'before making use of rotating discs for contrast phenomena it is needful, as a control, to see whether differences of mere radial distance influence the results. Marbe [note: 'Wundt's Philosophienstudien, XII. 280.'] and Schenk [sic. throughout] [note: 'Pflüger's Archiv, LXIV. p. 165. 1896.'] (with Schmidt) have examined this point on discs with alternate equal black and white sectors. The former finds fusion rather more easy along arcs further from than nearer to the centre of the disc; the latter that with increasing speed of rotation "flickering" persists longer in the peripheral zone than in the central.' (35-36)

'My results in this matter - as far as I have, in the above manner, studied it - agree with Marbe when the luminosity is low, with Schenk when the luminosity is high. To the question for which I particularly desired an answer I obtained the reply that in regard to the influence of radial distance upon "flicker" it is but small.' (37)

'Another excellent investigation by Schenk (and Schmidt) [note: 'Pflüger's Archiv, LXIV. p. 165. 1896.'] deals with "flicker" as influenced by the angular width of the sector. Filehne [note: 'v. Graefe's Archiv, XXXI. p. 20.'] noticed that with discs of equal alternate black and white sectors the frequency of intermittence of stimulation is not in exact agreement when discs of many sectors are compared with discs of few sectors. The discs of many sectors have, to extinguish flicker, to rotate relatively faster than theory demands. Mere linear velocity seems to assist the fusion of the sector sensations. Schenk's [note: 'loc. cit.'] examination of this phenomenon serves as a control in this respect for experiments brought forward in my communication. Fick [note: 'Cp. Schenk, loc. cit.']  had suggested that unnoticed movements of the eyeballs may be responsible for Filehne's phenomenon. Concordantly witlh that suggestion Schenk finds it very greatly reduced when the observations are carried on through a narrow slit cut radially to the disc in a screen covering the latter.' (37)

'Fick found that under certain conditions 170 alternations might be necessary to produce fusion; this was the case when parallel lines were drawn on a drum which was rotated around an axis parallel to the lines: if, however, the observations were made through a slit no flicker was seen above 40 per second.

Baader [note: 'Dissert. Freiberg, 1891 (quoted from Schenk).'] experimenting independently made similar observations, and came to the conclusion that the size of the field of vision was a factor that must be taken into consideration when determining the speed of alternation necessary to produce fusion.' (396)

Schenk [note: 'Pflüger's Archiv LXIV. p. 165. 1896.'] has recently taken up the question [of variations of rates at which flicker ceases under different experimental conditions], and found that in his own case fusion occurred when making observations through a definite aperture, on rotating discs with a variable number of black sectors, at approximately the same speed in all cases; a variation in the same direction as found by Filehne, Fick and Baader occurred in observations made by Schenk's co-observer Schmidt.' (397)

'In 1885, Marey's associate Adolph-Moïse Bloch adapted a version of the intermittently-obscured lamps that William Henry Fox Talbot and Simon von Stampfer had developed during the 1830s to physiological investigation. Where Talbot sought to measure light intensity itself, Bloch sought to establish a law regarding the rates at which individual sensation-flashes produced a continuous light-sensation under different conditions (Bloch 1885, 493-495; Schickore 2006, 254-255). Such studies prompted a range of physiological investigations into Stampfer's 'stroboscopic' effects during the 1890s (e.g. Charpentier 1890; Schenck 1896; Marbe 1898).'