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PubMed1985

Visual scanning behaviour in honeybees.

Freely flying bees were rewarded with sugar solution on a variety of black-and-white shapes as well as on coloured gratings in various training situations. In subsequent dual-choice tests, the bees' discrimination between the various shapes was measured. In addition, the bees were video-filmed while flying in front of the shapes. The scanning patterns thus obtained were then quantified in order to characterize scanning behaviour and its relationship to the geometrical parameters of the scanned shapes, investigate whether scanning plays a role in pattern discrimination and examine the influence of training on the characteristics of scanning. The scanning patterns clearly mirror the contours of the scanned shape in all cases, i.e. the bees fly along the contours contained in the shape. This behaviour does not depend on whether the scanned shape is one that was previously rewarded, or one that is completely novel to the bees. Comparison of the results of quantifying the scanning patterns with the results of dual-choice tests reveals that scanning behaviour is independent of discrimination performance. On the average, horizontal scanning directions occur more often than vertical directions. Variations of the training situation produce measurable differences in scanning behavior. However, except in the case of vertical scanning on a vertical grating, these differences are quite small, indicating that following contours is a largely stereotyped behaviour. Horizontal gratings are very well discriminated from vertical ones even if they offer contrast to only one receptor type, i.e. blue or green, demonstrating that the direction of contours is visible to the pattern recognition system even under these conditions. However, vertical and horizontal coloured gratings offering only blue-contrast do not elicit contour-following, whereas gratings offering only green-contrast do. Thus, the bees' scanning behaviour is colour-blind and most probably governed by the green receptors. We suggest that contour-following is the by-product of a behavioural mode which serves to prevent retinal image movement during flight in front of a contoured visual pattern.

Animals↗
PubMedDate not supplied

Relationship between the characteristics of visual short-term memory in monkeys and the spatial properties of images.

Experiments were performed on Rhesus macaques to study the relationship between delayed visual differentiation processes and stimulus properties. These investigations showed that the processes of short-term storage of visual information in monkeys has significant features associated with differences in stimulus properties. These consisted of different durations of storage and motor response times. Because of these differences, stimuli (15 pairs) could be grouped into compact clusters on the bases of similarity between their delayed differentiation characteristics. These experiments characterized the processes of short-term information storage during the differentiation of stimuli differing in terms of spatial relationships between elements, as compared with stimuli differing in terms of other attributes (shape, color, etc.); spatial information was stored for shorter periods of time and motor response times were longer. It is suggested that visual short-term memory involves a set of mechanisms operating on attributes of different types and which, along with signs and working programs associated with the visual system, stores spatial discriminatory signs, in which the major role is played by visual-vestibular interactions.

Animals↗
PubMed1989

Projective invariance and visual shape constancy.

As one moves about a table, the projection of its shape on the retina varies enormously, yet the table's shape appears constant. The various retinal images of a single object are nearly congruent in projective geometry. To explain apparent constancy, standard theories of vision assume that the visual system has access to this projective congruence. We present four experiments that undermine this assumption (i.e., the projective thesis). The basic result is that observers' estimates of shape in a simple production task represent gross departures from correct projection, even when observers are given aids to fixation. We manipulate both observer sample and experimental procedure in an attempt to find a source of these persistent errors. Our present hypothesis is that observers lack the sensitivity or implicit knowledge of projective geometry that has been attributed to them.

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PubMed1987

da Vinci's window facilitates drawings of total and partial occlusion in young children.

When two or more objects are present in a scene, children 5 and 6 years of age rarely draw the scene such that one object totally or partially occludes another object. Instead they draw complete objects. The present study separated two components of drawing: perspective taking and graphic skill. Perspective taking was examined by comparing a free viewing condition with a restricted viewing condition in which a model could only be viewed through four apertures. Graphic skill was examined by comparing drawings requiring total occlusion with drawings requiring partial occlusion under both viewing conditions. Experiment 1 showed that 90% of 5- and 6-year-olds drew total occlusions under restricted viewing conditions but only 32% did so in the free viewing condition. Experiment 2 showed that drawings of partial occlusion were unaffected by viewing condition among 5-year-olds, but that restricted viewing increased the number of partial occlusions that 6-year-olds drew. Thus, failures of young children to draw occlusions have less to do with graphic skill than was previously thought. Instead, it is suggested that young children have a more general difficulty selecting one perspective and maintaining it over time.

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