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At least 55 records · Page 3Linked to original sources
PubMed1990

Visual perception and the guidance of locomotion without vision to previously seen targets.

Two experiments were performed to assess the accuracy and precision with which adults perceive absolute egocentric distances to visible targets and coordinate their actions with them when walking without vision. In experiment 1 subjects stood in a large open field and attempted to judge the midpoint of self-to-target distances of between 4 and 24 m. In experiment 2 both highly practiced and unpracticed subjects stood in the same open field, viewed the same targets, and attempted to walk to them without vision or other environmental feedback under three conditions designed to assess the effects on accuracy of time-based memory decay and of walking at an unusually rapid pace. In experiment 1 the visual judgments were quite accurate and showed no systematic constant error. The small variable errors were linearly related to target distance. In experiment 2 the briskly paced walks were accurate, showing no systematic constant error, and the small, variable errors were a linear function of target distance and averaged about 8% of the target distance. Unlike Thomson's (1983) findings, there was not an abrupt increase in variable error at around 9 m, and no significant time-based effects were observed. The results demonstrate the accuracy of people's visual perception of absolute egocentric distances out to 24 m under open field conditions. The accuracy of people's walking without vision to previously seen targets shows that efferent and proprioceptive information about locomotion is closely calibrated to visually perceived distance. Sensitivity to the correlation of optical flow with efferent/proprioceptive information while walking with vision may provide the basis for this calibration when walking without vision.

Adult↗
PubMed1979

Auditory-visual perception of speech with reduced optical clarity.

Optical cues for visual and auditory-visual (A-V) perception of speech were varied by placing a sheet of rough-surfaced Plexiglas between talker and lipreader and systematically changing the distance between Plexiglas and talker. This distorts the optical environment in a way that is analogous to masking or filtering in the acoustic domain. In studies with normal-hearing adults and with hearing-impaired children, speech (words, sentences) was presented live under different degrees of optical distortion, and observers attempted to identify the stimuli. Visual-along (lipreading) scores dropped abruptly to the chance level as Plexiglas distance (blurring) was increased. A-V scores were relatively high for clear conditions but diminished gradually as Plexiglas distance (blurring) was increased. Under extremely poor optical conditions, A-V scores reached a plateau. This represents essentially auditory perception without meaningful optical cues for speech. Results parallel those of previous acoustic studies that compared auditory with A-V perception of speech as a function of S/N ratio or sensation level, demonstrating a reciprocal aspect of optical and acoustic cues for speech perception. Optical distortion seems to have potential as an auditory training technique to shift attention of hearing-impaired observers to non-dominant acoustic cues during A-V perception of speech.

Adolescent↗
PubMed1978

[Interhemispheric relations in the process of visual perception in schizophrenic patients].

The purpose of the performed study was to compare the time of visual stimuli perception for different hemispheres in normals and in schizophrenic patients. In normals there was a certain asymmetry in the speed of perception of letter stimuli between the right and left hemispheres. It was established, that in the right hemisphere there was a more rapid perception of the letters as compared to the left one. In schizophrenic patients there is no interhemispheric differences in the time of perception, owing to the fact that the right hemisphere loses the advantage in speed of processing visual information. The author makes an assumption of the possible role of disturbed activity of the right hemisphere in the psychopathological symptomatology.

Adolescent↗
PubMed1979

Relativistic effects in visual perception of real and apparent motion.

Timing in the visual field is regarded as an additive conjoint measurement structure, psychophysical extension of stimulus path as an extensive measurement structure. These two sets of postulates lead to the derivation of an essential maximum for velocity perception. Apparent phi motion perception under strictly stationary stimulus conditions is described as relative motion of the first stimulus' psychophysical mapping with respect to a moving perceptual subsystem. The essential maximum of velocity modifies the relative motion postulate: relativistic dilatation of seen length of path is predicted. Testable properties of the model, comparison with experimental data from "real" motion and apparent phi motion perception are discussed.

Humans↗
PubMed1977

Pattern evoked average EEG potentials and dichoptic visual percepts.

Monocular xenon flashes were used to evoke average EEG potentials while blank, dot or grid targets were shown simmultaneously in ten dichoptic stimulus conditions, either continuously illuminated (added to the flashes, or contraocularly), or presented only by the flashes. Mean evoked-EEG-potential waveforms over repeated conditions were computed from average evoked potentials (EPs) for each stimulus condition and each hemisphere. Correlation coefficients were computed between mena-EP waveforms of all stimulus condition for each subject. Mean correlation coefficients over subjects were treated in a cluster analysis to diagnose conditions associated with similar EP waveforms. Data from the two hemispheres yielded identical cluster results. Presence or absence of continuous target illumination for the flashed eye was the most powerful descriptor. Next important was continuously visible structure (regardless whether seen by the flashed or the nonflashed eye) in conditions with continuous illumination seen by the flashed eye, and flashed structure in conditions without continuous illumination for the flashed eye. It was concluded that a visual percept which enters the processor as non-EP-evoking information nevertheless is reflected by the EP waveform. However, the waveforms are different if the flashes carry the perceptual information exclusively. More powerful than visual structure is the mode of flash presentation (with or withoug continuous target illumination) for the EP waveform.

