EXPERIMENT 2
In the next experiment, to further verify that the initial trajectory
has no bearing on the direction of the perceived displacement, we designed
the flash and ring to appear on the screen at the same time, with the
movement of the ring beginning only in the next frame (Fig 1b in
manuscript). Thus, there is no trajectory (no previous motion) from
which to extrapolate. The results are unchanged from Fig. 1a,
strengthening the conclusion that only events after the flash
determine the perception. This paradigm is analogous to the
'flash-initiated cycle' used by Khurana and Nijhawan (1995); however,
the present result makes their interpretation of motion extrapolation
untenable. The juxtaposition of our Fig. 1a and 1b suggests that the
flash resets the motion integration in the visual system, making
motion after the flash effectively like motion that starts de novo
(as in Fig. 1b). One explanation may be that the flash temporarily
redirects attention
Click for an MPEG demonstration .
Note on the movie: for the purposes of demonstration, this movie shows
the 3 conditions sequentially (up, down, and stopped), and the
flash appears exactly in the middle of the ring each time. In the
real experiments, conditions were randomly interleaved, and the flash
was placed in different positions for quantification of the illusory displacement. Also, the size
of the presentation is much reduced for the movie, and the frame rate
will play differently on different browsers.
For more information, please see our manuscript: D. M. Eagleman and
T. J. Sejnowski, "Motion Integration and Postdiction in Visual
Awareness", Science, 287(5460), 2000.
Updated 2/2000, DME