PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Visual Perception”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

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

At least 1,171 records · Page 65Linked to original sources
PubMed2005

Recruitment of fusiform face area associated with listening to degraded speech sounds in auditory-visual speech perception: a PET study.

For the fast and accurate cognition of external information, the human brain seems to integrate information from multi-sensory modalities. We used positron emission tomography (PET) to identify the brain areas related to auditory-visual speech perception. We measured the regional cerebral blood flow (rCBF) of young, normal volunteers during the presentation of dynamic facial movement at vocalization and during a visual control condition (visual noise), both under the two different auditory conditions of normal and degraded speech sounds. The subjects were instructed to listen carefully to the presented speech sound while keeping their eyes open and to say what they heard. The PET data showed that elevation of rCBF in the right fusiform gyrus (known as the "face area") was not significant when the subjects listened to normal speech sound accompanied by a dynamic image of the speaker's face, but was significant when degraded speech sound (filtered with a 500 Hz low-pass filter) was presented with the facial image. The results of the present study confirm the possible involvement of the fusiform face area (FFA) in auditory-visual speech perception, especially when auditory information is degraded, and suggest that visual information is interactively recruited to make up for insufficient auditory information.

Acoustic Stimulation↗
PubMed1984

Children's perception of visual and auditory speech.

Preschool children's evaluation and integration of visual and auditory information in speech perception was compared with that of adults. Subjects identified speech events, which consisted of synthetic speech syllables ranging from /ba/ to /da/ combined with a videotaped /ba/, /da/, or no articulation. Both variables influenced the identification judgments for both groups of subjects. The results were used to test current views of the development of perceptual categorization and speech perception. Tests of quantitative models indicated that both preschool children and adults had available continuous and independent sources of information. The results were well described by a fuzzy logical model of perception, which assumes that the perceiver integrates continuous and independent sources of information and determines the relative goodness of match to prototype definitions in memory. The only developmental difference was less of an influence of the visual source of information for children relative to adults. 1 explanation is that the children simply attended less to the visual source. A second experiment eliminated the attentional explanation by showing identical results when the children were also required to indicate whether or not the speaker's mouth was moving.

Adolescent↗
PubMed1992

The perception of visual motion.

Recent developments have led to a greater insight into the complex processes of perception of visual motion. A better understanding of the neuronal circuitry involved and advances in electrophysiological techniques have allowed researchers to alter the perception of an animal with a stimulating electrode. In addition, studies have further elucidated the processes by which signals are combined and compared, allowing a greater understanding of the effects of selective brain damage.

Animals↗
PubMed1996

Abnormal motion processing and binocularity: infantile esotropia as a model system for effects of early interruptions of binocularity.

Infantile esotropia, a common form of strabismus with onset prior to 6 months of age, occurs at a time of rapid visual development. While monocular visual acuity is relatively unaffected in these patients, the majority of them fail to achieve fully normal stereopsis. In addition, these patients show a spectrum of abnormalities in their ocular following responses, visual perception and visual evoked potentials (VEPs) that suggest a failure to develop a normal complement of motion processing mechanisms. While abnormalities of of stereopsis have been studied for many years, motion processing in strabismus is a rapidly evolving area of current research. Motion mechanisms are normally binocular and may form a distinct binocular sub-system. This review summarises which is known about sensory and motor abnormalities in infantile esotropia, with special emphasis on recent motion VEP recordings. The monocular motion VEP shows directional biases early in infancy that are consistent with a nasalward/temporalward response bias. Patients with infantile esotropia maintain their neonatal biases beyond the age at which they normally disappear. The motion VEP biases persist into visual maturity in patients whose strabismus is treated after about 2 years of age. Treatment prior to age 2 can lessen the magnitude of the motion VEP asymmetry and these improvements can be maintained into visual maturity. A recording from the striate cortex of a visually deprived macaque monkey indicates that the motion VEP asymmetry arises early in the visual pathway.

Esotropia↗
PubMed1995

VS--a new computer program for detailed offline analysis of visual-spatial perception.

