EZ2 Diffusion Model

Description Usage Arguments Details Value Author(s) References See Also Examples

Given a boundary separation, a starting point, and a drift rate, this function computes the mean exit time/exit time variance of a one dimensional diffusion process under constant drift on an interval with absorbing boundaries. Used as a model of information accumulation, it is gives the mean decision time/decision time variance of responses in a speeded two-alternative forced choice (2AFC) response time task, regardless of whether the response is correct or incorrect.

1 2	EZ2.mrt(nu, z, a, s = 0.1, Ter) EZ2.vrt(nu, z, a, s = 0.1)

`nu`	Drift rate.
`z`	Starting point.
`a`	Boundary separation
`s`	Scaling parameter (Ratcliff's convention is `s = 0.1`, the default)
`Ter`	Lag (models non-decision time of a response time)

This model of information accumulation and decision is a simplified version of Ratcliff's diffusion model (1978). It can be used e.g., to compute the mean response times of the correct responses in a lexical decision time, given the drift rate, the bias (start point), and criterion (boundary separation).

EZ2.mrt returns the mean exit/decision time(s) EZ2.vrt returns the exit/decision time variance(s) The return value has the attribute "gradient" attached: the gradient with respect to each of the parameters.

Raoul P. P. P. Grasman

Ratcliff, R. (1978). Theory of Memory Retrieval. Psychological review vol. 85 (2) pp. 59-108

Grasman, R. P. P., Wagenmakers, E.-J., & van der Maas, H. L. J. (2007). On the mean and variance of response times under the diffusion model with an application to parameter estimation, J. Math. Psych. 53: 55–68.

EZ2-package, EZ2.cmrt, EZ2.cvrt