In previous experiments we tested the paradigm (De Brabander, Perceptual and Motor Skills, 69, 75-82, 1988) that phasic arousal reactions are reflected by retarded reactions after an unexpected preparatory signal in a visuospatial (right hemisphere) discrimination reaction time task. Phasic activation responses are shown by accelerated reactions after the preparatory signals in a semantic (left hemisphere) task. In the present experiment the results do again validate the paradigm. The main purpose of the study was to use this paradigm in order to investigate whether sensation seeking is related to more intense phasic arousal reactions (arousability) or to more pronounced phasic activation responses (activatability) or to both. At first sight the results indicate that only arousability is related to sensation seeking, especially boredom susceptibility. Other possible explanations of the results are also discussed.