An investigation of naming and category specific anomia using positron emission tomography

This thesis investigated the neural correlates associated with: (i) object and word processing and (ii) category specific object processing differences. The experiments confirmed the previous association of bilateral ventral occipital cortices with object processing, left extrasylvian temporal and parietal regions with semantic processing, and the left posterior inferior temporal cortex and frontal operculum with phonological retrieval. Experiment 1 differentiated, for the first time, 3 functionally distinct regions of the left ventral occipitotemporal cortex: a medial anterior region associated with semantic processing, a lateral region associated with phonological retrieval and a posterior region associated with object processing. This pattern was replicated in Experiment 2. Experiments 1, 2 and 3 also distinguished functional segregation in anterior inferior parietal cortices: a ventral region was associated with translating orthography into phonology and a dorsal region was associated with high demands on phonological processing. The former was activated implicitly in response to words, providing an anatomical basis for behaviourial evidence that implicit phonological processing is greater for words than objects. Experiments 4 and 5 investigated category specific object processing. Black and white outline drawings of natural relative to manmade objects activated bilateral anterior and right posterior temporal cortices. The right hemisphere regions were associated with the demands placed on object recognition. The left hemisphere region was associated with the demands placed on semantic processing. The results support 2 theories of category specificity: (i) anatomical segregation on the basis of perceptual and functional semantic knowledge with the former weighted for natural objects and the latter weighted for manmade objects, and (ii) the theory that natural objects place increased demands on pre-semantic object processing. Finally, Experiment 6 provides an example of the difficulties of applying functional imaging studies to patients