dmc_dm: Create the Diffusion Model for Conflict Tasks

In dRiftDM: Estimating (Time-Dependent) Drift Diffusion Models

Create the Diffusion Model for Conflict Tasks

Description

This function creates a drift_dm object that corresponds to the Diffusion Model for Conflict Tasks by \insertCiteUlrichetal.2015;textualdRiftDM.

Usage

dmc_dm(
  var_non_dec = TRUE,
  var_start = TRUE,
  instr = NULL,
  obs_data = NULL,
  sigma = 1,
  t_max = 3,
  dt = 0.001,
  dx = 0.001,
  b_coding = NULL
)

Arguments

var_non_dec, var_start	logical, indicating whether the model should have a normally-distributed non-decision time or beta-shaped starting point distribution, respectively. (see nt_truncated_normal and x_beta in component_shelf). Defaults are TRUE. If FALSE, a constant non-decision time and starting point is set (see nt_constant and x_dirac_0 in component_shelf).
instr	optional string with additional "instructions", see modify_flex_prms() and the Details below.
obs_data	data.frame, an optional data.frame with the observed data. See obs_data.
sigma, t_max, dt, dx	numeric, providing the settings for the diffusion constant and discretization (see drift_dm)
b_coding	list, an optional list with the boundary encoding (see b_coding)

Details

The Diffusion Model for Conflict Tasks is a model for describing conflict tasks like the Stroop, Simon, or flanker task.

It has the following properties (see component_shelf):

• a constant boundary (parameter b)

• an evidence accumulation process that results from the sum of two subprocesses:

  • a controlled process with drift rate muc

  • a gamma-shaped process with a scale parameter tau, a shape parameter a, and an amplitude A.

If var_non_dec = TRUE, a (truncated) normally distributed non-decision with mean non_dec and standard deviation sd_non_dec is assumed. If var_start = TRUE, a beta-shaped starting point distribution is assumed with shape and scale parameter alpha.

If var_non_dec = TRUE, a constant non-decision time at non_dec is set. If var_start = FALSE, a starting point centered between the boundaries is assumed (i.e., a dirac delta over 0).

Per default the shape parameter a is set to 2 and not allowed to vary. This is because the derivative of the scaled gamma-distribution function does not exist at t = 0 for a < 2. We generally recommend keeping a fixed to 2 for several reasons. If users decide to set a != 2, then a small value of 0.0005 is added to the time vector t_vec before calculating the derivative of the scaled gamma-distribution as originally introduced by \insertCiteUlrichetal.2015;textualdRiftDM. This can lead to large numerical inaccuracies if tau is small and/or dt is large.

The model assumes the amplitude A to be negative for incompatible trials. Also, the model contains the custom parameter peak_l, containing the peak latency ((a-2)*tau).

Value

An object of type drift_dm (parent class) and dmc_dm (child class), created by the function drift_dm().

References

\insertRef

Ulrichetal.2015dRiftDM

Examples

# the model with default settings
my_model <- dmc_dm()

# the model with no variability in the starting point and with a more coarse
# discretization
my_model <- dmc_dm(
  var_start = FALSE,
  t_max = 1.5,
  dx = .0025,
  dt = .0025
)

dRiftDM documentation built on April 3, 2025, 7:48 p.m.