Luminance as a factor in the ability of achromatic gratings to interfere with MeCollough effects

McCollough effects were reduced in assessed strength by having observers view achromatic gratings that varied in space-average luminance. Whether the gratings were presented before or after induction of McCollough effects, high luminance gratings interfered with the effects more than did low luminance gratings. If considered within the context of a conditioning model, this finding may be interpreted as inconsistent with other characteristics of McCollough effects.     

“Extinction” of the McCollough effect does not transfer interocularly

A McCollough effect was induced in subjects by having them view typical adapting stimuli binocularly for 5 min. In the control condition, the strength of the McCollough effect was measured 20 min after the end of the adaptation. The strength was measured during monocular and binocular viewing of a test pattern via a color cancellation technique. Monocular strengths for the two eyes of a given subject were equal to each other and slightly weaker than the binocular strength. In the test condition, 15 min of the 20 min between adaptation and testing were spent monocularly viewing black and white gratings of the same orientation and spatial frequency as the adapting gratings. The strength of the effect as measured ipsilaterally was markedly decreased from that in the control condition. The strength of the effect as measured with the contralateral eye showed only a small decrease from that of the control condition. This finding is relevant to various models of the McCollough effect and related color aftereffects, especially those that posit a “learning” type of mechanism between achromatic spatial channels (which exhibit clear interocular transfer of various achromatic effects) and monocular color channels.     

Contour specificity of the McCollough effect

Subjective estimates of McCollough aftereffect strength are significantly reduced when certain spatial features of the line grating patterns are manipulated. Results are dependent upon whether the spatial parameters of the test or inspection patterns are altered. Changing the angular slant, contour sharpness, or contour completeness of the inspection gratings does not affect aftereffect strength, but changing the spatial frequency, contour sharpness, or contour completeness of the test gratings does. The implications of these results are discussed with regard to theories offered to explain the McCollough effect.     

Establishment and decay of orientation-contingent aftereffects of color

We have used a null method to measure the orientation-contingent aftereffects of color first described by McCollough. After alternately inspecting, for example, a green horizontal line grating and a magenta vertical line grating, the Os report that in achromatic test gratings the horizontal lines appear pinkish and the vertical lines appear greenish. We have used a special color-mixing projector to add variable amounts of green and magenta light to the test gratings until they appear matched and nearly achromatic. The colorimetric purity needed to achieve this null setting is a quantitative measure of the strength of the colored aftereffect. Following inspections of the colored patterns ranging from 15 sec to 150 min, six Os showed aftereffects lasting from a few minutes to 7 or more days. The indices of colorimetric purity increase with inspection time and decline with time after inspection. The decay function is not quite linear either on semilog or on log-log coordinates. The rate of decay is mainly dependent on the magnitude of the effect built up during inspection. We conclude that the buildup and decay of these aftereffects show some of the time characteristics usually associated with central adaptability rather than sensory adaptation.     

Checkerboard-specific color aftereffects: A failure to find effects of perceptual organization

Two experiments investigated the effects of differing perceptual organizations of reversible figures on McCollough aftereffects. Experiment 1 used colored checkerboard inducing stimuli and achromatic grating test stimuli. While some subjects tended to organize the checkerboards into rows and/or columns and others to organize them into obliques, these variations did not result in differences in aftereffect direction or magnitude. Experiment 2 induced an aftereffect with colored gratings and tested with checkerboards, gratings, and a reversible concentric octagon pattern. Perceptual organization had no effect on results for checkerboards, but was related to aftereffect strength for the octagon pattern. Indirect evidence suggests that, in the latter case, differences in aftereffect strength may have influenced the perceived organization, rather than vice versa. Finally, regardless of the specific organization perceived, spontaneous viewing of all test stimuli produced stronger aftereffects than were found when subjects reorganized the pattern. This may have resulted from a viewing strategy associated with reorganization, since similarly small aftereffects were found when subjects concentrated their attention on a single pattern element.     

The McCollough effect: Influence of several kinds of visual stimulation on decay rate

An experiment was conducted to determine whether the decay rate of the McCollough effect could be differentially influenced by the type of visual stimulation that followed its induction. After acquiring this effect, Os were exposed to achromatic gratings, homogeneous chromatic fields, natural visual stimulation, or complete darkness. Exposure to achromatic gratings caused a marked fading of the effect; the other types of stimulation were associated with similar and much less rapid decay.     

