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Christopher C. Pagano, Robert W. Isenhower; Instructions affect verbal judgments but not reaches to visually perceived egocentric distances. Journal of Vision 2004;4(8):841. doi: 10.1167/4.8.841.
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© ARVO (1962-2015); The Authors (2016-present)
Two response measures for reporting visually perceived egocentric distances, verbal judgments and blind manual reaches, were compared using a within-trial methodology. Participants viewed a target at eye level and then from this single view they judged distance verbally and immediately reached to place the hand at a target's location. The experiment involved unrestricted binocular viewing of non-illusory stimuli. The expected range of distances was manipulated by instructing the participants that the targets would be between .50 and 1.00 of their maximum arm reach in one session, and between .25 and .90 in another session. The actual range of target distances was always .50 to .90. The ordering of the two sessions was counterbalanced among eight subjects. Regression equations predicting reported target distance from actual target distance for the reaches were y = .84x + .08 and y = .85x + .07 for the .50–1.00 and .25–.90 sessions, respectively. The regression equations predicting reported target distance from actual target distance for the verbal judgments were y = .89x + .05 and y = 1.17x − .32 for the .50–1.00 and .25–.90 sessions, respectively. Multiple regressions confirmed that these equations varied as a function of the range of expected distances for the verbal reports while the reaches remained unaffected. The observed range of verbal judgments matched very well the instructions of .50 to 1.00 or .25 to .90 in the respective sessions. The reaches, however, more closely matched the actual range of target distances of .50 to .90 in both sessions, and thus did not differ between the two expectation conditions. These results suggest that some action responses are not subject to a cognitive influence that affects verbal responses. It is suggested that action responses are indicative of definite (absolute) distance perception while cognitive responses may only support conclusions pertaining to relative perception.
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