Deficits in Working Memory

Amnesics with Deficits in Working Memory

Although hippocampal damage Opens in new window impairs long-term memory Opens in new window, it leaves working memory Opens in new window intact.

In contrast, there are amnesics who exhibit a selective impairment in verbal working memory, demonstrating a deficit in temporary maintenance in an active state of the information they are currently processing. Their working memory is so compromised as to preclude immediate verbatim recall of as few as two items (e.g., two digits).

The first well-recognized patient with such a disorder was a man known as K.F., who had a lesion in the left temporoparietal area Opens in new window, and showed a profoundly reduced capacity to hold in working memory even shorter strings of words or digits (Shallice & Warrington, 1970). Nonetheless, he had intact long-term memory for word lists, paired associates, and the content of stories and discourse across significant delays. The fact that a deficit in working memory does not also cause a deficit in long-term memory is in some ways surprising.

Earlier theories of memory had suggested that working memory and long-term memory handled information in a strictly serial manner. Information was first held in a short-term store, which served as the gateway to the long-term store.

The neuropsychological findings of a double dissociation between these syndromes indicate instead that working memory and long-term memory are systems that work somewhat in parallel. The working memory system operates to maintain information in an active state to support on-line processing, whereas the long-term memory system works to create enduring records of experience for later use.

Deficits of working memory tend to be closely tied to individual information processing systems, occurring for a narrow domain of processing. Thus, the best-known example of a working memory deficit, as in the case of K.F., involves impairment of auditory-verbal working memory, or what is currently known as the phonological store.

This deficit consists of difficulty in repeating aloud and verbatim the contents of the immediately preceding verbal utterance, such as is required in the digit span task. Nevertheless, patients with working memory deficits can retain and recover basic content of a verbal utterance and can even learn word lists. Importantly, their working memory for other processing domains, such as spatial processing or arithmetic, is perfectly intact.

Some researchers have reported further specificity among verbal working memory deficits with buffers linked to different aspects of language processing — that of comprehension versus production (Caramazza et al., 1985). They suggest that the input phonological buffer holds auditory-verbal information received by the listener on-line as a speaker is preparing his or her own utterance. Other patients have deficits in visual-verbal working memory, which involve difficulty in the ability to hold visual-verbal information on-line during reading.

Still other deficits occur in what Baddeley (1986) refers to as the visuospatial scratch pad, which involves deficits in the ability to hold nonverbal visual information while performing perceptual analyses of the stimulus array. Thus, each of these deficits is tied to a very specific processing domain, leaving working memory for other processing domains intact. This pattern has been interpreted to support the idea of multiple working memory capacities, each intimately tied to the operation of specific information processing systems in the brain.