'It is doubtful... to me whether the slight excess in brightness of the binocular image over its two equal uniocular components is really explicable as summation of the intensities of the reactions at the corresponding spots of the two retinae. Valerius [note: 'Poggendorff's Annalen, Bd. CL. S. 117, 1873.'] measured the increase to be one-fifteenth of the brightness of the uniocular image. Aubert's [note: 'Physiologie d. Netzhaut, S. 286, Breslau, 1865.'] diagram gives it as less than one-thirtieth.' (49)

That a perception initiated from corresponding retinal points is commonly referred without ambiguity to a single locus in visual space has often been regarded... as evidence of community of the nerve apparatus belonging to the paired retinal points... Later (cf. Aubert), the visual singleness, spatial fusion of right and left impressions to a single perception, was taken to mean confluence of the nerve-processes, started in right and left retinae respectively, to "a single common centre or point of the sensorium [note: Physiol, d. Netzhaut, 1865.']."' (53)