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PubMed1998

Psychic and somatic anxiety: worries, somatic symptoms and physiological changes.

Contrary to self-reports, patients with generalized anxiety disorder exhibit increased muscle tension but not autonomic hyperarousal. Under stress they tend to react autonomically in a less flexible manner than normal controls. There is only a weak relationship, and in some instances a desynchrony, between physiological changes and perception of change. The inconsistencies between self-reports of physiological states and physiological recordings can be explained by alterations of body sensations through psychological factors, predominantly expectations of and attention to bodily states, that lead to perceptual distortions.

Anxiety Disorders↗
PubMed2001

Visual discomfort: the influence of spatial frequency.

The response of different visual discomfort groups to a range of spatial frequencies at threshold and suprathreshold was investigated. In experiment 1, a paired-comparison task was conducted. The high visual discomfort group judged a spatial frequency of 4 cycles deg-1 as the most perceptually distorted and somatically unpleasant to view. The moderate and low visual discomfort groups judged 8 and 12 cycles deg-1 as more perceptually and somatically unpleasant to view than lower spatial frequencies. In experiment 2, the spatial contrast-sensitivity function (CSF) for the high visual discomfort group was depressed for spatial frequencies between 1 and 12 cycles deg-1 in comparison with the moderate and low visual discomfort groups. When these same spatial frequencies were modulated at 6 Hz, CSFs were the same for all groups. These results are discussed in relation to a failure of inhibition across spatial-frequency channels in the high visual discomfort group. This may be explained by a more generalised parvocellular system processing deficit. Possible similarities between some forms of migraine and visual discomfort are highlighted.

Adolescent↗
PubMed2000

Anxiety and arousal: physiological changes and their perception.

Contrary to self-reports, most patients with chronic anxiety disorders exhibit increased muscle tension but not autonomic hyperarousal when at rest. Under everyday stress they tend to react with less physiological flexibility than normal controls. However, they overreact subjectively and physiologically to stimuli that are anxiety-provoking. Diminished physiological flexibility may be either a constitutional trait in anxious individuals, a partial but inadequate adaptation to prolonged stress or the result of a disregard for stressors that are not related to psychopathology. The effects of diminished physiological flexibility on general health are not known. There is only a weak relationship, and in some instances a desynchrony, between physiological changes and perception of change under stress. The inconsistencies between self-reports of physiological states and physiological recordings can be explained by alterations of body sensations through psychological factors, predominantly expectations and attention to bodily states, that lead to perceptual distortions.

Adaptation, Psychological↗
PubMed1985

Amblyopic processing of positional information. Part I: Vernier acuity.

Psychometric functions for the recognition of vernier displacements have been measured in 6 strabismic amblyopes, 1 anisometropic amblyope, and 1 bilateral amblyope of unknown aetiology. In the non-amblyopic eyes of the 7 unilateral amblyopes the mean threshold vernier offset was about half of that of a group of 7 experienced normal observers. No correlation was found between vernier acuities and Snellen acuities in the abnormal eyes of squinters. These eyes also displayed massive distortions of horizontal spatial values causing perceptual distortions. In all but one of the amblyopic eyes tested hyperacuity virtually disappeared at the brief exposure duration of 50 ms. None of the observed effects could be predicted from the amblyopic contrast sensitivities, grating resolutions, or letter acuities. This suggests that the loss of positional information is an independent and most significant feature of amblyopic visual dysfunction.

Amblyopia↗
PubMed1991

Dysphoria in male alcoholics with a history of hallucinations.

This paper examines severity of depressive symptoms, as measured by the Beck Depression Inventory, in chronic alcoholics with and without a history of hallucinations. We found a) alcoholics entering alcohol treatment who have experienced hallucinations during detoxification report higher levels of subjective depression than alcoholics who have never experienced hallucinations, b) the level of subjective depression in alcoholics with a history of hallucinations remains higher at the end of inpatient alcohol treatment than in alcoholics without hallucinations, and c) hallucination is the important variable; alcoholics with blackouts, seizures, and delirium tremens, do not experience higher levels of depression during detoxification. The reporting of a significantly higher level of depressive symptoms by alcoholics with a history of experiencing hallucinations during withdrawal suggests that in some alcoholics, there exists a vulnerability for mood abnormalities which includes a predisposition toward other abnormal mental phenomena such as perceptual distortions.

