Emotion 2011, Vol. 11, No. 2, 445– 449

© 2011 American Psychological Association 1528-3542/11/$12.00 DOI: 10.1037/a0022599

BRIEF REPORT

Perception of the Color Red Enhances the Force and Velocity of Motor Output Andrew J. Elliot

Henk Aarts

University of Rochester

University of Utrecht

The present research examined whether perception of the color red influences basic motor functioning. Prior research on color and motor functioning has been guided by ill-defined theoretical statements, and has been plagued by methodological problems. Drawing on theoretical and empirical work on the threat-behavior link in human and nonhuman animals, we proposed and tested the prediction that perceiving red enhances the force and velocity of motor output. Experiment 1 demonstrated that red, relative to gray (matched to red on lightness), facilitates pinchgrip force. Experiment 2 demonstrated that red, relative to gray (matched to red on lightness) and blue (matched to red on lightness and chroma) facilitates handgrip force and the velocity of that force. These findings clearly establish a link between red and basic motor action, illustrate the importance of rigorous experimental methods when testing color effects, and highlight the need to attend to the functional, as well as aesthetic, value of color. Keywords: red, color, threat, motor functioning, physical strength

endocrine system functioning, whereas Goldstein (1942) posited that long wavelength colors are “disturbing” or “inciting” at the biological level, resulting in enhanced physical strength (p. 151). Empirical support for a link between color and strength output has proven elusive: Experiments testing the influence of pink or long wavelength colors have failed to produce clear findings (Etnier & Hardy, 1997; Pelligrini & Schauss, 1980), and those examining the influence of other, specific, colors have likewise yielded disappointing results (Dunwoody, 1998; Ingram & Lieberman, 1985). Inspection of the methods used in these experiments, however, suggests that carefully controlled empirical work on color and strength output has yet to be conducted. Many of the existing studies used imprecise color manipulations (e.g., having participants sit in a room with colored walls for a lengthy period) and, most importantly, in all prior studies hue was confounded with lightness and/or chroma. This confound alone renders the research conducted to date essentially uninterpretable. In the present research, we examined the influence of perceiving the color red on the force and velocity of motor output. We grounded our research in extensive theoretical and empirical work on the threat-behavior link in human and nonhuman animals. Many theorists contend that animals across phylogeny possess an avoidance/defense system responsible for processing and responding to threat-relevant stimuli (Dickson & Dearing, 1979; Masterson & Crawford, 1982). In humans and other primates, this avoidance/defense system is thought to involve a network of largely subcortical structures, most notably the amygdala and basal ganglia, that detect threat stimuli, trigger autonomic activity required to support action, and select and prepare motor programs responsible for fight or flight responses (Carretie´, Albert, Lo´pez-Martin, & Tapia, 2009). Threat stimuli necessitate emphatic and urgent responding to ensure safety and survival, thus such stimuli are posited to mobilize motor action that is particularly forceful and

In animal species across phylogeny, the color red functions as a signal of threat and danger. In several nonhuman primates (e.g., mandrills, rhesus macaques), for example, red on the face or chest of an opponent (due to a testosterone surge) is a signal of the dominance or attack-readiness of that conspecific (Setchell & Wickings, 2005). Likewise, in humans, red on the face of a competitor can be a testosterone-based indicator of anger or aggressiveness (Changizi, 2009) and, furthermore, red is used in performance evaluation to mark errors and mistakes, in language to represent negative events or possibilities (e.g., “in the red,” “code red”), and in society more generally to signal the need for vigilance (e.g., alarms, warning signals). Recent research with human participants has clearly documented that red is associated with threat in evaluation contexts (Elliot, Maier, Binser, Friedman, & Pekrun, 2009; Elliot, Maier, Moller, Friedman, & Meinhardt, 2007; Moller, Elliot, & Maier, 2009). Here we examine the implications of this red-threat link for basic motor functioning in humans, specifically, for strength output on simple isometric tasks. Several researchers over the years have examined the relation between color and physical strength output in humans. This research has either had no explicit theoretical basis or has been based on vague conceptual statements. For example, Ott (1979) proposed that pink weakens the muscles due to an unspecified influence on

