Matlab programming for psychophysical experiments
This case study was performed at the department of Ophthalmology at the University Medical Centre of Groningen. The supervisor of my project was dr. Nomdo Jansonius. The aim of the project was to produce several scripts in MATLAB/Linux Octave which can be used to perform psychophysical experiments. Psychophysical research uses experiments in which one obtains data about a subject by recording his or her response to certain stimuli. An example would be dots on a monitor which gradually turn brighter until the patient sees them; he or she presses a button which causes the dots to dim again.
There are roughly 3 main files which I produced during my project. The first one is stimulus to measure contrast sensitivity in a patient. A grating slowly appears on the screen; the subject presses the mouse when he or she sees it. The modulation of the grating (the luminosity of the grating lines compared to the background) at the point the subject sees the grating is a measure for that person’s ability to see contrast.
The second script I produced is used to characterize the light behaviour of a computer screen. Each monitor produces a certain light intensity as a function of the RGB value sent to its pixels. My script produced a function which tells you which RGB value one should use to make the screen produce a specific intensity.
The final script was a digital perimeter which measures contrast sensitivity in the entire field of view of a patient. The subject focuses in the middle of the screen and outside his or her focus dots appear of varying contrast compared to the background. The subject presses the mouse if he or she sees the dots. A distinctive advantage of this digital perimeter is that it is very easy to modulate (gradually lighten and darken) the background, which allows for measuring contrast sensitivity in varying light environments.
