The glare effect and the perception of luminosity

The impression of self-luminosity in the glare effect was studied in two experiments. In experiment 1 the target (CS) was set to the highest luminance of the field and subjects were asked to adjust the luminance ramp of the inducers (R) against five backgrounds (B) to the point where they began to see CS as self-luminous. It was found that there is a linear relationship between background and luminance ramp. Another group of subjects carried out the same task in experiment 2, but this time CS and R were linked together so that CS would always have the same luminance as the highest luminance level of R, as adjustments were performed. It was found that: (i) adjustments were always lower than the highest luminance available; (ii) the linear relationship between background and luminance ramp was confirmed; (iii) observers reported a compelling impression of self-luminous grays. Data are discussed in relation to Bonato and Gilchrist's model for the perception of luminosity. The authors advance the hypothesis that luminance ramps are used at an early stage of encoding for the perception of luminosity.     

Reaction times reveal the contribution of the different receptor components in luminance perception

Piéron (1914, 1920, 1952) demonstrated that simple reaction time decays as a hyperbolic function of luminance. Similarities between cell latencies and reaction time (RT) to luminance suggest that this relationship may be determined by retinal processes. If the exponent of the Piéron function is specific to a given sensory modality, as assumed by some authors (e.g., Bonnet, 1992a, 1992b; Norwich, 1987), it should reflect receptor activities. Consequently, functions with different exponents should fit data for different luminance ranges. In a contrast-discrimination experiment, we investigated this question with a large range of luminance levels in a two-alternative spatial forced-choice task. The results of the experiment show that three functions with different exponents fit RT to the three luminance ranges (scotopic, mesopic, and photopic). The exponent decreases with increasing luminance. The findings indicate that the exponent and the asymptotic latency of the RT function reflect receptor activities of the visual system.     

The role of transparency in perceptual grouping and pattern recognition.

The shortest stimulus exposure time for which transparency can be seen was examined. In the first experiment, overlapping digits were presented for 120 ms and the luminance in the overlapping regions was varied. Subjects reported, in separate blocks of trials, either the apparent transparency of the digits or the identity of the digits. When the luminance was set so that one set of digits appeared to be seen through the other, recognition of the digits was high. When the luminance in the overlapping regions did not produce impressions of transparency, digit recognition was low. In the second experiment, digit identification at several stimulus durations was compared between stimuli that had luminance that was valid for transparency and stimuli that had invalid luminance. Performance was found to be higher in the valid luminance condition than in the invalid condition after as little as 60 ms exposure duration. This result suggests that the impression of transparency requires only relatively short exposure durations.     

亮度对空间-数字反应编码联合效应的影响

本研究探讨亮度对空间-数字反应编码联合效应（Spatial-Numerical Association of Response Codes,简称SNARC效应）的影响及其机制。通过三个实验设计不同的亮度对比水平,要求被试对阿拉伯数字1~9（5除外）进行奇偶判断。实验一将数字亮度设为最高值255时,结果出现了数字的SNARC效应。实验二将数字的亮度值分别设为255和213时,结果仍存在SNARC效应。实验三将亮度值分别设置为213和42时,数字的SNARC效应却消失了。这些结果表明亮度会激活或抑制数字的空间表征,可能与亮度对比值的高低及所消耗认知资源的多少有关。     

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.     

When figure-ground segmentation modulates brightness: the case of phantom illumination

In the phantom illumination illusion, luminance ramps ranging from black to white induce a brightness enhancement on an otherwise homogeneous dark background. The strength of the illusion was tested with regard to the extension of the brightness inducing perimeter, surrounding the target area by manipulating the number of inducers (exp. 1) and the size of the inducers (exp. 2). Participants' task was to rate the difference in brightness between the target area and the background. Results show that the illusion occurs only when the target area is not completely segregated from the background by luminance ramps; vice versa, when the target area is delimited by a continuous gradient, it appears darker than the background. These findings suggest a major role of figure-ground organization in the appearance of the illusion. This hypothesis was tested in a rating task experiment with three types of target area shapes circumscribed by four types of edges: luminance contours, illusory contours, no contours, and ambiguous contours. Illusory contours, just as luminance contours, hinder the illusion and produce a darkening of the target area. A control experiment measured the brightness of the previous stimuli without luminance ramps: all configurations resulted in a darkening of the target area. Results from all experiments suggest that figure-ground segmentation plays a major role in the determination of both illumination and lightness in stimuli with luminance gradients.     

