Extraversion and Duration of the Archimedes Spiral Aftereffect

Instruction effects and relation between extraversion and the spiral aftereffect

The relation between extraversion (EPI) and length of aftereffect was investigated when spiral aftereffect was measured on the same Ss under three instructions: (a) normal— S is told to report “When the aftereffect appears to stop” and after Ss had been informed of two phases in the decay of the aftereffect and told to (b) report the end of the first, faster, phase of decay, or (c) report when “they were absolutely sure that the second phase of decay had ended.” Near zero correlations were obtained between E and SAE under conditions (a) and (c) but E and SAE were negatively and significantly correlated under condition (b). It is suggested that failure to differentiate these instruction conditions could account for many of the previous contradictory findings on the relation between E and SAE duration.

Extraversion and adaptation to intermittent light

47 non-neurotic extraverts and 47 non-neurotic introverts as determined by the Maudsley Personality Inventory were tested for local adaptation to intermittent light. The amount of adaptation was significantly greater for the introverts. This follows from McDougall's theory of cortical inhibition but is contrary to Eysenck's. However, the results would fit a combination of the two theories that takes into account moderation of the extraversion-adaptation relationship by neuroticism. According to such a theory, among neurotics cortical inhibition is greater for extraverts, and among non-neurotics it is greater for introverts. An alternative interpretation is also suggested which assumes an inverted-U relationship between adaptation and arousal.