Induction of the McCollough effect I: Figural variables

The effect of line orientation and line configuration on the induction of orientation-specific negatively colored aftereffects was investigated in three separate studies. In the first study, subjects viewed magenta-and-black vertical gratings with one eye, alternating with green-and-black vertical gratings to the other. Monocular tests revealed complementary aftereffects in each eye which disappeared when the test patterns were viewed with both eyes together. In Study 2, imposing a single colored bar against a black background induced negatively colored aftereffects in a white bar against a black background and in a black-and-white grating, while imposing a single black bar against a colored background was ineffective. In Study 3, presenting a magenta square outline elicited green aftereffects in vertical and horizontal bars and gratings as well as in outlines of squares and diamonds, while pairing the magenta square with a green cross had no effect. It was concluded that the induction mechanism responsible for the McCollough effect is sensitive to line orientation but not to shape. This specificity appears incompatible with a simple conditioning model.     

Pressure blindness and the interocular transfer of size aftereffects

After observation of a stimulus composed of a top grating with large bar widths (low spatial frequency) and a bottom grating of narrow lines (high spatial frequency), a subsequently presented test grating of medium bar width appears to have a higher spatial frequency on the top half than on the bottom. Although this size aftereffect can be obtained dichoptically, this does not necessarily imply a central locus, since retinal input from the adapted eye could produce the effect. Ss were tested for the aftereffect in the adapted eye and for interocular transfer with and without pressure blinding the adapted eye. In this last condition, input from the adapted eye cannot reach the cortex. However, the aftereffect was equally present under all three conditions. This result suggests that size and frequency adaptation have a central locus.     

Colored aftereffects produced with moving edges

Colored aftereffects that lasted as long as 6 weeks were produced with moving patterns of parallel black and white stripes or with black and white spirals. During adaptation, the patterns moved periodically in opposite directions, each direction paired with one illuminant, red or green. When the moving patterns were later viewed in white light, S saw the red and green colors, but they were related in the opposite way to the direction of motion. The red and green aftereffects were also produced by other pairs of illuminants, red and white, white and green, reddish-yellow and white, and white and greenish-yellow. The aftereffects did not occur unless, during adaptation, the stripes moved in both directions, each direction paired with a different color. The aftereffect was elicited by stripe motion over the retina—it was seen when the eye swept over a pattern of stationary stripes. The aftereffect desaturated when the retinal orientation of the stripes was changed from the adaptation orientation. Saturation was increased by longer exposure and slower speed during adaptation and by faster speed and a more rapid rate of altemation during the test. The luminance of the adaptation light seemed to have little effect. The aftereffect did not transfer from one eye to the other, and it did not change retinal locus, as was shown when clear images of a colored square that lasted several days were produced with a spiral. S ftxated the spiral’s center. The spiral rotated altemately in opposite directions. A red square with a green surround was projected on the center of the spiral when it rotated in one direction; a green square with a red surround was used when it rotated in the other direction. Following 50 min of adaptation, colored images of the squares were seen when the center of the spiral was ftxated and the direction of     

An orientation anisotropy in induced brightness

It is shown that an orientation anisotropy exists for the magnitude of induced brightness in a cruciform stimulus consisting of a grey test patch positioned at the intersection of two inducing bars, one black and one white, oriented at right angles to each other. When the cruciform was oriented such that the white bar was horizontal, the grey patch appeared darker than when the same cruciform was oriented such that the white bar was vertical. The contribution of the black and white inducing bars towards the brightness of the test patch was investigated. A simple mathematical function, which took into account both the contribution of the two component inducing bars and the orientation anisotropy, was fitted to the data. No consistent orientation anisotropy was found with inducing stimuli at oblique orientations.     

The representation of auditory source characteristics: Simple geometric form

Two experiments examined listeners’ ability to discriminate the geometric shape of simple resonating bodies on the basis of their corresponding auditory attributes. In cross-modal matching tasks, subjects listened to recordings of pairs of metal bars (Experiment 1) or wooden bars (Experiment 2) struck in sequence and then selected a visual depiction of the bar cross sections that correctly represented their relative widths and heights from two opposing pairs presented on a computer screen. Multidimensional scaling solutions derived from matching scores for metal and wooden bars indicated that subjects’ performance varied directly with increasing differences in the width/height (WIH) ratios of both sets of bars. Subsequent acoustic analyses revealed that the frequency components from torsional vibrational modes and the ratios of frequencies of transverse bending modes in the bars correlated strongly with both the bars’ WIH ratios and bar coordinates in the multidimensional configurations. The results suggest that listeners can encode the auditory properties of sound sources by extracting certain invariant physical characteristics of their gross geometric properties from their acoustic behavior.     

