Dissociation of perceptual and motor inhibition processes through the use of novel computerized conflict tasks

Abstract

Efficient behavioral functioning requires early perceptual inhibition of irrelevant stimuli and later motor inhibition of inappropriate responses. The Perceptual and Motor Conflict Tasks were developed to differentially assess perceptual and motor inhibition, and to determine whether these processes utilize separate or shared cognitive resources. The computerized tasks include six subtests involving a box or an arrow appearing in various locations. Subjects respond by pressing a key on the left or right side of a keyboard. In different subtests, arrow direction or stimulus location determines correct responses. Perceptual inhibition assessment requires the subject to respond to a conflicting arrow direction while ignoring stimulus location. Motor inhibition assessment involves the subject responding in the direction opposite to that indicated by a centrally located arrow. In a neurologically normal sample (N 5 44), reaction time analyses yielded significant Perceptual and Motor Conflict main effects, with slower performance under conflict conditions, but no significant Perceptual 3 Motor interaction. The lack of a significant Perceptual 3 Motor interaction, according to the additive factor model, indicates that these two processes utilize distinct cognitive resources. Nevertheless, performance on the two conflict tasks was significantly correlated with each other, and Perceptual Conflict performance was significantly correlated with Stroop interference. (JINS, 2003, 9, 25-30.)

Are perceptual and motor inhibition processes really dissociated? A comment on Nassauer and Halperin (2003)

“…For example, the size of the conflict effect can be weighted by the baseline condition and expressed as a percentage: (conflict 2 no conflict)0no conflict. In the present study, this leads to values of 40% for the perceptual con-flict, 26% in the motor conflict, and 64% for the combined conflicts (additivity), by taking the values used by Nassauer and Halperin (2003), but this leads to 57, 49, and 72%, respectively, by taking my method (underadditivity). Another method would be to compute the ratio (conflict 2 no conflict)0(conflict 1 no conflict), which leads to values between 21 and 11.…”

“…Concretely, in the former case, one should observe a significant main effect of each kind of inhibition but no interaction while, in the latter case, the interaction should be significant. Nassauer and Halperin (2003) claimed that their results support the dissociation thesis.Three qualifications apply. First, the dissociation thesis relies on the prediction of a null effect (of the interaction).…”

“…Therefore, an inhibition effect of, say, 100 ms, has not the same meaning in both tasks. And indeed Nassauer and Halperin (2003) reported a mean latency of 423 ms in the perceptual no-conflict, against 451 ms in the motor no-conflict. Clearly, some correction for overall accuracy (or speed) is needed.…”

“…However, given its potential impact, this study has to be examined carefully.According to Nassauer and Halperin (2003), their new computerized tasks would be able to show that perceptual inhibition and motor inhibition are dissociated, that is, independent mechanisms. The authors designed a set of six subtests by crossing two dichotomic variables, namely, absence vs. presence of a perceptual conflict, and absence vs. presence of a motor conflict, which led to four experimental conditions.…”

“…Now, the meaning of an absence of effect is generally overestimated, as it can result from a lot of factors not theoretically relevant, such as the power of the tests, the perceptiveness of the tools (floor and ceiling effects), and so on. To really argue such absence of effect, Nassauer and Halperin (2003) should report a control task where a significant interaction would be predicted and verified.…”