A bias interpretation of facilitation in perceptual identification

In a typical perceptual identification task, a word is presented for a few milliseconds and masked; then subjects are asked to report the word. It has been found that an earlier presentation of the test word will improve identification of the test word by as much as 30%. In addition, this facilitation has been shown to be preserved under amnesia. In this article we examine a fundamental question: Is the facilitation the result of bias toward the earlier presented item, an improvement in perceptual sensitivity, or both? The experiments presented here use a forced choice procedure to show that prior presentation of an item biases the subject to choose that item but does not improve discriminability. This result is obtained when the distractor items are visually similar to the target items. When distractors are dissimilar, earlier presentation affects neither bias nor discriminability. Two models of word identification are examined in light of the bias effects, and implications for understanding savings in amnesia are also examined.