Simultaneous use of different mental standards in magnitude estimation of line length.

Subjects making magnitude estimations of line length behave as if they were concatenating a mental standard with itself along the length being estimated. Using a 1-cm standard line (S) a chronometric analysis of magnitude estimation of line length revealed that subjects mentally concatenated S for lines up to ten times longer than S and mentally concatenated a multiple of S for lines more than ten times longer than S. Differences in mental standards and in strategies of mental concatenation account for the variation of individual exponents and the often reported deviations from unity of the mean exponent of the psychophysical function for length.