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PubMed1993

Visual processing delays alter the perceived spatial form of moving gratings.

This study shows that there are delays in processing high spatial frequencies relative to low frequencies, and that these may affect the perceived brightness profile of drifting waveforms. The stimuli were complex waveforms consisting of 2-3 sinusoidal components, either drifting or stationary. The phase of the components was varied until the brightness profile of the waveform appeared as a square, triangle, ramp or bar. The results indicate that stationary waveforms are perceived veridically, but drifting waveforms are not. The harmonics of a drifting complex wave must be phase advanced, relative to the fundamental, in order to cancel motion-induced waveform distortions. This suggests that during visual processing the harmonics must be phase delayed, indicating that they are being processed more slowly than the fundamental. The most significant delays appear to be those between the fundamental and its second and third harmonic. Furthermore, the results show that the magnitude of the delays is dependent on the phase relationship between the components at perceptually significant points in the waveform: delays are less when the components are in sine phase than when they are in cosine phase. Separate experiments show that the detectability of phase shifts is least when the components are in sine phase. Together, these results may explain why drifting "sharp-edged" stimuli are not perceptually distorted: the human visual system appears to be relatively insensitive to phase shifts around square-wave phase and may therefore tolerate differences in the processing times of certain harmonics. A discussion of the possible origin of these processing delays is presented, together with the hypothesis that frequency dependent delays may reflect the spatiotemporal inseparability of cortical visual units.

Form Perception↗
PubMed1990

Denial of separation anxiety as measured by a serial tachistoscopic technique.

A mother-child separation stimulus was repeatedly presented by standard Defense Mechanism Test procedure, at increasing durations of tachistoscopic exposure to 60 clinical and nonclinical subjects. Subjective verbal reports were coded blindly for evidence of perceptual distortions presumably indicative of denial of separation anxiety. Low scores on two items measuring sensitivity to separation anxiety and intolerance of aloneness were, as predicted, significantly more often characterized by codings of denial on the tachistoscopic exposures than subjects with high sensitivity to separation anxiety. Stability of effect became stronger when only very low and very high scores were compared for perceptual denial on the last four presentations of the series. This technique, employing other types of anxiety-evoking stimuli, may represent a reliable instrument to reveal the presence of defences toward each of the most relevant conflictual areas of the personality.

Adult↗
PubMed2001

How sensitive is hand transport to illusory context effects?

A recent report that hand transport was sensitive to a size-contrast illusion (SCI) implied that the distinction between visual processing for perception versus action might only affect visual information obtained late during reaching. In this study, the presence of a perceptual SCI did not affect reaction time, movement time, or movement amplitude. However, both perception and action became sensitive to the SCI with memory-based responses. It is concluded that the distinction between visual processing for perception versus action does extend to hand transport. Immediate action is entirely based on veridical visuo-motor representations, whereas even slightly delayed actions begin to reflect distorted perceptual representations.

Adult↗
PubMed2002

Can sex offenders who minimize on the MMPI conceal psychopathology on the Rorschach?

Rorschach sensitivity to minimization is important in forensic evaluations of sex offenders because these individuals frequently deny psychological problems. To study Rorschach minimization, we divided alleged sex offenders according to whether they minimized on the MMPI (Hathaway & McKinley, 1943) or MMPI-2 (Butcher, Dahlstrom, Graham, Tellegen, & Kaemmer, 1989) and compared their Rorschachs on indexes of distress, faulty judgment, interpersonal dysfunction, and cognitive distortions. We predicted there would be no differences between MMPI minimizers and nonminimizers on these indexes and that sex offenders of both groups would show greater psychopathology than normative adult samples. Results indicate that mini- mizers produce normal MMPI clinical profiles but still show evidence of psychopathology on the Rorschach. As predicted, sex offenders showed more Rorschach psychopathology than normative samples. Sex offenders' protocols that contained sexual content also showed perceptual distortions. These findings indicate that the Rorschach is resilient to attempts at faking good and may therefore provide valuable information in forensic settings where intentional distortion is common.

