Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Perceptual Distortion”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 163 records · Page 9Linked to original sources
PubMed2005

Kappa opioid receptor activation disrupts prepulse inhibition of the acoustic startle in rats.

BACKGROUND: Compelling evidence indicates that kappa opioid receptor (KOR) agonists produce perceptual distortions in animals and humans, yet the mechanism of action and clinical relevance of such effects remain unclear. Since abnormalities in preattentional functions and informational processing are hypothesized to underlie psychotic disorders, the present study has been designed to assess the role of KOR on sensorimotor gating. METHODS: The effects of the selective KOR agonist U50488 were evaluated on the behavioral paradigm of prepulse inhibition (PPI) of the acoustic startle reflex (ASR). RESULTS: U50488 (1.25, 2.5, and 5 mg/kg, subcutaneous [SC]) induced a dose-dependent reduction of PPI, which was efficiently prevented by the selective KOR antagonist norbinaltorphimine (nor-BNI, 10 mg/kg, SC), as well as by the atypical antipsychotic clozapine (5, 8 mg/kg, intraperitoneal [IP]) but not by the typical antipsychotic haloperidol (.1, .5 mg/kg, IP). Conversely, nor-BNI (10 mg/kg, SC) failed to reverse the PPI disruption mediated by both apomorphine (.25 mg/kg, SC) and dizocilpine (.1 mg/kg, SC). CONCLUSIONS: Our results support a pivotal role of KOR in the regulation of preattentional functions and sensorimotor gating, pointing to these receptors as a possible neurobiological substrate especially relevant to the clusters of psychosis unresponsive to typical antipsychotics.

3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cycloh↗
PubMed2005

Human EEG gamma oscillations in neuropsychiatric disorders.

Due to their small amplitude, the importance of high-frequency EEG oscillations with respect to cognitive functions and disorders is often underestimated as compared to slower oscillations. This article reviews the literature on the alterations of gamma oscillations (about 30-80 Hz) during the course of neuropsychiatric disorders and relates them to a model for the functional role of these oscillations for memory matching. The synchronous firing of neurons in the gamma-band has been proposed to bind multiple features of an object, which are coded in a distributed manner in the brain, and is modulated by cognitive processes such as attention and memory. In certain neuropsychiatric disorders the gamma activity shows significant changes. In schizophrenic patients, negative symptoms correlate with a decrease of gamma responses, whereas a significant increase in gamma amplitudes is observed during positive symptoms such as hallucinations. A reduction is also observed in Alzheimer's Disease (AD), whereas an increase is found in epileptic patients, probably reflecting both cortical excitation and perceptual distortions such as déjà vu phenomena frequently observed in epilepsy. ADHD patients also exhibit increased gamma amplitudes. A hypothesis of a gamma axis of these disorders mainly based on the significance of gamma oscillations for memory matching is formulated.

Alzheimer Disease↗
PubMed2005

The effect of perceived spatial separation on informational masking of Chinese speech.

The effect of perceived spatial separation, induced by the precedence effect, on release from noise or speech masking was investigated. Listeners were asked to orally repeat Chinese nonsense sentences, which were spoken by a female talker and presented by both the left (-45 degrees) and right (+45 degrees) loudspeakers, when maskers, which were either speech-spectrum noise sounds or Chinese nonsense sentences spoken by two other female talkers, were presented by the same two loudspeakers. Delays between identical sounds presented over the two loudspeakers were used to control the perceived locations of the target (right only) and masker (right, center, or left). The results show that perceived 45 degrees and 90 degrees separations of target speech from masking speech led to equivalently marked improvement in speech recognition, even though the degree of improvement was smaller than that reported in [J. Acoust. Soc. Am. 106 (1999) 3578 (using English nonsense speech)]. When the masker was noise, however, perceived separation only marginally improved speech recognition. These results indicate that release from informational masking, due to perceived target/masker spatial separation induced by the precedence effect, also occurs for tonal Chinese speech. Compared to the 45 degrees perceived within-hemifield separation, the 90 degrees perceived cross-hemifield separation does not produce further unmasking.

Acoustic Stimulation↗
PubMed1998

Effects of ketamine on thought disorder, working memory, and semantic memory in healthy volunteers.

