Psychophysiological responses to unpredictable threat: effects of cue and temporal unpredictability

Although threat unpredictability plays an important role in determining emotional responses, little is known about what elements of unpredictability are responsible for these results. The current study examined the single and combined effects of two elements of unpredictable threat: (a) uncertainty about the timing of an aversive event (temporal unpredictability), and (b) uncertainty about whether an aversive event will occur at all (cue unpredictability). Seventy-two healthy young adult participants were randomly assigned to receive either temporally predictable or unpredictable shocks at varying levels of cue unpredictability. Dependent variables included skin conductance responses (SCRs) and eyeblink startle reflex. Combined cue and temporal unpredictability elicited weaker SCRs than either element of unpredictability alone, indicating that high unpredictability may induce anxiety-like physiological inhibition. Combined cue and temporal unpredictability and combined cue and temporal predictability produced the largest startle. Findings provide evidence that both cue and temporal unpredictability should be included in human models of anxiety.