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Illumination, both natural and artificial, typically comes from above. Neurons in visual area V4--part of the object-processing pathway in the primate brain--may rely on this anisotropy to infer three-dimensional structure from shading cues.
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.
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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.
We examined the effects of the gravitational vertical on the perception of reversible figures. Each reversible figure had two interpretations depending on whether it was viewed vertically in one orientation or upside down. When it was presented horizontally, the two interpretations alternated. Subjects were required to indicate which interpretation was perceived after briefly viewing the horizontal presentation on a head-mounted display. When the subject was upright, each interpretation occurred by chance. When the subject was lying on one side, the horizontal figure was generally perceived as if it was presented vertically with the side down. The results suggest that the perception of reversible figures is influenced by the gravitational vertical, which might be reconstructed by multimodal integration of vestibular, proprioceptive, and tactile inputs.
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Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
1. We studied the effects of midazolam (MDZ), a benzodiazepine, on spatio-temporal contrast sensitivity, choice reaction time, and mood visual analogue scales in healthy volunteers. 2. Eight extensively trained, healthy volunteers were included in a placebo-controlled cross-over double-blind trial of MDZ (0.15 mg kg-1). Treatments were injected intramuscularly and evaluations were performed before and 0.5, 1, 2, 3 and 4 h after drug administration. Spatio-temporal contrast sensitivity was measured using a micro-computer with appropriate software. Stimuli were vertical gratings with adjustable contrast, with spatial frequencies of 0.25, 1 and 4 cpd. Four conditions of temporal modulation were used: the grating was either static or drifting laterally with temporal frequencies of 1, 3 and 9 Hz. 3. An analysis of variance was performed on the data. As compared with placebo, MDZ induced an increase in choice reaction time and sedation (as assessed on visual analogue scales). From 0.5-4 h after the injection, MDZ produced an overall decrease in visual sensitivity, as compared with placebo. More specifically, MDZ preferentially affected medium to high spatial frequencies and low temporal frequencies. Several non-exclusive hypotheses may account for the results: 1) an increase in the size of the receptive fields, 2) a preferential effect on the visual parvocellular pathways which mediate the sensitivity to high spatial and low temporal frequencies.
We studied 12 patients with static cortical blindness to evaluate residual vision after destruction of area 17 and to assess the visual capacity of the subcortical "second" visual system in humans. In each case, the cause was bilateral infarction of the occipital lobes. Five patients had total blindness, and four had residual rudimentary vision (RRV), characterized by homonymous areas of light perception in the peripheral field and ability to detect moving objects. Only three patients had the ability to read; two of these had spared macular vision, and the other had spared left homonymous hemimaculae and spared temporal crescent. Neuroimaging and visual evoked potentials (VEPs) correlated with the extent of the visual dysfunction. Total destruction of area 17 bilaterally was associated with total permanent visual loss. The larger the amount of spared visual cortex, the better the vision. Positron emission tomography (PET) or single photon emission computed tomography (SPECT) demonstrated retained metabolic activity in islands of preserved area 17 in patients with some residual vision. VEPs were present in totally blind individuals. We conclude that, in humans, useful visual function is preserved only when a critical amount of area 17 is spared. The subcortical second system may participate in the generation of VEPs, but is incapable of conscious visual perception.
Does mental imagery involve the activation of representations in the visual system? Systematic effects of imagery on visual signal detection performance have been used to argue that imagery and the perceptual processing of stimuli interact at some common locus of activity (Farah, 1985). However, such a result is neutral with respect to the question of whether the interaction occurs during modality-specific visual processing of the stimulus. If imagery affects stimulus processing at early, modality-specific stages of stimulus representation, this implies that the shared stimulus representations are visual, whereas if imagery affects stimulus processing only at later, amodal stages of stimulus representation, this implies that imagery involves more abstract, postvisual stimulus representations. To distinguish between these two possibilities, we repeated the earlier imagery-perception interaction experiment while recording event-related potentials (ERPs) to stimuli from 16 scalp electrodes. By observing the time course and scalp distribution of the effect of imagery on the ERP to stimuli, we can put constraints on the locus of the shared representations for imagery and perception. An effect of imagery was seen within 200 ms following stimulus presentation, at the latency of the first negative component of the visual ERP, localized at the occipital and posterior temporal regions of the scalp, that is, directly over visual cortex. This finding provides support for the claim that mental images interact with percepts in the visual system proper and hence that mental images are themselves visual representations.
On the basis of visual assessment of figure drawings and front/profile images, past researchers believed that the waist-hip ratio (WHR) and the body mass index (BMI) were two putative cues to female physical attractiveness. However, this view was not tested on three-dimensional (3D) female images. In the present study, 3D images of 31 Caucasian females having varying body weights (BMI ranged from 16 to 35) were shown to 29 male and 25 female viewers, who were asked to rate the physical attractiveness. The results showed that the body volume divided by the square of the height, defined as volume height index (VHI), is the most important and direct visual determinant of female physical attractiveness. In determining the female attractiveness, human observers may first use VHI as a visual cue, which is also a key indicator of health and fertility owing to its strong linear relation to BMI. To fine-tune the judgement, observers may then use body proportions, the most important of which are the ratio of waist height over the chin height (WHC) (a measure of the length of legs over total tallness) and the deviation of WHR from the ideal ratio. It also appears that the effect of the body's physical parameters on the perception of female physical attractiveness conforms to Stevens' power law of psychophysics.