The contributions of anatomical studies to knowledge of perceptual processing

In many contemporary studies and textbooks perceptual processing is treated as a ‘pure sensory’ phenomenon, one that can be understood on the basis of pathways passing information from the sensory periphery to the cerebral cortex, for processing within the cortex and subsequent passage to motor centers or memory stores. However, many physiologists, psychologists and philosophers have recognized perceptual processing as closely dependent upon action (e.g. the ‘sensorimotor contingencies’ of O’Regan and Noë, 2001), although the anatomical nature of the functional links is generally left unresolved. A survey of pathways that pass messages through the thalamus to the cerebral cortex (visual, tactile etc.) shows that these are not ‘pure sensory’ pathways. They are generally branching axons that convey messages to lower, motor centers with one branch and to the thalamus with the other. That is, since the two branches will be transmitting the same message, the thalamic relay receives information not only about sensory events but also about concurrent instructions that are on the way to motor centers. This dual information, about sensory events and motor instructions, is an implicit part of the message that the thalamus passes to cortex. The axonal branching patterns reveal an anatomical basis of sensorimotor contingencies, which cortical mechanisms are not likely to ignore even when experimental studies do not reveal them.