Cardiovascular reactivity assessment: effects of choice of difficulty on laboratory task responses.

This laboratory study of cardiovascular reactivity was designed to examine how a choice of difficulty element in a mental arithmetic task would affect cardiovascular responses. 20 healthy male subjects were tested on a computer-controlled mental arithmetic task, designed to standardize performance across subjects by keeping constant the proportion of correct responses. This was achieved by automatic adjustment of problem difficulty according to ongoing performance. Subjects were led to believe that they could take either a 'difficult' or an 'easy' version of the mental arithmetic task and were asked to make a choice; in fact, all subjects were given the same task. Subjects who chose the 'difficult' mental arithmetic task (N = 10) showed significantly greater increases in myocardial contractility, cardiac output and systolic blood pressure during task performance than those who chose 'easy' (N = 10). However, subjects who chose 'difficult' were presented with more difficult problems presumably due to their exerting greater levels of effort during the task. The differences in cardiovascular responses associated with choice of difficulty were absent during testing on four subsequent tasks which did not incorporate any choice options (reaction-time, speech, mirror trace, cold pressor). These findings are interpreted as being provocative, rather than in any way conclusive. Nevertheless, they are suggestive of the possibility that choice of difficulty in laboratory tasks may be one strategy for improving the ecological validity of laboratory reactivity assessment procedures.