Motion over the retina and the motion aftereffect.

The motion aftereffect (MAE) was measured with retinally moving vertical gratings positioned above and below (flanking) a retinally stationary central grating (experiments 1 and 2). Motion over the retina was produced by leftward motion of the flanking gratings relative to the stationary eyes, and by rightward eye or head movements tracking the moving (but retinally stationary) central grating relative to the stationary (but retinally moving) surround gratings. In experiment 1 the motion occurred within a fixed boundary on the screen, and oppositely directed MAEs were produced in the central and flanking gratings with static fixation; but with eye or head tracking MAEs were reported only in the central grating. In experiment 2 motion over the retina was equated for the static and tracking conditions by moving blocks of grating without any dynamic occlusion and disclosure at the boundaries. Both conditions yielded equivalent leftward MAEs of the central grating in the same direction as the prior flanking motion, ie an MAE was consistently produced in the region that had remained retinally stationary. No MAE was recorded in the flanking gratings, even though they moved over the retina during adaptation. When just two gratings were presented, MAEs were produced in both, but in opposite directions (experiments 3 and 4). It is concluded that the MAE is a consequence of adapting signals for the relative motion between elements of a display.     

Effects of attentional modulation of a stationary surround in adaptation to motion

The effect of varying the spatial relationships between an adapt/test grating and a stationary surrounding reference grating, and their interaction with diversion of attention during adaptation, were investigated in two experiments on the movement aftereffect (MAE). In experiment 1, MAEs were found to increase as the separation between the surrounding grating and the adapt/test grating decreased, but not with the area of the adapt/test grating. Although diversion during adaptation (repeating changing digits at the fixation point) reduced MAE durations, its effects did not interact with any of the stimulus variables. In experiment 2, MAE durations increased as the outer dimensions of the reference grating were increased, and this effect did interact with diversion, so that the effects of diversion were smaller when the surround grating was larger. This suggests that diversion may be affecting the inputs to an opponent process in motion adaptation, with a smaller effect on the surrounds than on the centres of antagonistic motion-contrast detectors with large receptive fields. A third experiment showed that, although repeating the word 'zero' during adaptation reduced MAEs, this reduction was smaller than that from naming a changing sequence of digits (and not significantly different from that from simply observing the changing digits), suggesting that MAE reductions are not produced only, if at all, by putative movements of the head and eyes caused by speaking.     

The surface and deep structure of the waterfall illusion

The surface structure of the waterfall illusion or motion aftereffect (MAE) is its phenomenal visibility. Its deep structure will be examined in the context of a model of space and motion perception. The MAE can be observed following protracted observation of a pattern that is translating, rotating, or expanding/contracting, a static pattern appears to move in the opposite direction. The phenomenon has long been known, and it continues to present novel properties. One of the novel features of MAEs is that they can provide an ideal visual assay for distinguishing local from global processes. Motion during adaptation can be induced in a static central grating by moving surround gratings; the MAE is observed in the static central grating but not in static surrounds. The adaptation phase is local and the test phase is global. That is, localised adaptation can be expressed in different ways depending on the structure of the test display. These aspects of MAEs can be exploited to determine a variety of local/global interactions. Six experiments on MAEs are reported. The results indicated that relational motion is required to induce an MAE; the region adapted extends beyond that stimulated; storage can be complete when the MAE is not seen during the storage period; interocular transfer (IOT) is around 30% of monocular MAEs with phase alternation; large field spiral patterns yield MAEs with characteristic monocular and binocular interactions.     

Duration, time constant, and decay of the linear motion aftereffect as a function of inspection duration

Subjects rated the strength of the motion aftereffect (MAE) produced by the upward motion of a horizontal grating in two experiments. Inspection periods ranged from 30 to 900 sec in Experiment 1 and from 20 to 120 sec in Experiment 2. A minimum of 22 h elapsed between trials. The decay time constant increased as the square root of the inspection duration for values between 1 min and 15 min of inspection. The ratings suggested that the MAEs consisted of three phases: an initial maximum-strength phase, a decay phase, and a tail. The duration of all three phases increased and the decay rate decreased with increasing inspection duration over the entire range. The results indicate that duration, time constant, and decay rate are not fixed properties of the motion-processing channels in the visual system.     

