Throughout our day, we continually make decisions to behave effectively in our environment. Imagine you want to cross a busy road. To ultimately decide when to cross, you accumulate sensory evidence about the vehicles on the road (e.g., “What is that object, where is it, and how is it moving?”). Only when sufficient evidence is accumulated to ensure safe passage is the decision to cross the road made (Fig. 1).
Sampling from external and internal sensations while deciding when to cross a busy road. To ultimately decide whether it is safe to cross, one can sample from external (i.e., from perception) or internal (i.e., memory) sensations. For example, the features, position, motion, and speed of the blue car are gathered from visual perception (on the left). In contrast, these properties of the red car are sampled from working memory (on the right). External and internal sensations are sampled to gradually accumulate evidence until a decision threshold is reached, and the decision is made that it is safe to cross the road.
Sequential-sampling models state that decisions are made in an accumulation-to-bound fashion: evidence gradually accumulates until a decision threshold is reached (Ratcliff and McKoon, 2008). When this threshold is reached, a decision is formed (i.e., “I can safely cross now”) and behavior follows (i.e., crossing the road). Given that decision-making is omnipresent in everyday behavior, there is a strong motivation to identify neural markers that sensitively index evidence accumulation. In order to truly reflect evidence accumulation, such a neural decision variable must not correlate with other ongoing processes such as the preparation of motor responses or sensory processing (O’Connell et al., 2012).
Neural decision variables were first identified in nonhuman primates, where single-unit recordings in the lateral intraparietal cortex sensitively …
Correspondence should be addressed to Damian Koevoet at d.koevoet{at}uu.nl.
