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PubMed1992

On using coherence to measure distortion in hearing aids.

Coherence is a frequency-domain measure of the degree to which the output of a system is linearly related to the system input. The signal-to-distortion ratio (SDR), where the distortion term includes all nonlinear effects and noise in the system, can be computed from the coherence. The coherence estimate, however, is subject to sources of variance and bias that reduce the accuracy of the measured SDR. The origins of the variance and bias and their effects on distortion measurements are presented. New procedures for reducing the variance and bias effects are described, and the processing effectiveness is demonstrated for a simulated hearing-aid response.

Fourier Analysis↗
PubMed2000

Direction-dependent distortions of retinocentric space in the visuomotor transformation for pointing.

The aim of this study was to: (1) quantify errors in open-loop pointing toward a spatially central (but retinally peripheral) visual target with gaze maintained in various eccentric horizontal, vertical, and oblique directions; and (2) determine the computational source of these errors. Eye and arm orientations were measured with the use of search coils while six head-fixed subjects looked and pointed toward remembered targets in complete darkness. On average, subjects made small exaggerations in both the vertical and horizontal components of retinal displacement (tending to overshoot the target relative to current gaze), but individual subjects showed considerable variations in this pattern. Moreover, pointing errors for oblique retinal targets were only partially predictable from errors for the cardinal directions, suggesting that most of these errors did not arise within independent vertical and horizontal coordinate channels. The remaining variance was related to nonhomogeneous, direction-dependent distortions in reading out the magnitudes and directions of retinal displacement. The largest and most consistent nonhomogeneities occurred as discontinuities between adjacent points across the vertical meridian of retinotopic space, perhaps related to the break between the representations of space in the left and right cortices. These findings are consistent with the hypothesis that at least some of these visuomotor distortions are due to miscalibrations in quasi-independent visuomotor readout mechanisms for "patches" of retinotopic space, with major discontinuities existing between patches at certain anatomic and/or physiological borders.

Adult↗
PubMed1997

Possible explanations for trajectory curvature in multijoint arm movements.

Although the straightness of hand paths is a widely accepted feature of human multijoint reaching movement, detailed examinations have revealed slight curvatures in some regions of the workspace. This observation raises the question of whether planned trajectories are straight or curved. If they are straight, 3 possible factors can explain the observed curvatures: (a) imperfect control, (b) visual distortion, or (c) interaction between straight virtual trajectories and the dynamics of the arm. Participants instructed to generate straight movement paths produced movements much straighter than those generated spontaneously. Participants generated spontaneously curved trajectories in the frontoparallel plane, where visual distortion is not expected. Electromyograms suggested that participants generated straighter paths without an increase in arm stiffness. These findings argue against the 3 factors. It follows that planned trajectories are likely to be curved.

Adult↗
PubMed2006

Abrupt, but not gradual visuomotor distortion facilitates adaptation in children with developmental coordination disorder.

A previous experiment investigating visuomotor adaptation in typically developing children and children with Developmental Coordination Disorder (DCD) suggested poor adaptation to an abruptly induced visuomotor perturbation. In the current study, using a similar center-out drawing task, but administering either an abrupt or a gradual perturbation, and twice as many adaptation trials, we show that typically developing children are well able to successfully update an existing internal model in response to a 60 degrees rotation of the visual feedback, independent of the perturbation condition. Children with DCD, however, updated their internal map more effectively during exposure to an abrupt visuomotor perturbation than to a gradual one. This may suggest that the adaptation process in children with DCD responds differently to small vs. large steps of visuomotor discrepancies. Given the known role of the cerebellum in providing an error signal necessary for updating the internal model in response to a gradual visuomotor distortion, the results of our study add to the growing body of evidence implicating compromised cerebellar function in DCD.

Attention↗
PubMed2003

Bidimensional regression: assessing the configural similarity and accuracy of cognitive maps and other two-dimensional data sets.

Bidimensional regression is a method for comparing the degree of resemblance between 2 planar configurations of points and, more generally, for assessing the nature of the geometry (Euclidean and non-Euclidean) between 2-dimensional independent and dependent variables. For example, it can assess the similarity between location estimates from different tasks or participant groups, measure the fidelity between cognitive maps and actual locations, and provide parameters for psychological process models. The authors detail the formal similarity between uni- and bidimensional regression, provide computational methods and a new index of spatial distortion, outline the advantages of bidimensional regression over other techniques, and provide guidelines for its use. The authors conclude by describing substantive areas in psychology for which the method would be appropriate and uniquely illuminating.

Adult↗
PubMed2002

The time course of spatial memory distortions.

