Working Memory Giovanni Pezzulo Institute of Cognitive Science and Technology - CNR Via S. Martino della Battaglia, 44 - 00185 Roma, Italy
[email protected] April 16, 2007 Working memory (WM) (Baddeley and Hitch, 1974) is a crucial concept in cognitive psychology and cognitive neuroscience. It refers to the “central” structures and processes that temporarily maintain, store and manipulate information for supporting human thought process. Working memory is is a limited capacity system: it permits to keep “active” a limited amount of information for a brief period of time, and to operate on it. For example, we can rehearse a phone number until we dial it, or recall different paths to a destination and compare them in our mind in order to select the shortest one. In particular, WM permits to temporarily maintain task-relevant information during performance of complex cognitive tasks that require willingness, awareness, and attention such as reasoning, planning, manipulation of linguistic information, and the executive control and coordination of perception and action in complex cognitive operations. WM provides also an interface to long-term memory (LTM) (Atkinson and Shiffrin, 1968), that is instead responsible for the “passive” storage of information for longer periods of time: WM can “upload” and “download” information to and from LTM. For example, when multiplying two-digit numbers like 76×17, it is possible to store the temporary outcome of 6 × 7 and then use this partial product for the rest of the computation. The emphasis on active manipulation rather than on solely storage of information distinguishes working memory theories from those of short-term memory (STM). A parallel can be done between the concept of working memory and the supervisory activating system (SAS) described in (Norman and Shallice, 1986; Cooper et al., 1995; Shallice, 1982) for the willed control of action. The Components of Working Memory The most popular model of working memory is the multicomponent model of Baddeley and Hitch (1974), further elaborated in (Baddeley and Hitch, 1974; Baddeley, 2000, 1992, 1986; Baddeley and Della Sala, 1996). Here working memory is not described as a unitary system, but as multicomponent: it includes a central component, the central executive, and three sub-systems: the phonological loop, and visuospatial sketch pad, and the episodic buffer. See fig. 1. 1
Figure 1: Multicomponent Model of Working Memory; from (Baddeley, 2003b) The central executive is the main component. It is responsible for the control of executive processes, including actions; the direction of attention to relevant information, as well as the suppression of irrelevant information and undesired actions; the supervision of information integration; the coordination of multiple cognitive processes to be executed in parallel; and the coordination of the sub-systems of WM. The phonological loop permits to maintain auditory information with a rehearsal mechanism that prevents its rapid decay. For example, you can maintain in memory a (short) list of words, or of numbers, as long as you continuously repeat these words or numbers to yourself. The visuo-spatial sketch pad permits to maintain and manipulate visual and spatial information. For example, you can create and navigate mental maps, form mental images and rotate them, etc. It is constituted of two subsystem, the former specialized for visual information, and the latter for spatial information. The episodic buffer temporarily integrates phonological, visual, and spatial information, and possibly other forms of information (e.g., semantic information, musical information) in a unitary, episodic representation. In this way it provides an interface between the subsystems of WM and the part of LTM specialized for episodic memory (EM) (Tulving, 1972) (i.e., recollection of specific events that integrate time, place, and emotions). Research on Working Memory In the last years WM has been the focus of much theoretical, empirical and computational research in cognitive psychology and cognitive neuroscience. (Baddeley, 2003b,a) are two excellent reviews of working memory, the latter with respect to language. (Andrade et al., 2002; Conway et al., 2007; Miyake and Shah, 1999) 2
review empirical work about working memory. (Cohen et al., 1997; Vallar and Papagno, 2002) report empirical data in neuropsychological patient studies. Brain imaging studies have revealed high activity in the frontal lobe when this central processor is working, and distinct neuroanatomical bases for the phonological loop (mainly related to areas in the left hemisphere that are associated with the production of language, such as Wernicke’s area and Broca’s area) and the visuo-spatial sketch pad (mainly related to a region of the occipital cortex generally associated with visual processing). However, several issues are still controversial: is working memory unitary or multicomponent? which are its limits? which are the relations between working memory and long-term memory? Several computational models of working memory exist, too; see for example (Burgess and Hitch, 2005). They have mainly focused on memorization and serial recall of items (e.g., a list of words or numbers), and they have been often compared with human data.
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Cohen, J. D., Perlstein, W. M., Braver, T. S., Nystrom, L. E., Noll, D. C., Jonides, J., and Smith, E. E. (1997). Temporal dynamics of brain activation during a working memory task. Nature, 386(6625):604–608. Conway, A., Jarrold, C., Kane, M., Miyake, A., and Towse, J., editors (2007). Variation in Working Memory. Oxford University Press, New York. Cooper, R., Shallice, T., and Farringdon, J. (1995). Symbolic and continuous processes in the automatic selection of actions. In Hallam, J., editor, Hybrid Problems, Hybrid Solutions, Frontiers in Artificial Intelligence and Applications, pages 27–37. IOS Press, Amsterdam. Miyake, A. and Shah, P., editors (1999). Models of Working Memory: Mechanisms of Active Maintenance and Executive Control. Cambridge Univ. Press, New York. Norman, D. A. and Shallice, T. (1986). Attention to action: Willed and automatic control of behaviour. In Davidson, R. J., Schwartz, G. E., and Shapiro, D., editors, Consciousness and Self-Regulation: Advances in Research and Theory. Plenum Press. Shallice, T. (1982). Specific impairments of planning. Royal Society of London Philosophical Transactions Series B, 298:199–209. Tulving, E. (1972). Episodic and semantic memory. In Tulving, E. and Donaldson, W., editors, Organization of memory. Academic Press, New York. Vallar, G. and Papagno, C. (2002). Neuropsychological impairments of verbal short-term memory. In Baddeley, A. D., Kopelman, M. D., and Wilson, B. A., editors, The handbook of memory disorders, volume 2, pages 249–270. John Wiley, NY.
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