The interest has increased in part due to the introduction of the sequential sampling framework (for reviews, see Bogacz et al., 2006 and Ratcliff and Smith, 2004). To make a decision, it is assumed that the brain accumulates samples of sensory evidence IOX1 price until an absorbing choice boundary is reached. The inherent noise in both the physical stimulus and the neural signal makes the process stochastic, potentially leading to an incorrect choice. The rate of approach to a boundary is called drift rate, and depends on the quality

of the extracted sensory evidence. The boundary is hypothesized to be under subjective control, and can be modulated depending on timing demands. A higher boundary criterion will require greater evidence accumulation, leading to slower and more accurate decisions. The interaction between drift rate and choice criteria has an obvious property: it provides an integrated account www.selleckchem.com/products/fg-4592.html of both response time (RT) and accuracy in choice laboratory experiments. The drift diffusion model (DDM) developed by Ratcliff and coworkers (Ratcliff, 1978 and Ratcliff and Rouder, 1998) belongs to

this theoretical frame. The model was originally developed to explain simple two-choice decisions in terms of psychologically plausible processing mechanisms, and has proven to account for a large range of paradigms (for a review, see Ratcliff & McKoon, 2008). However, its extension to more complex decisions is not straightforward and is currently the object of an intense field of research in both experimental psychology (e.g., Hübner et al., 2010, Leite and Ratcliff, 2010, Smith and Ratcliff, 2009, Stafford et al., 2011, White et al., 2011 and White et al., 2011) and neuroscience (e.g., Churchland et al., 2008 and Resulaj et al., 2009). The present study aims to evaluate whether the DDM can be extended to conflicting situations, and contributes to this emerging field. As other sequential sampling models, the DDM posits that RT is the sum of two components, a non-decision time and a decision-related

time. The decision process takes the form of an accumulation PJ34 HCl of evidence delimited by two boundaries representing alternative choices. The starting point of the diffusion depends on prior expectations, and can be located everywhere on the axis joining the two alternatives, being closer to the more expected alternative. In each moment, the incremental evidence is the difference between sensory inputs supporting choice 1 versus 2. This difference is a random variable which follows a Gaussian distribution, with mean μ (drift rate) and variance σ2 (diffusion coefficient). The combination of sensory evidence into a single variable and its linear stochastic accumulation over time present an interesting property.