Andrew J. Elliot, Department of Clinical and Social Sciences in Psychology, University of Rochester; Henk Aarts, Department of Psychology, University of Utrecht. Thanks are expressed to Erin Christensen for her assistance with Experiment 1 of this research. Correspondence concerning this article should be addressed to Andrew J. Elliot, 488 Meliora Hall, Department of Clinical and Social Sciences in Psychology, University of Rochester, Rochester, NY 14627. E-mail: [email protected] 445

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rapid (Lang, Bradley, & Cuthbert, 1990; Öhman & Mineka, 2001). Research with humans indicates that threat stimuli indeed activate the amygdala (Anderson & Phelps, 2001) and basal ganglia (Phelps et al., 2001) and, most directly relevant to the present research, produce voluntary motor behavior that is more forceful (Coombes, Cauraugh, & Janelle, 2006) and of greater velocity (Coombes, Janelle, & Duley, 2005) than that produced by appetitive or neutral stimuli. Interestingly, some experiments showing a link between threat and motor output have used angry faces as threat stimuli; angry faces are typically displayed in grayscale in experiments (Marsh, Ambady, & Kleck, 2005), but are red in real life (Changizi, 2009; Drummond & Quah, 2001). Given the documented links between red and threat, and threat and motor action, we predicted that perceiving red, relative to other achromatic and chromatic colors, would enhance both the force and velocity of strength output in humans. We focused on nondirectional (isometric) motor activation, not directional (approach-avoidance) motor movement in our research, because we were interested in examining the mobilization of energy in preparation for overt action (which can be approach-based fight or avoidance-based flight; Coombes et al., 2006), rather than the compatibility of stimulus valence and overt behavioral response (see Chen & Bargh, 1999). Critically, we tested our predictions using precisely controlled color manipulations, and hues equated on lightness and (as applicable) chroma. Each experiment used a between-subjects color manipulation so that participants would not see repeated color presentations that could make the color stimulus salient and, perhaps, alert them to the purpose of the experiment.

Experiment 1 Experiment 1 examined the influence of red versus gray on maximal force on a pinchgrip task. Gray is the only achromatic color that can be equated to a chromatic color on lightness.

clasp. Width was then measured in millimeters with a ruler, and served as an indicator of maximum force. Red and gray Crayola pencils were selected for the color manipulation after testing several different types of pens and pencils for their ability to produce a red and gray of equal lightness (gray is an achromatic color, so chroma is not relevant). Color samples were examined using the CIELCh color model and a GretagMacBeth Eye-One Pro spectrophotometer. The parameters for the selected colors were: red LCh(75.6/23.7/356.7) and gray LCh(75.2/–/305.3). Thus, red and gray were equivalent (within one unit) on lightness.1 The required procedures for ensuring human subjects protection were followed in both this and the following experiment.

Results and Discussion A unifactorial (color condition: red vs. gray) between subjects ANCOVA was conducted on maximum force (i.e., the maximum number of mm that the clasp was pinched open). Sex of participant was a covariate, and attained significance (males had higher scores). A preliminary analysis revealed no color x sex interaction. Color had a significant influence on maximum force, F(1, 27) ⫽ 11.73, p ⬍ .005, d ⫽ 1.32). Participants in the red condition (Madjusted ⫽ 16.26 mm, SE ⫽ .80) pinched the clasp open with greater force than those in the gray condition (Madjusted ⫽ 12.55 mm, SE ⫽ .81).2 In sum, the results from this experiment support our hypothesis that red facilitates strength output. Experiment 2 sought to replicate and extend Experiment 1 using a different participant population, a different color manipulation, a chromatic as well as achromatic control color, a different task, and an assessment of both the force and velocity of motor output.

