Visual Neuroscience ~2006!, 23, 489–493. Printed in the USA. Copyright © 2006 Cambridge University Press 0952-5238006 $16.00 DOI: 10.10170S0952523806233261
Inhibition or facilitation of return: Does chromatic component count?
LUIZ HENRIQUE M. DO CANTO-PEREIRA,1 GALINA V. PARAMEI,2 EDGARD MORYA,1 and RONALD D. RANVAUD 1 1 Department of Physiology and Biophysics, Institute of Biomedical Sciences, Neurosciences and Behavior Program, University of São Paulo, São Paulo, Brazil 2 Institute of Psychology, Darmstadt University of Technology, Darmstadt, Germany
(Received August 11, 2005; Accepted January 22, 2006!
Abstract Inhibitory effects have been reported when a target is preceded by a cue of the same color and location. Color-based inhibition was found using red and blue nonisoluminant stimuli ~Law et al., 1995!. Here we investigate whether this phenomenon depends on the chromatic subsystem involved by employing isoluminant colors varying along either the violet-yellow or purple-turquoise cardinal axis. Experiment 1 replicated Law et al.’s study: After fixating magenta, either a red or blue cue was presented, followed by a magenta “neutral attractor,” and, finally, by a red or blue target. In Experiment 2, violet and yellow, cue or target, varied along a tritan confusion line in the CIE 1976 chromaticity diagram. In Experiment 3, purple and turquoise, cue or target, varied along a deutan confusion line in the CIE 1976 chromaticity diagram. Normal trichromats ~n ⫽ 19! participated in all three experiments. In Experiment 1, color repetition indeed resulted in longer reaction times ~RTs! ~4.7 ms, P ⫽ 0.038!. In Experiment 2, however, no significant color repetition effect was found; RTs to violet and yellow were not significantly different, though tending toward slower responses ~2 ms! for violet repetition but faster ~5 ms! for yellow. Experiment 3 also showed no color repetition effect ~P ⫽ 0.58!; notably, RTs were overall faster for purple than for turquoise ~22 ms, P ⬍ 0.0001!. Furthermore, responses tended to be slower for purple repetition ~4 ms, P ⬎ 0.05!, but faster for turquoise ~7 ms, P ⬎ 0.05!. These findings demonstrate that color repetition is not always inhibitory but may turn facilitatory depending on the colors employed. The results indicate that disengagement of attention is an unlikely mechanism to be the sole explanation of previously reported color-based inhibition of return. We suggest a complementary, perceptual explanation: response ~dis!advantage depends on whether the stimuli are isoluminant and on the opponent chromatic subsystem involved. The choice of the colors employed and the cue-attractor-target constellation also may be of significance. Keywords: Color, Inhibition of return, Facilitation of return, Chromatic subsystems, Visual attention
from poorer performance with targets at the same locations as others. Conversely, if other processes, such as response-repetition advantage, happen to occur in parallel, IOR could be undetectable. Here we were interested in the effect of color on speed of the reaction to a repeatedly attended stimulus. Recent studies demonstrated color-based repetition disadvantage, IOR ~Law et al., 1995; Lupiañez et al., 1997!. However, Kwak and Egeth ~1992! found no evidence of color-based inhibition in any of their experiments. It is important to note that in the above studies color of the stimulus was not considered as an experimental variable. In the present study we performed a series of experiments designed to examine whether IOR or FOR depends on the choice of the colors and the chromatic subsystem involved. Experiment 1 replicated the design of Law et al. ~1995!, who used nonisoluminant blue and red. In our main study, we employed pairs of opponent colors that were isoluminant and varied along the tritan ~Experiment 2! or deutan ~Experiment 3! confusion lines in the CIE 1976 chromaticity diagram ~Mollon & Reffin, 2000; CantoPereira et al., 2005!. We questioned whether the color-based
