Adult Plasticity of a Binocular Integration Mechanism

Open Access
Hwang, Kenneth Robert
Graduate Program:
Master of Science
Document Type:
Master Thesis
Date of Defense:
May 16, 2012
Committee Members:
  • Rick Owen Gilmore, Thesis Advisor
  • binocular
  • vision
  • experience
  • plasticity
  • adaptation
Although the visual system’s susceptibility to plasticity early in development is especially pronounced (Hubel and Wiesel, 1965, 1970), research has shown that plasticity occurs in adult visual processing as well (Gilbert, 1992; Heinen & Skavenski, 1991). Previous research (Hollins & Hudnell, 1980; Klink, Brascamp, Blake, & Van Wezel, 2010) has proposed that inducing adult plasticity is possible through visual adaptation to dichoptically incongruent spatial gratings, so that each eye sees an independent image. This type of viewing produces a perceptual phenomenon called binocular rivalry. The visual system’s incapability of focusing on both images simultaneously subjects the viewer to constant perceptual switching, so that only one image dominates perceptual awareness at a time (Alias & Blake, 2005). Prolonged binocular rivalry may thus impose experience-driven plasticity on the binocular integration system. Persistent viewing of incongruent images weakens an interocular inhibition mechanism that normally suppresses the binocular integration of opposing stimuli, and remains weakened until exposed to normal, congruent binocular vision once more (Hollins & Hudnell, 1980; Klink et al., 2010). Perceptually, the viewer increasingly experiences mixtures of incongruent images or decreasing perceptual exclusivity. The present study extended this paradigm by randomly assigning participants to one of four interocular orientation difference (IOD) groups (90º, 45º, 37.5º, and 30º). It was expected that reducing IOD would also reduce interocular inhibition. The manipulation permits a direct test of the hypothesis that perceptual adaptation stems from weakened interocular inhibition. A significant reduction in perceptual exclusivity was found between the 30º IOD and other IOD conditions, as well as between the 37.5º and 45º IOD conditions. However, the study failed to produce decreased perceptual exclusivity with respect to time for any IOD condition, including the 90º IOD which was intended to replicate experimental conditions utilized in previous research (Hollins & Hudnell, 1980; Klink et al., 2010). The discrepancy in these findings may stem from a larger (n=60), more diverse, and inexperienced sample of observers. It is also possible that the small IOD conditions fell within a perceptual threshold that begins to elicit stereopsis (Blakemore, Fiorentini, & Maffei, 1972) in observers, despite the lack of adaptation effects.