Informational primacy of visual dimensions: specialized roles for luminance and chromaticity in figure-ground perception

Three experiments were conducted to examine the distinct contributions of two visual dimensions to figure-ground segregation. In each experiment, pattern identification was assessed by asking observers to judge whether a near-threshold test pattern was the same or different in shape to a high-contrast comparison pattern. A test pattern could differ from its background along one dimension, either luminance (luminance tasks) or chromaticity (chromaticity tasks). In each task, performance in a baseline condition, in which the test pattern was intact, was compared with performance in each of several degradation conditions, in which either the contour or the surface of the figure was degraded, using either partial occlusion (Experiment 1) or ramping (Experiments 2 and 3) of figure-ground differences. In each experiment, performance in luminance tasks was worst when the contour was degraded, whereas performance in chromaticity tasks was worst when the surface was degraded. This interaction was found even when spatial frequencies were fixed across test patterns by low-pass filtering. The results are consistent with a late (postfiltering) dual-mechanism system that processes luminance information to extract boundary representations and chromaticity information to extract surface representations.     

Color discrimination and luminance

This experiment studied the relation between luminance level and color discrimination at 570 millimicrons. A variety ofstimuli whose luminances varied from .1 to 100 ft-L were viewed against a variety of surrounds. 1t was found that color discrimination ability was a joint function of the luminance level of the stimulus and the ratio of the luminance of the stimulus to that of the surround.     

Informational primacy of visual dimensions: Specialized roles for luminance and chromaticity in figure-ground perception

Three experiments were conducted to examine the distinct contributions of two visual dimensions to figure-ground segregation. In each experiment, pattern identification was assessed by asking observers to judge whether a near-threshold test pattern was the same or different in shape to a high-contrast comparison pattern. A test pattern could differ from its background along one dimension, either luminance (luminance tasks) or chromaticity (chromaticity tasks). In each task, performance in a baseline condition, in which the test pattern was intact, was compared with performance in each of several degradation conditions, in which either the contour or the surface of the figure was degraded, using either partial occlusion (Experiment 1) or ramping (Experiments 2 and 3) of figure-ground differences. In each experiment, performance in luminance tasks was worst when the contour was degraded, whereas performance in chromaticity tasks was worst when the surface was degraded. This interaction was found even when spatial frequencies were fixed across test patterns by low-pass filtering. The results are consistent with a late (postfiltering) dual-mechanism system that processes luminance information to extract boundary representations and chromaticity information to extract surface representations.     

Border locking and the Café Wall illusion

The Café Wall illusion (seen on the tiles of a local café) is a Münsterberg chequerboard figure, but with horizontal parallel lines which may have any luminance separating the rows of displaced squares. These (the 'mortar' lines) display marked wedge distortion which is especially affected by: contrast of the squares ('tiles'); width of the 'mortar' lines, and their luminance which must not be significantly higher than that of the light squares or lower than that of the dark squares for distortion to occur. An experiment is described from which quantitative data have been obtained by varying these parameters. It is suggested that contiguous regions of different luminance (and contiguous colour regions) are normally held in spatial register by locking from common luminance boundaries. The Café Wall illusion is attributed to this border locking producing inappropriate contour shifts from neighbouring regions of contrasting luminance when separated by narrow gaps of neutral luminance. Further implications on the border-locking notion are discussed.     

Test of models of achromatic transparency

Consider an achromatic disk transparent on an achromatic background formed by two adjoining rectangles, with the common border of the rectangles dividing the disk in half. Current models of achromatic transparency contend that the perceived extent of transparency of the disk depends on the luminance contrast inside the disk and on the luminance contrast in the background outside the disk. Here, a model is proposed which contends that this perceived extent is determined only by the luminance contrasts inherent in the disk: inside the disk and between the disk and the background. Two experiments were designed to determine which luminance contrasts influence transparency. In the first experiment, subjects rated the perceived extent of transparency of the disk for different combinations of the luminances of the disk and of the background. The results strengthen the view that the perceived extent of transparency depends on the luminance contrasts inherent in the disk. In the second experiment, a test was made of the possibility that luminance contrasts between adjoining areas of the background outside the disk are nonessential for transparency. The results show that transparency occurred both when the areas of the background outside the transparent region adjoined one another and when they were separated, confirming that the perceived extent of transparency depended only on luminance contrasts between adjoining areas inherent in the disk.     

