UC San Diego

In nature, organisms not only process what is in the environment, but also continuously use the sensory information gathered in planning and acting upon the environment. Thus a theory of perception which regards it as a passive, receptive process is not likely to provide a complete picture. Instead, we can view perception as intimately related to processes and brain areas which were traditionally viewed as motor or executive in nature. I have studied the neural substrates of human perception in different modalities and at different levels of complexity. There are three main research areas represented in this dissertation: 1) The sensorimotor neural bases of language; 2) Sensory and motor areas involved in biological motion perception; 3) Representations of visual space in higher cortical areas and their response properties. First, in neuropsychological studies, I have examined the extent to which language comprehension shares processing and neural resources with other complex non-linguistic skills. The results support a view of language as a system which has considerable behavioral and neural links with related non- linguistic skills and sensorimotor substrates. Second, I explored brain areas involved in the visual perception of actions represented with motion cues (point-light biological motion) in both neuropsychological and neuroimaging (fMRI) experiments. The results suggest that these stimuli are processed in not only posterior, motion- sensitive areas of the brain, but also in premotor areas in frontal cortex. Third, using fMRI, I have aimed to identify retinotopic maps in the human brain and to explore their functional properties. I found significant, well-defined retinotopic maps in multiple areas in the brain, including some which are not traditionally thought to be visual areas. Furthermore, retinotopic responses were affected both by the complexity of stimuli and by attention, with attention as important as visual stimuli in several areas. These experiments highlight the embodied nature of perception and show that perceptual processes show a great deal of flexibility to subserve a variety of goals, and rely on multiple levels of representations across multiple modalities, often times including significant involvement of motor or executive neural resources