Four experiments investigated the memory distortions for the location of a dot in relation to two horizontally aligned landmarks. In Experiment 1, participants reproduced from memory a dot location with respect to the two landmarks. Their performance showed a systematic pattern of distortion that was consistent across individual participants. The three subsequent experiments investigated the time course of spatial memory distortions. Using a visual discrimination task, we were able to map the emergence of spatial distortions within the first 800 msec of the retention interval. After retention intervals as brief as 50 msec, a distortion was already present. In all but one experiment, the distortion increased with longer retention intervals. This early onset of spatial memory distortions might reflect the almost immediate decay of detailed spatial information and the early influence of an enduring spatial memory representation, which encodes spatial information in terms of the perceived structure of space.

Adult↗
PubMed1998

A shape-contrast effect for briefly presented stimuli.

When a suprathreshold visual stimulus is flashed for 60-300 ms and masked, though it is no longer visibly degraded, the perceived shape is vulnerable to distortion effects, especially when a 2nd shape is present. Specifically, when preceded by a flashed line, a briefly flashed circle appears to be an ellipse elongated perpendicular to the line. Given an appropriate stimulus onset asynchrony, this distortion is perceived when the 2 stimuli (approximately 4 degrees) are presented as far as 12 degrees apart but is not due to perception of apparent motion between the 2 stimuli. Additional pairs of shapes defined by taper and overall curvature also revealed similar nonlocal shape distortion effects. The test shapes always appeared to be more dissimilar to the priming shapes, a distortion termed a shape-contrast effect. Its properties are consistent with the response characteristics of the shape-tuned neurons in the inferotemporal cortex and may reveal the underlying dimensions of early shape encoding.

Adult↗
PubMed1988

Comparative investigations of progressive lenses.

Different types of progressive addition lenses were compared with each other. It was our aim to measure all parameters in such a way that they were consistent with the normal wearing situation. The distribution of the spherical power and astigmatism was measured with a special focimeter. The induced distortion, which is important for patient acceptance, was determined by a photographic method. There are significant differences between the various types of progressive addition lenses. However, objective information is not sufficient to resolve the subjective question of patient acceptance.

Eyeglasses↗
PubMed1979

Facial imagery and personality development.

The empirical relationship between judgments obtained with a motorized facial-distortion mirror and relevant personality and rating measures was examined. Subjects were 88 school children. The findings indicated general trend differences between males and females in perceiving facial distortion shown in a mirror. Although not statistically significant, a relationship between teachers' ratings on hygiene, self-concept, sociability, and two scales of the High School Personality Questionnaire were noted.

Adolescent↗
PubMed1993

Body-image distortion among male and female American and Costa Rican students and female Japanese students.

395 American male and female high school and college students, 286 Costa Rican male and female high school students, and 127 Japanese female college students were tested for body-image distortion using a computer-based body-image distortion task. A reliable negative relationship between stature and body-image distortion was observed. No reliable differences in body-image distortion were observed between different sex or cultural groups.

Adult↗
PubMed1993

Comparing the level of the acoustic distortion product 2f1-f2 with behavioural threshold audiograms from normal-hearing and hearing-impaired ears.

The level of the acoustic distortion product, 2f1-f2, was measured across frequency from two different groups of adults: (1) a group of 57 drawn from the university population who considered that they had normal hearing and (2) a group of 26 patients referred from the ENT Department of the County Hospital. These patients complained of reduced 'quality' of hearing, but no organic condition had been diagnosed to explain it. Behavioural audiograms were obtained for both groups. In both groups of listeners the distortion frequency sweep is related to the respective subjective threshold audiogram. In subjects from whom distortion can be recorded across a wide frequency range, acoustic distortion product level and auditory sensitivity were significantly correlated in one-third of the subjects. In hearing-impaired patients acoustic distortion is usually detectable across frequency regions of normal hearing, but falls below the noise floor if hearing threshold levels are above 15-20 dB.

Adolescent↗
PubMed1989

Reliability measures in distorting body-image.

This study is the first to make a direct comparison between the distorting mirror and the distorting videocamera with the same group of nonclinical subjects. It also establishes the internal consistency, the test-retest reliability and the convergent validity of both techniques. Analysis indicates, as with other studies, that perceived image is consistently over-estimated and ideal image is consistently under-estimated by both techniques. With the distorting mirror, the frontal orientation is repeatable over four days and with the video the profile is the more reliable orientation. A comparison between profile and frontal orientations on any single test occasion (internal consistency) indicates that the results correlate well so either orientation is acceptable for experimental purposes. The extent to which both techniques were measuring the same aspect (convergent validity) was more marked for the ideal image. A researcher using the distorting mirror can be confident that the ideal image is reliable over time using either orientation but that the perceived image requires a frontal orientation. The frontal or profile orientation is acceptable for the ideal image using the distorting video, but the profile orientation is advisable if one wishes a reliable perceived image. The researcher should also be cautious in assuming that both techniques are measuring an identical body-image construct.

Anorexia Nervosa↗
PubMed2006

Reality monitoring and memory distortion: effects of negative, arousing content.

