The final four chapters of this volume probe the theme of inter-individual variations in perceptual and cognitive performances in the chemical senses, a topic often encountered briefly in earlier chapters. Several chapters have described how group performances depend on previous exposure to odorants (e.g., Chapters 3, 8-10, and 21) and to tastants (Chapters 22 and 23). All those chapters have outlined emotional and memory processes evoked by odors and tastes that are at the core of an individual's functioning.

The chapters in this section more specifically address issues of chemosensory variability linked with individual constitution and with the interactions between individuals and given environments. Katharine Fast and colleagues (Chapter 24) offer a survey of the relationship between taste ability and an individual's genetic makeup. They highlight the phenomenon of taste blindness to bitter tastants as a window to individual variability in taste function. From that starting point they examine how it is possible to develop standard tools for measurements of taste intensity and hedonicity despite the considerable variability of individuals, ranging from nontaster to supertaster status. They examine the links between individual psychophysical data and the anatomical variations of the tongue, indicating that supertasters have higher fungiform papilla counts and rate stimuli as more intense. Similar structure-function correlates can explain sex differences.

In Chapter 25, Robyn Hudson and Hans Distel develop the argument that we will not be able to properly account for olfactory function without paying closer attention to the role of the conditions that have molded it in the individual-specific environment.