Cumulative Expectancy, Subjective Report of Alertness, and Electrodermal Activity

Skin conductance was monitored during a vigilance task in which the S responded to wanted signals. The wanted signal was a sequence of three consecutive odd digits (e.g. 1, 3, 7, +). Non‐wanted signals also contained three consecutive digits; of these, two, one, or none were odd (e.g. 1, 1, 2, +, or 1, 4, 6, +, or 2, 4, 6, +). (The plus signs following each signal served to separate the individual signals from each other and may therefore be treated as rest periods.) Since the S must respond to a series of odd digits the different signal types vary in their power to induce a state of cumulative expectancy in the S. S s were informed that a monetary reward was dependent upon fast and accurate response. Electrodermal activity was quantified in terms of change in conductance (SCR), either increase (SCR+) or decrease (SCR–) associated with particular sequences of digits. Results indicate: 1) SCR+ for wanted signals progressively increases as the sequence accumulates, with maximum SCR+ on the final digit and a large SCR– on the plus sign. 2) Odd numbers are generally associated with SCR+ whereas even numbers and plus signs are associated with SCR–. 3) S s report post‐test that they were more alerted by odd digits. 4) Reaction time to wanted signals does not correlate with SCL at time of response, with latency of the associated SCR, nor with pre‐ and post‐signal SCRs. 5) Intra‐individual analysis yields no evidence for operation of the Law of Initial Value.