Introduction How our attention is directed to different objects is of fundamental behavioral importance, since it determines the speed with which they can be detected and recognized. Temporal characteristics of attending repeatedly to the same item have been addressed by several researchers, but results are inconclusive. Kanwisher et al. ~1995, 334! infer an inhibitory process from their results and argue that “it may be more difficult to direct attention to an object or location if the features of that item have been recently attended.” Others, by contrast, found that when the task-relevant nonspatial feature remains the same between preceding and probe targets, facilitation of return ~FOR! is observed ~Pratt & Castel, 2001!. Klein ~2000! contends that inhibition of return ~IOR! is inferred
Address correspondence and reprint requests to: Luiz Henrique M. do Canto-Pereira, Department of Physiology and Biophysics, Institute of Biomedical Sciences, University of São Paulo, Av. Prof. Lineu Prestes, 1524, 05508-900 São Paulo, SP, Brazil. E-mail:
[email protected]
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repetition effect is explained solely in terms of attentional disengagement or whether the effect is contingent on chromatic ~sensory! stimulus characteristics. Materials and methods Observers Graduate and undergraduate students ~n ⫽ 19; 9 males! from the University of São Paulo, aged 20– 42 ~26.3 6 5.9! participated in the experiments. Inclusion criteria were ~i! normal color vision as assessed with the City University Dynamic Colour Vision Test ~Barbur et al., 1994!, ~ii! 20025 Snellen best-corrected visual acuity, and ~iii! absence of known ophthalmologic diseases. All participants signed their informed consent. Fig. 1. Time course of events ~fixation–cue–neutral attractor–target! in a trial. Numbers indicate each event’s duration ~in ms!.
Apparatus For stimulus presentation, we used a calibrated 19 ' Samsung SyncMaster 997DF monitor with a refresh rate of 100 Hz and a resolution of 800 ⫻ 600, powered by a PC Athlon XP 24000512 and driven by a 10-bit Matrox P650 graphics board. E-Prime software ~Schneider et al., 2002! was used for stimulus presentation and response registration. Subjects sat in front of the monitor at a distance of 57 cm; head position was maintained by a chin rest. All stimuli subtended 4 deg of visual angle. Experiments were performed in a darkened and sound-attenuated room. Procedure Experiment 1 Experiment 1 replicated the design of Experiment 1 in Law et al.’s study ~1995!. Blue ~u ' ⫽ 0.183, v ' ⫽ 0.149; 3.5 cd0m 2 !, red ~u ' ⫽ 0.404, v ' ⫽ 0.522; 8.0 cd0m 2 !, and magenta ~u ' ⫽ 0.325, v ' ⫽ 0.386; 6.8 cd0m 2 ! were used; these were presented against a gray background ~u ' ⫽ 0.201, v ' ⫽ 0.461; 8.7 cd0m 2 !. A trial began after a 400-Hz warning tone ~150 ms!; first a magenta fixation stimulus was presented ~500 ms!; it was followed by either a red or a blue stimulus, the cue ~900 ms!; then by magenta, the neutral attractor ~900 ms!; and finally by the target, either a red or a blue stimulus, presented for 1000 ms or until response. The magenta attractor was intended to disengage attention from the color of the cue ~Law et al., 1995!. Participants were requested to respond as quickly as possible to the onset of the target by pressing a button on the joystick connected to the PC’s game port ~Segalowitz & Graves, 1990!. RTs were registered with 1 ms accuracy ~Schneider et al., 2002!. Catch trials, without a target, comprised 20% of total presentations, to which participants were instructed not to respond. A 250-Hz error tone ~150 ms! sounded whenever there was an error, either a response made before the target onset, or no response within 1000 ms, or a response given on a catch trial. There were two types of valid trials: repeated ~cue and target of the same color! and nonrepeated ~cue and target of different colors!. A total of 250 trials included 100 repeated, 100 nonrepeated, and 50 catch trials. The sequence of events is shown in Fig. 1. Experiment 2 Isoluminant colors ~8.7 cd0m 2 ! lying along a tritan confusion line in the 1976 CIE chromaticity diagram were used. Violet ~u ' ⫽