Experiment 2 Method Thirty (20 female) 4 through 10th grade students (mean age ⫽ 13.00 years, range 10 –16) were randomly assigned to a red (n ⫽ 15) or gray (n ⫽ 15) condition. Participants were informed that the experiment involved holding a small metal clasp between their thumb and index finger and pinching to open the clasp as wide as possible. They were presented with the clasp, shown how to position it in their fingers, and allowed to get acquainted with the task. Next, participants were given a piece of white paper that contained the color manipulation, which was a red or gray participant number approximately 49 mm in height in the upper left corner of the page. The participant numbers had been written with a Crayola pencil by a research assistant blind to the experimental hypothesis. The piece of paper also contained questions regarding the current date and participants’ age and sex, and participants were instructed to complete these questions. Then, they were asked to look at and state their participant number aloud (thereby exposing them to red or gray), immediately prior to pinching the clasp open as wide as they could for approximately 4 seconds. Participants opened the clasp with it resting on the white piece of paper, and the experimenter, who was blind to the experimental hypothesis, marked the maximum width that the participant opened the th

Experiment 2 examined the influence of red versus blue and gray on motor output on a handgrip task. Blue is the preferred color of a majority of young adults, and blue, a chromatic color, may be equated to red on both lightness and chroma. We used an assessment device that afforded a more differentiated analysis of motor output than that typically seen in the literature (Aarts, Custers, & Marien, 2008; Vaillancourt, Thulborn, & Corcos, 2003); this assessment not only afforded a measure of maximum force, but also of total force over time and, critically, slope toward maximum force (which is a measure of velocity of force development). 1 It should be noted that the output from colored pencils may vary in lightness depending on how hard one presses on the paper while drawing. In addition, the colored numbers used in the manipulation were not of sufficient surface space to be assessed with a spectrophotometer. As such, it is possible that the lightness values of the colors in the experiment varied somewhat more (or less) than those reported in the text. 2 Given the considerable variation in age in our sample, we also examined age as a covariate. A main, but not interactive, effect of age was obtained (older participants had higher scores); the color effect reported in the text remained significant.

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Figure 1. Mean pattern of force as a function of color condition: A) Maximum force in Newtons, B) Mean force over time in Newtons, C) Slope toward maximum force (Newtons/second). The error bars represent the standard error from the mean.

Methods Forty-six (32 female) undergraduates (mean age ⫽ 21.52 years, range 18 –31) were randomly assigned to a red (n ⫽ 15), blue (n ⫽ 15), or gray (n ⫽ 16) condition.3 Participants were run in a soundproof cubicle containing a 100-Hz cathode ray tube computer monitor and a Biopac hand dynamometer system. They were informed that the experiment focused on physical exertion and simply entailed squeezing a handgrip as hard as possible. The device was then placed in their dominant hand, and they were allowed to get acquainted with it, prior to completing a brief demographics questionnaire. Next, participants were instructed to squeeze the handgrip as hard as they could when “squeeze” appeared on the monitor, and to continue until the word disappeared. “Squeeze” was then presented in black letters for 3500 ms on a red, blue, or gray background. The experimenter was blind to experimental hypotheses and condition. The force output was amplified through a pressure gauge amplifier, and the data were sampled at 200 Hz and digitally filtered with a 20-Hz low-pass cutoff. Three outcome measures were obtained: maximum force (in Newtons [N]), mean force over time (in Newtons), and slope toward maximum force (in Newtons/ second). Maximum force was the peak force during the squeeze period, mean force was the total force divided by force duration, and slope toward maximum force was the rate of force development from the initiation of force to peak force. The colors for the manipulation were selected using the CIELCh color model and a GretagMacBeth Eye-One Pro spectrophotometer. The parameters for the selected colors were: red LCh(47.2, 98.1, 37.3), blue LCh(46.8, 97.8, 281.5), and gray LCh(46.9, –, 238.2). Red, blue, and gray were equivalent on lightness; red and blue were equivalent on chroma.