A new IBM-AT-compatible software program, VS, for the analysis of visual-spatial (VS) perception in humans, especially brain-damaged patients, is described. VS is suitable for analysis of the following visual-spatial tests: (1) subjective visual vertical (SVV), (2) subjective visual horizontal (SVH), and (3) orientation, length, distance, form and position discrimination, as well as line/bar bisection. The program allows manipulation of a wide range of experimental tasks by varying relevant parameters, e.g., length, width, color, movement direction, step width, and position on screen of the stimuli. Psychophysical parameters are computed (methods of limits) and stored in dBASE files which can be retrieved for further data analysis with commercial statistics or graphics software. VS has a versatile text editor, with two macro languages which enables the user to define their own experimental configurations and realize individual graphic plots on screen or laser printer. VS incorporates two standard examinations together with normative data of control subjects and standard plots of the subject's performance. The results of separate investigations show highly stable results in normal control subjects in repeated examinations as well as good retest-reliability of these standard examinations in brain-damaged patients (rtt = 0.77). Representative case reports of a patient with left-sided visual neglect, a patient with Balint's syndrome as well as a patient with visual-spatial deficits subsequent to a left parietal brain lesion demonstrate the sensitivity and specificity of the program.

Adult↗
PubMed1999

From elements to perception: local and global processing in visual neurons.

Gestalt psychologists in the early part of the century challenged psychophysical notions that perceptual phenomena can be understood from a punctate (atomistic) analysis of the elements present in the stimulus. Their ideas slowed later attempts to explain vision in terms of single-cell recordings from individual neurons. A rapprochement between Gestalt phenomenology and neurophysiology seemed unlikely when the first ECVP was held in Marburg, Germany, in 1978. Since that time, response properties of neurons have been discovered that invite an interpretation of visual phenomena (including illusions) in terms of neuronal processing by long-range interactions, as first proposed by Mach and Hering in the last century. This article traces a personal journey into the early days of neurophysiological vision research to illustrate the progress that has taken place from the first attempts to correlate single-cell responses with visual perceptions. Whereas initially the receptive-field properties of individual classes of cells--e.g., contrast, wavelength, orientation, motion, disparity, and spatial-frequency detectors--were used to account for relatively simple visual phenomena, nowadays complex perceptions are interpreted in terms of long-range interactions, involving many neurons. This change in paradigm from local to global processing was made possible by recent findings, in the cortex, on horizontal interactions and backward propagation (feedback loops) in addition to classical feedforward processing. These mechanisms are exemplified by studies of the tilt effect and tilt aftereffect, direction-specific motion adaptation, illusory contours, filling-in and fading, figure--ground segregation by orientation and motion contrast, and pop-out in dynamic visual-noise patterns. Major questions for future research and a discussion of their epistemological implications conclude the article.

Contrast Sensitivity↗
PubMed2004

Neuromagnetic activity in medial parietooccipital cortex reflects the perception of visual motion during eye movements.

We usually perceive a stationary, stable world despite coherent visual motion induced by eye movements. This astonishing example of perceptual invariance results from a comparison of visual information with internal reference signals (nonretinal signals) predicting the visual consequences of an eye movement. The important consequence of this concept is that our subjective percept of visual motion reflects the outcome of this comparison rather than retinal image slip. To localize the cortical networks underlying this comparison, we compared magnetoencephalography (MEG) responses under two conditions of pursuit-induced retinal image motion, which were identical physically but--due to different calibrational states of the nonretinal signal prompted under our experimental conditions--gave rise to different percepts of visual motion. This approach allows us to demonstrate that our perception of self-induced visual motion resides in comparably "late" parts of the cortical hierarchy of motion processing sparing the early stages up to cortical area MT/V5 but including cortex in and around the medial aspect of the parietooccipital cortex as one of its core elements.

Attention↗
PubMed2000

The visuomotor system resists the horizontal-vertical illusion.

The effect of the horizontal-vertical illusion on the visual and visuomotor systems was investigated. Participants (N = 8) viewed horizontal and vertical lines in an inverted-T stimulus and judged whether the two line segments were the same or different lengths. Participants also reached out and grasped either the vertical or the horizontal line segment of the stimulus. Perceptually, participants succumbed to the illusion; that is, they judged Ts of equal horizontal and vertical line lengths to be different and Ts of unequal line lengths to be the same. When reaching toward the same stimuli, however, the size of their grip aperture was scaled appropriately for the various line lengths. Thus, whereas the perceptual system succumbed to the illusion, the visuomotor system did not. Those results support a model proposed by M. A. Goodale and A. D. Milner (1992), who posited separate cortical pathways for visual perception and visually guided action.

Adult↗
PubMed1990

Cerebral asymmetry in visual attention.

