Cited by C.S. Sherrington, 'On Binocular Flicker and the Correlations of Activity of 'Corresponding' Retinal Points', Journal of Psychology 1 (1) (1904), pp. 26-60.
Description:

'Helmholtz in opposition to Panum [note: 'Physiologische Untersuchung über das Sehen mit zwei Augen, Keil, 1858.'] argued in favour of a purely psychical origin for 'prevalence of contours.' He invoked an explanatory 'direction of attention.' An inference he drew at the time regarding retinal rivalry accords with the inference drawn above from the flicker observations dealt with here, viz.[note: 'Physiologische Optik, 2 Auf., Leipzig, 1896, S. 921.']: "dass der Inhalt jedes einzelnen Sehfeldes, ohne durch organische Einrichtungen mit dem des anderen verschmolzen zu sein, zum Bewusstsein gelangt, und dass die Verschmelzung beider Sehfelder in ein gemeinsames Bild, wo sie vorkommt, also ein psychisches Act ist." A finely illustrative experiment on contours given by E. Hering [note: 'Hermann's Handbuch d. Physiologie, Bd. III. S. 921.'] is applicable in the same sense.' (58)

 

'Of binocular colour mixture E. Hering writes [note: Hermann's Handbuch der Physiologie, Bd. III. Tl. I. S. 596, 1879.']: "Hat man durch haploskopische Betrachtung zweier farbigen Flächen eine Mischfarbe erhalten und lässt dann genau dieselbe farbigen Lichtmengen auf eine und dieselbe Netzhautstelle fallen, so ergibt sich eine ungleich hellere oder weisslichere Mischfarbe." "Mischt man aber die beiden Farben binocular, so ist die resultirende Mischfarbe nur ungefähr gleich hell, wie die Einzelfarbe. Diese Thatsachen genügen schon, um selbst in den Fällen, wo die binoculare Mischung vollkommen gelingt, dieselbe der unocularen nicht gleichzustellen." With this conclusion my rule given above (page 50) is in complete agreement.' (59)

Cited by O.F.F. Grünbaum, 'On Intermittent Stimulation of the Retina (Part II)', Journal of Physiology 22 (6) (1898), pp. 433-450
Description:

'Two main theories have been suggested to explain the fact that intermittent retinal stimuli repeated above a certain frequency give rise to a steady sensation.

The older, which I shall in future style the "persistence theory," seems to have been suggested by d'Arcy

'Two main theories have been suggested to explain the fact that intermittent retinal stimuli repeated above a certain frequency give rise to a steady sensation.

The older, which I shall in future style the "persistence theory," seems to have been suggested by d'Arcy [note: 'Mem. Akd. Sci. p. 439. 1765.'] in 1765 and maintains that a steady sensation results from intermittent stimuli, when the intervening periods do not exceed the time of duration of the positive after-image of undiminished brightness: in fact, attempts were made by this observer to determine this quantity by noting the minimum freouency with which a burning coal must be rotated in order to produce a sensation of a ring of fire: 0.133 secs. was his estimation.

All subsequent writers, Plateau, Talbot, Helmholtz, etc. adopt d'Arcy's view, Fick [note: Hernann's Handbuch, III. p. 215. 1879.'] being the first to suggest an alternative. This author accepted Exner's [note: Sitzungsberichte Akad. Wein. LVIII. p. 601. 1868, and Pflüger's Archiv, III. p. 240. 1870.'] conclusion, that if the eye be exposed to black after having been stimulated by light, there is at first a rapid fall in the brightiness of the positive after-image, which then more gradually disappears; the curve representing the decrease and disappearance being of exactly a similar nature to that representing the growth of sensation produced by a white stimulus.

Fick diagrammatically represented the sensation resulting from intermittent stimulus by a serrated line, the abscissa being the timerelation and the ordinates the strength of sensation, and pointed out that if the frequency become great, the amplitude of oscillation of sensation diminishes until a frequency is reached at which a continuous smooth sensation results.

It is surprising that writers after Fick's explanation did not adopt his view, since even if Exner's statement that under normal conditions the duration of the after-image of undiminished brightness is infinitely short, be disallowed, nevertheless the persistence-theory seems unsatisfactory' (443-444)