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McAnany J. Jason, Michael W. Levine; The highs and lows of magnocellular and parvocellular processing. Journal of Vision 2004;4(8):515. doi: 10.1167/4.8.515.
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© ARVO (1962-2015); The Authors (2016-present)
Many investigations have shown enhanced sensitivity for complex stimuli presented in the lower visual field (LVF) as compared to identical stimuli presented in the upper visual field (UVF). Enhanced sensitivity in the LVF is apparently related to task difficulty, as the disparity between the fields increases with increases in threshold. The differential UVF/LVF sensitivity has therefore been attributed to an asymmetry in attentional resolution between the two fields; this asymmetry has been used to argue for a high-level cortical area (post V1) for the neural correlate of visual awareness. However, conflicting reports have emerged regarding differences in UVF/LVF sensitivity, as enhanced sensitivity for visual search has been reported in the UVF. We presented a random pattern of disks and asked subjects to identify which of three possible regions differed from the other two; differences could be in color, contrast, apparent depth, or coherent motion in depth. When stimulus characteristics favored the parvocellular system (the retino-cortical pathway associated with form and color processing), performance in the LVF was better than in the UVF. Conversely, maximizing contributions of the magnocellular system (the retino-cortical pathway associated with depth and motion processing) yielded enhanced UVF performance over that of the LVF. Thus, contributions of the parvocellular and magnocellular systems, rather than attention, appear to govern the differential UVF/LVF sensitivity. Additionally, our results indicate that some higher level processing may be evident at an earlier level than previously thought.
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