Mental measurement in the magnitude estimation of length.

Two experiments employing 6 and 8 college students, respectively, estimated the length of lines at various orientations using a short length as a standard. Reaction times increased linearly with line length, consistent with Ss' introspective reports that lengths were estimated by laying off a mental image of the standard along the line to be judged. Judged length generally increased as the slant of the line approached the vertical. This was due, at least in part, to an anchoring effect of the end of the line from which S began the laying-off process. Results of a magnitude production task indicate that the anchoring effect varied as a function of the orientation of the line. The bottom of the display also exerted a small anchoring effect. It is proposed that Ss mentally place a marker at the farthest extent of the image of the standard at each laying off and that the remembered location of the marker is displaced by the anchoring effects.