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At least 1,225 records · Page 68Linked to original sources
PubMed2001

A coordinate system for visual motion perception.

The purpose of this research was to determine the reference axes used by the visual system to specify direction of motion of objects by the visual system at the perceptual level. Ten young adults aligned motion of a moving luminous dot on a computer display to body-fixed and external vertical and horizontal plane axes while operating in a dark room. Accuracy of aligning dot motion to earth-fixed vertical, a displayed luminous line (external visual axis) of varied orientations, and head and trunk longitudinal axes was tested in one experiment with the display in the vertical frontal plane. In a second experiment, dot motion was aligned to head and trunk anterior/posterior (A-P) axes and to an external visual axis presented on a horizontal computer screen. Head and trunk orientations were varied in the frontal plane (left/right tilt) when testing vertical plane axes and by rotation of the head and/or trunk about a vertical axis when testing horizontal plane axes. Perceptual errors were lowest when aligning to earth-fixed vertical in the vertical plane and to an external oblique line in the horizontal plane when head and trunk orientations were varied. Perceptions of horizontal plane motion direction were accurate relative to the trunk-fixed A-P axis when only head orientation was varied, but large errors were made when trunk orientation was varied. Proprioceptive influences on visual perceptions of motion direction were shown by a dependence of perceptual errors on trunk and neck orientations when aligning to all axes. Furthermore, when aligning motion to an external line, the errors depended on orientation of the line in addition to trunk and neck orientations, but not when aligning to intrinsic axes or earth-fixed vertical in the presence of an external line. We conclude that the visual motion system defines direction relative to earth-fixed vertical and an external horizontal reference axis when available. The trunk-fixed A-P axis can be used to accurately define motion direction when operating without an external reference if a neutral trunk orientation is maintained.

Adult↗
PubMed2003

Transcranial magnetic stimulation as an investigative tool in the study of visual function.

Transcranial magnetic stimulation (TMS) is a novel and powerful probe to study the relationship between human brain function and behavior. TMS is being widely used to investigate memory, language, attention, learning, and motor function and is even being utilized therapeutically in the treatment of depression. Some of the earliest applications of TMS have been directed toward the investigation of human visual perception. For example, a strong TMS pulse delivered to the occipital cortex in a sighted or even blind individual can evoke the sensation of perceiving light (visual phosphenes). TMS can also be used to suppress visual perception and investigate the timing of visual information processing. Furthermore, the functional connectivity between different brain areas can be mapped using TMS, thus establishing a causal link between visual cortical function and visual perception. The present article is meant as an overview of the technique of TMS and a review of the literature as it pertains to the study of visual function. The application of TMS in the diagnosis as well as possible therapeutic use in various visual disorders is also discussed.

Electromagnetic Fields↗
PubMed1978

An additional dimension to grating perception.

Visual acuity (A) for a two-dimensional multiplicative sinusoidal contrast grid (sinusoidal chessboard) was measured as a function of spatial frequency (omega) of modulation in one of the dimensions. The reduction in acuity as frequency was increased was well described by the equation: A = -2pikomega + c, where k and c are constants. At suprathreshold contrasts, the frequency of modulation appeared to be doubled relative to the underlying modulation frequency. This doubling is not related to the frequency of the harmonic components of the chessboard, but suggests the existence of a perceptual mechanism sensitive to areas of sinusoidal modulation which are seen at twice the frequency of the variation in contrast.

Depth Perception↗
PubMed1989

The role of structure in infant visual pattern perception.

The research of the authors and others on the role of structure in infant visual pattern perception is reviewed. Two new experiments are reported on preference for symmetry in infants. It is shown that infants reliably prefer patterns with multiple axes of bilateral symmetry relative to asymmetrical patterns. Also, the results demonstrate that vertically oriented single axis bilateral symmetry is more salient than horizontally oriented symmetry in infants as it is in adults. It is argued that sensitivity to various kinds of pattern structure reflects fundamental operations of the visual system.

Attention↗
PubMed2001

Linguistically mediated visual search.

During an individual's normal interaction with the environment and other humans, visual and linguistic signals often coincide and can be integrated very quickly. This has been clearly demonstrated in recent eye tracking studies showing that visual perception constrains on-line comprehension of spoken language. In a modified visual search task, we found the inverse, that real-time language comprehension can also constrain visual perception. In standard visual search tasks, the number of distractors in the display strongly affects search time for a target defined by a conjunction of features, but not for a target defined by a single feature. However we found that when a conjunction target was identified by a spoken instruction presented concurrently with the visual display, the incremental processing of spoken language allowed the search process to proceed in a manner considerably less affected by the number of distractors. These results suggest that perceptual systems specializedfor language and for vision interact more fluidly than previously thought.

Attention↗
PubMed2003

Kinesthetic perception of visually specified axes.

