Computational Modeling
developingintelligence | June 4, 2007Suppose that one day your computer's hard drive stops working, but everything else about the machine is fine. Your friend has an identical computer in which the hard drive works fine, but the keyboard suddenly stopped working. Based on this "double dissociation" between the two different problems, can you safely assume that the "hard drive system" and the "keyboard system" rely on distinct underlying mechanisms?
For years, cognitive neuropsychologists have felt safe in making equivalent assumptions about brain damage. If one type of damage leads to difficulty on task A, but not task B, and…
developingintelligence | May 29, 2007The capacity to use and manipulate symbols has been heralded as a uniquely human capacity (although we know at least a few cases where that seems untrue). The cognitive processes involved in symbol use have proven difficult to understand, perhaps because reductionist scientific methods seem to decompose this rich domain into a variety of smaller components, none of which seems to capture the most important or abstract characteristics of symbol use (as discussed previously).
So, it's important to specify how the simpler and better-understood aspects of symbol processing may interact and give…
developingintelligence | May 24, 2007Many will agree that algebra is difficult to learn - it involves planning, problem-solving, the manipulation of symbols, and the application of abstract rules. Although it's tempting to imagine a specialized region of the brain for each of these processes, they may actually recruit roughly the same widely-distributed and general-purpose "task network" of brain regions. The individual contribution of each region has been, and continues to be, a matter of much debate.
However, the functional specialization of each brain region may be best understood as fulfilling a particular balance between…
developingintelligence | May 16, 2007The analytic depth of cognitive neuroscience is, in many ways, a curse. Those aspects of high-level cognition most relevant to real-world applications are the least understood at a neurobiological level, and those mechanisms that are well-understood neurobiologically are too simple to inform real-world practices.
The explanatory gaps between these levels of analysis is a result of hyper-reductionism in science, itself rooted in a lasting preference (reverence?) for the simplistic and "parsimonious." But natural phenomena, like the emergence of behavior from the brain, are ultimately more…
developingintelligence | April 26, 2007People are remarkably bad at switching tasks - and research focusing on this fact has isolated a network of brain regions that are involved in task-switching (I'll call it the "frontal task network" for short). One of the stranger findings to emerge from this literature is the fact that we're actually worse at switching to a more natural or well-practiced task after having performed a less natural one.
One potential explanation for this "switch cost asymmetry" is that the task network may recognize the potential for errors when performing the unnatural task, and therefore "help it along"…
developingintelligence | April 25, 2007A lack of clear definitions for terms like "intelligence" and "consciousness" plagues any serious discussion of those concepts. A recent article by Seth, Baars & Edelman argues for a core set of 17 properties that are characteristic of consciousness, and could be used in the "diagnosis" of consciousness in humans and other animals.
Property 1: "Irregular" patterns of brain activity
Electrical oscillations occuring between 20 and 70 times per second are common in awake humans, but epilepsy, sleep, anesthesia and some forms of brain damage are accompanied by the dominance of highly regular…
developingintelligence | April 16, 2007Among nature's most impressive feats of engineering is the remarkably flexible and self-optimizing quality of human cognition. People seem to dynamically determine whether speed or accuracy is of utmost importance in a certain task, or whether they should continue with a current approach or begin anew with another, or whether they should rely on logic or intuition to solve a certain problem. A topic of intense research in cognitive neuroscience is how cognition can be made so flexible.
One possibility proposed by by Brown, Reynolds & Braver is that cognitive control is multi-faceted, in…
developingintelligence | April 11, 2007Very early in the history of artificial intelligence research, it was apparent that cognitive agents needed to be able to maximize reward by changing their behavior. But this leads to a "credit-assignment" problem: how does the agent know which of its actions led to the reward? An early solution was to select the behavior with the maximal predicted rewards, and to later adjust the likelihood of that behavior according to whether it ultimately led to the anticipated reward. These "temporal-difference" errors in reward prediction were first implemented in a 1950's checker-playing program,…
developingintelligence | March 27, 2007"A good metaphor is something even the police should keep an eye on." - G.C. Lichtenberg
Although the brain-computer metaphor has served cognitive psychology well, research in cognitive neuroscience has revealed many important differences between brains and computers. Appreciating these differences may be crucial to understanding the mechanisms of neural information processing, and ultimately for the creation of artificial intelligence. Below, I review the most important of these differences (and the consequences to cognitive psychology of failing to recognize them): similar ground is…
developingintelligence | February 20, 2007In the middle of the work day, you realize you'll need to stop at a store on your way home from work. Your ability to actually do so, hours later, relies on what some psychologists call "prospective memory." Although prospective memory is clearly important for human intelligence, very little is known about how it works.
Clearly there are at least two kinds of prospective memory. In the example above, you may tell yourself "stop at the store" again and again until you pull into the store's parking lot - this is known as a vigilance or monitoring strategy. Or the store may simply catch your…
developingintelligence | February 15, 2007Dopamine is probably the most studied neurotransmitter, and yet the neuroscience literature contains a huge variety of perspectives on its functional role. This post summarizes a systems-level perspective on the function of dopamine that has motivated several successful drug studies and informed the construction of artificial neural network models. The details of this perspective are maddeningly complex (at least for me), which is why I thought it would be useful to summarize it here, in the simplest terms possible.
There are at least two ways to talk about dopamine release. We can talk…
developingintelligence | February 14, 2007In a 2006 Psychopharmacology article, Niv et al. suggest that while transient dopamine release is frequently modeled computationally (as encoding reward-prediction error, for example, or as gating information into working memory) the role of more constant dopamine release is not. In the neuroscience literature, these two patterns of release are known as "phasic" and "tonic," respectively.
The authors argue that current models of dopamine release have three major shortcomings: first, they do not explicitly address the effect of dopamine manipulation on response latency or "vigor"; second,…
developingintelligence | February 13, 2007According to some perspectives, anterior cingulate cortex (ACC) may become activate in situations where the reward value of given representation or stimulus has decreased, resulting in more competition between representations. Activation of this region may help increase tonic norepinephrine, resulting in more exploratory behavior, and thus more variable responding.
A different perspective on ACC is advocated in this 2001 article by Braver, Barch, Gray, Molfese and Snyder. They also suggest that ACC is important for resolving conflict between multiple responses - and would therefore be…
developingintelligence | February 12, 2007Whereas yesteryear's artificial neural networks models were focused on achieving basic biological plausibility, today's cutting edge networks are modeling cognitive phenomena at the level of neurotransmitters. In a great example of this development, McClure, Gilzenrat & Cohen have an article in Advances in Neural Information Processing Systems where they propose a role for both dopamine and norepinephrine in switching behavior between modes of "exploration" and "exploitation."
First, a little background. In artificial intelligence circles, the "temporal difference" algorithm has been a…