Measuring surface achromatic color: toward a common measure for increments and decrements

Functional symmetry of the primary visual pathway evidenced by steady-state visual evoked potentials

The primary visual pathway exhibits a symmetrical anatomical structure, initially arising from the left and right retinas, passing through the lateral geniculate nucleus, and finally projecting to the left and right primary visual cortices. However, to our knowledge, studies based on scalp EEG have not provided adequate evidence of the functional symmetry of the primary visual pathway, as the usual visual ERP is often related to other higher-level brain areas. Steady-state visual evoked potentials (SSVEPs) can be considered as the direct response of the primary visual pathway to a repetitive stimulus, with a very limited correlation with responses of higher-level brain areas. Therefore, SSVEPs can be used to evaluate the functional symmetry of the primary visual pathway. In this study, we draw a comparison among the powers and distributions of SSVEPs of different frequencies when the left or right eye alone is stimulated, and when both the eyes are stimulated together. Our results indicate that the primary visual pathway is almost symmetrical in generating SSVEPs from either eye and that there is some functional interaction between the left and right primary visual pathways.

Measuring the meter: on the constancy of lightness scales seen against different backgrounds

The constancy of a 16-step achromatic Munsell scale was tested with regards to background variations in two experiments. In experiment 1 three groups of observers were asked to find lightness matches for targets in simultaneous lightness displays by using a 16-step achromatic Munsell scale placed on a white, black, or white-black checkered background. In experiment 2, a yellow-blue checkered background and a green-red checkered background replaced Munsell scales on the black and on the white backgrounds. Significant effects of scale background on matches were found only in experiment 1, suggesting that background luminance is a crucial factor in the overall appearance of the scale. The lack of significant differences in experiment 2, however, may stand for an overall robustness of the scale with respect to background luminance changes occurring within certain luminance ranges.