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PubMed2003

Visuospatial processing and the right-hemisphere interpreter.

Popular views of hemispheric asymmetry hold that the left hemisphere is specialized for linguistic and cognitive processes and fine motor control, whereas the right is specialized for visuospatial processing. Although this dichotomy contains more than a grain of truth, it is an oversimplification. Experiments with split-brain patients have demonstrated that the left hemisphere retains relatively sophisticated visuospatial abilities, and that the asymmetries that favor the right hemisphere are subtler than those that favor the left. A consideration of the constructive nature of visual perception, and the organization of the visual system in the two hemispheres suggests that asymmetries are likely to arise relatively late in visual processing in areas that represent both sides of visual space. I present evidence in favor of the view that the right hemisphere can be considered more "visually intelligent" than the left, and postulate the existence of a "right-hemisphere interpreter" dedicated to constructing a representation of the visual world.

Brain↗
PubMed1962

Visual depth perception of a 10-month-old monocular human infant.

A monocular infant tested on the "visual cliff" crawled over glass which had a patterned surface just beneath it and would not cross glass which had the same pattern 40 inches below its surface. Since this infant, using only monocular visual cues, was able to discriminate depth, the experiment disproves a general belief in the primacy of binocular cues in depth perception.

Child↗
PubMed2005

Theory of mind and motion perception in schizophrenia.

This study investigated the relationship between theory of mind (ToM) deficits and visual perception in patients with schizophrenia (N=52; 17 remitted and unmedicated) compared with healthy controls (N=30). ToM was assessed with the Eyes Test, which asked participants to choose which of 4 words best described the mental state of a person whose eyes were depicted in a photograph. Visual perception was evaluated with form and motion coherence threshold measurements. Results revealed that patients with schizophrenia (both remitted and nonremitted) showed deficits on the Eyes Test and the motion coherence task. ToM dysfunctions were associated with higher motion coherence thresholds and more severe negative symptoms. This suggests that ToM deficits are related to motion perception dysfunctions, which indicates a possible role of motion-sensitive areas in the pathophysiology of schizophrenia.

Adult↗
PubMed1987

Perceptual "blankout" of monocular homogeneous fields (Ganzfelder) is prevented with binocular viewing.

The loss of visual perception or "blankout" which occurs when a homogeneous field (Ganzfeld) is presented monocularly is prevented when the same field is viewed binocularly. Thus, blankout cannot be retinal; and contours or transients in time and space are unnecessary for the continuous maintenance of visual perception. Experiments are reported in which blankout ensues only if the two eyes receive luminance disparities ca 0.75 log I. Furthermore, blankout is only marginally affected by stimulus intensity, nor is it dependent on stimulus hue. However, equally luminant but disparate hues presented to the two eyes produce perceptions reminiscent of blankout, with the darkness of blankout replaced with that of color. It is hypothesized that the underlying mechanisms have a commonality in the phenomena of blankout and binocular rivalry but several noncongruent features require explanation.

Depth Perception↗
PubMed1989

Emergent features, attention, and perceptual glue in visual form perception.

We examined the grouping of line segments into unitary shapes and attempted to identify procedures to diagnose when such grouping is taking place. Previous research has indicated that attentional measures may diagnose grouping: With grouped parts, selective attention to individual parts is difficult and divided attention across parts is easy, whereas with ungrouped parts selective attention is easy and divided attention is difficult. This result suggests that grouping operates via a perceptual glue binding parts into wholes that are difficult or impossible to divide. Other studies have suggested in addition that grouped parts produce emergent features, possibly including symmetry and closure, that make possible configural superiority effects, where whole shapes are more discriminable than are their distinguishing contours shown in isolation. The 13 experiments reported here indicate that perceptual glue is not needed to explain known findings about grouping, a claim that agrees with conclusions by other investigators using other criteria. Rather, emergent features alone may suffice to explain grouping, provided that reliable and accurate diagnostic criteria can be identified. It is shown that the diagnostics now available are not fully adequate for this purpose. Surprisingly, it appears that some prime candidates for emergent features--namely, closure and line terminators--may not be of central importance to form perception.

Adult↗
PubMed2005

Role of the superior temporal region in human visual motion perception.

