Main results

Mental effort has been operationalized as cardiovascular reactivity, especially PEP reactivity which represents the purest noninvasive indicator of β-adrenergic impact on the

heart (Kelsey, 2012). Additionally, HR, SBP, and DBP were also assessed in order to control for preload—by assessing HR—or afterload—by assessing blood pressure—effects which can potentially influence PEP (Sherwood et al., 1990). Moreover, these indicators have already been used in the past for the quantification of effort mobilization during cognitive tasks (e.g., Freydefont, Gendolla, & Silvestrini, 2012; Gendolla & Richter, 2010), and so they can offer us a fuller picture of cardiovascular activity.

Based on the predictions of the IAPE model (Gendolla, 2012, 2015), the purpose of the present research was to test whether implicit aging has similar effects on effort mobilization as implicit sadness or fear had in previous studies (see Gendolla, 2012, 2015), whereas implicit youth has effects that are comparable to those of implicit happiness or anger in that earlier research. More specifically, we predicted that implicit aging—as sadness and fear—should activate the performance difficulty concept and in turn, lead to higher subjective demand and stronger cardiovascular reactivity as long as success is possible and worthwhile. On the other hand, we suggested that youth primes—as happiness and anger—should activate the performance ease concept and in turn reduce the experienced task demand and effort mobilization. We will now summarize the main findings of this thesis.

3.1.1. Pre-ejection period reactivity

According to our predictions based on the IAPE model logic, elderly primes should activate the performance difficulty concept and in turn, lead to higher subjective demand and stronger PEP reactivity as long as success is possible and justified. On the contrary, youth primes should activate the ease concept, which should lead to lower subjective demand and weaker PEP reactivity. However, we did not systematically find evidence for the expected age-prime effect on PEP reactivity—our primary measure of effort mobilization. Indeed, we obtained PEP reactivity effects in two of our four studies. Therefore, Study 1 revealed a Prime x Prime Presentation Time interaction effect, meaning that the youth primes led to stronger PEP reactivity than the elderly primes—the opposite pattern of what we had expected—when the age primes were presented for 27 ms. However, this surprising effect on PEP reactivity could have been caused by a behavior correction effect because of the primes’ high visibility due to their high contrast. Such an effect due to prime visibility has been reported earlier (see Lasauskaite Schüpbach et al., 2014), where contrast effects emerged when the affect primes were presented in an optimal—visible—way. According to the IAPE model, the predicted

effect of the affect primes on effort mobilization is based on the individuals’ unawareness of the influence of this affective information. Consequently, when individuals are aware of this available affective influence, the result is a weakened or even reversed prime effect due to a correction process. Study 3 was conducted to investigate the role of incentive in the process of effort mobilization when participants performed a difficult task while being exposed to age primes. The results on PEP reactivity largely supported our hypotheses. Accordingly, in the elderly-prime condition we found stronger PEP reactivity when the incentive was high meaning that high incentive boosted effort and thus compensated the motivational deficit anticipated for this prime condition. However, effects in the youth-prime condition were less clear.

3.1.2. Heart rate reactivity

As previously mentioned, PEP reactivity was our main dependent physiological measure of mental effort. However, β-adrenergic activity can also influence HR, which should thus reflect effort mobilization when the sympathetic impact is stronger than the parasympathetic impact on this measure. HR is a less reliable index of β-adrenergic activity, because it can also increase due to parasympathetic withdrawal. Nevertheless, in the present work we found a marginal HR reactivity effect in Study 2 and significant HR reactivity effects in Studies 3 and 4. The latter effects described the cardiac response pattern that was anticipated for age-prime effects on effort mobilization. More specifically, in Study 2 HR response tended to be stronger in the elderly-prime condition than in the youth-prime condition when the age primes were very briefly presented (13 ms). In Study 3, high incentive led to a significant boost in HR in the elderly-prime condition, while it did not so in the youth-prime condition. This fitted our hypotheses, because we reasoned that individuals who were exposed to elderly primes should have perceived task demand as too difficult, leading to disengagement when incentive was low. But this effort mobilization deficit due to expected disengagement could be compensated by high monetary incentive that justified the subjectively high necessary effort. Finally, in Study 4, elderly primes led to relatively strong HR reactivity, whereas youth primes led to weak responses and a neutral-prime control condition fell, as expected, in between these conditions.

