Electrophysiological correlates of detection and identification awareness for digits and letters.

A central feature of consciousness is the association between external events and subjective experiences of content. These experiences range from low level (detection) to high level (identification). For example, a visual experience may range from seeing something on a computer screen (detection) to seeing the digit 3 (identification). In research, neural processes that correlate with these experiences are called neural correlates of consciousness (NCCs). In vision, a candidate NCC is the visual awareness negativity (VAN) that is derived from event-related potentials, occurring about 200 ms after stimulus onset over posterior electrode sites. Because previous research does not resolve whether VAN is more sensitive to low-level experiences (detection awareness) than high-level experiences (identification awareness), we conducted two preregistered experiments. In both experiments, two staircases continuously adjusted stimulus opacity to separately target detection awareness and identification awareness. In Experiment 1, subjects viewed either individual digits (N = 15) or individual letters or digits (N = 15). For both types of stimuli, VAN was similarly sensitive to detection awareness and identification awareness. As a follow up, Experiment 2 (N = 28) examined whether stimulus size affects VAN to identification awareness using digit stimuli. Results showed identification VAN for both digit sizes, and VAN was unaffected by stimulus size. These results confirm the sensitivity of VAN to both low-level experiences (detection) and high-level experiences (identification). However, results emphasize the limited specificity of VAN in separating between low-level and high-level experiences, suggested by the similarity of VAN in both conditions.