Spatial Cues in 3D Visualization - Ambient Intelligence for Scientific Discovery - page 118

Fig. 10. This is an example of an initial resizing task trial with one shadow in a room
with a 'zig-zag' background surface of checkerboard texture. The task was to resize the
smaller sphere so as to match the size of the other slightly larger sphere displaced in
depth.
from the viewer; (4) the experimental trial software created 2D and 3D 'virtual
rooms' instead of 'virtual worlds;' and (5) the shadow condition always used
exactly one (unseen) light source, fixed and stationary at the azimuth position.
In the positioning task, subjects viewed 'virtual rooms' containing three equally-
sized, spherical objects suspended in space (see Fig. 8). Subjects were asked to
reposition one of the spheres, the target object, in 3D space (i.e. in the x, y and
z dimensions) as quickly and accurately as possible so as to symmetrically com-
plete a straight line segment (or vector/vector segment) characterized as three
spheres located equidistant from each other. In each positioning trial solution,
the correctly placed spheres always subtended an oblique angle from the viewer's
perspective, so that each of the three spheres were displaced at different depths
from the viewer.
In the resizing task, subjects viewed 'virtual rooms' containing two differently-
sized spheres suspended in 3D space (see Figs. 9 and 10). Unlike the positioning
task, in the resizing task, the objects were fixed in position. Subjects were asked
to adjust the size of the target object, as quickly and accurately as possible, to
make it correspond with the perceived size of the referent object. The target and
referent spheres were always positioned at different depths from the viewer, and
were always presented in different, and random, sizes and locations, relative to
each other. In one half of the trials, the target sphere was initially larger than the
referent, and in the other half of the trials, initially smaller. Consequently, from
trial to trial, subjects were randomly increasing, or decreasing, the size of the
target sphere. In both the positioning and resizing tasks, subjects manipulated
the target objects using a spaceball input device.