The traditional view of cerebral lateralization of various cognitive functions has been challenged by results from recent experimental and clinical studies. Evidence has been gathered to suggest that a seemingly unitized cognitive function can be further broken down into various processing subcomponents which are distributed across the two hemispheres. For instance, according to such a more complex conceptualization of cerebral lateralization, language is seen not as a unitary ability, but rather as a collection of syntactic, semantic, and prosodic components, with each lateralized in particular manners. In much the same way, the present study attempts to examine the cerebral lateralization patterns of the seemingly unitary visual perception process. In a visual half-field experiment, 20 normal subjects were asked to make same/different judgments to laterally presented arrays of stimuli of the same type as previously studied by Treisman and her colleagues in experiments attempting to separate the preattentive and attentive stages of visual perception. Hemispheric differences were obtained only in tasks requiring attentive processing (i.e., Treisman's glueing). Results indicate a local attentional strategy for the left hemisphere and a global attentional strategy for the right hemisphere.

Adult↗
PubMed2002

The relationship between cortical activation and perception investigated with invisible stimuli.

The aim of this work was to study the relationship between cortical activity and visual perception. To do so, we developed a psychophysical technique that is able to dissociate the visual percept from the visual stimulus and thus distinguish brain activity reflecting the perceptual state from that reflecting other stages of stimulus processing. We used dichoptic color fusion to make identical monocular stimuli of opposite color contrast "disappear" at the binocular level and thus become "invisible" as far as conscious visual perception is concerned. By imaging brain activity in subjects during a discrimination task between face and house stimuli presented in this way, we found that house-specific and face-specific brain areas are always activated in a stimulus-specific way regardless of whether the stimuli are perceived. Absolute levels of cortical activation, however, were lower with invisible stimulation compared with visible stimulation. We conclude that there is no terminal "perceptual" area in the visual brain, but that the brain regions involved in processing a visual stimulus are also involved in its perception, the difference between the two being dictated by a higher level of activity in the specific brain region when the stimulus is perceived.

Color Perception↗
PubMed2001

Evidence for dissociation between the perceptual and visuomotor systems in humans.

When a visual stimulus is continuously moved behind a small stationary window, the window appears displaced in the direction of motion of the stimulus. In this study we showed that the magnitude of this illusion is dependent on (i) whether a perceptual or visuomotor task is used for judging the location of the window (ii) the directional signature of the stimulus, and (iii) whether or not there is a significant delay between the end of the visual presentation and the initiation of the localization measure. Our stimulus was a drifting sinusoidal grating windowed in space by a stationary, two-dimensional, Gaussian envelope (sigma=1 cycle of sinusoid). Localization measures were made following either a short (200 ms) or long (4.2 s) post-stimulus delay. The visuomotor localization error was up to three times greater than the perceptual error for a short delay. However, the visuomotor and perceptual localization measures were similar for a long delay. Our results provide evidence in support of the hypothesis that separate cortical pathways exist for visual perception and visually guided action and that delayed actions rely on stored perceptual information.

Humans↗
PubMed1997

Perception and visualization of human posture information for computer-aided ergonomic analysis.

This article reports three experiments that examined the effects of photographic method, computerized visualization scheme, and posture complexity on posture perception and specification for computer-aided ergonomic analysis. The subjects were presented with photographs of working postures, and were required to manipulate human forms generated by an ergonomics software program to match the postures in the photographs. The first experiment showed a clear advantage of using a three-dimensional (3-D) human form graphic with two photographs when complex, asymmetric postures were analysed. However, the use of a 3-D human graphic display and two photographs jeopardized the subjects' posture specification performance when simple, symmetric postures were analysed. The results of the second and the third experiment demonstrated the importance of achieving congruency between photographic and computer display perspectives in improving posture specification performance. Implications for ergonomic job analysis and ergonomics software design are discussed.

Adult↗
PubMed2004

Attitudes towards and perceptions of visual loss and its causes among Hong Kong Chinese adults.