Motion aftereffects and retinal motion

Two experiments are described in which it was investigated whether the adaptation on which motion aftereffects (MAEs) are based is a response to retinal image motion alone or to the motion signal derived from the process which combines the image motion signal with information about eye movement (corollary discharge). In both experiments observers either fixated a stationary point or tracked a vertically moving point while a pattern (in experiment 1, a grating; in experiment 2, a random-dot pattern) drifted horizontally across the field. In the tracking condition the adapting retinal motion was oblique. In the fixation condition it was horizontal. In every case in both conditions the MAE was horizontal, in the direction opposite to that of pattern motion. These results are consistent with the hypothesis that the adaptation is a response to the motion signal derived from the comparison of eye and image motion rather than to retinal motion per se. An alternative explanation is discussed.     

Apparent velocity of motion aftereffects in central and peripheral vision

Adapting to a drifting grating (temporal frequency 4 Hz, contrast 0.4) in the periphery gave rise to a motion aftereffect (MAE) when the grating was stopped. A standard unadapted foveal grating was matched to the apparent velocity of the MAE, and the matching velocity was approximately constant regardless of the visual field position and spatial frequency of the adapting grating. On the other hand, when the MAE was measured by nulling with real motion of the test grating, nulling velocity was found to increase with eccentricity. The nulling velocity was constant when scaled to compensate for changes in the spatial 'grain' of the visual field. Thus apparent velocity of MAE is constant across the visual field, but requires a greater velocity of real motion to cancel it in the periphery. This confirms that the mechanism underlying MAE is spatially-scaled with eccentricity, but temporally homogeneous. A further indication of temporal homogeneity is that when MAE is tracked, by matching or by nulling, the time course of temporal decay of the aftereffect is similar for central and for peripheral stimuli.     

Effects of illusory stripes on the Helmholtz illusion

This study examined the Helmholtz illusion by using "illusory stripes." A square patch is perceived as wider when vertical lines are drawn on it and is perceived as taller when horizontal lines are drawn on it, i.e., Helmholtz illusion. With vertical lines curved sinusoidally, horizontal "illusory stripes" are perceived; and with horizontal lines curved sinusoidally, vertical "illusory stripes" are perceived. The purpose of the present study was to test whether the "illusory stripes" produce the Helmholtz illusion. We measured the apparent size of a square patch filled with sinusoidal lines. Our subjects (N=27) judged the patch with horizontal "illusory stripes" taller than the square patch filled with vertical straight lines. The subjects also judged the square patch with vertical "illusory stripes" wider than the square patch filled with horizontal straight lines. These results demonstrate that "illusory stripes" can produce the Helmholtz illusion.     

Recovery from adaptation as a function of stimulus orientation

These experiments examined the oblique effect in an adaptation paradigm. Reaction times (RT) to the presence of a grating test stimulus were obtained following adaptation to either a blank field or a grating of the same orientation as the test stimulus. Horizontal, vertical, and oblique test and adaptation orientations were employed. Test gratings were presented at several interstimulus intervals following offset of the adaptation stimulus. RTs following grating adaptation were elevated to a greater extent (relative to blank adaptation) for oblique then for horizontal or vertical stimuli, for two grating spatial frequencies. Differences in RT can be related to differences in sensitivity among channels responsible for detection of the various orientations.

     

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     

Movement aftereffects contingent on color,intensity, and pattern

We have found contingent movement aftereffects (CMAEs) lasting several days, contingent upon the color, intensity, and stripe width of moving patterns. Ss adapted for 10 min to a patterned disk rotating clockwise under red light, alternating every 10 sec with counterclockwise under green light. When stopped, the disk then appeared to rotate counterclockwise under red light and clockwise under green light. The effect lasted only a second or two, reappearing each time the field’s color was changed. But it increased in strength over the first 1/2 hand was still present 1 or 2 days later. Color transposition effects were found: after adaptation to red-clockwise (long wavelength) alternating with green-counterclockwise (short wavelength), a stationary yellow (long wavelength) test field appeared to rotate counterclockwise and a blue (short wavelength) field appeared to rotate clockwise. Relative, not absolute, color of the test triggered the CMAE. Similar CMAEs and transposition effects were produced by pairing direction of movement with intensity, with width of moving stripes and with orientation of a stationary grating projected onto a rotating patterned disk.     

