Chromatic induction in space and time

Abstract

The color appearance of a light depends on variation in the complete visual field over both space and time. In the spatial domain, a chromatic stimulus within a patterned chromatic surround can appear a different hue than the same stimulus within a uniform surround. In the temporal domain, a stimulus presented as an element of a continuously changing chromaticity can appear a different color compared to the identical stimulus, presented simultaneously but viewed alone. This is the flash-lag effect for color, which has an analog in the domain of motion: a pulsed object seen alone can appear to lag behind an identical pulsed object that is an element of a motion sequence. Studies of the flash-lag effect for motion have considered whether it is mediated by a neural representation for the moving physical stimulus or, alternatively, for the perceived motion. The current study addresses this question for the flash-lag effect for color by testing whether the color flash lag depends on a representation of only the changing chromatic stimulus or, alternatively, its color percept, which can be altered by chromatic induction.

Methods: baseline measurements for spatial chromatic induction determined the chromaticity of a flashed ring within a uniform surround that matched a flashed ring within a patterned surround. Baseline measurements for the color flash-lag effect determined the chromaticity of a pulsed ring presented alone (within a uniform surround) that matched a pulsed ring presented in a sequence of changing chromaticity over time (also within a uniform surround). Finally, the main experiments combined chromatic induction from a patterned surround and the flash-lag effect, in three conditions: (1) both the changing and pulsed rings were within a patterned chromatic surround; (2) the changing ring was within a patterned surround and the pulsed ring within a uniform surround; and (3) the changing ring was within a uniform surround and the pulsed ring within a patterned surround.

Results: the flash-lag measurements for a changing chromaticity were affected by perceptual changes induced by the surrounding chromatic pattern. Thus, the color shifts induced by a chromatic surround are incorporated in the neural representation mediating the flash-lag effect for color.

Fig. 1

Experimental stimuli (schematic drawings, not precisely to scale). A, examples of spatial chromatic induction. The chromatic patterned surround at top left [top right] has contiguous rings bordering the test ring with −S [+S] chromaticity (see text). At bottom, the test ring is within a uniform surround metameric to EES. Dashed lines demonstrate that all test rings have the same chromaticity, although their color appearances differ. Stimuli adapted from [7]. B, “Chromatic Induction Without Flash-Lag”: both rings (one within a patterned and the other within a uniform unpatterned surround) were briefly pulsed. C, “Both Stimuli Not Patterned”: both the changing and pulsed test rings had unpatterned surrounds (no spatial chromatic induction). D, “Pulsed Stimulus Patterned”: the pulsed test ring had a patterned surround; the changing ring had an unpatterned surround. E, “Changing Stimulus Patterned”: test ring changing in chromaticity had a patterned surround, the pulsed test ring had an unpatterned surround. F, “Both Stimuli Patterned”: both the pulsed and changing test rings had patterned surrounds.

Fig. 2

Spatial chromatic induction magnitude along the S/(L + M) axis from patterned surrounds without the flash-lag effect (as in Fig. 1B); observers AC, EL, and LW, left to right). Plus [minus] symbols represent test rings with +S [−S] contiguous contours; circles represent isomeric matches. Error bars are ±1 SEM. The black horizontal line shows the S/(L + M) value of the fixed test ring.

Fig. 3

Shift in color appearance along the S/(L + M) axis (left ordinate) with both the changing and pulsed rings on unpatterned surrounds. The right ordinate expresses the shift in terms of flash-lag duration (see text); the sign of lag duration always is positive, so the time on the right ordinate is positive on either side of zero. The circles [triangles] represent average matches with the ring changing from −S to +S (orange to purple) [+S to −S, purple to orange]. Error bars are ±1 SEM. Horizontal line at 1.0 (left ordinate) shows the S/(L + M) value of the changing ring at the moment the pulsed ring was presented (thus equivalent to zero lag time on the right ordinate).

Fig. 4

Shift in color appearance along the S/(L + M) axis (left ordinate) from flash-lag and also spatial chromatic induction (each column shows results for a different observer). Measurements are shown for the “Pulsed Stimulus Patterned” (top row), “Changing Stimulus Patterned” (middle row), and “Both Stimuli Patterned” (bottom row). The dashed horizontal line in each panel shows the S/(L + M) value of the changing test ring at the moment of the pulsed test ring (left ordinate), corresponding to a flash-lag duration of zero (right ordinate). The solid black lines in the left [right] half of each panel show the average match with unpatterned surrounds and the test ring changing from −S to +S [+S to −S], replotted from Fig. 3. The chromaticity of the contiguous contour is −S (minus symbols in plots) or +S (plus symbols in plots). The left [right] part of each panel is with the changing chromaticity from −S to +S [+S to −S], as indicated on the horizontal axis. Error bars show ±1 SEM. Asterisks represent a sum of the individual shifts from the patterned surround alone and the flash-lag effect alone (see text).

Fig. 5

Average difference in color shift caused by −S versus +S contiguous contours in patterned surrounds for flash-lag matches for the three main experimental conditions (“Pulsed Stimulus Patterned,” “Changing Stimulus Patterned,” and “Both Stimuli Patterned,” horizontal axis). Results for each observer are in a separate panel. Error bars are ±1 SEM across the four repeated days and +S to −S and −S to +S directions of chromatic change. Asterisks indicate whether each value is different from zero (*** p < 0.001, ** p < 0.01, * p < 0.05).