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Results for “Perceptual Distortion”

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At least 973 records · Page 54Linked to original sources
PubMed2003

Maximum permissible lateral decentration in aberration-sensing and wavefront-guided corneal ablation.

PURPOSE: To investigate the lateral alignment accuracy needed in wavefront-guided refractive surgery to improve the ocular optics to a desired level in a percentage of normally aberrated eyes. SETTING: Department of Ophthalmology, University of Zurich, Zurich, Switzerland. METHODS: The effect of laterally misaligned ablations on the optical outcome was simulated using measured wavefront aberration patterns from 130 normal eyes. The calculations were done for 3.0 mm, 5.0 mm, and 7.0 mm pupils. The optical quality of the simulated correction was rated by means of the root-mean-square residual wavefront error. RESULTS: To achieve the diffraction limit in 95% of the normal eyes with a 7.0 mm pupil, a lateral alignment accuracy of 0.07 mm or better was required. An accuracy of 0.2 mm was sufficient to reach the same goal with a 3.0 mm pupil. CONCLUSION: Procedures must be developed to ensure that the ablation is within a tolerance range based on each eye's original optical error. Rough centration based on the surgeon's judgment might not be accurate enough to achieve significantly improved optical quality in a high percentage of treated eyes.

Adolescent↗
PubMedDate not supplied

Inflated perception of responsibility for harm in obsessive-compulsive disorder.

The present study examined the proposition that inflated responsibility is implicated in obsessive compulsive disorder (OCD). Compared to non-anxious control participants (NACs), and an anxious control group with generalized social phobia (GSPs), we predicted that individuals with OCD (OCs) would exhibit a greater urge to rectify situations involving potential risk, would report more distress upon leaving such situations unrectified, and would feel more personal responsibility if the unrectified situations resulted in harm. Fifteen OCs, 15 NACs, and 15 GSPs completed the Obsessive Compulsive Responsibility Scale (OCRS), which included low-risk, OC-relevant, and high-risk situations. Compared to NACs and GSPs, OCs reported more urges, distress, and responsibility in low-risk and OC-relevant situations; no group differences were detected on high-risk situations. GSPs and NACs differed only in their responsibility in OC-relevant situations, with GSPs reporting higher responsibility than controls. Our results suggest that compared to OCs, NACs, and GSPs can better differentiate between situations that merit concern and ones that do not.

Adult↗
PubMed2002

Inflated perception of responsibility for harm in OCD patients with and without checking compulsions: a replication and extension.

In a follow-up study to [J. Anxiety Disord., in press] examination of inflated perception of responsibility for harm among individuals with obsessive compulsive disorder (OCs), 22 OC checkers, 24 OC non-checkers, and 25 non-anxious controls (NACs) completed the Obsessive Compulsive Responsibility Scale (OCRS), which consisted of written descriptions of Low-Risk (LR), Moderate-Risk (MR), and High-Risk (HR) scenarios. In LR and MR scenarios, OC checkers reported greater perception of responsibility for harm and greater relief upon rectifying the situation, than did NACs. OC checkers also reported greater urges to rectify LR situations than did NACs. OC non-checkers did not differ from NACs on any of the scales. No group differences emerged for HR scenarios. The results suggest that, compared to OC non-checkers and to NACs, OC checkers have an inflated perception of responsibility for harm; and that this perception leads to a need to rectify potentially harmful situations.

Analysis of Variance↗
PubMed2003

Neurocognitive, behavioural and neurodevelopmental correlates of schizotypy clusters in adolescents from the general population.

