Effects of overt and covert tasks on orienting response under unimodal and bimodal stimulations

The present study examined the occurrences of "selective" and "alertive" orienting responses (ORs) in relation to stimulus modality under overt and covert tasks by using electrodermal response (EDR). Two sets of 36 university students received two stimuli (figure and/or toe) during both habituation and test sessions either unimodally (Exp. I) or bimodally (Exp. II). The subjects were assigned to one of three groups during a test session: (1) Key-press which required pressing a key at the offset of the test stimulus, (2) Perceptual-judgment which requested estimating the duration of the test stimulus, or (3) Neutral-instruction which received no task for stimulus presentation. Analysis showed in Exp. I, the first two groups indicated significant increases in EDR magnitudes only in response to the test stimulus, and this EDR increase demonstrated the occurrence of selective OR. In Exp. II, key-press alone showed a significant increase in EDR magnitudes to the nontest stimulus, and this EDR demonstrated the elicitation of alertive OR. The alertive OR emerged clearly when the subject perfored an overt task under binodal stimulation.