The purpose of this research was to determine whether human subjects could align the forearm more accurately to the orientation of an external object than to earth-fixed vertical and trunk-fixed anterior-posterior (a-p) axes. Ten young adults aligned the unseen forearm to earth-fixed vertical and trunk-fixed a-p axes, and to a visually presented rod (external visual axis) held by an experimenter in various oblique vertical and horizontal orientations. The head and trunk orientations were varied by left/right lateral flexion when aligning the forearm to vertical plane axes and by rotation about the vertical axis when aligning the forearm to horizontal plane axes. Perceptual errors for aligning the forearm to vertical plane axes were much lower when aligning the forearm to earth-fixed vertical than to an external visual axis positioned in a vertical plane. Furthermore, the perceptual errors for aligning the forearm to the visually presented rod were correlated with rod orientation while errors for aligning the forearm to vertical while viewing the rod were unaffected by rod orientations. Clearly, human subjects cannot use an oblique external visually presented axis to provide a frame of reference for accurate perception of forearm orientation in vertical planes. Perceptual errors were similar for aligning the forearm to the horizontal trunk-fixed a-p axis and external visual axis when head and trunk orientation were varied. These perceptual errors were not correlated with rod orientation in the horizontal plane, giving no evidence of bias toward the trunk or external visual axis in horizontal plane perception of forearm orientation. Thus, humans can use either the trunk-fixed a-p axis or the visually specified orientation of an external object as a frame of reference for the kinesthetic system to specify forearm orientation in the horizontal plane.

Adult↗
PubMedDate not supplied

Electrophysiological studies of visual word perception, lexical organization, and semantic processing: a tutorial review.

Visual word recognition requires the matching of an orthographic unit to its meaning via a phonological unit in the mental lexicon. The nature and the speed of this process are affected by "bottom-up" factors (e.g., the manner in which the phonology is represented by the orthography) and by "top-down" factors (e.g., network connections between related words in the lexicon, and contextual semantic information). Event-related potentials (ERPs) provide a relatively new tool that complements behavioral measures of word recognition. ERP components recorded during word perception tasks have been found to be sensitive to orthographic, phonological, and semantic manipulations. They go beyond behavioral measures by providing continuous information about the activity of the cognitive system from stimulus onset to the occurrence of the response. In addition, ERPs enable the researcher to examine word perception and reading in more natural situations, without time constraints and overt responses. Finally, intra-cranial ERP recording in humans and modern analytical techniques may shed light on the relations between cognitive linguistic processes and brain structures. Collaboration between cognitive psychologists, linguists, and ERP researchers will be necessary to exploit the great potential of these electrophysiological techniques.

Cognition↗
PubMed1992

Visual field loss after attacks of migraine with aura.

Visual fields were mapped with kinetic are perimetry in 23 migraine with aura subjects and, for comparison, in 20 migraine without aura subjects and in 21 non-headache controls. Central vision on the Amsler eye chart and visual perception threshold on a computer task were also investigated. Measures were obtained at least seven days after an episode of migraine. In addition, 10 of the migraine with aura subjects and 10 migraine without aura subjects were studied the day after an attack. The day after migraine with aura, visual sensitivity in the periphery of the visual fields was depressed, central vision was blurred, and visual perception threshold was elevated. These visual disturbances had resolved 7 to 10 days later. With the exception of a minor increase in visual perception threshold, vision was normal after attacks of migraine without aura. Residual effects of the migraine aura could mediate the subclinical visual disturbances which persist for at least one day after attacks of migraine with aura.

Adolescent↗
PubMed1997

Constructional dyspraxia in preterm diplegia: isolation from visual and visual perceptual impairments.

OBJECTIVE: To evaluate ophthalmological profiles, visual perception and constructional function in preterm children with spastic diplegia (SD) and to clarify their neuropsychological deficits in comparison with a control group. METHODS: Thirty-five SD and 34 control children were investigated for visual acuity, eye position, stereoacuity, depth perception, visual perception, visuo-spatial construction and constructional praxis. Each of the results was compared among the four groups as SD with and without strabismus, and control with and without strabismus. RESULTS: Strabismic SD showed worse visual acuity, worse stereoacuity and worse depth perception than the other groups. Constructional dyspraxia was detected in 94.1% of SD either with or without strabismus, while it was rare in the control group. There was no significant contribution of visual acuity, eye position, stereoacuity or depth perception to constructional dyspraxia by stepwise multiple linear regression analysis. CONCLUSION: Strabismic preterm SD children are at high risk for visual dysfunction. Constructional dyspraxia was frequently found in SD children and may be a dysfunction isolated from ophthalmological and visual perceptual dysfunctions.

Adolescent↗
PubMed2000

Visuoperceptual impairment in dementia with Lewy bodies.

