Attention,brightness contrast,and assimilation: The influence of relative area

A model of information transmission in the visual system which describes the effect of attention on apparent brightness is examined. This model states in part that the luminance of the portion of the visual field which captures the attention is overweighted in arriving at an overall average luminance level across the visual field. As this average must be computed with respect to both luminance and relative area, it is hypothesized that increasing the relative area of the portion of the visual field that captures the attention will result in a greater effect on the apparent brightness of all parts of the visual field. Two predictions, which involve the effect of relative area on apparent brightness, are experimentally tested and confirmed.     

A new visual illusion: flickering fields are localized in a depth plane behind nonflickering fields

Flickering regions of the visual field are perceived to lie well behind regions which are not flickered. The depth segregation is not due to luminance differences since the average temporal luminance across all the regions was equal. This depth effect produced by flicker is not dependent on the texture of the visual field; nor does it depend on a specific configuration of the flickering and nonflickering areas. It is optimal at a temporal frequency around 6 Hz, which suggests that visual channels responding maximally to high temporal frequencies are involved in the segregation of perceptual regions in depth.     

Light and dark adaptation of visually perceived eye level controlled by visual pitch

The pitch of a visual field systematically influences the elevation at which a monocularly viewing subject sets a target so as to appear at visually perceived eye level (VPEL). The deviation of the setting from true eye level averages approximately 0.6 times the angle of pitch while viewing a fully illuminated complexly structured visual field and is only slightly less with one or two pitched-from-vertical lines in a dark field (Matin & Li, 1994a). The deviation of VPEL from baseline following 20 min of dark adaptation reaches its full value less than 1 min after the onset of illumination of the pitched visual field and decays exponentially in darkness following 5 min of exposure to visual pitch, either 30° topbackward or 20° topforward. The magnitude of the VPEL deviation measured with the dark-adapted right eye following left-eye exposure to pitch was 85% of the deviation that followed pitch exposure of the right eye itself. Time constants for VPEL decay to the dark baseline were the same for same-eye and cross-adaptation conditions and averaged about 4 min. The time constants for decay during dark adaptation were somewhat smaller, and the change during dark adaptation extended over a 16% smaller range following the viewing of the dim two-line pitched-from-vertical stimulus than following the viewing of the complex field. The temporal course of light and dark adaptation of VPEL is virtually identical to the course of light and dark adaptation of the scotopic luminance threshold following exposure to the same luminance. We suggest that, following rod stimulation along particular retinal orientations by portions of the pitched visual field, the storage of the adaptation process resides in the retinogeniculate system and is manifested in the focal system as a change in luminance threshold and in the ambient system as a change in VPEL. The linear model previously developed to account for VPEL, which was based on the interaction of influences from the pitched visual field and extraretinal influences from the body-referenced mechanism, was employed to incorporate the effects of adaptation. Connections between VPEL adaptation and other cases of perceptual adaptation of visual direction are described.     

Mislocalization of a target toward subjective contours: attentional modulation of location signals

This study examined whether a briefly presented target was mislocalized toward a subjective contour. Observers manually reproduced the position of a briefly presented peripheral target circle above a central fixation cross. A luminance contour, a subjective contour, or a no-contour stimulus was presented in either the left of right visual field, and a no-contour control was presented in the opposite visual field. After these stimuli vanished, a target circle was then presented. Consequently, the degree of mislocalization toward the subjective and luminance contours was the same; this indicated that image integration at a coarse spatial scale cannot explain mislocalization. Experiment 2 revealed that the mislocalization in Experiment 1 was not a result of eye movements. Experiment 3 found that the spatial attention allocated at the location of the luminance and subjective contours was more than that allocated at the no-contour stimulus. An attentional shift toward the task-irrelevant stimulus resulted in a mislocalization of the target.     

Brightness perception in the visual field

Summary Apparent brightness was measured at different positions in the visual field for scotopic, mesopic, and photopic adaptation levels by means of a magnitude estimation technique. Apparent brightness of targets with a given luminance remained rather constant throughout the visual field for the mesopic and photopic adaptation level; for the scotopic adaptation level targets in the foveal and perifoveal area had to be more intense in order to appear as bright as targets in the far periphery (beyond 20° eccentricity). For the photopic range, two brightness power functions with different exponents were obtained for the luminance range from 1 to 100 mL at each eccentricity. The exponent for the range from 1 to 10 mL is considerably greater than the exponent beyond 10 mL, and appears to increase with increasing eccentricity.The experiments described in this paper were partly supported by Deutsche Forschungsgemeinschaft and SFB 50-C 6.     