Variation in hue of a contour-contingent aftereffect due to color adaptation during inspection of the stimulus patterns

The McCollough Effect (a colored line-orientation-contingent aftereffect) has been attributed to the presence of edge detectors specific to wavelength in the human visual system. The present study tests this hypothesis by introducing unlined colored fields into the inspection condition and by comparing the subsequent aftereffect with the aftereffect induced by the inspection condition not including the unlined colored fields. The data indicate that the hues of the aftereffects differ, suggesting that the color and line stimuli may be processed by different populations of neural elements, and that the color-coded edge detector model is not adequate to account for the observations.     

Induction of the McCollough effect II: Two different mechanisms

An orientation-specific chromatic aftereffect was observed when a single colored grating was used as an induction stimulus. The magnitude of the aftereffect was compared to that obtained when alternating orthogonal gratings in complementary hues were used as induction stimuli. The two-stimulus condition produced a stronger aftereffect than a single-stimulus condition. This facilitation was also obtained when a colored plain square with no grating was substituted for the second colored grating in the two-stimulus condition. The results suggest that the McCollough effect involves adaptation of two different mechanisms, one which is orientation-specific and one which is not.     

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.     

Color-luminance relationships and the McCollough effect

The McCollough effect is an orientation-specific color aftereffect induced by adapting to colored gratings. We examined how the McCollough effect depends on the relationships between color and luminance within the inducing and test gratings and compared the aftereffects to the color changes predicted from selective adaptation to different color-luminance combinations. Our results suggest that the important contingency underlying the McCollough effect is between orientation and color-luminance direction and are consistent with sensitivity changes within mechanisms tuned to specific color-luminance directions. Aftereffects are similar in magnitude for adapting color pairs that differ only in S cone excitation or L and M cone excitation, and they have a similar dependence on spatial frequency. In particular, orientation-specific aftereffects are induced for S cone colors even when the grating frequencies are above the S cone resolution limit. Thus, the McCollough effect persists even when different cone classes encode the orientation and color of the gratings.     

Color—luminance relationships and the McCollough effect

The McCollough effect is an orientation-specific color aftereffect induced by adapting to colored gratings. We examined how the McCollough effect depends on the relationships between color and luminance within the inducing and test gratings and compared the aftereffects to the color changes predicted from selective adaptation to different color—luminance combinations. Our results suggest that the important contingency underlying the McCollough effect is between orientation and color—luminance direction and are consistent with sensitivity changes within mechanisms tuned to specific color—luminance directions. Aftereffects are similar in magnitude for adapting color pairs that differ only in S cone excitation or L and M cone excitation, and they have a similar dependence on spatial frequency. In particular, orientation-specific aftereffects are induced for S cone colors even when the grating frequencies are above the S cone resolution limit. Thus, the McCollough effect persists even when different cone classes encode the orientation and color of the gratings.     

The associative basis of contingent color aftereffects.

According to a conditioning analysis of the orientation-contingent color aftereffect (McCollough effect, ME), orientation stimulus (grids) become associated with color. Contrary to this interpretation are reports that simple forms cannot be used to elicit illusory color and that the ME is not degraded by decreasing the grid-color correlation. The present results indicate: (a) Form stimuli can contingently elicit color aftereffects; (b) even a non-patterned stimulus--the lightness of a frame surrounding a colored area--can contingently elicit color aftereffects; (c) this frame lightness-contingent aftereffect, like the ME, persists for at least 24 hr; and (d) the frame lightness-contingent aftereffect can be used to demonstrate that correlational manipulations affect the ME, as they affect other types of conditional responses.     

Effects of element orientation on apparent motion perception

We present an ambiguous motion paradigm that allows us to quantify the influence of aspects of form relevant to the perception of apparent motion. We report on the role of bar element orientation in motion paths. The effect of orientation differences between bar elements in a motion path is small with respect to the crucial role of the orientation of bar elements relative to motion direction. Motion perception between elements oriented along the motion direction dominates motion perception between elements oriented perpendicularly to motion direction. The perception of apparent motion is affected by bar length and width and is anisotropic.     

Interaction between perceived and imagined rotation

In Experiment 1, subjects performed a mental-rotation task in which they were timed as they decided whether rotated letters were normal or backwards. Between presentations of the letters, they watched a rotating textured disk that induced an aftereffect of rotary movement on the letters. The function relating reaction times to orientation was influenced asymmetrically by the aftereffect, suggesting that perceived movement interacts with imagined movement. Experiment 2 showed that the aftereffect produced a negligible influence on perceived orientation, suggesting that the influence of the aftereffect on mental rotation was not caused by changes in the perceived orientations of the letters. Detailed analysis of the mental-rotation functions suggested that the aftereffect may sometimes have induced subjects to rotate letters through the larger rather than the smaller angle back to the upright where the aftereffect was in the appropriate direction.     

