Computational Modeling
developingintelligence | January 7, 2009The ability to suppress unwanted thoughts and actions is thought (by some) to be crucial in your ability to control behavior. However, alternative perspectives suggest that this emphasis on suppression or "inhibition" is misplaced. These perspectives, largely motivated by computational models of the brain, suggest that alternative abilities (such as the activation or "active maintenance" of wanted thoughts and actions) are the real underlying mechanisms of inhibition and suppression.
This debate is given new life by the emerging science of "executive function training," which carefully…
developingintelligence | January 6, 2009For the basics about multivariate fMRI "mind-reading" techniques, see the video below. Some of it is based on this 2007 Haynes et al paper from Current Biology, described in more detail following the video.
What Haynes et al have done is to ask 8 subjects to freely decide either to add or subtract two numbers, and to select among 4 options an answer corresponding to the task they chose. After repeating this process many times, the authors ran a pattern classifier on the metabolic activity recorded in the brain.
This pattern classifier was run on the unsmoothed fMRI data - smoothing is…
developingintelligence | November 26, 2008Play cognitive engineer: if you were designing an intelligent system, you'd probably use the same system to detect novelty as that used to detect familiarity. After all, one is simply the inverse of the other - so novelty can be thought of as a below-threshold value for some familiarity signal.
Upon reflection, however, you might notice some subtle problems with your design. First, novelty is informative only insofar as it is engages a change in the behavior of your system: novelty indicates an opportunity for learning which has not been exploited by the system. Critically, this includes…
developingintelligence | September 15, 2008Much has been written about the nonspatial functions of the parietal lobe, but these nonspatial functions are rarely evaluated as to whether they are also nonmotoric or reflect some covert form of spatial attention. Establishing whether the parietal lobe has truly nonmotoric and nonspatial functions is essential for understanding why parietal cortex appears to be involved in so many different tasks. Here I've attempted to evaluate whether the parietal lobe truly has nonspatial, and perhaps also nonmotoric functions by reviewing the relevant literature...
Magnitude processing - the size…
developingintelligence | September 2, 2008An absence of evidence is not itself evidence for the absence of a particular effect. This simple problem - generally known as the problem of null effects - yields many difficulties in cognitive science, making it relatively easier to parcellate cognitive and neural processes into ever-finer detail than to show when two processes are identical. Recently, this problem has emerged for the wonder child of cognitive science, functional magnetic resonance imaging (fMRI). The problem in this case is how to determine whether two tasks recruit at least one of the same areas of the brain in the…
developingintelligence | June 16, 2008In a recent issue of Science, Dahlin et al report the results of an executive function training paradigm focused on the process of mental updating. "Updating" is thought to be one of the core executive functions (as determined through confirmatory factor analysis), is thought to rely on the striatum (as determined through computational neural network modeling), and provides the dynamic gating capacity to working memory which may allow for "perceptual filtering" in which some items are attended and others ignored (as confirmed with neuroimaging).
24 subjects matched for age, education,…
developingintelligence | June 12, 2008Could something be perceived if there is no sensory system which is dedicated to it? For everyone except parapsychologists, the obvious answer is no - but this raises questions about the ability to perceive short temporal intervals, for which there appears to be no dedicated sensory system.
In their newly in-press TICS article, Ivry and Schlerf review the state of the art in cognitive modeling of time perception - perhaps the most basic form of perception which has no sensory system dedicated to it.
Ivry and Schlerf review the attractive qualities of time perception modules, such as the…
developingintelligence | June 9, 2008Working memory - the ability to hold information "in mind" in the face of environmental interference - has traditionally been associated with the prefrontal cortices (PFC), based primarily on data from monkeys. High resolution functional imaging (such as fMRI) have revealed that PFC is just one part of a larger working memory network, notably including the parietal cortex, which has long been the focus of research in the visual domain, and is primarily thought to carry out spatial computations.
What role might such spatial computations have in working memory? Wendelken, Bunge & Carter…
developingintelligence | May 23, 2008The organization of the human prefrontal cortex (PFC) is a lasting mystery in cognitive neuroscience, but not for lack of answers - the issue is deciding among them, since all seem to characterize prefrontal function in very different but apparently equally-valid ways. If this mystery were resolved, it could revolutionize cognitive neuroscience and neuropsychology as well as education and artificial intelligence - prefrontal cortex is crucial for the most high-level cognitive abilities we know of, including the executive functions, but no existing theory of intelligence specifies the exact…
developingintelligence | May 22, 2008"It has attained a certain mystique in the physical and biological sciences because it manages to be both rare and ubiquitous. Examples [...] are found in quasar luminosity, tide and river height, traffic flow, and human heartbeat..." (Gilden & Hannock)
Since the mid-90s, a small group of cognitive psychologists have turned their attention to variability in human performance which cannot be explained by existing theories and appears not to be affected by experimental manipulations. "One-over-f" or "pink" noise refers to one way in which human performance across time correlates with…
developingintelligence | May 7, 2008Complex cognition can be predicted by remarkably simple tasks. For example, the speed with which you choose one of two possible responses can reliably predict IQ. Some theories propose that this relationship is due to differences in something called "processing speed," but more recent work has shown the effect is really due to the slowness of your slowest reaction times on such simple tasks. Known as the "worst performance rule," this can be revealed through various RT distribution decomposition techniques (e.g., "binning" of reaction times or ex-gaussian analysis).
