Objects are grouped into categories through a complex combination of statistical and structural regularities. We sought to better understand the neural responses to the structural features of object categories that result from implicit learning. Adult participants were exposed to 32 object categories that contained three structural properties: frequency, variability, and co-occurrences, during an implicit learning task. After this exposure, participants completed a recognition task and were then presented with blocks of learned object categories during fMRI sessions. Analyses were performed by extracting data from ROIs placed throughout the fusiform gyri and lateral occipital cortex and comparing the effects of the different structural properties throughout the ROIs. Behaviorally, we found that symbol category recognition was supported by frequency, but not variability. Neurally, we found that sensitivity to object categories was greater in the right hemisphere and increased as ROIs were moved posteriorly. Frequency and variability altered the brain activation while processing object categories, although the presence of learned co-occurrences did not. Moreover, variability and co-occurrence interacted as a function of ROI, with the posterior fusiform gyrus being most sensitive to this relationship. This result suggests that variability may guide the learner to relevant co-occurrences and this is supported by the posterior ventral temporal cortex. Broadly, our results suggest that the internal features of the categories themselves are key factors in the category learning system.

Complex visual–motor behaviors dominate human–environment interactions. Letter production, writing individual letters by hand, is an example of a complex visual–motor behavior composed of numerous behavioral components, including the required motor movements and the percepts that those motor movements create. By manipulating and isolating components of letter production, we provide experimental evidence that this complex visual–motor behavior is supported by a widespread neural system that is composed of smaller subsystems related to different sensorimotor components. Adult participants hand-printed letters with and without “ink” on an MR-safe digital writing tablet, perceived static and dynamic representations of their own handwritten letters, and perceived typeface letters during fMRI scanning. Our results can be summarized by three main findings: (1) Frontoparietal systems were associated with the motor component of letter production, whereas temporo-parietal systems were more associated with the visual component. (2) The more anterior regions of the left intraparietal sulcus were more associated with the motor component, whereas the more posterior regions were more associated with the visual component, with an area of visual–motor overlap in the posterior intraparietal sulcus. (3) The left posterior intraparietal sulcus and right fusiform gyrus responded similarly to both visual and motor components, and both regions also responded more during the perception of one's own handwritten letters compared with perceiving typed letters. These findings suggest that the neural systems recruited during complex visual–motor behaviors are composed of a set of interrelated sensorimotor subsystems that support the full behavior in different ways and, furthermore, that some of these subsystems can be rerecruited during passive perception in the absence of the full visual–motor behavior.