Repetition and acoustic contrast in short-term memory for letter sequences.

Memory for sequences of briefly presented letters was examined to discover the effects of intraserial repetition and acoustic contrast on recall of a critical letter pair. The critical pairs were either repeated or nonrepeated letters presented in an acoustically contrasting or noncontrasting sequence. The hypothesis was tested that recall of repeated letters and contrasting nonrepeated letter pairs would depend on the lag between their presentations. Immediate recall of both letters (but not recall of at least one letter) of a critical pair was enhanced when the pair was a repetition or acoustically contrasting but only when the letters of the pair were adjacent. Recall of pairs separated by a lag of two intervening letters was not affected by repetition or contrast. When recall was delayed by a retention interval of eight random digits, the contrast effects disappeared and only the repetition effect remained. The findings are discussed in terms of the coding of attribute tags as cues for retrieval from short-term memory.