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M23. Visual Acuity Differences Within the Normal Range Strongly Alter Visual Perception: A Cautionary Tale for Schizophrenia Research

Year: 2017
Type: article
Abstract: Background: The vast majority of studies that examine visual processing in schizophrenia ensure that subjects have normal or corrected-to-normal vision without also reporting whether subject groups are matched on visual acuity (VA) within the normal range. This is problematic because individuals with schizophrenia typically have impaired VA and because optimal VA among healthy adults is better than 20/20. Therefore, we ask: Could VA be a confounding variable even when all subjects have normal or corrected-to-normal vision? Methods: The question was addressed in 2 separate investigations of healthy adults. In the first, we measured binocular VA with a logarithmic eye chart, and compared individuals with 20/20 vision (N = 14) to those with better-than 20/20 vision (“SharpPerceivers”, N = 30) on 3 behavioral tasks. In the contour integration (CI) task, subjects located an integrated shape embedded in varying quantities of randomly-oriented noise elements; in the collinear facilitation (CF) task, subjects detected a low-contrast element flanked by collinear or orthogonal high-contrast elements; in the orientation discrimination task, subjects discerned the orientation of 4 briefly-presented, high-contrast pac-man elements. Spatial frequency was modulated in the CI and CF tasks (4–12 cycles/deg) by scaling the entire display. In the second study, 13 healthy adults with 20/20 uncorrected binocular VA performed the same 3 tasks as above—once without eyeglasses and once with eyeglasses so that they could read an additional line (0.11 logMAR units) on the eye chart. Results: In the first study, the SharpPerceivers integrated contours under noisier conditions (P < .001), had higher contrast sensitivity (P = .01), and discriminated orientation more accurately than the 20/20 group (P = .02). In the second study, optical correction enabled observers to integrate contours under noisier conditions (P = .001), detect elements of lower contrast (P = .001) but did not quite improve orientation discrimination ability (P = .14). When elements were composed of high (rather than lower) spatial frequency, optical correction conferred a greater benefit for contour integration (P < .01) and contrast sensitivity (P < .05). Conclusion: Previous schizophrenia studies reporting contour integration, contrast sensitivity, or perhaps orientation discrimination deficits may need to be re-evaluated if they did not match for VA within the normal range. Our results also show that modest reductions in refractive blur strongly improve visual perception and that fitting patients with appropriate eyewear even in cases of questionable impairment may offer a host of benefits for normal visual functioning.
DOI: 10.1093/schbul/sbx022.022
Language: English
Open Access status: green
OpenAlex ID: W2598711495
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