[Visual Recognition of the Shitsukan, or Material Properties, of Objects]

Natural objects, such as animals, flowers, and wood, as well as artificial objects, such as Japanese lacquerware, glass, and metal coins, have their own shape and surface appearances. Although object shapes play important roles in visual object recognition, the material properties or Shitsukan of objects are relevant for the recognition of visual objects. In this review, we introduce recent advances in the understanding of the neural basis of the cognition of Shitsukan. First, we introduce the results of single-neuron recording studies that examined neuronal activity in the inferior temporal cortex of macaque monkeys in response to the presentation of two-dimensional and three-dimensional shapes. Next, we introduce the studies of neuronal response property to the Shitsukan of objects, such as color, texture, glossiness, and the combinations of these features. Then, we discuss how the selective responses to Shitsukan are constructed by hierarchical processing in the ventral visual cortical pathway, which consists of V1, V2, and V4. Finally, we discuss the encoding of Shitsukan information in the inferior temporal cortex.