Do not prime too much: Prime frequency effects of masked affective stimuli on effort-related cardiovascular response

Abstract

This experiment investigated the prime frequency effect of masked affective stimuli on effort-related cardiovascular response. Cardiovascular reactivity was recorded during a baseline period and an attention task in which either 1/3, 2/3, or 3/3 of the trials included the presentation of masked emotional facial expressions (sad vs. happy). In the resting trials participants were exposed to masked neutral expressions. As expected, and replicating previous findings (Gendolla and Silvestrini, in press), participants in the 1/3 priming condition showed stronger systolic blood pressure reactivity – indicating more effort – when they were exposed to masked sad faces than when they were exposed to masked happy faces. This effect disappeared in the 2/3 and 3/3 conditions. Findings are interpreted as demonstrating habituation effects of masked affective stimuli on effort mobilization.

Introduction

In the recent decade, the idea that human behavior is largely influenced by automatically processed stimuli has received strong support by numerous studies (see Bargh and Chartrand, 1999, Custers and Aarts, 2005, Dijksterhuis and Aarts, 2010, Kruglanski et al., 2002, Wilson, 2002 for reviews). Not only attitudes, stereotypes, but also goals, or emotions may be activated and operate without awareness (see Bargh, 1997, Greenwald and Banaji, 1995). Contributing to this evidence, recent research has revealed that masked affective stimuli have a systematic impact on effort intensity – the mobilization of resources to carry out instrumental behavior. Studies by Gendolla and Silvestrini (in press) found that exposure to masked emotional facial expressions during the performance of cognitive attention and short-term memory tasks systematically influenced effort-related cardiovascular response: under “do-your-best” instructions exposure to masked sad faces led to stronger effort-related cardiovascular response than masked happy and angry faces. Another experiment by Silvestrini and Gendolla (in press) additionally manipulated objective task difficulty and investigated the impact of affective primes during the performance of an objectively easy and difficult attention task. As expected, the masked affective expressions moderated the impact of objective task difficulty: when the task was easy, sadness primes led to stronger cardiovascular response than happiness primes, but during a difficult task cardiovascular response was higher when participants were exposed to masked happy faces than when they processed masked sad faces.

These effects have been explained by the influence of affective stimuli on the level of experienced task demand during task performance, which determines the actual amount of resources people mobilize for instrumental behavior as long as success is worthwhile and possible (Brehm and Self, 1989, Wright, 1996, Wright and Kirby, 2001). Accordingly, sadness cues augment experienced task demand in comparison with happiness cues resulting in higher effort during “do-your-best” or easy tasks but in lower effort during difficult tasks due to disengagement (too high subjective difficulty). By contrast, masked happiness cues during an objectively difficult task result in high effort because subjective difficulty is high but still possible. Referring to affective influences on mental effort, there is replicated evidence that sad and happy moods have similar effects on task engagement: sadness is associated with difficulty and happiness is associated with ease (see Gendolla and Brinkmann, 2005 for a review). In support of the idea that masked affective stimuli also have an effect on experienced task demand, Gendolla and Silvestrini (in press) found that participants who processed masked sadness expressions rated subjective task difficulty as higher than those who processed masked happiness expressions. Likewise, subjective difficulty ratings in the study by Silvestrini and Gendolla (in press), which manipulated also objective task difficulty, were influenced by the masked affective stimuli and objective task difficulty in an additive manner. This suggests that masked affective stimuli systematically influence effort-related cardiovascular response because they take effect on the level of subjective task demand.

The present study is concerned with boundary conditions of masked affective stimuli's effect on effort-related cardiovascular response. Specifically, it deals with prime frequency effects – i.e. the impact of the amount of repetitive exposures to masked affective stimuli. Repeated exposure to emotional stimuli usually leads to habituation and thus to a decrease of their respective influence (e.g., Bradley et al., 1993, Klorman, 1974, Wright et al., 2001). This affective habituation has also been demonstrated in affect priming procedures (e.g., Breiter et al., 1996, Wong and Root, 2003). Considering these findings, participants in our previous studies were only exposed to masked affective stimuli in 1/3 of the experimental trials of a cognitive task. In the other 2/3 of the trials we presented neutral stimuli to avoid habituation effects. As discussed above, this manipulation was successful and had significant and replicated effects on effort-related cardiovascular response. It remained, however, unclear if higher prime frequencies would really weaken this effect due to habituation, as discussed above, or maybe still strengthen it due to stronger activation and thus increased accessibility (see Förster and Liberman, 2007). The present experiment addressed this question.

Participants performed an attention task under “do-your-best” instructions. Masked happy vs. sad standardized facial expressions were presented in 1/3, 2/3, or 3/3 of the experimental trials. Given the replicated evidence that systolic blood pressure (SBP) sensitively responds to the exposure of masked affective stimuli (Gendolla and Silvestrini, in press, Silvestrini and Gendolla, in press) and variations of experienced task difficulty in general (e.g., Bongard, 1995, Brinkmann and Gendolla, 2008, Gendolla and Krüsken, 2001, Light, 1981, Lovallo et al., 1985, Richter et al., 2008, Sherwood et al., 1990, Silvestrini and Gendolla, 2009a, Silvestrini and Gendolla, 2009b, Smith et al., 1997, Smith et al., 2000, Wright et al., 1986, Wright et al., 2003), we focused on this parameter of cardiovascular activity.¹ On the basis of our previous studies, we expected stronger reactivity in the sad-prime condition than in the happy-prime condition when participants were exposed to the masked affective stimuli in 1/3 of the experimental trials. Given that it remained unclear if higher prime frequencies would lead to a weaker (habituation) or stronger (higher accessibility) effect, we had no specific predictions for the effect of prime valence on SBP reactivity in the other two prime-frequency conditions.