Abstract
Human Color Vision and Tetrachromacy is an Element in Cambridge University Press’ new and innovative publishing model that encourages authors to consider recent advances and important outstanding questions in focussed areas of research. From that perspective, the authors of Human Color Vision and Tetrachromacy use the Element format well.
In Sections 1 and 2, the book offers a succinct overview of the genetic complexities underlying human colour perception. The authors, who have made many valuable contributions to this area and are experts in the field, highlight how scientific advances over the past 30 years have led to vital insights into the genetics of human colour perception. It has become increasingly clear that the photoreceptors in the eye allowing for colour perception are varied in both their spectral sensitivity and density across individuals, due in part to the similarity between the genes that encode for the middle and long wavelength sensitive cone opsins and their closeness on the X chromosome. Quite rightly, the authors argue that the breadth of evidence in this direction calls for the field to rethink standard models of human trichromacy. Specifically, the authors encourage investigations into the possibility of functioning human tetrachromats who may see colour in four dimensions, rather than three, due to X-linked opsin gene heterozygosity. They support this suggestion not only by reviewing the wealth of evidence that shows expression of four distinct cone classes in people with opsin gene heterozygosity, but by carefully discussing several studies that find enhanced colour perception in these individuals. These studies suggest that colour processing mechanisms are plastic enough to incorporate the extra signal from a fourth receptor class into normal processing.
The authors discuss how current methods for assessing, modelling, and analysing human colour perception are often incapable of detecting variants in trichromatic or tetrachromatic colour perception that differ from the normal range. They argue that novel experimental methods must be developed for individual differences in “normal” human colour perception to be explored and characterised more fully in the future. In Section 3, the authors describe one of their own experimental designs capable of detecting superior colour perception. The design is identical to an experiment reported previously by the same group and assesses colour reproduction by asking participants to use mixtures of pigments to match a reference patch of colour (Bochko & Jameson, 2018). Here, the authors present new data where eight of nine participants show enhanced colour reproduction ability that is predicted by their underlying genotypes.
The book will certainly be of interest to readers of Perception, but those with some prior knowledge in the field of colour perception and genetics will likely find it more accessible than others. The concise introduction to colour perception is a positive for those already familiar with the topic, but may be too sparse for others who are new to the area. This is highlighted by examples of terminology use such as SWS, MWS, L’WS, and LWS to refer to short, middle, anomalous-long, and long wavelength sensitive cone types without explicitly defining this shorthand or informing the reader that L’ is commonly used to represent anomalous long wavelength sensitive cones. Similarly, the book is not self-contained, as the reader is often referred to the earlier publication for details on the novel method introduced in Section 3.
Personally, I would have preferred to see the authors take a firmer stance on their suggestion that there is a need to rethink models of colour perception to account for individual differences in photoreceptor sensitivity. From the abstract and initial introduction, I expected the authors to spend more time thinking about how colour perception may vary greatly even in trichromacy, not just tetrachromacy. The authors touch on this throughout, but focus on reviewing the literature that searches for functioning tetrachromats. Subsequently, the scope of the literature review is narrow. The same is true in Section 3, where the authors could have devoted more time to exploring alternative methods for investigating enhanced colour perception, but chose instead to use this section (almost half of the text) to discuss a single piece of their own research in detail.
Overall, the book is a comprehensive account of research and current thinking regarding the possibility of human tetrachromacy. By bringing together the literature in this way, the authors make a compelling case for a change in thinking and push the field to expand on the standard trichromatic model of human colour perception. The first two sections are the most detailed and coherent summary of human tetrachromacy research I have seen and should serve the community well as a general reference. It can also serve as a source for introducing the idea of human tetrachromacy to those who already have some basic knowledge on the topic of human colour perception. However, I think the book will have the greatest impact on those already actively doing research in the field of human colour perception who may benefit from incorporating some of the ideas presented here into their own thinking.
