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Steven R. Holloway, Igor Dolgov, Michael K. McBeath; New objective psychophysical methodology for independently assessing dorsal and ventral processing systems in human vision. Journal of Vision 2009;9(8):672. doi: https://doi.org/10.1167/9.8.672.
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© ARVO (1962-2015); The Authors (2016-present)
Anatomical specialization suggests that useful behavioral neural pathway models should have distinct, measurable psychophysical correlates. In this work, we developed objective psychophysical measures that target information-processing associated with dorsal and ventral neural system areas. We predicted that an objective psychophysical measure of the temporal onset of apparent motion would be a good general measure of magnocellular or dorsal system functioning; one that is correlated with critical flicker fusion (CFF), but with less variance. We also predicted that an objective psychophysical measure of the temporal onset of ability to recognize direction of shape-change would target the parvocellular or ventral system. In the apparent motion test, we successively displayed one of four dots in either a clockwise or counterclockwise direction in a square configuration. This provided an objective measure of the threshold of apparent motion, since participants could only correctly discern direction of travel when the display rate was slow enough to experience apparent motion. In the shape-changing test, we successively added or subtracted to the number of sides of equilateral polygon stimuli, and participants indicated the direction of shape-change. This provided an objective measure of the threshold of shape-processing, and was designed to limit magnocellular influence by minimizing shape-contrast and number of stimulus object edges. Our findings revealed a strong correlation between CFF thresholds and threshold scores on the apparent motion test. Moreover, thresholds for the shape-changing task were markedly slower and inversely correlated with thresholds for apparent motion and CFF. We suggest that the apparent motion test shows promise as a reliable measure of dorsal stream processing, and the shape-changing test shows promise as a reliable measure of ventral stream processing. The opposing or inverse relationship between the two measures supports the validity that they tap into two distinct processing systems, consistent with independent dorsal and ventral system functioning.
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