The effect of stimulus intensity on force output in simple reaction time task in humans

The force needed to press the key in a simple reaction time task was measured as a function of stimulus intensity for visual and auditory stimuli in three experiments using a total 45 male and female human subjects. Intensity ranged from 0.316 to 1995 cd/m2 for visual stimuli and from ranged from 47 to 102 dB for auditory stimuli. We found, in agreement with Angel's (1973) original study, that for auditory stimuli higher intensity is accompanied by a larger force. Surprisingly, in the case of visual stimuli the intensity does not influence the force. These findings are explained by the assumption that the changes of force reflect the changes of unspecific activation level evoked by immediate arousal. Thus, the different behaviour of force for these two modalities is in agreement with the common view that loud auditory stimuli are arousing while intense visual ones are not.