BACKGROUND: In dementia with Lewy bodies (DLB), vision-related cognitive and behavioral symptoms are common, and involvement of the occipital visual cortices has been demonstrated in functional neuroimaging studies. OBJECTIVES: To delineate visuoperceptual disturbance in patients with DLB in comparison with that in patients with Alzheimer disease and to explore the relationship between visuoperceptual disturbance and the vision-related cognitive and behavioral symptoms. DESIGN: Case-control study. SETTING: Research-oriented hospital. PATIENTS: Twenty-four patients with probable DLB (based on criteria of the Consortium on DLB International Workshop) and 48 patients with probable Alzheimer disease (based on criteria of the National Institute of Neurological and Communicative Disorders and Stroke-Alzheimer's Disease and Related Disorders Association) who were matched to those with DLB 2:1 by age, sex, education, and Mini-Mental State Examination score. MAIN OUTCOME MEASURES: Four test items to examine visuoperceptual functions, including the object size discrimination, form discrimination, overlapping figure identification, and visual counting tasks. RESULTS: Compared with patients with probable Alzheimer disease, patients with probable DLB scored significantly lower on all the visuoperceptive tasks (P<.04 to P<.001). In the DLB group, patients with visual hallucinations (n = 18) scored significantly lower on the overlapping figure identification (P = .01) than those without them (n = 6), and patients with television misidentifications (n = 5) scored significantly lower on the size discrimination (P<.001), form discrimination (P = .01), and visual counting (P = .007) than those without them (n = 19). CONCLUSIONS: Visual perception is defective in probable DLB. The defective visual perception plays a role in development of visual hallucinations, delusional misidentifications, visual agnosias, and visuoconstructive disability charcteristic of DLB.

Aged↗
PubMed1988

Underlying structure of auditory-visual consonant perception by hearing-impaired children and the influences of syllabic compression.

The identification of consonants in (a)-C-(a) nonsense syllables, using a fourteen-alternative forced-choice procedure, was examined in 4 profoundly hearing-impaired children under five conditions: audition alone using hearing aids in free-field (A), vision alone (V), auditory-visual using hearing aids in free-field (AV1), auditory-visual with linear amplification (AV2), and auditory-visual with syllabic compression (AV3). In the AV2 and AV3 conditions, acoustic signals were binaurally presented by magnetic or acoustic coupling to the subjects' hearing aids. The syllabic compressor had a compression ratio of 10:1, and attack and release times were 1.2 ms and 60 ms. The confusion matrices were subjected to two analysis methods: hierarchical clustering and information transmission analysis using articulatory features. The same general conclusions were drawn on the basis of results obtained from either analysis method. The results indicated better performance in the V condition than in the A condition. In the three AV conditions, the subjects predominantly combined the acoustic parameter of voicing with the visual signal. No consistent differences were recorded across the three AV conditions. Syllabic compression did not, therefore, appear to have a significant influence on AV perception for these children. A high degree of subject variability was recorded for the A and three AV conditions, but not for the V condition.

Adolescent↗
PubMed1981

Effects of vestibular and visual motion perception on task performance.

The effects of foveal and peripheral visual, as well as vestibular, cues on the performance and control behaviour of subjects in two different roll control tasks were studied in a moving base flight simulator with low noise motion characteristics. Two different roll control tasks were used, one being a following task (or compensatory tracking task) where a displayed random signal was to be tracked, the other being a disturbance task in which a random signal perturbed the controlled system and the roll angle was to be kept at zero. Consistent improvement in controller performance was found after adding visual peripheral or vestibular (motion) cues to the basic configuration consisting of a central CRT display. Control behaviour, as expressed by controller transfer functions was also markedly influenced by the addition of these extra motion cues, the changes in control behaviour being dependent on the type of control task. Some possible causes for this dependence are discussed.

Cues↗
PubMed2006

Improving residual vision by attentional cueing in patients with brain lesions.

Visual attention is crucial for almost all processes of visual perception, particularly when perception is difficult. We were interested in the effects of cueing spatial attention in patients with cerebral lesions who face difficulties in visual perception in areas of residual vision at the border of visual field defects. In 23 patients with visual field loss due to post-geniculate brain lesions, stimulus detection performance and reaction times were mapped with high-resolution computer-based perimetry. A cueing procedure using Gestalt completion to attract attention to areas of residual vision was implemented in this test and performance compared in attended and unattended conditions. Stimulus detection and reaction times in areas of residual vision improved significantly under attended conditions. The extent of this effect depended on the size of areas of residual vision within the cued field. Unexpectedly, facilitation was also observed, though to a lesser extent, in invalid cueing conditions, suggesting an unspecific increase of alertness in unattended areas. Our findings show that top-down influences are relevant for visual field testing. Visuo-spatial attention may change patterns of neural activation and induce short-term plasticity not only in the intact visual system but also in the presence of visual field loss after brain lesions. Attentional cueing induces a co-activation of the lesioned visual system and (intact) attentional networks in the brain inducing immediate facilitation of visual perception. This effect may be relevant for designing new strategies to permanently improve vision during neuropsychological rehabilitation.