Classical and inverted White's effects

In classical White's effect, intermediate-luminance targets appear lighter when they interrupt the dark stripes of a grating and darker when they interrupt the light stripes. The effect is reversed when targets are of double-increment or double-decrement luminance, relative to the luminances of grating stripes. To find a common explanation for classical and inverted effects, we ran two experiments. In experiment 1, we utilised intermediate-target displays to show that perceived transparency dominates over occlusion only when the target luminance is close to the luminances of top regions. This result weakens transparency-based accounts of White's effect. In experiment 2, we varied grating contrast and target luminance to measure the classical effect in seven intermediate-target cases, as well as the inverted effect in four double-increment and four double-decrement cases. Both types of effect are explained by a common model, based on assimilation to the top region and contrast with the interrupted region, weighted by adjacency along the luminance continuum.     

Background luminance and input devices on clicking performance with a tablet PC

This study investigated the effects of input devices and background luminance on clicking performance with a Tablet PC. The experiment was designed in complete block design within subjects. Participants were 19 men and 11 women, college students whose ages were 19 to 22 years (M=20.1 yr.). All had 0.8 corrected visual acuity or better and normal color vision. Three kinds of input devices, mouse, light pen, and touchpad, were used in this experiment. An analysis of variance showed that input devices significantly affected clicking performance as did background luminance (contrast ratio) on visual recognition (a higher contrast ratio gave better visual recognition).     

Hess and Pretori revisited: Resolution of some old contradictions

An early experiment by Hess and Pretori (1894) was replicated and modified in an attempt to determine why they failed to find the ratio principle later discovered by Wallach (1948). Separating the two surround-infield patterns by darkness made very little difference. However, allowing the observer to adjust the infield luminance (as in Wallach) rather than the surround luminance (as in Hess & Pretori) revealed some startling effects. At surround:infield luminance ratios greater than approximately 100∶1, there is no ratio effect; all infields appear equal and totally dark. Converging evidence is presented that Hess and Pretori’s data in this region actually represent surround-matching by the observers. Nor are ratio effects found with increments (infield brighter than surround). When free to match either infield luminances or ratios (by controlling infield luminance), observers match luminances. For decrements with ratios between 1∶1 and approximately 100∶1, lightness constancy and the ratio principle hold.     

Dancing shapes: a comparison of luminance-induced distortions

We present an illusory display in which a grid of outlined squares is positioned in front of a moving luminance gradient. Observers perceive a strong, illusory, 'wavelike' motion of the superimposed squares. We compared luminance effects on dynamic and static aspects of this illusion. The dynamic aspect was investigated by means of a temporal gradient, which induced an illusory pulsing of the outlined squares. The static aspect was investigated in two different ways. In one experiment, the outlined squares were positioned on a spatial gradient, which caused the squares to look like trapezoid shapes. In another experiment, the squares were positioned on different luminance fields, which affected their apparent size. In all experiments, luminance settings were the same, and observers were asked to indicate the direction and strength of the induced distortions. The overall results show large agreements between the dynamic distortion and the first-mentioned static distortion, whereas different tendencies emerged for the second static distortion. In a second series of experiments, we examined these distortions for various ranges of the luminance gradient and for border gradients as well. On the basis of these data, we explored how the directions of the perceived distortions of the single-gradient displays examined in this paper could be related to each other.     

Picture perception: effects of luminance on available information and information-extraction rate

In each of four experiments, complex visual stimuli--pictures and digit arrays--were remembered better when shown at high luminance than when shown at low luminance. Why does this occur? Two possibilities were considered: first that lowering luminance reduces the amount of available information in the stimulus, and second that lowering luminance reduces the rate at which the information is extracted from the stimulus. Evidence was found for both possibilities. When stimuli were presented at durations short enough to permit only a single eye fixation, luminance affected only the rate at which information is extracted: decreasing luminance by a factor of 100 caused information to be extracted more slowly by a factor that ranged, over experiments, from 1.4 to 2.0. When pictures were presented at durations long enough to permit multiple fixations, however, luminance affected the total amount of extractable information. In a fifth experiment, converging evidence was sought for the proposition that within the first eye fixation on a picture, luminance affects the rate of information extraction. If this proposition is correct and, in addition, the first eye fixation lasts until some criterion amount of information is extracted, then fixation duration should increase with decreasing luminance. This prediction was confirmed.     

