Predicting the effect of spatial articulation on lightness

Agostini and Bruno (1996 Perception & Psychophysics 58 250 - 258) found that, under Gelb lighting (an illumination border is made to coincide with the outer border of the display and the rest of the visual field is left in near darkness), the magnitude of the simultaneous lightness contrast effect increases significantly relative to measures taken under homogeneous illumination, and that a similar increase is observed on using CRT simulation. Few years ago, Agostini and Galmonte (1999 Perception & Psychophysics 61 1345 - 1355) studied the effect of spatial articulation on simultaneous lightness contrast, on the Benary display, and on related displays by using both methods: Gelb lighting and monitor presentation. Both methods revealed a decrease of the simultaneous lightness contrast effect as the spatial articulation increases. In the present work, the same stimuli have been simulated on a CRT monitor and a model of human visual perception (ACE) has been applied to them in order to verify its ability in predicting lightness induction. Observers had to perform lightness matches by choosing from a simulated Munsell scale; these data have been compared with ACE processing result. Agostini and Galmonte's results have been replicated. Furthermore, ACE shows an interesting precision in predicting quantitatively the induction effects. ACE is a powerful model for predicting human visual perception. Developing a computational tool, like the one considered in this work, has the advantage that a particularly complex configuration can be first analysed by ACE and then tested by psychophysics methods.