On the determinants of surface brightness

The brightness of an achromatic surface with luminance S on an achromatic background with luminance B varies with S, with B, and with the luminance step DL at the border of the surface. In agreement with previous findings indicating that the visual system can perform as a photometer, the results of the two experiments reported here show that S and B determined surface brightness independently of DL when the surface was adjacent to and when it was separated from the background. This finding suggests that surface brightness depends on the integration of neural signals representing magnitudes of absolute luminance. A weighted-average model of this integration is proposed.