Learning to reproduce a list and memory for the learning.

The ability to reproduce from memory a short list of verbal items immediately following presentation is known to improve over successive trials on that list, even if these trials are embedded in a sequence of trials on other lists of the same sort (Hebb, 1961). Less clear is whether this "Hebb effect" arises without the list repetition being noticed. This question has long been pondered and has recently taken on particular theoretical significance, but the available evidence is scant and inconsistent. Two experiments are described in which, in essence, a sequence of immediate reproduction trials was followed by tests that called for list recognition (Experiments 1 and 2) and/or estimates of list presentation frequency (Experiment 1). These tests provided quantitative measures of repetition awareness. Typical Hebb effects were found, but there was no evidence that the effects occurred without the subjects' being aware of the repetition; effect-size analyses indicated that both the recognition and frequency responses were more sensitive to repetition than were the reproduction responses. Therefore, not only could the recognition and frequency responses not have been made solely on the basis of how readily the test lists were reproduced, but the Hebb effect could have required an awareness of repetition.

Adapting to an irrelevant item in an immediate recall task.

Recall of the last one or two items of a spoken list is impaired when the list is followed by a nominally irrelevant item. At issue here was whether this suffix effect is reduced with repeated exposure to the irrelevant item. The effect was found to decline over successive blocks of trials, but only slightly (Experiment 1). No decisive evidence for adaptation to the irrelevant item was found when it was spoken after each of the list items rather than after the last one only (Experiments 2 and 3). The strongest evidence for adaptation was obtained when the irrelevant item was repeated in an unbroken stream that extended through the presentations and recall periods of successive lists: The recency effect and the level of recall at the last position within a list were greater under these conditions than when the irrelevant item was presented only once after each list (Experiments 4, 5, and 6).

Recency effect in recall of a word list when an immediate memory task is performed after each word presentation.

Subjects studied 12-word lists for free recall. During presentation of the lists, each word was followed by a supraspan sequence of digits, which the subjects tried to reproduce. This task, unlike those used in previous research with this continual distractor procedure, presumably taxed immediate memory capacity to the full. Nevertheless, the word recall data showed a pronounced recency effect. Moreover, the magnitude of the recency effect was found to be just as great with this task as with a more typical task in which the demands on immediate memory are likely to be fewer. These findings reinforce the emerging view that the recency effect need not be the product of immediate memory.