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At least 1,045 records · Page 58Linked to original sources
PubMed1989

Selective spatial attention and length representation in normal subjects and in patients with unilateral spatial neglect.

The aim of this study was to assess whether perceptual representation along the horizontal axis is affected by hemispace position of the stimulus or by orienting attention to one side. Ten control subjects and 10 right brain damaged patients with left unilateral spatial neglect (USN) were asked to bisect lines of five lengths in three space positions (left, center, right) and under three cueing conditions (no cue, left cue, right cue). Normal controls showed significant displacement of bisection opposite to the side of hemispace presentation and toward the side of cueing. USN patients showed a bisection error toward the right end which increased with lines placed in the left hemispace and decreased with lines placed in the right hemispace and when attention was oriented toward the left side. We conclude that (1) In absence of cues normal subjects tend to overestimate the portions of space closer to their body midline; (2) both normal and USN patients tend to overestimate portions of space that they direct their attention to; (3) USN patients' performance without cueing is consistent with an attentional shift toward the right hemispace implying a gradient of overestimation of the right-most portions of space. A common neural substratum for directing attention and space representation can explain these findings.

Aged↗
PubMed1992

Beyond the search surface: visual search and attentional engagement.

Treisman (1991) described a series of visual search studies testing feature integration theory against an alternative (Duncan & Humphreys, 1989) in which feature and conjunction search are basically similar. Here the latter account is noted to have 2 distinct levels: (a) a summary of search findings in terms of stimulus similarities, and (b) a theory of how visual attention is brought to bear on relevant objects. Working at the 1st level, Treisman found that even when similarities were calibrated and controlled, conjunction search was much harder than feature search. The theory, however, can only really be tested at the 2nd level, because the 1st is an approximation. An account of the findings is developed at the 2nd level, based on the 2 processes of input-template matching and spreading suppression. New data show that, when both of these factors are controlled, feature and conjunction search are equally difficult. Possibilities for unification of the alternative views are considered.

Arousal↗
PubMed1994

Intact visual imagery and impaired visual perception in a patient with visual agnosia.

Although it is now well accepted that visual mental imagery and visual perception share common underlying mechanisms, there are several reports in which they are dissociated. Evidence for the separability of these processes is provided by a patient, C.K., who has a profound visual object recognition deficit attributable to an impairment in grouping or segmenting visual images. Despite this perceptual deficit, C.K. was able to draw objects in considerable detail from memory, and his knowledge of the visual appearance of objects was preserved on a variety of mental imagery tasks. Together with previous cases, these findings confirm the double dissociation between object recognition and perception. Interestingly, C.K. could also recognize newly constructed objects in his internal imagery. To accommodate these results, we propose a model in which imagery and perception are strongly associated but are also functionally specialized.

Adult↗
PubMed1992

Looking at pictures but remembering scenes.

Ss tend to remember close-up photographs as having had extended boundaries (Intraub & Richardson, 1989). Three alternate explanations were tested: object completion, distortion toward a perceptual schema, and normalization toward a prototypic view. In three experiments, 55-130 undergraduates viewed 16 close-up, prototypic, or wide-angle views of objects for 15 s each. Immediately or 48 hr later, they rated test pictures on a 5-point scale as "same", "closer up", or "father away." Results ruled out object completion because boundary extension occurred when the picture contained no incomplete objects. Immediate tests supported the perceptual schema hypothesis because all unidirectional distortions involved boundary extension. Delayed tests were more suggestive of a memory schema effect because wide-angle pictures yielded boundary restriction. A two-component model of picture processing is proposed.

Adult↗
PubMed2006

Looking at perspective pictures from too far, too close, and just right.

A central problem for psychology is vision's reaction to perspective. In the present studies, observers looked at perspective pictures projected by square tiles on a ground plane. They judged the tile dimensions while positioned at the correct distance, farther or nearer. In some pictures, many tiles appeared too short to be squares, many too long, and many just right. The judgments were strongly affected by viewing from the wrong distance, eye height, and object orientation. The authors propose a 2-factor angles and ratios together (ART) theory, with the following factors: the ratio of the visual angles of the tile's sides and the angle between (a) the direction to the tile from the observer and (b) the perpendicular, from the picture plane to the observer, that passes through the central vanishing point.

Adolescent↗
PubMed1978

The role of apparent depth and context in the perception of the Ponzo illusion.

The role of apparent depth features and the proximity of the test lines to the adjacent contours in the actuation of the Ponzo illusion was examined. Six versions of the Ponzo figure were employed: a standard Ponzo figure and five modified figures in which the test lines varied in orientation (horizontal or vertical) and in location (inside or outside the converging contours). Both manipulations resulted in a significant decrease in the magnitude of the illusion in comparison to the standard Ponzo figure. The results suggest that the Ponzo illusion is significantly affected by contextual factors.

Depth Perception↗
PubMed1980

Control stimuli in investigations of the acute-angled and obtuse-angled Müller-Lyer illusions.

Over the past decade, attention has been drawn to the importance of intertip distance (the distance between the tips of the arrowheads or featherheads) as a possible determinant of the Müller-Lyer illusion. Investigation of this stimulus property for the arrowhead and featherhead components of the Müller-Lyer figure has indicated that the two components exhibit a lack of symmetry, a conclusion supported by other studies using rather different approaches to the investigation of symmetry. This article argues that the control stimuli used in previous investigations are inadequate. It is proposed that in addition to the conventional straight-line control stimulus, in which the standard shaft is stripped of the oblique inducing lines. H-shaped figures in which the inducing lines are vertical should be included. Results are reported of an experiment in which both types of control stimuli are used to investigate the effects of intertip distance, and the spatial separation of that distance from the standard shaft, upon the arrowhead and featherhead figures.

Adult↗
PubMed1995

Trajectory mapping: a new nonmetric scaling technique.

Trajectory mapping is a new scaling technique designed to recover the parameterizations, axes, and paths used to traverse a feature space. Unlike with multidimensional scaling, there is no assumption that the space is homogeneous or metric. Although some metric ordering information is obtained with trajectory mapping, the main output is the feature parameterizations that partition the given domain of object samples into different categories. After an introductory example, the technique is further illustrated by using first a set of colors and then a collection of textures.

Color Perception↗
PubMed1976

Effects of a memory aid of the three types of conservation in institutionalized retarded children.

Qualitative identity, quantitative identity, and equivalence conservation were assessed in 60 retarded boys and girls in three groups (MAS 5.4,6.3, and 7.5)9 Half of the Ss were provided a memory aid while the other half were not. The memory aid did not facilitate conservation on any of the tasks. The order of task difficulty found was qualitative identity, quantitative identity, and equivalence conservation. These data were discussed in terms of memory deficits and factors contributing to conservation and M.A.

Audiovisual Aids↗