7.2: Invited Paper: Quantification and Modulation of Stereopsis in Humans

Abstract

Binocular vision in general and stereopsis in particular are fundamental to human vision and visual actions. It is widely thought that about 5% of the population have a lazy eye and lack stereo vision, so it is often supposed that most of the population (95%) have good stereo abilities. We show that this is not the case; 68% have good to excellent stereo (the haves) and 32% have moderate to poor stereo (the have‐nots). Why so many people lack good 3‐D stereo vision is unclear but it is likely to be neural and reversible.Interocular suppression and stereopsis are two important binocular functions. To date, it still remains unclear about the relationship between them. Here, we use the binocular phase combination paradigm and a comparable paradigm to provide a normative dataset for perceptual eye dominance and stereo acuity in 142 normal‐sighted human adults and analyze their correlation. We show that our eye dominance and stereopsis are not strongly correlated in the normalsighted subjects. These results thus support the idea that the binocular phase combination and stereopsis may be limited by different factors in normal‐sighted adults.At present there is no good way of reliably measuring stereopsis in the clinic other than the standard book tests designed for children. These are convenient but coarsely quantized in disparity with no measure of variance. This makes it difficult to be able to assess the significance of differences from visit to visit contingent on therapy. We report an iPod app that has been developed from laboratory studies of normal stereopsis, to measure stereo in the clinic that is not limited by these factors. The application enables measurements over the wide disparity range and not just at the finest disparities. In addition, it allows changes in stereopsis of the order of 1.9 to be statistically distinguished.Luminance plays a modulating role in the processes of several visual tasks, which in turn provides significant information for the understanding of visual processing. To study the relationship between luminance and stereopsis, we manipulated the mean luminance seen by both eyes or the interocular difference in mean luminance by using ND filters placed in front of both eyes or just one eye respectively. We found that disparity processing was little affected by a binocular change in luminance, but was greatly affected by a luminance mismatch between the two eyes. To investigate its origin we manipulated two factors, the temporal synchrony between the two eyes and the interocular contrast. Both factors are implicated in the loss of stereo performance when the mean luminance is different between the eyes, suggesting an underlying explanation in terms of temporal low‐pass filtering resulting in the combination of a luminance‐dependent temporal delay and a luminance‐dependent change in contrast gain.These results add to our knowledge of stereopsis and have therapeutic potential in re‐establishing stereopsis in patients with binocular disorders.