In the Light of Evolution Volume VII: The Human Mental Machinery (2014) / Chapter Skim
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5 Evolution of Working Memory--Peter Carruthers
5 Evolution of Working Memory--Peter Carruthers
Pages 75-94
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From page 75... ...
WM has been inten sively studied for many decades, and there is a growing consensus about its nature, its components, and its signature limits. Remarkably, given its central importance in human life, there has been very little comparative investigation of WM abilities across species.
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From page 76... ...
. WM is generally thought to consist of an executive component that is distributed in areas of the frontal lobes working together with sensory cortical regions in any of the various sense modalities, which interact through attentional processes (Postle, 2006)
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From page 77... ...
The resulting sensory forward models, when targeted by attention, can gain entry into WM. Hence one can imagine oneself saying something and "hear" the result in so-called "inner speech," or one can imagine oneself doing something and "see" or "feel" the results in visual or proprioceptive imagination.
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From page 78... ...
The timescales involved, as well as the number of items that can be recalled, far exceed human WM abilities. Indeed, some writers are quite explicit that "working memory" in such studies should be defined as a memory that is used within a testing session (often lasting for minutes or hours)
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From page 79... ...
WORKING MEMORY IN ANIMALS As we have seen, there are a number of aspects or components of normal WM function in humans, including capacities to sustain, rehearse, and manipulate active representations, with a signature limit of three to four items or chunks of information. We also know that WM is attention dependent and hinges critically on capacities to resist interference from competing representations.
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From page 80... ...
There are extensive data sufficient to exclude this possibility, much of it using match-to-sample or non–match-to-sample tasks. (Recall that data from animal experiments using the radial maze involve timescales too great to serve as direct tests of WM ability.)
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From page 81... ...
This is because the brain mechanisms subserving episodic-like memory are highly conserved among mammals. In particular, all mammals share homologous hippocampal and parahippocampal structures organized into homologous subregions, which have strong reciprocal connections to areas of the frontal cortex (Allen and Fortin, Chapter 6, this volume)
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From page 82... ...
. In the serial recall test just described, in contrast, the monkey may have used mental rehearsals of its planned movements to support its WM of the sequence of positions, thereby extending its pure memory-sustaining limits.
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From page 83... ...
. (In a complex span test, one has to undertake some other task, such as judging whether a simultaneously presented sentence makes sense or performing some simple mental arithmetic while also retaining an unrelated list in WM.
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From page 84... ...
Why should tests using interrupted search in a radial-arm maze involve interactions between short-term and long-term WM? When commencing search following an interruption, the animal will need to access long-term representations of the four arms previously visited, holding those in active WM long enough to select a fifth.
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From page 85... ...
The results of this experiment were that retention time did not correlate with g at all and that WM capacity correlated moderately with g, whereas selective attention was strongly correlated with g. This, too, is what one might have predicted from what we know about human WM.
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From page 86... ...
However, it would be possible to claim that a creature can have a capacity for generic semantic imagery without being capable of episodic memory, perhaps because representations of specific episodes are never stored in memory at all. So even if animals are incapable of mental time travel (including episodic remembering)
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From page 87... ...
This consideration would provide a stronger argument, of course, if corvids were not so evolutionarily distant from us. However, despite this distance, we noted earlier that birds possess brain networks that are similar to, and at least partly homologous with, those that support episodic memory in humans and other mammals (Allen and Fortin, Chapter 6, this volume)
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From page 88... ...
Evidence of mental rehearsal of action comes from studies of longterm planning in animals. We know that in humans such planning is conducted in large part through rehearsal of alternative actions, with people responding affectively to the WM representations that result (Damasio, 1994; Gilbert and Wilson, 2007)
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From page 89... ...
The evidence of future planning in apes and corvids suggests that they are capable of doing just that. In another sense, however, manipulation involves targeting an image with a mentally rehearsed action, thereby transforming it.
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From page 90... ...
Among the classic findings in this literature are that participants take longer to judge shapes whose orientations are further apart from one another, suggesting that the movement of the initial image through the intervening space takes time. What we know from brain-imaging and transcranial magnetic stimulation studies using the visual rotation paradigm is that activity in the motor or premotor cortex precedes and causes the subsequent transformation of the visual image (Ganis et al., 2000)
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From page 91... ...
. Similar regions of the brain displayed greater activity at rest in both species, including in the medial prefrontal cortex and posterior cingulate cortex, suggesting that chimpanzees, too, spend much of their time ruminating when not engaged in other tasks.
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From page 92... ...
In humans, we know that these default-network hubs play an important role in mind wandering. However, it does not follow that any animal with similar brain connectivity will also make use of its WM when at rest to replay the past and explore the future in the ways in which humans do.
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From page 93... ...
system 2 processes use mental rehearsals of sentences and phrases in inner speech, so in this respect system 2 is uniquely human. Moreover, given that WM and fluid g largely coincide, differences in WM capacities explain a significant portion of the variance between people in tests of their reasoning abilities, with the remainder of the variance being accounted for by differences in people's disposition to stop and reflect before answering and in their knowledge of norms of reasoning, or their "mindware" (Stanovich, 2009)
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From page 94... ...
94 / Peter Carruthers that humans may be unique in making frequent task-independent use of their WM abilities. However, until there is a sustained effort by comparative psychologists to devise and carry out matching tests of WM ability involving humans and various other species of animal, many of these claims must remain at least partly speculative.
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