Neurosemantics of Visual Objects

Humans, like several other primates, are visual creatures, and almost half of our neurons are devoted to the processing of visual signals. The excellence found in our ability to do so, is not just due to our ophthalmological capabilities, which are outperformed by other species, such as birds, it is instead on the semantic side, in our ability to classify hundreds of object categories on the basis of their visual appearance only. Vision has historically been the earliest and most investigated function in the brain, thanks to its unique correspondence between the two dimensional organization of the distal stimulus and cortical processing units. Taken together, these two factors have led us to investigating the semantics of objects whose essential features are captured by their visual appearance. The first model presented in this chapter is a sort of prelude to a full blown semantics, with a simulation of the full visual pathway that brings light signals into recognition of object categories, together with the auditory pathway, in a simulation of the emergence of a first lexicon, that in infants begins exactly with visual objects. Most of the components of this model, and the methods used for its development and subsequent analyses, will be shared by the models that follow. The second model presented in this chapter, taps into a range of semantic phenomena typically observed in the early stages of language development in children, such as the change in the speed of learning, and the so called “fast-mapping” phenomenon.