Study 1: Preliminary Findings of Implicit Aging Influences on Effort-Mobilization

Abstract

This experiment investigated the effect of implicit aging on the mobilization of mental effort based on the effort-related predictions of the Implicit-Affect-Primes-Effort (IAPE) model and on evidence that aging is associated with cognitive difficulties. We predicted that the implicit activation of the aging stereotype during a cognitive task should render the performance difficulty concept accessible, which in turn should augment experienced demand and thus effort mobilization. To test this, we exposed participants to masked faces of elderly vs. young individuals while they performed a short-term memory task. Given the high contrast of the here used age stimuli, we also manipulated the presentation time of those primes (13 ms vs. 27 ms) without having specific predictions concerning the prime’s duration. We found an interaction effect on cardiac pre-ejection period (PEP) which was carry on by the 27 ms prime presentation condition. The findings are preliminary and do not provide yet any evidence for the systematic impact of implicit aging on effort-related cardiac response, but they allow us to work on the stimuli used as to decrease their visibility due to their high contrast.

Introduction

Multiple studies from our laboratory have revealed that affective stimuli that are implicitly processed during cognitive tasks systematically influence effort-related responses of the cardiovascular system (e.g., Chatelain & Gendolla, 2015; Freydefont & Gendolla, 2012;

Freydefont, Gendolla, & Silvestrini, 2012; Gendolla & Silvestrini, 2011; Lasauskaite, Gendolla

& Silvestrini, 2013). Accordingly, they have demonstrated that the mere implicit activation of individuals’ knowledge about emotions is sufficient for influencing their behavior. These studies on implicit affect were guided by the Implicit-Affect-Primes-Effort (IAPE) model (Gendolla, 2012, 2015), which posits that affect stimuli influence mental effort in the context of a cognitive challenge through their impact on experienced difficulty. According to this model, people learn in everyday life that coping with challenges is easier in some affective states than in others. For example, they learn that performance is relatively easy in a happy

mood or when one is angry, but relatively difficult in a sad mood or when one is fearful (see Chatelain & Gendolla, 2015; Freydefont et al., 2012; Gendolla & Brinkmann, 2005). That way ease and difficulty become features of the mental representations of different emotions and activating these features by exposing people to implicitly processed affective stimuli influences physiological reactions related to resource mobilization: According to the principles of motivational intensity theory, effort rises with subjective demand as long as success is possible and the amount of effort that is necessary for success is justified.

In general, the IAPE model (Gendolla, 2012, 2015) postulates that any concept that is associated with difficulty should increase subjective demand in a performance context and thus influence effort mobilization. This allows us to wonder if similar and corresponding effects to the implicit affect can occur by the mere activation of the aging stereotype—a social stereotype which is strongly associated with cognitive difficulties. Social stereotypes are fixed, simplified, and overgeneralized cognitive structures (Rust & See, 2010) that help humans to simplify their perceptions, judgments, and actions. A typical and strong stereotype in the Western culture concerns the elderly, and more particularly, the idea that 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). Except Westerns’ beliefs about aging, there is also evidence that many aspects of basic cognitive functioning indeed become less efficient with age and that older adults have to cope with higher difficulties than younger people when they are confronted with cognitive tasks (Hess & Ennis, 2012). Consequently, older people are obligated to mobilize more effort—

mirrored by stronger cardiovascular responses—than younger people to achieve the same level of cognitive performance (e.g., Ennis, Hess, & Smith, 2013; Smith & Hess, 2015). Older people also experience cognitive tasks as subjectively more demanding, leading to disengagement due to subjective over-challenge at lower levels of objective task difficulty which young people regard as feasible (Hess, Smith, & Sharifian, 2016). All this indicates that aging is indeed associated with cognitive difficulties.

Based on the evidence from the aging research discussed above and guided by the IAPE model (Gendolla, 2012, 2015), the present research is an attempt to extend the IAPE’s model logic to the effect of age primes on effort mobilization. Thus, we tested the idea that the mere implicit activation of the aging stereotype can systematically influence biologically young

adults’ effort-related cardiovascular response when they are confronted with a cognitive challenge.

