Investigating the Presence of 'Leaky' Accumulation in a Human Evidence Integration Signal

Abstract

A feature common across sequential sampling models is that decisions are formed by accumulating sensory information up to an action-triggering bound. Aside from this central ingredient, numerous model variants exist that invoke distinct algorithmic elements and adaptations. A key area of disagreement has been whether decisions are achieved by integrating evidence 'perfectly', without the loss of already obtained information, or whether evidence accumulation is subject to 'leak' whereby older samples of information are discarded or lost as time passes. The present study used EEG to investigate a previously identified signal of human evidence accumulation (the centro-parietal positivity; CPP) for signatures of leak. Twenty-three participants completed a continuous random dot motion task with the goal of detecting periods of coherent upward motion. Within half of these coherent targets, a brief 200ms 'gap' of incoherent motion was inserted. Preliminary analyses indicate that these evidence gaps produced substantial reaction time delays and a corresponding deceleration in the build-up of the CPP. However, initial analyses do not identify a negative CPP slope during the gap which would be diagnostic of leak. Our data do not support the role of leak in evidence accumulation.