Dynamic form perception in the bending

As a white hourglass moves across a black background, the middle appears to lag behind its true position, resulting in the apparent bending of the axis of the hourglass. No such distortion occurs with a black hourglass moving across a white background. The results of two experiments support a visual persistence hypothesis, as opposed to a latency hypothesis.     

A new dynamic visual illusion: The bending hourglass

Attention, Perception, & Psychophysics - A white hourglass moving laterally across a black surface appears to bend in such a way that the narrow portion lags behind its true position, but only...     

Footsteps and inchworms: illusions show that contrast affects apparent speed

A horizontal grey bar that drifts horizontally across a surround of black and white vertical stripes appears to stop and start as it crosses each stripe. A dark bar appears to slow down on a black stripe, where its edges have low contrast, and to accelerate on a white stripe, where its edges have high contrast. A light-grey bar appears to slow down on a white stripe and to accelerate on a black stripe. If the background luminances at the leading and trailing edges of the moving bar are the same, the bar appears to change speed, and if they are different the bar appears to change in length. A plaid surround can induce 2-D illusions that modulate the apparent direction, not just the speed, of moving squares. Thus, the motion salience of a moving edge depends critically on its instantaneous contrast against the background.     

Aversive racism and selection decisions: 1989 and 1999

The present study investigated differences over a 10-year period in whites' self-reported racial prejudice and their bias in selection decisions involving black and white candidates for employment. We examined the hypothesis, derived from the aversive-racism framework, that although overt expressions of prejudice may decline significantly across time, subtle manifestations of bias may persist. Consistent with this hypothesis, self-reported prejudice was lower in 1998–1999 than it was in 1988–1989, and at both time periods, white participants did not discriminate against black relative to white candidates when the candidates' qualifications were clearly strong or weak, but they did discriminate when the appropriate decision was more ambiguous. Theoretical and practical implications are considered.     

Word learning is 'smart': evidence that conceptual information affects preschoolers' extension of novel words

We examined electrophysiological correlates of conscious change detection versus change blindness for equivalent displays. Observers had to detect any changes, across a visual interruption, between a pair of successive displays. Each display comprised grey circles on a background of alternate black and white stripes. Foreground changes arose when light-grey circles turned dark-grey and vice-versa. Physically stronger background changes arose when all black stripes turned white and vice-versa. Despite their physical strength, background changes were undetected unless attention was directed to them, whereas foreground changes were invariably seen. Event-related potentials revealed that the P300 component was suppressed for unseen background changes, as compared with the same changes when seen. This effect arose first over frontal sites, and then spread to parietal sites. These results extend recent fMRI findings that fronto-parietal activation is associated with conscious visual change detection, to reveal the timing of these neural correlates.     

The perception of foreground and background as derived from structural information theory

Subjects were instructed to order stimuli, consisting of a white and a black part, in accordance with the perceived foreground-strength of the white (or black) part. It appeared that this task can be carried out consistently. The order is explained on the basis of Structural Information Theory. It is argued that this task involves central processes, and that the strength depends on the preference for an interpretation, in which the white (black) part is a foreground on a black (white) background, with respect to the opposed interpretation in which the white (black) part is the background and the black (white) part is foreground.     

The structure of memory: Evidence concerning the recall of surface and background colour of shapes

In the first of four experiments, two groups of subjects were shown a series of cards, each displaying a different shape. For one group the shapes were of different colours, and each was located on either a black or a white background. For the other group a shape was black or white, and its background was coloured. Subjects in both groups were instructed to memorize the colour and brightness (black or white) assigned to each shape. Recall of the colours, in response to the names of the shapes, was superior for the group for which the shapes themselves had been coloured. In the other three experiments the finding was extended, with the aim of limiting possible explanations of the effect. One of these experiments showed that the effect is obtained when the relevant stimuli are imagined rather than being physically shown to a subject. This suggests that the effect is not the result of processes of attention that are dependent upon the perceptual analysis of a display. In discussion, it is argued that the effect may shed light on the constraints that govern the process of association. One hypothesis that specifically accounts for the results is that the structure of memory for visually presented information is that of a network of propositions.     

Image-processing algorithms for behavior analysis of group-housed pigs

Computational algorithms of image processing were developed and evaluated to select, by motion detection, images of resting artificial pigs and to segment the pigs (mixture of black and white pigs) from their background. Motion detection of the pigs was implemented by detecting interframe differences of postural behavioral images. This algorithm combines the advantages of likelihood ratio method and shading model method and shows a stable performance under noisy and dynamic illumination conditions. Segmentation of the pigs from their background was implemented by employing multilevel thresholding and background reference techniques. The algorithm automatically determines the number of thresholds needed and produces satisfactory segmentation when both black and white pigs with different image intensities are present at the same time (the most complicated situation). The reference background image is updated so that temporal changes in illumination and/or spatial changes of the pen condition have little effect on the performance of image segmentation. The algorithm employs statistical models of the pigs and background and Bayes hypothesis testing to obtain and update the exposed portion of the reference background. Linear filters were used in this process for updating the parameters. These algorithms will serve as essential components for a novel, behavior-based, interactive approach to assess and control thermal comfort of group-housed pigs, which is expected to result in enhanced animal health and well-being.     