Absence of binocular interaction between spatial and color attributes of visual stimuli

The hypothesis that induction of the McCollough effect (spatially selective color aftereffects) entails adaptation of monocularly driven detectors tuned to both spatial and color attributes of the visual stimulus was examined in four experiments. The McCollough effect could not be generated by displaying contour information to one eye and color information to the other eye during inspection, even in the absence of binocular rivalry. Nor was it possible to induce depth-specific color aftereffects following an inspection period during which random-dot stereograms were viewed, with crossed and uncrossed disparity seen in different colored light. Masking and aftereffect in the perception of stereoscopic depth were also nonselective to color; in both cases, perceptual distortion was controlled by stereospatial variables but not by the color relationship between the inspection and test stimuli. The results suggest that binocularly driven spatial detectors in human vision are insensitive to wavelength.     

Hue difference contours can be used in processing orientation information

In most studies of orientation processing, chromatic information and achromatic information have been combined or confounded. The present experiments investigated the relative sizes of tilt aftereffect induced by these two types of information. In these experiments, the tilt aftereffect is the error in adjusting a test contour to vertical, following the scanning of an inspection contour. For inspection and test contours identical except for orientation, the tilt aftereffects varied with inspection contour orientation but not with chromatic or achromatic condition. Smaller tilt aftereffects were obtained when the inspection contour was produced by a hue difference (chromatic information) and the test contour was produced by a luminance difference (achromatic information), or vice versa. These results indicate that achromatic and chromatic information is processed in a similar manner with respect to orientation. Furthermore, there is substantial, but incomplete, pooling of chromatic and achromatic orientation information.     

Overprediction and blocking in the McCollough aftereffect

The Rescorla-Wagner theory (Rescorla & Wagner, 1972) of associative learning offers specific predictions about the associative strength of CS-US pairs when two or more CSs are conditioned to the same US separately and subsequently paired in a compound with the same US. The magnitude of orientation-contingent color aftereffects (AEs) was used as an index of associative strength in this study. The results of experiments using an "overprediction" (Rescorla, 1970) and a "blocking" (Kamin, 1969) paradigm conformed to the predictions of the Rescorla-Wagner theory. In Experiment 1, AEs were established simultaneously for horizontal-vertical and diagonal patterns. When observers subsequently viewed compound induction patterns, AE magnitude was found to be significantly decreased, relative to a condition in which observers did not view such an induction pattern. In Experiment 2, AE magnitude for a given test pattern following inspection of compound induction stimuli was significantly reduced by inspection of the other component prior to viewing the compound induction stimuli. The applicability of associative learning and feature-adaptation models of the McCollough effect is discussed.     

Further evidence against the classical conditioning model of McCollough effects

McCollough effects (MEs) have been portrayed by Murch (1976) as classically conditioned responses which result from the pairing of color (unconditioned stimulus) with line orientation (conditioned stimulus). In the present experiment, we sought evidence that ME characteristics resembled those of undisputed conditioned responses. According to Rescorla (1968) and others, conditioned responses may not develop if the unconditioned stimulus is presented in the absence as well as in the presence of the conditioned stimulus. However, in our experiment, MEs induced by inspection sequences containing presentations of color alone in addition to color/ contour pairs were not weaker than controls. This discrepancy challenges the applicability of the conditioning model to MEs.     

Associative blocking of the mccollough effect

After exposure to two simultaneously presented achromatic grids (A and B) on a coloured field, subjects reported colour aftereffects on each of the separately presented grids. These aftereffects were shown to be examples of the McCollough effect, since they were contingent upon the subjects having experienced the grid in combination with the coloured field. Exposure to the coloured field in advance of combining the colour field with the grids attenuated the strengths of the aftereffects on the A and B grids. Moreover, exposure to the A grid on the coloured field in advance of combining the B grid with the A grid on the coloured field abolished the aftereffect on the B grid. The failure of the B grid to arouse the aftereffect was due to the presence of the already trained A grid, since exposure to the A grid on the coloured field followed by exposure to the B grid on that field yielded the aftereffect on the B grid. The conditions under which the McCollough effect was attenuated are those under which learning fails to occur in Pavlovian conditioning procedures. The results, therefore, supported the view that the pairing between the grids and the colour resulted in a learned association between the grids and some aspect of the response by the visual system to the colour.     

