An Experimental Study of Linear Inclination

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Abstract
Two mechanisms have been proposed to account for perceptual distortion of angular subtension. The first implies that errors made when estimating sizes of angles should correspond to inaccuracies of estimating the inclinations of their two component lines. From the second it follows that the two types of judgement are unrelated. This paper considers which of these mechanisms accounts most consistently for apparent angular distortion. Two experiments are reported. In the first, four independent groups of subjects estimated the bearing of a single straight line presented in a series of inclinations throughout the entire circular range. Subjects themselves attempted to place the same line into specified inclinations in the second experiment. The results reveal errors in both tasks. An attempt is made to distinguish between the two proposed mechanisms by predicting angular distortions from those of corresponding linear inclinations. Possible reasons for failure of this prediction are discussed.