An experimental study of short-term memory for lists of familiar English words is reported. Lists of 10, 20, and 30 unrelated words were presented at a 1-sec. rate. Retention was measured by free recall after intervals of 0, 15 and 30 sec. A counting task was used to prevent rehearsal during the retention interval. The absolute level of recall increased with length of list whereas the percentages retained showed the reverse trend. The recall scores decreased steadily as a function of retention interval, with the rates of forgetting comparable for the three lengths of list. The decline in the amount recalled was due in large measure to the loss of the terminal items in the list. Consequently, the pronounced recency effect present on the immediate test of recall was progressively reduced as a function of time. By contrast retention of the initial part of the list was relatively stable. These variations in rate of forgetting are attributed to differences among serial positions in susceptibility to proactive inhibition.

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Abstract-The subject of this study was a 43-year old man who developed a disorder of memory following herpes simplex encephalitis six years earlier. Recent memory was severely affected in contrast to the preservation of both intellect and immediate and remote memory. The impairment of recent memory functions was evident on tasks using verbal material whereas memory for motor tasks such as maze learning and the rendering of new compositions for the piano was preserved. The deficit in remembering verbal items varied with (1) the type of retrieval (recall vs. recognition), (2) the modality of stimulus presentation (acoustic vs. visual), and (3) the way in which learning was attempted (serial presentation vs. self-ordering and classification). Evidence of proactive interference in memory formation was demonstrated by intrusion errors.

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