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Masahiko Terao, Ikuya Murakami; Compensation for equiluminant chromatic motion during smooth pursuit. Journal of Vision 2010;10(7):544. doi: 10.1167/10.7.544.
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© ARVO (1962-2015); The Authors (2016-present)
When we move our eyes, the world appears to remain stable. The visual system reconstructs a stable world in spite of the motion of the retinal image resulting from eye movements. During smooth pursuit eye movements, the retinal image moves in the opposite direction. To compensate for such retinal image slip, the visual system is arguably comparing retinal image velocity and estimated eye velocity. Our interest was whether equiluminant motion is compensated in a similar way by velocity comparison. According to the conventional view that color and motion are processed through separate neural pathways, compensation for color motion could have different properties. Alternatively, as we argued previously (VSS, 2007), early processes for luminance and color motions mediated by the magnocellular and parvocellular pathways might feed into a common velocity comparator. It is also unclear whether S-cone chromatic modulation, for which the koniocellular pathway is suggested to be responsible, is also compensated by similar velocity comparison. We measured the retinal image velocity required to reach subjective stationarity for a sinusoidal grating, using chromatic modulations determined in reference to a cone contrast color space in which two axes correspond to the chromatic tunings of the LGN neurons (L-M axis and S axis). The grating was drifting at various velocities. Results indicated that the retinal velocity at the point of subjective stationarity for both L-M-axis and S-axis chromatic modulations were faster than that for luminance modulation. Equiluminant chromatic motion is known to appear to move slower than luminance stimuli (e.g. Cavanagh et al. 1984). Our results suggest that speed reduction at equiluminant motion mediated by both parvocellular and koniocellular pathways takes place at an early processing level with retinocentric coordinates, followed by velocity comparison in which reduced retinal image velocity is compared with estimated eye velocity to compensate equiluminant motion during smooth pursuit.
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