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PubMed2002

[Visual perception of Kanji characters and complicated figures. II. Visual P300 event-related potentials in patients with mental retardation].

In order to objectively evaluate visual perception of patients with mental retardation (MR), the P300 event-related potentials (ERPs) for visual oddball tasks were recorded in 26 patients and 13 age-matched healthy volunteers. The latency and amplitude of visual P300 in response to the Japanese ideogram stimuli (a pair of familiar Kanji characters or unfamiliar Kanji characters) and a pair of meaningless complicated figures were measured. In almost all MR patients visual P300 was observed, however, the peak latency was significantly prolonged compared to control subjects. There was no significant difference of P300 latency among the three tasks. The distribution pattern of P300 in MR patients was different from that in the controls and the amplitudes in the frontal region was larger in MR patients. The latency decreased with age even in both groups. The developmental change of P300 latency corresponded to developmental age rather than the chronological age. These findings suggest that MR patients have impairment in processing of visual perception. Assessment of P300 latencies to the visual stimuli may be useful as an objective indicator of mental deficit.

Adolescent↗
PubMed1999

Is vision continuous with cognition? The case for cognitive impenetrability of visual perception.

Although the study of visual perception has made more progress in the past 40 years than any other area of cognitive science, there remain major disagreements as to how closely vision is tied to cognition. This target article sets out some of the arguments for both sides (arguments from computer vision, neuroscience, psychophysics, perceptual learning, and other areas of vision science) and defends the position that an important part of visual perception, corresponding to what some people have called early vision, is prohibited from accessing relevant expectations, knowledge, and utilities in determining the function it computes--in other words, it is cognitively impenetrable. That part of vision is complex and involves top-down interactions that are internal to the early vision system. Its function is to provide a structured representation of the 3-D surfaces of objects sufficient to serve as an index into memory, with somewhat different outputs being made available to other systems such as those dealing with motor control. The paper also addresses certain conceptual and methodological issues raised by this claim, such as whether signal detection theory and event-related potentials can be used to assess cognitive penetration of vision. A distinction is made among several stages in visual processing, including, in addition to the inflexible early-vision stage, a pre-perceptual attention-allocation stage and a post-perceptual evaluation, selection, and inference stage, which accesses long-term memory. These two stages provide the primary ways in which cognition can affect the outcome of visual perception. The paper discusses arguments from computer vision and psychology showing that vision is "intelligent" and involves elements of "problem solving." The cases of apparently intelligent interpretation sometimes cited in support of this claim do not show cognitive penetration; rather, they show that certain natural constraints on interpretation, concerned primarily with optical and geometrical properties of the world, have been compiled into the visual system. The paper also examines a number of examples where instructions and "hints" are alleged to affect what is seen. In each case it is concluded that the evidence is more readily assimilated to the view that when cognitive effects are found, they have a locus outside early vision, in such processes as the allocation of focal attention and the identification of the stimulus.

Agnosia↗
PubMed1983

Individual variation in directional bias in visual perception.

Directional biases in visual perception were examined for individual differences in sixty-five subjects on two tasks. One task required judgments of the onset asynchrony of pairs of dots presented at random, either one dot in each visual field, or both in the left visual field (LVF), or the right visual field (RVF). The second task required the recall of four letter strings presented randomly in either visual field. Dot-asynchrony judgments were influenced by two main biases: first, an outward from the centre bias in both visual fields, and second, a lateral bias which was significantly from left to right (L-R) in the total sample. A substantial minority of subjects were biased to judge the dots as occurring in right to left (R-L) order. Accuracy of letter report decreased fairly consistently from L-R in the RVF but varied in the LVF. Some subjects showed a L-R report gradient, some a R-L gradient, and some a U-shaped recall pattern. Significant correlations between measures of L-R and R-L biases on the two tasks show that the biases have some stable foundation. The findings suggest that there are directional biases affecting visual perception which are due neither to learned reading habits, nor to cerebral specialization of function.

Female↗
PubMed1999

Comparing visual perception on conventional cabinet tachistoscopes and computer monitor tachistoscopes.

Computer monitor-based tachistoscopes (using a cathode ray tube, CRT) and conventional tachistoscopes differ in experimental control over stimulus continuity, duration, and timing accuracy. This study evaluated the perception of visual stimuli presented with the two different types of devices. An experiment was conducted to compare recognition of visuospatial stimuli (random shapes) presented laterally and centrally in the visual fields for short exposure durations (14, 29, and 43 msec), first with one device and then with another. Results indicated that the subjects' error rates and laterality patterns were similar on both types of tachistoscopes. It was concluded that perception of visual stimuli presented as continuous images on a conventional tachistoscope may be equivalent to perception of visual stimuli presented as pulsating images on a CRT. Further studies are needed using other types of visual materials to determine the range of visual stimuli for which both types of tachistoscopes measure equivalent perceptual processes.