INTRODUCTION: Studies on the neurocognitive correlates of schizotypy dimensions have found inconsistent results. This might stem from the fact that correlational methods, in contrast to cluster analysis, do not account for the possibility that a subject presents high scores on more than one dimension simultaneously. We aimed to establish clusters of normal adolescents based on schizotypy dimensions and compare them on neurocognitive, behavioural, and neurodevelopmental markers. METHODS: Two hundred seventy normal adolescents from the general population (mean age 13.4, SD=0.72) attending obligatory education were evaluated. RESULTS: A K-means iterative cluster analysis was performed with the Perceptual Aberration, Revised Social Anhedonia and Physical Anhedonia Scales. A forced four-cluster model yielded the following clusters: 'negative schizotypy', 'high or mixed schizotypy', 'positive schizotypy', and 'normal scorers'. Comparisons with ANOVAs showed that 'high schizotypes' performed poorly on neurocognition (Wechsler Intelligence Scales for Children-Revised (WISC-R) and Verbal Fluency (FAS)) and obtained the highest teacher ratings (TRF) of behavioural problems. 'Negative schizotypes' had the worst WCST results and more dermatoglyphic abnormalities. Both clusters had more neurological soft signs than 'normal scorers' and 'positive schizotypes'. CONCLUSIONS: Our results with community adolescents found the same cluster structure than the previous cluster analytic studies conducted in adult college subjects. Furthermore, we showed differences among them on neurocognitive and malneurodevelopment markers consistent with the adult literature on schizotypy.

Adolescent↗
PubMed2003

Somatosensory evoked potentials during a rubber-hand illusion in schizophrenia.

The rubber-hand illusion (RHI), an illusion in which tactile sensations are referred to a synthetic alien limb, is enhanced in schizophrenia patients. Somatosensory evoked responses of the illusion were compared between schizophrenia patients and normal control subjects. Schizophrenia patients had significant alterations in long latency evoked responses during the illusion. These findings support the hypothesis of alterations in associative higher-level neuronal activity in schizophrenia. The findings support previous results pointing to alterations in associative brain regions in schizophrenia.

Adult↗
PubMed1999

Antisaccade task performance in questionnaire-identified schizotypes.

Individuals who scored high on Perceptual Aberration-Magical Ideation Scales (Per-Mag; n = 90), the Social Anhedonia Scale (SocAnh; n = 39), and control participants (n = 89) were administered saccadic refixation (prosaccade) and saccadic suppression (antisaccade) tasks. Eye movements were scored in terms of error rates and latency. None of the groups differed in terms of their performance on the prosaccade task. Both the Per-Mag (p < 0.01) and SocAnh (p < 0.05) groups exceeded the controls in terms of mean antisaccade errors. The high-risk groups did not differ from each other. Eighteen of the Per-Mag individuals and 10 of the SocAnh individuals displayed deviant antisaccade performance. These findings are particularly interesting in light of suggestive evidence that antisaccade task deficits may serve as a marker of susceptibility to schizophrenia. It is hypothesized that the individuals who scored aberrantly on the Chapman scales and displayed antisaccade performance deficits are most likely to be at risk for the development of psychosis.

Adult↗
PubMed1999

A rating scale for psychotic symptoms (RSPS) part I: theoretical principles and subscale 1: perception symptoms (illusions and hallucinations).

The authors present a new rating scale for the psychotic symptoms of schizophrenia and related psychoses. The scale links specific symptoms of psychopathology to dysfunction and overactivity of dopaminergic mechanisms underlying the processes of reward and selective attention. The Rating Scale for Psychotic Symptoms (RSPS) is a 44-item rating instrument with a seven-point severity scale for each item. Psychotic symptoms are classified into three groups: Pathological amplification of mental images (perception symptoms) (subscale 1), Distraction symptoms (including catatonia and passivity experiences) (subscale 2), and Delusions (subscale 3). A dimensional, rather than a categorical, conceptualization of psychosis is assumed. Rating is accomplished through a manual and a semi-structured interview (SSCI-RSPS). In this first of two papers, general issues about the construction of the scale and the derivation of symptom groups are discussed. Dopamine-mediated modification of cortico-striatal synapses is seen as being of critical importance in all three groups of symptoms. In this first paper, we present subscale I (perception symptoms), which includes both amplified perceptual images (illusions) and hallucinations. A total of seven illusions and 11 hallucinations are rated as individual items.

