Abstract
Three experiments were conducted to test Hoffman and Richards's (1984)
hypothesis that, for purposes of visual recognition, the human visual
system divides three-dimensional shapes into parts at negative minima
of curvature. In the first two experiments, subjects observed a simulated
object (surface of revolution) rotating about a vertical axis, followed
by a display of four alternative parts. They were asked to select
a part that was from the object. Two of the four parts were divided
at negative minima of curvature and two at positive maxima. When
both a minima part and a maxima part from the object were presented
on each trial (experiment 1), most of the correct responses were
minima parts (101 versus 55). When only one part from the object--either
a minima part or a maxima part--was shown on each trial (experiment
2), accuracy on trials with correct minima parts and correct maxima
parts did not differ significantly. However, some subjects indicated
that they reversed figure and ground, thereby changing maxima parts
into minima parts. In experiment 3, subjects marked apparent part
boundaries. 81\% of these marks indicated minima parts, 10\% of the
marks indicated maxima parts, and 9\% of the marks were at other
positions. These results provide converging evidence, from two different
methods, which supports Hoffman and Richard's minima rule.
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