ARCHIMEDES SPIRAL AFTEREFFECT AS A TEST OF AROUSABILITY

The idea of the Archimedes spiral after‐effect (SAE) providing an estimate of the change of arousal that can be induced in an individual by stimulation (i.e. arousability) has been derived from personality studies of normal subjects and psychiatric patients. However, the concept of arousability has been formulated from group studies and the results from normal subjects are equivocal. An experiment was therefore conducted to test the hypothesis that the SAE measures arousability in normal subjects. After‐effect duration at three levels of activation brought about by riding a bicycle ergometer was measured in 12 subjects. The index of arousal used was beat‐by‐beat heart rate. The results show that (a) the ergometer significantly altered heart‐rate levels; (b) after‐effect duration did not alter significantly at different heart‐rate levels; (c) after‐effect duration did not correlate significantly with heart‐rate level; (d) after‐effect duration did correlate significantly and negatively with change in heart‐rate level. These findings are taken as support for the hypothesis that after‐effect duration is related to the magnitude of change of activation. The relationship of heart rate, as an autonomic index of arousal, to cortical arousal indices is discussed and it is concluded that the SAE is a test of individual differences in arousability. 1979 The British Psychological Society