FORM AND OBJECTIVE OF THE DECISION RULE IN ABSOLUTE IDENTIFICATION

In several conditions of a line length identification experiment, the subjects' decision making strategies were systematically biased agains t the responses on the edges of the stimulus range. When the range and number of the stimuli were small, the bias caused the percentage of c orrect responses to be highest in the center and lowest on the extreme s of the range. Two general classes of decision rules that would expla in these results are considered. The first class assumes that subjects intend to adopt an optimal decision rule, but systematically misrepre sent one or more parameters of the decision making context. The second class assumes that subjects use a different measure of performance th an the one assumed by the experimenter: instead of maximizing the chan ces of a correct response, the subject attempts to minimize the expect ed size of the response error (a ''fidelity criterion''). In a second experiment, extended experience and feedback did not diminish the bias effect, but explicitly penalizing all response errors equally, regard less of their size, did reduce or eliminate it in some subjects. Both results favor the fidelity criterion over the optimal rule.