Takao SATO
Motion and depth perception with dichoptic-sequential presetntation of random-dot patterns
Abstract:It is known that apparent motion can not be perceived when two patterns of
random-dot kinematograms are presented dichoptically, although classical
apparent motion can be perceived under dichoptic and sequential(D-S)
presentation (Braddick, 1974). These results suggest that D-S motion perception is
dependent on dot-density. However, it is also known that stereoscopic perception
is possible with D-S presentation when SOA is small (Ogle, 1963). The relationship
between the two perception has not been clarified, since all past D-S studies
examine either only motion or only depth. To clarify the relationship, relative
frequency and accuracy of motion and depth perception were measured while
varying dot-density (1-50%), SOA (15-240 ms, ISI=0, SOA=duration), and disparity (3-
48'). Two 6属x6属 random-dot patterns (dot-size=3') with a central disparate square
target and an identical background were used. Each pattern was presented only
once. The subject's task was to say whether the target was in depth or in motion,
and then to discriminate direction of depth(near/far) or motion (right/left).
Depth perception was dominant at shorter SOAs(<100 ms), while motion perception
became dominant at longer SOAs(>100 ms). Relative frequency of depth decreased,
while that of motion increased as SOA was increased. At intermediate
SOAs, depth perception was more frequent with high dot-densities, but motion was
more frequent with low dot-densities, i.e. depth favors high, but motion favors low
dot-density. As for accuracy, it was nearly 100% for depth in favorable conditions,
but for motion, it was about 50% in most conditions. The perceived direction
depended almost completely on eye-order, i.e. rightward motion was perceived
when the first stimulus was presented to the right eye. Better motion-accuracies
were obtained only with very low dot density, long SOA, and large displacement,
i.e. conditions favorable for the classical motion. It is concluded that (1) Dichoptic
information is fed primarily into the stereo system when SOA is short, and that
(2) the short-range motion mechanism does not seem to functio under D-S
presentation; motion perception under D-S presentation is either eye-order-dependent
motion or classical apparent motion.