Stimulus omission and dishabituation of the electrodermal orienting response: the allocation of processing resources.

The present research investigated the effects of stimulus omission on electrodermal orienting, dishabituation. and the allocation of processing resources as assessed by reaction time (RT) to a secondary probe stimulus. All experiments employed 33 tone-light or light-tone (S1-S2) pairings, and for experimental groups, S2 was omitted on 4 trials, experiment 1 (N = 24) demonstrated reliable electrodermal responding when S2 was omitted for a trial, and subsequent dishabituation when S2 was then re-presented after SI on the immediately following trial. Experiment 1 (N=96) employed probe RT as the dependent variable. White noise probe stimuli were presented 300 ms or 1300 ms following the omission of S2 and following its onset on re-presentation trials. Reaction time to probes presented during S2 omission was slower in experimental groups than in control groups. Reaction time on S2 re-presentation trials was also slower in experimental groups than in control groups, but only when S3 was a tone. Experiment 3 (N=48) employed auditory and visual probes presented 1300 ms following S2 omission and S2 re-presentation, and measured both electrodermal activity and probe RT, Some evidence of electrodermal omission responding and dishabituation was obtained. Reaction time was again slowed during the omission and re-presentation of S2. regardless of the modality of S2 and regardless of the modality of the probe. The results are interpreted as consistent with an information-processing approach to orienting and habituation in that they indicate that both the omission and re-presentation of an expected stimulus command processing resources.