Effects of parametric manipulation of inter-stimulus similarity on 3D object categorization

Shimon Edelman, Heinrich Bulthoff, Isabelle Bülthoff

Research output: Contribution to journalArticle

11 Citations (Scopus)

Abstract

To explore the nature of the representation space of 3D objects, we studied human performance in forced-choice categorization of objects composed of four geon-like parts emanating from a common center. Two categories were defined by prototypical objects, distinguished by qualitative properties of their parts (bulging vs waist-like limbs). Subjects were trained to discriminate between the two prototypes (shown briefly, from a number of viewpoints, in stereo) in a 1-interval forced-choice task, until they reached a 90% correct-response performance level. After training, in the first experiment, 11 subjects were tested on shapes obtained by varying the prototypical parameters both orthogonally (ORTHO) and in parallel (PARA) to the line connecting the prototypes in the parameter space. For the eight subjects who performed above chance, the error rate increased with the ORTHO parameter-space displacement between the stimulus and the corresponding prototype; the effect of the PARA displacement was weaker. Thus, the parameter-space location of the stimuli mattered more than the qualitative contrasts, which were always present. To find out whether both prototypes or just the nearest one to the test shape influenced the decision, in the second experiment we varied the similarity between the categories. Specifically, in the test stage trials the distance between the two prototypes could assume one of three values (FAR, INTERMEDIATE, and NEAR). For the 13 subjects who performed above chance, the error rate (on physically identical stimuli) in the NEAR condition was higher than in the other two conditions. The results of the two experiments contradict the prediction of theories that postulate exclusive reliance on qualitative contrasts, and support the notion of a representation space in which distances to more than one reference point or prototype are encoded.

Original languageEnglish
Pages (from-to)107-123
Number of pages17
JournalSpatial Vision
Volume12
Issue number1
Publication statusPublished - 1999 Jan 1
Externally publishedYes

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ASJC Scopus subject areas

  • Biophysics
  • Computer Vision and Pattern Recognition
  • Psychology(all)

Cite this

Effects of parametric manipulation of inter-stimulus similarity on 3D object categorization. / Edelman, Shimon; Bulthoff, Heinrich; Bülthoff, Isabelle.

In: Spatial Vision, Vol. 12, No. 1, 01.01.1999, p. 107-123.

Research output: Contribution to journalArticle

Edelman, Shimon ; Bulthoff, Heinrich ; Bülthoff, Isabelle. / Effects of parametric manipulation of inter-stimulus similarity on 3D object categorization. In: Spatial Vision. 1999 ; Vol. 12, No. 1. pp. 107-123.
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