Do Inhibitory Skills Improve with Practice?

The 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 crafts experiences designed to enhance abilities like inhibition and active maintenance. One study - described below - fails to find any effect of cognitive training on inhibition tasks, in marked contrast to the training-related improvements observed on active maintenance or "working memory" tasks.

In this Dev Sci article, Thorell et al describe the results of a 5-week executive function training program in a community sample of 3- and 5-year-old children. Children were randomly assigned to a training group (focusing either on inhibition or working memory) or to a control group (either an active or passive control). Children completed 15 minutes per day of computerized, adaptive training from the CogMed battery. The inhibition group completed tasks involving the suppression of a planned response (stop signal), the suppression of a prepotent response (go/nogo), and the suppression of irrelevant stimuli (flanker). Conversely, the working memory group trained on a task requiring the active maintenance of different items, their spatial locations, and their sequential order. Both before and after the 5-weeks of training, children in all groups completed different pre- and post-tests measuring all of these abilities (the day/night stroop, go/nogo, word span, the span board task from WAIS-R-NI) as well as attention (via block design, ommission errors in an auditory CPT, and ommissions and RT in go/nogo).

While there were no differences between groups at the pre-test, only the group trained on working memory improved at post-test relative to controls. Importantly, this improvement was limited to the tests of attention and working memory. In contrast, the inhibition group failed to significantly improve even on one of their trained tasks (stop signal) across the course of training. (Using changes in response speed or problem solving as covariates did not alter this pattern of results.)

While it may be tempting to suggest that "inhibition" is a process impure construct which cannot be unitarily affected by training, such strong conclusions cannot be drawn on the basis of the null effect. (Unfortunately, the authors did not report the contrast of of pre-post test change between the working memory and inhibition groups, which could partially circumvent this shortcoming.)

In addition, other studies have found training effects on the closely-related construct of interference control (although that ability can be reduced to an active maintenance mechanism in computational modeling and some factor analyses, though the latter is less clear).

Another caveat is that this is only the second study to investigate training of preschoolers, and they represent a special case: at this age, normal children have yet to develop executive functions similar to those used by adults. It is possible that inhibition or "interference resolution" as it exists in the adult brain is insufficiently developed to show training effects. On the other hand, one might assume that especially weak inhibitory abilities should yield even larger training effects among children.

For example, children of this age generally opt for small immediate rewards over larger delayed rewards, fail to maintain even simple thoughts or representations when appropriate, and often cannot even switch from one task to another when asked. To the extent that inhibition influences any of these abilities, one would expect relatively wide-ranging effects of inhibition training.