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At least 1,045 records · Page 58Linked to original sources
PubMed1993

Activation of human primary visual cortex during visual recall: a magnetic resonance imaging study.

The degree to which the process involved in visual perception and visual imagery share a common neuroanatomical substrate is unclear. Physiological evidence for localization of visual imagery early in the visual pathways would have important bearing on current theories of visual processing. A magnetic resonance imaging technique sensitive to regional changes in blood oxygenation was used to obtain functional activation maps in the human visual cortex. During recall of a visual stimulus, focal increases in signal related to changes in blood flow were detected in V1 and V2 cortex in five of seven subjects. These experiments show that the same areas of the early visual cortex that are excited by visual stimulation are also activated during mental representation of the same stimulus. Some of the processes used in topographically mapped cortical areas during visual perception may also be utilized during visual recall.

Adult↗
PubMed1973

Analysis of perception of complex visual stimulus-patterns.

This paper deals with the analysis of visual perceptions of complex patterns consisting of two simple patterns placed one above the other in one frame (united pattern) or in two separate frames each (divided pattern). The upper pattern consisted of a configuration of lines, the lower one of a configuration of dots. There were one positive pattern which a subject had to recognize in tachistoscopic exposure and a number of negative patterns which a subject had to reject. When the dot component of the positive pattern consisted of two dots situated near its left edge, the subjects committed a great number of errors in recognition of the positive pattern and also the negative patterns with dot-negative components. Errors in recognition of negative patterns with line-negative components were much less numerous. Generally less errors were committed with divided patterns than with united patterns. When in the dot component of the positive pattern the distance between the dots was increased and they were placed symmetrically, the number of errors in recognition of this pattern decreased considerably; errors made in rejecting the negative patterns were, however, the same as in the previous test. Contrary to the previous test, errors with united patterns were less numerous than with divided patterns. The data obtained are discussed with reference to the concept of lateral inhibition between components of the complex unknown patterns. It is postulated that this inhibition can be partially overcome if the components of the complex pattern are easy integrated as is the case with symmetric united patterns.

Analysis of Variance↗
PubMed1998

Laterality in visual speech perception.

The lateralization of visual speech perception was examined in 3 experiments. Participants were presented with a realistic computer-animated face articulating 1 of 4 consonant-vowel syllables without sound. The face appeared at 1 of 5 locations in the visual field. The participants' task was to identify each test syllable. To prevent eye movement during the presentation of the face, participants had to carry out a fixation task simultaneously with the speechreading task. In one study, an eccentricity effect was found along with a small but significant difference in favor of the right visual field (left hemisphere). The same results were found with the face articulating nonlinguistic mouth movements (e.g., kiss). These results suggest that the left-hemisphere advantage is based on the processing of dynamic visual information rather than on the extraction of linguistic significance from facial movements.

Adolescent↗
PubMed1994

Selective deficit of visual size perception: two cases of hemimicropsia.

Hemimicropsia is a rare disorder of visual perception characterized by an apparent reduction of the size of objects when presented in one hemifield. We report two cases of hemimicropsia resulting from focal brain lesions. The first patient was an art teacher and could accurately depict his abnormal visual perception. He subsequently died and his brain was examined post mortem. In the second patient, micropsia was assessed by a quantified size comparison task. The size of a given object is normally perceived as constant across any spatial position. Hemimicropsia may thus be considered a limited violation of the size constancy principle. Behavioural and anatomical data are discussed in relation to the neural basis of visual object perception in humans.

Autopsy↗
PubMed2005

Dopaminergic modulation of arousal in Drosophila.

BACKGROUND: Arousal levels in the brain set thresholds for behavior, from simple to complex. The mechanistic underpinnings of the various phenomena comprising arousal, however, are still poorly understood. Drosophila behaviors have been studied that span different levels of arousal, from sleep to visual perception to psychostimulant responses. RESULTS: We have investigated neurobiological mechanisms of arousal in the Drosophila brain by a combined behavioral, genetic, pharmacological, and electrophysiological approach. Administration of methamphetamine (METH) suppresses sleep and promotes active wakefulness, whereas an inhibitor of dopamine synthesis promotes sleep. METH affects courtship behavior by increasing sexual arousal while decreasing successful sexual performance. Electrophysiological recordings from the medial protocerebrum of wild-type flies showed that METH ingestion has rapid and detrimental effects on a brain response associated with perception of visual stimuli. Recordings in genetically manipulated animals show that dopaminergic transmission is required for these responses and that visual-processing deficits caused by attenuated dopaminergic transmission can be rescued by METH. CONCLUSIONS: We show that changes in dopamine levels differentially affect arousal for behaviors of varying complexity. Complex behaviors, such as visual perception, degenerate when dopamine levels are either too high or too low, in accordance with the inverted-U hypothesis of dopamine action in the mammalian brain. Simpler behaviors, such as sleep and locomotion, show graded responses that follow changes in dopamine level.

Animals↗
PubMed2001

When sound affects vision: effects of auditory grouping on visual motion perception.

Two identical visual targets moving across each other can be perceived either to bounce off or to stream through each other. A brief sound at the moment the targets coincide biases perception toward bouncing. We found that this bounce-inducing effect was attenuated when other identical sounds (auditory flankers) were presented 300 ms before and after the simultaneous sound. The attenuation occurred only when the simultaneous sound and auditory flankers had similar acoustic characteristics and the simultaneous sound was not salient. These results suggest that there is an aspect of auditory-grouping (saliency-assigning) processes that is context-sensitive and can be utilized by the visual system for solving ambiguity. Furthermore, control experiments revealed that such auditory context did not affect the perceptual qualities of the simultaneous sound. Because the attenuation effect is not manifest in the perception of acoustic characteristics of individual sound elements, we conclude that it is a genuine cross-modal effect.

