Time Course of Perceptual Adaptation Differs among Odorants

Perceptual adaptation, a fundamental property of all sensory systems, functions to attenuate neural and perceptual responses to sustained or redundant stimulation as a means of limiting neural saturation and of enhancing the detection of new transient stimuli. While our understanding of the complex physiological mechanisms underlying adaptation has grown in recent years, how these processes are affected by individual odorant properties remains unclear. Recent data from our laboratory demonstrate that the onset time course of perceptual odor adaptation can be estimated by use of a simultaneous-odorant-stimulus paradigm, where the delay from the onset of a relatively long-duration adapting odorant to the onset of a brief target odorant is varied. Adaptation was observed as an increase in threshold with increasing adapting-to-target-odorant onset delay. Using this technique, we compared the estimated onset time course for four common odorants (vanilla extract, coconut extract, vinegar and propanol). Thresholds were estimated for a brief target odorant presented during a simultaneous adapting odorant in a group of college-aged student volunteers (n = 124; 88 females). Onset of adaptation for the vanilla and coconut mixtures was more rapid than for vinegar and propanol, though the asymptotic levels (approximately 400 ms) of adaptation were similar for coconut extract, vanilla extract and vinegar. In contrast, propanol did not reach asymptotic levels within the 1,000-ms timeframe. Considering propanol is a pure alcohol, relative differences in trigeminal reactivity may partially explain this variance in adaptation contours. Practical Applications A method for capturing rapid changes in response to odor adaptation is described. The automated method can be reliably used to compare both the magnitude and time course for a wide range of stimuli. The technique may be reproduced to evaluate how individual olfactory sensitivity changes in response to prolonged stimulation. Importantly, this procedure can be used to assess shifts in odor perception on rapid timescales – in the 50–100-ms range, rather than seconds or minutes.