Study 2: Effects of Suboptimal versus Optimal Age Primes on Effort-Related Cardiac

Abstract

Based on the Implicit-Affect-Primes-Effort model and evidence that aging is associated with cognitive difficulties, this experiment investigated the effect of suboptimally vs. optimally presented age primes on effort-related cardiovascular response. Young participants processed elderly vs. youth primes under suboptimal (13 ms) vs. optimal (760 ms) prime presentation time conditions during a short-term memory task. According to an application of the IAPE model’s predictions for implicit aging, we expected that suboptimally presented elderly primes would result in stronger effort-related cardiovascular response than suboptimally presented youth primes. In the optimal prime presentation condition, we expected diminished or even reversed age prime effects due to behavioral correction. Unfortunately, the present findings do not provide clear evidence for the differential effects of implicitly vs. explicitly processed age primes on cardiovascular response.

Introduction

Especially the Western culture maintains a negative aging stereotype. Accordingly, aging is associated with cognitive difficulties and a decline of mental capacities (e.g., Cuddy, Norton, & Fiske, 2005; Harada, Love, & Triebel, 2013; Kite & Smith-Wagner, 2002; Kite, Stockdale, Whitley, & Johnson, 2005). Research in social psychology has also revealed that negative traits are mostly associated with the label “old” and positive traits with the label

“young”, supporting the idea of an unintentional and unconscious aging bias (e.g., Perdue &

Gurtman, 1990). Also, large-scale online measures of attitudes toward social groups revealed strong negative implicit attitudes towards older people (Nosek, Banaji, & Greenwald, 2002).

Beside the mere stereotypic belief, there is also empirical evidence that older individuals’ basic cognitive functioning indeed declines and that the elderly face more difficulties than younger adults when they are confronted with cognitive tasks (Hess & Ennis, 2012; Ennis, Hess, & Smith, 2013). Accordingly, older people mobilize more cognitive resources and show stronger effort-related cardiovascular responses than younger individuals to perform cognitive challenges of the same level of difficulty (Smith & Hess, 2015). Moreover,

neuroimaging research has shown that older adults recruit more regions of the brain to perform at similar levels as young adults (Cappell, Gmeindl, & Reuter-Lorenz, 2010).

Based on the evidence that aging is associated with cognitive difficulties, the general idea of our research program was that the mere implicit activation of the aging stereotype could systematically influence effort-related cardiovascular response during a cognitive challenge. The reason for our hypothesis is that cognitive difficulties are a central feature of the aging stereotype and that the implicit activation of this stereotype should thus render the performance difficulty concept accessible, which in turn influences experienced task demand and thus effort mobilization.

Our hypothesis is grounded in the Implicit-Affect-Primes-Effort (IAPE) model (Gendolla, 2012, 2015), which posits that implicitly processed affective stimuli—affect primes—can influence effort mobilization through their impact on experienced task demand. The IAPE model builds on the idea that effort mobilization is grounded in a resource conservation principle. Consequently, because people avoid mobilizing more resources than necessary, effort is proportional to subjective demand as long as success is possible and justified (Brehm

& Self, 1989). In performance contexts, people thus use all available information for evaluating task demand. The IAPE model posits that people learn in everyday life that coping with challenges is easier in some affective states than in others. Therefore, performance ease or difficulty become features of individual’s mental representations of different affective states.

Implicit affect primes can automatically activate knowledge about the respective affective states, including information about performance ease or difficulty, which then influences physiological reactions related to resource mobilization. More specifically, the IAPE model posits that sadness and fear are associated with difficulty, while happiness and anger with ease. Several studies have supported the IAPE model and found clear and replicated evidence for the systematic impact of implicitly processed affect primes on effort-related cardiovascular response (e.g., Chatelain & Gendolla, 2015; Gendolla & Silvestrini, 2011; Lasauskaite, Gendolla, & Silvestrini, 2013; Silvestrini & Gendolla, 2011a).

