Objective:

To inform how odor concentration may change color perception in a synesthete.

Background:

In a synesthete, different concentrations of the same odor inducing different colors has not heretofore been described.

Design/Methods:

Case Study: This 27-year-old right-handed single male presented with a lifelong history of odor-color synesthesia. Each odor is associated with a specific color. While odors induce perception of color, colors do not induce perception of odors.

Results:

Amyl acetate in concentrations diluted in USP grade mineral oil to 10%, 1%, 0.1% 0.01% (Moberg, 2003; Doty, 1995) was presented randomly six times. This demonstrated retest reliability as well as change in color as identified on the Hexadecimal Real Color Wheel (Jusko, 2022), as opposed to change in brightness, with the most intense, 10% and 1%: yellow; 0.1%: orchid; and 0.01%: light pink. This revealed change in intensity correlated with change in color as opposed to change in luminescence.

Conclusions:

Some odorants, when presented with higher concentration, induce perception of entirely different aromas, as occurs with hydrogen sulfide (Hirsch, 1996). This would be consistent with each percept of odor inducing its own color. Peradventure, the increased intensity of each of the odors may decrease the perception of brightness or luminance (Zellner, 2008). This, minimal but still discreet, well-defined inducers, precipitating superimposition of specific colors, may be viewed as a variant of synesthesia, a super-synesthete. This suggests the presence of an underlying synesthetic network hyperconnectivity with the V4 occipital lobe, the primary color area of the visual cortex (Gennaro, 2021), and the hippocampal representation of memory of aroma (White, 2015), or olfactory lobe (orbital frontal cortex and insular cortex) (Mauric, 2013), and V4 occipital lobe hyperconnection (Hubbard, 2005). Further exploration of such connections may reveal greater understanding of olfactory and visual system.