Do the short‐wave cones signal blueness?

A simple correspondence between S‐cone response and the sensation of blueness has long been questioned. We measured color appearance using a series of S‐cone isolating stimuli and a paired comparison paradigm to identify a direct correspondence between S‐cone response and perceived hue strength. The results revealed a non‐monotonic reversal in perceived blueness at the unique‐blue line: The S‐cone increment initially increased blueness, but as S‐cone excitation grew past the pure‐blue line, blueness decreased and redness increased. It is difficult to account for this pattern of results by supposing that the sensation of blueness is mediated by a conventional linear channel that extracts (S+M)/L: If the ratio L:M is held constant, the output of such a channel should always increase with increasing S, and so inhibition from a second channel would be needed to account for our result. We also consider another category of explanation: The appearance of a given chromaticity may depend on its position relative to the fundamental axis of daylight locus, which serves as an internalized reference. In an account of the latter kind, there is a systematic mapping between chromaticities and sensations, but there does not need to be a distinct neural signal that represents “blueness.” © 2014 Wiley Periodicals, Inc. Col Res Appl, 40, 323–328, 2015