Objective performance measures and subjective ratings of visual awareness yield similar thresholds for detecting and discriminating visual stimuli, supporting the validity of both approaches. In a temporal two-alternative forced choice task, participants' accuracy in detecting stimulus presence and discriminating letter case was compared with their subjective ratings using the Perceptual Awareness Scale (PAS) at high and low contrast. Thresholds for objective and subjective measures showed a comparable pattern across tasks and contrast levels, suggesting that both methods provide converging information about the feature-content of a percept and are likely veridical measures of awareness.
Fractal dimension of brain activity—a measure of complexity beyond simple randomness—is lower in patients with disorders of consciousness than in healthy volunteers. Using fMRI data, fractal dimension was computed for cortical functional connectivity networks, adjacency matrices, and BOLD time-series. Healthy volunteers (n=15) had the highest fractal dimensions, followed by patients in a minimally conscious state (n=10), and patients in a vegetative state (n=8). Decreases in fractal dimension correlated with decreasing level of consciousness regardless of injury mechanism. The findings support the hypothesis that consciousness is associated with brain complexity and that fractal structures may indicate proximity to a critical point between low- and high-entropy states.
In binocular rivalry, when each eye sees a different image, perception alternates between the two. A small imbalance in the strength of the two stimuli strongly determines which image is seen first, even when the imbalance is too weak to affect how long each percept lasts. Only larger imbalances shorten percept durations. The interval between stimulus onset and the first percept, during which the two images appear fused, shortens as the imbalance increases, suggesting that the imbalance accelerates the process that sets the initial percept.