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PubMed1989

Acoustic distortion products can be used to monitor the effects of chronic gentamicin treatment.

Acoustic distortion has been measured from the ear canals of guinea pigs treated with the aminoglycoside antibiotic gentamicin. The correlation between pre- and post-treatment levels of distortion can be related to the extent of outer hair cell (OHC) pathology induced by gentamicin. All animals that were treated and show functional changes also show changes in OHC morphology. Changes in distortion properties are evident before clear changes in surface hair cell morphology are seen. In the early stages of intoxication, thin sections of the organ of Corti are necessary to reveal the underlying structural changes accompanying functional impairment. Where OHCs have been affected by gentamicin treatment, the greatest change in 2f1-f2 level is for distortion generated by widely spaced stimuli. With closely spaced stimuli, 2f1-f2 may be unchanged in level, but higher order distortion components are depressed. Functional evidence of mild OHC disruption is only revealed by stimulus levels at or below 60 dB SPL. With higher sound levels, apparently normal levels of distortion can be generated by ears in which there is clear evidence of OHC pathology. In a single, untreated animal with an extensive basal turn lesion, some 2f1-f2 distortion was generated when the stimulus frequency region lacked OHCs.

Animals↗
PubMed2006

Dancing shapes: a comparison of luminance-induced distortions.

We present an illusory display in which a grid of outlined squares is positioned in front of a moving luminance gradient. Observers perceive a strong, illusory, 'wavelike' motion of the superimposed squares. We compared luminance effects on dynamic and static aspects of this illusion. The dynamic aspect was investigated by means of a temporal gradient, which induced an illusory pulsing of the outlined squares. The static aspect was investigated in two different ways. In one experiment, the outlined squares were positioned on a spatial gradient, which caused the squares to look like trapezoid shapes. In another experiment, the squares were positioned on different luminance fields, which affected their apparent size. In all experiments, luminance settings were the same, and observers were asked to indicate the direction and strength of the induced distortions. The overall results show large agreements between the dynamic distortion and the first-mentioned static distortion, whereas different tendencies emerged for the second static distortion. In a second series of experiments, we examined these distortions for various ranges of the luminance gradient and for border gradients as well. On the basis of these data, we explored how the directions of the perceived distortions of the single-gradient displays examined in this paper could be related to each other.

Contrast Sensitivity↗
PubMed1993

Memory processes in children: implications for investigations of alleged child sexual abuse.

Allegations of child sexual abuse naturally raise the ire of the populace at large, as well as the fears and apprehensions of those who may be falsely accused as perpetrators. Within this emotionally charged and litigious climate, the memory functions of children have become a matter of acute interest for those professionals involved in the ensuing investigations and legal proceedings. This is especially true, given that the child witness, approaching a court of law, is likely to encounter numerous circumstances that will invite memory distortion. These circumstances include interviews by concerned adults and protective service workers, as well as cross-examination by a defense attorney. Well-intentioned efforts may be replete with leading questions or subtle inferences that may distort episodic memory. The present paper will discuss developmental aspects of long-term memory functions in children, events, and cognitive processes that may contribute to memory distortion, and recommendations for improving procedures related to the investigations of alleged child sexual abuse.

Child↗
PubMed1986

Shape constancy and polar perspective.

The distortion of polar perspective depends on the depth of the tridimensional shape and on the observation distance. In four experiments using 54 undergraduates as subjects, we found that a compensation process which takes depth and observation distance into account corrects for such distortions. Compensation was demonstrated in experiments in which deceptive information on depth and on observation distance was provided. The result was distortions of the perceived shapes that would be expected if compensation were based on the deceptive information.

Cues↗
PubMed1998

Distortion of body image among elite female dancers.

To examine body image and possible distortion of body image among elite female dancers 10 members of a professional ballet company rated both current and ideal body shape. In addition, an objective measure of body composition was obtained via skinfold techniques. t tests indicated that the mean rating for current body image was significantly higher than the rating for ideal, despite the fact that body-composition measures for all subjects were in an "ideal" range according to normative standards. Analysis indicated a high distortion of body image among these dancers and support psychophysiological concerns previously raised.

Adipose Tissue↗
PubMed2003

The influence of contrast and spatial factors in the perceived shape of boundaries.

