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At least 865 records · Page 48Linked to original sources

PubMed2006

Gamma amplitudes are coupled to theta phase in human EEG during visual perception.

Human subjects typically keep about seven items (plus or minus two) in short-term memory (STM). A theoretical neuronal model has been proposed to explain this phenomenon with physiological parameters of brain oscillations in the gamma and theta frequency range, i.e., roughly 30-80 and 4-8 Hz, respectively. In that model, STM capacity equals the number of gamma cycles (e.g., 25 ms for 40 Hz), which fit into one theta cycle (e.g., 166 ms for 6 Hz). The model is based on two assumptions: (1) theta activity should modulate gamma activity; and (2) the theta/gamma ratio should correlate with human STM capacity. The first assumption is supported by electrophysiological data showing that the amplitude of gamma oscillations is modulated by the phase of theta activity. However, so far, this has only been demonstrated for intracranial recordings. We analyzed human event-related EEG oscillations recorded in a memory experiment in which 13 subjects perceived known and unknown visual stimuli. The paradigm revealed event-related oscillations in the gamma range, which depended significantly on the phase of simultaneous theta activity. Our data are the first scalp-recorded human EEG recordings revealing a relationship between the gamma amplitude and the phase of theta oscillations, supporting the first assumption of the above-mentioned theory. Interestingly, the involved frequencies revealed a 7:1 ratio. However, this ratio does not necessarily determine human STM capacity. Since such a correlation was not explicitly tested in our paradigm, our data are not conclusive about the second assumption. Instead of theta phase modulating gamma amplitude, it is also conceivable that focal gamma activity needs to be downsampled to theta activity, before it can interact with more distant brain regions.

Adult↗

PubMed2001

Hemispheric asymmetries for global and local visual perception: effects of stimulus and task factors.

Although neurotogical and physiological studies indicate a right hemisphere superiority in global processing and a left hemisphere superiority in local processing of Navon-type hierarchical letters (D. Navon, 1977), most investigations of lateralized perception in healthy participants report neither asymmetry. In 6 experiments the authors examined the influence of attentional demands, stimulus properties, and mode of response on perceptual asymmetries for global and local perception. Consistent with their theoretical predictions, asymmetries were more robust on divided- than focused-attention tasks and in response to stimuli in which local and global levels were equally salient compared with those with greater global than local saliency. Contrary to their prediction, perceptual asymmetries were not influenced by the complexity of the motor response.

Adolescent↗

PubMed1975

The function of shifting fixations in the visual perception of infants.

The processes underlying infants' shifts of fixation from 1 stimulus to another were explored in 3 studies. The results suggest that infants 3 months and older shift more when the 2 stimuli of a pair are similar than when they are different. Shifting is affected by stimulus repetition as well. There were age differences in the number of shifts per trial, with older infants shifting more. The possibility that shifting may facilitate stimulus recognition is discussed.

Age Factors↗

PubMed2003

Visual perception in a blind subject with a chronic microelectronic retinal prosthesis.

A retinal prosthesis was permanently implanted in the eye of a completely blind test subject. This report details the results from the first 10 weeks of testing with the implant subject. The implanted device included an extraocular case to hold electronics, an intraocular electrode array (platinum disks, 4 x 4 arrangement) designed to interface with the retina, and a cable to connect the electronics case to the electrode array. The subject was able to see perceptions of light (spots) on all 16 electrodes of the array. In addition, the subject was able to use a camera to detect the presence or absence of ambient light, to detect motion, and to recognize simple shapes.

Aged↗

PubMed1978

Dimensions of visual perceptions of clothing.

The relation of two descriptive properties of clothing, "complexity" and "fashionability," with evaluative preference responses of "like" and "would-like-to-own" was explored for two selected groups of untrained females who differed in age. The students agreed more than the older women on the judged "fashionability" of 10 photographs of clothing and also were influenced more by "fashionability" in their responses of "like" and "would-like-to-own." For both groups "complexity" was judged consistently but was not highly related to preferences.

Adult↗

PubMed2005

The visual perception coordinate system uses axes defined by the earth, trunk, and vision.

Eight young adults adjusted a line located on one side of a computer display parallel to internally specified Earth-fixed vertical (display in frontal plane), to the horizontal trunk-fixed anterior-posterior axis (display in horizontal plane), and to an oblique line (display in horizontal and vertical planes). All tasks were completed in a dark room with the head and trunk in both a standard erect posture and varied postures. Errors were lowest when setting the line to internally specified vertical in the frontal plane and to an oblique line in the horizontal plane when head and trunk orientations were varied. Constant errors for setting one line parallel to a second line were in opposite directions when the second line was located on the left versus right side of the display, but did not differ in direction when setting the line parallel to internally specified axes. Also, the oblique effect was preserved when the head and trunk were tilted to various orientations, suggesting that it results from integration of an internally specified gravitational reference with visual input. We conclude that the visual perceptual coordinate system uses internally specified vertical and, when available, a visually specified horizontal reference axis to define object orientation.

