Proefschrift_Holstein

Reward modulation of cognitive function: aging

Table 5.2 Reward x Task-switching effects for younger and older subgroups* Younger (n=35) Older (n=33) Difference

-0.164 (-10.50;10.17)

-0.486 (-9.58;8.61) -2.21 (-5.70;1.27) 0.15 (0.01;0.29)

-0.055; P > 0.1 -1.061; P > 0.1

RT

0.66 (-3.24;4.56) 0.43 (0.25;0.61)

Accuracy

-2.755; p = 0.006

SAT

SAT = Speed-Accuracy-Tradeoff = (z-speed- z-accuracy) / 2 ; RT = response times * subgroups (study A, C and D in table 1 and figure 3a) were not confounded by differential reward size

0.010). A between subject analysis in this subgroup revealed that the older group earned more reward than did the younger group (mean €9.01 (SE 0.32) vs. mean €10.50 (SE 0.20); t(26.448) = 11.343, p < 0.001). We were puzzled by this effect and reasoned that the age-related increase in total earnings might originate from differences in the response deadline, which was set during a pre-test practice phase ( methods ). When the response deadline was determined, participants were instructed to respond as fast and accurately as possible. We reasoned that participants who put more emphasis on the accuracy instruction would not respond as fast as possible during practice. This would then result in longer, less stringent response deadlines during the actual test. In the current paradigm, inaccurate responses, no matter how fast, are never rewarded. Therefore, adopting such a cautious (slow and accurate) response strategy during practice may result in higher earnings. For example, imagine two participants (A and B) who are theoretically both able to respond within 400ms. If participant A responds cautiously during the practice phase, the average response time during practice will be slower (e.g. 900ms) than that of someone who emphasized speed during practice (participant B, e.g. 500ms). As a consequence, participant A will have plenty of time to respond accurately on test, thereby increasing the number of rewarded trials. By contrast, participant B will need to continue to respond relatively fast. Participant B will thus make more errors, and therefore a lower number of trials will be rewarded. To test the idea that the response strategy during practice differed with age and that this would lead to the observed age-related differences in earnings, we first assessed whether age was associated with the length of the individually determined response deadlines. We observed an overall age-related increase in the response deadline (i.e. across 4 trial-types: Arrow/Word x Switch/Repeat), so that older participants were allowed to respond more slowly on test than did younger participants (Age x Response deadline: (ρ) = 0.587, p <0.001). One might argue that the differential Age x Reward effects on repeat and switch trials reported above might

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