Adult↗
PubMed1988

Some proprioceptive influences on the perceptual representation of body shape and orientation.

Perception of the surface contour of the body is generally thought to depend on topographically organized neural maps of somatosensation in the thalamus and cortex. Recent neurophysiological studies indicate that these maps are potentially modifiable through alterations in their sensory input. We present evidence that the apparent shape and orientation of the body can be changed within seconds by using muscle vibration to generate proprioceptive misinformation about limb position. Depending on the position of the hands or feet in relation to the rest of the body and to the test chamber, it is possible to generate systematic perceptual distortions of the body and changes in the apparent orientation of the body. Some implications of these observations for the maintenance of an accurate body schema, for spatial orientation, and for the encoding of ocular position are described.

Adolescent↗
PubMed2003

Effects of illusory spatial anisometry in unilateral neglect.

Patients with visuospatial neglect tend to underestimate horizontal magnitudes in contralesional space. It has been recently hypothesised that this behaviour might be due to anisometry of space perception, by which horizontal stimuli would be progressively underestimated proceeding from the ipsi towards the contralesional side of space. We investigated the effects of modulating space perception through the Oppel-Kundt illusion (i.e. a filled space is perceived as more expanded than an empty space) on the behaviour of 28 neglect patients and 28 normal subjects. The two groups bisected lines on backgrounds of vertical lines evenly spaced or unevenly spaced, with distances which decreased progressively from one side of the page to the other. On the same backgrounds, they extended segments to the left or to the right so as to double them. Patients also had to cancel targets, the density of which was evenly distributed or horizontally increased from one side of the page to the other. Both groups were prone to the illusion. Neglect bias was modulated by the illusion in the expected direction. It was reduced when the illusion induced a perceptual distortion opposite to that thought to underlie neglect. On bisection and cancellation tasks, illusory effects were greater in patients with higher values of response bias on the Milner Landmark task. These findings, taken together with patients' anatomical data, suggest that a modulation of neglect through a visual illusion can normally be induced in patients with relatively intact visual input processes.

Aged↗
PubMed2005

The neurological basis of visual neglect.

PURPOSE OF REVIEW: A recent study has confirmed the enormous impact of visual neglect on the health services of the western world. Neglect was present in 48% of a sample of 166 right hemisphere stroke patients, and the severity of neglect predicted the extent of functional disability and family burden more accurately than did the extent of brain damage. Given the medical significance of neglect and its tantalizing relevance to understanding human conscious experience, it is unsurprising that the neuropsychological literature concerning the syndrome continues to grow rapidly. RECENT FINDINGS: We include brief surveys of six topics currently attracting attention in the field: the anatomical focus of neglect; the visual input pathways implicated; impairments of spatial working memory; the nature of visual extinction; perceptual distortions in neglect; studies on healthy subjects using transcranial magnetic stimulation; and the use of prism adaptation for the rehabilitation of neglect. SUMMARY: There is steady progress in understanding the essential components of neglect and their brain localization. Every step towards clarity, however, seems to be matched by a new discovery of the inherent complexity of the syndrome. The clinical expression of neglect may reflect the interaction of a variety of spatially lateralized and non-lateralized impairments, not all of which are present in all patients. The quest for an effective technique for the clinical rehabilitation of neglect continues, with prism adaptation emerging as the most promising approach to date.

Attention↗
PubMed2006

Psychological effects of ketamine in healthy volunteers. Phenomenological study.

BACKGROUND: The psychosis-inducing effect of ketamine is important evidence supporting the glutamate hypothesis of schizophrenia. However, the symptoms the drug produces have not been described systematically. AIM: To examine the effects of ketamine in healthy people using a structured psychiatric interview. METHOD: Ketamine (200 ng/ml) or placebo was administered by continuous infusion to 15 healthy volunteers. Symptoms were rated using the Present State Examination, the Thought, Language and Communication Scale and the Scale for Assessment of Negative Symptoms. RESULTS: Ketamine induced a range of perceptual distortions, but not hallucinations. Referential ideas were seen in nearly half the sample. There were only mild and infrequent ratings on the thought disorder scale. Affective flattening and alogia were seen in some volunteers. CONCLUSIONS: Ketamine does not reproduce the full picture of schizophrenia. The main point of similarity concerns referential thinking. Phenomena resembling negative symptoms are also seen, but the distinction of these from the drug's sedative effects requires further elucidation.

