An examination of holism in the visual processing of faces using the crowding effect and general recognition theory

Open Access
Author:
Sullivan, Brianna M
Graduate Program:
Psychology
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
April 28, 2008
Committee Members:
  • Michael J Wenger, Thesis Advisor
Keywords:
  • GRT
  • Crowding Effect
  • Holism
  • Face Processing
Abstract:
This study examined the extent to which holism in visual perception can be revealed by way of the presence or absence of crowding. Martelli, Majaj, and Pelli (2005) used crowding to propose an operational definition for holism. Specifically, they argued that holistic perception of an object is implicated if that object can be identified when the entire object is presented within an isolation field (defined as an area proportional to one-half eccentricity). Conversely, parts-based processing is implicated if identification is impaired when the entire object is within an isolation field, with an attenuation or elimination of that impairment when each part of the object is isolated by critical spacing. Martelli et al. found evidence of crowding—increases in threshold contrast as a function of eccentricity for faces and words—suggesting that foveally-presented objects are processed holistically, and peripherally-presented objects are processed by parts. This operational definition is considered from the perspective of general recognition theory (GRT, Ashby & Townsend, 1986). GRT provides theoretical characterizations of perceptual and decisional independence and separability, with violations of independence and separability allowing for multiple characterizations of holism. In this study, accuracy of identification responses was used to link Martelli et al.’s operational definition to the definitions of holism provided by GRT. Two sets of face stimuli were presented under conditions modeled on those used by Martelli et al. The faces were used to replicate the patterns documented by Martelli et al.: specifically, evidence for the benefit of a facial context in foveal presentation, and impairment in peripheral presentation—benefit and impairment that were eliminated in both presentations when critical spacing isolated the featural parts of the face stimuli. In addition, the GRT analyses revealed disparities between the current operational and theoretical definitions of holistic processing which suggest that the visual crowding effect cannot serve as a method for defining holism in face processing. These results contribute to a more systematic definition of holism, and an improved understanding of the visual processing of faces.