Time and intensity factors in identification of components of odor mixtures

Abstract

Identification of odors of compounds introduced into changeable olfactory environments is the essence of olfactory coding, which focuses perception on the latest stimulus with the greatest salience. Effects of stimulus intensity and adapting time on mixture component identification after adapting with one component were each studied in 10 human subjects. Odors of 1 and 5 mM vanillin (vanilla) and phenethyl alcohol (rose) were identified, with adapting time varied by sniffing naturally once or twice, or sniffing 5 times, once every 2 s. Odors of water-adapted single compounds were identified nearly perfectly (94%), self-adapted to 51% but did not cross-adapt (94%), showing the 2 compounds had quickly adapting independent odors. Identifications of the vanilla and rose odors in water-adapted mixtures were reduced to 59% and 79%, respectively. Following single-component adaptation, the average 33% identification of odors of adapted (ambient) mixture components contrasted with the greater average 86% identification of new unadapted (extra) mixture components. Identifications were lower for 1 than 5 mM components when concentrations were not matched, and ambient component identifications were lower after 10-s adaptation than after 1 or 2 sniffs. Rapid selective adaptation and mixture component suppression manipulate effective intensity to promote emergence of characteristic odor qualities in dynamic natural settings.

Figure 1

Data matrix for experiment 1—stimulus concentration: total responses and average percentages identified by 10 subjects. V = 5 mM vanillin, v = 1 mM vanillin, R = 5 mM PEA, r = 1 mM PEA, 0 = water. Gold background highlights correct responses of 10 subjects for the 2 sessions, averaged for % identification. The 36 adapt–test pairs were presented to each subject in each session. Each row represents a separate trial.

Figure 2

Data matrix for experiment 2—adapt stimulus time: total responses and average percentages identified by 10 subjects. V = 5 mM vanillin, v = 1 mM vanillin, R = 5 mM PEA, r = 1 mM PEA, 0 = water. 1 sniffs = 1–2 natural sniffs of adapting stimulus, 5 sniffs = 5 timed sniffs, 2 s apart of adapting stimulus. Gold background highlights correct responses of 10 subjects for the 2 sessions, averaged for % identification. Thirty-two adapt–test pairs were presented at 1 or 5 mM concentrations in separate sessions. Each row represents a separate trial.

Figure 3

Experiment 1—single component cross- and self-adapted stimuli. Regardless of concentration, characteristic odors of vanillin (VAN) and PEA were readily identifiable after water (dotted horizontal lines) or cross-adaptation (Cross); but, after self-adaptation (Self), odors of single compounds were less salient, the rose odor even less than the vanilla odor. Means (+standard error of the mean) are plotted.

Figure 4

Experiment 1—mixture component extra and ambient test stimuli. Within a binary mixture, the vanilla odor of vanillin (VAN) was less identifiable than the rose odor of PEA at high and at low concentrations (dotted horizontal lines, 2 for each compound). The 2 characteristic odors were more salient when they were extra components and less salient when they were ambient components, regardless of concentration. The dotted horizontal lines are separate controls for the 2 compounds at the 2 concentrations. Means (+standard error of the mean) are plotted.

Figure 5

Experiment 2—test stimulus identification, matched concentrations, and adapting times. (A) Concentration did not affect identification when concentrations of adapt–test stimulus pairs were matched. (B) Adapting time had little influence on identification, with one exception. Ambient mixture components were better identified after the shorter adaptation time. 1 sniff = 1–2 natural sniffs; 5 sniffs = 5 timed 2-s sniffs. Means (+standard error of the mean) are plotted.

Figure 6

Experiment 2—cross-adapted, self-adapted, and mixture-adapted single components. Characteristic odors of vanillin (VAN) and PEA were equally identifiable when preceded by water (dotted horizontal lines) or after cross-adaptation (CROSS). But, after self-adaptation (SELF) or mixture adaptation (MIXTURE) the rose odor and vanilla odors of single stimuli were less salient. Means (+standard error of the mean) are plotted.

Figure 7

Experiment 2—extra, ambient, and mixture-adapted mixture component test stimuli. Within a binary mixture, the vanilla odor of vanillin (VAN) was less identifiable than the rose odor of PEA (dotted horizontal lines). Characteristic odors of extra mixture components were as identifiable as unadapted single stimuli (cf. Figure 4). Characteristic odors of ambient mixture components were as identifiable as components presented after the mixture (ADAPTED) and less identifiable than self-adapted single components (cf. Figure 4). Means (+standard error of the mean) are plotted.