impeded calculation, and the amount of effort used to stop/reduce the thoughts. A final question asked participants to indicate whether they had experienced intrusive thoughts that were non-math-task related, for example relationship problems or health problems. The study also included a measure of trait anxiety, taken from the State-Trait Anxiety Inventory (Spielberger, Gorsuch, Lushene, Vagg & Jacobs, 1984) but, the zero-order correlations showed no relationship between trait anxiety and error rates and response time, so analyses including trait anxiety are not presented here (these are available from the first author). Experimental stimuli and procedure Using the experiment-building software E-prime, 80 two-digit addition problems were presented using a verification task, for example 18 = of these problems had a ‘37 + 52’. Sixty solution that was true; 20 had an incorrect solution. Of the 60 true problems, 30 involved a carry operation, for example + 18 = and 30 involved no carry, for example + 12 “17 35”, “17 = were randomly taken from a range of 10-89. Problem-size was 29”. Addends counterbalanced across addends and carry/no-carry conditions so that performance could be attributed to factors other than the size of the problems. Problems where both addends ending in zeros, for example + or fives, for example + were not included. Incorrect ‘20 30’, ‘25 35’, problems were divided approximately equally with splits of +/- 1, +/- 3, and +/- 5, counterbalancing the number of positive and negative splits. Participants gave informed consent and completed the mathematics anxiety scale. Stimuli were presented in the centre of a VDU, in Times New Roman, size 40, bold font. Following the on-screen instructions and five practice trials, participants were asked to respond or to the proposed answers. This was achieved by pressing the and ‘true’ ‘false’ ‘z’
impeded calculation, and the amount of effort used to stop/reduce the thoughts. A final question asked participants to indicate whether they had experienced intrusive thoughts that were non-math-task related, for example relationship problems or health problems. The study also included a measure of trait anxiety, taken from the State-Trait Anxiety Inventory (Spielberger, Gorsuch, Lushene, Vagg & Jacobs, 1984) but, the zero-order correlations showed no relationship between trait anxiety and error rates and response time, so analyses including trait anxiety are not presented here (these are available from the first author). Experimental stimuli and procedure Using the experiment-building software E-prime, 80 two-digit addition problems were presented using a verification task, for example ‘37 + 18 = 52’. Sixty of these problems had a solution that was true; 20 had an incorrect solution. Of the 60 true problems, 30 involved a carry operation, for example “17 + 18 = 35”, and 30 involved no carry, for example “17 + 12 = 29”. Addends were randomly taken from a range of 10-89. Problem-size was counterbalanced across addends and carry/no-carry conditions so that performance could be attributed to factors other than the size of the problems. Problems where both addends ending in zeros, for example ‘20 + 30’, or fives, for example ‘25 + 35’, were not included. Incorrect problems were divided approximately equally with splits of +/- 1, +/- 3, and +/- 5, counterbalancing the number of positive and negative splits. Participants gave informed consent and completed the mathematics anxiety scale. Stimuli were presented in the centre of a VDU, in Times New Roman, size 40, bold font. Following the on-screen instructions and five practice trials, participants were asked to respond ‘true’ or ‘false’ to the proposed answers. This was achieved by pressing the ‘z’ and
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