0.208, v ' ⫽ 0.367! and yellow ~u ' ⫽ 0.180, v ' ⫽ 0.556! served as cue or target. Greenish-gray ~u ' ⫽ 0.191, v ' ⫽ 0.488! resulting from blending violet and yellow served as the fixation stimulus and “neutral attractor.” The procedure was otherwise the same as in Experiment 1. Experiment 3 A procedure identical to that in the two first experiments was used, but the choice of the colors differed; now they varied along a deutan confusion line in the CIE 1976 chromaticity diagram. Isoluminant ~8.7 cd0m 2 ! purple ~u ' ⫽ 0.253, v ' ⫽ 0.439! and turquoise ~u ' ⫽ 0.137, v ' ⫽ 0.458! were cue and target, and bluish-gray ~u ' ⫽ 0.186, v ' ⫽ 0.448! resulting from blending purple and turquoise was the fixation color and “neutral attractor.” Coordinates of the stimuli used in the three experiments are shown in projection on the CIE 1976 chromaticity diagram ~Fig. 2!. Analysis Errors, trials with either RTs ⬍ 150 ms or RTs ⬎ 750 ms, and false alarms on catch trials were excluded from the following analysis. For RTs in valid trials, a two-way repeated measures analysis of variance ~ANOVA! was performed separately for each experiment, with the factors “target color” and “condition” ~repeated; nonrepeated!. Results Experiment 1 A target color ~red ⫻ blue! ⫻ condition ~repeated ⫻ nonrepeated! ANOVA revealed that repeated trials were slower ~339.4 6 20.7 ms! than nonrepeated ~334.7 6 19.8 ms!; F~1,18! ⫽ 5.06, P ⫽ 0.038 ~Fig. 3a!. No other effect or interaction was found. Experiment 2 A target color ~ yellow ⫻ violet! ⫻ condition ~repeated ⫻ nonrepeated! ANOVA revealed neither the effect of repetition nor the effect of the color, nor any interaction. Data are presented in Fig. 3b. However, RTs for violet were faster in nonrepeated ~314.6 6 19.8 ms! than in repeated trials ~316.8 6 20.7 ms!; for
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Fig. 2. Stimuli employed in the three experiments defined in the CIE 1976 chromaticity diagram. R ⫽ red, M ⫽ magenta, B ⫽ blue, T ⫽ turquoise, gg ⫽ greenish-gray, P ⫽ purple, V ⫽ violet, bg ⫽ bluish-gray, and Y ⫽ yellow.
yellow the opposite was found, that is, responses in nonrepeated trials were slower ~322 6 19.4 ms! than in repeated ~316.5 6 21.3 ms! but without reaching significance ~P ⫽ 0.16!. Experiment 3 A target color ~turquoise ⫻ purple! ⫻ condition ~repeated ⫻ nonrepeated! ANOVA revealed that in both conditions, responses to turquoise were slower ~338.5 6 17.6 ms! than those to purple ~316.3 6 17.2 ms!, F~1,18! ⫽ 55.26, P ⬍ 0.001. Also, an interaction was found between repetition and color @F~1,18! ⫽ 4.74, p ⫽ 0.044#, whereby for turquoise the repeated condition resulted in shorter RTs ~335.1 6 18.1 ms! than in the nonrepeated condition ~341.9 6 17.1 ms!. The opposite was true for purple; that is, the repeated-condition RTs were longer ~318.4 6 17.3 ms! than the nonrepeated ~314.2 6 17.1 ms!. Data are presented in Fig. 3c. Discussion Results of our Experiment 1 indeed replicate findings in previous studies with the same colors, namely, by Law et al. ~1995; Experiment 1!, Taylor and Klein ~1998; for 900-ms cue-target interstimulus interval!, and Fox and Fockert ~2001; Experiment 1a!. We
found significantly slower responses at color repetition in the cue-target relationship. As in the previous studies, the three colors used were nonisoluminant. We therefore cannot exclude the possibility that the observed inhibition of return is the effect of luminance inequality between the magenta attractor ~6.8 cd0m 2 ! and the target, either blue ~3.5 cd0m 2 ! or red ~8.0 cd0m 2 !. Data presented in Fig. 3a indicate that target detection is more inhibited when its luminance is lower than that of the color serving as the attractor. Potential effect of variation in luminance on response speed is also suggested by Gibson and Amelio ~2000!, who did not find IOR when only color was altered in cues. In accord with this is Irwin et al.’s finding ~2000! of the role of luminance increments: these were shown to capture attention in a visual search task when an array of color singletons was used. By comparison, in our Experiments 2 and 3, when isoluminant colors were employed, the response pattern was either inhibitory or tended to reverse from inhibition to facilitation, depending on the stimuli constellation ~though the differences in RTs were not significant!. Thus, the results found by other authors earlier, that is, a consistent and significant IOR, could not be replicated when the probe and target colors were equal in luminance. Instead, we found either a facilitation ~for turquoise and yellow! or an inhibition ~for purple and violet! response pattern when the stimuli were isolu-
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Fig. 3. RTs ~mean, SE; ms! for responses to the target as a function of the target color and condition ~repeated vs. nonrepeated!. ~a! Experiment 1: nonisoluminant red and blue; ~b! Experiment 2: isoluminant yellow and violet; ~c! Experiment 3: isoluminant turquoise and purple.