BACKGROUND: The N-methyl-D-aspartate receptor antagonist, ketamine, produces a clinical syndrome of thought disorder, perceptual distortion, and cognitive impairment. METHODS: We have administered ketamine to healthy volunteers to characterize the formal thought disorder and specific memory dysfunction associated with ketamine. Ten healthy volunteers underwent a double-blind, placebo-controlled, ketamine infusion (0.12 mg/kg bolus and 0.65 mg/kg/hour). Thought disorder was evaluated with the Scale for the Assessment of Thought, Language and Communication. Cognitive testing involved working and semantic memory tasks. RESULTS: Ketamine produced a formal thought disorder, as well as impairments in working and semantic memory. The degree of ketamine-induced thought disorder significantly correlated with ketamine-induced decreases in working memory and did not correlate with ketamine-induced impairments in semantic memory. CONCLUSIONS: This study characterizes the formal thought disorder associated with ketamine and may suggest that ketamine-induced deficits in working memory are associated with ketamine-induced thought disorder.

Adult↗
PubMed1999

Schizotypal personality disorder and MRI abnormalities of temporal lobe gray matter.

BACKGROUND: Structural MRI data indicate schizophrenics have reduced left-sided temporal lobe gray matter volumes, especially in the superior temporal gyrus (STG) and medial temporal lobe. Our data further suggest a specificity to schizophrenia spectrum disorders of STG volume reduction. Interpretation of research studies involving schizophrenics may be complicated by the effects of exposure to neuroleptics and chronic illness. Sharing the same genetic diathesis of schizophrenics, subjects with schizotypal personality disorder (SPD) offer a unique opportunity to evaluate commonalities between schizophrenia and SPD, particularly as SPD subjects are characterized by cognitive and perceptual distortions, an inability to tolerate close friendships, and odd behavior, but they are not psychotic and so have generally not been prescribed neuroleptics nor hospitalized. Evaluation of brain structure in SPD may thus offer insight into the "endophenotype" common to both disorders. In addition, differences between groups may suggest which are the brain structures of schizophrenics that contribute to the development of psychosis. METHODS: To test the hypothesis of whether SPD subjects might show similar STG abnormalities, STG and medial temporal lobe regions of interest (ROI) were manually drawn on high resolution coronal MRI 1.5 mm thick slices. Images were derived from 16 right-handed male SPD subjects, without regard to family history, and 14 healthy, right-handed, comparison males who did not differ from the SPD group on parental socio-economic status, age, or verbal IQ. RESULTS: As predicted, SPD subjects showed a reduction in left STG gray matter volume compared with age and gender matched comparison subjects. SPD subjects also showed reduced parahippocampal left/right asymmetry and a high degree of disordered thinking. Comparisons with chronic schizophrenics previously studied by us showed the SPD group had a similarity of left STG gray matter volume reduction, but fewer medial temporal lobe abnormalities. CONCLUSIONS: These abnormalities strengthen the hypothesis of a temporal lobe abnormality in SPD, and the similarity of STG findings in schizophrenia and SPD suggest that STG abnormalities may be part of the spectrum "endophenotype." It is also possible that presence of medial temporal lobe abnormalities may help to differentiate who will develop schizophrenia and who will develop the less severe schizophrenia spectrum disorder, SPD.

Adult↗
PubMed1994

The failure of context shifts to alter the recognition of faces: implications for contextual deficits in amnesia.

The effects of contextual changes were examined in a group of divers performing a test of face recognition. No evidence was found that the shift from above to below water, or vice versa, disrupted recognition. The fact that the same test of visual recognition is sensitive to amnesic subjects poses a challenge to certain versions of the contextual deficit theory of amnesia.

Adult↗
PubMed1985

Familiarity, spatial frequency and task determinants in processing laterally presented representations of faces.

Laterally presented portraits were judged as familiar or unfamiliar (Experiments 1 and 2), or were processed in a target matching task (Experiment 3). Exposure durations (100 or 190 msec.) were varied between (Experiments 1 and 2) or within (Experiment 3) the experiments. Clear and degraded faces appeared either randomly intermingled (Experiment 1) or in blocked sequences (Experiments 2 and 3). In Experiment 3 familiar and unfamiliar stimuli also appeared in blocks. Stimulus degradation was achieved by coarse quantization of the image into blocks, so replacing relevant high-spatial-frequencies (the features) by spurious information, preserving only the original lower-spatial-frequency components. Left hemisphere mediation was strongest and most consistent with long exposures and random sequences of clear and degraded stimuli. Right hemisphere mediation tended to appear with shorter exposures and degraded stimuli presented in blocks. Though the interactions were often complex, the general pattern of results was consistent with the analytic-holistic processing dichotomy.

