Apparent combined length of two-line and four-line sets

Recent studies, using single-line stimuli, show apparent length to be a power function, with exponent 1.0, of objective or physical length. If apparent lengths are additive, then, given the 1.0 exponent, two lines should appear to S to have the same total length as the single line they would form if physically joined. When S adjusted the length of one line to match the combined length of two other lines, however, he generally made the variable line much longer than the actual combined length of the two lines. Dividing the total length equally between the two lines, so that each had 50%, represents the greatest departure from a single line, yet the largest overestimation occurred when one of the two lines had 65% to 75% of the total length. The overestimation was greater when the lines were spaced farther apart, suggesting that the amount of area occupied by the lines affected apparent combined length.