Effects of luminance oscillations on simulated lightness discriminations

The speed of processes underlying lightness constancy was studied by having observers discriminate small differences in simulated lightness under an oscillating illumination. The period of oscillation varied from 0.25 to 120 sec. The target was a 1 degrees square which appeared for 150 msec at random intervals either directly against a uniform background or separated from the background by a 1 degrees dark gap. When the target and background were adjacent to each other, discrimination accuracy approached control levels (fixed illumination) at all but the shortest periods of oscillation. When the gap was introduced, accuracy increased as the period of oscillation increased, but never approached control levels. The results suggest that a fast local contrast mechanism is the primary mediator of lightness constancy for this task, but that there is also a slower mechanism that may be related to adaptation.     

Relative area and relative luminance combine to anchor surface lightness values

The anchoring of lightness perception was tested in simple visual fields composed of only two regions by placing observers inside opaque acrylic hemispheres. Both side-by-side and center/surround configurations were tested. The results, which undermine Gilchrist and Bonato’s (1995) recent claim that surrounds tend to appear white, indicate that anchoring involves both relative luminance and relative area. As long as the area of the darker region is equal to or smaller than the area of the lighter region, relative area plays no role in anchoring. Only relative luminance controls anchoring: The lighter region appears white, and the darker region is perceived relative to that value. When the area of the darker region becomes greater than that of the lighter region, relative area begins to playa role. As the darker region becomes larger and relative area shifts from the lighter region to the darker region, the appearance of the darker region moves toward white and the appearance of lighter region moves toward luminosity. This hitherto unrecognized rule is consistent with almost all of the many previous reports of area effects in lightness and brightness. This in turn suggests that a wide range of earlier work on area effects in brightness induction, lightness contrast, lightness assimilation, and luminosity perception can be understood in terms of a few simple rules of anchoring.     

Relative area and relative luminance combine to anchor surface lightness values.

The anchoring of lightness perception was tested in simple visual fields composed of only two regions by placing observes inside opaque acrylic hemispheres. Both side-by-side and center/surround configurations were tested. The results, which undermine Gilchrist and Bonato's (1995) recent claim that surrounds tend to appear white, indicate that anchoring involves both relative luminance and relative area. As long as the area of the darker region is equal to or smaller than the area of the lighter region, relative area plays no role in anchoring. Only relative luminance controls anchoring: The lighter region appears white, and the darker region is perceived relative to that value. When the area of the darker region becomes greater than that of the lighter region, relative area begins to play a role. As the darker region becomes larger and relative area shifts from the lighter region to the darker region, the appearance of the darker region moves toward white and the appearance of lighter region moves toward luminosity. This hitherto unrecognized rule is consistent with almost all of the many previous reports of area effects in lightness and brightness. This in turn suggests that a wide range of earlier work on area effects in brightness induction, lightness contrast, lightness assimilation, and luminosity perception can be understood in terms of a few simple rules of anchoring.     

A fair test of the effect of a shadow-incompatible luminance gradient on the simultaneous lightness contrast

Shadow-compatibility of simultaneous lightness contrast is discussed by Alexander D Logvinenko and Paola Bressan, with examples claiming to provide a test of the hypothesis.     

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.     

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.

     

Effects of contour proximity and lightness on Delboeuf illusions created by circumscribed letters

32 observers judged the size of a letter, either an "A" or an "S," which was surrounded by a circle. Both letters were overestimated, but larger surrounding circles reduced the illusion. Decreasing the lightness contrast of the surrounding circle relative to the central letter diminished the illusion. The results suggest that, like the Delboeuf illusion, these circumscribed letters illusions are produced by interactions among size-coding neurons.     

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.     

