We show that EEG stimulus-locked negative peaks occurring between 150 and 275 milliseconds (N200 latencies) reflect visual processing time that occurs before evidence accumulation, labeled visual encoding time (VET), in the context of drift-diffusion theory of human decision making of reaction time and choice. VET was found to be a component of non-decision time, allowing accurate time measurements of VET, decision-time, and residual motor response during decision-making. We confirm this finding across multiple subjects by directly testing 1-to-1 relationships between EEG potentials and non-decision time parameters with Bayes Factors using the Savage-Dickey ratio, calculated from posterior distributions of hierarchical Bayesian parameters. We also directly test this hypothesis by quantifying 1-to-1 slope relationships in linear regression between EEG potentials and reaction time percentiles, methods more immune to contaminant trials due to subject mind-wandering. By confirming VET as the first component of non-decision time, we then estimate residual motor response time. These combined neurocognitive techniques (merging Cognitive Neuroscience techniques with Mathematical Psychology theory) add to existing knowledge of the chronometry of human neural networks and allow accurate measurement of processing stages during simple human decision making.
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