Experimentelle Bestimmung der Verrechnungszeiten beim Stereosehen anhand der verzögert wahrgenommenen Tiefenumkehr von bewegten, teilweise verdeckten Objekten

How much time does our visual system need to perform stereopsis? Viewed
pseudoscopically, an opaque square floating above a random-dot pattern
appears as a rectangular cut-out. When the pattern moves vertically
upwards, an illusory gap with undefined depth position is perceived at
the upper edge of the square. This phenomenon is called Delayed
Stereopsis Illusion (DSI). The "DSI-gap" carries the pattern of the
moving plane, its spatial depth, however, is perceived somewhere between
the moving pattern and the cut-out. In analogy with Julesz's "noman's-
land" we called this DSI-gap "trailing-edge no-man's-land". Its width
indicates the 3-D computation time needed to determine spatial depth of
the pattern, which virtually appears "from nowhere". Data were gathered
psychophysically with a computer generated model system. In three
experimental series E1-E3 14 subjects marked the width of the DSI-gap
under various welldefined conditions with two different methods. A total
of 881 single measurements were performed, 212 of them in E1, 384 in E2
and 285 in E3. The results indicate interindividually different 3-D
computation times between 50 and 80 ms. Learning, and pattern parameters
like spatial frequency did not significantly influence the perceived
width of the DSI-gap. Regarding the perceived shift of moving patterns
according to de Valois and de Valois (1991), an adequate correction of
the delays concluded from the measured DSI gaps is discussed. In any
case, the minimum presentation time of 17 ms, at which Julesz" dynamic
random-dot-stereograms are just recognizable, is much too short to
determine the position in depth in each single frame. The 3-D system
rather seems to check that the depth situation has not changed, and
maintains the percept of the floating square.