Alcoholism↗
PubMed1979

Hypnotic deafness: a psychophysical study of responses to tone intensity as modified by hypnosis.

Hypnotic deafness was suggested for 1000 Hz tones presented in random orders at seven intensities between 17 and 70 db. Subjects were 70 college students stratified into four levels of hypnotic susceptibility, ranging from low to high. Four conditions were presented within a single session. Two conditions tested normal hearing, one in waking and one in hypnosis; two tested reported loudness of the tones as reduced by hypnotic suggestion. The method of magnitude estimation was employed. Hearing reduction was found to correlate .59 with hypnotic susceptibility in the total sample. Few high hypnotizables reduced their hearing to zero; their mean residual hearing during the deafness conditions was 55% of normal. Power functions for the relationship between tone intensity and magnitude estimates for conditions of normal hearing and deafness were found to be relatively parallel and orderly, differing primarily in intercept value. Order effect anomalies are discussed. The "hidden observer" method showed that for 4 of the 70 subjects the covert hearing was found to be at least 20% greater than that reported overtly within hypnotic deafness and approached normal hearing. As in our previous hypnotic analgesia research, not all subjects who reduced their hearing significantly gave subsequent covert reports which differed from reported overt hearing. Discussion is given for evidence of two levels of information processing during hypnotically suggested perceptual distortions.

Audiometry↗
PubMed1998

Antisaccades and smooth pursuit eye tracking and schizotypy.

BACKGROUND: Eye tracking deficits are one of a few widely validated behavioral markers of risk for schizophrenia. Recently, it has been proposed that antisaccade performance may also constitute a marker of schizophrenia risk. This study investigated whether eye tracking and antisaccade deficits could be found in another population with putative liability to schizophrenia-nonclinical subjects with elevated scores on a psychometric index of perceptual aberrations. METHODS: Subjects were 55 university students who received either high or normal scores on the Perceptual Aberration Scale, a measure of schizotypy indexing body image and perceptual distortions. Subjects completed a smooth pursuit eye tracking task and an antisaccade task. Eye movements were monitored using an infrared limbus tracker. RESULTS: Subjects with high Perceptual Aberration Scale scores (putative "schizotypes") had lower pursuit quality and a lower percentage correct on the antisaccade task than the controls. The 2 groups did not differ in antisaccade or error latencies. The increase in antisaccade errors in the schizotypes was accounted for almost entirely by an increase in perseverative errors, but virtually no difference between groups on random errors. Antisaccade performance was significantly related to pursuit quality. CONCLUSIONS: Subjects with elevated Perceptual Aberration Scale scores have performance deficits on oculomotor tasks that have been linked to latent liability to schizophrenia, namely, smooth pursuit and antisaccade performance. The antisaccade errors in the schizotype group were primarily perseverations, a behavioral pattern often associated with frontal lobe dysfunction and observed in the performance of schizophrenic patients.

Adult↗
PubMed1993

The use of ego-state therapy in the treatment of posttraumatic stress disorder.

Ego-state therapy has been cited in the literature as a promising tool for the treatment of patients who suffer from the effects of past trauma experiences. In this paper, I review various methods to activate ego states and to uncover traumatic experiences and their related internal conflicts in sexually abused patients with posttraumatic symptoms. I also discuss ego-state-therapy techniques that promote the integration and resolution of trauma. Three clinical case examples illustrate the use of ego-state therapy with posttraumatic patients. I suggest ways in which ego-state-therapy methods can be useful with some of the symptomatology specific to this population. The effectiveness of ego-state therapy is also explored in dealing with certain features of posttraumatic conditions that can complicate treatment, including dissociation and fragmentation, cognitive and perceptual distortion, and rigidification of personality and behavior.

Adult↗
PubMed2004

Deficits of spatial localization in children with strabismic amblyopia.