A motion aftereffect for long-range troboscopic apparent motion

The existence of a directional motion aftereffect (MAE) for long-range (LR) stroboscopic apparent motion (SAM) was examined with the use of a directionally ambiguous test stimulus. The spatial and temporal parameters were such that the LR, rather than the short-range, mechanism was likely to be implicated. MAEs were found for SAM, which were in the same direction, but somewhat weaker than those for a comparable stimulus in real motion. The MAEs for SAM were present only when good apparent motion was perceived, and could be shown also when only the unstimulated area between the two stroboscopic flashes was tested. The LR mechanism was further implicated, since the MAEs were also obtained under dichoptic adaptation conditions. It is concluded that the LR-motion mechanism does show a usual MAE under proper testing conditions.     

Footsteps and inchworms: illusions show that contrast affects apparent speed

A horizontal grey bar that drifts horizontally across a surround of black and white vertical stripes appears to stop and start as it crosses each stripe. A dark bar appears to slow down on a black stripe, where its edges have low contrast, and to accelerate on a white stripe, where its edges have high contrast. A light-grey bar appears to slow down on a white stripe and to accelerate on a black stripe. If the background luminances at the leading and trailing edges of the moving bar are the same, the bar appears to change speed, and if they are different the bar appears to change in length. A plaid surround can induce 2-D illusions that modulate the apparent direction, not just the speed, of moving squares. Thus, the motion salience of a moving edge depends critically on its instantaneous contrast against the background.     

Contextual modulation of the motion aftereffect

The authors examined center-surround effects for motion perception in human observers. The magnitude of the motion aftereffect (MAE) elicited by a drifting grating was measured with a nulling task and with a threshold elevation procedure. A surround grating of the same spatial frequency, temporal frequency, and orientation significantly reduced the magnitude of the MAE elicited by adaptation to the center grating. This effect was bandpass tuned for spatial frequency, orientation, and temporal frequency. Plaid surrounds but not contrast-modulated surrounds that moved in the same direction also reduced the MAE. These results provide psychophysical evidence for center-surround interactions analogous to those previously observed in electrophysiological studies of motion processing in primates. Collectively, these results suggest that motion processing, similar to texture processing, is organized for the purpose of highlighting regions of directional discontinuity in retinal images.     

Psychophysical evidence for an extrastriate contribution to a pattern-selective motion aftereffect

A stationary vertical test grating appears to drift to the left after adaptation to an inducing grating drifting to the right, this being known as the motion aftereffect (MAE). Pattern-specific motion aftereffects (PSMAEs) induced by superimposed pairs of gratings in which the component gratings drift up and down but the observer sees a single coherent plaid drifting to the right have been investigated. Two experiments are reported in which it is demonstrated that the PSMAE is tuned more to the motion of the pattern than to the orientation and direction of motion of the component gratings. However, when subjects adapt to the component gratings in alternation, aftereffect magnitude is dependent upon the individual grating orientations and motion directions. These results can be interpreted in terms of extrastriate contributions to the PSMAE, possibly arising from the middle temporal area, where some cells, unlike those in striate cortex (V1), are tuned to pattern motion rather than to component motion.     

Velocity dependence of the interocular transfer of dynamic motion aftereffects

It is well established that motion aftereffects (MAEs) can show interocular transfer (IOT); that is, motion adaptation in one eye can give a MAE in the other eye. Different quantification methods and different test stimuli have been shown to give different IOT magnitudes, varying from no to almost full IOT. In this study, we examine to what extent IOT of the dynamic MAE (dMAE), that is the MAE seen with a dynamic noise test pattern, varies with velocity of the adaptation stimulus. We measured strength of dMAE by a nulling method. The aftereffect induced by adaptation to a moving random-pixel array was compensated (nulled), during a brief dynamic test period, by the same kind of motion stimulus of variable luminance signal-to-noise ratio (LSNR). The LSNR nulling value was determined in a Quest-staircase procedure. We found that velocity has a strong effect on the magnitude of IOT for the dMAE. For increasing speeds from 1.5 deg s(-1) to 24 deg s(-1) average IOT values increased about linearly from 18% to 63% or from 32% to 83%, depending on IOT definition. The finding that dMAEs transfer to an increasing extent as speed increases, suggests that binocular cells play a more dominant role at higher speeds.     

