Visual acuity measurement: Account of the optotype structure G Rozhkova, D Lebedev |
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IITP Russ Acad Sci, Russian Federation
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| Many optotypes used nowadays for visual acuity measurements were created without analysis of information processing that underlies subject’s decision making during examination. In the cases of complex optotypes, such analysis requires taking many functional modules into account. We studied some theoretical aspects of measuring visual acuity with simple optotypes – 3-bar resolution targets – in the task of orientation discrimination. Earlier, in our experiments, we found 3 types of psychometric functions indicating that some subjects were capable to use the low-frequency information (LFI) contained in the Fourier spectra of the optotypes while other subjects either ignored LFI or misused it (Rozhkova et al., 2012 Sensory Systems 26(2) 169-171). The new experiments carried out in conditions of presenting single stimulus line and starting from the smallest size, have shown that, at the beginning of examination, the naïve subjects often misuse LFI but, later, use it properly. For modeling subject’s behavior, we developed a mathematical model of orientation discrimination mechanism describing visual stimulus transformations from the optical retinal image to the neuronal one on the basis of Gabor filters and implying a possibility of creating autonomous low-frequency and high-frequency neuronal images. |
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