'McDougall' [note: '"The Principle underlying Fechner's 'Paradoxical Experiment' and the Predominance of Contours in the struggle of two Visual Fields." This Journ. p. 114.'], in applying to 'retinal rivalry' and 'prevalence of contours' his principle of competition of inter-related nerve-elements for energy, also argues a "separateness of the visual cortical areas for the two eyes." He brings forward striking experiments in evidence of this. In one of these he [note: Mind, 1901, N.S. X. p. 56.'] shows that an after-image, left from excitation of one retina, is more strongly revived by subsequent weak diffuse excitation of that same retina than of its fellow. More recently, in experiments proving reinforcement of visual sensations by the activity of the ocular muscles, as evidenced by after-image observations, he [note: Mind, 1903, N.S. XII. p. 473.'] shows that activity of the intrinsic muscles of an eye sends up to the brain an influence, reinforcing the activity of the cerebro-retinal tract of that eye, while it exerts no such effect upon the corresponding tract of the other eye, or exerts it in a minor degree only.' (58)