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4.3
Shadows
Objects casting shadows can provide more depth information about the relative
positions of objects viewed in space. When moving and positioning objects that
are casting shadows, the viewer recovers information about the location of the
object through the geometry that is implied by the position of the object's
shadow on the background surface.
However, the utility of shadows to improve spatial task performances in 2D
and 3D visual scenes is focused and limited. In our experiments, shadows were
most useful for enhancing object positioning (and not resizing) performances
when the scenes were viewed monoscopically, in 2D. The contributions of shad-
ows to the enhancement of object positioning performances when the scenes were
viewed in 'true 3D' stereo were negligible. Furthermore, when the object shadows
were cast on increasingly complex background surfaces and textures, positioning
task performances suffered. Also, shadows were useful only when there was one
light source. In scenes (in the 'virtual world' experiment) in which there were
two light sources, positioning performances were diminished to the same level at
which no shadows were present. Thus, there are caveats and limitations to the
ecacy of cast shadows in promoting spatial task performances in general.
4.4
Scene Background Complexity
The findings of the 'virtual world' and 'virtual room' experiments both suggest
that the introduction of more complex background scenery in visual 3D scenes
can impair the perception and understanding of the spatial attributes of other
objects contained within the scene. In general, having less complex detail in the
scenery background promotes a better understanding of the relative positions
and sizes of foreground objects. More complex background scenery introduces
“perceptual clutter” that seemingly disrupts the visual attention afforded to
foreground objects.
4.5
Gender
We deliberately balanced each of the three experiments by gender so that we
could analyze the effects of gender on these particular spatial tasks performances.
We expand the results originally presented in [60].
Table 1 summarizes relative task performances by gender. Males were more
accurate and faster than females recognizing and matching object shapes. Con-
sistent with the spatial abilities literature indicating a male advantage on men-
tal rotation tasks, it is not surprising that the male subjects outperformed the
females in accurately and quickly matching objects. Moreover, controlling the
motion of the right hand 'comparison object' significantly reduced male object
matching error rates, but had no effect on female error rates. Furthermore, males
were more accurate positioning objects, whereas females were more accurate re-
sizing objects (although there were no significant differences in male-female re-
sponse times for either of the positioning and resizing tasks). Also, males made
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