Adolescent↗
PubMed1976

Physiological aspects of visual perception. II. The subcortical visual direction of behavior.

The second part of the Bennett Lecture for 1975 by Denny-Brown examined the subcortical representation of the dissociation of function described by Denny-Brown and Chambers. Complete removal in the macaque monkey of the corticomesencephalic fibers where they pass from pulvinar to colliculus, and of the colliculus, resulted in the same loss of visual object identification, binocular fixation, and visuosocial behavior that followed removal of area 17. Vision for peripheral movement and spatial orientation ("panoramic vision") remained excellent, with release of catatonia. Conversely, unilateral electrolytic lesions of the mesencephalic tegmentum produced visuospatial distortion, asymmetry of optic righting, and directional difficulties in eye movement (Parinaud syndrome and skew deviation). When bilateral, tegmental lesions produced great constriction of visual field with release of convergence and fixation spasm. Suppression of peripheral attention resulted from perceptual rivalry.

Animals↗
PubMed2005

Strength of visual percept generated by famous faces perceived without awareness: effects of affective valence, response latency, and visual field.

Participants who were unable to detect familiarity from masked 17 ms faces (Stone and Valentine, 2004 and Stone and Valentine, in press-b) did report a vague, partial visual percept. Two experiments investigated the relative strength of the visual percept generated by famous and unfamiliar faces, using masked 17 ms exposure. Each trial presented simultaneously a famous and an unfamiliar face, one face in LVF and the other in RVF. In one task, participants responded according to which of the faces generated the stronger visual percept, and in the other task, they attempted an explicit familiarity decision. The relative strength of the visual percept of the famous face compared to the unfamiliar face was moderated by response latency and participants' attitude towards the famous person. There was also an interaction of visual field with response latency, suggesting that the right hemisphere can generate a visual percept differentiating famous from unfamiliar faces more rapidly than the left hemisphere. Participants were at chance in the explicit familiarity decision, confirming the absence of awareness of facial familiarity.

Adult↗
PubMed2004

[Visual perception of Kanji characters and complicated figures. Part 3. Visual P300 event-related potentials in patients with attention deficit/hyperactivity disorders].

In order to evaluate visual perception, the P300 event-related potentials (ERPs) for visual oddball tasks were recorded in 11 patients with attention deficit/hyperactivity disorders (AD/HD), 12 with mental retardation (MR) and 14 age-matched healthy controls. With the aim of revealing trial-to-trial variabilities which are neglected by investigating averaged ERPs, single sweep P300s (ss-P300s) were assessed in addition to averaged P300. There were no significant differences of averaged P300 latency and amplitude between controls and AD/HD patients. AD/HD patients showed an increased variability in the amplitude of ss-P300s, while MR patient showed an increased variability in latency. These findings suggest that in AD/HD patients general attention is impaired to a larger extent than selective attention and visual perception.

Attention↗
PubMed2003

Zolpidem-induced distortion in visual perception.

OBJECTIVE: To describe a patient who developed visual perception distortion after a single dose of zolpidem. CASE SUMMARY: A 50-year-old Asian woman had been prescribed conjugated estrogen 1 tablet daily for hormone replacement therapy and tricalcium phosphate twice daily for osteoporosis. One day, she took zolpidem 10 mg for insomnia as well as acetaminophen 500 mg for headache at bedtime and began to have visual perception distortion (e.g., the shapes of objects were twisted, houses were crooked) within 20 minutes, lasting for approximately 30 minutes, and then her vision returned to normal. She only partially recalled the event. She had never taken zolpidem before, and she had not had any such disturbances in the past. DISCUSSION: There have been 21 case reports of zolpidem-related psychotic symptoms in the literature; however, the exact mechanism by which zolpidem may cause visual perception changes is undetermined. Many factors have been correlated with zolpidem-induced visual experiences, such as pharmacokinetic factors, gender, age, and hypoalbuminemia. This patient shared certain similarities such as gender, dosage, and time of onset and duration of adverse reactions. CONCLUSIONS: An objective causality assessment revealed that the zolpidem-induced visual perception distortion in this patient was probable. Clinicians should be aware of the potential for visual perception distortion, as this is an uncommon adverse effect.

Female↗
PubMed1988

Naso-temporal asymmetry of visual perception and of the visual cortex.

The decrease of visual performance from the fovea towards the periphery depends upon the task tested. The slope of the decrease is generally steeper for hyperacuity than for spatial resolution and is steeper in the nasal than in the temporal hemifield. The naso-temporal asymmetry in the periphery of the visual field, beyond 20 deg eccentricity, is much more pronounced for hyperacuity than for spatial resolution. The psychophysical results show a close correlation to the cortical organization as revealed by autoradiography.

