Changes in the Apparent Lengths of Lines as a Function of Degree of Retinal Eccentricity

Abstract

Magnitude estimates were obtained for the apparent lengths of (i) seven vertical lines of different lengths at eleven positions along the horizontal meridian and (ii) the same seven lines presented horizontally at ten different angles of elevation. In experiments 1 and 2 (experienced and naive subjects, respectively) the seven vertical lines were permutated randomly in the eleven azimuth positions within a session. In experiment 3, the seven vertical lines were all presented first at a single azimuth position before being presented at another azimuth position. In experiment 4, the same seven line lengths (presented in horizontal orientation) were permutated randomly within the ten angles of elevation. The results showed that the apparent length of a line decreases as the line was moved away from the midline position into the periphery. Power functions described the growth of line lengths at each azimuth position and each angle of elevation. The exponents of the power functions in experiments 1,2, and 4 were smallest at the midline position and became larger for the line lengths presented more peripherally. For lines presented vertically the exponents tended to decrease again at the more extreme azimuth positions. Equal-length contours were derived from the power functions of experiments 1, 2, and 4.