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Do Vernier acuity thresholds depend on perceived or actual retinal eccentricity?

Beg├╝m Erten, Huseyin Boyaci

This project was presented at 33rd European Conference of Visual Perception (ECVP), held in Lausanne, Switzerland, August 22-26, 2010. Click here to view the poster.

The study was supported by research grants from Turkish Scientific and Technological Association (TUBITAK 1001-108K398), and from European Commission (PIRG-GA-2008-239467).

Vernier acuity (VA) thresholds increase with retinal eccentricity, and correlate with cortical magnification in human V1 (Duncan & Boynton 2003). On the other hand, 3d context can dramatically affect the perceived retinal eccentricity of an object, and the spatial distribution of neural activity in human V1 correlates better with the perceived retinal eccentricity.Motivated by these results, we investigated whether Vernier acuity thresholds depend on the actual or perceived retinal eccentricity. Using a 2IFC adaptive procedure we measured the Vernier acuity thresholds by manipulating the perceived eccentricity while keeping the actual eccentricity constant. We placed a rectangular object either at a “near” or “far” position in computer-rendered 3d scenes rich with depth cues. We then superimposed the Vernier stimuli to the left or right of a central fixation mark painted on the object. When the stimuli were presented at the far position, they appeared to be at a larger eccentricity compared to when they were presented at the near position, even though the actual eccentricity was always the same. We found no effect of the manipulation on the VA thresholds, suggesting that VA depends on actual but not perceived retinal eccentricity.