How the brain detects invariance and inhibits variance during category induction.

A stepwise category-learning task was designed to examine brain activation associated with invariance detection and variance inhibition during category induction (CI). Three stimuli were displayed sequentially and participants were asked to learn the target category based on the invariant feature among stimuli. The processes of invariance detection and variance inhibition were necessary during certain events; however, these processes were not required for other events. Functional magnetic resonance imaging (fMRI) results indicated that the processes of detecting invariant features and inhibiting variant features were associated with significant activation in the left prefrontal cortex, including the left superior frontal gyrus, middle frontal gyrus, and mid-ventrolateral prefrontal cortex, as well as other regions (e.g., bilateral parietal cortex and putamen). These findings confirmed the important role of the fronto-parietal network and striatum in the invariance detection of category learning.