An analysis of letter expertise in a levels-of-categorization framework

While there has been increasing effort in dissociating the neural substrates recruited by perception of different objects, the theoretical and behavioural work needed to understand such dissociation lags behind. In an attempt to compare expertise in letter and face perception, we outline a theoretical framework that characterizes different types of object expertise based on the task demand (level of abstraction) required in object categorization. Face perception requires categorization at a subordinate level, whereas letter perception involves mainly basic-level categorization. Accordingly face and letter perception should represent two different types of expertise and display different neural and behavioural markers. Results from three behavioural experiments supported the predictions of the framework in that letter expertise is characterized by an enhancement of the basic-level advantage, instead of its attenuation as typically found for face perception. We compare this framework with Farah's taxonomy of visual abilities based on cooccurrence of deficits in visual agnosias.