Attentional modulation of desensitization to odor

Abstract

Subjective and behavioral responsiveness to odor diminishes during prolonged exposure. The precise mechanisms underlying olfactory desensitization are not fully understood, but previous studies indicate that the phenomenon may be modulated by central-cognitive processes. The present study investigated the effect of attention on perceived intensity during exposure to a pleasant odor. A within-subjects design was utilized with 19 participants attending 2 sessions. During each session, participants continuously rated their perceived intensity of a 10-minute exposure to a pleasant fragrance administered using an olfactometer. An auditory oddball task was implemented to manipulate the focus of attention in each session. Participants were instructed to either direct their attention toward the sounds, but still to rate odor, or to focus entirely on rating the odor. Analysis revealed three 50-second time windows with significantly lower mean intensity ratings during the distraction condition. Curve fitting of the data disclosed a linear function of desensitization in the focused attention condition compared with an exponential decay function during distraction condition, indicating an increased rate of initial desensitization when attention is distracted away from the odor. In the focused-attention condition, perceived intensity demonstrated a regular pattern of odor sensitivity occurring at approximately 1-2 minutes intervals following initial desensitization. Spectral analysis of low-frequency oscillations confirmed the presence of augmented spectral power in this frequency range during focused relative to distracted conditions. The findings demonstrate for the first time modulation of odor desensitization specifically by attentional factors, exemplifying the relevance of top-down control for ongoing perception of odor.

Keywords: Adaptation and aftereffects; Cognitive and attentional control; Olfaction.

Fig. 1

Mean perceived intensity ratings and desensitization curves. Blue indicates mean intensity ratings (arbitrary units) with shading to indicate standard error distribution for all 720 timepoints in the focused attention condition; red indicates the distraction condition. Gray rectangles indicate time periods when mean intensity ratings differ significantly between conditions. (Color figure online)

Fig. 2

Desensitization data and curve functions of best fit. Black dashed and solid lines show mean intensity ratings (arbitrary units) and curve fitting, respectively, for 120 seconds following maximum perceived intensity in the focused attention condition; gray solid and dashed lines represent data and curve fitting for the distraction condition. Note the divergence between curves in the period 10–80 seconds following maximum perceived odor intensity.

Fig. 3

a Perceived odor intensity ratings for a single subject in focused attention (solid line) and distraction conditions (dashed line). b Log power spectral density for slow oscillations (<0.2 Hz) in same single subject for focused attention (solid) and distraction (dashed) conditions. c Log power spectral density for all subjects for focused attention (solid) and distraction (dashed) conditions. Gray rectangle indicates frequencies demonstrating a significant difference in relative power between conditions