Tips and Glossary

Example paradigms

Introduction

So, what is DMDX? It is your friend. It is the Windows 95 Version of the Dmastr experimental software developed by Professor K. I. Forster and J.C. Forster at the University of Arizona. It is a reliable and easy to learn tool for experimental presentation of visual and auditory stimuli. The accurate timing of events and reaction times has led to DMDX being currently used in a wide range of experimental paradigms.

This is not supposed to be a comprehensive documentation for DMDX. It is designed to get you started, give you the basics for running DMDX. It can only take you so far, however. You will need to read the full documentation eventually (unfortunately?). It will be a lot easier for folk who have previously used Dmastr to use these pages to start using DMDX, but I hope that eventually that this will be a comprehensive. tutorial for setting up and running experiments using DMDX.

PLEASE DO NOT CONTACT PROFESSOR FORSTER WITH PROBLEMS. First you should check you have the most up-to-date version of DMDX, your problem may be an old bug that Jonathan has sorted. Then check the help files and the documentation and finally you should use the DMDX list serve.

Please acknowledge the use of the system in publications e.g., "This experiment was run using the DMDX experimental software programmed by Jonathan Forster at the University of Arizona. DMDX is a member of the DMASTR family of experimental software developed at Monash University and at the University of Arizona by K.I.Forster and J.C.Forster."

Please have a look at Matt Davis's DMDX tutorial which goes through how to set up and run DMDX experiments from a different angle.

Getting Started

• Before you download DMDX from the DMastr website you should check out the information on the website about what hardware is and isn't compatible with DMDX. One of the main limiting factors is that you need large amounts video memory to run DMDX. You will need to install the DirectX graphics software either from the DMastr download page or from the Microsoft DirectX site.

• If all is OK, then set it up.

If you work here at the CBU you should read the CBU specific information.

Moving On

DMDX experiments are run using control files written in Rich Text Format. Rich text format is an option when using both Word and Wordpad. If you save a text file in DOS Edit with the extension .rtf then it will be read as rich text file by DMDX. There are some problems with editors explained both in the Help files and here .

A control file contains two parts. The first part is a parameter line, which sets out the basic settings for the experiment, for example for a lexical decision experiment it would include items that control what colour the text will be, how long the text will be displayed, how long the subject has to respond what kind of data output file will be created, etc.

An example of a DMDX parameter line would be something like below.

• <n 16> <s 16> <azk> <cr> <nfb> <fd 125> <t 2000> <id "PIO12"> <id "keyboard"> <dbc 0> <dwc 255000>

Clear? Actually it's not that difficult. Most of the parameters are fairly straight forward, e.g. <nfb> means " no feed back", no feedback on subject responses is sent to the the subject's screen. <dbc 0> means the default background colour of the screen is black. This will be explained further below.

The second part is the main part of the experiment, that is the words to be displayed, the sound files to be played, the coding for what kind of response is expected etc. A simple one, for a single word lexical decision might look like below. The words inside the quotes are what the subject would see, the rest of the coding is explained in the example pages.

-1 * "SKELVE"/; +2 * " GAME "/; +3 * " BACON "/;

Rich Text Format(.rtf), enables usage of multiple / bold / italic / colour fonts. You simply write the text as you wish it to be displayed. Be careful with less standard fonts. DMDX has some problems with non standard fonts like, e.g. "Blood of Dracula" and non Latin fonts, e.g ARABIC. The problem with non standard fonts is that sometimes a few pixels are not erased, if you have this problem you should have a look at the DMDX tips page.

Sometimes you may see scripts written with old DMastr parameter/switch notation. Here is a small table of common old DMastr notation and their DMDX equivalent and I have made a simple HTML version (no links etc.) of the DMastr manual

-- Main.CarolineWhiting - 23 Mar 2007