Personality and Affective Modulation of the Startle Reflex

The human startle reflex, as indexed by strength of eyeblink to a sudden, loud noise, has been shown to vary according to the presence of pleasant and unpleasant stimuli. An experiment was conducted to determine whether this effect is in turn dependent on the personality of the subject. Subjects viewed a series of slides classified as pleasant, unpleasant or neutral, with acoustic startle probes being presented unpreditably during and between slides. Electromyographic (EMG) measures of eyeblink responses confirmed the expected pattern of modulation, with pleasant slides reducing and unpleasant slides Increasing the amplitude of startle. Harm Avoidance (HA), as measured by Cloninger’s Tridimensional Personality Questionnaire (TPQ), mediated these effects: only subjects high in HA showed modulation to unpleasant slides. while only subjects low in HA showed modulation to pleasant slides. Affective modulation, as measured by response latency, was mediated by Extraversion (E) and Neuroticism (N), as measured by the Eysenck Personality Questionnaire (EPQ): only subjects who were extraverted and stable showed the expected linear pattern of modulated startle. The implications of these data for Cloninger’s. Gray’s and Eysenck’s theories of personality are discussed.