Orientation-specific aftereffects to mentally generated lines

After staring at a pattern of tilted lines, subsequent lines appear to be tilted in the opposite direction (direct tilt aftereffect, TAE). In a previous fMRI study we have demonstrated a direct TAE solely induced by the mental imagination accompanied by adaptation of orientation-selective neurons located in the extrastriate cortex, supporting the assumption of a perception-like coding of mental images. In this study we enlarge and specify the evidence for a perception-like coding of orientation-imagination. First, we replicated the previously detected direct TAE induced by line imagination with altered design-variations to control possible perceptual task confounds. Second, we tried to induce two other orientation-specific aftereffects: indirect TAE and contrast-threshold elevation aftereffect by mental imagery. The results replicate a robust direct TAE by mental imagery and by visual stimulation, with no influence of attentional resource allocation or perceptual task confounds. We could not induce an indirect TAE, but observed a perception bias in the opposite direction of the indirect TAE. The mental imagery of lines induced no orientation-selective contrast-threshold elevation aftereffect. In general, mental imagery seems to influence visual perception, indicating that perceptual resources are used by mental imagery. However, the utilisation of visual resources seems to be somewhat different from utilisation by perception.     

Effects of luminance contrast on color spreading and illusory contour in the neon color spreading effect

The present study examined whether color spreading and illusory contours in the neon color spreading effect of Ehrenstein figures are governed by different mechanisms. In the experiment, Ehrenstein figures with colored crosses inserted in the central gaps were used. There were three luminance conditions: the luminance of the Ehrenstein figures was lower than, the same as, or higher than the luminance of the background. In each condition, 16 trials (2 sets of instructions X 8 repetitions) were conducted in a random order. Subjects were required to adjust the luminance of the colored crosses according to one of the two sets of instruction given before each trial. One was to adjust the upper and lower thresholds in the luminance of the colored crosses such that their color was seen to spread out of the crosses. The other was to adjust the thresholds such that circular illusory contours were visible. It was found that illusory contours disappeared and the color spreading remained when the crosses and the Ehrenstein figures were in or nearly in isoluminance or when the Ehrenstein figures and the background were in isoluminance. These results suggest that color spreading and illusory contours are governed by different mechanisms.     

Brightness for different surround conditions: the effect of transient glare

We measured the effect of a transient glare source on t heperceived brightness of astandard luminance (L(STD)) patch (0.5 cd/m2) as a function of the surround luminance (Ls). In the experiment, both increment and decrement stimuli were dependent on the value of the Ls (0.01, 0.2, 0.4, 0.6, 0.8, 1.0, 1.5, or 2.0 cd/m2). We adopted a magnitude comparison paradigm using constant stimuli to determine the test matching luminance (L(M)). When L(S) was lower than the luminance of the patch, which corresponds to increments, LM was lower than L(STD), and this effect was highest for the lowest L(S). There was a small but noticeable cusp as increments shifted to decrements. As L(S) increased further (i.e., as the decrement grew), L(M) flattened out below L(STF). The overall pattern of results could be interpreted in terms of the concept of contrast brightness, with consideration of the intrinsic differences in brightness evaluations between decrements and increments.     

局部亮度与语义关系对真实情景识别的影响

以真实情景图片为材料,探讨局部亮度与语义关系对情景识别的影响,以及情景背景线索和语义关系的获得。实验一结果显示,被试对有无语义关系情景图片的识别反应时存在显著差异,且对拼接图片的识别正确率更高,反应时更短。实验二探讨了局部亮度与呈现时间变化条件下情景背景线索和语义关系的获得。结果发现,情景语义关系和背景信息的获得受到局部亮度变化和呈现时间的影响。这表明,语义关系和呈现时间对情景识别存在显著影响,而且这种影响与情景背景线索和语义关系的获得有关。呈现时间越长,越易获得情景语义关系。局部亮度变化越小,背景线索越易获得,呈现时间的影响越小。