Ratio models of perceptual transparencies for stimuli with three surfaces.

A surface is transparent if it is possible to see other objects behind it (Koffka 1935). There are two kinds of transparency: the transparency that is visible on stimuli composed by four surfaces and the transparency that is visible on stimuli composed by three surfaces. The perception of the degree of transparency of a surface depends on the chromatic differences between stimulus surfaces (Kanizsa 1980, Metelli 1970, 1974, 1985). In this experiment the validity of some models predicting the degree of transparency was tested in stimuli composed by three surfaces with different lightnesses. These models are mathematically expressed as a ratio between the lightness differences. The predicted degrees of transparency were compared tho the observed degrees fo transparency obtained by participants' judgments. Experimental findings show that in stimuli with three surfaces the degree of transparency of a figure is the result of the comparison of the lightness difference between the surfaces of the transparent figure with the greatest lightness difference between the surfaces of the stimulus.