Adult↗
PubMed1998

Cerebral perfusion in children with Alice in Wonderland syndrome.

Alice in Wonderland syndrome (AIWS) is characterized by visual hallucinations and bizarre perceptual distortions. Technetium-99m hexamethylpropyleneamine tomography (SPECT) brain scans were performed in four patients during the acute stage of AIWS. Two patients were demonstrated to have Epstein-Barr virus infections. One had abnormal (EEG) findings. The visual-evoked potential, cranial CT, and MRI findings were negative. The decreased cerebral perfusion areas in all patients were near the visual tract and visual cortex. All involved some regions of the temporal lobe. In most patients with AIWS, the EEG, CT, and MRI are unable to determine the precise pathologic areas. However, a SPECT brain scan may demonstrate abnormal perfusion areas and explain the clinical presentations.

Cerebrovascular Circulation↗
PubMed2001

Spatiotemporal visual function in tinted lens wearers.

PURPOSE: Tinted lenses have been widely publicized as a successful new treatment for reading disorders and visual stress in children. The present study was designed to investigate a variety of visual deficits reported by children who experience high levels of visual stress and perceptual distortions when reading (Meares-Irlen syndrome; MIS) and to assess the improvements in visual comfort they report when tinted lenses are worn. METHODS: Twenty children (13.1 +/- 0.9 years of age) were recruited who had successfully worn tinted lenses for at least 6 months and were compared with an age-matched control group (12.6 +/- 2.2 years of age) of 21 children who were not lens wearers. A range of psychophysical tasks was adapted to identify specific anomalous visual perceptions. Spatiotemporal contrast sensitivity and contrast increment thresholds were used to investigate subjective reports of dazzle and hypercontrast, and a minimum motion perception (D(min)) and a motion-coherence task were used to assess subjective reports of visual instability and motion. RESULTS: In all viewing conditions (with versus without lens), no selective functional visual loss was demonstrated with any of the tasks used. Psychometric functions also revealed no significant difference between subject groups (control versus MIS). CONCLUSIONS: Under thorough psychophysical investigation, these results revealed no significant difference in visual function between subject group, and this finding is consistent with the absence of any effect of the tinted lenses in the group with MIS.

Adolescent↗
PubMed1979

Selective inattention to anxiety-linked stimuli.

The term selective inattention as used here subsumes those phenomena whose primary function is the active blocking or attenuation of partially processed contents en route to conscious expression. Examples are anxiety-motivated forgetting or perceptual distortion and hypnotically induced negative hallucinations. Studies in the field of selective attention have typically been designed to explain what takes place in a task in which the subject is first instructed to attend to a particular stimulus and then to consciously execute that instruction as well as he can. The rejection of content in process is examined only sceondarily as a consequence of the acceptance of relevant information. In the present experiments and theorizing, the emphasis instead is on inhibitory operations that take place automatically, without conscious intent, in response to a potential anxiety reaction. Experiment 1 explored the interaction of anxiety-linked inattention with strength of a target stimulus. Three female subjects were programmed under hypnosis to respond posthypnotically in the On condition with prescribed degrees of anxiety when certain Blacky pictures popped into mind later ,t the end of experimental trials; in the Off conditionall pictures were to become neutral. With the three female subjects still under hypnosis, each of the loaded pictures was then paired with a four-letter work relevant to the individual's own version of what was happening in the picture. The waking recognition task, carried out with amnesia for the prior hypnotic programming, consisted of tachistoscopic exposure of loaded words and physically similar filler words at four durations within a baseline range of recognition accuracy from 50%--75% correct. The data yielded a curvilinear relationship in which the recognition of only the loaded words was significnatly lower in the On condition at the 60%--70% range of recognition accuracy but not at shorter or longer stimulus durations. Experiment 2, for which the prior hypnotic programming of the same three subjects was similar to Experiment 1, used an anagram approach to comparable four-letter words, except that pleasure-loaded words were introduced as a control along with filler words. Four durations of tachistoscopic exposure of the anagrams were used with each individual, and the major dependent variable was response latency measured in milliseconds. An independent measure of perceptual discriminability of the scrambled stimulus letters was obtained to isolate perceptual from cognitive aspects of the task. The results indicated that both low perceivability and high solvability increase the likelihood of response delays specifically in the presence of anxiety-linked stimuli. Experiment 3 was a nonhypnotic replication of Experiment 2, using 12 male and 13 female subjects. The potential affective loading of key anxiety and pleasure words was accomplished by structured scenarios for the Blacky pictures in which subjects were asked to place themselves as vividly as possible...

