## Introduction

## The diffusion modeling approach to RT analysis

### The concept of the diffusion model

### The four main parameters of the DM

### Parameter interpretation from a psychological point of view

#### Boundary separation a

#### Response bias z

#### Drift parameter \({\nu }\)

#### Non-decision time component \({t}_{{0}}\)

### The model equations

### Parameter variability/variability parameters

#### Distributional assumptions and estimation

#### Further extensions

## The diffusion model visualizer

### The DMV GUI

`PgUp`

and `PgDown`

buttons, or by entering values into the respective text fields. Below, three entries allow for setting \(s^2\), the number of iterations to approach the infinite sum of Eq. (2), and the number of nodes to be used for the numerical integration required for the variability parameters. The middle section of the GUI shows the resulting density curves along with a symbolic depiction of the actual model parameters. At the right, graphical and computational options allow for fine-tuning the plot. On top of the screen, there are four tabs allowing for switching from the `PLOT`

page to a `HELP`

page with some basic instructions and usage hints, the `LIMITS`

page, which allows for increasing the parameter limits (for experimental purposes), and the `LOG`

page with some numerical details of the calculations. The `DRAW`

button invokes the calculations and delivers the diagram with the currently set options. The `CLEAR`

button empties the canvas, the `CLIP`

button copies the current diagram to the clipboard, and the `SAVE`

button allows for storing the plot to disk. A bold face caption of the `DRAW`

button indicates pending parameter changes.`DRAW`

button there is the `Animation`

checkbox. It causes the plot to be drawn instantly upon slider movements, which gives a vivid impression how the curves change with parameter modifications. Next to this option, there is a `Superimpose densities`

checkbox, which helps to compare various parameter constellations.`Plot options`

panel allows for adaption of the diagram to specific scenarios (e.g., for a closer inspection of the densities’ ascending tails by decreasing the `Time span`

). The `fill area`

option might prove useful in cases, in which a very small image is to be conveyed, for example in a matrix plot.### DMV usage

`Superimpose densities`

checkbox allows for plotting multiple curves in one plot. Note that this option becomes automatically unchecked, if the `Draw model parameters`

options is checked and the value of a is changed. Otherwise, the dislocated baselines (indicating the de-/increasing a) would be drawn one over the other, thus rendering the diagram distorted. Alternatively, one could also uncheck the `Draw model parameters`

option, which will leave the two baselines in place thus keeping the diagram intact (this applies only if you want to change a; for examining the other parameters, using `Superimpose densities`

and `Draw model parameters`

conjointly will provide highly informative diagrams).### Behind the scenes: a few technical details

`Kmax`

option. However, program testing showed that too small a `Kmax`

(simulations suggest below approximately 50) may cause artifacts (spikes in the vicinity of \(t_0\)) with certain parameter configurations due to numerical inaccuracies. A preliminary sensitivity analysis revealed that the default value should suffice for most cases (in most cases, the sum converges after much fewer iterations). Readers are, therefore, advised to increase `Kmax`

with caution, as larger values will increase the computational burden considerably, in particular when working with the variability parameters.`nodes`

option allows for changing the number of nodes, but again, use this option with caution, increasing it will also cause considerable computational burden, while decreasing will lead to numerical inaccuracies.`Animation`

feature regarding the \(s_z\)-, the \(s_\nu\)-, and the \(s_{t_0}\)-sliders only update the plot upon releasing the mouse button, while the a-, z-, \(\nu\)-, and \(t_0\)-sliders invoke the plot update immediately upon mouse movement.`wine`

emulator).