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Scientific Understanding of Consciousness |
Activated Long-Term Memory? -- Working MemoryActivated long-term memory? -- The bases of representation in working memory(paraphrase of Bradley R. Postle from Working Memory, p. 333) This chapter will advance the argument, built largely on evidence from neuroimaging, neurophysiology, and neuropsychology, that the short-term retention (STR) of information during working memory tasks is accomplished via sustained activity in brain regions whose primary function is not working memory (nor short-term memory). Rather, the critical brain areas are the very same as those that are necessary for the 'primary' processing of the information in question. Thus, for example, the STR of the precise direction of a field of moving dots is supported by activity in the neurons of visual area MT/V5 that are required for the perception of motion direction. The STR of a spoken sentence depends on sustained activity in the networks responsible for perceiving and recognizing the lexical content and syntax of the sentence (as well as the volume, timbre, and identity of the talker's voice), on sustained activity in the networks responsible for understanding the meaning of the sentence, and on covertly activating the speech production routines required for the rehearsal of the sentence. Thus, although it might be said that working memory depends on sustained activation of portions of long-term memory this idea is most accurate if one construes ‘long-term memory' in the broadest of senses. (This is because perceiving, recognizing, understanding and rehearsing are all abilities that we have acquired and refined as a result of extensive experience, and that can thus be construed as the products of long-term memory. A second important property of working memory that will be emphasized in this chapter is that, just as with real-time perception, the STR of information in working memory is not restricted to the channel or channels by which this information enters the nervous system. Although this multiple encoding property complicates the evaluation of the representational bases of working memory, it also addresses some of the concerns that might be raised by the concept of activated long-term memory as the basis of storage in working memory. Since the early 1970s, the dominant view of working memory has held it to be supported by a cognitive system of domain-specific memory buffers that effect the storage of information, making it available for manipulation, for interaction with other cognitive systems, and/or for the guidance of behavior. Complementarily, many of those who have studied the brain bases of working memory have argued that these cognitive systems are instantiated in working-memory brain systems located in the prefrontal cortex (PFC). Recently, however, a growing body of data has prompted an alternative view that calls into question the existence of specialized working memory systems in either mind or brain. Instead, it suggests that working memory is better understood as an emergent property produced by sustained attention to information represented in systems that have evolved to perform perception-, representation-, or action-related functions (e.g., Postle 2006). This chapter will summarize evidence that the STR of information in working memory tasks is supported by sustained activity in the same nonPFC brain regions that process this information in situations that do not require memory. Examples will be drawn from experimental psychology and psychophysics, human and monkey neuropsychology, human and monkey electrophysiology and human neuroimaging. Complementary reviews that focus in greater detail on just one or another of these sources of data can be found in Jonides et al. (2005), Pasternak and Greenlee (2005) and Slotnick (2005). The sections that follow will be organized by domain of information to be remembered: spatial/kinetic; object identity; and linguistic. (end of paraphrase)
Further discussion -- Covington Theory of Consciousness |