3.1.3. Blood pressure reactivity

Cardiac contractility can also have a systematic influence on SBP. For this reason, it has been used as an index of effort mobilization (see Gendolla & Richter, 2010; Gendolla, Wright,

& Richter, 2012; Wright & Kirby, 2001). However, SBP is also influenced by total peripheral vascular resistance, which is not systematically influenced by β-adrenergic impact (Levick, 2003). In the present research, we found a significant effect of our manipulations on SBP only in Study 3, in which the SBP reactivity pattern paralleled the pattern of PEP reactivity with the expected findings for the elderly-prime condition, but also an unexpected significant incentive effect in the youth-prime condition. Indeed, Study 3 revealed that high incentive led to stronger SBP reactivity even in the youth-prime condition, which should have been unaffected by our incentive manipulations. This finding may be attributed to a higher measurement error for SBP reactivity, which was constituted by averaging five 1-minute measures. By contrast, PEP and HR reactivity scores were based on about 370 cardiac cycles, meaning that the reliability of the PEP and HR measures should have been higher than that of the blood pressure assessments.

DBP is even more strongly related to vascular resistance than SBP. However, Study 4 revealed a DBP reactivity effect on effort mobilization in line with our effort-related predictions. Accordingly, Study 4 revealed that participants who were exposed to elderly primes showed the strongest reactivity, whereas exposure to youth primes led to the weakest reactivity. The neutral-prime control condition fell in between these conditions.

To sum up, despite the absence of systematic evidence for our main measure of mental effort mobilization—PEP reactivity—the correlation analyses between the different cardiovascular reactivity measures (Studies 2 and 4), suggested that the effects found on HR and blood pressure occurred due to increased β-adrenergic activity.

3.1.4. Subjective task ratings

The IAPE model posits that the affect stimuli influence mental effort in the context of a cognitive challenge through their impact on experienced difficulty—subjective task demand.

Accordingly, affect primes activate knowledge about the respective affective states, including information about performance ease or difficulty, which then influences subjective demand and thus effort mobilization. Applying the IAPE model logic to the effect of implicit aging, age primes should impact effort-mobilization by influencing the evaluation of task demand. More

specifically, elderly primes should increase task demand—as sadness and fear primes do—by activating the difficulty concept, whereas youth primes should activate the ease concept and lower task demand—as happiness and anger primes do. Previous research from our laboratory has only sometimes found prime effects on ratings of subjective demand (e.g., Gendolla & Silvestrini, 2011; Lasauskaite et al., 2013, Lasauskaite Schuppbach et al., 2014;

Silvestrini & Gendolla, 2011b). Other studies have revealed the expected effects on effort without significant effects on these subjective demand ratings (e.g., Chatelain & Gendolla, 2016; Freydefont & Gendolla, 2012; Freydefont et al., 2012).

In the present thesis, only Study 2 found a marginal age prime effect on the self-report measure of subjective task demand. Accordingly, elderly primes let participants perceive the task as more demanding than youth primes. This finding brings some support to the idea that activation of the aging concept during a performance context can lead to higher experienced task demand. However, the absence of a systematic prime effect on ratings of subjective demand can be explained by the fact that task demand is assessed retrospectively after the completion of the task which subjects this measure to a number of possible biases (Robinson

& Clore, 2002). Moreover, the IAPE model predicts a prime impact on subjective demand online—during task performance—rather than thereafter. This prime influence on experienced demand may happens on the implicit level—effort mobilization influenced in an automatic way—without being explicitly accessible to self-reports. This suggests the need of a more implicit measure to detect such an effect. For example, Lasauskaite et al. (2017) have used a sequential priming paradigm to measure the associative links between implicit affect and ease or difficulty. In support of the IAPE model, these authors have found that sadness was associated with difficulty, whereas happiness was associated with ease. This sequential paradigm seems more appropriate to test for associative links between age and performance ease or difficulty than the retrospective self-report measures. Future research should test for such links in experiments on cognitive accessibility. Finally, regarding a reliability issue, subjective demand was assessed with a single item whereas cardiovascular scores were based on about 370 cardiac cycles. For this reason, the effect on these subjective ratings must be rather strong to be detected, which seems not to be the case in the majority of the studies in the present thesis.

3.1.5. Effort and performance

It is not surprising that we have not systematically found age prime effects on performance measures. Effort and performance refer to different constructs and their relationship is complex. Indeed, effort is defined as mobilization of resources to carry out instrumental behavior, whereas performance is the outcome of this resource mobilization.

However, task performance depends also (or even more) on task-related ability and chosen strategies rather than on effort alone, which renders a direct link between effort and performance difficult. Moreover, the IAPE model does not make any specific predictions about prime effects on task performance measures.

However, in Study 2 we found a marginally significant effect on participants’ response times. Accordingly, participants in the elderly-prime condition took more time to respond in comparison to participants in the youth-prime condition. We found higher experienced demand and slower responses in the elderly condition. In no other study, we found age-prime effects on cognitive performance.