Proefschrift_Holstein

Chapter 7

TRIAL 1

TRIAL 2 low reward task switch response repeat

TRIAL 3 low reward task repeat response switch

TRIAL 4 high reward task switch response switch

reward cue

15 cent

1 cent

1 cent

15 cent

2-6s

task cue (600ms)

word

arrow

arrow

word

400ms

target

le

right

le

le

response

correct! 15 cent le

incorrect! 0 cent right

le

right

le

right correct! 1 cent

le

right

correct! 1 cent

incorrect! 0 cent

incorrect! 0 cent

correct! 15 cent

incorrect! 0 cent

feedback (600ms)

Figure 7.3 Task and response switching paradigm with reward manipulation Participants had to respond to response-incongruent arrow-word combinations (targets) with a left or right button press, either by responding to the direction indicated by the arrow (i.e. <- or ->) or to the direction indicated by the word (i.e. ‘left’ or ‘right’). A task cue preceding the target (by 400ms) indicated which task (arrow or word) the participant had to respond to on the current trial. Which task was performed on a particular trial could either change unpredictably with respect to the preceding trial (i.e. task switch trial; e.g. arrow – word as in trial 4, or word - arrow as in trial 2) or remain the same (i.e. task repeat trial; arrow-arrow (trial 3), or word-word). In addition to such task switches, the paradigm allowed us to look at response switches, i.e. whether the correct response (left or right button), remained the same compared with the previous trial, or switched. In the current version of the paradigm we made sure that the task switches occurred independently from response switches; half of the task- switch trials and half of the task-repeat trials required a switch of the response button (e.g. trial 4 and 3 respectively, whereas the other half of the trials required a response repetition (e.g. trial 2). In addition we manipulated the amount of anticipated reward (€0.01 vs. €0.15) on a trial-by-trial basis by means of a reward anticipation cue. At the start of each trial this reward cue indicated the amount of reward on that trial, contingent on a correct and sufficiently fast button press. Immediately following the response, feedback was given (e.g., “correct! 15 cents”) (see also Aarts et al., 2015). The inter-trial-interval varied (jitter of 2 – 6 seconds). Paradigm Participants performed a task-switching paradigm with a reward manipulation that has been extensively described elsewhere (Aarts et al., 2015), with minor changes to include a response- switching component. Details of the task are described in the legend of ( figure 7.3, box 2.3 ). At the start of each session, participants practiced the task ( figure 7.3 ). The first practice block (24 trials), which was only administered during the intake session, was merely a switching task. During this block the task (i.e. whether to respond to the arrow or the word) alternated unpredictably from trial to trial ( figure 7.3 ) without any reward cues, and the feedback on

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