A particular class of…
developingintelligence | April 10, 2008Peter Hankins has written an excellent commentary criticizing the "positive comparisons" I make after contrasting brains with computers.
Peter says:"... the concept of processing speed has no useful application in the brain rather than that it isn't fixed."
While this statement may intuitively appeal to some philosophers, temporal limitations in neural processing are both critical for neuronal function and well accepted in both neuroscience and psychometrics. At the biological level, the membrane capacitance of neurons is important for regulating the firing rate of neurons, which itself has…
developingintelligence | January 11, 2008One of the bottlenecks in human memory capacity is its "filtering efficiency" - irrelevant information in memory only detracts from an already-constrained memory span. New work by McNab & Klingberg images the neural structure directly responsible for such filtering, and shows it can predict behavioral measures of memory span. Impressively, the location of this "memory filter" is the globus pallidus, as predicted by a computational network model of cortex, but in contrast to that model, it shows functional correlations with parietal in addition to frontal areas. This work has immediate…
developingintelligence | November 29, 2007The world wide web can be understood as a giant matrix of associations (links) between various nodes (web pages). At an abstract level, this is similar to human memory, consisting of a matrix of associations (learned relationships, or neuronal connections) between various nodes (memories, or the distributed representations constituting them). In the new issue of Psych. Science, Griffiths et al. ask whether Google's famously accurate and fast PageRank algorithm for internet search might behave similarly to the brain's algorithm - whatever that might be - for searching human memory.
About…
developingintelligence | November 19, 2007Geoff Hinton has a new TiCS paper describing recent advances in algorithms used to train multilayered neural networks.
First, a little background: neural networks of a sufficient size can calculate any mathematical function (an infamous proof among neural network modelers). Unfortunately, the tricky part is figuring out how to set the connections in that network to calculate those functions.
This is where learning algorithms become necessary - unless you want to tweak each connection by hand until you get a working network (not a problem if you don't care how the brain works), then you…
developingintelligence | November 7, 2007Speech recognition remains a daunting challenge for computer programmers partly because the continuous speech stream is highly under-determined. For example take coarticulation, which refers to the fact that the auditory frequencies corresponding to a given letter are strongly influenced by the letters both preceding and following it - sometimes interpreted to mean that there is no invariant set of purely auditory characteristics defining any given letter. Thus it's difficult to recover the words that a person is saying, since each part of that word is influenced by the words surrounding it…
developingintelligence | October 3, 2007Ambiguity is a constant problem for any embodied cognitive agent with limited resources. Decisions need to be made, and their consequences understood, despite the probabilistic veil of uncertainty enveloping everything from sensory input to action execution. Clearly, there must be mechanisms for dealing with or resolving such ambiguity.
A nice sample domain for understanding ambiguity resolution is language, where problems of uncertainty have been long appreciated. The meaning of words in general (not to mention referents like "that" or "he") can be highly ambiguous (see "the gavagai…
developingintelligence | July 13, 2007Well, maybe it's "exotic" only to neuroscientists. Inhibitory structure in neocortex has usually been seen as fairly homogenous and simple, where the wide variety of inhibitory interneuron types was viewed as misleading: at bottom, they all perform a simple regulatory function of keeping only a few representations active at once. Thus, in contrast to subcortical regions, inhibitory networks in cortex were thought to involve mostly "vanilla" axon-to-dendrite connections in a semi-regular latticework of connections. However, in the current issue of Nature Neuroscience, Conners &…
developingintelligence | June 27, 2007Though widely separated in terms of both neuroanatomical location and evolutionary development, there are surprising parallels between parietal cortex and the hippocampus:
- Both structures are important for spatial cognition, although parietal cortex is thought to maintain a "self-centered" map of the environment (i.e., where locations are represented relative to the direction of gaze) whereas hippocampus may maintain a "world-centered" or allocentric map (i.e., where locations are represented with respect to landmarks or surrounding geometry).
- Both structures are thought to represent…
developingintelligence | June 18, 2007How does your brain represent the feelings and thoughts that are a part of conscious experience? Even the simplest aspects of this question are still a matter of heated debate, reflecting science's continuing uncertainty about "the neural code." The fact is that we still don't have a clear picture of the ways in which neurons transmit information. Here's a quick guide to current theories, beginning with well-established theories and moving into ideas that are considered more theoretical.
The canonical model: firing rate
Clearly, neurons encode some information in the rate of their firing…