The objective of our research is to generalize the IAPE model to other social stereotypes—like the elderly stereotype. Given that aging is associated with cognitive performance difficulties, we posit that age primes should have similar effects as sadness or fear primes—they should render the performance difficulty concept accessible and thus influence subjective demand and effort mobilization. The predictions of the IAPE model refer

to implicitly presented primes, which means an automatic activation of concepts without awareness. Moreover, as it has been shown by Lasauskaite Schüpbach, Gendolla, and Silvestrini (2014), affect primes have the predicted effects if they are presented suboptimally.

But when the same primes are presented optimally—i.e., clearly visible—the prime effects were reversed, which was explained by behavior correction due to controlled prime processing (cf. Herr, 1986).

Moreover, from the stereotype activation literature and its effects on behavior, we know that people’s behavior can be either consistent (assimilation effect) or inconsistent (contrast effect) with the primed stereotype. When stereotypes are activated without awareness, they most likely result in assimilation effects—stereotype-consistent behavior.

Most relevant, Bargh, Chen, and Burrows (1996) found that young participants’ walking speed slowed down after being unconsciously exposed to a series of words linked to the elderly stereotype—an assimilation effect. Dijksterhuis, Aarts, Bargh, and van Knippenberg (2000), also found that college students who were unconsciously exposed to words related to the elderly stereotype showed decreased memory performance—an assimilation effect. However, this assimilation effect manifested only for participants who had a lot of contact with older individuals. By contrast, when stereotypes are consciously activated and individuals are aware of the stereotype’s biasing influence, behavior correction is likely, because individuals attempt to avoid the undesired influence of the activated stereotype (see Wheeler & Petty, 2001). Most relevant for the present research, this suggests that the conscious activation of the elderly stereotype in young individuals may lead to a contrast effect, because the relevant social group (the elderly) is highly discrepant from themselves (young people).

In the present experiment, we manipulated the prime presentation time—13 ms (suboptimal) vs. 760 ms (optimal). We did so, because our previous study (cf. Study 1), found an effort-related cardiac response pattern that was opposite of that we had expected when the age primes were presented for 27 ms: Cardiac PEP reactivity tended to be stronger in the youth-prime condition than in the elderly-prime condition. We have attributed this unexpected finding to the high contrast and thus the relatively high visibility of the pictures we had used as age primes. This high prime visibility could have resulted in controlled prime processing and thus behavior correction. By contrast, the PEP reactivity pattern fitted the predictions when the primes were presented for 13 ms, but this effect did not attain significance.

To test our prime visibility interpretation, we (1) applied a filter to reduce the high contrast and render the age primes blurrier and (2) applied a stronger manipulation of prime visibility—the primes were either presented clearly visible (optimal) or very hardly visible (suboptimal).

Effort-related Cardiovascular Response

Based on Wright’s (1996) integration of motivational intensity theory (Brehm & Self, 1989) with Obrist’s (1981) active coping approach, our primary measure of effort intensity was again cardiac pre-ejection period (PEP)—the time interval between the beginning of left ventricular excitation and the opening of the left ventricular cardiac valve in a cardiac cycle (Berntson, Lozano, Chen, & Cacioppo, 2004), which becomes shorter with increasing myocardial contractility. Additionally, we assessed again systolic blood pressure (SBP, the maximal pressure in the vascular system between two heartbeats), diastolic blood pressure (DBP, the minimal arterial pressure between two heartbeats), and heart rate (HR, the number of heart’s contractions per minute) to get a fuller picture of cardiovascular activity and to control for preload and afterload effects. However, as outlined above, due to its direct link to

-adrenergic sympathetic impact, PEP was again our primary measure of effort mobilization (seen also Kelsey, 2012).

The Present Experiment

Extending the IAPE model logic (Gendolla, 2012, 2015) to the effect of age primes on effort mobilization, we tested the effects of suboptimally versus optimally presented age primes on effort-related cardiovascular response. Participants worked on a short-term memory task during which they were exposed to suboptimally (13 ms) versus optimally (760 ms) presented age primes. In the suboptimal prime presentation condition, where the primes were supposed to be processed implicitly, we predicted a prime assimilation effect. Here, exposure to elderly primes during the cognitive task should result in stronger effort-related cardiovascular reactivity than processing youth primes. In the optimal prime presentation condition, where the primes were clearly visible during the cognitive task, we expected a diminished or even reversed age prime effect because of behavioral correction due to controlled prime processing.

