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Xiaohua Zhuang, Dingcai Cao, Joel Pokorny; Flicker adaptation desensitizes the magnocellular but not the parvocellular pathway. Journal of Vision 2014;14(10):791. doi: 10.1167/14.10.791.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Previous studies reported that flicker adaptation reduces temporal contrast sensitivity (Robinson & de Sa, 2012). To assess whether flicker adaptation occurs in the magnocellular (MC-) or parvocellular (PC-) pathway, or in both, contrast detection and discrimination thresholds were measured following adaptation to a flickering light, using the steady- and pulsed-pedestal paradigms that separately measure contrast sensitivity of the inferred MC- and PC- pathways (reviewed by Pokorny, 2011). Methods: The stimulus was a pedestal array with four squares, each subtending either 1°x1° or 0.57°x0.57°. The array was presented within a 37°x27° steady surround (12 cd/m2). In the steady-pedestal paradigm, observers adapted to either a steadily presented or square-wave modulated pedestal (2 or 10 Hz, 50% contrast) at various mean pedestal luminances. After adaptation, the pedestal at mean adapting luminance was present briefly (26.6 ms), with a test square having incremental or decremental luminance. In the pulsed-pedestal paradigm, observers adapted to a steadily presented or square-wave modulated pedestal with a fixed mean luminance at 12 cd/m2. The pedestal with an incremental or decremental luminance from the mean adapting luminance was then briefly pulsed (26.6 ms), with a test square having a larger luminance change. The task was to identify the test square in a four-alternative-force-choice staircase procedure estimating contrast thresholds. Results: For both stimulus sizes, adaptation to a flickering pedestal significantly reduced the sensitivity of the inferred MC-pathway but did not alter sensitivity of the inferred PC-pathway. This effect was stronger for 10 Hz than for 2 Hz (about 0.2 and 0.1 log unit desensitization respectively, p<0.001). Notably, contrast detection threshold was not determined by the PC-pathway even after the MC-pathway was desensitized. Conclusion: The MC-pathway can be desensitized independently from the PC-pathway, providing a powerful tool for independent examination of visual processing in these two pathways.
Meeting abstract presented at VSS 2014
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