Loss of wavelength selectivity in contour masking and aftereffect following dichoptic adaptation

Two experiments measured the apparent orientation (aftereffect) and the threshold for detection (masking) of a colored grating viewed by one eye after exposure to a colored grating to the same or the opposite eye (monoptic inspection) or after stimulation of one eye by color and the other eye by contours (dichoptic inspection). Under the monoptic condition, the color relationship between the inspection and test stimuli exerted control over the extent of aftereffect and masking when the two stimuli were viewed with the same eye, but not when they were seen with different eyes. Aftereffect and masking were nonselective to wavelength following dichoptic inspection, irrespective of whether the test stimulus was presented to the color-adapted or to the contour-adapted eye. The results support other claims that visual detectors with chromatic and spatial tuning have monocular specificity.     

Binocular interaction of orientation and spatial frequency channels: Evoked potentials and observer sensitivity

The interaction between size and orientation feature processing in the human visual system was investigated. Both observer sensitivity (d’ss) and the visual evoked potential (VEP) to test gratings flashed to one eye were investigated as a function of the nature of a continuously presented suppressing grating viewed either by that same eye or the opposite eye. The test and suppressing gratings were varied both in bar width (9′ss vs. 36′ss) and orientation (vertical vs. horizontal). The continuous grating intra- and interocularly suppressed the monocular VEPs to the flashed grating, the specificity of the suppression depending on the latency at which VEP amplitude was measured. VEP amplitude measured at early latencies (100–125 msec) was suppressed primarily when the flashed and continuous gratings were the same orientation, regardless of size. Starting at about 200 msec, and thereafter, VEP amplitudes were suppressed when the continuous bars were either the same orientationor size as the flashed bars. Late latencies, starting at 220 msec, and thereafter, were suppressed primarily when the bars in the two gratings were the same orientation and size. The reduction in observer sensitivity (d′ss) paralleled the changes found in the late VEP measures. These effects were evident under both the intraocular and interocular suppressing conditions. This pattern of VEP suppression, measured across eight points in the VEP waveform, was interpreted as indicating the existence of a sequence of channels that are specific first to a particular grating orientation, then to either a particular grating spatial frequency or orientation, and finally to the conjunction of a particular orientation and spatial frequency. Both sequential and parallel feature processing appears to take place in the human visual cortex, with grating orientation being encoded earlier than grating size.     

Parallel processing in a multifeature whole-report paradigm

Observers given brief exposures of pairs of colored bars and asked to report both the color and the orientation of each bar showed evidence of stochastic independence between reports of the 4 features (2 colors and 2 orientations). The authors also found virtually perfect stochastic independence between reports of colors and directions of motion of pairwise presented circular disks at each of 3 levels of exposure duration that varied unpredictably from trial to trial. Stimulus triples, rather than pairs, yielded more complex results. However, the findings provide strong evidence that the relevant features of the 2-3 stimuli were identified and localized in parallel across the display.     

A test for contrast-polarity selectivity in the tilt aftereffect

The tilt aftereffect (TAE) was studied with adapting and test stimuli consisting of black or white bars (experiment 1), and of luminance edges (experiment 2). Both experiments failed to demonstrate selectivity of the TAE to the polarity of luminance contrast.     

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.     

The structure of frontoparallel haptic space is task dependent

In three experiments, we investigated the structure of frontoparallel haptic space. In the first experiment, we asked blindfolded participants to rotate a matching bar so that it felt parallel to the reference bar, the bars could be at various positions in the frontoparallel plane. Large systematic errors were observed, in which orientations that were perceived to be parallel were not physically parallel. In two subsequent experiments, we investigated the origin of these errors. In Experiment 2, we asked participants to verbally report the orientation of haptically presented bars. In this task, participants made errors that were considerably smaller than those made in Experiment 1. In Experiment 3, we asked participants to set bars in a verbally instructed orientation, and they also made errors significantly smaller than those observed in Experiment 1. The data suggest that the errors in the matching task originate from the transfer of the reference orientation to the matching-bar position.     

Visibility of an afterimage in the presence of a second afterimage

Visibility of an afterimage has been measured for a single rectangular bar on its own and in the presence of a second bar. Visibility of each bar is increased if the two bars are in the same orientation and closer than 1 deg (this effect being called “facilitation”) and is decreased if the bars are in different orientations (this effect being called “inhibition”). These interactions also depend on the relative size of the bars. If a pattern of two bars is viewed dichoptically, rivalry between the bars occurs causing a mutual decrease in visibility. The rivalry effect and the orientation-specific effects discussed above are additive in the dichoptic viewing condition. The orientation-specific effects have been likened to those found in other psychophysical studies of angle detection.