Although individuals often claim to vividly remember negatively arousing information, few studies have been performed to examine whether this emotional information is remembered more accurately than nonemotional information. In the present study, we investigated whether the emotional content of items modulates the accuracy with which individuals make reality-monitoring decisions. Participants (young adults, 18-35 years of age) distinguished imagined from seen words (Experiments 1 and 3A) or objects (Experiments 2 and 3B). Half of the items studied in each condition (presented and imagined) were negative and arousing, and half were neutral. The participants mistook imagined items for presented ones, but the number of reality-monitoring errors was lower for the arousing items than for the neutral items. Negative, arousing items appear to be remembered with contextual detail more frequently than are neutral items, leading memory for this emotional information to be less prone to distortion than is memory for neutral information. Thus, negative arousal can enhance not only the subjective vividness of a memory, but also a memory's accuracy.

Adolescent↗
PubMed1990

Body-image distortion among male and female college and high school students, and eating-disordered patients.

For 179 male and female college and high school students, and 26 female eating-disordered patients body-image distortion was measured using a computer-based image-analysis of redrawn images of standardized human figures. Statistical analysis indicated that body-image distortion was the same for all groups. Body-image distortion was significantly and negatively related to weight:height ratio as a function of a simple polynomial. These results suggest this evaluation of distortion of body-image yields a quantitative measure reliably related to weight status but also suggests the technique, and possibly measurement of body-image distortion in general, may not be a valid discriminator between eating-disordered and normal persons.

Adolescent↗
PubMed2000

A laser-based technique for measuring accuracy and distortion in judgments of linear dimensions.

A new technique is described that permits precise measurement of accuracy and distortion in judgments of linear dimensions based on either perception or memory. This technique involves the use of a single laser beam and a reference line placed on a projection surface. By rotating a laser device, the distance between the reference line and the point created by the beam may be continuously varied. This procedure avoids unintentional distortion from misjudgment of standard metrics, while the semicircular movement required by this technique eliminates body-referenced estimation and some other potential confounds. Potential applications to research in visual perception, spatial memory, and body image are discussed.

Adolescent↗
PubMed1998

[Metamorphopsia of the Alice in Wonderland-syndrome].

A boy aged 9 had had two years previously and again since a few weeks complaints of observing objects with distortion and reduction in size. He was known to suffer from asthma for which he received beclomethasone in a low dosage. Physical and supplementary examinations revealed no abnormalities. The condition was diagnosed as 'metamorphopsia'.

Asthma↗
PubMed1993

Theoretical and empirical considerations on the relation between 'body image', body scheme and somatosensation.

The authors first discuss possible interactions between the hitherto neglected neurophysiological and neuropsychological factors and the traditionally accepted cognitive and affective factors in 'body image' formation. They then report on a study of the relation between body size perception (video distortion technique, image marking procedure, kinaesthetic size estimation apparatus) and somatosensation (thermal, pain and vibration thresholds) in young women. Included in the study were questionnaires on eating behaviour and motivation, body attitude or body satisfaction, and depressive mood and thoughts. Neither the somatosensory nor the questionnaire variables explained the difference between 'overestimators' and 'underestimators' of body size. However, these variables did explain the difference between 'good perceivers' and 'poor perceivers' (degree of deviation from actual body size) in the video distortion technique, with a somewhat larger contribution by the somatosensory variables. The latter finding, although clearly preliminary, should stimulate further investigations of the relationship between somatosensory variables and body size perception.

Adult↗
PubMed2003

Effect of cochlear damage on the detection of complex temporal envelopes.

Recent studies have demonstrated that the detection of complex temporal envelopes relies - at least partially - on the perception of a distortion component generated by a peripheral (cochlear) and/or central (post-cochlear) non-linearity. In the present study, first- and second-order amplitude modulation (AM) detection thresholds were obtained in normally hearing (NH) and hearing-impaired (HI) listeners using a 2-kHz pure-tone carrier. In both groups of listeners, first-order AM detection thresholds were measured for AM rates fm ranging between 4 and 87 Hz, and second-order AM detection thresholds were measured for second-order AM rates fm' ranging between 4 and 23 Hz, using a fixed first-order 'carrier' AM rate fm of 64 Hz. When the sound pressure level was adjusted in order to yield equal detectability in both groups for the 64-Hz first-order carrier modulation, (i) first-order AM detection thresholds for the HI listeners were normal at fm=87 Hz, and better-than-normal at fm=4 and 16 Hz, and (ii) second-order AM detection thresholds were identical at all modulation rates in NH and HI listeners. Similar results were obtained when the audibility of the 2-kHz pure-tone carrier was equated for both groups, i.e. when listeners were tested at the same sensation level. These results demonstrate clearly that cochlear damage has no effect on the detection of complex temporal envelopes, and indicate that the distortion component must be generated by a more central non-linearity than cochlear compression, transduction, or short-term adaptation.

Acoustic Stimulation↗