Effects of luminance and contrast on direction of ambiguous apparent motion

A study is reported of the role of luminance and contrast in resolving ambiguous apparent motion (AM). Different results were obtained for the short-range (SR) and the long-range (LR) motion-detecting processes. For short-range jumps (7.5 min arc), the direction of ambiguous AM depended on brightness polarity, with AM only from white to white and from black to black. But for larger jumps, or when an interstimulus interval (ISI) was introduced, AM was less dependent on polarity, with white often jumping to black and black jumping to white. Two potential AMs were pitted against each other, one carried by a light stimulus and the other by a dark stimulus. The stimulus whose luminance differed most from the uniform surround captured the AM. Visual response to luminance was linear, not logarithmic. When the stimulus was modified to give continuous AM in one direction it was followed by a negative aftereffect of motion only when the spatial displacement was 1 min arc. A larger displacement (10 min arc) gave good AM but no motion aftereffect. Thus only short-range motion adapts motion-sensitive channels.     

Effects of surround/test field luminance ratio on induced colour

Abstract.— According to Kirschmann's third law the induced colour is at its maximum when the inducing and induced fields are of equal luminance. Later studies (Kinney, 1962) show the induced colour to be most pronounced at a luminance ratio (inducing/induced) of about 4/1. In the present study the amount of colour induced into an achromatic test field was determined for one inducing colour, red, by letting observers judge the colour strength of the induced field. The test (or induced) field luminance was varied to give luminance ratios between 0.5/1 and 2/1. The results show that both colour strength and blackness increase as the luminance ratio is increased. The fact that the test field was judged even to have maximum chromatic colour strength and maximum blackness at the same time is discussed in relation to the method used and in relation to earlier studies on the "mode of appearance" of colours and the bidimensionality of achromatic colours.     

Effects of algebraic and absolute luminance differences on achromatic surface grouping

The algebraic luminance difference corresponding to a uniform achromatic surface on a uniform achromatic background determines the dark or light quality and the extent of this quality in the achromatic colour of the surface, while the absolute value of this difference determines the amount of perceived contrast between the achromatic colours of the surface and of the background. The results of an experiment designed to test whether grouping of achromatic surfaces depends on one or on both of these differences are here reported. Grouping was found to depend prevailingly on algebraic luminance difference in some subjects, prevailingly on absolute luminance differences in other subjects, and on both of these differences with similar probabilities in still other subjects.     

Effects of flash luminance and positional expectancies on visual response latency

It is well established that human observers respond more quickly to visual targets that appear in expected locations than they do to ones in unexpected locations. These variations in simple reaction time have been attributed to a covert alignment of an attentional mechanism to the expected target location. The present experiments investigated the influence of strength of signal and strength of subject’s positional expectancy on the magnitude of this attentional effect. In the first experiment, target luminance was varied over a range of three log units, and it was found that the effects of luminance were essentially additive with the effect of the positional expectancy (i.e., the attention effect). The second experiment found that the magnitude of visual attention interacts with the information value of the precue used to create the spatial expectancy, although, once again, luminance had additive effects. The resuls are interpreted as indicating that, rather than influencing early visual processing, the act of attending to a spatial location operates fairly late in the detection process.     

Effects of overtraining on reversal learning by rats in concurrent and single discriminations

Two experiments examined the whole-partial effect of overtraining in concurrent discriminations and assessed the effect against single discrimination training in rats. In Experiment 1 overtraining facilitated reversal in Group W, in which rats were given concurrent training on two simultaneous discrimination tasks (A and B) in original learning before both tasks were reversed. By contrast, overtraining delayed reversal in Group P, in which animals were given the same training as in Group W in original learning, but only Task A was reversed. After overtraining, Group W reversed more rapidly than Group P. Without overtraining, Group P reversed more rapidly than both Group W and Group C, in which animals were trained only on Task A before this task was reversed. Experiment 2 investigated the effects of overtraining on the reversal of a successive discrimination in Groups W, P, and C. In addition, animals in a further group, Group S, received the same concurrent training as Group W before Task B was omitted and Task A reversed. Overtraining facilitated reversal in Groups W, C, and S but delayed it in Group P. After overtraining, Group W reversed more rapidly than Groups P, S, and C. Both Groups S and C also reversed more rapidly than did Group P. Without overtraining, Group P reversed more rapidly than Groups W, S, and C. There were no significant differences in reversal performance among Groups W, S, and C. These findings indicate that the effects of overtraining on reversal learning in concurrent discriminations differ from those observed in single discriminations.     

