Page 150 - Migraine, the heart and the brain

Chapter 8
right (calling for a left or right button press, respectively). The central arrow is flanked by four irrelevant symbols, two on either side. These flankers can be either congruent (arrowheads pointing into the same direction as the target, e.g. >>> > >), incongruent (arrowheads pointing into the opposite direction, e.g. < < > < <), or neutral (e.g. - -> - -). The row of symbols randomly appears at the top or bottom of the screen and it may or may not be preceded by a cue informing about target location. In particular, there are four cue conditions: the no-cue condition, where the cue is omitted, the centre-cue condition, in which an asterisk appears at the centre of the screen, the double-cue condition, where two asterisks appear at the centre of the possible target- stimulus locations, and the spatial-cue condition, where just one asterisk appears at the location where the target stimulus will be appearing.
The combinations of the three flanker conditions and four cue conditions provide the data base for calculating three indices of theoretical relevance (alertness, orientation, and executive control) (15).
Each trial would begin with the presentation of a cue, except in the no-cue condition, for 100 ms. After a blank interval of 400 ms, the target was presented for 1700 ms or until a response was being made. Three blocks of 96 randomly determined trials were presented. Target and flankers were presented in black on a white background. Each symbol measured about 5 x 7 mm, seen from a distance of about 60 cm. Before each session, a 2-minute training block was included in the protocol. Reaction time and accuracy were recorded, the primary dependent variable being reaction time for correct responses.
Working memory (N-back) task
The N-back task requires the monitoring, updating, and manipulation of remembered information and places great demands on working memory. The participant is required to monitor a series of letters shown on the screen and to respond whenever a stimulus appears that is the same as the one presented in trials before. In our study the n was 0, 1, 2, or 3. The 0-back condition served as a kind of control or baseline condition, the target letter was the letter ‘X’ and participants were to respond to any ‘X’ they would see by pressing the space bar of the computer keyboard. In the three remaining conditions, the target letter was de ned as any letter that was identical to the one presented in the preceding trial (1-back, that is), two trials before (2-back), or three trials before (3-back).
There was a block for each of the four levels. Each block consisted of 60 stimuli of which 12 were target stimuli, that is, the probability of a target stimulus was 20%.
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