In the clinical practice, the evaluation of binocular vision is carried out with the traditional Worth-4-dot test, which is based on his classic theory, suggesting three hierarchical stages of stereovision (Worth, 1906). However, according to research nowadays, binocular vision rather involves parallel pathways. We do not know how the hierarchical organizational principles set forward in the Worth model can be related to the parallel processing pathway theory. We aimed to use reaction time (RT) measurement, a traditional psychophysical method, in a series of experiments, to examine the processing time of mechanisms in stereovision by using different types of cyclopean stimuli that are only visible binocularly by individuals who have intact stereopsis. We tested the effect of correlation, disparity and contrast on RT. Overall, the results suggest that the processing of cyclopean stimuli is more time consuming than non-cyclopean ones and that the speed further depends on the disparity and contrast of the stimuli. We have failed to prove that the processing of the different types of cyclopean stimuli takes a hierarchical order, rather, the results support the idea of parallel systems.