Discrimination Learning↗
PubMed1999

More thoughts on perceiving and grasping the Müller-Lyer illusion.

It has been suggested that the insensitivity of the visuomotor system to various visual illusions is based on mechanisms in the so-called 'dorsal stream' of primate extrastriate cortex, which may depend upon binocular cues for their functions. The present study investigated the effects of binocular and monocular viewing on perception of and action to Müller-Lyer figures. Fourteen participants were required to match and grasp the shaft of a Müller-Lyer display under both viewing conditions. In the matching condition, participants were required to show the perceived extent of the central shaft of one of the two Müller-Lyer figures, using the extent of the gap between their finger and thumb. In the grasping task, participants were required to quickly and accurately reach out and grasp the central shaft of the specified Müller-Lyer figure. First, there was a striking effect of the illusion on the matching performance under both viewing conditions. However, the maximum grip aperture remained unaffected by the illusion figures. These results add to the theory of distinct modes of visual processing for perception and action. However, we did not find that grasping performance was affected by the illusion under monocular conditions. It is plausible that monocular depth cues distinct from those responsible for the illusion can successfully drive accurate grasping. Additional concerns regarding claims of action system resistance to the perceptual distortions of various illusions are discussed.

Adult↗
PubMed2001

Changes in visual perception at the time of saccades.

We frequently reposition our gaze by making rapid ballistic eye movements that are called saccades. Saccades pose problems for the visual system, because they generate rapid, large-field motion on the retina and change the relationship between the object position in external space and the image position on the retina. The brain must ignore the one and compensate for the other. Much progress has been made in recent years in understanding the effects of saccades on visual function and elucidating the mechanisms responsible for them. Evidence suggests that saccades trigger two distinct neural processes: (1) a suppression of visual sensitivity, specific to the magnocellular pathway, that dampens the sensation of motion and (2) a gross perceptual distortion of visual space in anticipation of the repositioning of gaze. Neurophysiological findings from several laboratories are beginning to identify the neural substrates involved in these effects.

Animals↗
PubMed2004

Perisaccadic mislocalization orthogonal to saccade direction.

Saccadic eye movements transiently distort perceptual space. Visual objects flashed shortly before or during a saccade are mislocalized along the saccade direction, resembling a compression of space around the saccade target. These mislocalizations reflect transient errors of processes that construct spatial stability across eye movements. They may arise from errors of reference signals associated with saccade direction and amplitude or from visual or visuomotor remapping processes focused on the saccade target's position. The second case would predict apparent position shifts toward the target also in directions orthogonal to the saccade. We report that such orthogonal mislocalization indeed occurs. Surprisingly, however, the orthogonal mislocalization is restricted to only part of the visual field. This part comprises distant positions in saccade direction but does not depend on the target's position. Our findings can be explained by a combination of directional and positional reference signals that varies in time course across the visual field.

Adult↗
PubMed2003

[Effects of a subanaesthetic dose of ketamine on emotional and behavioral state in healthy subjects].

