Introduction

The importance of phonological coding to immediate memory performance has been apparent for many years, starting with Conrad's (1964) important demonstration of phonological errors in a memory task for visually presented letters. The specific characteristics of the phonological code have been the subject of debate, however. For example, Besner has argued (Besner, Davies, & Daniels, 1981; Besner & Davelaar, 1982) that the phonological representations underlying reading and short-term memory (STM) tasks are dissociable and that there are at least two kinds of phonological representations. A number of other distinctions among speech-based codes and processes have been described as well, including a distinction between a sensory “echoic” and a more abstract phonological representation (e.g., Crowder, 1978), between “auditory” and “phonetic” codes used in speech perception (e.g., Pisoni, 1973), between “assembled” and “addressed” phonological processes in reading (e.g., Patterson, 1982), and between a phonological store and an articulatory loop in working memory (e.g., Vallar & Baddeley, 1984b; Baddeley, 1986).

The neuropsychological literature certainly seems to suggest that multiple representations are available for use in immediate memory tasks. Indeed, much of the recent literature on STM impairments has been interpreted in the context of a model of working memory that includes a phonological store and an articulatory rehearsal process that are separable (e.g., Shallice & Butterworth, 1977; Vallar & Baddeley, 1984a, b; Baddeley, 1986; Vallar & Cappa, 1987). It remains unclear how many different types of representations are available, what the relationships between the different types of representations are, and how multiple, simultaneously active representations might contribute to immediate memory performance.