12/19/2005

The Tyranny of Inhibition

In the children's game called "Simon Says," players are to perform a specific action if and only if the action is preceeded by the phrase "simon says." The traditional and intuitive explanation for Simon Says is that successful players must inhibit responding unless the action is preceeded by "simon says." Similar explanations abound for a variety of tasks, including Stroop, False-Belief, Dimensional Change Card Sort, etc, all involving the use of suppression or inhibition.

However, several recent papers seem to suggest that this kind of "high-level" inhibition (as distinct from low-level concepts like lateral inhibition) may not be necessary to explain any behavior, despite how frequently it is invoked as an explanatory principle in cognitive psychology!

In Egner & Hirsch's '05 paper in Nature Neuroscience, the authors use fMRI and a stroop-like task to demonstrate that inhibition of the fusiform-face area does not occur when faces are distractors in the presence of another stimulus, but that increased activation of this area occurs while attending to a face in the presence of other distractors. According to their logic, good performance in stroop tasks is caused by amplification of relevant information, rather than inhibition of irrelevant or inappropriate information. As Nieuwenhuis and Yeung put it: "a short-circuit in your desktop computer might conceivably cause random blotches of color to appear on your monitor, but you would not infer that the damaged region usually functions as a 'color inhibition' system. Instead, it would be more accurate to conclude that the damaged region—the video card—previously performed detailed, sophisticated computations that resulted in the delivery of meaningful, rather than random, patterns of color to your screen."

A new paper by Vogel, et al. mentions what I find to be a more useful explanatory concept than inhibition: selection efficiency. To use the example given above, while it may be inaccurate to conclude that the system normally performs color inhibition, it would be accurate to conclude that the system normally shows more efficient color selection. Vogel et al. rely on differential sustained EEG amplitudes for various loads on visual working memory, which asymptote at each individual's visual WM capacity, to show that those with higher visual WM capacity are the ones that can most reliably encode only the relevant items in a given display: they have a more efficient selection mechanism than those with lower memory capacity.

Metabolically speaking, these discoveries almost seem obvious: why would the brain evolve to spend resources inhibiting things it doesn't want to pay attention to, when instead it can simply select and amplify those things that should be attended to?

The applications for reconceptualizing working memory and inhibition are profound. Educationally, how can we enhance selection efficiency? Could ADHD be a disorder of selection efficiency, a disorder of the system that directs selection, or both?

2 Comments:

Anonymous Anonymous said...

Yeah, I agree.

On the one hand, maybe the computation operation going on in many of these tasks really is "inhibition" (and actually I don't think the fMRI contradicts that; maybe it takes "activation" of neurons to perform the computational task of inhibition).

But on the other hand, it's totally possible that the computation going on is something more complex, and people seem to overlook this alot. All we can really say is that there is a change in "selection efficiency".

1/06/2006 02:02:00 PM  
Blogger Chris Chatham said...

I actually find the fMRI evidence pretty convincing (it certainly takes activation of inhibitory neurons to accomplish inhibition, but then wouldn't you still expect to see less activity in FFA when faces are distractors, which they do not find?). But you bring up a good point, as was recently pointed out to me, given that proponents of inhibition are usually talking about inhibition of competing motor responses, not necessarily of higher cortical areas. So therefore, they would not have ever expected inhibition of the FFA.

1/06/2006 03:16:00 PM  

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