sponse expectancy cues can also facilitate short-term retention (e.g., Chatlosh & Wasserman, 1987; Honig & Dodd, 1983; Honig & Wasserman, 1981; Smith, 1967; for an alternative explanation under successive discrimination procedures, see Urcuioli & Zentall, 1990). And, it is likely that anticipation of other trial characteristics, such as the duration of the retention interval ( Wasserman, Grosch, & Nevin, 1982), influence discriminative performance as well (for a review, see Honig & Dodd, 1986). All these anticipatory mechanisms presumably reflect prospective memory processes.
Thus, we are no longer inquiring whether short-term memory is a prospective or a retrospective process. Clearly, both memory mechanisms are important to delayed discrimination performance. Indeed, as others have suggested (e.g., Grant, 1982; Urcuioli & Zentall, 1986), it is probable that animals, like people, are flexible information processors and that they use the most reliable and simple means available to remember significant stimuli. Therefore, the task that lies ahead involves specifying the conditions that give rise to each individual memory process or to both memory processes. Although we may or may not ultimately determine that one process is more important than the other, we must surely conclude that animal short-term memory is much more flexible and complex than was once thought.
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