What's the difference between a tiger and a cat? From visual object to semantic concept via the perirhinal cortex.

Editor's Note: These short, critical reviews of recent papers in the Journal, written exclusively by graduate students or postdoctoral fellows, are intended to summarize the important findings of the paper and provide additional insight and commentary. For more information on the format and purpose of the Journal Club, please see Review of Clarke and Tyler When we see an object, we interpret the visual image that is projected on the retina , giving it meaning. The transformation from visual image to meaningful object takes place along the human ven-tral visual stream. Early in the ventral stream, brain activity represents low-level visual information, such as orientation and contrast. Higher up in the ventral stream, in posterior inferior temporal (IT) cortex, brain activity represents high-level object information. This includes a broad categorical organization of individual objects based on biological relevance, reflecting , for example, the division between animate and inanimate objects and between faces and places (Kriegeskorte et al. 2008b; Mur et al., 2012). Category membership is an important piece of information for object recognition. However, knowing which category an object belongs to is not sufficient for identifying individual objects, especially those which belong to the same category. Successful recognition of individual objects requires object-specific knowledge. This is knowledge which allows us to distinguish, for example, a tiger from a domestic cat. The combination of four legs, fur, and a carnivorous diet is not specific enough to distinguish these two objects. Additional information is needed, in particular information about features that are not shared between a tiger and a domestic cat, for example size and potential threat. In fact, many objects we encounter in life cannot be distinguished based on a few simple feature combinations. Successful discrimination requires a rich multidimensional representation that captures the complex feature conjunctions that make each object unique. Where in the brain is this object-specific knowledge represented? One strong candidate is the anterior temporal lobe (ATL). Damage to the medial ATL, especially perirhinal cortex, has been reported to impair the discrimination of objects that have a high degree of feature overlap (Bussey et al., 2005). Semantic de-mentia, a degenerative neuropathology characterized by an impaired capacity to identify specific objects, affects neurons primarily in ATL. Critically, this impairment in object-specific knowledge does not appear to affect one sensory modality in particular. For instance, cueing a patient with an image of a tiger, or the sound of a tiger's …