Effort-related Cardiovascular Response

Effort mobilization refers to the resources a person is mobilizing in order to carry out a certain behavior. Integrating the predictions of motivational intensity theory (Brehm & Self, 1989) with Obrist’s (1981) active coping approach, Wright (1996) posited that β-adrenergic sympathetic impact on the heart responds proportionally to the level of experienced task demand as long as success is possible and worthwhile. Beta-adrenergic impact on the heart is best assessed as cardiac pre-ejection period (PEP)—a cardiac contractility index defined as the time interval between the onset of left ventricular depolarization and the opening of the aortic valve in a cardiac cycle (Berntson, Lozano, Chen, & Cacioppo, 2004). The shorter this time interval, the stronger is cardiac contractility. In support of Wright’s integrative model, PEP sensitively responds to variations in experienced task demand (e.g., Richter, Friedrich, &

Gendolla, 2008), incentive value (e.g., Richter & Gendolla, 2009), and combinations of both variables (e.g., Silvestrini & Gendolla, 2011a).

Several studies have found that also systolic blood pressure (SBP)—the maximal pressure in the vasculature after a heartbeat—increases with task engagement (e.g., Gendolla

& Richter, 2010; Richter & Gendolla, 2009; Wright & Gendolla, 2012; Wright & Kirby, 2001).

That is, SBP is systematically influenced by cardiac contractility via its impact on cardiac output.

However, SBP also depends on the peripheral resistance in the vasculature, which is not systematically influenced by β-adrenergic impact (Levick, 2003) and can mask contractility effects on SBP. The same is true for diastolic blood pressure (DBP)—the minimal pressure in the vasculature between two heartbeats. DBP effects are even more dependent on changes in total peripheral resistance than SBP responses (Levick, 2003). There is also some evidence that heart rate (HR)—the number of heart’s contractions per minute—has been assessed to quantify effort (e.g., Brinkmann & Gendolla, 2007; Eubanks, Wright, & Williams, 2002;

Freydefont, Gendolla, & Silvestrini, 2012). However, HR is determined by both sympathetic and parasympathetic activation and should only reflect effort mobilization when the sympathetic impact is stronger (e.g., Berntson, Cacioppo, & Quigley, 1993). Consequently, PEP is the most reliable and valid indicator of effort mobilization among these parameters (Kelsey, 2012).

The Present Experiment

As discussed above, the IAPE model (Gendolla, 2012, 2015) postulates that any concept that is associated with difficulty should increase subjective demand in a performance context and thus influence effort mobilization. Subsequently, this was the first attempt of a series of experiments to test if the IAPE model could be generalized to other concepts that are associated with ease and difficulty than the affective ones. According to the IAPE model, implicitly processing elderly primes during task performance should make the performance difficulty concept accessible and thus augment subjective demand and effort-related cardiovascular reactivity. By contrast, processing youth primes should render the performance ease concept accessible and thus reduce subjective demand and effort mobilization.

Considering that the visual stimuli that served as age primes were highly contrasted, we decided to manipulate their presentation time to control for possible prime visibility effects without having specific hypotheses.

Method Participants and Design

Seventy-seven healthy undergraduate students of the University of Geneva (62 women, 15 men, mean age 22 years) were randomly assigned to a 2 (Prime: elderly vs. youth) x 2 (Prime Presentation Time: 13 ms vs. 27 ms) between-persons design. Participation was anonymous, voluntary, and recompensed with course credit. Four participants from the original dataset were excluded because they indicated taking medication that could have influenced their cardiovascular responses. Although we had aimed at recruiting 20 participants for each cell, as recommended (see Simmons, Nelson, & Simonsohn, 2011), this left a final sample of N = 73 participants whose characteristics regarding sex and age were balanced across conditions: elderly-prime/13 ms condition (14 women, 4 men, mean age 20 years), elderly-prime/27 ms condition (15 women, 4 men, mean age 21 years), youth-prime/13 ms condition (14 women, 4 men, mean age 23 years), and youth-prime/27 ms condition(15 women, 3 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.

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, Lozano, Chen, & Cacioppo, 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.

In addition, SBP and DBP (in millimeters of mercury [mmHg]) were assessed with a Vasotrac® APM205A monitor (MEDWAVE®, St. Paul, MN) that uses applanation tonometry.

