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M.F. Couto, J.P. Brasil-Neto, V.F. Pessoa; Hemifield Anisotropy for Perceptual Filling-in: Comparison between Dichromats and Trichromats . Invest. Ophthalmol. Vis. Sci. 2003;44(13):1918.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To investigate perceptual filling-in difference between upper, lower and horizontal field positions, in trichromats and in dichromats. Filling-in time varies according to artificial scotoma and surrounding parameters, increasing at higher contrasts. Better reaction time and higher contrast sensitivity of the lower visual field has been demonstrated (Previc 1990). We examined whether the filling-in time at the lower visual field would be longer than at the upper visual field due to the alleged functional specialization. Also, whether the dichromats would have different filling-in performance, considering that they lack part of their parvo system and seem to compensate this with better magno function (e.g. brightness perception) than the trichromats (Verhulst & Maes 1998). Since we used gray stimuli, we expected similar or longer filling-in times for the dichromats, compared to trichromats. Methods: Stimuli were presented on a 17-inch monitor. The surrounding area had a luminance of 20 cd/m², target had 22 cd/m². Target was a circular patch, 0,8° diameter, with an eccentricity of 9° from fixation point, and presented at the angles 0°, 90°, 180° and 270°. We measured target fading time. Each angle was tested 30 times. All subjects gave their informed consent and the Brasília University’s Human Research Ethics Committee has approved this protocol. Results: Trichromats took more time for horizontal than vertical positions (p<0,01) and more for angle 270° than 90° (p<0,01). Dichromats were faster than the trichromats at all angles tested, took more time for horizontal than vertical positions (p<0,01), but showed no significant difference between 90° and 270° (p=0,043). Conclusions: We concluded, for conditions tested here, that the dichromats have more homogeneous field sensitivity for perceptual filling-in, than the trichromats do. We did not confirm our hypothesis of similar or longer filling-in times for dichromats and concluded, for these specific parameters and function, that the dichromat visual sensitivity may be lower than the trichromat’s may. The trichromat’s longer filling-in times at horizontal and 270° suggest higher visual sensitivity at these positions than at 90°.
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