Aim: To explore the effect that colour has on fusion range. An illusion of depth can be created by colour (chromostereopsis). To most observers chromostereopsis is the perception that a red stimulus is in front of a blue stimulus when it originates from the same fronto-parallel surface, and is due to chromatic aberration. Chromostereopsis cues can complement or conflict with disparity cues in a stereogram. This may result in an increase or decrease in an observer’s binocular control over the stereogram. In this study, fusional range was used as a measure of binocular control.
Methods: A group of students aged 18–22 years (n = 30) participated in a repeated measures design experiment. Three stereograms, viewed on a synoptophore, consisted of a ‘control’ stereogram with disparity cues only, a stereogram with ‘complementing’ chromostereopsis cues and a stereogram with ‘conflicting’ chromostereopsis cues. The participants’ positive and negative fusion ranges were recorded for each stereogram and were analysed separately to account for any possible shift in total fusion range.
Results: There was a statistically significant difference between the three stereograms. Where ‘complementing’ chromostereopsis cues are present the positive and total fusion ranges increased, whilst ‘conflicting’ chromostereopsis cues caused a decrease in the positive and total fusion ranges.
Conclusion: Chromostereopsis does have an effect on the binocular control of a stereogram and may have applications to orthoptic exercises.