The human ventral stream consists of regions in the lateral and ventral aspects of the occipital and temporal lobes and is involved in visual recognition. One robust characteristic of selectivity in the adult human ventral stream is category selectivity. Category selectivity is manifested by both a regional preference to particular object categories, such as faces, places and bodyparts, as well as in specific (and reproducible) distributed response patterns across the ventral stream for different object categories. However, it is not well understood how these representations come about throughout development and how experience modifies these representations and how do. I will describe two sets of experiments in which we addressed these important questions. First, I will describe experiments in which we examined changes in category selectivity throughout development from middle childhood (7-11 years), through adolescence (12-16) into adulthood. Surprisingly, we find that it takes more than a decade for the development of adult-like face and place-selective regions. In contrast, the lateral occipital object-selective region showed an adult-like profile by age 7. Further, recent findings from our research indicate that face-selective regions have a particularly prolonged development as they continue develop through adolescence in correlation with improved face, but not object or scene recognition memory. Development manifests as increases in the size of face-selective regions, increases in face-selectivity as well as increases in the distinctiveness of distributed response patterns to faces compared to nonfaces. Second, I will describe experiments in adults in which we examined the effect of repetition on categorical responses in the ventral stream. Repeating objects decreases responses in the human ventral stream. Repetition in lateral ventral regions manifests as a proportional effects in which responses to repeated objects are a constant fraction of nonrepeating stimuli with no change in selectivity. In contrast in medial ventral temporal cortex, we find differential effects across time scales whereby immediate repetitions produce proportional effects, but long-lagged repetitions sharpen responses, increasing category selectivity. Finally, I will discuss the implications of these results on plasticity in the ventral stream and our theoretical models linking between fMRI measurements and the underlying neural mechanisms.