PSYCHOPHYSICAL INVARIANTS OF ACHROMATIC COLOUR VISION: I. The multidimensionality of achromatic colour experience

L ie . I. Psychophysical invariants of achromatic colour vision. I. The multi-dimensionality of achromatic colour experience. Scand. J. Psychol ., 1969, 10, 167–175.—The literature relevant to the question of multidimensionality of achromatic colour is briefly reviewed. An experiment confirms that the achromatic scale is bidimensional, and indicates that the dimension of brightness is a direct function of the luminance of the local area inspected, while the dimension of whiteness is a direct function of luminance relations of adjacent areas in the visual field.     

VDT屏面亮度和文件背景照度对视觉核读作业的影响

研究VDT屏面亮度和文件背景照度对视觉核读作业的影响效应。以核读速度、限肌调节辐合时间和主观舒适性为测评指标。结果上述三项指标均随VDT屏面亮度和文件背景照度的变化而发生变化。结论推荐VDT屏面亮度的合适范围为15～20cd／m^2,文件背景照度的合适范围为300～450lux。VDT屏而亮度与背景照度水平的匹配性也应加以考虑。     

Effects of absolute luminance and luminance contrast on visual discrimination in low mesopic environments

Recent research revealed considerable decline in visual perception under low luminance conditions. However, systematic studies on how visual performance is affected by absolute luminance and luminance contrast under low mesopic conditions (<0.5 cd/m²) is lacking. We examined performance in a simple visual discrimination task under low mesopic luminance conditions in three experiments in which we systematically varied base luminance and luminance contrast between stimulus and background. We further manipulated eccentricity of the stimuli because of known rods and cones gradients along the retina. We identified a “deficiency window” for performance as measured by d’ when luminance was < 0.06 cd/m² and luminance contrast as measured by the luminance ratio between stimulus and background was below < 1.7. We further calculated performance-based luminance as well as contrast efficiency functions for reaction times (RTs). These power functions demonstrate the contrast asymptote needed to decrease RTs and how such a decrease can be achieved given various combinations of absolute luminance and luminance contrast manipulations. Increased eccentricity resulted in slower RTs indicative of longer scan distances. Our data provide initial insights to performance-based efficiency functions in low mesopic environments that are currently lacking and to the physical mechanisms being utilized for visual perception in these extreme environments.     

Visual search for direction of shading is influenced by apparent depth.

Recent reports of rapid visual search for some feature conjunctions suggested that preattentive vision might be sensitive to scene-based as well as to image-based features (Enns & Rensink, 1990a, 1990b). This study examined visual search for targets defined by the direction of a luminance gradient, a conjunction of luminance and relative location that often corresponds to object curvature and direction of lighting in naturalistic scenes. Experiment 1 showed that such search is influenced by several factors, including the type of gradient, the shape of the contour enclosing the gradient, and the background luminance. These factors were varied systematically in Experiment 2 in a three-dimensionality rating task and in a visual-search task. The factors combined interactively in the rating task, supporting the presence of an emergent property of three-dimensionality. In contrast, each factor contributed only additively to the speed of the visual-search task. This is inconsistent with the view that search is guided by specialized detectors for surface curvature or direction of lighting. Rather, it is in keeping with the view that search is governed by a number of "quick and dirty" processes that are implemented rapidly and in parallel across the visual field.     

Visual search for direction of shading is influenced by apparent depth

Recent reports ofrapid visual search for some feature conjunctions-suggested that preattentive vision might be sensitive to scene-based as well as to image-based features (Enns & Rensink, 1990a, 1990b). This study examined visual search for targets defined by the direction of a luminance gradient, a conjunction of luminance and relative location that often: corresponds to ob-= ject curvature and direction of lighting in naturalistic scenes. Experiment 1 showed that such search is influenced by several factors, including the type of gradient, the shape of the contour enclosing the gradient, and the background luminance. These factors were varied systematically in Experiment 2 in a three-dimensionality rating task and in a visual-search task. The factors combined interactively in the rating task, supporting the presence of an emergent property of three-dimensionality. In contrast, each factor contributed only additively to the speed of the visualsearch task. This is inconsistent with the view that search is guided by specialized detectors for surface curvature or direction of lighting. Rather, it is in keeping with the view that search is governed by a number of “quick and dirty” processes that are implemented rapidly and in parallel across the visual field.     