Interocular transfer of orientation-contingent color aftereffects with external and internal adaptation

The issue of whether McCollough effects transfer interocularly was examined in two experiments. In Experiment 1, as in previous experiments, no interocular transfer of McCollough effects was obtained when subjects adapted monocularly to externally present patterns with their unused eyes fully occluded. However, when subjects adapted monocularly (with the unused eye fully occluded) to visual images of those patterns superimposed on physically present chromatic backgrounds, McCollough effects transferred interocularly. In Experiment 2, subjects adapted to either physically present patterns or to images of those patterns (as in Experiment 1), but the unused eye was exposed to unpatterned diffuse white light. In contrast to Experiment 1, the externally adapted subjects showed interocular transfer of McCollough effects. In Experiment 2, the magnitude of the interocular transfer effects produced by imagery was significantly larger than the magnitude of the effects produced by external adaptation, but the magnitude of the imagery-induced aftereffects did not differ from Experiment 1 to Experiment 2. These results extend earlier findings by Kunen and May (1980) and show that McCollough effects can be produced through adaptation to imagery, even though the direction of the imagery-induced aftereffects indicates adaptation to higher spatial frequencies whereas externally derived aftereffects indicate adaptation to lower spatial frequencies. It is concluded that failure of previous studies to obtain interocular transfer of McCollough effects may have resulted from complete occlusion of the contralateral eye. These data point up some interesting similarities and some important differences between imagery and actual vision. The implications for analogical models of visual imagery are discussed.     

Movement-induced modulation of orientation-specific color aftereffects

The intensity of the McCollough effect is modified when, following exposure to the inducing chromatic stimuli, the achromatic test gratings are seen oscillating orthogonally to their orientations. Green aftereffect seen on stationary test gratings is enhanced by oscillations, while pink aftereffect present on the stationary gratings fades upon oscillation of the test stimulus. These opponent changes are tentatively accounted for in terms of an interaction between Fechner-Benham type induced color and processes that mediate the orientation-specific chromatic aftereffects.     

Satiation or availability? Effects of attention,memory, and imagery on the perception of ambiguous figures

The prolonged-inspection technique has been used to demonstrate effects of satiation on the perception of ambiguous figures. We propose that the inspection phase, in which subjects view an unambiguous version of the stimulus prior to observing the ambiguous figure, does not create neural fatigue but rather provides a context in which the alternative percept is apprehended and gains perceptual strength through processes such as imagination or memory. The consequent availability of the alternative organization drives the perceptual phenomena that have been thought to reflect satiation. In Experiment 1, we demonstrated that (1) preexperimental exposure to the target figures and (2) allocation of attention to the-inspection figures-were both necessary in order to obtain results similar to those predicted by the satiation model. In Experiment 2, we obtained similar results, finding that effects of prior inspection were greater the greater the amount and availability of information regarding the alternative percept during the inspection phase. Subjects who generated visual images of the noninspected alternative during inspection yielded results comparable to those from subjects to whom both versions were presented isuaily.     

Negative afterimages and the McCollough effect

Four experiments were conducted to test earlier claims about the relationship between the negative afterimage and the McCollough effect. The first claim (Hansel & Mahmud, 1978) is that long-lasting afterimages occur when induced by the same alternating-stimulus procedure as that used to induce the McCollough effect. The second claim (Murch & Hirsch, 1972) is that afterimages can themselves induce McCollough effects if they are induced and paired sequentially with grating patterns. In testing these claims, a reliable computer-controlled color-cancellation technique developed earlier was used to measure the apparent color of both afterimages and McCollough effects objectively. No support was found for the first claim following alternative presentation of two homogeneously colored regions for total periods of 5 min (Experiment 1) and 20 min (Experiment 2). The second claim was fully supported: After an induction period of 7.3 min, a McCollough effect occurred for a red-vertical pairing but not for a green-horizontal pairing (Experiment 3); but after an induction period of 20 min, McCollough effects occurred strongly for both pairings (Experiment 4). The theoretical implications of these outcomes are considered in the context of recent theories of color and pattern processing in the visual system.     

