The Effect of Tilt on the Visual Perception of Parallelness

This experiment is part of a program of research designed to analyze the visual perception of spatial relationships. Earlier experiments in the series have yielded functional dependencies for several simple spatial structures. In a study by Salomon, on the ability of Ss to align a dot in such a manner that it appears to fall on an extrapolated extension of a tilted reference line, a linear relation was found between accuracy of setting and line-to-dot distance, the slope of the function varying inversely with the length of line.' Sulzer demonstrated the importance of essentially the same stimulusdeterminants-line-length and inter-line distance-for the perception of parallelism.2 In both studies, evidence of the importance of yet a third stimulus-determinant-tilt of line-was found. The rl6e of tilt in the perception of parallelness was investigated in the present experiment.