The effects of level of difficulty of mental arithmetic challenge on heart rate and oxygen consumption

Heart rate plus various metabolic and ventilatory indices were monitored while 18 young males engaged in a mental arithmetic task, structured to include 3 levels of difficulty; easy, difficult and impossible. Measurements were also taken while subjects undertook graded isotonic exercise on a bicycle ergometer; for each subject heart rate was plotted against oxygen consumption over the various exercise loads. Knowing oxygen consumption during the psychological tasks, these regression equations permitted the calculation of expected heart rates during each task condition and thus the computation of 'additional heart rate' as the difference between actual and predicted heart rate values. Additional heart rate was sensitive to variations in difficulty level; the difficult condition elicited reliably more additional heart rate than the easy and impossible conditions. Subjects' performance as well as their perceptions closely reflected the a priori classification of difficulty. Although subjects rated the easy condition as particularly unengaging, the impossible condition attracted relatively high rates of task involvement. It was argued that self-reports of this sort are probably more susceptible than cardiac activity to social demand characteristics.