Reproducibility of peak clusters and the effect of luminance. (A)-(C) Repeated imaging of the clusters shown in panels D-F, after five hours. Only four hues (red, yellow, green, blue) were used in this experiment, but the same red stimulus was repeated six times, producing six red-associated peaks in each cluster. In addition, a brighter red stimulus and a darker red one were also used, and their associated peaks are marked over two red squares by a white and black cross, respectively. (D)-(F) Re-drawn of the clusters shown in panels I, F, and L of Fig. 6, respectively. Scale bar: 100 μm.