The bisection point across variants of the task
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Bisection tasks are used in research on normal space and time perception and to assess the perceptual distortions accompanying neurological disorders. Several variants of the bisection task are used, which often yield inconsistent results, prompting the question of which variant is most dependable and which results are to be trusted. We addressed this question using theoretical and experimental approaches. Theoretical performance in bisection tasks is derived from a general model of psychophysical performance that includes sensory components and decisional processes. The model predicts how performance should differ across variants of the task, even when the sensory component is fixed. To test these predictions, data were collected in a within-subjects study with several variants of a spatial bisection task, including a two-response variant in which observers indicated whether a line was transected to the right or left of the midpoint, a three-response variant (which included the additional option to respond “midpoint”), and a paired-comparison variant of the three-response format. The data supported the model predictions, revealing that estimated bisection points were least dependable with the two-response variant, because this format confounds perceptual and decisional influences. Only the three-response paired-comparison format can separate out these influences. Implications for research in basic and clinical fields are discussed.
KeywordsBisection task Landmark task Method of single stimuli Single-presentation method Two-alternative forced-choice Response bias Indecision
This research was supported by Grant Nos. PSI2009-08800, from Ministerio de Ciencia e Innovación, and PSI2012-32903, from Ministerio de Economía y Competitividad, to M.A.G.-P., and by NIH Grant Nos. R01EY05957 and R01EY12890 to E.P. We thank Zachary Reynolds for his help in participant recruitment and data collection.
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