Influence of shape and perimeter length on induced color contrast.

The magnitude of induced color contrast was measured for tests whose areas, perimeter lengths, and shapes were independently varied. Test shapes were smoothly contoured, multiple-lobed figures generated from unitary Fourier shape descriptors. The shapes had from 3 to 40 lobes and were equal in area to a disk of diameter 2 deg, with perimeter lengths of 1.25, 1.75, 2.25, and 2.75 times the circumference of a 2-deg disk. The surround was a 5-deg disk. The surround was modulated sinusoidally along one of the three cardinal directions of color space around an equal-energy white of 50 cd/m2. The observer nulled the modulation induced into the test by adjusting the amplitude of real modulation in the test. The amplitude of nulling modulation was the measure of induction. The main result was that the amount of induction was similar for all tests of equal area irrespective of the shape or the length of perimeter.