Method Participants and Design

One-hundred-and-ten university students with different majors (90 women, mean age 21 years) voluntarily participated in this experiment for course credit or monetary remuneration (10 CHF, equivalent approximately to 10 USD). They were randomly assigned to the conditions of a 2 (Prime: elderly vs. youth) x 2 (Prime Presentation Time: 13 ms vs. 760 ms) between-persons design. We had to remove three participants, because they indicated taking medication that could have influenced their cardiovascular responses and one other participant, because of incomplete cardiovascular data. This left a final sample of N = 106 participants.

Concerning the different cardiovascular measures, we excluded one more participant, because her PEP responses exceeded the grand mean for 3.76 SDs. Consequently, she was considered an outlier. The final sample for this measure was thus N = 105—elderly-prime/13 ms condition (24 women, 5 men, mean age 20.5 years), elderly-prime/760 ms condition (21 women, 5 men, mean age 21.5 years), youth-prime/13 ms condition (19 women, 5 men, mean age 21 years), and youth-prime/760 ms condition (21 women, 5 men, mean age 20 years). We excluded another participant, because his HR responses were 3.38 SDs above the grand mean, leaving a sample of N = 105 for the HR analyses—elderly-prime/13 ms condition (24 women, 5 men, mean age 20.5 years), elderly-prime/760 ms condition (21 women, 5 men, mean age 21.5 years), prime/13 ms condition (20 women, 5 men, mean age 21 years), and youth-prime/760 ms condition (21 women,4 men, mean age 20 years). Finally, we excluded two participants, because their systolic responses exceeded the grand mean for more than 2.70 SDs, leaving a sample of N =104 for the SBP analyses—elderly-prime/13 ms condition (23 women, 4 men, mean age 19.6 years), elderly-prime/760 ms condition (21 women, 5 men, mean age 21.5 years), youth-prime/13 ms condition (20 women, 5 men, mean age 21 years), and youth-prime/760 ms condition (21 women, 5 men, mean age 20 years).

Age Primes

Highly standardized front perspective greyscale pictures of young (age 19 to 25 years) and old (age 71 to 84 years) individuals of the Lifespan-Adult-Faces database (Minear & Park, 2004) were used as primes (picture codes: Wfemale19, Wfemale20, Wfemale22, Wmale20-2, Wmale22-2, Wmale25-2, Wfemale71, Wfemale76, Wfemale84, Wmale78, Wmale79,

Wmale82). Half the pictures showed female faces and half showed male faces. By means of the image organizer Picasa software—for editing digital photos—we applied a filter to reduce the primes’ high contrast to render them blurrier.

Apparatus and Physiological Measures

PEP (in milliseconds [ms]) and HR (in beats per minute [bpm]) were continuously and noninvasively assessed with electrocardiogram (ECG) and impedance cardiogram (ICG) signals using a Cardioscreen® 1000 haemodynamic monitoring-system (Medis, Ilmenau, Germany) (for a validation study see Scherhag, Kaden, Kentschke, Sueselbeck, & Borggrefe, 2005). Four pairs of spot electrodes (Medis-ZTECT™) were placed on each side of the base of the participant’s neck and on each side of the thorax along the mid axillary line at the level of the xiphoid. The Cardioscreen® 1000 monitoring-system automatically sampled the ECG and ICG signals with a rate of 1000 Hz. ECG and ICG signals were offline processed with Bluebox 2 V1.22 software (Richter, 2010) applying a 50 Hz low pass filter. R-peaks in the ECG signal were identified using a threshold peak-detection algorithm and visually confirmed (ectopic beats were deleted). The first derivative of the change in thoracic impedance was calculated and the resulting dZ/dt-signal was ensemble averaged over periods of 1 min using the detected R-peaks (Kelsey & Guethlein, 1990). B-point location was estimated based on the RZ interval of artifact-free cardiac cycles (Lozano et al., 2007), visually inspected, and—if necessary—

corrected as recommended (Sherwood et al., 1990). PEP was determined as the interval (in ms) between ECG R-onset and the ICG B-point (Berntson et al., 2004). Shorter PEP indicates a stronger β-adrenergic impact on the heart, and therefore stronger reactivity in terms of effort intensity. HR (in beats per min [bpm]) was determined by means of the same software.

