Academic journal article Cognitive, Affective and Behavioral Neuroscience

Dissociations among Tasks Involving Inhibition: A Single-Case Study

Academic journal article Cognitive, Affective and Behavioral Neuroscience

Dissociations among Tasks Involving Inhibition: A Single-Case Study

Article excerpt

Recent theories of working memory have emphasized the role of inhibition in suppressing irrelevant information. Moreover, psychometric studies have reported that several inhibition tasks with very diverse requirements load on a single inhibition factor. A patient with left inferior frontal damage, Patient M.L., previously reported to have a semantic short-term memory deficit (R. C. Martin & He, 2004), showed evidence of difficulty with inhibition on short-term memory tasks. We investigated whether he would show evidence of inhibition difficulty on two verbal tasks (a Stroop task and a recent-negatives task) and two nonverbal tasks (a nonverbal spatial Stroop task and an antisaccade task). M.L. was impaired on both verbal tasks but performed normally on the nonverbal tasks. M.L.'s data also represent a dissociation between Stroop and antisaccade performance, two tasks that load on a single factor in factor-analytic studies. The implications of these data for theories of inhibition and executive function are discussed.

Executive function is associated with complex planning and the ability to organize behavior. A core component of executive processes is inhibition-a term referring to the suppression of irrelevant information and overlearned or prepotent responses. Tasks commonly associated with inhibition measure a seemingly diverse set of abilities, and one might question whether all such tasks measure the same cognitive processes. For example, it is not obvious that the processes necessary to inhibit reflexive eye movements to sudden stimulus onsets in an antisaccade task are the same as those necessary to inhibit the tendency to name the word, rather than the color, in the Stroop task. Rather than positing a global inhibitory process, it may be necessary to further fractionate the processes involved in inhibition. In the present study, we begin to address these issues concerning the nature of inhibitory processes by examining whether these processes dissociate in a braindamaged patient with left inferior frontal damage.

Previous research with normal subjects has suggested that several different tasks involving inhibition do share common processes. In an effort to delineate the components of executive function, Miyake et al. (2000) collected data from a dozen tasks commonly assumed to involve executive processes and performed a latent variable analysis. This analysis yielded three factors, which Miyake et al. identified as shifting, updating, and inhibition. According to Miyake et al., shifting represents the ability to shift cognitive control between different tasks or routines. Updating is the ability to update and monitor representations in working memory (WM). Finally, inhibition is described as the ability to inhibit irrelevant information or prepotent responses. Tasks that loaded on the inhibition factor included the antisaccade task, the stop signal task, and the Stroop task. Miyake et al. made no explicit predictions as to whether these factors may be associated with distinct and separable neural substrates. However, one might predict that a patient who performed poorly on one inhibition task would show a deficit on other tasks loading on the inhibition factor but would not necessarily have difficulty with tasks loading on the other factors. In fact, Miyake et al. recommended that their results be carefully evaluated in neuropsychological populations in order to provide converging evidence. The present study takes this approach.

In addition to its fundamental role in executive function, inhibition and the ability to resist interference have been the subject of an increasing number of studies in the memory literature. Recent theories of WM have emphasized resistance to interference as accounting for much of the individual variability in memory performance among normal individuals (see Rosen & Engle, 1997; Whitney, Arnett, Driver, & Budd, 2001; Zacks & Hasher, 1994). Among college age subjects, Engle and colleagues have also demonstrated a relationship between WM capacity and susceptibility to interference in a number of different paradigms (Rosen & Engle, 1997, 1998). …

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