A very inexpensive MRI-compatible method for dichoptic visual stimulation

Here I describe a very simple, very effective, and very inexpensive method of dichoptic stimulus presentation, designed for use in a head-only MRI scanner with a standard back-projection system. The method can also be used outside of the scanner. Images are presented separately and simultaneously to the two eyes, without the use of colored lenses, with no constraints on stimulus properties (other than size: stimuli must be less than half of the width of the viewing screen), no degradation in luminance reaching the eye, and zero crosstalk between the two eyes. Simultaneous infrared eye tracking and/or pupilometry can also be performed. Components include a two-part cardboard divider (one part in the bore of the magnet, and one in the head coil) and prism lenses (readily obtainable from the local eyeglass shop) cut to fit scanner-compatible eyeglass frames. The total cost (in 2007) was approximately US$ 300.