Additionally, SBP and DBP (in millimeters of mercury [mmHg]) were assessed with a Dinamap ProCare monitor (GE Medical Systems, Information Technologies Inc., Milwaukee, WI) that uses oscillometry. The Dinamap’s blood pressure cuff was placed over the brachial artery above the elbow of participant’s non-dominant arm and automatically inflated in 1-min intervals to assess arterial pressure. Assessed values were stored on computer disk.

Procedure and Experimental Task

The study was conducted in accordance with the ethical guidelines of the University of Geneva and the procedure had been approved by the local ethical committee. The study was run in individual sessions, which took about 30 min each. After having obtained signed

consent, participants took a seat in a comfortable chair in front of a computer. The experimenter applied the electrodes for ECG and ICG signals and the blood pressure cuff and went to an adjacent control room. The procedure was computerized with a script running in E-Prime 2.0 (Psychology Software Tools, Pittsburgh, PA), which controlled the presentation of instructions and stimuli and collected participants’ responses. Participants read some introductory information and rated 2 items related to happiness (happy, joyful) and 2 items related to sadness (sad, downcast) from the UWIST mood checklist (Matthews, Jones, &

Chamberlain, 1990) on 7-point scales (1 – not at all, 7 – very much) to assess their global affective state before exposure to the age primes in the cognitive task. Next, participants watched an 8 min extract of a hedonically neutral documentary film about Portugal that served as habituation period during which cardiovascular baseline activity was recorded.

After the habituation period, participants received instructions (“Please respond as quickly and accurately as possible”) for a short-term memory task adapted from Sternberg (1966). Task trials started with a fixation cross (1000 ms), followed by a picture of an individual of the Lifespan-Adult-Faces database either for a duration of 13 ms (i.e., 1 frame on a 75 Hz monitor) or of 760 ms (i.e., 58 frames on a 75 Hz monitor). According to the prime condition, a picture of an old human face or of a young human face was presented. Faces were randomized and the same picture did not appear successively. The face pictures were immediately backward masked with a random dot pattern (133 ms), which was followed by a string of 5 letters, presented for 750 ms. Next, a target letter appeared in the middle of the screen and a row of the letter “X” masked the previously presented letter string. Participants indicated by pressing a “yes” or “no” key on the numerical keyboard with the fingers of their choice of their dominant hand if the target letter was part of the previously presented letter string or not. The target letter remained on the screen until participants gave a response within a maximal response time window of 3 sec. After responding, the message “response entered”

appeared. If participants did not respond within 3 sec., the message “please answer more quickly” was presented for 1 sec. To assure that all participants worked for the same time on the main task and were exposed to the same number of face pictures independently of their working speed, the respective message appeared for 4 sec minus participants’ reaction time.

The inter-trial interval varied randomly between 1.5 and 3 sec.

Before onset of the main task, which consisted of 36 trials, participants worked on 10 training trials with correctness feedback including only dotted silhouettes as primes. No

correctness feedback was given during the main task to prevent performance-related affective reactions (e.g., Kreibig, Gendolla, & Scherer, 2012) that could interfere with the effect of the age primes.

After the task, participants rated the level of subjective task difficulty (“Was it difficult for you to succeed on the task?”) and the importance of succeeding on the task (“How important was for you to succeed the task?”) on 7-point scales (1 – very low, 7 – very high) retrospectively. Then, participants evaluated their global affective state again with the same four affect items as at the procedure’s onset to assess whether the processed age primes had influenced participants’ conscious feelings. Finally, participants indicated some personal data (e.g., sex, age) and indicated possible medication, hypertension family history, and smoking habits.

At the end of the experimental session, the experimenter interviewed participants in a standardized funnel debriefing procedure about the study’s purpose and what they had seen during the trials. Participants who mentioned “flickers” or “flashes” were asked to describe their content to assess to which extent they had been aware of the age primes’ content. They were also debriefed, thanked for their participation, and received their course credit.

