Binocular Vision, Training and Lightness Constancy

Lightness constancy refers to the ability to estimate an object's lightness (ie, surface reflectance), regardless of variations in the light being reflected from the object—for example, when the illumination changes or the object moves. Buckley et al (1994) observed that binocular cues improve lightness constancy. Here we explored how training improved lightness constancy under binocular, bi-ocular (identical images to each eye), and monocular viewing. Stimuli consisted of a diffusely illuminated Lambertian grey box, containing a single target: a faceted rectangular block that could be presented at a range of depths within the box. Stimuli were presented stereoscopically (to provide full binocular cues), monocularly, and bi-ocularly. In the experiment, participants were asked to select one of a number of blocks, presented below the box, that was of the same material as the target block. Four groups of participants received differing training regimes. Active training involved moving a block of fixed reflectance within the box along a user-defined path (by pressing keyboard buttons). Passive training was the same as active, except block movements were pre-recorded. One group received both active and passive training. No-training used a static presentation of blocks to indicate depth. We found that stereoscopic presentation produced the best lightness constancy. Training regimes delivered a performance difference for stereoscopic, monocular, and bi-ocular presentations, with passive and active training being equally effective. With some training regimes participants took longer to achieve their best performance.