Measures of the acoustic startle reflex: comparative sensitivity to stimulus and prestimulus manipulation

This thesis examined physiological reactions characteristic of the Acoustic Startle Response (ASR) under several different experimental conditions. Two measures of the startle eyeblink were extensively compared: (1) Electromyogram (EMG) measures of orbicularis oculi muscle activity, and (2) Electrooculogram (EOG) measures of vertical eye movement. In a first set of experiments, Heart Rate (HR) and Skin Conductance (SC) response measures, as well as the startle blink, were recorded in response to simple startle stimuli. When a single stimulus intensity was used, reliable startle response elicitation and habituation were noted in all measures except HR. These results changed slightly when stimulus intensity was also varied, yet comparative analyses of EMG and EOG were highly similar. A second, more extensive, set of experiments explored startle eyeblink modification (SEM) using different selections of prestimuli. The main results of the major exerimental series indicated that (a) the duration of ASR testing sessions can be reduced without loss of information; (b) EMG and EOG responses are equally sensitive to changes in prestimulus interval; (c) the effects of transient and sustained prestimuli, as elicitors of SEM, grow less similar with longer prestimulation; and (d) thorough accounts of SEM require concurrent EMG and EOG recording. Overall, the results suggest that the sensitivity and efficiency of ASR recording, as a useful probe of brain activity, can be enhanced by using both EMG and EOG measures.