Adult↗
PubMed1984

Visual perception in hemiplegic patients.

Visual perceptual disturbances have been identified as a complication associated with hemiplegic syndrome that can interfere with rehabilitation progress. In this study a test battery was developed to identify visual perceptual disturbances in stroke patients. Forty-six patients (mean age 49.9 years) were first categorized according to the severity and complexity of their various impairments. This classification revealed a previously unremarked high proportion of patients who had sensorimotor disorders of the nonparetic hand and arm. Patients were subsequently tested for visual perceptual disorders, which were detected in 25 of the 46 patients. No correlations were found between the presence of these disorders and the factors of age, time since cerebrovascular accident, aphasia, and severity of the syndrome. However, significant correlations (p less than 0.01) were revealed between visual perceptual scores and disturbances in function of the nonparetic hand. The nature of the tests used to identify visual perceptual problems meant that this relationship could not be attributed to motor deficits. Possible explanations linked visual and motor systems. Left-side paretic patients performed significantly worse than right-side patients on visual perception tests, which is in accordance with earlier studies. This result was interpreted in terms of hemispheric dominance for specific functions.

Adolescent↗
PubMed2004

Prediction of visual perceptions with artificial neural networks in a visual prosthesis for the blind.

Within the framework of the OPTIVIP project, an optic nerve based visual prosthesis is developed in order to restore partial vision to the blind. One of the main challenges is to understand, decode and model the physiological process linking the stimulating parameters to the visual sensations produced in the visual field of a blind volunteer. We propose to use adaptive neural techniques. Two prediction models are investigated. The first one is a grey-box model exploiting the neurophysiological knowledge available up to now. It combines a neurophysiological model with artificial neural networks, such as multi-layer perceptrons and radial basis function networks, in order to predict the features of the visual perceptions. The second model is entirely of the black-box type. We show that both models provide satisfactory prediction tools and achieve similar prediction accuracies. Moreover, we demonstrate that significant improvement (25%) was gained with respect to linear statistical methods, suggesting that the biological process is strongly non-linear.

Blindness↗
PubMedDate not supplied

[Comparative characterization of changes in visual perception after ketamine and brietal anesthesia in children].

Visual perception is disordered in children aged 10-15 years subjected to surgery under ketamine and brietal anesthesia in an outpatient setting. Psychological testing was carried out during 24 h after intervention. Results of the Rorschach's test indicate that ketamine impairs the quality of visual perception (inadequate evaluation of the size, shape, velocity, etc.). Brietal disorders mainly the integrity of visual image. Visual perception did not normalize 24 h after both anesthesias. Disorders typical of each drug persisted.

Adolescent↗
PubMed1990

[Disturbances of visual perception and the lesions on spastic diplegia].

In a study of 12 cerebral palsy with spastic diplegia, the relationship between their disturbances of visual perception and their lesions was discussed. All of them were performed Frostig Developmental Test of Visual perception and Tanaka-Binet Intelligence Test. Six of them showed disturbances of visual perception on Frostig Test. Subtest II, figure-ground, was the lowest of all subtests. The mean of perceptual quotient was under that of intelligence quotient significantly (p less than 0.05 t-test). MRI examination was performed to all and the lesions were detected at 10 of them. Six who showed disturbances of visual perception had the lesions and two who showed good visual perception had no lesions. The lesions were periventricular white matter and extended to semioval center and subcortical white matter at parietal and occipital lobes. Anatomically, their lesions correspond to superior longitudinal bundle and vertical occipital bundle and their bundles have important functions as the pass way of visual perception. Therefore, it was suggested that the disturbances of visual perception detected at spastic diplegia were based on the lesions and the mechanism was disconnection of higher visual pass way.

Brain↗
PubMed1982

Drugs and visual perception: effects of LSD, morphine and chloropromazine on accuracy, bias and speed.

Ten pigeons were trained to discriminate between the intensities of two white lights (projected behind a center response "key") using a discrete trial procedure in which choice behavior involved pecking at red or green lights projected behind left or right side keys. LSD (0.02-0.08 mg/kg) did not alter the accuracy of the brightness discrimination (percent correct) although it did lower response speed and may have differentially affected spatial (position) bias. Morphine (2.5--10.0 mg/kg) decreased accuracy of discrimination as well as response speed and had greater effects on trials when the bright stimulus was presented than when the dim stimulus was presented. Chlorpromazine (7.5-3.0 mg/kg) lowered accuracy without significantly altering any other measure of performance.

Animals↗