title: Estimates of shape by eye, or, the little invariant that could.
abstract: Five experiments were conducted to test the hypothesis that observers apprehend specific constancies under change in perspective. The constancies were projective properties of ellipses pictured to slant and tilt in depth. Observers were asked to reproduce the static upright view of a moving pair of ellipses, using a computer graphics display and interface. Projective invariants for pairs of conics were computed on the observers' productions. A few experimental conditions revealed near-perfect performance. When pairs of coplanar ellipses were viewed under dynamic transformation in perspective, then invariants calculated on the observers' productions were a match--in value on average--to the invariants of the transforming ellipse pairs. It is proposed that measures of projective properties afford a family of techniques that can be applied to gauge acuity for complex shapes in the study of visual form perception.
authors.affiliation: Air Force Research Laboratory (AL/HRAE), Mesa, AZ 85206-0904, USA.
authors.forename: K K
authors.initials: KK
authors.lastname: Niall
mesh_terms: D000704:Analysis of Variance; D005260:Female; D005556:Form Perception; D006801:Humans; D008297:Male; D012044:Regression Analysis; D013028:Space Perception; D014792:Visual Acuity