Contrast and frequency competition for orientation-contingent color aftereffects

A “competition” paradigm was developed to examine separately the effects of pattern contrast and spatial frequency characteristics on the strength of orientation-contingent color aftereffects (McCollough effects). After adapting to alternately presented red/black and green/black square-wave gratings (one horizontal, one vertical), 11 subjects viewed seven different kinds of test patterns. Unlike Standard McCollough effect test stimuli, the present patterns had variable luminance profiles running both horizontally and vertically within each test pattern area. Forced choice responses were used to determine which aftereffect color (red or green) appeared, as characteristics of vertical and horizontal luminance profiles were varied separately among test stimulus types. We conclude that pattern contrast and human contrast sensitivity account for aftereffect colors in such stimuli. When contrast is taken into consideration, aftereffects are not predicted by similarity between adaptation and test pattern Fourier characteristics, nor are they predicted by the width, per se, of pattern elements.     

Orientation-contingent color aftereffects mediated by subjective transparent structures.

We examined whether the orientation-contingent color aftereffect (the McCollough effect) could be mediated by subjective horizontal and vertical structure induced by the perception of transparency. In our experiments, red vertical bars and green horizontal bars were alternated as an adapting stimulus. After adaptation, subjects (n = 6) were asked to adjust the green and red saturation of a test pattern until they obtained a neutral gray. Horizontal and vertical stripes were combined in the test pattern in three different ways: (1) overlapping with a luminance combination that gave rise to a perception of transparent overlays of horizontal and vertical stripes (valid transparency condition), (2) overlapping with luminance combinations that did not induce a perception of transparency (invalid transparency condition) and that appeared more as a patchwork of checks, and (3) presented in adjacent, nonoverlapping areas. Our results showed that the McCollough effect was significantly greater in the valid transparency condition than in the invalid transparency conditions. The effect in the valid transparency condition was nevertheless less strong than was the effect seen with the standard test stimulus made up of nonoverlapping vertical and horizontal stripes. Our results suggest that the McCollough effect can be mediated by the subjective spatial organization (inner representation of vertical and horizontal stripes) that accompanies the perception of transparency in our stimulus.     

Orientation-contingent color aftereffects mediated by subjective transparent structures

We examined whether the orientation-contingent color aftereffect (the McCollough effect) could be mediated by subjective horizontal and vertical structure induced by the perception of transparency. In our experiments, red vertical bars and green horizontal bars were alternated as an adapting stimulus. After adaptation, subjects (n=6) were asked to adjust the green and red saturation of a test pattern until they obtained a neutral gray. Horizontal and vertical stripes were combined in the test pattern in three different ways: (1) overlapping with a luminance combination that gave rise to a perception of transparent overlays of horizontal and vertical stripes (valid transparency condition), (2) overlapping with luminance combinations that did not induce a perception of transparency (invalid transparency condition) and that appeased more as a patchwork of checks, and (3) presented in adjacent, nonoverlapping areas. Our results showed that the McCollough effect was significantly greater in the valid transparency condition than in the invalid transparency conditions. The effect in the valid transparency condition was nevertheless less strong than was the effect seen with the standard test stimulus made up of nonoverlapping vertical and horizontal stripes, Our results suggest that the McCollough effect can be mediated by the subjective spatial organization (inner representation of vertical and horizontal stripes) that accompanies the perception of transparency in our stimulus.     

Practice does not facilitate acquisition of McCollough effects: Evidence against a learning model

Previous investigators (Schmidt, Pinetts, & Finke, 1978) have asserted that McCollough effects (MEs) are acquired more readily by experienced than by inexperienced subjects. The present experiments examine this claim in a paradigm that utilizes quantitative measurements of MEs to evaluate possible changes in subjects’ susceptibility to them. MEs were induced every few days for approximately 2 months; results revealed no progressive increments in either strength or acquisition rats. The lack of facilitation due to practice is inconsistent with learning models proposed to account for MEs.     

THE UNIDIMENSIONAL CONCEPTION OF SIMULTANEOUS ACHROMATIC CONTRAST

H eggelund P. The unidimensional conception of simultaneous achromatic contrast. Scand. J. Psychol ., 1972, 13 , 66–70.—The perceptual changes involved in simultaneous achromatic contrast have been presumed to be specifiable as variation in brightness alone. This conception was not supported when attempts were made to produce identical appearance of two achromatic fields, with different inducing luminance, by varying the luminance in one of them. It was possible to match with respect to either achromatic quality or colour strength, but when matched with respect to quality the fields differed in strength, the field of lowest luminance appearing weaker.