Effects of simulated stuttering on listener recall

In an investigation of the effects of simulated stuttering on listener recall, a presentation was varied on two factors: degree of stuttering (mild or severe) and information value of stuttered words (low or high). A control presentation featuring non-stuttered speech also was prepared. Five groups of 16 subjects were randomly assigned to, and participated in, one of the five listening conditions. Then they completed a 20-item recall test. A one-way analysis of variance revealed sognificant differences among the five conditions. Two-way analysis of variance disclosed no main effects. However, a significant interaction showed that recall was lowest in the severe stuttering-high information condition. The results are discussed in terms of attention to critical information.     

Effects of target-background luminance ratios upon the autokinetic illusion

This study investigated effects of the target-background luminance ratios upon the autokinetic illusion, with special emphasis on manipulation of the background intensity. Exp. 1, in which the effects of four levels of target luminance were examined against the completely dark background, showed that the target luminance did not affect the illusion as long as the target was small enough in size (0.17 degrees in visual angle). This result confirmed the suggestion by Edwards in 1954. In Exp. II effects of the target-background luminance ratios were examined by varying the luminance of target and background independently. Dominant illusory patterns at the luminance ratio 1 were "pendulum-like" and "bobbing"; these differed from those at higher ratios ("winding"). On the other hand, latency and duration were not affected by the ratios. These findings suggest that the movement pattern is effective in specifying the autokinetic illusion, if it is appropriately categorized and represented.     

The unbearable lightness of priming

Repetition priming from text to isolated words has been difficult to observe. One explanation for this difficulty is that previous attempts to observe this type of priming have utilised conditions that normally reduce priming. Two experiments were conducted to evaluate this hypothesis. Experiment 1 involved participants being presented with words in isolation and in text passages. The words were then presented again in a lexical decision test. Results indicated that priming occurred as a result of exposure to both isolated words and words in text, although priming was greater in the word-word condition. Experiment 2 investigated whether priming occurred in a lexical decision test on words that had been read prior to the test in Milan Kundera's novel "The Unbearable Lightness of Being." There was some evidence that participants who had read the book recently were faster at lexical decision to words from the book than participants who had not read the book. The two experiments therefore indicate that priming can occur from text to isolated words, although it is smaller in magnitude to that observed from word to word. Reasons for this difference, as suggested by Kirsner and Speelman (J. Exp. Psychol.: Learn. Mem. Cogn. 22 (1996) 563) model of repetition priming, are discussed.     

Effects of cocaine and d-amphetamine on the repeated acquisition and performance of conditional discriminations.

The acute and chronic effects of cocaine and d-amphetamine on food-reinforced behavior were investigated in pigeons responding on a two-component multiple schedule. In one component, the behavioral task consisted of the same chain of conditional discriminations each session (performance). In the other component, the chain of conditional discriminations was changed from session to session (learning). In comparison to control sessions, both acute cocaine and d-amphetamine increased errors in each component of the multiple schedule. Responding in the learning component, however, was generally disrupted at lower doses than those that affected responding in the performance component. At high doses, both drugs produced pauses in responding in each component in three of the four subjects. Pausing engendered by d-amphetamine was approximately twice as long as that under cocaine. Upon chronic administration, both the pausing and error-increasing effects of each drug diminished. Drug-induced changes in timeout responding, however, did not decrease during chronic administration. Redeterminations of the d-amphetamine dose-effect curves following chronic cocaine administration suggested the existence of cross-tolerance between cocaine and d-amphetamine. Both the acute and chronic data are consistent with the view that conditions of stimulus control may modulate the behavioral effects of drugs.     

Simultaneous lightness contrast on plain and articulated surrounds

Simultaneous lightness contrast is stronger when the dark and light backgrounds of the classic display (where one of the targets is an increment and the other is a decrement) are replaced by articulated fields of equivalent average luminances. Although routinely attributed to articulation per se, this effect may simply result from the increase in highest luminance in the light articulated, vs plain, background; by locally darkening the decremental target, such an increase would amplify the difference between the targets. We disentangled the effects of highest luminance and articulation by measuring, separately, the magnitude of lightness contrast on dark and light plain and articulated backgrounds. We found that highest luminance and articulation contribute separately to the final illusion.