Abstract
Two theories define the relationship between sensory experience and perception of location. The doctrine of specific nerve energies relies on hard-wired, genetically specified relationships between stimulation and perception, modifiable only within limits by adaptation. In a newer sensorimotor account (O'Regan & Noë, BBS 2001), experience tunes the relationship between stimulation and perception and even the modality of experience. Vision for example is characterized by changes in input that correlate with eye and head movements, while audition requires change by head but not eye movements. Eye movements along a straight line result in no change in the retinal elements stimulated by the line, while movements along curved lines change the elements stimulated. Perception of pressure phosphenes can differentiate the two theories, because the phosphene appears at a location predicted by physiological optics and in a modality predicted by specific nerve energies. Moving a finger vertically along the eye's outer orbit while pressing on it through the lid during nasally directed gaze results in apparent motion of the phosphene out of phase with the finger, therefore contradicting information from motor efference to the finger, tactile sense at the fingertip, eyelid and bulb, joint receptors, and proprioception of muscles driving the finger. The contradiction between these observations and the sensorimotor account might occur because of limited time of the phosphene observation and simultantous contradictory information from the rest of the visual field. A test of the sensorimotor theory giving it every advantage had six observers in complete darkness moving their fingers along the eye, observing phosphenes for one hour and 2400 motion cycles; this extent of exposure is more than adequate for other sensory adjustments such as prism adaptation. The phosphene always obeyed the doctrine of specific nerve energies, and never adapted as the sensorimotor account predicts.