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At least 1,207 records · Page 67Linked to original sources
PubMed1997

Spatial perception during laparoscopy: implementing action-perception coupling.

Laparoscopy is a telepresence task since the surgeon has no direct contract with the patient. Performance of the surgeon will increase if his sense of telepresence is improved. This can be achieved by restoring the hampered action perception coupling. With respect to visual perception this means that the surgeon should be informed about the spatial lay-out of the environment; depth information and information about the location of observation. Both types of information can be provided by allowing the surgeon to explore. This paper describes our work on restoring the action perception coupling with respect to visual perception. It provides an overview of different technical solutions which balance between what information should be provided from an perceptual stand point and what information can be provided from a technical viewpoint.

Depth Perception↗
PubMed1999

[Basic patterns of learning disability: follow-up study of very low birth weight children].

The purpose of this study was to characterize learning disability (LD) in low birth weight children (VLBW). Longitudinal mental development of VLBW without major handicap was investigated using several neuropsychological tests (ITPA, BGT, WISC-R) suitable for their ages. The tests at ages of 5-6 years demonstrated delays in visual perception and visual motor integration. In the school-age, impairments of language understanding and abstraction were suggested. The process of mental development in VLBW with LD was reported in detail on the cases requiring special education. Some cases with a pervasive developmental disorder (PDD) were also presented to show difference from LD.

Child↗
PubMed1989

Influence of malnutrition on intellectual development.

The relationship between malnutrition and intellectual performance was studied in 1336 rural primary school children (6-8 yr). Observations showed that the relative risk of having an IQ less than or equal to 89 in severe, moderate and mild malnutrition was 3.5, 2.7 and 1.4 times for boys and in girls it was 2.4, 1.7 and 1.4 times respectively. Mean full scale, verbal and performance IQ as well as the scores for various subtests decreased with the severity of malnutrition. However, though the decrease in IQ scores was significant, below average performance of malnourished children was observed only for performance IQ (87.6 +/- 9.13), and subtests information (87.9 +/- 10.5), digit span (79.6 +/- 11.9), picture completion (88.6 +/- 13.9), object assembly (81.1 +/- 18.1), and coding (80.5 +/- 14.4). Further, the stunted children had lower IQ scores as compared to those who were wasted. Multiple regression analysis showed that besides nutrition, socio-economic status had significant influence on verbal IQ; economic sufficiency on picture completion and block design, psychosocial and family environment on vocabulary and digit span subtests. However, the values of correlations obtained were too low to be used for prediction of scores. The overall observations demonstrate that even moderate degree of malnutrition influences the IQ scores and its effect is of a higher magnitude on immediate memory, visual perception, and visual motor integration as compared to verbal reasoning and comprehension.

Child↗
PubMedDate not supplied

[Hemispheric interaction during the processing of spatial information].

As a result studying the features of single neurons of prestrial cortex (field 21) of a cat the interhemispheric differences are revealed. It is found that the sizes of receptive fields (RF) of the neurons of this region in the left hemisphere is 1.5 larger as in the right one. The RFs of the left hemisphere consist of zones (mainly 5-9) than the RFs of the right hemisphere which in turn consist of 1-4 zones. About 70% of neurons of the left hemisphere are invariant to a direction of the movement of stimulus, the similar number of the right hemisphere neurons are selective with respect to orientation of a stimulus. The study of the spatial-frequency characteristics of RTs of this region indicated that the left hemisphere neurons are tuned to more lower frequencies (0.05-0.89 cycle/grade) than neurons of the right hemisphere (0.11-3.5 cycle/grade). The study of an activity of the neurons of field 21 after commissurotomy has demonstrated that in this case the hemispheres are fully lost the possibility to receive information from contralateral semifield of the vision. The sizes of RFs are significantly less and become equal in the both hemispheres. The neurons of this region become selective to an orientation of stimulus both in the left and right hemispheres. On the basis of the results of clinical and psychophysical studies it is customary to assume that the two sides of the visual perception--concrete and abstract--to a certain extent are disintegrated between each other and are supplied chiefly by different hemispheres.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

[Interrater reliability of expert assessment by the health insurance medical service in determining eligibility for disability benefits].

In this paper, we present the first study on the inter-rater reliability of a standardised examination of functional disability, employed by the medical service of the German statutory health insurance system ("Medizinischer Dienst der Krankenversicherung", MDK). 215 elderly adults (mean age 84) living in 6 nursing homes in Munich were included in the study. They were assessed by three medical students and two nurses of the respective nursing homes using the standardised questionnaire of the MDK. Inter-rater reliability of both a summary judgement of disability and of single items, such as impairments in activities of daily living, was assessed by kappa-coefficients. Inter-rater reliability was higher for the overall assessment of disability (kappa = 0.82 between nurses, kappa = 0.57 between medical students) than for most single items. Reliability was particularly low for some items on mental status (such as "restlessness") or perceptions (particularly visual perception) which require clearer definition. This pattern was consistently observed for the two types of comparisons (inter-students, nurse-nurse) and for different subgroups of the study population.

