L. Zemany et al., MOTION DETECTION ON FLASHED, STATIONARY PEDESTAL GRATINGS - EVIDENCE FOR AN OPPONENT-MOTION MECHANISM, Vision research, 38(6), 1998, pp. 795-812
Contrast thresholds were measured for discriminating left vs right mot
ion of a vertical, 1 c/deg luminance grating lasting for one cycle of
motion, This test was presented on a 1 c/deg stationary grating (pedes
tal) of twice-threshold, hashed for the duration of the test motion, L
u and Sperling [(1995), Vision Research, 35, 2697-2722] argue that the
visual system detects the underlying, first-order motion of the test
and is immune to the presence of the stationary pedestal (and the 'fea
ture wobble' which it induces), On the contrary, we observe that the s
tationary pedestal has large effects on motion detection at 7 and 15 H
z, and smaller effects at 0.9-3.7 Hz, evidenced by a spatial phase dep
endency between the stationary pedestal and moving test, At 15 Hz the
motion threshold drops as much as five-fold, with the stationary pedes
tal in the optimal spatial phase (i.e., pedestal and test spatially in
phase at middle of motion), and the perceived direction of the test m
otion reverses with the pedestal in the opposite phase. Phase dependen
cy was also explored using a very brief (similar to 1 msec) static ped
estal presented with the moving test, The pedestal of Lu and Sperling
(flashed for the duration of the test) has a broad spectrum of left an
d right moving components which interact with the moving test, The ped
estal effects can he explained by the visual system's much higher sens
itivity to the difference of the contrast of right vs left moving comp
onents than to either component alone. (C) 1998 Elsevier Science Ltd.
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