A statistical test leads to a Type I error whenever it leads to the rejection of a null hypothesis that is in fact true. The probability of making a Type I error can be characterized in the following three ways: the conditional prior probability (the probability of making a Type I error whenever a true null hypothesis is tested), the overall prior probability (the probability of making a Type I error across all experiments), and the conditional posterior probability (the probability of having made a Type I error in situations in which the null hypothesis is rejected). In this article, we show (a) that the alpha level can be equated with the first of these and (b) that it provides an upper bound for the second but (c) that it does not provide an estimate of the third, although it is commonly assumed to do so. We trace the source of this erroneous assumption first to statistical texts used by psychologists, which are generally ambiguous about which of the three interpretations is intended at any point in their discussions of Type I errors and which typically confound the conditional price and posterior probabilities. Underlying this, however, is a more general fallacy in reasoning about probabilities, and we suggest that this may be the result of erroneous inferences about probabilistic conditional statements. Finally, we consider the possibility of estimating the (posterior) probability of a Type I error in situations in which the null hypothesis is rejected and, hence, the proportion of statistically significant results that may be Type I errors.We are grateful to Larry Phillips for his comments on a previous version of this article and to an anonymous reviewer for bringing the article by Carver (1978) to our attention.

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Stimulus selection in paired-associate learning is assumed to be the result of an active organized process. From this standpoint, a methodological analysis and review of the studies of stimulus selection are presented. Some suggestions are made for further studies of stimulus selection. Underwood (1963) called attention to the fact that subjects often select part of the nominal stimulus as the functional stimulus. He discussed some of the implications of stimulus selection and suggested that selection occurs in rote paired-associate learning as well as in concept formation. Shepard (1963), in his comments on Underwood's paper, maintained that some stimuli (e.g., nonsense trigrams and geometrical figures) are almost inevitably analyzed into components or dimensions, while others (e.g., colors and olfactory stimuli) are almost invariably reacted to as unitary, unanalyzable wholes. He distinguished between selective attention or abstraction which applies to the former type of stimuli and pure stimulus generalization which applies to the latter. Shepard also suggested that functional stimuli, in some cases, are not merely constructed from the individual nominal stimuli but, in addition, are organized into an array or "cognitive map."These discussions emphasized the fact that, even during paired-associate learning, human subjects are not passive receivers of stimuli, but are active selectors and organizers. When presented with a complex stimulus, subjects abstract part of it for use as the functional 1 The author is grateful to Benton J. Underwood for his comments on an earlier draft.2 Request for reprints should be sent to Jack

A series of 5 recall trials, without informational feedback, were given following IL in an RI paradigm. The recall trials produced an increase in the number of correct responses and an increase in the stability of the correct responses. Relearning took fewer trials following the recall trials and there was no evidence that practice of errors during the recall trials interfered with relearning.