Abstract
Several studies have suggested that the centro-parietal positivity (CPP), an EEG potential occurring approximately 500 ms post-stimulus, reflects the accumulation of evidence for making a decision. Yet, most previous studies of the CPP focused exclusively on perceptual decisions with very simple stimuli. In this study, we examined how the dynamics of the CPP depended on the type of decision being made, and whether its slope was related to parameters of an accumulator model of decision making. We show initial evidence that memory- and perceptual decisions about carefully-controlled face stimuli exhibit similar dynamics, but offset by a time difference in decision onset. Importantly, the individual-trial slopes of the CPP are related to the accumulator model’s drift parameter. These findings help to further understand the role of the CPP across different kinds of decisions.
Highlights
Accumulator models of decision making have been very successful in accounting for behavioural data in various decision making paradigms
Our study shows that the centro-parietal positivity (CPP), which was previously suggested to be a neural correlate of a decision variable during a perceptual decision making task, exhibits dynamics somewhat consistent with being a decision variable during more complex decisions
The CPP effects occur later for the perceptual condition relative to the memory condition, most likely because these trials have a non-decision time that is approximately 300 ms longer, as we demonstrated with our drift diffusion model fits (Table 1)
Summary
Accumulator models of decision making have been very successful in accounting for behavioural data in various decision making paradigms. Van Vugt et al (2012) examined what brain oscillations would show a signal dynamics consistent with the accumulation of evidence over time, and demonstrated that parietal 4–9 Hz theta oscillations covaried with the accumulation of evidence during a random dot motion task In other words, they found that the power of theta oscillations increased until the moment of the response in trials in which there was information to be accumulated, while theta power stayed flat in control trials in which there was no information to be accumulated, apart from the stimuli that were being presented. The CPP gradual build-up predicted by accumulator models is visible for both perceptual and memory decisions, and—importantly—its slope covaries with estimates of drift parameters of the DDM in line with the idea that the CPP is a specific reflection of the evidence accumulation process
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