Activities of Daily Living↗
PubMed2001

Surgeon-specific factors in the acquisition of laparoscopic surgical skills.

BACKGROUND: Training and experience vary widely among surgeons performing laparoscopic surgery (LS). Visual perceptual demands are greater for LS than for traditional surgery, necessitating greater understanding of surgeon variables in skill acquisition and performance. METHODS: During an LS skills course incorporating didactic and simulator-based instruction, 94 surgeons completed an experience/demographic questionnaire, a test of course-specific knowledge acquisition, 10 trials of three dexterity drills, 15 suturing trials using course-specific methods, and 3 standardized tests of visual perception. RESULTS: Age, years posttraining, and visual perception correlated significantly with time required to complete drills and suturing trials (Pearson correlations ranged from r = 0.21, P <0.05, to r = 0.51, P <0.001) even after statistically controlling for variations in knowledge acquisition, which correlated (r = 0.30, P <0.01) with suturing speed. CONCLUSIONS: Surgeon variables play a significant role in speed of acquisition and performance of LS skills. Further studies need to elucidate their role in quality of LS performance.

Adult↗
PubMed1979

On the limits of Fourier decompostitions in visual texture perception.

Recent discoveries of nonlinear perceptual analyzers in effortless texture discrimination cast serious doubt on the usefulness of Fourier image decompositions to describe suprathreshold visual-texture perception. We now explain the meaning of these results.

Discrimination, Psychological↗
PubMed1998

Effect of eye movements on the magnitude of functional magnetic resonance imaging responses in extrastriate cortex during visual motion perception.

We have studied the effects of pursuit eye movements on the functional magnetic resonance imaging (fMRI) responses in extrastriate visual areas during visual motion perception. Echoplanar imaging of 10-12 image planes through visual cortex was acquired in nine subjects while they viewed sequences of random-dot motion. Images obtained during stimulation periods were compared with baseline images, where subjects viewed a blank field. In a subsidiary experiment, responses to moving dots, viewed under conditions of fixation or pursuit, were compared with those evoked by static dots. Eye movements were recorded with MR-compatible electro-oculographic (EOG) electrodes. Our findings show an enhanced level of activation (as indexed by blood-oxygen level-dependent contrast) during pursuit compared with fixation in two extrastriate areas. The results support earlier findings on a motion-specific area in lateral occipitotemporal cortex (human V5). They also point to a further site of activation in a region approximately 12 mm dorsal of V5. The fMRI response in V5 during pursuit is significantly enhanced. This increased response may represent additional processing demands required for the control of eye movements.

Adult↗
PubMed2002

Deficits in auditory and visual temporal perception in schizophrenia.

INTRODUCTION: Characteristics of time perception have not been well documented in patients with schizophrenia. The current study investigated time estimation to (1) test whether visual and auditory time perception varied between patients and controls, (2) assess the degree to which patients and controls can differentiate changes in experimental intervals, and (3) explore whether the temporal deficits suggest a general time perception deficit versus modality-specific differences. METHODS: Participants were asked to decide whether temporal intervals were shorter or longer than standard intervals on computer-based auditory and visual temporal perception tasks. Data are presented for a sample of 10 patients with schizophrenia and 10 normal controls. RESULTS: Data suggest that patients with schizophrenia exhibit deficits in differentiating subtle differences in intervals in the tens of milliseconds range, compared to their normal control peers on both auditory (p < .01) and visual perception tasks (p < .01). CONCLUSIONS: Preliminary data suggest that there is a general temporal processing deficit in schizophrenia. However, future research using complementary techniques may provide useful information regarding the specific types of temporal deficits that affect patients with schizophrenia and the physiology of the dysfunction.

Journal Article↗
PubMed1996

Functional neuroanatomy of visual object naming: a PET study.

