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At least 793 records · Page 44Linked to original sources
PubMed1981

The many illusions of the Müller-Lyer: comparisons of the wings-in and wings-out illusions and manipulations of standard and dot forms.

The assumed role of peripheral distortion mechanisms in both wings-in and wings-out Müller-Lyer illusions was investigated by requiring subjects to reproduce the central extent of standard Müller-Lyer figures and dot variations. Illusory magnitude of the line and dot variations was also examined with increasing wing length and wing angle. A reduction in the overestimation for the wings-out illusion occurred with the removal of intersecting lines; the dot variations evidenced a significant overestimation effect. In contrast, no reliable decrease in underestimation was found with the removal of intersecting lines in the wings-in illusion, and both standard and dot variations were significantly underestimated. These results support a conclusion that the wings-in and wings-out Müller-Lyer illusions are two distinct illusions, and may be differentially determined at the loci of distortion within the visual system. Parallel changes in illusory magnitude were noted with configural manipulations of standard and dot wings-out illusions. However, standard and dot forms of the wings-in illusion were not equivalently affected by equivalent configural manipulations, which suggests that they are different illusions. Thus, the use of the wings-in dot variation to separate empirically peripheral from non-peripheral distortion mechanisms may be ill-advised.

Discrimination Learning↗
PubMed1988

Apparent movements induced by luminance modulations: a model study.

When the receptive-field profiles of the different units in the primary visual cortex are described by a series of different functions which are given by a Gaussian distribution and its first, second, and so on, spatial derivatives, a full analysis of the input-output processing of these units (under the assumption of linearity for small signals) can be achieved for a wide variety of optical stimuli consisting of closely adjacent fields modulated independently in intensity. Once the input-output relationship for one particular unit has been obtained, it is possible to calculate in a straightforward manner the spatial representation of the stimulus pattern in a two-dimensional distribution of such units. Investigations are reported into how a stimulus pattern (a dark or bright bar between two fields modulated in illuminance) is represented in a hierarchical structure of such layers of units, each layer containing just one type of receptive-field profile from the Gaussian family of derivatives. It is shown that if a visual percept is associated with the behaviour of the extrema or zero-crossings of the representations in the first few layers of such an architecture, a complete description can be given of the experimental results obtained by Gregory and Heard in their psychophysical experiments on illusory movement perception induced by luminance intensity modulations.

Attention↗
PubMed1990

Stereo and motion cues in preattentive vision processing--some experiments with random-dot stereographic image sequences.

Low-level preattentive vision processing is of special interest since it seems the logical starting point of all vision processing. Exploration of the human visual processing system at this level is, however, extremely difficult, but can be facilitated by the use of stroboscopic presentation of sequences of random-dot stereograms, which contain only local spatial and temporal information and therefore limit the processing of these images to the low level. Four experiments are described in which such sequences were used to explore the relationships between various cues (optical flow, stereo disparity, and accretion and deletion of image points) at the low level. To study these relationships in more depth, especially the resolution of conflicting information among the cues, some of the image sequences presented information not usually encountered in 'natural' scenes. The results indicate that the processing of these cues is undertaken as a set of cooperative processes.

Attention↗
PubMed1990

Illusory displacement of equiluminous kinetic edges.

A stationary window was cut out of a stationary random-dot pattern. When a field of dots was moved continuously behind the window (a) the window appeared to move in the same direction even though it was stationary, (b) the position of the 'kinetic edges' defining the window was also displaced along the direction of dot motion, and (c) the edges of the window tended to fade on steady fixation even though the dots were still clearly visible. The illusory displacement was enhanced considerably if the kinetic edge was equiluminous and if the 'window' region was seen as 'figure' rather than 'ground'. Since the extraction of kinetic edges probably involves the use of direction-selective cells, the illusion may provide insights into how the visual system uses the output of these cells to localize the kinetic edges.

Attention↗
PubMed1992

Vision with equiluminant colour contrast: 2. A large-scale technique and observations.

A simple technique is described for producing large-scale, tritanopic displays. The technique reproduces the various phenomena of vision with equiluminous-colour contrast that have previously been reported with red/green stimuli. It is, however, much less demanding technically, robust against artifacts, and can be used on large-scale scenes. One advantage of the technique is that a piece of blue filter can be used individually by each observer to compare quickly tritanopic and luminance conditions.

Attention↗
PubMed2005

Geometric and perceptual effects of the location of the observer vantage point for linear-perspective images.

New geometric analyses are presented of three impressive examples of the effects of location of the vantage point on virtual 3-D spaces conveyed by linear-perspective images. In the 'egocentric-road' effect, the perceived direction of the depicted road is always pointed towards the observer, for any position of the vantage point. It is shown that perspective images of real-observer-aimed roads are characterised by a specific, simple pattern of projected side lines. Given that pattern, the position of the observer, and certain assumptions and perspective arguments, the perceived direction of the virtual road towards the observer can be predicted. In the 'skewed balcony' and the 'collapsing ceiling' effects, the position of the vantage point affects the impression of alignment of the virtual architecture conveyed by large-scale illusionistic paintings and the real architecture surrounding them. It is shown that the dislocation of the vantage point away from the viewing position prescribed by the perspective construction induces a mismatch between the painted vanishing point of elements in the picture and the real vanishing point of corresponding elements of the actual architecture. This mismatch of vanishing points provides visual information that the elements of the two architectures are not mutually parallel.

Art↗
PubMed1989

S+ versus S- fading in teaching visual discriminations to severely mentally handicapped children.

Twenty-seven severely mentally handicapped children in three matched groups were trained on both a complex and a simple visual discrimination task with: (1) prompt fading on S+; (2) prompt fading on S-; or (3) no prompting (trial-and-error training). On the complex discrimination task, differences between groups were obscured by a floor effect. Only one subject from each group acquired the discrimination. However, on the simple discrimination task all nine S+ fading, eight S- fading and six trial-and-error training subjects attained criterion. Both S+ and S- fading groups made significantly fewer errors than the trial-and-error group but did not differ significantly from each other. Sixteen children who failed to acquire the complex discrimination in Experiment 1 also participated in Experiment 2. Subjects received additional training on the task by one of four procedures. Neither continued trial-and-error training, continued S+ or S- fading, reversals of the prompt between S+ and S-, or intensity fading resulted in acquisition of the task. Results are discussed in terms of overshadowing and task difficulty.

Adolescent↗
PubMedDate not supplied

The disturbances of object vision and spatial vision in Alzheimer's disease.

Thirty-one patients with mild-to-moderate Alzheimer's disease (AD) underwent a test battery of complex visual tasks. We assessed the scores using a principal-factor analysis to elucidate the underlying deficits. There were three independent factors: The first factor included the tasks of identifying and comparing forms of visual stimuli. The second factor consisted of digit span and digit symbol tasks, and the third factor consisted of a specified visual counting task. We considered these three factors as representing the dysfunctions of object recognition, general attention and spatial recognition, respectively. These results underline the disturbances of the two visual systems, object vision and spatial vision, in early-AD patients.

Aged↗