BACKGROUND: Besides loss of visual acuity and binocularity, spatial localization deficits (comprising both increased spatial uncertainty and spatial distortions) are an important feature of strabismic amblyopia. Although they have been extensively investigated in adult amblyopes, there are still many open questions concerning their substrate and relationship to clinical parameters. Our aim was to develop a procedure for assessing vertical alignment, which enabled us to find out whether children with strabismic amblyopia had similar spatial localization deficits, and their relation to the children's clinical condition. METHODS: Vertical alignment was assessed in children by comparing the visual direction in space of three loci along the vertical meridian, separated by 5 deg of visual angle. We tested alignment in the amblyopic and dominant eyes of 32 strabismic and in both eyes of 35 control children from 4.5 to 10 years, together with a careful orthoptic examination. RESULTS: In the amblyopic eyes, increased uncertainty and systematic distortions outside the normal range occurred. Large angles of deviation and pathological fixation patterns were necessary, but not sufficient conditions for gross spatial deficits to occur. The fellow dominant eyes showed spatial localization similar to normal eyes. CONCLUSIONS: Children with strabismic amblyopia exhibited localization deficits and relationship to clinical data similar to those in adult amblyopes. These data are important for further investigations about the substrate, plasticity and the clinical relevance of perceptual distortions.

Amblyopia↗
PubMed1997

Evaluating Müller-Lyer effects using single fin-set configurations.

Four experiments were conducted to study the bias of perceived length for Müller-Lyer configurations that contained a single set of fins (i.e., two segments that join to form a vertex). The experiments manipulated several factors that have been shown to be critical to the effect: (1) version (which way the apex pointed), (2) length of the stimulus span, (3) presence or absence of a line segment in the span being judged, (4) fin length, (5) fin angle, and (6) the zone in which the response was rendered. Using percent error as the index of perceptual distortion, the major finding was that the two versions show an opposite slope for strength of effect as a function of span. When stimulus spans were plotted against response means (not converting to percent error), an almost perfect linear relation was found. These results indicate that the perceptual effects can be modeled as a linear system having two parameters through which the treatments exert their influence. The results are discussed in relation to major theories of mechanism for the Müller-Lyer illusion.

Adult↗
PubMed1995

Distortion of size perception in visuospatial neglect.

BACKGROUND: A number of studies have shown that most patients with symptoms of unilateral (left-sided) visuospatial neglect make consistently rightward errors when attempting to bisect a horizontal line at its midpoint. One possible interpretation of this impairment is that such patients misperceive the left half of the line: that is, that they underestimate its extent relative to the right half. RESULTS: We have carried out direct tests for such a perceptual distortion in three neglect patients by asking them to make matching judgements on pairs of horizontal rectangles, vertical rectangles or nonsense shapes, of varying relative size, presented on a computer screen. We report here that all of the patients tested showed a significant and substantial relative underestimation of the horizontal extent or area of stimuli presented on the left side of their egocentric space. There was no such misperception of vertical extent. CONCLUSIONS: It is suggested that size perception may be partially determined by a representational system that is anatomically centred in the parieto-temporal region of the brain. The results are interpreted in terms of damage to this system in neglect patients.

Attention↗
PubMed1982

Perception of eye scans with the Müller-Lyer stimuli: evidence for filter theory.

Ginsburg's filter theory successfully accounts for the perceptual distortions perceived in a wide range of illusions and bistable phenomena. Essentially, the theory proposes that illusory distortions are the natural consequence of low-pass spatial filtering (based upon the human modulation transfer function) of the physical stimulus. With regard to the Müller-Lyer illusion, predictions based upon filter theory and human scan-path data are in accord. However, data linking filter theory's predictions regarding perceptual experiences associated with the illusion to the eye-scan results have been missing. In the present experiment subjects provided subjective estimations of their own eye scans while viewing each of the following stimuli: the fins-out member of the Müller-Lyer illusion, the fins-in member of the Müller-Lyer illusion, and a finless horizontal line (variations of each stimulus consisted of one, two, and three line segments). The analysis of these data supported three predictions that were derived from filter theory. Potential problems facing filter theory are also addressed.

Adolescent↗
PubMed2005

Effect of saccadic adaptation on localization of visual targets.