When an edge can be perceived to continue either with a collinear edge of the opposite contrast polarity or with a noncollinear edge of the same contrast polarity, observers perceive an alignment between the edges of the same contrast polarity, even though they are noncollinear. Using several stimulus configurations and both free and tachistoscopic viewing, we studied the luminance and spatial factors affecting the perceived distortion and binding. The results showed that the two noncollinear edges tended to align when they had the same contrast polarity (Experiment 1A) and to misalign when they had opposite contrast polarity (Experiment 2), providing that (1) they were separated by a distance larger than 1 arcmin and smaller than 3-4 arcmin (for all configurations) and (2) they laterally overlapped for about 7 arcmin (Experiment 1B). The results also showed that the direction of apparent distortion depended on the direction of overlapping. The results of Experiment 3 ruled out the local attraction/repulsion explanation but, instead, supported the suggestion that the interaction concerned the global edges, or part of them, and produced an inward tilt, which made the edges of the same contrast polarity perceptually to align, or an outward tilt, so that the edges of opposite contrast polarity were perceived to be more misaligned. From the overlap and distance limits found, it can be inferred that for two noncollinear contours to join perceptually, the tilt must not exceed 18 degrees, a limit compatible with the orientation bandwidth of contrast-sensitive early cortical mechanisms.

Attention↗
PubMed2001

Adolescents' reactions to hypothetical peer group conversations: evidence for an imaginary audience?

The theory of adolescent egocentrism holds that early adolescents have a distorted understanding of self-other relations; because of flaws in the traditional methods used to assess adolescent egocentrism, this notion has never received adequate empirical scrutiny. In the present research, the nature of early adolescent social cognition as characterized by that theory was investigated by examining age differences in judgments of hypothetical peer group conversations. In Study 1, children and early adolescents (N = 264) rated the attentiveness, criticalness, and admiration expressed in three conversations, in which the subject or a peer was mentioned in either an admiring, critical, or nonevaluative manner. In Study 2, a similar procedure was used with middle and late adolescents, as well as children and early adolescents (N = 187); two memory tasks were also administered to visit the issue of distortion in social cognition. In Study 3, a new sample (N = 1,019) representing the four age groups from Study 2 was presented with an ambiguous conversation and then asked to interpret who was the target (object of focus) and how that target was regarded. The findings from the three studies do not support the notion that adolescents believe others are attentive to and critical of their every move, or that their social cognition and perception is egocentric and distorted. Conceptual and methodological contributions are discussed, along with directions for additional research.

Adolescent↗
PubMed1987

Speech distortion measures for hearing aids.

Advances in digital technology and the associated introduction of new forms of distortion led us to investigate supplementary measures of electroacoustic distortion for hearing aids. Mathematical techniques were used to formulate a working model in which the hearing aid acts as a time varying linear filter. This model embodies an approach to separating distortion into perceptually relevant and irrelevant categories. Digitized speech was converted to analog form, routed through a commercial hearing aid, and the output of the aid was redigitized and stored. For a given input signal, output speech waveforms were then compared to the model output and performance measures were derived. Distortion was plotted in three dimensions to permit interpretation with respect to time, frequency, and amplitude. These results provide a more comprehensive and general format for the analysis of hearing aid distortion.

Acoustics↗
PubMed2006

Perceptual image hashing via feature points: performance evaluation and tradeoffs.

We propose an image hashing paradigm using visually significant feature points. The feature points should be largely invariant under perceptually insignificant distortions. To satisfy this, we propose an iterative feature detector to extract significant geometry preserving feature points. We apply probabilistic quantization on the derived features to introduce randomness, which, in turn, reduces vulnerability to adversarial attacks. The proposed hash algorithm withstands standard benchmark (e.g., Stirmark) attacks, including compression, geometric distortions of scaling and small-angle rotation, and common signal-processing operations. Content changing (malicious) manipulations of image data are also accurately detected. Detailed statistical analysis in the form of receiver operating characteristic (ROC) curves is presented and reveals the success of the proposed scheme in achieving perceptual robustness while avoiding misclassification.

Algorithms↗
PubMedDate not supplied

Distortions in two-dimensional visual space perception in strabismic observers.

Amblyopic subjects were asked to memorize circles of different radii (2, 4 and 6 degrees), and then to reconstruct them monocularly with each eye, point by point (12 points per circle). The resulting two-dimensional maps of visual space showed considerable distortions, including expansion, shrinkage and torsion of specific regions of the visual field of the amblyopic eye, but not the normal eye. Based on the differences between the two eyes, we computed complex two-dimensional patterns (gratings, checkerboards, optotypes, written text, natural scenes) as "seen" monocularly with the amblyopic eye. These reconstructed patterns were then compared with drawings of the same patterns observed through the amblyopic eyes of the same subjects. The reconstructed patterns only partially reflected the actual perception for the amblyopic eyes. The compensation of complex, globally-extended scenes in comparison to the distortions obtained by local, punctate settings probably reflects cooperative interactions occurring at higher brain levels.