Behavioral Symptoms↗
PubMed2001

Variable practice with lenses improves visuo-motor plasticity.

Novel sensorimotor situations present a unique challenge to an individual's adaptive ability. Using the simple and easily measured paradigm of visual-motor rearrangement created by the use of visual displacement lenses, we sought to determine whether an individual's ability to adapt to visuo-motor discordance could be improved through training. Subjects threw small balls at a stationary target during a 3-week practice regimen involving repeated exposure to one set of lenses in block practice (x 2.0 magnifying lenses), multiple sets of lenses in variable practice (x 2.0 magnifying, x 0.5 minifying and up-down reversing lenses) or sham lenses. At the end of training, adaptation to a novel visuo-motor situation (20-degree right shift lenses) was tested. We found that (1) training with variable practice can increase adaptability to a novel visuo-motor situation, (2) increased adaptability is retained for at least 1 month and is transferable to further novel visuo-motor permutations and (3) variable practice improves performance of a simple motor task even in the undisturbed state. These results have implications for the design of clinical rehabilitation programs and countermeasures to enhance astronaut adaptability, facilitating adaptive transitions between gravitational environments.

Adaptation, Physiological↗
PubMed2003

Self-consciousness, self-agency, and schizophrenia.

Empirical approaches on topics such as consciousness, self-awareness, or introspective perspective, need a conceptual framework so that the emerging, still unconnected findings can be integrated and put into perspective. We introduce a model of self-consciousness derived from phenomenology, philosophy, the cognitive, and neurosciences. We will then give an overview of research data on one particular aspect of our model, self-agency, trying to link findings from cognitive psychology and neuroscience. Finally, we will expand on pathological aspects of self-agency, and in particular on psychosis in schizophrenia. We show, that a deficient self-monitoring system underlies, in part, hallucinations and formal thought (language) disorder in schizophrenia. We argue, that self-consciousness is a valid construct and can be studied with the instruments of cognitive and neuroscience.

Awareness↗
PubMed2003

Observing one's hand become anarchic: an fMRI study of action identification.

The self seems to be a unitary entity remaining stable across time. Nevertheless, current theorizing conceptualizes the self as a number of interacting sub-systems involving perception, intention and action (self-model). One important function of such a self-model is to distinguish between events occurring as a result of one's own actions and events occurring as the result of somebody else's actions. We conducted an fMRI experiment that compared brain activation after an abrupt mismatch between one's own movement and its visual consequences with an abrupt mismatch between one's own movement and somebody else's visually perceived hand movement. A right fronto-parietal network was selectively active during a sudden mismatch between one's own observed and performed hand action.

Awareness↗
PubMed2003

Modulating the experience of agency: a positron emission tomography study.

This study investigated agency, the feeling of being causally involved in an action. This is the feeling that leads us to attribute an action to ourselves rather than to another person. We were interested in the effects of experimentally modulating this experience on brain areas known to be involved in action recognition and self-recognition. We used a device that allowed us to modify the subject's degree of control of the movements of a virtual hand presented on a screen. Four main conditions were used: (1) a condition where the subject had a full control of the movements of the virtual hand, (2) a condition where the movements of the virtual hand appeared rotated by 25 degrees with respect to the movements made by the subject, (3) a condition where the movements of the virtual hand appeared rotated by 50 degrees, and (4) a condition where the movements of the virtual hand were produced by another person and did not correspond to the subject's movements. The activity of two main brain areas appeared to be modulated by the degree of discrepancy between the movement executed and the movement seen on the screen. In the inferior part of the parietal lobe, specifically on the right side, the less the subject felt in control of the movements of the virtual hand, the higher the level of activation. A reverse covariation was observed in the insula. These results demonstrate that the level of activity of specific brain areas maps onto the experience of causing or controlling an action. The implication of these results for understanding pathological conditions is discussed.

