Bridgeman B, Huemer V
Department of Psychology, University of California, Santa Cruz, Santa Cruz 95064, USA.
Conscious Cogn. 1998 Sep;7(3):454-64. doi: 10.1006/ccog.1998.0357.
Visual information follows at least two branches in the human nervous system, following a common input stage: a cognitive "what" branch governs perception and experience, while a sensorimotor "how" branch handles visually guided behavior though its outputs are unconscious. The sensorimotor system is probed with an isomorphic task, requiring a 1:1 relationship between target position and motor response. The cognitive system, in contrast, is probed with a forced qualitative decision, expressed verbally, about the location of a target. Normally, the cognitive system is influenced by context-induced illusions of visual direction, while the sensorimotor system is not. Here, we inquire whether the process of making a spatially based decision is critical in forcing subjects to use the information in the cognitive system for spatial tasks. Subjects hear a tone that determines whether they jab an "X" or an "O" with the forefinger. Despite making a decision about which target to contact, the jab is not influenced by the position of a surrounding frame, indicating that choice can be handled within the context-insensitive sensorimotor system.
