# How to set up a binocular rivalry experiment which splits a single image in two separately controlled ones?

The question is about the actual physical setup and steps needed to take in order to experiment with the phenomena. I found a tutorial on jove.com, "How to Create and Use Binocular Rivalry", and it also has a dedicated explanatory article. However, the experiment I want to make is tricky in the following sense:

A regular binocular rivalry experiment has two separate images set up, and normally the image features are controlled in a way that is suitable to exhibit a whatever the experimenters want. In the case that I want to make, images are not separate, they are basically left and right parts of a single image that is usually viewed as a single image as well.

In the experiment, I will manipulate left and right halves of that single image separately, but I want to present halves to different eyes. The particular problem is that I want to calibrate the physical setup so that the physical boundary between images is not exactly visible. I can't just split left and right - the border between the images in the eyes of the observer has to be as small as possible.

How can I present each half of a face, split vertically down the middle, independently to each eye (e.g., left half-left eye), without putting a visible physical boundary between the two image halves?

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This is interesting. But the first thing I don't understand about this is what will be in the "other" half of the images. White? Black? 50% Grey? Because, you know, there is no "empty", visually, there has to be something, and that will be an image in itself. So what kind of image do you want to split, and what are you trying to research? – what Sep 21 '13 at 22:05
Sry for being ambiguously abstract, I should've explained right away that halves of the image are halves of the face. The face is the same, but halves express different emotion. Curiosity here is about whether I would get the regular switching between percepts or something else. The trick here is to calibrate it in the way that would not let the observer to see the border between the left/right halves because then it can destroy the perceptual effect. – Leonid Fedorov Sep 23 '13 at 13:41

This is an interesting methodological problem. On the one hand, it seems that any method which would present the halves to the correct eye, and only that eye, would entail a visible boundary, and any method with an invisible boundary would be unable to present the halves as desired. Virtual reality systems present stimuli to each eye separately (e.g., the commercial Oculus Rift), and may therefore present a solution here. It is, however, conceivable that the brain will not correctly integrate two separately presented halves of a face into a percept, and I am not aware of any direct studies, nor can I find any.

One related and interesting example of using virtual reality to study complex visuo-motor behavior, the outfielder problem, was provided by Fink, Foo and Warren (2009). They equipped participants catching baseballs in the air with a Cybermind Visette-Pro HMD virtual reality helmet in order to manipulate the perceived motion of the baseballs. Their ability to successfully execute such a complex visual manipulation suggests that virtual reality systems should be a viable solution for presenting halves of faces independently to each eye.

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