Schizophrenic patients suffer from positive (delusions, hallucinations) and negative signs (social withdrawal) as well as emotional disturbance that included quantitative (blunted affect) and qualitative impairments (discordance of emotional level). Ketamine, a phencyclidine derivative, is a non competitive N-methyl-D-aspartate (NMDA) glutamate receptor antagonist. In healthy subjects its administration induces some positive symptoms (perceptual distortions.), negative symptoms (emotional deficit, apathy, social withdrawal) and cognitive changes (memory impairments and perseverations) that resemble some aspects of the symptoms of schizophrenia. A double blind cross over, placebo controlled was performed in 12 normal subjects with 2 sessions separated by one week of wash-out to determine ketamine-induced effects on behavioral and emotional responses. During each session, subjects received either ketamine or placebo (saline) infusion. A subanesthetic dose of ketamine (0,5 mg/kg) was administered by constant perfusion over 60 min. Behavioral and cognitive responses were assessed using positive and negative symptoms scales (BPRS, items from SAPS and SANS), vigilance and mood visual analog scale, subjective feelings using the Addiction Research Center Inventory (ARCI) and the Profile of Mood States (POMS). Using Philippot's method, emotions were elicited by films segments which induce a diversity of predictable emotions (fear, anger, sadness, joy, disgust and neutral state) and emotional responses were assessed by the Differential Emotions Scale (DES Izard). Low dose of ketamine induced significant effects on 7-items BPRS score (positive and negative items) and significant effects on positive and negative symptoms from SANS and SAPS. This was associated with emotional blunting of visually-induced responses that resemble aspects of schizophrenic emotional impairments. Ketamine impaired ARCI subscales (benzedrine subscale, pentobarbital-chlorpromazine subscale and LSD subscale). The recent findings of ketamine's pharmacology and imaging studies allow to draw several hypothesis related to neurotransmitter systems (glutamate, dopamine, serotonin interactions) and cerebral areas (particularly prefrontal cortex, anterior cingulate cortex, hippocampus) underlying some of these ketamine-induced effects.

Adult↗
PubMed2004

The man behind the mask: accuracy and predictors of eyewitness offender descriptions.

An archival study was conducted using 250 offender descriptions by witnesses of armed bank robberies. The accuracy of the descriptions was gauged against authentic video documentation of the witnessed crimes. In general, witnesses provided accurate descriptions of the offenders but reported few identifying details. Multiple regression analyses revealed that the witnesses' role (bank tellers vs. customers), the type of weapon used, and the number of perpetrators involved were moderately predictive of the quality of offender descriptions. However, several of the observed relationships were conditional on whether descriptions of basic attributes (e.g., height, age, build) or more detailed features were considered. Hence, the authors concluded that verifying all aspects of witness descriptions is crucial when studying memories for actual crimes.

Adolescent↗
PubMed1990

A model of character recognition and legibility.

This article presents a model of character recognition and the experiments used to develop and test it. The model applies to foveal viewing of blurred or unblurred characters and to tactile sensing of raised characters using the fingerpad. The primary goal of the model is to account for variations in legibility across character sets; a secondary goal is to account for variations in the cell entries of the confusion matrix for a given character set. The model consists of two distinct processing stages. The first involves transformation of each stimulus into an internal representation; this transformation consists of linear low-pass spatial filtering followed by nonlinear compression of stimulus intensity. The second stage involves both template matching of the transformed test stimulus with each of the stored internal representations of the characters within the set and response selection, which is assumed to conform to the unbiased choice model of Luce (1963). Though purely stimulus driven, the model accounts quite well for differences in the legibility of character sets differing in character type, size of character, and number of characters within the set; it is somewhat less successful in accounting for the details of each confusion matrix.

Adult↗
PubMed2006

Enhanced discrimination between flavor stimuli: roles of salience modulation and inhibition.

Rats were given intermixed preexposure to the compound flavors AX and BX and to the compound CX in a separate block of trials (4 presentations of each compound). In Experiment 1, rats showed less generalization of conditioned aversion from AX to BX than from CX to BX, a perceptual learning effect. Experiment 2 showed that the formation of an excitatory association proceeded more readily between A and B than between C and B, suggesting that intermixed preexposure maintains the effective salience of A and B and does not establish inhibition between them, a process that would require prolonged preexposure. According to this analysis, salience modulation and associative inhibition may contribute to perceptual learning at different stages of preexposure.

Animals↗
PubMed2006

Inhibitory associations contribute to perceptual learning in humans.

Perceptual learning in humans was examined in 2 experiments. In Experiment 1, participants received intermixed exposure to 2 similar compounds (AX, BX, AX, BX, . . .) and blocked exposure to a 2nd pair of similar compounds (CY, CY, . . . , DY, DY, . . .). Aversions established to AX and CY generalized less to BX than to DY. In Experiment 2, 1 pair of compounds was presented in a forward order (i.e., AX3BX), whereas the 2nd pair of compounds was presented in a backward order (i.e., DY-->CY). Aversions established to AX and CY generalized less to BX than to DY. These results indicate that inhibitory associations contribute to perceptual learning in humans and thereby establish a fundamental similarity between the mechanisms that underlie perceptual learning in humans and rats.

Adolescent↗