Color had a significant influence on maximum force, F(1, 42) ⫽ 4.85, p ⬍ .05, d ⫽ .68. Participants in the red condition (Madjusted ⫽ 289.44 N, SE ⫽ 20.09) squeezed with greater maximum force than those in the blue condition (Madjusted ⫽ 221.42 N, SE ⫽ 25.12), t(42) ⫽ 2.62, p ⬍ .05, d ⫽ 1.01, and the gray condition (Madjusted ⫽ 217.36 N, SE ⫽ 22.73), t(42) ⫽ 2.78, p ⬍ .01, d ⫽ 1.05. The blue and gray conditions showed no difference, t ⫽ .16, p ⫽ .88. Color also had a significant influence on mean force over time, F(1, 42) ⫽ 9.28, p ⬍ .001, d ⫽ .94. Participants in the red condition (Madjusted ⫽ 154.26 N, SE ⫽ 11.87) squeezed with greater total force than those in the blue condition (Madjusted ⫽ 110.02 N, SE ⫽ 14.62), t(42) ⫽ 3.22, p ⬍ .005, d ⫽ 1.29, and the gray condition (Madjusted ⫽ 97.84 N, SE ⫽ 8.48), t(42) ⫽ 4.10, p ⬍ .001, d ⫽ 1.55. No difference was observed in the blue and gray conditions, t ⫽ .89, p ⫽ .38. Color also had a significant influence on slope toward maximum force, F(1, 42) ⫽ 5.24, p ⬍ .01, d ⫽ .67. Those in the red condition (Madjusted ⫽ 588.64 N/sec, SE ⫽ 66.02) increased the force of their squeeze more rapidly than those in the blue condition (Madjusted ⫽ 418.48 N/sec, SE ⫽ 57.67), t(42) ⫽ 2.25, p ⬍ .05, d ⫽ .79, and the gray condition (Madjusted ⫽ 350.15 N/sec, SE ⫽ 39.97), t(42) ⫽ 3.01, p ⬍ .005, d ⫽ 1.14. The blue and gray conditions showed no difference, t ⫽ .91, p ⫽ .37. Figure 1 presents a pictorial summary of the results across outcome measures.4 In sum, the results from this experiment replicated those from Experiment 1 and extended them beyond amount of applied force to the immediacy with which that force was applied. The results also extended the prior findings by using a different participant population, a different contrast color, a different color manipulation, and a different motor task.

Results and Discussion A unifactorial (color condition: red vs. blue vs. gray) between subjects ANCOVA was conducted on each outcome measure, followed by planned comparisons when significant results were obtained. Sex of participant was a covariate in all analyses; it attained significance (or marginal significance) in all analyses (males exhibited higher scores in each instance). Preliminary analyses revealed no color ⫻ sex interactions.

3 Data for one individual with a color deficiency and two individuals who were aware that the experiment focused on color and strength were not included in the analyses. 4 In an ancillary analysis, we tested the influence of color condition on the variability of force output (standard deviation/mean force; Coombes, Gamble, Cauraugh, & Janelle, 2008). Null results were obtained on this variable (see Coombes et al., 2008, for a conceptually analogous null finding).

