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Jared Abrams, Aaron J. Nizam, Marisa Carrasco; The extent of the vertical meridian asymmetry. Journal of Vision 2011;11(11):1146. doi: 10.1167/11.11.1146.
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© ARVO (1962-2015); The Authors (2016-present)
Goals: How does visual perception vary as a function of location? Performance decreases as eccentricity increases, but performance at isoeccentric locations is not homogenous. Performance is better along the horizontal meridian than along the vertical meridian. Along the vertical meridian, performance is better along the lower than the upper portion. This pattern of asymmetries is referred to as a performance field (e.g. Carrasco, Talgar, & Cameron, 2001). Some have reported a general upper versus lower visual field asymmetry, which is considered to reflect the ecological constraints of the environment (e.g., Previc, 1990). Here, we investigate the angular extent of the vertical meridian asymmetry.
Methods: In two experiments, observers performed an orientation discrimination task on Gabor stimuli of varying contrast at a series of isoeccentric locations. Interleaved adaptive staircases controlled stimulus contrast, enabling the measurement of sensitivity at each location. In Experiment 1, we measured sensitivity at sixteen equally spaced isoeccentric locations. In Experiment 2, we narrowed this range to focus on the locations within ±45° of the upper and lower vertical meridian.
Results: Consistent with previous studies, we found that contrast sensitivity is lowest along the upper vertical meridian, higher along the lower vertical meridian, and highest along the horizontal meridian. The upper versus lower asymmetry is most pronounced along the vertical meridian, but it does extend beyond the vertical meridian. The asymmetry gradually decreases as angular distance from the vertical meridian increases, disappearing by ±45°. This behavioral asymmetry mirrors the asymmetries of the LGN (e.g., Connolly and van Essen, 1984), suggesting that anatomical constrains underlie behavioral performance fields. These data do not support a general upper versus lower visual field asymmetry related to ecological constraints.
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