Abstract
The stimulation received in the upper and lower regions of the visual field during natural viewing can often differ in its environmental origins and functional relevance. In consequence, our perception of surface properties may depend on the region of the vertical visual field that is stimulated. Here, we investigated whether the perception of a fundamental surface property, glossiness, is constant between presentations in the upper and lower regions of the visual field. Participants (n=20) viewed digital renderings of two objects (randomly-perturbed spherical geometry, Ward reflectance model, 20% diffuse reflectance, 5.2° in diameter) that were simultaneously presented in the upper and lower regions of the visual field (5.8° eccentricity) and rotated back and forth about the vertical axis for 500ms. The standard object had a specular reflectance of either 15% or 30% and was presented in either the upper or lower region of the visual field, and the comparison object had a specular reflectance that varied across trials according to an adaptive staircase. The probability of judging the comparison object as glossier was modelled as a logistic function of its log specular reflectance, and the effect of visual field location on the point of subjective equality (PSE) was the key parameter of interest. A Bayesian mixed-effects model indicated that this effect was more likely to be zero (Bayes factor of 3.8, ‘moderate’ evidence) than an alternative in which the size of the effect was described by a normal distribution that could scale the PSE in either direction (with 2σ approximately halving/doubling). Hence, we conclude that the gloss of the two objects was perceived similarly. This finding is consistent with perceived surface gloss being constant for stimulation at equal distances from fixation across presentations in the upper and lower regions of the visual field.