The Vasotrac’s pressure sensor was placed around the wrist on the top of the radial artery of participant’s nondominant arm (see Belani et al., 1999 for a validation study). This device yields one blood pressure measure every 12-15 heartbeats (i.e., 4-5 values per minute), which were directly stored on computer disk. Values were offline averaged to 1-min intervals.

Aging Stereotype Questionnaire

We created a questionnaire to assess participants’ explicit aging stereotype that was

composed of the following items: “Older people are slow in processing information”, “Older people have a good concentration capacity”, “Older people are physically active”, “Older people have attentional difficulties”, and “Older people have good memory capacities”.

Participants indicated their agreement with each of these items on 7-point scales (1 – not at all, 7 – very much). Two items were reversed coded (“Older people are slow in processing information” and “Older people have attentional difficulties”) to create a global stereotype score for each participant.

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 participants had been greeted by the experimenter, they took seat in a comfortable chair in front of a computer monitor and signed an informed consent form. Then, the experimenter applied the electrodes for the ECG and ICG measures and the blood pressure sensor. After that, she left the room and monitored the experiment from an outside 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 answered questions about their momentary affective state with two items assessing positive affect (happy, joyful), one item assessing sadness (downcast), and one item assessing anger (angry). Participants responded to the 4 items (“Right now, I’m feeling…”) on 7-point scales (1 – not at all, 7 – very much) to assess their affective state before exposure to the age primes. Next, participants watched an 8 min extract of a hedonically neutral documentary film that served as habituation period during which cardiovascular baseline values were 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 27 ms (i.e., 2 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 4 letters, presented for 750 ms. Afterwards, 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 (maximal response time window: 3 sec). After responding, the message “response entered” appeared.

If participants did not respond during the maximal response time window (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 2 and 4 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 task difficulty they had experienced during task performance (“Was it difficult for you to succeed on the task?”), their subjective ability (“Did you feel able to succeed the task?”), the amount of mobilized effort (“How much effort did you invest to succeed on the task?”), the importance of successful completion of the task (“How important was for you to succeed the task?”), and the value of successful completion of the task (“What value had for you to succeed the task?”) on a 7-point scale (1 – very low, 7 – very high). 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. Moreover, participants indicated some personal data (e.g., sex, age) and indicated possible medication, hypertension family history, and smoking habits.

Finally, 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. At the end of each experimental

session, participants replied to the aging stereotype questionnaire, were 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.

Comparisons without directed hypotheses were made with two-tailed Tukey tests. Affect ratings were subjected to a 2 (Prime) x 2 (Prime Presentation Time) x 2 (Time) mixed model ANOVAs. The other self-reported evaluations (difficulty, ability, effort, importance and value of success), the task performance measures, and the scores on the aging stereotype questionnaire were analyzed in the context of 2 (Prime) x 2 (Prime Presentation Time) between-persons ANOVAs. The alpha-error level for all tests was 5%.

Results Cardiovascular Baselines

For PEP, cardiovascular baseline scores were created by averaging the 1-minute scores of the last 5 minutes of the habituation period. These values were internally high stable (Cronbach’s  = 0.99) and did not differ significantly according to a repeated measures ANOVA, F(4, 288) = 1.61, p = 0.17, η² = 0.02. However, for HR, SBP, and DBP, the cardiovascular baselines were calculated by averaging the last 2 minutes of the habituation period because there were significant differences between the other minutes according to repeated measures ANOVAs, F > 2.49, ps < 0.04, η² < 0.10. The retained measures taken during the last two minutes were highly correlated (rs > 0.95). 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 values between the experimental conditions. No significant baseline differences were found for any cardiovascular index (ps > 0.18). Due to the relatively small number of men in the sample, we did not include sex as a between factor in the analyses. However, excluding men from the analyses revealed basically the same results as the here reported analyses of the entire sample.