Adult↗

PubMed1986

Improving visual perception in older observers.

Younger observers (M = 21 years) proved to be better than older observers (M = 68 years) at discriminating one direction of motion from another, highly similar one. Several days' practice steadily improved performance for both groups equally. Improvement was well restricted to the direction with which that observer practiced, and the full gains were retained for at least 1 month. Control measurements with various degrees of optical blur demonstrate that direction discrimination does not require a well-focussed retinal image. This rules out optical factors as the potential cause of the prepractice differences between groups.

Adult↗

PubMed1995

Individual assessment of visual perception by surgeons observing the same laparoscopic organs with various imaging systems.

Laparoscopic surgery necessitates that operations be performed via a television screen; therefore, image quality is crucial in determining the final outcome. Electronic imaging systems are constantly undergoing revisions and incorporating new ideas. Recently, we have been confronted with a variety of systems, and we, as operators, have no idea what the differences are between the old and the newer systems. As clinicians, we have no electronic yardstick available to compare the options presented or to check the specifications. This study examines critical aspects of image perception. General surgeons, gynecologists, operating-room nurses, as well as allied health personnel all experienced in laparoscopic surgery participated as test subjects. A blinded study was performed in which various camera systems (single chip, three-chip, digitized and nondigitized) were displayed in random fashion. Porcine abdominal areas were displayed using the various imaging units. Participants graded image perception based on the following characteristics: sharpness, color, contrast, and depth of field. The audience were blinded to the types, brand, and number of cameras utilized. A significant preference was shown for digitized systems (P < 0.0001). Also, digitized single-chip cameras scored higher than three-chip cameras (P < 0.05). We propose thorough testing by surgeons and nursing personnel before deciding what type of equipment to purchase.

Allied Health Personnel↗

PubMed1978

Visuo-motor skill and visual perception in left and right handed children of superior intelligence.

It was thought possible that the proximity of the right parietal cortex to the leading hand area in left handed subjects may confer an advantage in tasks requiring visuo-motor function. However, the study showed the left handed group to be defective in the performance of the Wechsler Block-design Sub-test. As some mature left handed individuals may excel in tasks requiring refined visuo-motor skill, it is suggested that any constitutional deficiency is not fixed, but may be expected to disappear with increased maturity, or as the result of training.

Child↗

PubMed1989

Visual perception and learning: issues and answers.

The role of the optometrist in treating children who are identified as learning disabled is not always understood by members of an interdisciplinary team. It is the purpose of this paper to develop a brief philosophical foundation for optometric intervention and to review some of the literature which supports the validity of optometric therapy. Correlational studies are cited to establish a basic relationship between perceptual dysfunctions and learning readiness in normal children. After establishing that perceptual training does indeed improve perceptual skills, we cite a number of investigations where intervention enabled children who had been classified as learning disabled to respond more effectively to school learning. The role of the optometrist as a member of an interdisciplinary team is addressed.

Humans↗

PubMed1988

A model for the visual perception of direction.

An attempt is made to explain how the eyes can be moved with respect to the head and the observer can still assess the direction of an object in space fixed with respect to the head. My explanation is based on the assumption that the subject is made aware of the direction in which the eyes are pointing by the output from the brain center controlling the direction of fixation. He associates this signal with an awareness of "looking in a certain direction." The image falling on a certain point of the retina (usually near the center of the fovea), which I call the anchor point, is perceived as lying in the direction in which he "perceives himself to be looking." The directions of other objects are judged relative to the object that forms its image on the anchor point.

Humans↗

PubMed2003

Internal models for visual perception.

Although the extrapolation of past perceptual history into the immediate and distant future is a fundamental phenomenon in everyday life, the underlying processing mechanisms are not well understood. A network model consisting of interacting excitatory and inhibitory cell populations coding for stimulus position is used to study the neuronal population response to a continuously moving stimulus. An adaptation mechanism is proposed that offers the possibility to control and modulate motion-induced extrapolation without changing the spatial interaction structure within the network. Using an occluder paradigm, functional advantages of an internally generated model of a moving stimulus are discussed. It is shown that the integration of such a model in processing leads to a faster and more reliable recognition of the input stream and allows for object permanence following occlusion. The modeling results are discussed in relation to recent experimental findings that show motion-induced extrapolation.

Neural Networks, Computer↗

PubMed1975

The effects of hydrocephalus on intelligence, visual perception and school attainment.

A group of 59 children with spina bifida, and a group of matched controls, were given detailed psychological and educational tests at five and seven years. The scores of the control group were similar to the national figures. The scores of the children with spina bifida only (without hydrocephalus) were closest to normal, but still below average. Those with spontaneously arrested hydrocephalus were in the backward range of abilities, and those with shunt-treated hydrocephalus had scores which generally were incompatible with normal levels of intelligence and attainment. Abnormal visuo-perceptual functioning closely correlated with defects in intelligence. The results of the school-attainment tests paralleled the distribution of intelligence but many of the children were found to be functioning below expectation for both age and measured intelligence.