minant. These results are in accord with those obtained by Irwin et al. ~2000; Experiment 3! that indicate the role of luminance increments as attention capturers. The present outcome implies that previous findings in favor of color-based IOR may have been due to luminance inequalities between the chromatic stimuli rather than to mechanisms of disengagement of attention. Further, the results indicate that the response pattern, either inhibition or facilitation of return, strongly depends on perceptual interactions within the color-processing channels. Before considering a possible explanation for the present findings, we briefly survey explanatory schemes that are entertained for inhibition or facilitation of return. In all, attention to target location vs. target feature is considered critical for the response pattern. The effect of target feature as opposed to target location was addressed in a study by Bichot and Schall ~2002!, who found FOR for feature repetition but IOR for location repetition of a target. In addition, in a series of experiments, using single stimulus or color pop-out search displays, it was shown that the effect of location repetition of a target depends on the task ~Tanaka & Shimojo, 1996, 2000!. The authors found an increase in response time following repetition of target location ~i.e. IOR! when the task
L.H.M. do Canto-Pereira et al. involved spatial orienting. However, when the task required discrimination of target feature ~e.g. color!, repetition of target location speeded the response, that is, FOR. A different explanatory scheme regarding the conditions under which FOR or IOR would emerge is suggested by Pratt and Castel ~2001!. According to their view, FOR would be observed when the task-relevant nonspatial feature remains the same in preceding and probe targets, whereby a priming mechanism is expected to facilitate ~speed up! the response. Conversely, responses for targets at repeated locations would be slowed, or IOR would occur, if the task-relevant nonspatial feature varies between the preceding and probe targets or if the nonspatial feature is irrelevant to the task ~e.g. detection or location tasks!. Thus, if a “critical feature” is the same on the preceding and probe targets, its repetition will promote FOR, but if there is a change in the “critical feature,” successive presentation will cause IOR. Results of our Experiments 2 and 3 prompt us to question what “critical feature” was the same in stimulus constellation when the tendency of FOR was observed or, conversely, in which way the “critical feature” varied when the tendency of IOR emerged. As a reminder, a facilitatory response ~though insignificant! was obtained at the color constellations of greenish-gray–yellow and bluish-gray–turquoise. In contrast, a tendency to inhibitory response was observed at greenish-gray–violet and bluish-gray– purple constellations. In other words, yellow and turquoise are supposed to be less different from gray attractors than are purple and violet with respect to invoked chromatic components. Based on the findings in the present experiments, we propose that color-based repetition effects cannot be solely due to attentional mechanisms. Instead, the effects appear to be inhibitory or facilitatory depending on ~i! whether the stimuli are isoluminant and ~ii! which of the two opponent chromatic subsystems is involved and also ~iii! due to chromatic and luminance ~sensory! components shared between the cue, target, and attractor.
Acknowledgments This research was supported by CNPq grant 14195102002-8 to L.H.M.C.P. ~doctoral fellowship! and a fellowship from the Hanse Institute for Advanced Studies to G.V.P. The first author is grateful to the International Colour Vision Society ~ICVS! for the travel award enabling him to present these results at the 18th ICVS symposium in Lyon, France. We thank an anonymous reviewer for very helpful comments on a previous version of the paper.
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