Independent Objective Timing Tests Designed to Measure Processing Rates of the Dorsal and Ventral Visual Systems

Abstract

Th is study introduces new objective psychophysical measures for assessing speed thresholds of two levels of te m- poral processing: One measure occurs at a lower perceptual level designed to test functional limits of the dorsal how or where system; and the second measure occurs at a higher cognitive level designed to test functional limits of the ventral what system. The tests are objective because each trial has a correct answer, as opposed to relying on participants subjectively indicating the point at wh ich they experience the transition fro m an indistinct and blurry percept to a d istinct and clear one. Twenty six par- ticipants performed three rate threshold tests: (1) An objective psychophysical rate o f apparent motion measure, as a test of the dorsal system, (2) an objective psychophysical rate of serial shape-change measure, as a test of the ventral system, and (3) a traditional method-of-limits crit ical flicker fusion threshold measure, as a comparison control test . We hypothesized that indi- viduals' maximu m rate of apparent motion would correlate with thresholds of crit ical flicker fusion (CFF), and that their maximu m rate of serial shape-change would be much slower and uncorrelated with the CFF measure. Results confirmed both hypotheses, revealing a strong correlation between CFF thresholds and threshold rates on the apparent motion test, as well as marked ly slower threshold rates for recognizing direction of shape change. The findings support the apparent motion test as a promising, reliable, objective psychophysical measure associated with the dorsal how or where processing system, and the serial shape-change test as a pro mising, reliab le, objective psychophysical measure associated with the ventral what processing system.