'To Hering we owe especially important observations on the subject. By him the reciprocal process influencing the excitability of retinal points across space or time is referred to as "induction."' (33)

'the delicacy of the flicker method led me to enquire whether "flicker" may be applied with success to the exarnination of the influence exerted on the intensity of light-sensations by contrast both of place and time, that is, using Hering's term "induction," by areal and by temporal induction.' (35)

'At the basis of the phenomenon of simultaneous contrast lies, as Fechner [note: 'Poggendorff's Annal. XXXVII, XLIV. &c. 1837, &c.'], Mach [note: 'Sitzungsb. d. kais. Akad. d. Wiss. Wien, 1866 &c.'], and Hering [note: 'Sitzungsb. d. kais. Akad. d. Wiss. Wien, 1872 and later.'] may be said to have proved, a reciprocal physiological relation between units of the retino-cerebral apparatus such that activity of the apparatus connected with a point of retinal surface P affects the reactions of the apparatus belonging to the retinal area circumjacent about P. This reciprocity, subconscious in origin, affects consciousness; it is a factor in the production of sensations, and influences inferences dependent upon comparison of those sensations. So intrusive is it psychologically that Joh. Müller [note: Physiologie, 1841. Bk. V., Sect. 1, Cap. 3.'] and Helmholtz [note: Physiol. Optik.p. 417. Part II. 1860.'] treated it as wholly a product of processes of judgment, a doctrine ably controverted by Hering.' (38)

'The question whether "white-black value" alone or "colour-brightness value" with " white-black value" (Hering) has to be reckoned with in flicker-photometry, has been recently treated by Schenk [note: Pflüger's Archiv, LXIV. p. 607. 1896.']. In connection with that interesting work it is noteworthy that the replacement of yellow (chrome) in disc (figure 1) by white (chinese) does not appreciably increase the difference in flicker between the two ring-bands.' (43)

'The above experiment proves a difference in excitability in the retinal apparatus to have been induced in the places of incidence of stimuli Bl and Bl', and that without permitting consciousness of any difference between the backgrounds. Consciousness of that difference is thus excluded altogether from the problem. This result quite supports Hering's position as to "simultaneous contrast." "Simultaneous-contrast " and "reciprocity-flicker" are obviously related: both are properties of the same surfaces, e.g. the above discs. The view that the former arises in "judgment" clearly accords less with that naturally suggested by the foregoing examination of the latter than the view which considers contrast to be of subconscious physiological origin. But I hold that an "areal induction flicker" experiment cannot directly contribute to a "simultaneous contrast" discussion. Accurate comparison between the flickering colour from ring-band Bl Bk' and the steady colour from ring-band Bl' Bk is difficult, if not impossible. So long as a sensation is of markedly flickering quality its intermittence obscures its other qualities.' (44-45)