Laser optometer incorporating the Badal principle

The refractive state of the eye can be accurately determined while performing a visual task by introducing the diverged beam of a laser, reflected from a moving drum, into the visual field. The direction of the apparent motion of the resultant interference pattern is a direct indicator of refractive state. By incorporation of the Badal principle into the optical system, a measurement can be completed within approximately 30 sec. The advantage of this method over other techniques is that it permits evaluation of refractive state but does not itself influehce the magnitude of accommodation. A number of applications of this principle are cited.     

Effects of luminance ratio in a liquid-crystal display on discrimination of separation by elderly people

In a 2006 study the influence of spacing between vertical lines, exposure time, and number of vertical lines on visual performance was identified. The present study further explored the effects of luminance ratio on discrimination of separation. Analysis showed the luminance ratio of target vertical lines affected the visual performance of both younger and elderly people. The luminance ratio was greater, as was accuracy; however, accuracy might not become greater when the luminance ratio was too high. Further, the effect of the number of vertical lines on accuracy was significant, as was consistent with the 2006 study. Two interactive two-way effects were found, group x luminance ratio and luminance ratio x number of vertical lines.     

Effects of ball color on horizontal perimetry detection

The subjects were 16 college students assessed as having normal, uncorrected visual abilities. Each subject responded to the appearance of each of five variously colored ball sections as they were introduced into the subjects' visual field. Analysis indicated that colors with luminance values greater than 70 CD/M2 (black, blue, green) were detected further in the horizontal peripheral plane than were colors possessing values less than 36 CD/M2 (red, purple).     

Brightness enhancement and the Talbot level in stationary gratings

At low spatial frequencies, the perceived brightness of the light phase of a stationary square-wave grating is greater than the brightness of a solid field of equal physical luminance. That increase in the perceived brightness of a grating at low spatial frequencies is analogous to the brightness enhancement observed in a flickering light at low temporal frequencies. At or above the critical spatial frequency—the visual resolution threshold—the brightness of a grating is determined by its space-average luminance, just as the brightness of a flickering light at or above the critical flicker frequency is determined by its time-average luminance in accordance with Talbot’s law. Thus, Talbot’s law applies in the spatial as well as the temporal domain. The present study adds to the evidence that temporal and spatial frequency play analogous roles in some aspects of brightness vision.     

The role of facial colour and luminance in visual and audiovisual speech perception

We conducted four experiments to investigate the role of colour and luminance information in visual and audiovisual speech perception. In experiments 1a (stimuli presented in quiet conditions) and 1b (stimuli presented in auditory noise), face display types comprised naturalistic colour (NC), grey-scale (GS), and luminance inverted (LI) faces. In experiments 2a (quiet) and 2b (noise), face display types comprised NC, colour inverted (CI), LI, and colour and luminance inverted (CLI) faces. Six syllables and twenty-two words were used to produce auditory and visual speech stimuli. Auditory and visual signals were combined to produce congruent and incongruent audiovisual speech stimuli. Experiments 1a and 1b showed that perception of visual speech, and its influence on identifying the auditory components of congruent and incongruent audiovisual speech, was less for LI than for either NC or GS faces, which produced identical results. Experiments 2a and 2b showed that perception of visual speech, and influences on perception of incongruent auditory speech, was less for LI and CLI faces than for NC and CI faces (which produced identical patterns of performance). Our findings for NC and CI faces suggest that colour is not critical for perception of visual and audiovisual speech. The effect of luminance inversion on performance accuracy was relatively small (5%), which suggests that the luminance information preserved in LI faces is important for the processing of visual and audiovisual speech.     