While moving objects are usually seen using luminance (first-order) cues, humans can perceive the motion of objects via non-luminance (second-order) cues. Contrary to previous case reports, no physiological studies have elucidated distinct differences in the cortical regions involved in first- and second-order motion processes. We investigated brain responses related to these two types of motion perception in human subjects using 3 T functional magnetic resonance imaging and strictly controlled apparent motion stimulus pairs. Comparison of brain activation to moving versus static states of each motion stimulus isolated cortical activity related to each type of motion perception. We found a selective neural response to second-order motion stimulus in the anterior part of the superior temporal sulcus (STS) contralateral to stimulus presentation and cue-invariant activation of MT/V5+. No significant activation in the STS was observed by the first-order motion, even when its visibility was reduced to levels comparable to that of second-order motion. Furthermore, the STS demonstrated significant activation for highly visible motion stimulus with both first- and second-order attributes. The STS represents the cardinal structure for perception of second-order motions, although further studies are needed to elucidate the exact neural process occurring in this area.

Adult↗
PubMed1997

The neural generation of a unified illusion in human vision.

The neural mechanisms of visual binding in humans were investigated by measuring the brain's high-frequency electric responses (36-44 Hz) to the subjective visual perception of a unified three-dimensional illusion. 40 Hz synchronization was found over occipital and right parieto-temporal areas 500-300 ms before visual awareness of the three-dimensional Gestalt was reported, but not during the viewing of the illusion. At lower frequency bands (8-13 Hz and 13-20 Hz) no corresponding synchronization was found. 40 Hz synchronization thus directly correlates with the construction and emergence of a unified visual percept and may reflect the rapid formation of transient functional connections between spatially separated cortical areas.

Adult↗
PubMed2002

Visual motion stimulation, but not visually induced perception of self-motion, biases the perceived direction of verticality.

Large-field torsional optokinetic stimulation is known to affect the perceived direction of gravity with verticality judgements deviating towards the direction of visual stimulus rotation. The present study aimed to replicate this effect and to examine it further by subjecting participants to optokinetic stimulation in roll, resulting in spontaneous alternations between the perception of object-motion and that of contradirectional self-motion (vection), as reported by the subjects. Simultaneously, subjects were oscillated laterally in a flight simulator and indicated their perception of postural verticality. Results confirmed that rotation of the visual environment in the frontal plane biases the perceived orientation of gravity towards the direction of visual stimulus motion. However, no differential effect of perceptual state on postural verticality was obtained when contrasting verticality judgements made during the perception of object-motion with those obtained during reported self-motion perception. This finding is likely to reflect a functional segregation of central nervous visual-vestibular subsystems that process the perception of self-tilt and that of self-rotation to some degree independently.

Adult↗
PubMed1990

[Edgar Degas, photography and voyeurism].

Degas has drawn his paintings in a voyeuristic perspective. This voyeurism is not due to the painter's personal psychopathology. Instead, Degas has recognized the voyeuristic change of visual perception as a result of the development of photography as a new medium; meanwhile this change has become unconscious. Degas' paintings thus confront us with the historicity of visual perception and of the visual partial instinct.

Body Image↗
PubMed1997

[The Parity technique as an example of an analytical approach to designing computerized psychological tests].

The new computer technique "Paritet" for studying the function of attention and visual perception was developed by the author in 1995. This technique has been tested in the combined experiment "ECOPSI-95". The study results reveal the differences in the visual perception of symmetric and nonsymmetric images, combined and separate elements of the image. For solution of the problem of developing the methodology of designing the computer tests it is suggested to develop the system of ranging the visual images to suit the complexity of perception.

Attention↗
PubMed1995

'When is VISION asked too much'?

The last two decades a shift took place from substitutional/compensatory training to utilisation of residual vision regarding rehabilitation of the visually impaired. Some of the visually impaired are able to use their visual perception nearly as complete as normal seeing people in spite of a severe visual disability. On the other hand, people with nearly normal functions can be severely visually handicapped. To illustrate this, two cases are presented. The first case is a man, aged 47 years, with a juvenile macular degeneration on both eyes. In spite of a very low visual acuity of less then 0.05, he finished an university education and he is able to maintain himself very well in a leading position in a scientific environment, by using adequate low vision devices. Also for his leisure activities, as photography and speed skating, he relies upon visual perception. The second case is a woman, aged 30 years, with nearly normal visual functions, who is not able to read for longer periods caused by conflicting information from the body- and eye movements, and the visual input. This causes sickness during reading. She is unable to use books for her study and is working with recordings on tape. The results of a comprehensive visual assessment will be related to the specific low vision devices and its use.