Adult↗
PubMed1984

Genetic and nosological aspects of schizotypal and borderline personality disorders. A twin study.

The aim of this study was to investigate etiological and nosological aspects of the schizotypal and borderline personality disorders. The sample consisted of 44 schizotypal, 15 schizotypal and borderline, and ten borderline same-sexed twin probands. The investigation of the co-twins indicated that genetic factors seemed to influence the development of the schizotypal, but not the borderline, personality disorders. The basic genetic core of the schizotypal syndrome seemed to consist of schizoid and paranoidlike features, and not psychoticlike cognitive and perceptual distortions. The study did not indicate any relationship between schizotypal and borderline personality disorders and affective and schizophrenic disorders. Further research is needed to confirm the independent status of the schizotypal syndrome in relation to the schizoid, avoidant, and paranoid personality disorders, and the borderline syndrome in relation to the histrionic , narcissistic, and antisocial personality disorders.

Adult↗
PubMed1977

Psychological aspects of pain patient treatment.

Acute and chronic pain complaints are in part determined by psychological factors unrelated to disease or trauma. Suffering associated with acute pain is greatly influenced by the anxiety of the patient, and it can be managed by helping him form useful defensive attitudes toward the pain he will experience. Chronic pain, in contrast, tends to be linked to personality problems and payoffs in the home and job situation for adopting a sick role. Both pain states may be usefully construed as problems of perceptual distortion. A model for the perception of pain is presented and suggestions for applying psychological considerations in the diagnosis and management of pain states are offered.

Activities of Daily Living↗
PubMed1997

A cognitive neuropsychological approach to the study of delusions in late-onset schizophrenia.

OBJECTIVE: Hypotheses to explain delusion formation include distorted perceptual processing of meaningful stimuli (e.g. faces), abnormal reasoning, or a combination of both. The study investigated these hypotheses using standardized neuropsychological tests. DESIGN: A three-patient case-study, compared with a small group (n = 8) of age-matched normal control subjects. SETTING: Hospital in- and outpatients. Age-matched normal controls were from local residential homes. PATIENTS: Three subjects with late-onset schizophrenia, two currently deluded and one in remission. Both deluded subjects had persecutory beliefs. One had a delusion of misidentification. INTERVENTIONS: All subjects were administered standardized neuropsychological tests of facial processing and tests of verbal reasoning. MAIN OUTCOME MEASURES: The test scores of the three patients were compared with published normal values and the age-matched control data. RESULTS: The tests demonstrated impaired matching of unfamiliar faces in deluded subjects, particularly in the subject with delusional misidentification. Increasing the emotional content of logical reasoning problems had a significant effect on the deluded subjects' reasoning but not that of the normal controls. CONCLUSION: The findings suggest impaired visual processing plus abnormal reasoning in deluded subjects. However, these impairments are relatively subtle given the severity of psychiatric disorder in the patients studied.

Age of Onset↗
PubMed1998

Rorschach patterns of response in Vietnam veterans with posttraumatic stress disorder versus combat and normal controls.