Attention↗

PubMed1988

Enhancement of visual perception under conditions of short-term exposure to sensory isolation: a comparison of procedures for altering vigilance.

An experiment was conducted to determine the pre- and posttest performance of subjects on a signal-detection task for the following three experimental conditions: sensory isolation, sensory alertness, and sensory relaxation. All subjects were assessed on 36 pretest and 36 posttest trials. Each block of 36 trials consisted of 12 "strong signals," 12 "weak signals," and 12 "no signals." Exposure durations for each experimental condition lasted for one hour. Analyses showed significant improvements in hits from the pretest trials to the posttest trials on the "strong" and "weak signals" for the sensory isolation condition. Moreover, on the posttest "weak signal" trials, subjects in the sensory isolation condition scored a significantly greater number of hits than did those in the sensory alertness or sensory relaxation conditions. It was concluded that sensory isolation produces perceptual enhancement, as measured by a signal-detection task.

Arousal↗

PubMed1977

Heart rate and cardiac phase influences on visual perception.

Twenty-six subjects were tested with a tachistoscopic recognition task while heart rate and several other autonomic indexes were monitored. In Experiment 1, heart rate was employed as an independent variable, and stimulus presentation was contingent upon the presence of individually determined low, middle, and high heart rates. The results indicated that low heart rate facilitated performance especially for stimuli presented at the fastest exposure. In Experiment 2, stimulus presentation was dependent upon cardiac phase. The findings indicated that stimulus recognition was enhanced during the cardiac P wave, but the effect was apparent only during the fastest exposure. Multiple regression analyses of the individual subject's data during both experiments indicated that highly idiosyncratic patterns of physiological responses predicted perceptual performance. The results were interpreted as being consistent with the formulations of the Laceys and also suggested that cerebral perfusion be considered as a relevant determinant of behavior.

Adult↗

PubMed1992

Paradoxical effects of mild hypoxia and moderate altitude on human visual perception.

1. Prolonged (> 10 h) exposure to hypoxia and high altitude (> 5000 m) invariably have detrimental effects on cognitive performance. Paradoxically, mild improvements in cognitive function in patients with chronic obstructive pulmonary disease after cessation of oxygen therapy have been reported. 2. We studied in each of 10 healthy subjects the effect of an acute altitude challenge [rapid helicopter transport to the Jungfraujoch (3450 m), experiment 1] and of an acute exposure to mild hypoxia (fractional inspiratory oxygen concentration 14.5% experiment 2) on a simple test of cognitive performance (the time needed to read briefly displayed letters). 3. Under both hypoxic conditions the time needed to read briefly presented letters decreased, from 12.1 +/- SD 3.8 ms to 8.3 +/- 1.5 ms (P < 0.01) in experiment 1, and from 11.9 +/- 1.9 ms to 8.1 +/- 1.1 ms (P < 0.01) in experiment 2. 4. A rapid and mild hypoxic challenge seems to improve a simple measure of cognitive performance above normal values. The common notion that exposure to hypoxia and altitude invariably impairs cognitive performance may have to be re-evaluated.

Adult↗

PubMed1976

Visual perception of rigidity of solid shape.

Organisms react to objective properties of bodies in their visual field instead of to the perpetually changing retinal images of those bodies. We show how such a faculty can be mechanized. The organism synthesizes an internal model of the external object, that is a bundle of expectations of how the visual input will transform in response to the organism's exploratory movements. We deduce the necessary structure of the internal model and we show how the organism can extract this structure from the invariant features of the sensory input transformations. With this internal model it is possible to predict the subsequent aspects (contours) of the visual object as the spatial relations of organism and object change.

Form Perception↗

PubMed1997

Muscle power, dexterity skill and visual perception in community home girls trained in yoga or sports and in regular school girls.

The present study was conducted to compare critical flicker fusion frequency (CFF), degree of optical illusion ("di"), dexterity scores, and grip strength in three groups of subjects, viz community home girls who had learned yoga for 6 months (CHY), age-matched community home girls who had physical activity training for 6 months (CHP), and girls who were attending a regular school (SCH). There were equal numbers in each group for each of the 4 assessment (range 11 to 30 subjects) and age range was 12 to 16 years of age. The CHP group had significantly lower CFF and "di" was significantly higher (one factor ANOVA, t test for unpaired data) in the CHP group, both compared to CHY and SCH groups. Right hand grip strength was also significantly less in the CHP group compared to SCH. The results were explained by previous reports of high levels of anxiety and aggression in community-home groups, which is known to influence the four parameters described here. The better performance of the CHY group compared to CHP, suggested that yoga practice has a beneficial effect in these subjects.

Adolescent↗