BACKGROUND: The ability to name objects depends partly on visual perception. We used positron emission tomography (PET) to measure activity-related changes in regional cerebral blood flow (r-CBF) in order to identify regions of the brain activated during visual object naming. METHODS: Four right-handed volunteers were recruited. Following an intravenous injection of 15O-labeled water, r-CBF was measured during visual object naming, counting numbers, and resting. PET and MRI images were coregistered, the size of the brain was proportionally adjusted in each axis to Talairach's and Tournoux's atlas, and the comparison of stimulated versus resting blood flow images revealed activated brain regions. RESULTS: In the subtraction of resting from naming, activation was observed in the bilateral primary visual cortex, bilateral fusiform gyrus, left lingual gyrus, bilateral inferotemporal cortex, bilateral inferior frontal gyrus, bilateral precentral gyrus, anterior cingulate gyrus, left parietal operculum, and left putamen. In the subtraction of counting from naming, most of the those areas were activated, but no significant activity was observed in the left lingual gyrus, left parietal operculum, or bilateral precentral gyrus (motor cortex). The areas activated with the paradigm included those dedicated to visual perception (primary and associate visual cortex), visual recognition (inferior temporal cortex), and phonological output (Broca's area). CONCLUSION: Our results indicated that the major neural network from occipital lobe to frontal cortex, which is mainly involved in the ventral visual pathway, demonstrated activation in these tasks. Result of this study will serve as base line data for analyzing the findings in patients with impaired visual perception.

Adult↗
PubMed2004

Phosphene threshold as a function of contrast of external visual stimuli.

Transcranial magnetic stimulation (TMS) of the occipital lobe is frequently used to induce visual percepts by direct stimulation of visual cortex. The threshold magnetic field strength necessary to elicit a visual percept is often regarded as a measure of electrical excitability of visual cortex. Using single-pulse TMS during visual motion stimulus presentation, we investigated the relationship between different degrees of visual cortical preactivation and cortical phosphene threshold (PT). The two possible, mutually exclusive, predictions on the outcome of this experiment were that a) PT increases with stronger preactivation because of a decrease in the signal-to-noise ratio, or b) that PT decreases with increased preactivation because of the increase in neuronal response towards some threshold. PTs for single-pulse stimulation of the occipital lobe were determined for eight subjects while they passively viewed a horizontally drifting luminance-modulated sinewave grating. Gratings used were of four different luminance contrasts while the spatial and temporal frequencies remained constant. PTs were shown to increase significantly as the background grating increased in contrast. These results suggest that the neural activity underlying the perception of a phosphene can be considered a type of signal that can be partially masked by another signal, in this case the visual cortical activation produced by passive viewing of drifting gratings.

Adult↗
PubMed2004

Perceiving object motion using vision and touch.

In a previous experiment, we showed that bistable visual object motion was partially disambiguated by tactile input. Here, we investigated this effect further by employing a more potent visuotactile stimulus. Monocular viewing of a tangible wire-frame sphere (TS) rotating about its vertical axis produced bistable alternations of direction. Touching the TS biased simultaneous and subsequent visual perception of motion. Both of these biases were in the direction of the tactile stimulation and, therefore, constituted facilitation or priming, as opposed to interference or adaptation. Although touching the TS biased visual perception, tactile stimulation was not able to override the ambiguous visual percept. This led to periods of sensory conflict, during which visual and tactile motion percepts were incongruent. Visual and tactile inputs can sometimes be fused to form a coherent percept of object motion but, when they are in extreme conflict, can also remain independent.

Cues↗
PubMed2003

Experience-dependent visual cue recalibration based on discrepancies between visual and haptic percepts.

We studied the hypothesis that observers can recalibrate their visual percepts when visual and haptic (touch) cues are discordant and the haptic information is judged to be reliable. Using a novel visuo-haptic virtual reality environment, we conducted a set of experiments in which subjects interacted with scenes consisting of two fronto-parallel surfaces. Subjects judged the distance between the two surfaces based on two perceptual cues: a visual stereo cue obtained when viewing the scene binocularly and a haptic cue obtained when subjects grasped the two surfaces between their thumb and index fingers. Visual and haptic cues regarding the scene were manipulated independently so that they could either be consistent or inconsistent. Experiment 1 explored the effect of visuo-haptic inconsistencies on depth-from-stereo estimates. Our findings suggest that when stereo and haptic cues are inconsistent, subjects recalibrate their interpretations of the visual stereo cue so that depth-from-stereo percepts are in greater agreement with depth-from-haptic percepts. In Experiment 2 the visuo-haptic discrepancy took a different form when the two surfaces were near the subject than when they were far from the subject. The results indicate that subjects recalibrated their interpretations of the stereo cue in a context-sensitive manner that depended on viewing distance, thereby making them more consistent with depth-from-haptic estimates at all viewing distances. Together these findings suggest that observers' visual and haptic percepts are tightly coupled in the sense that haptic percepts provide a standard to which visual percepts can be recalibrated when the visual percepts are deemed to be erroneous.