Lightness constancy: Ratio invariance and luminance profile

The term simultaneous lightness constancy describes the capacity of the visual system to perceive equal reflecting surfaces as having the same lightness despite lying in different illumination fields. In some cases, however, a lightness constancy failure occurs; that is, equal reflecting surfaces appear different in lightness when differently illuminated. An open question is whether the luminance profile of the illumination edges affects simultaneous lightness constancy even when the ratio invariance property of the illumination edges is preserved. To explore this issue, we ran two experiments by using bipartite illumination displays. Both the luminance profile of an illumination edge and the luminance ratio amplitude between the illumination fields were manipulated. Results revealed that the simultaneous lightness constancy increases when the luminance profile of the illumination edge is gradual (rather than sharp) and homogeneous (rather than inhomogeneous), whereas it decreases when the luminance ratio between the illumination fields is enlarged. The results are interpreted according to the layer decomposition schema, stating that the visual system splits the luminance into perceived lightness and apparent illumination components. We suggest that illumination edges having gradual and homogeneous luminance profiles facilitate the luminance decomposition process, whereas wide luminance ratios impede it.     

Visual perception of thick transparent materials

Under typical viewing conditions, human observers readily distinguish between materials such as silk, marmalade, or granite, an achievement of the visual system that is poorly understood. Recognizing transparent materials is especially challenging. Previous work on the perception of transparency has focused on objects composed of flat, infinitely thin filters. In the experiments reported here, we considered thick transparent objects, such as ice cubes, which are irregular in shape and can vary in refractive index. An important part of the visual evidence signaling the presence of such objects is distortions in the perceived shape of other objects in the scene. We propose a new class of visual cues derived from the distortion field induced by thick transparent objects, and we provide experimental evidence that cues arising from the distortion field predict both the successes and the failures of human perception in judging refractive indices.     

Efficient visual search without top-down or bottom-up guidance

Two types of mechanisms have dominated theoretical accounts of efficient visual search. The first are bottom-up processes related to the characteristics of retinotopic feature maps. The second are top-down mechanisms related to feature selection. To expose the potential involvement of other mechanisms, we introduce a new search paradigm whereby a target is defined only in a context-dependent manner by multiple conjunctions of feature dimensions. Because targets in a multiconjunction task cannot be distinguished from distractors either by bottom-up guidance or top-down guidance, current theories of visual search predict inefficient search. While inefficient search does occur for the multiple conjunctions of orientation with color or luminance, we find efficient search for multiple conjunctions of luminance/size, luminance/shape, and luminance/topology. We also show that repeated presentations of either targets or a set of distractors result in much faster performance and that bottom-up feature extraction and top-down selection cannot account for efficient search on their own. In light of this, we discuss the possible role of perceptual organization in visual search. Furthermore, multiconjunction search could provide a new method for investigating perceptual grouping in visual search.     

Brightness inhibition re size of surround

The amount by which the apparent brightness of a visual field is inhibited by a surrounding field depends on the area of the inhibiting field. Interocular brightness matches showed that, as the size of a surrounding annulus is increased from a thin ring, the degree of inhibition on the brightness of an inner disk increases rapidly at first and then more slowly as the effect approaches an asymptote. The increase of the inhibition with size of annulus can be expressed as an increase in the exponent of the power function that relates the apparent brightness of the dish to its physical luminance.     

Effects of absolute luminance and luminance contrast on visual search in low mesopic environments

Diverse adaptive visual processing mechanisms allow us to complete visual search tasks in a wide visual photopic range (>0.6 cd/m²). Whether search strategies or mechanisms known from this range extend below, in the mesopic and scotopic luminance spectra (<0.6 cd/m²), has yet to be addressed. Based on a study that addressed simple target discrimination in luminance environments using contrast-dependent behavioral efficiency functions, we assessed visual search in more complex-feature and conjunction-search paradigms. The results verify the previously reported deficiency windows defined by an interaction of base luminance and luminance contrast for more complex visual-search tasks. Based on significant regression analyses, a more precise definition of the magnitude of contribution of different contrast parameters. Characterized feature search patterns had approximately a 2.5:1 ratio of contribution from the Michelson contrast property relative to Weber contrast, whereas the ratio was approximately 1:1 in a serial-search condition. The results implicate near-complete magnocellular isolation in a visual-search paradigm that has yet to be demonstrated. Our analyses provide a new method of characterizing visual search and the first insight in its underlying mechanisms in luminance environments in the low mesopic and scotopic spectra.