Recency effects may also reflect the use of the phonological store. Dedicating the phonological store to other tasks does not always disrupt them and it can also arise in other parts of the system.
Brooks (1968) had reported an important imagery study that Baddeley cited as evidence for a separate working memory component for visual representations. Brooks showed that an imagery task was made more difficult by requiring participants to respond to an imagined visual shape using a spatial pointing system response as compared to a spoken response. In contrast, when the task was to judge the words in a remembered sentence the vocal response mode was more difficult than the special. If imagery and sentence memory used the same working memory, then this pattern would be unlikely. Baddeley concluded that a separate working memory component, the visual-spatial scratch pad was used in the memory task (Shulman, 1997). The visual-sketch pad is hypothesized to be involved in the processing and manipulation of visual information.
The central executive is the principal component of working memory. Baddeley .
describes the central executive as controlling and integrating actions and activities. The behaviour of patients with frontal lobe brain damage was cited as evidence for the existence of the central executive. Short-term memory problems are associated with damage to the left cerebral hemisphere in an area close to that involved in speech. The patients may, but not necessarily have language problems. Amnesic patients who show defective long-term memory tend to have damage to the temporal lobes of the cortex and to deeper structures such as the hippocampus and the mammillary bodies. The fact that tasks associated with STM are intact, and vice versa, speaks strongly for the view that different memory systems are involved.
More recently Muscovite (1992a), proposed that the frontal lobes are involved in the control and executive aspects of memory, whereas other functions are situated elsewhere.