Changes in colour and location as cues of generative transmission in perception of causality

Observers viewed modified launching effect displays containing a spatial gap between the final location of the launcher (a black square) and the initial location of the target (a black outline square with a white interior). In some conditions, a set of stationary objects (black outline squares with white interiors) filled the spatial gap, and these objects began changing colour upon contact from the launcher. The colour changes could involve all gap objects turning black, the first gap object turning dark grey and subsequent gap objects turning successively lighter grey, or first gap object turning light grey and subsequent gap objects turning successively darker grey. The colour changes could move from the launcher to the target or from the target to the launcher. The gap objects could also remain unchanged. Participants rated whether the launcher caused subsequent motion of the target and how much force the launcher imparted to the target. The sequence of colour changes, and the sequence of locations in which colour changes occurred, influenced ratings; sequences of colour changes consistent with the idea that influence of the launcher was transmitted across gap objects to the target resulted in higher ratings. Implications for visual perception of causality are discussed.     

Persistence of simple and contingent motion aftereffects

Jones and Holding (1975) showed that orientation-contingent color aftereffects can persist for at least 3 months, but are depleted by repeated testing. We applied the same paradigm to a simple motion aftereffect (MAE) and found that it can persist for up to 1week and is only slightly diminished by testing. It was further found that simple MAEs appear to persist longer than color-contingent MAEs, although when procedures for inducing and measuring both kinds of aftereffect are equalized, contingent MAEs last longer. Finally, no tendency was found for color-contingent MAEs to diminish with repeated testing. Although both simple and color-contingent MAEs can be relatively persistent, there are certain differences between them. Furthermore, contingent aftereffects should not be considered interchangeable, as there appear to be large differences in the persistence of orientation-contingent color aftereffect and color-contingent MAEs.     

Further studies of the McCollough effect

Following prolonged viewing of black and white striped pattems in colored light, red and green aftereffects that lasted as long as 3 days were seen on the patterns, illuminated with white light. Altemate exposures of a vertical pattern of stripes in green light and a horizontal in white light (or a vertical in white light and a horizontal in red light) produced a red aftereffect on the vertical pattern and a green on the horizontal. The red and green aftereffects were also produced with a single vertical pattern. Adaptation colors that were at all greenish produced a red aftereffect on a vertical pattern and a green on a horizontal, whereas colors that were at all reddish produced a green aftereffect on a vertical pattern and a red on a horizontal. Colors near pure blue and pure yellow, which had little red or green content, produced weak aftereffects. The saturation of the aftereffects on the vertical grating varied in proportion to the red or green content of the adaptation color. Vivid red and green aftereffects were frequently obtained with the vertical and horizontal adaptation patterns paired with colors that closely bracketed pure yellow or pure blue. In all cases, the aftereffects gradually desaturated as the head was gradually tilted down to the side; the colors on each test pattern, vertical and horizontal, vanished at 45-deghead tilt and reversed beyond 45 deg.     

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.     

Background stripes affect apparent speed of rotation

A gray line that rotated about its own center against a stationary background of vertical stripes appeared to double in perceptual speed as it rotated through the vertical position and thus momentarily aligned with the background. Four factors may contribute to this speed-up: (i) landmarks, in which the tip of the moving vertical line moves horizontally across the maximum number of stationary stripes; (ii) orientation repulsion of the moving line by the vertical stripes, which may distort the line's perceived position and hence its perceived speed; (iii) the orientation of an induced brightness pattern along the line; and (iv) the motion of the induced brightness pattern, which moves physically most rapidly along the line when the line is near vertical. To test these possibilities, an annulus display provided landmarks but no intersections, and this almost abolished the effect. A rotating-slit display provided an oriented, moving pattern that mimicked the induced brightness but had no landmarks, and this increased the effect. We conclude that the motion, but not the orientation, of the intersections [option (iv)] was responsible for the illusion. The fact that this motion along the length of the line affected the perceived speed of the line orthogonal to its own length indicates a failure on the part of the visual system to fully decouple tangential from radial motion.