Nelson Cowan

In addition to basic scientific work, Cowan's collaborative research related to working memory has led to clarification of the role of memory in language disorders, dyslexia, autism, schizophrenia, Parkinson's disease, amnesia, and alcoholic intoxication, as explained further on his web site and CV. For example, the work on amnesia indicates that individuals who usually cannot form new memories because of stroke or brain damage often demonstrate considerable ability to do so when the information to be memorized is surrounded by several minutes with minimal visual or acoustic interference.

Main scientific contributions

Working memory capacity limits

Cowan's theoretical model addresses key puzzles in information processing using a new approach in which there are two aspects of working memory: the activated portion of long-term memory, which includes rapidly-learned information limited only by decay and interference among similar features and, within this activated portion, a focus of attention limited to about 3-4 separate items or chunks in typical adults. Cowan contends that previous models did not sufficiently distinguish between these temporary-storage mechanisms. In this theory, why is there interference between words and visual objects like colors when both are held in mind? Because the focus of attention is involved in maintaining information of all types and, when the procedure discourages mnemonic strategies like grouping and rehearsal, the focus of attention is limited to just a few separate units of information - as argued in a review cited over 6,900 times according to Google Scholar. In the brain, an area of the intraparietal sulcus plays a large role in the focus of attention, perhaps serving as an index connected to posterior areas representing the content of active memories.

Attention filtering by habituation of orienting

In another part of the theory of Cowan, conceptual difficulties of the idea of an attention filter were addressed. If unattended information is filtered out, how can it come to attract attention? In the theory, the attention filter is replaced by the well-known mechanism of orienting of attention. Stimuli with changed physical features attract attention, whereas stimulus features or patterns that are repeated or continuous become a part of the neural model of the environment; there is habituation of the orienting response, and such stimuli stop attracting attention. For example, Emily Elliott and Cowan showed that pre-exposure to sounds to be used as distractors reduced their capability to distract.

In another kind of research on attention, Noelle Wood and Cowan replicated an often-discussed but until then poorly-understood phenomenon termed the cocktail party phenomenon. Using methodology improved from the 1950s, they found that people take a long time to notice subtle acoustic changes in an ignored channel of speech while repeating different speech presented in the other ear, a selective listening task. They also used the improved methodology to replicate the early, poorly-studied finding that about a third of participants notice their names unexpectedly presented in a channel to be ignored . That finding, however, was ambiguous. It could be that high-working-memory-span individuals are better able to monitor the channel to be ignored, or it could be that the low-span individuals cannot fix their attention on the assigned task, so that it wanders over intermittently to sample the channel to be ignored. The results have come out strongly in that direction, with many more low-span individuals noticing their names in the ignored channel. Proving that the results did not have to turn out that way, they were different for healthy older adults; their spans are like relatively low-span younger adults, yet the older adults rarely noticed their names in the channel to be ignored, suggesting that their focus of attention is strategically intact but with possibly a smaller capacity than young adults.

Development of working memory

In Cowan's work on the childhood development of working memory, a major task has been to deconfound development given that many processes develop together and need to be disentangled. Could it be that working memory capacity increases with age only because of some other factor? Cowan has examined this question repeatedly in different ways and has found that a number of factors are not sufficient. These factors that could not completely account for working memory capacity growth include the allocation of attention to relevant items, encoding speed and rehearsal, and knowledge. In memory for simple, spoken sentences, for example, more mature participants remembered more units, not larger ones. Recent evidence suggests that older children become better able to notice patterns in the stimuli that allow them quickly to memorize information and thereby ease the load on the focus of attention. Consequently, older participants can remember tones or words and colors at the same time, better than younger children with less interference between the two modalities Similar findings have been obtained in the area of adult aging, with a U-shaped development across the life span in the number of items that can be held in working memory without mnemonic strategies. Simple working memory tasks account for aptitudes better in children too young to apply mnemonic strategies, and Cowan has made considerable use of a simple task that maximizes the correlation with aptitudes by making the endpoint of a list unpredictable, known as running memory span. Minimizing mnemonic strategies may mean that more attention is needed for recall, which may also be needed in typical tasks of intellectual aptitudes.