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PubMed1989

Some observations upon perceptual organization and the mere exposure effect.

The mere repetition of events tends to enhance subjective familiarity and subjective preference for those events. It has been shown that the enhancement of subjective preference is neither contingent upon a feeling of familiarity nor an awareness of the physical identity of the stimulus during learning. This finding is surprising since the weight of existing theoretical and empirical evidence suggests that subjective preference is derivative of familiarity. An experiment was conducted to test the hypothesis that at least one preattentive/preconscious product, figure-ground organization, is shared between the processes responsible for preference enhancement and those responsible for the enhancement of recognition memory. There were two significant findings. First, subjects were able to discriminate between objectively familiar stimuli and objectively unfamiliar stimuli on the basis of preference judgments but were unable to do so on the basis of familiarity judgments. Second, preference enhancement occurred only for those objectively familiar stimuli for which the figure-ground aspects had not been phenomenally reversed. The significance of these findings is discussed.

Adult↗
PubMed1993

A flaw in the explanation of the stereokinetic cone illusion and two guiding hypotheses for new research.

The basic conceptions used in the literature for the explanation of the stereokinetic cone illusion are examined and shown to contain an important flaw which concerns the presumed equivalence of retinal images projected by 2- versus 3-dimensional structures. Upon showing that such equivalent does not prevail, two hypotheses are proposed, pointing out that the illusion must arise from inherent characteristics of the nervous system and their interaction with the stimulus at critical parameters.

Attention↗
PubMed1997

Mental chronometry with simple linear regression.

Typically, mental chronometry is performed by means of introducing an independent variable postulated to affect selectively some stage of a presumed multistage process. However, the effect could be a global one that spreads proportionally over all stages of the process. Currently, there is no method to test this possibility although simple linear regression might serve the purpose. In the present study, the regression approach was tested with tasks (memory scanning and mental rotation) that involved a selective effect and with a task (word superiority effect) that involved a global effect, by the dominant theories. The results indicate (1) the manipulation of the size of a memory set or of angular disparity affects the intercept of the regression function that relates the times for memory scanning with different set sizes or for mental rotation with different angular disparities and (2) the manipulation of context affects the slope of the regression function that relates the times for detecting a target character under word and nonword conditions. These ratify the regression approach as a useful method for doing mental chronometry.

Attention↗
PubMed1997

Object-based and location-based shifting of attention in Parkinson's disease.

Research into Parkinson's disease has made much use of the precuing paradigm developed by Posner to examine patients' ability to shift visuospatial attention. The majority of studies indicate that patients with Parkinson's disease have significantly reduced shift costs when compared with normal controls. This reduction in costs is ascribed to abnormal maintenance of attention resulting from Parkinson's disease. We know that visual attention is not directed to spatial locations alone but that it may also be directed to object representations. To date, however, it has not been clear whether the reduced shift costs apparent in Parkinson's disease patients are evident only on spatial locations or on both spatial locations and object representations. Therefore, in the current study we have adopted a new technique with a view to studying both location-based and object-based attentional components within the same paradigm. Our results with 17 patients with Parkinson's disease suggest, at least in the early stages, patients do not show deficits in maintenance of attention to the miscued source of stimulation as reflected in their normal magnitude of cuing effect related to shifting between locations and between objects. 14 normal persons were control subjects.

Aged↗
PubMed1998

Novelty and complexity in human infants' exploratory behaviour.

The effect of novel and complex stimulus cubes on the exploratory behaviour of human infants was analysed in two studies (ns = 30 and 20). Infants showed relatively greater preference for complex patterned cubes, and their exploratory behaviour habituated over 5 days.

Analysis of Variance↗
PubMed1998

Stroop interference is the result of comparable, not of differential processing speeds of two stimulus dimensions.

On a digit-counting Stroop task, processing of the slower, nonverbal, i.e., number, dimension was slowed further by a large-number set (6 to 9), as compared with a small-number set (1 to 4). In the task, neutral symbols or conflicting digits were arranged on a horizontal line (e.g.,@@, 444) and on two separate sheets. Each sheet contained 120 stimulus arrays. Subjects counted out loud the number of symbols or digits in each array, and their counting times for each sheet were recorded. 23 subjects received the small-number set while 21 received the large-number set. It was found that counting a large number of symbols took significantly longer time (by 162 sec. per 120 stimulus arrays) than counting a small number of symbols. Moreover, interference was nonexistent (2 msec. per stimulus array) when a large number of conflicting digits were counted but was of a typical magnitude (110 msec. per stimulus array) when a small number of conflicting digits were counted. This suggests that Stroop interference is better explained as the result of comparable, not of differential, processing speeds of the two stimulus dimensions. Implications for the cause and the locus of Stroop interference are discussed.

Color Perception↗
PubMed2000

Color discrimination under chronic hypoxic conditions (simulated climb "Everest-Comex 97").

Hypoxia is known to alter visual functions. In the present study, the effects of chronic hypobaric hypoxia upon visual color discrimination were studied in 8 subjects participating in a simulated climb from sea level (PO2 = 210 hPa) to 8,848 m (PO2 = 70 hPa) over a 31-day period of confinement in a decompression chamber ('Everst-Comex 97'). During these investigations, the subjects were required to discriminate between colors of different hue in the red, blue, and green ranges. Alterations in color discrimination increased slightly but significantly as altitude increased. Impairments occurred mainly in the red and blue ranges. In addition, our results further indicate that color discrimination would be affected only when a minimum threshold of difference between color stimuli is not present. Methodological and physiological implications are discussed.

Adaptation, Psychological↗
PubMed2000

Discrimination of rotation from linear motion: influence of interference gratings and dichoptic viewing.

