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The information in this document is for owners of a Lumina MRI response pad who want to use it with programs other than the ones listed on the Lumina Support main page.

Available Resources

The Presentation extension (C++ code) and Python code libraries are supported by Cedrus as far as fixing bugs and providing updates. However, we are unable to provide help in debugging your own code.

C++ Code

Cedrus developed an extension for the Presentation software. The resulting C++ code is open sourced at GitHub and is an excellent starting point if you want to program in C++. This code is currently Windows-only. If you are developing for Mac, you might find this Apple serial port code sample helpful.

Python

Cedrus developed sample Python code that is open sourced at GitHub.

Matlab

See the Matlab support forum where sample Matlab code has been posted.

The Various Protocols

Cedrus response devices support four different protocols. A protocol simply means a method or format used to send the information to the host computer.

The four protocols supported are: XID (shown as “Lumina” on the controller), RB-x20 (shown as “Cedrus RB Series”), ASCII, and PST SRB (shown as “E-Prime”). Each has advantages and disadvantages:

Protocol

How it Works

Pros and Cons

XID (eXperimental Interface Device)

The computer triggers the XID device at the onset of a trial. When the subject or patient responds, the device sends back information that includes reaction time.

Reaction time is measured in hardware; this eliminates timing uncertainties in Mac OS & Windows

You can detect when two or more keys are pressed simultaneously

You can detect when a key has been released

You can detect input from the Accessory Connector

It takes the most programming to handle the XID protocol

RB-x20

Each bit within the byte indicates which key is pressed

One and only one byte is sent every time a key is pressed or released

You can detect when two or more keys are pressed simultaneously

You can detect when a key has been released

It takes some programming to decode the individual bits

ASCII

An ASCII value is sent when a key is pressed

One and only one byte is sent every time a key is pressed

Simplest protocol

You can see readable output from the response device using a terminal emulation program

You cannot detect when two or more keys are pressed simultaneously

You cannot detect when a key has been released

PST SRB (Psychology Software Tools Serial Response Box)

Each bit within the byte indicates which key is pressed

A stream of bytes is sent approximately 800 or 1600 times per second

You can detect when two or more keys are pressed simultaneously

You can detect when a key has been released

It might take some programming to decode the individual bits

The constant stream of bytes makes it more difficult to deal with

Which Protocol to Use

For adapting a Cedrus response device to your own software package, the choice boils down to XID, RB-x20 or ASCII protocols. We do not recommend the use of PST SRB protocol except with E-Prime, mainly because the constant stream of bytes can be a hassle to deal with.

If you want to offload the task of measuring reaction time and have the response device do it for you, the XID protocol is the only and best way to go.

If your experiments do not require knowing when two keys are pressed simultaneously or when a key has been released, then ASCII protocol is the simplest and easiest to deal with. Otherwise, we recommend that you use the RB-x20 protocol.

Last revision:  January 3, 2011

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