Adult↗
PubMed1992

High frequency distortion products from the ears of two bat species, Megaderma lyra and Carollia perspicillata.

In two echolocating bat species, Megaderma lyra and Carollia perspicillata 2f1-f2 distortion products were measured acoustically in the outer ear canal for f1 frequencies between 5 and 95 kHz in an attempt to study nonlinear cochlear processes at high frequencies. Similar to other mammals, the input/output (I/O) functions of 2f1-f2 show non-monotonicities and notches at f1 levels between 40-70 dB SPL. The slope of the initial rise of the 2f1-f2 I/O functions increased with f1 frequency from 0.73 (5 kHz) to 1.41 (95 kHz) in Megaderma and from 0.66 (7.5 kHz) to 1.47 (95 kHz) in Carollia. With increasing f1 frequency the optimum frequency ratio f2/f1 in order to evoke maximum distortion level decreases from 1.18 (5 kHz) to 1.09 (95 kHz) in Megaderma and from 1.21 (7.5 kHz) to 1.11 (95 kHz) in Carollia. This is taken as indication of a general increase of the quality of tuning of the distortion generating mechanism with frequency. The f1 levels that were sufficient to elicit distortion levels of -10 dB SPL were used to construct iso-distortion threshold curves which lay on average 37.2 dB (Megaderma) and 33.9 dB (Carollia) above the neuronal threshold curves [Rübsamen et al., J. Comp. Physiol. A 163 (1988); Sterbing et al., Proc. 18th Göttingen Neurobiol. Conf. Thieme Verlag, Stuttgart (1990)] and roughly paralleled these. Highest distortion levels (40-50 dB SPL with f1 levels of 80 dB SPL) and lowest distortion thresholds were measured in the f1 frequency range of 10-30 kHz (Megaderma) and 15-30 kHz (Carollia).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2006

Event-related fMRI of category learning: differences in classification and feedback networks.

Eighteen healthy young adults underwent event-related (ER) functional magnetic resonance imaging (fMRI) of the brain while performing a visual category learning task. The specific category learning task required subjects to extract the rules that guide classification of quasi-random patterns of dots into categories. Following each classification choice, visual feedback was presented. The average hemodynamic response was calculated across the eighteen subjects to identify the separate networks associated with both classification and feedback. Random-effects analyses identified the different networks implicated during the classification and feedback phases of each trial. The regions included prefrontal cortex, frontal eye fields, supplementary motor and eye fields, thalamus, caudate, superior and inferior parietal lobules, and areas within visual cortex. The differences between classification and feedback were identified as (i) overall higher volumes and signal intensities during classification as compared to feedback, (ii) involvement of the thalamus and superior parietal regions during the classification phase of each trial, and (iii) differential involvement of the caudate head during feedback. The effects of learning were then evaluated for both classification and feedback. Early in learning, subjects showed increased activation in the hippocampal regions during classification and activation in the heads of the caudate nuclei during the corresponding feedback phases. The findings suggest that early stages of prototype-distortion learning are characterized by networks previously associated with strategies of explicit memory and hypothesis testing. However as learning progresses the networks change. This finding suggests that the cognitive strategies also change during prototype-distortion learning.

Brain↗
PubMed1995

Comparison of three psychophysical techniques for estimating body-size perception.

Perception of body size was recorded for 63 university students (M age = 25.3 yr., 41 women) who estimated their own body size using three methods. Using the method of adjustment, subjects over- or underestimated their body size. A signal-detection analysis indicated that subjects were sensitive to detecting a 4% distortion in body size and that there was no systematic bias for reporting distortion as present or absent. Scores on the adaptive probit estimation task were significantly correlated with values for point of subjective equality and the size judgements with the method of adjustment. Over-all, this experiment demonstrated adaptive probit estimation as a reliable indicator of perceived body size, sensitivity in detecting size distortion, and response bias in making body-size judgements.

Adolescent↗
PubMed2004

Are size illusions in simple line drawings affected by shading?