Adult↗
PubMed1978

Op art and visual perception.

An attempt is made to list the visual phenomena exploited in op art. These include moire frinlude moiré fringes, afterimages, Hermann grid effects, Gestalt grouping principles, blurring and movement due to astigmatic fluctuations in accommodation, scintillation and streaming possibly due to eye movements, and visual persistence. The historical origins of these phenomena are also noted.

Afterimage↗
PubMed1976

The visual perception of accelerated motion.

The present research is an investigation of how changes in the rate of motion are percieved. Five separate experiments were performed with the use of filmed stimulus material and a variety of response measures, including both categorical judgments and reporduction techniques. It was found that (a) the smaller the ratio of terminal to initial velocity, the less frequent the judgments of acceleration or deceleration, (b) deceleration was significantly easier to perceive than acceleration, (c) the perception of acceleration was facilitated when the velocity of a lead-in segment was the same as the velocity at onset of motion, (d) a short tunnel centered in the motion path facilitated the perception of acceleration and deceleration, and (e) instantaneous changes in velocity were much more easily perceived than gradual changes. A one-event model for the perception of motion change in which there is a continuous interplay between earlier, later, and interpolated motion segments is favored over a two-event model in which earlier and later segments of velocity are compared.

Acceleration↗
PubMed1978

Functional representations common to visual perception and imagination.

Subjects determined whether probe dots appearing in component squares of a 5 X 5 grid fell on a figure that, depending on the condition, was (a) visually presented as a pattern of darkened squares, (b) only remembered from a preceding presentation of such a pattern, or (c) imaginally generated from a verbal code. The speed and accuracy of the responses to the probes as well as the functional dependencies of the reaction times on structural variables were essentially the same whether the figural pattern was imagined, remembered, or actually seen. Reaction times averaged between 400 and 500 msec and were consistently faster (a) for on-figure than for off-figure responses, (b) for simpler figures that had fewer squares, (c) for off-figure probes that were more distant from the figure, and (d) for on-figure probes that consisted either of more dots on the figure or of a dot at the intersection of a horizontal and a vertical bar. The reults were consistent with a model in which a subject's perceptual or imaginal representations of these forms contain barlike units that respond independently to the probes.

Discrimination, Psychological↗
PubMed1979

Aspects of visual perception in radiography.

The author has presented experimental results to validate the hypothesis that visual search techniques are related to the practice of radiography. A group of radiographers raised their performance on a film-viewing task from 56%-76% as a consequence of visual search practice and it is suggested that this is important to radiographers undertaking quality control, evaluation of imaging systems and pattern recognition. The final part of the paper considers the need to match the visual abilities of prospective students with the job requirements. Two simple tools are described.

Personnel Selection↗
PubMed1977

The development in very young children of tacit knowledge concerning visual perception.

The purpose of this study of early social-cognitive development was to assess the very young child's behaviorally expressed knowledge of people's visual-attentional acts and abilities. Boys and girls (N = 60) 1, 1 1/2, 2, 2 1/2, and 3 years of age were tested in their homes with their mother's help. Three sorts of tasks were used: 1. Percept production. The child's task was to produce a visual percept in the other. Examples include pointing to objects ("productive pointing") and a wide variety of object-showing problems. 2. Percept deprivation. The opposite, exemplified by a variety of object-hiding problems. 3. Percept diagnosis. The child's task was to determine what the other was already visually attending to, either by looking where his or her finger was pointed ("receptive pointing") or where his eyes were directed. It was found that the majority of 1-year-olds produced and comprehended pointing, and would sometimes hold out a toy to show it, but did little else. The 3-year-olds were at ceiling on virtually all tasks. At 1 1/2 years, children usually showed a picture by holding it flat so that both they and the other could see it. Jrom 2 on, they usually turned it toward the other in the adult fashion. Very few children of any age showed egocentrically--i.e., orienting the picture so only they could see it. By age 2, the children solved what were presumably novel showing problems for them: e.g., successfully showing to another a picture pasted on the inside bottom of a hollow cube. Hiding ability emerged later than showing ability but seemed well established by age 3. The role of the other's eyes in seeing appeared to be quite well understood at least by age 2-2 1/2. As examples, children of this age took the other's hands away from her or his eyes before trying to show her something, and could usually tell where she was looking from her eye orientation alone. These age trends presumably reflect important developments in the area of social interaction and communication, as well as with respect to cognition about percepts.

Age Factors↗