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Toshio Kubodera, Takao Sato; Non-classical receptive field structure for motion mechanisms revealed by lateral masking. Journal of Vision 2002;2(7):393. doi: 10.1167/2.7.393.
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Purpose: The main objective was to examine non-classical receptive field structure for motion mechanisms using lateral masking paradigm. Length-width ratio for classical motion-dependent receptive fields has been estimated close to one by using masking and spatial summation techniques, while the ratio for motion-independent mechanisms are known to be elongated with ratios approximately 1.8 or 2. As for non-classical receptive fields, Polat and his collaborators found elongated receptive fields by using lateral masking paradigm.
Methods: Stimuli consisted of three Gabor patches arranged vertically or horizontally. The central patch was the target signal, and peripheral patches were the mask signals. The target signal drifted at the same temporal frequency as the mask signals in a direction either the same as or opposite to the mask. Consequently, there were four experimental conditions. The separation between target and masks were 3 cycles of wavelength. With these stimuli, we measured the contrast threshold for target motion as a function of mask contrast.
Results: For the same direction conditions, the threshold first decreased to its minimum and then increased. However, for the opposite direction conditions, threshold did not change regardless of mask contrast. Results were quite similar to vertical and horizontal arrangements. In addition, we estimated the relative magnitudes of contrast for vertical and horizontal conditions using the results. Although Polat and his collaborators have reported a higher enhancement for vertical than for horizontal arrangement, we obtained similar enhancements for the two conditions.
Conclusions: The present results together indicate that the non-classical motion-dependent receptive fields have characteristics fundamentally different from those of motion-independent non-classical as well as classical receptive fields.
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