Bisections on backgrounds with different luminances

Psychophysical methods are valid if participants' judgments are uneffected by the context wherein stimuli are presented. In this paper, the validity of brightness judgments obtined by bisections is tested. Standards were squares of different brightnesses presented on a bipartite background. By matching the brightnesses of standards on one side of the background with those of the standards of the other side, participants produced two equal brightness intervals for the two backgrouds. If bisection is unaffected by background variations, then the luminance of the square obtained by matching its brightness with that of the square obtained by bisection on the other background would be equal to that of the square obtained by bisection on the same background. Results show that bisection is substantially unaffected by context, because the luminance of bisecting squares are substantially similar to those of matched squares.