6 - Neuropsychological evidence for lexical involvement in short-term memory

Summary

Introduction

According to the standard approach to short-term memory (STM), set forth by Baddeley in chapter 2, verbal STM depends on a phonological store of limited capacity. It is not clear, however, how this capacity is to be defined. Thus, if we take span (number of items recalled in correct order) to be our index of STM capacity, it is necessary to deal with the fact that this number does not represent some fixed quantity. Rather, it varies substantially across material type: span for digits (7.98) is greater than span for familiar words (5.86), which is in turn greater than span for nonword materials (2.49) (Brener, 1940). Various manipulations also affect span for words and nonwords differently: Performance on word lists is more resistant to suffix effects (Salter, Springer, & Bolton, 1976), and less affected by such factors as presentation modality and phonemic similarity (Richardson, 1979). Lexicality is evidently a sustaining factor in STM.

There has been little attempt to deal with these lexical influences, however, either from a theoretical perspective or as a matter for empirical study. Far from their being a focus of attention in STM research, experimenters have tended to minimize the effects of lexical variables by relying on digit materials or, when using words as stimuli, by sampling from a restricted item pool. It has sometimes been acknowledged that the information in the phonological store is “postexical,” the implication being that the information represented in this store consists of phonological units filtered through the lexical system (e.g., Richardson, 1979).