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448 General Discussion

The present research provides clear support for a link between red and basic motor functioning in humans. We found that perceiving red enhanced the force of motor output, and did so for both children and young adult participants, with manipulations that placed color on a participant number and on the background of an instruction, with achromatic and chromatic contrast colors, and with a pinchgrip and a handgrip task. Red not only facilitated the force of motor output, but also facilitated the rapidity with which that force was expressed. Our findings suggest an intriguing parallel between humans and other vertebrates in the signal function of red. Red appears to play an important role in avoidance/defense system functioning across vertebrate species, serving as a threat cue that mobilizes energy for protective action. Red seems particularly well-suited to serve as a threat cue in primates, including humans. Primate vision is extremely sensitive to red displayed on the skin (Changizi, Zhang, & Shimojo, 2006), and red displayed on the skin conveys dynamic and important information about the emotional state (and accompanying behavioral predisposition) of a conspecific (e.g., it indicates anger and attack readiness; Changizi, 2009; Setchell & Wickings, 2005). In the present research, we presented red to participants in a static manner on an inanimate object, and in subsequent work it would be interesting to extend this work using a dynamic red display presented on the face of another person. Dynamic red displays would also be interesting to use in research in romantic contexts, where red has been shown to carry amorous meaning, with appetitive implications (Elliot & Niesta, 2008; Elliot et al., 2010). A noteworthy aspect of our research is that we focused on nondirectional motor activation, rather than directional approachavoidance movement. This neutrality with regard to movement direction enabled us to evade the valence-direction confound that plagues much existing research on the link between valenced stimuli and behavioral response (Marsh et al., 2005). It is also important to reiterate that our experiments focused on the initial mobilization of energy in response to threat, rather than overt behavioral responses to threat. Once energy is mobilized, various interpersonal (e.g., the proximity of a competitor or agonist), intrapersonal (e.g., self perceived strength or ability), and situational (e.g., the availability and feasibility of escape) factors dictate how the energy is channeled to produce an overt behavioral response (e.g., aggressive approach or protective avoidance; Lang et al., 1990). Future work is needed to determine whether red facilitates certain types of overt actions more than others. Although our assessment of motor action was nondirectional, it is possible to view the physical movements required in the pinchgrip and handgrip tasks as being relevant to anger/aggression (i.e., pinching and making a fist). This raises the question of whether our findings may be explained by a cognitive-neoassociationistic account in which perceiving red activates anger/aggression that leads directly to anger-/aggression-relevant behavior (Berkowitz, 1993) or, similarly, a grounded cognition account in which perceiving red automatically activates conceptual knowledge (e.g., anger/aggression) and prepares motor tendencies (e.g., hitting) associated with encountering red (Barsalou, 2008). We do not view these as alternative explanations per se, as both are quite compatible with the account that we have highlighted herein. We

favor the avoidance/defense system explanation because it a) specifies the neurophysiological structures that are likely responsible for the observed findings, b) places the operation of these structures in motivational and functional context, c) suggests intriguing parallels across animal species, and d) fits extremely well with the existing data on the threat-motor action link (see Coombes et al., 2006; Lang et al., 1990). Nevertheless, subsequent work focused directly on neural (e.g., amygdala, basal ganglia) and perhaps horomonal (e.g., testosterone) activity would be helpful, as it would provide additional clarity on the precise way that individuals’ respond to red in evaluative contexts. From an applied perspective, our research shows that viewing red enhances strength output on simple motor tasks of a brief duration, suggesting that red may be beneficial for activities such as athletic events requiring short bursts of brute force (e.g., weightlifting). Threat mobilizes energy that can be directly translated into simple ballistic movements (Coombes et al., 2005), but threat also evokes worry, task distraction, and self-preoccupation, all of which have been shown to tax mental resources and interfere with effective self-regulation (Elliot & Harackiewicz, 1996). As such, viewing red is likely to be inimical for skill-based motor tasks (e.g., hitting a tennis ball) and analytical tasks (e.g., solving anagrams) requiring concentration, mental manipulation, and/or the coordination of multiple systems. In accord with this position, recent research has shown that athletes competing against an opponent wearing red are more likely to lose (Hill & Barton, 2005) and that viewing red undermines performance on challenging intellectual tasks (e.g., an IQ test; Elliot et al., 2007). Red may even prove deleterious for engagement in simple motor tasks over an extended period of time, as this requires sustained mental focus and executive control (Muraven & Baumeister, 2000). Subsequent research would be welcomed on issues pertaining to the length of exposure to red and the duration of the red effect. As noted in the Introduction, prior research on color and strength output has yielded disappointing results, even when examining the colors used in our research. We think the most important reason for this is that prior research failed to control for the lightness and chroma properties of color. Lightness alone (Frank & Gilovich, 1988) and chroma alone (Mekellides, 1990) have been shown to influence behavior, thus comparing hues that unsystematically vary on lightness and chroma is destined for difficulty. Our research shows, for the first time, that when hue is varied alone it can influence strength output in a theoretically meaningful and empirically replicable manner. We suspect that the influence of color on biological and psychological functioning is actually quite pervasive, and anticipate that future empirical work in this area will bear much fruit, as long as it carefully attends to the critical issue of lightness and chroma confounds.

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Received November 10, 2009 Revision received May 19, 2010 Accepted July 13, 2010 䡲