Data Analyses

To test our hypotheses about cardiovascular reactivity, all data for PEP, HR, SBP, and DBP, were analyzed with 2 (Prime) x 2 (Prime Presentation Time) between-persons ANOVAs.

Task ratings and task performance measures were analyzed by the means of the same between-persons ANOVAs. Finally, the affect ratings were subjected to a 2 (Prime) x 2 (Prime Presentation Time) x 2 (Time) mixed model ANOVAs. The alpha-error level for all tests was 5%.

Results Cardiovascular Baselines

Repeated measures ANOVAs of the last five 1-minute scores of PEP, HR, SBP, and DBP activity assessed during the habituation period revealed significant Time main effects, Fs >

3.21, ps < 0.01, η²s > 0.04. Consequently, we calculated cardiovascular baselines for each cardiovascular measure by averaging the last minutes which did not differ significantly.

Consequently, PEP baseline scores were created by averaging the last 3 minutes of the habituation period, which were internally highly stable (Cronbach’s  = 0.99) and did not differ

significantly according to Tukey tests (ps > 0.50). The HR baseline values were calculated by averaging the last 2 minutes of the habituation period, which were highly correlated (rs > 0.97).

However, for SBP and DBP values we retained only the last minute for the baseline values, because it differed significantly from the values assessed in the minutes before. Cell means and standard errors appear in Table 1.

We conducted 2 (Prime) x 2 (Prime Presentation Time) between-persons ANOVAs to test for a priori differences in baseline scores between the experimental conditions. No significant differences were found for PEP, HR, and DBP (ps > 0.10). However, for SBP, the analysis revealed a Prime main effect, F(1,100) = 4.06, p = 0.05, η² = 0.04. Below we will deal with this finding with an analysis of covariance (ANCOVA). Moreover, preliminary analyses revealed that PEP and SBP baseline values were higher for men (M = 106.20, SE = 2.23; M = 115.74, SE = 1.57 respectively) than for women (M = 100.29, SE = 1.20; M = 103.35, SE = 0.98 respectively), Fs > 4.63, ps  0.03, η²s > 0.05. This gender difference in blood pressure is a common finding (Wolf et al., 1997). Also the gender difference in PEP is not surprising given the link between PEP and SBP. No significant sex effects emerged for HR and DBP baselines (ps > 0.21).

Table 1

Means and standard errors (in parentheses) of the cardiovascular baseline values.

Elderly Primes Youth Primes

Note: PEP = pre-ejection period (in ms), HR = heart rate (in beats/min), SBP = systolic blood pressure (in mmHg), DBP = diastolic blood pressure (in mmHg).

Cardiovascular Reactivity

We created cardiovascular task scores for each participant by averaging the five 1-min scores of PEP, HR, SBP, and DBP assessed during performance (Cronbachʼs αs > 0.97). Then we calculated cardiovascular reactivity scores by subtracting the baseline values from these averaged task scores. Preliminary ANCOVAs of the reactivity scores revealed significant associations between baseline values and reactivity scores for HR, SBP, and DBP, Fs > 4.44, ps

 0.03, η²s > 0.05, but not for PEP (p = 0.56). Consequently, we analyzed HR, SBP, and DBP reactivity with baseline adjustment. Moreover, there were no significant sex main or interaction effects on any cardiovascular response (ps > 0.06).

PEP, HR, SBP, and DBP Reactivity

For PEP reactivity, a 2 (Prime) x 2 (Prime Presentation Time) between-persons ANOVA did neither reveal significant main effects (ps > 0.20), nor a Prime x Prime Presentation Time

interaction effect (p = 0.44). For baseline-adjusted HR responses, the between persons ANOVA did not reveal significant main effects (ps > 0.91) but a tendencial Prime x Prime Presentation Time interaction effect, F(1,100) = 2.80, p = 0.09, η² = 0.03. Looking at Table 2, reveals that the pattern of cell means corroborates our effort-related hypotheses in the 13 ms condition.

However, additional focused age prime cell comparisons within each presentation time

However, additional focused age prime cell comparisons within each presentation time