On objective and subjective visual perception
- Author(s): Knotts, Jeffrey David
- Advisor(s): Lau, Hakwan
- et al.
GOAL: The goal of this dissertation is to investigate three major questions in the field of conscious visual perception. First, to what extent do objective and subjective perception dissociate in normal observers? Second, is prefrontal cortex necessary for conscious awareness? Third, is phenomenology rich or sparse, and what would an effective operational approach to this question look like? These questions are examined in three sets of experiments with human subjects, summarized by the following aims.
AIM 1: Investigating the impacts of binocular suppression and monocular pattern masking on the relationship between objective and subjective perception in normal observers. There is considerable disagreement in the literature about whether or not normal human observers can perform forced-choice perceptual tasks unconsciously (e.g., Kolb & Braun, 1995; Morgan, Mason, & Solomon, 1997; Peters & Lau, 2015). In the first study of this dissertation, we examined whether any of four commonly used visual suppression techniques can facilitate unconscious forced-choice orientation discrimination. In three initial experiments we looked for differences in the relationship between objective and subjective perception under different pairs of monocular and binocular suppression techniques by comparing each pair directly in an unbiased two-interval forced choice paradigm. In a fourth experiment, we examined whether continuous flash suppression can facilitate absolute unconscious perception using a similar two- interval forced choice task.
AIM 2: Using decoded fMRI neurofeedback to investigate the role of prefrontal cortex in the conscious perception of color. A second debate in consciousness science concerns whether prefrontal cortex is critical for conscious visual perception. Some metacognitive theories hypothesize that the frontoparietal activity underlying perceptual confidence judgments is indeed critical for consciousness. In the second study of this dissertation, we decoded multivariate functional magnetic resonance imaging (fMRI) patterns corresponding to perceptual confidence. We then used neurofeedback to test a potential causal relationship between activation of decoded confidence patterns and the subjective experience of color.
AIM 3: Investigating the richness of phenomenology by looking for subjective inflation effects in dot motion discrimination. A third major debate concerns whether visual phenomenology is rich or sparse. In the third part of this dissertation we review this debate and argue that subjective inflation, an effect in which peripheral or minimally attended perception appears to be subjectively richer than would be expected based on objective performance, may provide an intermediate answer: phenomenology is sparse, but it is subjectively inflated such that it feels rich. We then use a series of psychophysical experiments to test the extent to which subjective inflation occurs for random dot motion discrimination at different retinal eccentricities, and discuss the results in terms of the richness debate.