Adult↗
PubMed1981

Visual spatial perception in adolescents and their parents: the X-linked recessive hypothesis.

If high ability in visual spatial perception is determined by an X-linked recessive major gene, then the following pattern of correlations is expected across the four groups of parents and children, this is, the mother-son, father-daughter, mother-daughter, and father-son groups: rMS=rFD greater than rMD greater than rFS=0. In a sample of 129 adolescents and their parents, the Spatial Relations Test of the Differential Aptitude Test and the Identical Blocks Test showed the pattern of correlations expected under the above hypothesis, but the Water Level Test did not. The present results provide but limited support for the X-linked recessive hypothesis.

Adolescent↗
PubMed1996

Lorazepam impairs perceptual integration of visual forms: a central effect.

Previous studies have shown a lorazepam effect on visual perception. We tested whether this impairment resulted from a peripheral effect induced by benzodiazepines. A first experiment showed that a single dose of lorazepam induces an oculomotor imbalance without impairing visual acuity or accommodation. In a second experiment, we tested whether the impairment induced by lorazepam on visual perception still occurred in monocular vision. Subjects matched incomplete forms controlled on the spacing and alignment of their local contour elements. A reference object was first displayed and followed by two laterally displayed objects, a target and a distractor. The distractor was the mirror-reversed version of the target. Performance was impaired in the lorazepam group when the reference was an incomplete form with a spacing of 10.8' or 22.2' of arc. These results were not correlated with sedation. They confirm that lorazepam has a central deleterious effect on visual perception. A post-hoc analysis also suggested that lorazepam-treated subjects used asymmetry in the stimuli as a compensatory strategy. This result is discussed in relation to previous hypotheses about the physiological mechanisms that determine the effects of lorazepam on visual perception.

Accommodation, Ocular↗
PubMed2002

Auditory-visual speech perception and aging.

OBJECTIVE: This experiment was designed to assess the integration of auditory and visual information for speech perception in older adults. The integration of place and voicing information was assessed across modalities using the McGurk effect. The following questions were addressed: 1) Are older adults as successful as younger adults at integrating auditory and visual information for speech perception? 2) Is successful integration of this information related to lipreading performance? DESIGN: The performance of three groups of participants was compared: young adults with normal hearing and vision, older adults with normal to near-normal hearing and vision, and young controls, whose hearing thresholds were shifted with noise to match the older adults. Each participant completed a lipreading test and auditory and auditory-plus-visual identification of syllables with conflicting auditory and visual cues. RESULTS: The results show that on average older adults are as successful as young adults at integrating auditory and visual information for speech perception at the syllable level. The number of fused responses did not differ for the CV tokens across the ages tested. Although there were no significant differences between groups for integration at the syllable level, there were differences in the response alternatives chosen. Young adults with normal peripheral sensitivity often chose an auditory alternative whereas, older adults and control participants leaned toward visual alternatives. In additions, older adults demonstrated poorer lipreading performance than their younger counterparts. This was not related to successful integration of information at the syllable level. CONCLUSIONS: Based on the findings of this study, when auditory and visual integration of speech information fails to occur, producing a nonfused response, participants select an alternative response from the modality with the least ambiguous signal.

Acoustic Stimulation↗
PubMed2004

Perception of visual space at the time of pro- and anti-saccades.

The localization of peri-saccadically flashed objects shows two types of errors: first, a uniform shift in saccade direction, and second, a compression of visual space around the saccade target. Whereas the uniform shift occurs when the experiment is performed in complete darkness compression occurs when additional visual references are available. Thus peri-saccadic mislocalization contains motor and visual components. To distinguish between both factors we compared peri-saccadic localization errors during pro- and anti-saccades. In the case of anti-saccades, the visual cue that elicits the saccade and the actual eye movement are in opposite directions. We asked whether peri-saccadic compression can be observed with anti-saccades, and if so, whether the compression is directed toward the visual cue or follows the actual eye movement. In blocked trials, subjects performed saccades either toward a visual cue (pro-saccade) or to the mirrored position opposite to a visual cue (anti-saccade). Peri-saccadically, we flashed a thin vertical bar at one of four possible locations. Subjects had to indicate the perceived position of the bar with a mouse pointer about 500 ms after the saccade. Experiments were performed in complete darkness and with visual references. Peri-saccadic mislocalizations occurred during anti-saccades. The mislocalizations were very similar for pro- and anti-saccades in magnitude and direction. For both, pro- and anti-saccades, mislocalizations were directed toward the actual eye movement and not the visual cue.

Adult↗