In a number of simple line drawings, such as the Müller-Lyer or Judd figures, we can experience strong distortions of perceived space-geometric illusions. One way of explaining these effects is based on the perspective information that can be read from the line drawings. For instance, the 'inappropriate constancy scaling' theory advocates that the inferred three-dimensional structure of the pictured object is used by the perceptual system to adjust the size of line-drawing components. Such a theory would predict that additional depth cues, for instance shading added to line drawings, should affect these illusions because they influence the three-dimensional appearance. We present here systematic measurements of the magnitude of length misjudgments in horizontal Müller-Lyer and Judd figures for three configurations: (i) pure line drawings, and with shading attached to (ii) the top, and (iii) the bottom of the figures. The latter two configurations are unambiguously interpreted as 'folded' structures with a horizontal edge behind the image plane or protruding from it, respectively. While we could not find any effect of shading in our experimental data, we did observe a length misjudgment in Judd figures that corresponds precisely to the asymmetry that can be observed in the Müller-Lyer illusion for inward and outward fins. This pattern of results is not consistent with notions of inappropriate constancy scaling but is fully coherent with the view that neural filtering mechanisms, which are affecting the perceived position of line intersections, are responsible for this type of geometrical illusions.

Cues↗
PubMed1996

Distortion generated by the ear: its emergence and evolution during development.

Physiologically vulnerable active mechanics associated with the transduction of sounds in adults distort cochlear output. Specifically, frequencies not present in the incoming acoustic signal are represented in its output (ie., the spike trains of auditory nerve fibers). The purpose of this investigation was to study the appearance and evolution of intermodulation distortion during development. Established surgical and electrophysiologic techniques were used to record the extracellular electrical activity of individual auditory nerve fibers from developing kittens. Discharge-rate or synchrony-based responses to two tones (f1 and f2) presented simultaneously at various ratios of f2/f1 were recorded. The cubic distortion product (CDP; 2f1-f2, where f1<f2) and the difference tone (f2-f1) were the intermodulation distortion products (DPs) emphasized in the investigation. CDPs were first observed nearly 10 days after the earliest auditory nerve fiber responses to simple tone-burst stimuli could be elicited in neonatal cats. Furthermore, the spectrum of DPs generated in the cochlea changed dramatically during the second postnatal week and achieved adultlike characteristics after the first postnatal month. Findings reported here support the notion that cochlear transduction is initially linear in neonatal cats, possibly representing a critical period of auditory development, and that the content of distortion-related spectral information carried in auditory nerve fiber spike trains increases during development, in concert with other peripheral auditory attributes.

Animals↗
PubMed1993

Body-image distortion and mental imagery.

This study explored whether body-image distortion is a function of difficulties with imagery or problems with judgment. 49 subjects were given the Modified Video Camera Technique to measure body-image distortion. Mental imagery was measured by a modified version of the Vividness of Visual Imagery Questionnaire and the Spatial Relations subtest of the Woodcock-Johnson Psycho-educational Battery. Visual recall was assessed on the Meier Art Judgment Test. Judgment bias was assessed by the Stunkard Silhouette Method and the shape and weight subscales of the Eating Disorder Examination. Subjects who distorted body-image scored significantly more poorly on mental imagery than those who did not distort. No differences were found between groups on visual memory recall or in judgment bias.

Adult↗
PubMed2006

Illusory scene distortion occurs during perceived self-rotation in roll.

We report a novel illusory distortion of the visual scene, which became apparent during both: (i) observer rotation inside a furnished stationary room; and (ii) room rotation about the stationary observer. While this distortion had several manifestations, the most common experience was that scenery near fixation appeared to sometimes lead and other times lag more peripheral scenery. Across a series of experiments, we eliminated explanations based on eye-movements, distance misperception, peripheral aliasing, differential motion sensitivity and adaptation. We found that these illusory scene distortions occurred only when the observer perceived (real or illusory) changes in self-tilt and maintained a stable fixation.

Adult↗
PubMed1987

Rigidity in cinema seen from the front row, side aisle.

Pictures and cinema seen at a slant present the optics of virtual objects that are distorted and inconsistent with their real counterparts. In particular, it should not be possible for moving objects on slanted film and television screens to be seen as rigid, at least according to rules of linear perspective. Previous approaches to this problem have suggested that some process (perhaps cognitive) rectifies the optics of objects in slanted pictures to derive true shape and preserve shape constancy. The means for this rectification is usually thought to be based on recovery of true screen slant. In three experiments I show that this account is unnecessary and insufficient to explain the perception of rotating, rectangular objects in slanted cinema. I present data in favor of an alternate view, one in which the information is sufficient for perceivers to determine rigidity in an object on slanted screens, at least for parallel projections. In the human visual system, local measurements of objects are apparently made according to projective geometry; in those measurements, small amounts of certain distortions in projection are tolerated. Stimuli that appear nonrigid are ones that violate certain local principles, known as Perkins's laws, of projections of rectangular solids.

Humans↗