Null effects of exposure duration and heterogeneity of difference on thesame-different disparity in letter matching

The rechecking and external-noise postulates of Krueger’s (1978) noisy-operator theory were examined in three letter-matching experiments. Rechecking was tested by varying exposure duration, both without (Experiment 1) and with (Experiment 2) a subsequent noise mask. Predictions of a decreasedsame-different reaction time disparity and an increase in falsedifferent errors at brief exposures were not borne out. The external-noise postulate was tested by varying the degree of heterogeneity of difference between letter sets. The prediction of a smallersamedifferent reaction time disparity for the more heterogeneous letter set was not obtained. Thus, the results did not support internal noise as the basis of thesame-different disparity, but were more consistent with response-inhibition accounts.