Observers viewed a screen on which a number of patches containing horizontally moving pixels were presented. Target patches consisted of pixels whose motion simulated the rotation of a cylinder around its Y-axis; distractors, of pixels whose motion was linear. The task was to assess whether a display contained a target patch. Exp. 1 showed that the superposition of the displays with drifting sine-wave gratings interfered with rotation detection in a spatial- and temporal-frequency specific manner. In Exp. 2, dichoptic presentation greatly reduced the interference of the drifting gratings. It is argued on various grounds that the process(es) responsible for the detection and discrimination of rotating structure in depth exists at a low level of the visual system.

Attention↗
PubMed2000

Influences of occlusion, color, and luminance on the perception of fragmented pictures.

The contribution of the magnocellular (M) pathway to perceptual completion and depth processing was examined by comparing performance under black-and-white conditions with isoluminant color and diffuse red background conditions expected to suppress M pathway activity. Participants identified the repeated figure in pictures where only fragments of the figures were visible. The fragments were presented either alone (unoccluded) or with an occluder (occluded) filling the space between them. Identification with an occluder involved amodally completing the fragments behind it, i.e., depth processing. All unoccluded versions were easy to identify indicating perceptual completion of the fragments was not influenced by suppressing M pathway activity. Black-and-white occluded versions were also easy to identify. The significantly longer identification times for occluded versions under isoluminant and diffuse red background conditions indicates amodal completion of the fragments was hindered when M pathway activity was reduced, supporting the importance of M pathway activity for depth processing.

Color Perception↗
PubMed1975

Figural after-effects of Köhler and Wallach reinterpreted.

A theory of perception is extended to figural after-effects which has been used already to rationalize the illusory phenomena of static visual illusions, fluctuating figures and visual illusions of motion. The theory proposes three laws of perception. All of the extensive observations of Köhler and Wallach are rationalized under these laws embodying the present theoretical orientation. The theory maintains that the experience of perception occurs only during the interaction of forces introduced by a pattern with the forces characteristic of the brain in order to produce the greatest equilibrium within the two systems of forces. A pattern is not reproduced in the brain. A pattern produces a system of forces. Neither the image of the pattern nor its forces impinging on the nervous system produce the perceptual experience. It is during the process of interaction of the forces of the pattern with the forces of the brain and only during this interaction that perception is experience. This interaction is a constant process to integrate the incompatibilities existing between the two system of forces.

Brain↗
PubMed2001

Curvature discontinuities are cues for rapid shape analysis.

Using the visual search method, we show that stimuli that contain curvature discontinuities (i.e., points where the second derivative along an image contour is not defined) are easily found among stimuli containing only smooth changes in curvature. Curved stimuli that lack curvature discontinuities, however, are difficult to find among distractors that have them. These results suggest that the visual system detects and analyzes abrupt changes in curvature in the image quickly to extract vital information about the 3-D structure of the visual environment.

Attention↗
PubMed2001

Detection of shape orientation depends on salient axes of symmetry and elongation: evidence from visual search.

Three experiments investigated the role of the global spatial structure of two-dimensional (2-D) shapes in terms of symmetry and elongation on visual search for shape orientation. Experiment 1 demonstrated the often reported orientation search asymmetry (i.e., a faster detection of a tilted target among vertical distractors than the reverse) for the global orientation of 2-D polygons that possess a salient, "principal" axis of symmetry or elongation. Moreover, the search asymmetry depended on the orientation of the principal axis, rather than on the orientation of local contours. Further exploration of this effect with polygons (Experiment 2) showed that the search asymmetry for global orientation occurred for shapes containing an axis of symmetry; elongation, on the other hand, did not seem to be crucial. Finally, Experiment 3 demonstrated orientation search asymmetries with shapes composed of curved rather than straight contours: Here, the search asymmetry occurred as a function of the orientation of both axes of symmetry and elongation. Overall, search for global orientation was less efficient than search for local orientation. The results suggest that the perception of the global orientation of shapes is mediated by axis-based descriptions in terms of perceptually salient axes of symmetry and elongation.

Attention↗
PubMed2002

The perception and discrimination of local 3-D surface structure from deforming and disparate boundary contours.

In a series of four experiments, we evaluated observers' abilities to perceive and discriminate ordinal depth relationships between separated local surface regions for objects depicted by static, deforming, and disparate boundary contours or silhouettes. Comparisons were also made between judgments made for silhouettes and for objects defined by surface texture, which permits judgment based on conventional static texture gradients, conventional stereopsis, and conventional structure-from-motion. In all the experiments, the observers were able to detect, with relatively high precision, ordinal depth relationships, an aspect of local three-dimensional (3-D) structure, from boundary contours or silhouettes. The results of the experiments clearly demonstrate that the static, disparate, and deforming boundary contours of solid objects are perceptually important optical sources of information about 3-D shape. Other factors that were found to affect performance were the amount of separation between the local surface regions, the proximity or closeness of the regions to the boundary contour itself, and for the conditions with deforming contours, the overall magnitude of the boundary deformation.

Depth Perception↗
PubMed2003

Attentional and oculomotor capture with static singletons.

Previous research has shown that in visual search static singletons have the ability to capture attention (Theeuwes, 1991a, 1992). The present study investigated whether these singletons also have the ability to capture the eyes. Participants had to make an eye movement and respond manually to a shape singleton while a color singleton was present. When participants searched for a unique shape while a unique color singleton was present there was strong attentional and oculomotor capture (Experiment 1). However, when participants searched for a specific-shape singleton (a green circle) when a specific-color singleton (a red element) had to be ignored, there was attentional capture but no oculomotor capture (Experiment 2). The results suggest that an attentional set for a specific feature value defining both the target and the distractor (as in Experiment 2) allows such a fast disengagement of attention from the location of the distractor that a saccade execution to that location is prevented.

Attention↗