Objects flashed briefly around the time of a saccadic eye movement are grossly mislocalized by human subjects, so they appear to be compressed toward the endpoint of the saccade. In this study, we investigate spatial localization during saccadic adaptation to examine whether the focus of compression tends toward the intended saccadic target or at the endpoint of the actual (adapted) movement. We report two major results. First, that peri-saccadic focus of the compression did not occur at the site of the initial saccadic target, but tended toward the actual landing site of the saccade. Second, and more surprisingly, we observed a large long-term perceptual distortion of space, lasting for hundreds of milliseconds. This distortion did not occur over the whole visual field but was limited to a local region of visual space around the saccade target, suggesting that saccadic adaptation induces a visuo-topic remapping of space. The results imply that the mechanisms controlling saccadic adaptation also affect perception of space and point to a strong perceptual plasticity coordinated with the well-documented plasticity of the motor system.

Adaptation, Physiological↗
PubMed1975

Effect of speed adaptation on performance in a self-paced tracking task.

12 Ss were required to perform a self-paced tracking task designed to simulate 'hazardous' road conditions. Those 6 Ss who had previously been exposed to a simple, high-speed version of the task travelled faster and made more errors on the hazardous task than 6 control Ss who performed the hazardous task throughout the experiment. The findings supplement earlier studies of the effect of speed adaptation on the judgment of speed and suggest that, in addition to perceptual distortions, an acquired motivation for speed may be an important factor in the behaviour of drivers leaving high-speed roads.

Accidents, Traffic↗
PubMed2006

Induced movement: the flying bluebottle illusion.

Two small objects (flies) followed identical circular orbits. However, a large background that circled around behind them in different phases made one orbit look twice as large as the other (size illusion) or made the circles look like very thin horizontal or vertical ellipses with aspect ratios of 7.5:1 or more (shape illusion). The nature of the perceptual distortion depended upon the relative phase between the movements of the background and those of the flies. Brief snatches of the moving background that added up to a circular motion were also effective.

Humans↗
PubMed2000

The task-dependent use of binocular disparity and motion parallax information.

Binocular disparity and motion parallax are powerful cues to the relative depth between objects. However to recover absolute depth, either additional scaling parameters are required to calibrate the information provided by each cue, or it can be recovered through the combination of information from both cues (Richards, W. (1985). Structure from stereo and motion. Journal of the Optical Society of America, 2, 343-349). However, not all tasks necessarily require a full specification of the absolute depth structure of a scene and so psychophysical performance may vary depending on the amount of information available, and the degree to which absolute depth structure is required. The experiments reported here used three different tasks that varied in the type of geometric information required in order for them to be completed successfully. These included a depth nulling task, a depth-matching task, and an absolute depth judgement (shape) task. Real world stimuli were viewed (i) monocularly with head movements, (ii) binocularly and static, or (iii) binocularly with head movements. No effect of viewing condition was found whereas there was a large effect of task. Performance was accurate on the matching and nulling tasks and much less accurate on the shape task. The fact that the same perceptual distortions were not evident in all tasks suggests that the visual system can switch strategy according to the demands of the particular task. No evidence was found to suggest that the visual system could exploit the simultaneous presence of disparity and motion parallax.

Depth Perception↗
PubMed1978

Aspects of body image perception in obese and normal-weight youngsters.

Perceptual and projective aspects of body image in obese youngsters (not in psychological treatment) and normal-weight youngsters 8-9 years of age and 12-13 years of age were investigated. The results indicate that perceptual distortions in estimating various body dimensions of oneself are primarily a function of age rather than weight status. The accuracy of estimating the weight of peers and an adult showed an association with the sex of the subject. No group differences were found in terms of projective aspects of body image as measured by barrier and penetration responses. This study suggests that obese youngsters in the middle childhood and entering puberty periods in comparison to normal-weight youngsters of the same age do not manifest differences in perceptual factors of body image.

Adolescent↗
PubMed2005

Symptoms of schizotypy precede cannabis use.

The current investigation uses a large non-clinical sample of undergraduate college students (N=189) to investigate schizotypal traits among cannabis and non-cannabis users, as well as the temporal order of the onset of these traits and cannabis use. Findings suggest that regular cannabis users are significantly more prone to cognitive and perceptual distortions as well as disorganization, but not interpersonal deficits, than non-regular users and those who have never used. Additionally, the onset of schizotypal symptoms generally precedes the onset of cannabis use. The findings do not support a causal link between cannabis use and schizotypal traits.

Adolescent↗