Adult↗
PubMed2004

The validity of subjective measures of body image disturbance.

OBJECTIVE: We examined weight dissatisfaction (actual weight minus self-stated ideal weight) and weight goal (normative weight minus self-stated ideal weight) subjective indices in a large clinical sample to determine how the indices discriminate between diagnostic categories and relate to other measures of body image disturbance. METHOD: Approximately 200 anorexic, bulimic, and eating disorder not otherwise specified (NOS) participants reported their self-stated ideal weight and completed the Mizes Anorectic Cognitions (MAC) Questionnaire, Eating Disorders Inventory (EDI), and Restraint Scale-Revised. RESULTS: Compared with bulimic and NOS participants, anorexics reported less weight dissatisfaction but had an ideal weight that is farthest from normative weight. The weight dissatisfaction measure correlates well with other measures of body image disturbance, and both measures show evidence of discriminant validity. DISCUSSION: These two measures highlight the substantial differences in the nature of body image disturbance between the eating disorder diagnostic groups. Theoretical, clinical, and practical implications are discussed.

Adolescent↗
PubMed1976

An investigation of psychological factors involved in the predisposition to auditory hallucinations.

Previous research by the author (Slade, 1972, 1973) and others has suggested that psychological stress plays an important role in triggering off the experience of auditory hallucinations. Clearly, however, predispositional factors are involved as well. The present study is an attempt to investigate some of the psychological factors which may predispose the individual to such experiences. A battery of tests involving cognitive, personality and mental imagery variables and the verbal transformation effect was administered to two small groups of psychotic patients differing only in respect of a history of auditory hallucinations and a normal control group. The main conclusion was that the results lend direct support to the proposition of Mintz & Alpert (1972) that a combination of vivid mental imagery and poor reality-testing in the auditory modality provides the basic predisposition for the experience of auditory hallucinations.

Adolescent↗
PubMed1994

An experimental phenomenological approach to delusional memory in schizophrenia and late paraphrenia.

A preliminary model is described to account for the 'reality testing' of memories (after Johnson & Raye, 1981) in an attempt to explain delusional memory. Two routes are proposed: route one involves evaluation of the factual content of the memories against stored general knowledge. Route two relies on the evaluation of the perceptual and narrative characteristics of memories with the assumption that the stronger these characteristics, the more likely the memory is to be real. The integrity of these routes is examined in four patients with delusional memories, using standardized tests. The results suggest that in these cases, general knowledge is essentially intact while the perceptual characteristics of delusional memories are stronger than real memories which in turn, are stronger than fantasies. This could lead the evaluation system to accept delusional memories as true memories despite their implausibility. The roles of rehearsal and affect are probably important in this and require further study.

Adult↗
PubMed1977

A reappraisal of body perception disturbance in anorexia nervosa.

Previous research has suggested that patients suffering from anorexia nervosa tend to overestimate their body size, whereas normal females tend to be very accurate in this respect. This paper presents the results of further investigations of body perception amongst anorexic and normal females. The results, in contrast to earlier findings, indicate no such difference between groups. Detailed analysis of the data, however, points to the likelihood of certain differences between the present group of anorexic patients and previous groups. Moreover, it seems that body perception disturbance is not a consistent feature of anorexia nervosa and is only present amongst some patients at certain stages during their illness. On subdividing the anorexic group it was demonstrated that patients who vomit tend to overestimate their size more than do non-vomiters. It also seems likely that normal females are far from homogeneous in terms of body perception. In line with previous findings, a direct relationship was found between marked overestimation of body size and an early relapse. Evidence is also discussed which suggests that body perception disturbance is not specific to anorexia nervosa and may reflect an abnormal sensitivity about body size associated with such factors as the anticipation of an undesired change in weight, extreme concern about slimness and anxiety about putting on weight.

Adolescent↗