Adult↗
PubMed2006

Subjective visual vertical perception relates to balance in acute stroke.

OBJECTIVE: To determine whether misperception of the subjective visual vertical (SVV) underlies balance difficulties in hemiplegic patients. DESIGN: Descriptive study, using a convenience sample. SETTING: Department of physical medicine of a university hospital. PARTICIPANTS: Thirty inpatients with hemiplegia after a hemispheric stroke during the 3 previous months. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: The SVV was tested while subjects sat in a dark room and were asked to adjust a luminous line to the vertical position. Mean SVV deviation and uncertainty, defined as the standard deviation, were calculated for 8 trials. Balance was assessed by the Postural Assessment Scale for Stroke (PASS) and while patients sat on a laterally rocking platform placed on a Satel force platform. The mean body position and the instability score (Lx), calculated as the length of the course of the center of pressure, were recorded. Functional outcome was also evaluated by the FIM instrument. RESULTS: An abnormal SVV was recorded for 20 of 30 patients. Balance (ie, PASS, Lx) and FIM correlated significantly with SVV tilt (P<.001, P=.01, and P<.001, respectively) and with uncertainty (PASS, P=.006; FIM, P=.003). CONCLUSIONS: Verticality misperception was related to poor balance and might be an important element in the assessment of contributing factors to balance disorders after stroke. It should probably be taken into account when establishing balance rehabilitation programs for patients with hemiplegia.

Adult↗
PubMed1991

Perception of visual illusions in a sample of Nigerian children.

This study examined the effects of cultural factors on perception of 15 boys and 21 girls in Nigeria. The five geometric illusions of Segall, Campbell, and Herskovitz were shown in booklets. Previously tested Afghan boys gave evidence of greater illusion than the Nigerian children. The findings also supported previous research on perception of illusion.

Attention↗
PubMed2003

Visual perspective in causal attribution, empathy and attitude change.

The aim of the present study was to test the effect of visual perspective on the actor-observer bias. For this aim, we examined the effects of different visual perspectives on individuals' external and internal attributions. In addition to this, we examined the presence or absence of an attitude change toward the death penalty due to participants' visual perspective. One week before the experiment, we measured the participants' attitudes toward the death penalty. Then, during the experiment, films produced by one of the authors of this study were shown to two separate groups of participants. There were two films, each film constituting one of the two levels of visual perception. The content of each film was the memories of a person who was given the death penalty for the murder of his own brother. Level of visual perception was manipulated by using different camera perspectives, one from the actor's point of view and the other from the observer's point of view. At the end of the experiment, participants' attitudes toward the death penalty were measured again.

Adult↗
PubMed1979

Visual pattern perception: a multidimensional analysis of development of children's reading skills.

This study was designed to assess the extent to which there are visual pattern processing deficits which are related to differential reading skill of young children. Discrimination problems were constructed using visual patterns with features known to be processed differentially by the central nervous system based upon neurophysiological data. Analysis of variance and multidimensional scaling techniques were used to analyze the discrimination latencies of kindergarten through third grade children (12 per grade) who were classified either as good or poor readers. The results show that there are no pattern-specific effects which discriminate good from poor readers. Rather, good readers process all patterns more efficiently than do poor readers, and efficiency improves with age for all readers studied. This suggests that the locus of the reading deficit occurs at levels in the nervous system beyond where pattern-feature processing occurs.

Child↗
PubMed1985

Two visual systems in mental imagery: dissociation of "what" and "where" in imagery disorders due to bilateral posterior cerebral lesions.

We studied two patients with impaired visual perception and imagery caused by bilateral posterior cerebral lesions. The first had prosopagnosia and achromatopsia, and the imagery disorder involved the description of objects from memory, especially faces and animals, and colors of objects. The second had visual disorientation; the imagery problem involved the description of spatial relations from memory. Impairments of visual imagery, like disorders of visual perception, can be dissociated. Object and color imagery may be dissociated from imagery for spatial relations. A given imagery deficit tends to be associated with the corresponding type of perceptual deficit.

Adolescent↗