It is given by F=af1+(1−a)f2=af1+(1−a)f1NN−k A hit occurs on an attended change trial if, and only if, either of the following two mutually exclusive events occurs: (i) the changed item is held in memory or (ii) the changed item is not held in memory but the observer guesses that there was a change (which he/she does at rate f1).
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