Irradiation illusion

Abstract: Heuse (1957) found a sharp racial difference on the irradiation illusion; whereas 100% of his French white Ss reported seeing the illusion (enclosed white square reported as larger than same-sized enclosed black square), 85% of his French African Ss resisted the illusion (either reporting the black as larger or the two squares as equal). This note presents two tentative replications of this finding with American Ss of normal vision. Fifty Negro and 50 white 10to 14-yr.-old boys of working-class origins were individually administered an array of visual illusions, including variously-colored irradiation illusion cards. Each illusion was on an 8-in. x 4-in. card held I 0 ft. from S; the enclosed squares were 5/8 x 5/8 in. Only the black-white irradiation illusion rendered a significant intergroup difference. While 90% of the white Ss reported the same-sized white square as larger, only 6 8 % of the Negro Ss did so (corrected x' = 6.03; P < .02) . Two scaled series of 21 black-white irradiation cards, with black squares varying berween 9S% and 116% the area of the white squares, were then individually administered in balanced order to 20 Negro adults and 20 white adults roughly matched on age and education. Again, the white Ss tended more often to report the white square as larger, though significance was approached only when the black squares ranged from 100% to 107% the size of the white squares. These data probably reflect the greater visual acuity among Negroes (Karpinos, 1944, 1960) and other native differences. Social factors may also be important. In an opinion survey, 200 Negro adults were administered in balanced order three irradiation cards (black squares 102%, 105%, and 107% the area of the white) . Ss correctly judging the black as larger were lower i n need achievement (product-moment r = -.18; p < .02) and more often chose a non-militant figure (Louis Armstrong over Martin Luther King) as their favorite Kegro (corrected 2 X 2 Xk 6.14; p < .02) . These trends held regardless of the interviewer's race, though more \"black\" responses were given to Negroes ( 2 X 4 X ' = 10.23; p < .02). A \"perceived-size, valuedobject hypothesis\" is suggested: those Negro Americans least oriented to the whke-dominuted general society tend to resist the irradiation illzbsion best. Experimentation, using \"racially pure\" Ss and controlling for visual acuity and eye color, is indicated.

Abstract: There is a group of visual illusions which give the impression that straight border lines of a rectangle are bent or that rectangles look wedge shaped. In a simple form, it may be described in the following way: On a white surface area, e.g., an upright rectangle is surrounded by a black border line. At half height, the interior of the rectangle is black, while on moving towards the bottom and the upper end, the black gradually turns into grey and finally fades away into white. When the width of the contour line is chosen such that it approaches the resolution limit of the eye, the rectangle seems to change its shape, giving the impression of being wider at the top and the bottom and narrower in between. Consequently this effect may be considered to be a size illusion. Arrays of such rectangles produce a variety of effects. We have investigated this illusion experimentally on 13 different examples. Numerical results are given. Possible explanations are discussed: 1. Blurring of the border line. Calculations have been performed in order to check to what amount this may contribute to the illusion. 2. Perceived contrast of the borderline depending on the hue of the adjacent area. 3. Structure effect. Variation of the conspicuity range is related to the existence of fine structural details. An explanation is given based on the fundamental law of data transmission and processing. Examples are presented which seem to support this hypothesis. 4. The irradiation illusion. Though several effects seem to contribute to the illusion it is concluded that the main cause of the illusion is the structure effect.