Retinotopy Stimulus
Related Links:: Stimulus WIKI :: Retinotopy WIKI
PRE-INTRODUCTION
Before you start, you should be aware that this is all a bit complicated. You will need to be familiar with MATLAB, Macs and the Brainard/Peli Psychophysics toolbox. You should also know how to calibrate your monitor for best results. If any of the above mean nothing to you, stop now!
INTRODUCTION
The code we distribute here is what we use for running retinotopy scans in our fMRI experiments. Broadly speaking, these stimuli can be grouped into
1) Expanding rings
2) Rotating wedges
Expanding rings are flickering annuli that start in the middle of the screen and move towards the edge. Rotating wedges are flickering sectors that move around the center of the screen. They are useful because they generate distinctive patterns of activation in the early visual areas that can be used to determine visual field angle and eccentricity. Once again, if you are lost by now then stop.
OVERVIEW
The retinotopy code comprises a set of MATLAB m-files. These files are in the Ret directory of the package that you downloaded along with this readme. The file that you use to call the stimuli is ret.m Once you have everything set up, you can type
ret
from the command line and a nice graphical interface will pop up to allow you to configure the stimuli for an fMRI scan. It will work out how many fMRI frames you have, how long the stimulus will last, what priority to run the stimulus at etc etc. It will also allow you to choose from a list of about 10 different variations on the basic themes of rotating wedges and expanding rings. The retinotopy code is built on two software libraries that you will also need.
BP - PSYCHTOOLBOX
The first is the Brainard-Peli psychophysics toolbox which you can download and install from the same website you got this readme from.
It comes with its own installation instructions and we do not cover this here.
EXPTTOOLS2 / VISTADISP
Download VISTADISP
This library is our own set of tools built on this toolbox. We call this exptTools. You can get the exptTools stimulus presentation code from our Software Download Page. Before downloading the code please ensure that you have downloaded PSYCHTOOLBOX and have it installed. If the PTB demos run then you're on your way.
HOW TO INSTALL EXPTTOOLS
Unzip the exptTools folder into your MATLAB toolbox directory. Then bring up the path browser in MATLAB (hit the button on the toolbar that looks like two folders on top of each other with barcodes to their right). From the path browser, click the 'default path' button. This will tell matlab to search the toolbox directory and include any new folders in there. See if exptTools has been installed by typing
installCheckET
in matlab. you should see something on the command line telling you that the path is okay. Now be aware of this: To run psychophysics properly, you need to have a properly calibrated monitor. In fact, matlab needs to know a lot about your monitor: its frame rate, the color of its phosphors, its size, position, the number of bits in the video card and other things like that. We store all this information in a set of files, called displayParams.m gamma.mat spectra.mat These files are in a default folder on our machines:
Applications:Matlab:MRI:Displays:Default
exptTools expects these files to exist when it initiates. If they don't, you will get a set of errors. You might get something working (if exptTools defaults to something useful). More often than not, you will get garbage. We have included some sample display calibration files in the retinotopy code distribution. We have also changed the retinotopy code so that it uses these sample files rather than looking in the default folder above. But this is for demonstration purposes only. Our monitors are not your monitors and our frame rates will be different to yours as well. That means that the timings for the retinotopies will be wrong. Do not email us about this. Or anything. You are welcome to examine the code to see what we have done and modify it to your hearts' content but we cannot provide technical support on this. It is hard enough making it work on our >own< machines.
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RUNNING THE RETINOTOPY CODE
Once both these libraries are in place, you can run the retinotopy code. Extract the code in retinotopyCode.zip to a directory called 'ret' somewhere in your directory path. Change to this directory in MATLAB and type ret Now you can start debugging your installation.
Happy retinotopies