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

Cardiovascular reactivity scores (delta scores) were calculated for each participant by averaging the 1-min scores of PEP, HR, SBP, and DBP assessed during task performance (Cronbach’s αs > 0.98) and subtracting the cardiovascular baseline values from these averaged task scores (see Kelsey, Ornduff, & Alpert, 2007). Preliminary analyses of covariance (ANCOVA) of the reactivity scores revealed a significant association between baseline values and reactivity scores for HR, F(1,68) = 6.24, p = 0.01, η² = 0.08, and DBP, F(1,65) = 4.67, p = 0.03, ɳ²

= 0.07, but not for PEP (p = 0.84). For SBP, the association between baseline values and reactivity scores fell short of significance (p = 0.055). Consequently, we analyzed HR and DBP reactivity with baseline adjustment.

PEP Reactivity

A 2 (Prime) x 2 (Prime Presentation Time) between-persons ANOVA found a significant Prime x Prime Presentation Time interaction, F(1,69) = 4.44, p = 0.04, ɳ² = 0.06, in absence of significant main effects (ps > 0.70). Cell means of the PEP responses are depicted in Figure 1.

Additional focused cell comparisons within each presentation time condition revealed a significant difference, t(69) = 1.75, p = 0.04, η² = 0.04, between the weaker reactivity in the elderly-prime cell (M = -0.42, SE = 0.63) and the stronger reactivity in the youth-prime cell (M

= -2.83, SE = 0.91) in the 27 ms prime presentation time condition. No significant difference emerged between the prime conditions in the 13 ms prime presentation time condition (p = 0.11).

Figure 1. Cell means and standard errors of cardiac pre-ejection period reactivity (in ms) during task performance.

HR, SBP, and DBP Reactivity

2 (Prime) x 2 (Prime Presentation Time) between-persons ANOVAs for baseline-adjusted HR and DBP responses revealed no significant effects (ps > 0.19). The same ANOVA for SBP reactivity did not reveal any significant main or interaction effect (ps > 0.57). Cell means and standard errors appear in Table 2.

Table 2

Means and standard errors (in parentheses) of heart rate, systolic, and diastolic blood pressure reactivity during task performance.

Note: HR = heart rate (in beats/min), SBP = systolic blood pressure (in mmHg), DBP = diastolic blood pressure (in mmHg).

Participants’ Age and Aging Stereotype

An ANOVA of participants’ age revealed no significant differences between the conditions (ps > 0.16, average M = 20.97, SE = 0.57). An ANCOVA of PEP response—the cardiovascular measure on which the manipulations had a significant effect—revealed a significant association with participants’ age, F(1,68) = 6.27, p = 0.01, ɳ² = 0.08. However, the above reported 2 (Prime) x 2 (Prime Presentation Time) between-persons ANOVA for PEP reactivity remained significant, F(1,68) = 6.65, p = 0.01, ɳ² = 0.09, after controlling for the participants’ age. That is, we cannot attribute the observed significant interaction effect for PEP reactivity to this variable.

An ANOVA of participants’ aging stereotype scores (Cronbach’s  = 0.67) revealed no significant differences between the conditions (ps > 0.43, average M = 18.03, SE = 0.53).

Furthermore, an ANCOVA of PEP—the cardiovascular measure on which the manipulations had a significant effect—revealed no significant association with participants’ stereotype scores (p = 0.25).

Affect Ratings

Since internal consistency for the two items related to happiness was high (rs > 0.76), we created pre-task and post-task happiness scores and subjected these scores to a 2 (Prime) x 2 (Prime Presentation Time) x 2 (Time) mixed model ANOVA. The analysis of these happiness scores did not reveal any significant effects (ps > 0.10; pre-task M = 9.42, SE = 0.20, post-task M = 9.10, SE = 0.25). Sadness and anger had been assessed with single items. Two (Prime) x 2 (Prime Presentation Time) x 2 (Time) mixed model ANOVAs of these ratings did not reveal any

Since internal consistency for the two items related to happiness was high (rs > 0.76), we created pre-task and post-task happiness scores and subjected these scores to a 2 (Prime) x 2 (Prime Presentation Time) x 2 (Time) mixed model ANOVA. The analysis of these happiness scores did not reveal any significant effects (ps > 0.10; pre-task M = 9.42, SE = 0.20, post-task M = 9.10, SE = 0.25). Sadness and anger had been assessed with single items. Two (Prime) x 2 (Prime Presentation Time) x 2 (Time) mixed model ANOVAs of these ratings did not reveal any