Is visual consciousness graded? : A comparison of conscious detection and identification

Sammanfattning

A current controversy in the science of visual consciousness is whether conscious awareness of a stimulus emerges gradually or appears directly in an all-or-none fashion. Windey et al. (2013) observed that evidence supporting the gradual explanation often used low-level stimuli (simple shapes, colours), while evidence for a dichotomous divide of awareness used high-level stimuli (letters, numbers). Windey later constructed the level of processing (LoP) hypothesis, which states that different stimulus levels impact the transition to awareness, i.e. whether it occurs gradually or in an all-or-none fashion. Koivisto et al. (2017) further showed, using high-level stimulus, that different conceptualizations of awareness (detection and identification) impact different electrophysiological correlates of awareness. Specifically, the visual awareness negativity (VAN) only occurred for awareness based on detection, while the late positivity (LP) occurred for both detection and identification. The purpose of this thesis is to further investigate the VAN and LP for detection and identification, but with a low-level stimulus. Following the level of processing hypothesis, I expect that the mean amplitudes will be more negative in the VAN time range and more positive in the LP time range for identification trials compared to detection trials. Similarly, I expect VAN and LP to occur for both detection and identification. Unfortunately, the current results did not find any significant differences due to the low sample size. However, the results for the identification threshold hint towards a VAN but no LP.