Acoustic Stimulation↗
PubMed2004

Association of binocular lower visual field impairment, impaired simultaneous perception, disordered visually guided motion and inaccurate saccades in children with cerebral visual dysfunction-a retrospective observational study.

The principal pathways serving higher visual function comprise the dorsal stream and the ventral stream. The dorsal stream runs between the occipital lobes and the parietal lobes and subserves the ability to process the whole visual scene and carry out visually guided movement. The ventral stream runs between the occipital lobes and temporal lobe tissue and primarily subserves visual recognition and memory. These tissues are susceptible to dysfunction in children with brain damage. We report a series of 40 children in whom damage to the brain has led to a common symptom complex affecting vision. Lower visual field loss was frequently elicited. This was associated with impaired ability to make accurate visually guided movement (particularly of the lower limbs) accompanied by impaired simultaneous perception, and in some cases, with inaccurate saccades and in others, impaired perception of movement. These features are consistent with parietal/dorsal stream dysfunction. Difficulty recognising faces and problems with route finding (which are ventral stream functions) were also present in a number of the children. These visual difficulties can be manifest in the presence of normal visual acuity. Recognition of these problems leads to understanding of the child's visual difficulties and facilitates adaptation of curriculum delivery at school.

Adolescent↗
PubMed1975

A profile for managing sensory integrative test data.

A concise method for compiling a data profile from a general sensory integrative test battery has been presented. Subtests from each test used were categorized according to the sensory integrative and motor functions being tested. These categories have been defined and include: tactile-kinesthetic perception, visual perception-figure ground, visual perception-constancy, ocular control, gross motor control, fine motor control, integration of function-two sides of the body, orientation in space, body awareness, and auditory discrimination. A method for converting the various scores into descriptive terminology is provided in which the test results are reported as above age expectancy, appropriate for age, somewhat deficient for age, and markedly deficient for age. The clinical implications of the technique are discussed.

Auditory Perception↗
PubMed1994

Neural network approaches to visual motion perception.

This paper concerns certain difficult problems in image processing and perception: neurocomputation of visual motion information. The first part of this paper deals with the spatial physiological integration by the figure-ground discrimination neural network in the visual system of the fly. We have outlined the fundamental organization and algorithms of this neural network, and mainly concentrated on the results of computer simulations of spatial physiological integration. It has been shown that the gain control mechanism, the nonlinearity of synaptic transmission characteristic, the interaction between the two eyes, and the directional selectivity of the pool cells play decisive roles in the spatial physiological integration. In the second part, we have presented a self-organizing neural network for the perception of visual motion by using a retinotopic array of Reichardt's motion detectors and Kohonen's self-organizing maps. It has been demonstrated by computer simulations that the network is able to learn to solve the ambiguities given by local motion detection mechanism. The resultant self-organized configuration in the output layer is resembling direction selective columns which first appear in area MT of the primate visual system. It has been explored that the spatio-temporal coherences, mapping, cooperation, competition, and Hebb rule are the basic neural principles for visual motion perception.

Animals↗
PubMed1995

Visual motion perception.

The primate visual motion system performs numerous functions essential for survival in a dynamic visual world. Prominent among these functions is the ability to recover and represent the trajectories of objects in a form that facilitates behavioral responses to those movements. The first step toward this goal, which consists of detecting the displacement of retinal image features, has been studied for many years in both psychophysical and neurobiological experiments. Evidence indicates that achievement of this step is computationally straightforward and occurs at the earliest cortical stage. The second step involves the selective integration of retinal motion signals according to the object of origin. Realization of this step is computationally demanding, as the solution is formally underconstrained. It must rely--by definition--upon utilization of retinal cues that are indicative of the spatial relationships within and between objects in the visual scene. Psychophysical experiments have documented this dependence and suggested mechanisms by which it may be achieved. Neurophysiological experiments have provided evidence for a neural substrate that may underlie this selective motion signal integration. Together they paint a coherent portrait of the means by which retinal image motion gives rise to our perceptual experience of moving objects.

Animals↗
PubMed2005

Perception of visual speed while moving.

During self-motion, the world normally appears stationary. In part, this may be due to reductions in visual motion signals during self-motion. In 8 experiments, the authors used magnitude estimation to characterize changes in visual speed perception as a result of biomechanical self-motion alone (treadmill walking), physical translation alone (passive transport), and both biomechanical self-motion and physical translation together (walking). Their results show that each factor alone produces subtractive reductions in visual speed but that subtraction is greatest with both factors together, approximating the sum of the 2 separately. The similarity of results for biomechanical and passive self-motion support H. B. Barlow's (1990) inhibition theory of sensory correlation as a mechanism for implementing H. Wallach's (1987) compensation for self-motion.

Biomechanical Phenomena↗
PubMed2002

Shadows of artistry: cortical synchrony during perception and imagery of visual art.

Functional and topographical differences between two groups, artists and non-artists, during the performances of visual perception and imagery of paintings were presented by means of EEG phase synchrony analysis. In artists as compared with non-artists, significantly higher phase synchrony was found in the high frequency beta and gamma bands during the perception of the paintings; in the low frequency bands (primarily delta), phase synchrony was mostly enhanced during imagery. Strong decreases in phase synchrony of alpha were found primarily in artists for both tasks. The right hemisphere was found to present higher synchrony than the left in artists, whereas hemispheric asymmetry was less significant in non-artists. In the artists, enhanced synchrony in the high frequency band is most likely due to their enhanced binding capabilities of numerous visual attributes, and enhanced synchrony in the low frequency band seems to be due to the higher involvement of long-term visual memory mostly in imagery. Thus, the analysis of phase synchrony from EEG signals yields new information about the dynamical co-operation between neuronal assemblies during the cognition of visual art.

Adult↗