Every agent must sample and act on its world through a sense-select-act (or stimulus, cognition, response) cycle. The IDA/GW model hypothesizes for us humans a complex , involving perception, several memory systems, attention and action selection, that samples the world at five to ten times a second. This frequent sampling allows for an exceptionally fine grained analysis of common cognitive phenomena such as process dissociation, recognition vs. recall, and the availability heuristic. At a high level of abstraction, these analyses, which are included in the paper, support the commonly held explanations of what is generally found in studies of the explicit (i.e., conscious and reportable) components of memory processes (e.g. Tulving, 1985; Baddeley et al, 2001). Nothing new here. At a finer grained level, however, our analyses flesh out these common explanations, adding detail and functional mechanisms. Therein lies the value of our analyses.
Current techniques for studying these phenomena at a fine grained level, such as PET, fMRI, EEG, implanted electrodes, etc., are still lacking either in scope, in spatial resolution, or in temporal resolution. PET and fMRI have temporal resolution problems, EEG is well-known to have localizability difficulties, and implanted electrodes (in epileptic patients), while excellent in temporal and spatial resolution, can only sample a limited number of neurons; that is they are limited in scope. As a result, many of our hypotheses, while testable in principle, seem difficult to test at the present time. Improved recording methods are emerging rapidly in cognitive neuroscience. When GW theory was first proposed, the core hypothesis of “global activation” or “global broadcasting” was not directly testable in human subjects. Since that time, however, with the advent of brain imaging, widespread brain activation due to conscious, but not unconscious, processes has been found in dozens of studies (see Baars, 2002; Dehaene, 2001). We expect further improvements to make our current hypotheses testable as well.
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There is some evidence from neuroscience in support of various elements of these hypotheses. As mentioned above, experiments with rats learning to search properly for food in an eight-armed maze support the role of the hippocampal system in transient episodic memory, but not in perceptual memory (Olton, Becker and Handelman 1979). Also, an eye blink in response to a tone can be classically conditioned without appeal to the hippocampus if the unconditioned stimulus (puff of air) immediately follows the conditioned stimulus (tone). If the unconditioned stimulus is delayed, the hippocampus (transient episodic memory) is needed (Lavond, Kim and Thompson 1993). fMRI studies indicated dissociation between possible neural correlates of PM and TEM. “Engagement of hippocampal and parahippocampal computations during learning correlated with later source recollection, but not with subsequent item recognition. In contrast, encoding activation in perirhinal cortex correlated with whether the studied item would be subsequently recognized, but failed to predict whether item recognition would be accompanied by source recollection.” (Davachi, Mitchell & Wagner 2003)
In Step 5 of the cognitive cycle, a single coalition of codelets, typically composed of one or more attention codelets and their covey of relevant information codelets, wins the competition, gains access to the global workspace, and has its contents broadcast to all the codelets in the system. This broadcast is hypothesized to be a necessary condition for conscious experiences as reported in scientific studies (Baars, 1988, 2002). This “global access” broadcast step embodies the major hypothesis of global workspace theory, the linking of the broadcast with conscious cognition , which has been supported by a number of recent neuroscience studies (Dehaene 2001; Dehaene and Naccache 2001; Baars 2002; Cooney and Gazzaniga 2003).
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In this paper we employ a theoretical methodology that is quite different from that which is currently standard in the experimental literature. Although the model is heavily based on experimental findings in cognitive psychology and brain science, there is only qualitative consistency with experiments. Rather, there are a large number of hypotheses derived from an unusual computational model of cognition, the IDA/GW model. The model is unusual in two significant ways. First, it functionally integrates a particularly broad swath of cognitive faculties. Second, it does not predict numerical data from experiments, but rather, is implemented as a software agent, IDA, that performs a real-world personnel task for the US Navy. The IDA/GW model generates hypotheses about human cognition by way of its design, the mechanisms of its modules, their interaction, and its performance. All of these hypotheses are, in principle, testable. With the advent of more sophisticated brain and behavioral assessment methods, some earlier hypotheses in this research program have been confirmed (Baars, 2002). We expect the current set of hypotheses to become directly testable with continuing improvements in cognitive neuroscience.
Why may I not invent the hypothesis of Natural Selection (which fromthe analogy of domestic productions, and from what we know of thestruggle of existence and of the variability of organic beings, is, insome very slight degree, in itself probable) and try whether thishypothesis of Natural Selection does not explain (as I think it does) alarge number of facts…. (Letter to Henslow, May 1860 in Darwin 1903)
This starts a heuristic search using rearrangements of the "tree bisectionand reconnection" type (TBR). TBR is more elaborate than both NNI and SPR. TBRis the default swap mode for heuristic searching in PAUP*, and NNI or SPRshould mostly be used if you are interested in reducing search time.
To say that a hypothesis is plausible is to convey that it hasepistemic support: we have some reason to believe it, even priorto testing. An assertion of plausibility within the context of aninquiry typically has pragmatic connotations as well: to say thata hypothesis is plausible suggests that we have some reason toinvestigate it further. For example, a mathematician working on aproof regards a conjecture as plausible if it “has some chancesof success” (Polya 1954 (v. 2): 148). On both points, thereis ambiguity as to whether an assertion of plausibility is categoricalor a matter of degree. These observations point to the existenceof two distinct conceptions of plausibility, probabilistic andmodal, either of which may reflect the intended conclusion ofan analogical argument.
In the recognition memory literature dual-process models have been put forward proposing that two distinct memory processes, referred to as and , support recognition (Mandler 1980, Jacoby and Dallas 1981). Familiarity allows one to recognize the butcher in the subway as someone who is known, but not to recollect the context of the butcher shop. In the IDA model, PM alone provides the mechanism for such a familiarity judgment, while both PM and DM are typically required for recollection. Recent brain imaging results from cognitive neuroscience support a dual-process model (Rugg and Yonelinas 2003), and so are compatible with our Perceptual Memory Hypotheses. (For an analysis, see the section of Recognition Memory below.)