Introduction

Memory span for spoken lists of random digits, letters, and words has been the subject of numerous experimental investigations in normal subjects. The basic phenomena of the span task have been well established. It is known that only a limited number of items can be retained, that storage appears to be based on phonological representations, and that in the absence of rehearsal these items are susceptible to very rapid forgetting. However, the functional significance of this short-term representation, the auditory–verbal span of apprehension, remains somewhat mysterious.

Span for random lists of spoken material may be gravely and very selectively impaired in patients with brain damage. Analysis of preserved and impaired skills in these cases has been used as a means of investigating the normal functional role of the short-term representation that is measured by span. Thus, by establishing what other abilities are preserved, and what abilities are impaired, we can go some way towards a specification of the types of information processing that require the integrity of this level of representation.

Such an approach is not without its difficulties; for example, failure on a task may be attributable to associated disorders that happen to arise as a consequence of damage to areas that are functionally independent but anatomically close together. This means that it has been easier to establish independence of this type of representation from other forms of processing (or processing systems), rather than their necessary relationship. Thus in the 1960s a widely held model was that short-term representations were a necessary precursor for long-term memory.