Uncertainty Level Of Expectancy And Rate Of Accumulation

Uncertainty is a factor classically related to expectation in psychological research (e.g., Kahneman and Tversky, 1982; Sanders, 1966; for a discussion related to timing, see also Barnes and Jones, 2000). According to a probabilistic view of expectancy, the more certain you are about some event, the greater your expectation is about this event. Consequently, increasing the degree of certainty about break occurrence should increase the level of expectancy for this occurrence. The increase in expectancy level should intensify attentional shifting between accumulation and monitoring for the break signal, which should in turn reduce the rate of pulse accumulation. Two new experiments are reported here where evidence supporting this hypothesis was found.

In experiment 1, uncertainty was manipulated by varying the relative frequency of trials with and without breaks. Two main conditions were compared: a break was highly probable in the high-frequency condition and less probable in the low-frequency condition. The expectancy level about break occurrence should be higher in the high-frequency condition, thus leading to stronger effects of break location.

In experiment 2, all trials included a break. There was therefore no uncertainty concerning the break occurrence itself, but uncertainty concerning the time of break occurrence was manipulated. Two main conditions were compared: a cued condition, where a cue, presented at a fixed 500-msec duration before the break onset, informed participants that the break was imminent, and a no-cue condition, where this information was not provided. By eliminating uncertainty about the time of its occurrence, the cue should induce a maximum level of expectancy for the break, thus interrupting pulse accumulation.

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