WHY ARE JUDGMENTS LESS CONSISTENT IN LESS PREDICTABLE TASK SITUATIONS

Subjects made a series of six forecasts for each of four 58-point time-series. The stimulus series were noisy sinusoids of various frequencies. Individual subjects' forecasts were regressed on to the time period for which they were made. The residual variance in these regressions was greater when the stimulus series were noisier. This effect cannot have arisen from memory overload because simultaneous presentation of all points in the stimulus series meant that there were no memory demands. It cannot have been a side effect of a learning process because presenting each series just once excluded opportunities for learning, It cannot have been caused by deterministic rule switching consequent on feedback about a noisy process because no feedback was presented, Instead it appears that subjects tried to simulate the noise as well as the pattern in the series when making their forecasts. In support of this, similar results were obtained in a second experiment in which subjects were asked to simulate rather than to forecast the series. Two possible reasons for subjects' simulation of series noise are discussed. (C) 1995 Academic Press, Inc.