The psychology of visual motion / by Henry J. Watt.

  • Watt, Henry J. (Henry Jackson), 1879-1925.
Date:
1913
Catalogue details

Licence: In copyright

Credit: The psychology of visual motion / by Henry J. Watt. Source: Wellcome Collection.

Provider: This material has been provided by The University of Glasgow Library. The original may be consulted at The University of Glasgow Library.

    11/20 (page 35)
    CIO “ Pseudo-movements, e.g. stroboscopic movements, produce C7—9 an after-effect exactly as an actual movement does.” “ The after-effect increases in one or several ways, within limits, with the number of stimuli simultaneously affecting a given area ol the retina, and or with the frequency with which the stimuli pass given retinal elements.” £10—13 “ The after-effect at first increases very rapidly with the objective velocity, but soon reaches a maximum and then gradually diminishes with further increase of speed.” £14 Quoted above. 7721,1—4 In the periphery of the field of vision the after-effect is at E 21, 5 first more vigorous, but diminishes and disappears very rapid l}7. “Any after-effect in a not-stimulated area is of opposite direction to that of the stimulated area.” [Not weaker or less rapid.] 77 5—6,1 Here Wohlgemuth says that “distinctness of contours is £28 not the essential factor in the production of the after- effect.” But it is evident from page 37 that “distinct- ness of contours” is only an alternative reading for “difference of brightness.” “After fatigue has been produced by a long series of movements alternating in sign (so that the after-effect is greatly reduced), the after-effect of movements at right angles to the direction of the previous ones is only very slightly affected, if at all.” £26 “ When several objective movements of different directions stimulate the same retinal area simultaneously or successively, an after-effect is produced which is the resultant of the after-effects of the various movements.” G1 obviously admits the influence of order aud (72 provides a better basis for its regular introduction. . Contour is the chief form of accentuation of visual position, so that the greater the number and frequency of the moving contours the greater the variation of orders (El—9). The impression of motion comes into full effectiveness more or less suddenly after a certain rate of motion has been obtained, but it becomes less clear with the higher velocities (E 8, 7710—13). 7714 calls for the operation of a factor which is independent of the division of the period between the light and dark portions. It is, on the other