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Yingchen He, Gordon Legge; Crowded Letter Recognition in Peripheral Vision Is Not Solely Determined by Target-Flanker Cortical Distance. Journal of Vision 2016;16(12):1415. doi: 10.1167/16.12.1415.
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Letter recognition and reading in peripheral vision is limited by crowding. It has been proposed that the spatial extent of crowding corresponds to a fixed distance on primary visual cortex (Pelli, Current Opinion in Neurobiology, 2008). Hypothetically, if peripheral letter recognition is only determined by crowding, then same target-flanker cortical distance will yield the same performance, regardless of other factors such as eccentricity or letter size. To test this idea, we re-analyzed the data from Legge, Mansfield & Chung (Vision Research, 2001), where triplets of letters were shown at different locations on a horizontal line to measure recognition ability. This measurement was performed at different vertical eccentricities, from 0° (central field) to 20° (lower field) with acuity-compensated print sizes. In the original work, the accuracy-vs-letter-position visual-span curves were bell-shaped, peaking at the vertical midline. As the vertical eccentricity increased, the curves became narrower and lower. Here, we have estimated the cortical distance between a target letter and its neighboring letter using target eccentricity, center-to-center letter spacing, and cortical magnification factor (Horton & Hoyt, Arch. Ophthalmol., 1991). Unlike our initial hypotheses, we found that cortical distance alone cannot account for our letter recognition performance. When target-flanker cortical distance is equated, recognition performance worsens as the target letter eccentricity increases. Surprisingly, when we further compute the ratio of cortical distance over target letter eccentricity, we found that recognition performance only depends on this ratio. Our findings here show that if crowding is determined by cortical distance alone, it does not entirely account for flanked letter recognition performance in peripheral vision. Some other property of visual processing also plays a role, one that reduces recognition performance with eccentricity. Identifying this visual function will help us better understand what limits letter recognition and reading in peripheral vision, and how to improve peripheral reading.
Meeting abstract presented at VSS 2016
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