The effects of peripheral and central fixation on a Poggendorff-like vernier alignment task

Observers judged oblique line-to-dot alignments both when the oblique line abutted a vertical Inducing line (Condition E) and in the absence of the vertical line (Condition C). Five groups of 10 subjects each completed these C and E judgments under one condition of inspection. There were three major findings: (1) contrary to expectations arising from results obtained by Novak (1966), there was no difference between the condition in which observers were instructed to fixate the point at which the oblique line abutted the inducing line and the condition in which free inspection was permitted; (2) contrary to a recent report by Greist and Grier (1977), alignment errors were not eliminated in conditions involving fixation directly above or below the point of abuttal; instead, effects sirnilar to those reported by Prytulak (1973) occurred in both Conditions C and E, and these effects consequently were not significant in the corrected (E-C) difference measures; and (3) when alignment errors were converted to angular displacements, mean errors decreased linearly as a function of the distance between the tip of the oblique line and the response dot. This third finding was attributable to nonzero intercepts of error functions, and the result was considered in relation to the tenability of various hypotheses concerning the nature of abutting line effects.