Fig. 5.

Perceptual ratings of melanopsin, luminance, and light flux. Subjects rated nine qualities of spectral pulses that targeted melanopsin, luminance, and their combination (light flux). (A) The set of perceptual ratings was subjected to a principal components analysis. Each circle corresponds to the ratings provided by one subject for one stimulus type within the space defined by the first two dimensions of the PCA solution. A linear support-vector machine was trained to distinguish ratings for melanopsin stimulation from the other two stimulus types within this 2D space. The classification boundary is shown. (B) The classification dimension (normal to the classification boundary) describes how melanopsin stimulation was perceived differently from light flux and luminance. The mean weights (across bootstrap resamples) that define the classification dimension are shown.