BACKGROUND: As part of a study of visual function among Hong Kong Chinese adults, their attitudes and perceptions related to visual loss were examined. These included fear of visual loss, negative functional impacts of visual loss, the relationship between ageing and visual loss and help-seeking behaviours related to visual loss. Demographic factors associated with these variables were also studied. METHODS: The study population were people aged 40 and above randomly selected from the Shatin district of Hong Kong. The participants underwent eye examinations that included visual acuity, intraocular pressure measurement, visual field, slit-lamp biomicroscopy and ophthalmoscopy. The primary cause of visual disability was recorded. The participants were also asked about their attitudes and perceptions regarding visual loss using a structured questionnaire. RESULTS: The prevalence of bilateral visual disability was 2.2% among adults aged 40 or above and 6.4% among adults aged 60 or above. Nearly 36% of the participants selected blindness as the most feared disabling medical condition, which was substantially higher than conditions such as dementia, loss of limbs, deafness or aphasia. Inability to take care of oneself (21.0%), inconvenience related to mobility (20.2%) and inability to work (14.8%) were the three most commonly mentioned 'worst impact' effects of visual loss. Fully 68% of the participants believed that loss of vision is related to ageing. A majority of participants would seek help and advice from family members in case of visual loss. CONCLUSIONS: Visual function is perceived to be very important by Hong Kong Chinese adults. The fear of visual loss is widespread and particularly affects self-care and functional abilities. Visual loss is commonly seen as related to ageing. Attitudes and perceptions in this population may be modified by educational and outreach efforts in order to take advantage of preventive measures.

Adult↗
PubMed2005

Vertical linear self-motion perception during visual and inertial motion: more than weighted summation of sensory inputs.

We evaluated visual and vestibular contributions to vertical self motion perception by exposing subjects to various combinations of 0.2 Hz vertical linear oscillation and visual scene motion. The visual stimuli presented via a head-mounted display consisted of video recordings of the test chamber from the perspective of the subject seated in the oscillator. In the dark, subjects accurately reported the amplitude of vertical linear oscillation with only a slight tendency to underestimate it. In the absence of inertial motion, even low amplitude oscillatory visual motion induced the perception of vertical self-oscillation. When visual and vestibular stimulation were combined, self-motion perception persisted in the presence of large visual-vestibular discordances. A dynamic visual input with magnitude discrepancies tended to dominate the resulting apparent self-motion, but vestibular effects were also evident. With visual and vestibular stimulation either spatially or temporally out-of-phase with one another, the input that dominated depended on their amplitudes. High amplitude visual scene motion was almost completely dominant for the levels tested. These findings are inconsistent with self-motion perception being determined by simple weighted summation of visual and vestibular inputs and constitute evidence against sensory conflict models. They indicate that when the presented visual scene is an accurate representation of the physical test environment, it dominates over vestibular inputs in determining apparent spatial position relative to external space.

Adolescent↗
PubMed2003

Visual recognition and recall after right temporal-lobe excision in man.

A further effort was made to determine the effects of right anterior temporal lobectomy in man on visual perception and visual memory. Groups of patients with cortical resections from right or left temporal, frontal, or parietal regions were required to recognize photographs of faces within a larger array, after having been shown the faces previously. Three variations of this task were used: in the first, the interval between initial presentation and recognition test was filled with an irrelevant visual task. In the second, the delay remained but the interpolated task was omitted. In the third, there was only minimal delay ("immediate recognition"). On the first two tasks, patients with right temporal-lobe lesions had marked deficits compared with all other groups, but on the third task (minimal delay) no clearcut group differences were seen, because the normal control group did worse than with delay. Normal subjects (unlike patients with right temporal-lobe excisions) apparently use the delay period to consolidate and possibly recode their visual impressions. In the context of other tasks sensitive to right temporal-lobe lesions, the findings suggest a mild impairment in the perception of complex patterns after right anterior temporal lobectomy, and a much more severe one in the retention of the perceived material.

Adolescent↗
PubMed2004

What is common to brain activity evoked by the perception of visual and auditory filled durations? A study with MEG and EEG co-recordings.

EEG and MEG scalp data were simultaneously recorded while human participants were performing a duration discrimination task in visual and auditory modality, separately. Short durations were used ranging from 500 to 900 ms, among which participants had to discriminate a previously memorized 700-ms "standard" duration. Behavioral results show accurate but variable performance within and between participants with expected modality effects: the percentage of responses was greater and the mean response time was shorter for auditory than for visual signals. Sustained electric and magnetic activities were obtained correlatively to duration estimation, but with distinct spatiotemporal properties. Electric CNV-like potentials showed fronto-central negativity in both modalities, whereas magnetic sustained fields were distributed with respect to the modality of the interval to be timed. Time courses of these slow brain activities were found to be dependent on stimulus duration but not on its modality nor on the recording signal (EEG or MEG). Source reconstruction demonstrated that these sustained potentials/fields were generated by superimposed contributions from visual and auditory cortices (sustained sensory responses, SSR) and from prefrontal and parietal regions. By using these two complementary techniques, we thus demonstrated the involvement of frontal and parietal cerebral cortex in human timing.

Acoustic Stimulation↗