIHL.(ABSTRACT TRUNCATED AT 250 WORDS)

Audiometry, Pure-Tone↗
PubMed1991

Central, auditory mechanisms of perceptual compensation for spectral-envelope distortion.

The spectral envelope is a major determinant of the perceptual identity of many classes of sound including speech. When sounds are transmitted from the source to the listener, the spectral envelope is invariably and diversely distorted, by factors such as room reverberation. Perceptual compensation for spectral-envelope distortion was investigated here. Carrier sounds were distorted by spectral envelope difference filters whose frequency response is the spectral envelope of one vowel minus the spectral envelope of another. The filter /I/ minus /e/ and its inverse were used. Subjects identified a test sound that followed the carrier. The test sound was drawn from an /Itch/ to /etch/ continuum. Perceptual compensation produces a phoneme boundary difference between /I/ minus /e/ and its inverse. Carriers were the phrase "the next word is" spoken by the same (male) speaker as the test sounds, signal-correlated noise derived from this phrase, the same phrase spoken by a female speaker, male and female versions played backwards, and a repeated end-point vowel. The carrier and test were presented to the same ear, to different ears, and from different apparent directions (by varying interaural time delay). The results show that compensation is unlike peripheral phenomena, such as adaptation, and unlike phonetic perceptual phenomena. The evidence favors a central, auditory mechanism.

Auditory Cortex↗
PubMed2000

Perceptual assumptions and projective distortions in a three-dimensional shape illusion.

We examine a shape illusion, in which the balconies of a building appear to tilt up or down, depending on the viewpoint. The balconies are actually level parallelogram shapes, but appear as tilted rectangles. We measured the illusory tilts observed when parallelogram shapes are viewed above the line of sight, using three-dimensional stimuli consisting of parallelograms of various tilts viewed at different orientations. Under perspective projection, parallelism and orthogonality are not preserved. However, perspective distortions alone cannot account for the perceived tilts measured in these experiments, since observers perceived illusory tilts even for stimuli in the frontoparallel plane. We introduce a model, based on the theory that observers assume ambiguously projected three-dimensional angles to be equal to 90 degrees, but revise their predictions on the basis of observation. In the model, perceived tilt is predicted as a weighted sum of the tilts predicted by the assumptions that the shape is rectangular, and that the shape is level (i.e. that the angle between the shape and the vertical backboard is equal to 90 degrees). We prove that it is mathematically impossible for a planar rectangle to share a projection with a nonrectangular parallelogram. A less restrictive assumption that just the two leading internal angles are equal to 90 degrees is suggested as an alternative, and it is further proven that this new configuration of angles leads to a unique perceived tilt. The relative weights in the model reflect the amount that each prediction is revised, and are shown to vary systematically with stimulus orientation. For some observers a better fit was found by replacing the level-tilt assumptions with an assumption that physical tilt was equal to the projected tilt.

Form Perception↗
PubMed1993

Perceptual assessment of resonance distortion in unoperated clefts of the secondary palate.

The purpose of this study was to examine the frequency with which five speech-language pathologists made judgments of hypernasality during the clinical assessment of young children with unoperated and repaired clefts of the secondary palate. Among the 293 nonsyndromic patients with secondary palate clefts included in this study, 219 were between 1 and 2 years of age. Of those, 83 had undergone primary palatoplasty whereas 136 had not. The remaining 74 children were between the ages of 4 and 5 years and presented with repaired secondary palatal clefts. The results showed that the clinicians were unable or unwilling to assess hypernasality in 31% of the 1 to 2 year old children with unoperated clefts. The same clinicians failed to evaluate oral-nasal resonance balance in only 12% of the children in the 1- to 2-year age group who had undergone palate repair. Only 1 of the 74 older children (1.4%) was not evaluated for hypernasality. Possible explanations for these findings are presented and discussed.

Child Language↗
PubMed1996

Effects of spectral contrast on perceptual compensation for spectral-envelope distortion.

Features in a sound's spectral envelope are important for perceptual identification but they are likely to be accompanied by spurious features due to distortion by the transmission channel between source and listener. Previous experiments have demonstrated that there is perceptual compensation for this distortion, and the present experiments ask whether the compensation involves a separation of spurious and salient features. Listeners identified words containing a vowel test sound in an /aept/ to /ppt/ continuum, with a carrier phrase before each word. Effects of transmission channels were simulated by filtering the carrier and the /pt/ following the test sound. Filters were pairs with frequency responses that were the difference of the spectral envelopes from the end-point vowels. Contrasts were altered by multiplying decibel values of the carrier filter's frequency response or the test sound's spectral envelope by a positive number. This keeps features such as peaks at the same frequencies but changes the difference in level between peaks and valleys. When the contrasts of the carrier filters and test sound were the same, the continuum's phoneme boundary was shifted in a manner consistent with a perceptual compensation for the filters that affects the neighboring test sound. However, this shift decreased when the carrier-filter's contrast was less than that of the test sound, and increased slightly when the test-sound's contrast was less than the carrier-filter's contrast. Therefore, the amount of compensation increases with the amount of distortion, even when spectral features such as peaks are kept at the same frequencies. So compensation seems to occur before any perceptual extraction of these features.

Humans↗
PubMed1988

The distorted room illusion, equivalent configurations, and the specificity of static optic arrays.

The distorted room illusion (DRI) and the attendant argument for perceptual ambiguity is critically analyzed from a Gibsonian/ecological point of view. The notions of multiple specification, conflicting information, and perceptual skill are invoked in showing how the ecological approach can accommodate illusion effects that may remain under mobile binocular viewing conditions. Static optic arrays are shown not to be ambiguous. So-called equivalent configurations are found to be analytic artifacts, appearing when the problem of information is treated in geometrical terms without regard for constraints due to physical and ecological regularities. The relative importance of motion-based and motion-independent information is discussed.

Depth Perception↗
PubMed1998

The significance of body size estimation in eating disorders: its relationship with clinical and psychological variables.

OBJECTIVE: To assess the relationship between body size estimation on the one hand and clinical and psychological variables on the other. METHOD: Body size estimation was tested with the video distortion method on a life-size screen in normal women (n = 45) and compared to a total of 189 female eating disorder patients (100 with restricting anorexia nervosa, 41 with binging/purging anorexia nervosa, 48 with bulimia nervosa). The subjects' cognitive responses (what they think they really look like), affective responses (what they feel they look like), and optative responses (what they want to look like) were correlated with clinical parameters (including body composition) and with the scores on a series of self-report questionnaires assessing general psychological well-being and body experience. RESULTS: No significant relationship was found between the body size estimations and the clinical variables. The cognitive and affective responses showed a moderate relationship with self-reported body attitude. Body dissatisfaction was negatively correlated with the optative response (desired body size). DISCUSSION: This study contributes to the construct validity of the video distortion method. Body size estimation includes more than just a perceptual task. Hence, the narrow notion of body image should be replaced by the more complex construct of "body experience," the multidimensionality of which should be addressed in both research and treatment of eating-disordered patients.

Adolescent↗