Evidence for an all-or-none perceptual response: single-trial analyses of magnetoencephalography signals indicate an abrupt transition between visual perception and its absence.
Neuroscience March 29, 2012 K Sekar, W M Findley, R R Llinás
Whether consciousness is all-or-none or graded remains debated. In a magnetoencephalography (MEG) study using sub-threshold, threshold, and supra-threshold duration inputs, averaged evoked responses showed a gradual increase in amplitude with increasing perceptual strength. However, single-trial analyses demonstrated that stimulus perception correlated with an all-or-none response, the temporal precision of which increased systematically as perception transitioned from ambiguous to robust states. Due to poor signal-to-noise resolution, whether perception-related responses were invariant in amplitude could not be unambiguously demonstrated. The findings strongly suggest that visual perception of simple stimuli is associated with an all-or-none cortical-evoked response whose temporal precision varies with perceptual strength.