Brain oscillations are known to modulate detection of visual stimuli, but it is unclear if this is due to increased guess rate or decreased precision of the mental representation. Here we estimated quality and guess rate as a function of electroencephalography (EEG) brain activity using an orientation perception task. Errors on each trial were quantified as the difference between the target orientation and the orientation reported by participants with a response stimulus. Response errors were fitted to standard mixed model by Zhang and Luck (2008) to quantify how participants’ guess rate and standard deviation parameters varied as a function of brain activity. Twenty-four participants were included in the analysis. Within subjects, the power and phase of delta and theta post-target oscillatory activity were found to vary along with performance on the orientation perception task in that greater power and phase coherence in the 2-5 Hz band range was measured in trials with more accurate responses. In addition, the phase of delta and theta correlated with the degree of response error while oscillatory power did not have a relationship with trial-by-trial response errors. Analysis of task-related alpha activity yielded no significant results implying that alpha oscillations do not play an important role in orientation perception at single trial level. Across participants, only the standard deviation parameter correlated with oscillatory power in the high alpha and low beta frequency ranges. These results indicate that post-target power is associated with the precision of mental representations rather than the guess rate, both across trials within subjects and across subjects.
bioRxiv Subject Collection: Neuroscience