To further evaluate Rorschach indicators of posttraumatic stress disorder (PTSD), test protocols of 16 combat veterans so diagnosed were compared with those of 9 combat controls and 12 noncombat subjects. Results replicated Rorschach abnormalities previously associated with this disorder, including signs of low stress tolerance, poor affect modulation, perceptual distortion, and interpersonal disengagement. However, only two indicators, EB (Erlebnistypus) and CC (combat-related content), differentiated PTSD subjects from controls (P < .05). Examination of negative findings revealed that all three groups similarly deviated from Exner nonpatient norms (Exner, 1993: The Rorschach, Vol 1. New York: John Wiley and Sons) on many Rorschach variables. Possible explanations for these findings are considered, and the need for control subjects in Rorschach investigation is underscored.

Adult↗
PubMed1988

The right cerebral hemisphere: emotion, music, visual-spatial skills, body-image, dreams, and awareness.

Based on a review of numerous studies conducted on normal, neurosurgical and brain-injured individuals, the right cerebral hemisphere appears to be dominant in the perception and identification of environmental and nonverbal sounds; the analysis of geometric and visual space (e.g., depth perception, visual closure); somesthesis, stereognosis, the maintenance of the body image; the production of dreams during REM sleep; the perception of most aspects of musical stimuli; and the comprehension and expression of prosodic, melodic, visual, facial, and verbal emotion. When the right hemisphere is damaged a variety of cognitive abnormalities may result, including hemi-inattention and neglect, prosopagnosia, constructional apraxia, visual-perceptual disturbances, and agnosia for environmental, musical, and emotional sounds. Similarly, a myriad of affective abnormalities may occur, including indifference, depression, hysteria, gross social-emotional disinhibition, florid manic excitement, childishness, euphoria, impulsivity, and abnormal sexual behavior. Patients may become delusional, engage in the production of bizzare confabulations and experience a host of somatic disturbances such as pain and body-perceptual distortions. Based on studies of normal and "split-brain" functioning, it also appears that the right hemisphere maintains a highly developed social-emotional mental system and can independently perceive, recall and act on certain memories and experiences without the aid or active reflective participation of the left. This leads to situations in which the right and left halves of the brain sometime act in an uncooperative fashion, which gives rise to inter-manual and intra-psychic conflicts.

Aphasia↗
PubMed1984

Somatosensory cortical map changes following digit amputation in adult monkeys.

The cortical representations of the hand in area 3b in adult owl monkeys were defined with use of microelectrode mapping techniques 2-8 months after surgical amputation of digit 3, or of both digits 2 and 3. Digital nerves were tied to prevent their regeneration within the amputation stump. Successive maps were derived in several monkeys to determine the nature of changes in map organization in the same individuals over time. In all monkeys studied, the representations of adjacent digits and palmar surfaces expanded topographically to occupy most or all of the cortical territories formerly representing the amputated digit(s). With the expansion of the representations of these surrounding skin surfaces (1) there were severalfold increases in their magnification and (2) roughly corresponding decreases in receptive field areas. Thus, with increases in magnification, surrounding skin surfaces were represented in correspondingly finer grain, implying that the rule relating receptive field overlap to separation in distance across the cortex (see Sur et al., '80) was dynamically maintained as receptive fields progressively decreased in size. These studies also revealed that: the discontinuities between the representations of the digits underwent significant translocations (usually by hundreds of microns) after amputation, and sharp new discontinuous boundaries formed where usually separated, expanded digital representations (e.g., of digits 1 and 4) approached each other in the reorganizing map, implying that these map discontinuities are normally dynamically maintained. Changes in receptive field sizes with expansion of representations of surrounding skin surfaces into the deprived cortical zone had a spatial distribution and time course similar to changes in sensory acuity on the stumps of human amputees. This suggests that experience-dependent map changes result in changes in sensory capabilities. The major topographic changes were limited to a cortical zone 500-700 micron on either side of the initial boundaries of the representation of the amputated digits. More distant regions did not appear to reorganize (i.e., were not occupied by inputs from surrounding skin surfaces) even many months after amputation. The representations of some skin surfaces moved in entirety to locations within the former territories of representation of amputated digits in every monkey studied. In man, no mislocation errors or perceptual distortions result from stimulation of surfaces surrounding a digital amputation.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