An experimental test of Jameson and Hurvich’s theory of brightness contrast1

Two hundred and fifty-two brightness functions for seven simultaneously presented black, gray, and white squares on black, gray, and white backgrounds approximated power curves with positive exponents when illuminance was varied in seven steps over 1.9 log fL. Mean exponents were significantly larger for whiter vs blacker squares and for squares on the white vs the gray background. Mean exponents also increased more for squares on white than on black or gray backgrounds. Finally, a white replacing a black background elicited increasingly larger décrémentai responses as the squares varied from black to white. Jameson and Hurvich’s opponent-process theory, tested by the experiment, was not predictive.     

Achromatic color matching as a function of apparent target orientation,target and background luminance,and lightness or brightness instructions

In two experiments, achromatic color matches for a fixed target, under constant illumination, were compared under conditions where the target appeared perpendicular to illumination direction and coplanar with the background (monocular viewing) and where the target appeared nonperpendicular to illumination direction and noncoplanar with the background (binocular viewing). Contrary to the coplanar ratio hypothesis, which predicts a “lightening” of the target seen coplanar with a darker background, a general “darkening” of the target occurred for both white (N9.5/) and black (N3/) backgrounds and for both dark (N5.5/) and light (N6.5/) targets. This darkening effect was greatest for the darker target and black background, and approximately equal for other combinations of target value and background. The direction of the darkening effect is consistent with the albedo hypothesis, which assumes an inferential correction for changes in conditions of illumination. However, variation in the magnitude of the darkening effect is problematical, and cannot be easily explained by any existing theory. In both experiments, instructions to judge “lightness” or “brightness” failed to produce any substantial differences in performance, although postexperimental questioning suggested that subjects had a verbal understanding of these concepts. Apparently, under reduction conditions, subjects lack cues to illumination and make only lightness matches, regardless of instructions.     

An experimental test of Jameson and Hurvich’s theory of brightness contrast

Two hundred and fifty-two brightness functions for seven simultaneously presented black, gray, and white squares on black, gray, and white backgrounds approximated power curves with positive exponents when illuminance was varied in seven steps over 1.9 log fL. Mean exponents were significantly larger for whiter vs blacker squares and for squares on the white vs the gray background. Mean exponents also increased more for squares on white than on black or gray backgrounds. Finally, a white replacing a black background elicited increasingly larger decremental responses as the squares varied from black to white. Jameson and Hurvich’s opponent-process theory, tested by the experiment, was not predictive.     

Message framing and color combination in the perception of medical information

A 2 x 2 between-subjects design was used to examine the effects of message framing (gain vs loss) and color combination (red background with white characters vs white background with black characters) on 120 university students' perception of materials promoting the H1N1 flu vaccine and their willingness to receive the vaccine after they had read the materials. Each participant completed a 6-item questionnaire, and the results of an analysis of variance showed that participants rated vaccine information presented through loss-framed messages as having greater interest and leading to greater understanding. Loss-framed messages presented on a white background with black characters significantly increased the willingness of the participants to receive the vaccine.     

Some characteristics of psychophysical data obtained with a group version of the up-and-down method

Effects of backgroun reflectance on the shapes of scales of lightness were investigated in two experiments. In Experiment I, 25 Ss compared similaritiesofpairs ofgray chips that were viewed against black, gray. or white backgrounds. In Experiment 2, 33 Ss positioned a series of gray chips, viewed against a white, gray. or black background, so that the distances between successive chips represented the perceived differences in lightness between them. The results of both studies indicated that scale shape was influenced by background. The nature of the effect was that interstimulus differences in the region of a background were enhanced relative to interstimulus differences far from a background.     

Facial Recognition: Weapon Effect and Attentional Focus1

The present experiment investigated the hypothesis that a weapon can serve as a cue that will interfere with the eyewitness’ encoding of the weapon-holder's facial features. Extrapolating from Easterbrook's cue utilization hypothesis, an interaction between arousal and attentional focus was predicted. White female college students played a bogus visual discrimination game in which they saw a total of 24 target photos: six black targets holding a weapon in their hands, six white targets holding weapons, six black targets holding objects other than weapons, and six white targets holding objects other than weapons. Subjects were randomly assigned to view the photos while experiencing white noise and threat of electric shock (high arousal) or without such factors (low arousal). Subjects were also randomly assigned to one of four attentional focus levels: face focus, hand focus, background focus, and free focus. A signal detection-type task provided an assessment of identification accuracy. The data revealed a significant “weapon effect”: Subjects were better at identifying photos of targets who were not holding a weapon than they were at identifying photos of targets who were holding a weapon. Focus of attention and race of target also significantly affected recognition accuracy, as did arousal in one of two analyses. No support was found, however, for the predicted interaction between arousal and attentional focus. Finally, subjects showed a strong criterion shift according to the race of target; they were much more likely to make a “seen before” response to other-race (black) faces than to same-race faces.     