Adolescent↗
PubMed1995

Dissociation between two modes of spatial processing by a visual form agnosic.

We report a dissociation between two aspects of visuospatial processing in a patient with a profound impairment in the visual perception of objects ('visual form agnosia'). The orientation-in-depth of a visual field ('visual pitch') was found to systematically influence the elevation at which she perceived her own eye level, just as it does in normal individuals; but at the same time, she was unable to discriminate perceptually the orientation-in-depth of the same visual field, a trivial task for individuals with normal vision. These results suggest that, in the normal brain, the processes that integrate orientation information from the visual field with extraretinal information about eye position are separable from those supporting the perception of the orientation of the visual field itself. The pattern of brain damage in D.F., in conjunction with the reported dissociation, suggests that the former set of processes maps onto the stream of information flowing from primary visual cortex to the posterior parietal cortex, the so-called dorsal stream, whereas the latter involves the projections from primary visual cortex to the inferotemporal cortex, the so-called ventral stream.

Adult↗
PubMed2005

Changes in visual motion perception before saccadic eye movements.

Execution of a saccadic eye movement influences subsequent motion perception [Park, J., Lee, J., & Lee, C. (2001). Non-veridical visual motion perception immediately after saccades. Vision Research, 41, 3751-3761]. In the current study, we determined the pattern of perceptual changes for visual motion presented before saccades. The accuracy of judging the direction of a moving target was variable depending on the direction of target motion. Based on the pattern of judgment errors, the direction associated with no error, or DNE, could be defined. When a moving target was seen by stationary eyes, the DNE was roughly vertical, and the perceptual judgment for adjacent directions was biased away from the vertical direction. When the same visual motion was seen before horizontal saccades, the DNE shifted in the direction of the impending saccade, and the perceptual judgment of adjacent directions was shifted away from the new DNE, thus, shifting the perceived direction of the vertical in the direction opposite to the saccade. These changes improved the accuracy of direction judgment for visual motion in the visual field ipsiversive to impending saccades. In addition to shift of the DNE, perceptual judgment for oblique directions became near veridical before saccades, which we call the anti-oblique effect. These results suggest that motion perception is dynamically and anisotropically modulated at the time of saccades, and the DNE shift may be a part of processes dynamically reallocating computational resources, improving perceptual performance in advance for sensory events to be acquired by impending saccades.

Adult↗
PubMed2001

Heading and path percepts from visual flow and eye pursuit signals.

The percept of self-motion through the environment is supported by visual motion signals and eye movement signals. The interaction between these signals by decoupling of the eye movement and the pattern of retinal motion during brief simulated ego-movement on straight or circular trajectories was studied. A new response method enabled subjects to report perceived destination and perceived curvature of their future path simultaneously. Various combinations of simulated gaze rotation in the retinal flow and eye pursuit were investigated. Simulated gaze rotation ranged from consistent and larger than, to opponent and larger than eye pursuit. It was found that the perceived destination shifts non-linearly with the mismatch between simulated gaze rotation and eye pursuit. The non-linearity is also revealed in the perceived tangent heading direction and perceived path curvature, although to different extent in different subjects. For the same retinal flow, eye pursuit that is consistent with the simulated gaze rotation reduces heading error and the perceived path straightens out. In contrast, perceived path and/or heading do not become more curved or more biased in the direction opposite to pursuit when the eye -in-head rotation is opposite to the simulated gaze rotation. These observations point to modulation of the effect of the extra-retinal pursuit signal by the visual evidence for eye rotation. In a second experiment, one presented to a stationary eye the sum of a component of simulated gaze rotation and radial flow. It was found that the bi-circular flow component, that characterizes the change in pattern of flow directions by the gaze rotation, induces a shift of perceived heading without appreciable perceived path curvature. Conversely, the complementary component of simulated gaze rotation (bi-radial flow) evokes a percept of motion on a curved path with a small tangent heading error. It was suggested that bi-circular and bi-radial flow components contribute primarily to percepts of heading and path curvature, respectively.

Humans↗
PubMed2002

Visual illusion induced by sound.

We present the first cross-modal modification of visual perception which involves a phenomenological change in the quality-as opposed to a small, gradual, or quantitative change-of the percept of a non-ambiguous visual stimulus. We report a visual illusion which is induced by sound: when a single flash of light is accompanied by multiple auditory beeps, the single flash is perceived as multiple flashes. We present two experiments as well as several observations which establish that this alteration of the visual percept is due to cross-modal perceptual interactions as opposed to cognitive, attentional, or other origins. The results of the second experiment also reveal that the temporal window of these audio-visual interactions is approximately 100 ms.

Acoustic Stimulation↗