Impairment of short‐term memory

IT IS CUSTOMARY to consider several kinds of memory which may be distinguished by relative permanence of storage. Long-term memory is referred to in the context of retrieval long after presentation, usually after hours, days, or years. Immediate memory is meant when information is retrieved immediately after presentation, within seconds or a few minutes. Retrieval after roughly several minutes to an hour is usually defined as short-term memory. In this discussion, the terms immediate memory and short-term memory will be used interchangeably, since the distinction between these and long-term memory is presently clearer than the difference between kinds of short-term mem0ry.l Immediate memory is of interest because it may play an important role both as a first stage of storage in development of longterm memory and in temporary storage of incoming and outgoing information necessary for effective participation of long-term memory in behavior. By providing temporary storage, immediate memory may be crucial for serial organization of behavior.2 Through processing in immediate memory, the redundancy of incoming information may be reduced and its meaningfulness enhanced by recoding into nonredundant “chunks” of high information value.3 Similarly, “chunks” of outgoing information from long-term memory may be transiently stored in immediate memory to allow appropriate serial organization. However, “memory” may be a confusing term because it is often not clear whether its use refers to information retained, to storage of information, or to retrieval of information. This confusion is in part due to the difficulty of distinguishing experimentally between storage and retrieval, since the nature of both must usually be inferred from data about information retrieved. Although the use of sampling methods which require only partial retrieval of randomly selected portions of stored information has confirmed that more may be retained than can be retrieved,*-G independent analysis of storage may be required because the relative retention of information in storage is obscured by the effects of order of retrieval. Furthermore, unless storage and retrieval can be differentiated, experimentally and conceptually, the nature of the information retained may itself remain uncertain. Are traces retained in immediate memory those of representations of the presented event itself, of the occurrence of events already known because their traces are retained in long-term memory, of the retrieval process necessary to find and read out some trace of either the event or its occurrence, or some other kind of information? The present study was undertaken to explore the possibility of differential impairment of two kinds of short-term memory by focusing on the question of what kinds of information may be stored and retrieved. Specifically, it was designed to investigate impairment of “address” and “marker” short-term storage systems. An “address” storage is one in which information is stored for retrieval by retention of the address of an item (or its locus in a series of sequentially presented items). As an illustration, consider a memory consisting of a row of cells labeled sequentially 1 through 16; the numbers to be stored may be 8, 2, 15, 6, presented in that order. In an address storage system, retention would be effected by indicating “start retrieval” in cell 8, which would