Cortical and striatal contributions to automaticity in information-integration categorization

Abstract

In information-integration categorization, accuracy is maximized only if information from two or more stimulus components is integrated at some pre-decisional stage. In many cases the optimal strategy is difficult or impossible to describe verbally. Evidence suggests that success in information-integration tasks depends on procedural learning that is mediated largely within the striatum. Although many studies have examined initial information-integration learning, little is known about how automaticity develops in information-integration tasks. To address this issue, each of ten human participants received feedback training on the same information-integration categories for more than 11,000 trials spread over 20 different training sessions. Sessions 2, 4, 10, and 20 were performed inside an MRI scanner. The following results stood out. 1) Automaticity developed between sessions 10 and 20. 2) Pre-automatic performance depended on the putamen, but not on the body and tail of the caudate nucleus. 3) Automatic performance depended only on cortical regions, particularly the supplementary and pre-supplementary motor areas. 4) Feedback processing was mainly associated with deactivations in motor and premotor regions of cortex, and in the ventral lateral prefrontal cortex. 5) The overall effects of practice were consistent with the existing literature on the development of automaticity.

Figure 1

The category structures for this experiment. Each stimulus was a circular sine-wave grating that varied across trials in spatial frequency (i.e., bar width) and bar orientation. Each plus denotes an exemplar of category A and each star denotes an exemplar of category B. The disk in the upper left is the prototype of category A (i.e., the category mean) and the disk in the lower right is the prototype of category B. The dashed line is the optimal category decision boundary.

Figure 2

Timing of a trial scaled in TR (one TR = 2,000 ms). The number of blank TRs between stimulus and feedback events was jittered with a truncated geometric distribution with p = 0.5 (max. 5 TRs). When at least one blank TR was inserted between the feedback and the following stimulus (~50% of the trials), a crosshair was displayed in the second half of the TR immediately preceding stimulus presentation.

Figure 3

(a) Individual accuracies of participants across the 20 sessions. (b) The mean accuracy across sessions. Error bars are standard errors. Scanning occurred on sessions 2, 4, 10, and 20.

Figure 4

Response times for individual subjects. Note that sessions 2, 4, 10 and 20 were completed inside the scanner. The thick line is the power function that best fits the mean RTs from sessions outside the scanner.

Figure 5

Group maps for the stimulus – baseline contrast (from the whole-brain analysis) for each scanning session. From left to right, 8 different axial slices are shown for each scanning session at the following MNI152 z coordinates: −8, −4, 0, 4, 8, 12, 16, and 20 respectively.