Icon flickering, flicker rate, and color combinations of an icon's symbol/background in visual search performance

The effects of color combinations of an icon's symbol/background and components of flicker and flicker rate on visual search performance on a liquid crystal display screen were investigated with 39 subjects who searched for a target icon in a circular stimulus array (diameter = 20 cm) including one target and 19 distractors. Analysis showed that the icon's symbol/background color significantly affected search time. The search times for icons with black/red and white/blue were significantly shorter than for white/yellow, black/yellow, and black/blue. Flickering of different components of the icon significantly affected the search time. Search time for an icon's border flickering was shorter than for an icon symbol flickering; search for flicker rates of 3 and 5 Hz was shorter than that for 1 Hz. For icon's symbol/background color combinations, search error rate for black/blue was greater than for black/red and white/blue combinations, and the error rate for an icon's border flickering was lower than for an icon's symbol flickering. Interactions affected search time and error rate. Results are applicable to design of graphic user interfaces.     

Measuring the meter: on the constancy of lightness scales seen against different backgrounds

The constancy of a 16-step achromatic Munsell scale was tested with regards to background variations in two experiments. In experiment 1 three groups of observers were asked to find lightness matches for targets in simultaneous lightness displays by using a 16-step achromatic Munsell scale placed on a white, black, or white-black checkered background. In experiment 2, a yellow-blue checkered background and a green-red checkered background replaced Munsell scales on the black and on the white backgrounds. Significant effects of scale background on matches were found only in experiment 1, suggesting that background luminance is a crucial factor in the overall appearance of the scale. The lack of significant differences in experiment 2, however, may stand for an overall robustness of the scale with respect to background luminance changes occurring within certain luminance ranges.     

吊车工人深度视觉阈值的测定

本研究对１０９名吊车工人进行了红橙黄绿蓝紫黑白等八种颜色的深度知觉阈限的测定．结果发现：在白色背景条件下,绿蓝两色为最佳深度色,最易辨别深度差异;黑紫红三色为二级深度色;橙黄两色为三级深度色;白色为四级深度色．易于深度辨别的颜色．,平均阈值小,分布较集中;不易深度辨别的颜色,平均阈值大,分布较分散．建议吊车设计部门,在吊钩臂部位的黄色背景上,涂上黑色条子．使吊车的吊钧本身具有颜色对比,少受作业环境的影响。     

Evidence against independent processing of black and white pattern features

Following adaptation to a rectangular grating, subjects observed a shift in the perceived duty cycle of a test grating (Burton, Nagshineh, & Ruddock, 1977; DeValois, 1977). This suggests that size information about black and white pattern components may be analyzed independently. We have tested this hypothesis by combining adaptation to a 2-cpd rectangular wave grating (narrow white bars and wide black bars or vice versa) with adaptation to a 4-cpd sine wave (narrow white and black bars. The data do not support the independent analysis of white and black components, but they may be accounted for by mechanisms sensitive to the relative phase relations among the spatial frequency components of the input.     

A static geometrical illusion contributes largely to the footsteps illusion

When a black and a white rectangle drifts across a stationary striped background with constant velocity, the rectangles appear to alternately speed up and slow down. Anstis (2001, Perception 30 785-794; 2004, Vision Research 44 2171-2178) suggested that this 'footsteps' illusion is due to confusion between contrast and velocity signaling in the motion detectors of the human visual system. To test this explanation, three experiments were carried out. In experiment 1, the magnitudes of the footsteps illusion in dynamic and static conditions was compared. If motion detectors play an important role in causing the illusion, it should be reduced in the static condition. Remarkably, however, we found that the illusory misalignment between the black and the white rectangle was even more prominent in the static condition than in the dynamic condition. In experiment 2, we measured the temporal-frequency properties of the footsteps illusion. The results showed that the footsteps illusion was tuned to low temporal frequencies. This suggests that the static illusory misalignment can contribute sufficiently to the dynamic illusory misalignment. In experiment 3, the magnitude of the illusion was measured with the rectangles drifting on a temporally modulated background instead of a spatially modulated background. If contrast affects the apparent velocity of the rectangles, temporal modulation of a uniform background should also cause the footsteps illusion. However, the results showed that the magnitude of the illusion was much reduced in this condition. Taken together, the results indicate that the footsteps illusion can be regarded as a static geometrical illusion induced by the striped background and that motion detectors play a minor role at best.     

Effects of display characteristics and individual differences on preferences of VDT icon design

This study explored the effects of display characteristics such as target/background color combination, single/simultaneous presentation, and individual differences by sex, and design specialty on preferences of VDT icon design. The results indicated black targets (black-on-white, black-on-yellow) and black backgrounds (red-on-black, yellow-on-black) were the most popular and white targets (white-on-red, white-on-black) and white backgrounds (blue-on-white, red-on-white) were the second most popular. As for the chromatic color combinations, yellow-on-blue was the most favored. Subjects rated color combinations under single presentation higher than those under simultaneous presentation. Women rated purplish targets and rated purplish and blue backgrounds higher than men. Subjects with design background favored black more either as a target or background, but they favored turquoise less than those without design background.