Neural Basis Of Color Brightness At Different Temporal Frequencies

Color and luminance are crucial in human visual experience,and luminance is the standard of stimulus in visual research.However,many phenomena show that human heterochromatic brightness perception is very different from luminance.For example,when the luminance is consistent,high-saturation chromatic blocks appear brighter than achromatic blocks.As the color channel is known to be insensitive to high temporal frequency stimulus,and luminance is determined by an experimental paradigm(Heterochromatic flicker photometry)at high temporal frequencies,while brightness is determined by some experimental paradigms at low temporal frequencies,so exploring the neural responses to color stimuli at different temporal frequencies is crucial to understanding color brightness.In experiment 1,the behavioral task was used to explore the brightness weights of different colors through the brightness ranking task.The stimulus is the seven colors determined by the combination of the three primary colors.The behavioral results were analyzed by the psychophysical method to obtain the brightness weights of each of the seven colors;then the results were analyzed by fitting a non-linear model to obtain the brightness weights of the red,green and blue primary colors,which differ from the ratio of the luminance of the three primary colors,and the brightness is more in line with the maximum rule under the non-linear model.In experiment 2,functional magnetic resonance imaging(f-MRI)was used to explore the neural response in different visual cortexes at two frequencies.Seven colors in the same combination as in Experiment 1 were used,flickering sinusoidally at two temporal frequencies(3 Hz and 15 Hz).(1)The results of correlation analysis showed that there was a significant positive correlation between activation intensity and brightness weights at 3 Hz in V2 and V4 regions,and a significant positive correlation between activation intensity and luminance at 15 Hz in both V1,V2 and V4 regions.(2)Two-way ANOVA and paired-samples t-test on the Euclidean distance between activation intensity and two models at two temporal frequencies showed that the interaction between two temporal frequencies and two models(luminance and brightness)was significant in V1 and V4 regions.In V1 and V4 regions,the activation intensity at 3Hz was more consistent with the brightness model compared to the 15 Hz condition.In V1,V2 and V4,the activation intensity at 15 Hz is more consistent with the luminance model compared to the brightness model.(3)The results of multivariate pattern analysis showed that in the V1 region,the decoding accuracy of distinguishing different colors at 3Hz was greater than that at 15 Hz,and the high temporal frequency better characterized the luminance.In summary,the neural responses at low temporal frequencies were more consistent with the color brightness pattern,and those at high temporal frequencies were more consistent with the luminance pattern.At low temporal frequencies,the integrated encoding of color and luminance information is more likely to occur in regions V2 and V4 than in region V1,resulting in color brightness.