Figure 9. Mean recall accuracies by odor stability.
5.2 Valence Ratings
As seen in Figure 10, objects with congruent odors seem to be rated as more pleasant than incongruent and odorless ones. One-way ANOVA showed a significant effect of odor congruency on the ratings of valence, F(2, 14) = 5.743, p = 0.015. Post hoc pairwise comparisons showed that congruent objects were rated significantly more pleasant than incongruent MD = 1.3, p = 0.03, or odorless, MD = 1.1, p = 0.03 ones. The difference of ratings between incongruent and odorless objects was not significant MD = 0.95, p = 0.595.
Figure 10. Mean valence ratings by odor congruency.
0 20 40 60 80 100
Static Dynamic
Recall accuracy %
-4 -3 -2 -1 0 1 2 3 4
Congruent Incongruent Odorless
Valence
To find out the effects of odor stability on valence, an independent samples t-test was conducted (see Figure 11). There was no statistically significant difference in the ratings of valence between static and dynamic objects, t(6) = -0.079, p = 0.940.
Figure 11. Mean valence ratings by odor stability.
5.3 Arousal Ratings
As seen in Figure 12, objects with incongruent odors were rated slightly more arousing than congruent and odorless objects and the odorless slightly more relaxing than congruent and incongruent objects. One way ANOVA, however, showed no statistically significant effect of odor congruency on the ratings of arousal F(2, 14) = 1.425, p = 0.273.
-4 -3 -2 -1 0 1 2 3 4
Static Dynamic
Valence
Figure 12. Mean arousal ratings by odor congruency
Dynamically scented objects were rated as slightly more arousing than the other objects (see Figure 13). Independent samples t-test showed no statistically significant difference in the ratings of arousal between static and dynamic objects, t(6) = -1.197, p = 0.277.
Figure 13. Mean arousal ratings by odor stability.
-4 -3 -2 -1 0 1 2 3 4
Congruent Incongruent Odorless
Arousal
-4 -3 -2 -1 0 1 2 3 4
Static Dynamic
Arousal
5.4 Discussion
The present results showed that there were no statistically significant effects of scent dynamics or scent congruence on the number of recalled objects immediately after the interaction with the experimental maze. There was, however, a nonsignificant trend towards better recall of congruent objects, which would be in line with previous studies [Rantala et al. 2019]. Odor stability also did not have other than a nonsignificant trend towards better recall of dynamic objects.
These trends would indicate that the object-odors pairs that have the most natural quality combinations, or in other words, objects that have matching, dynamic odors, would be recalled the best.
Highly arousing stimuli are shown to be remembered more accurately in free recall tasks [Bradley et al. 1992]. However, in the current study incongruent objects trended towards evoking the highest arousal ratings but were not recalled better than congruent or odorless ones. On the other hand, dynamic objects trended towards evoking higher arousal ratings than static ones and were recalled better. This difference might indicate that better recall of congruent and dynamic objects versus incongruent and static is not mediated by arousal.
Congruency and changing odor intensity might guide attention towards the objects more than incongruency and static odor intensity, and with that increases also the number of recalled objects. Congruency also helps with the dual coding of the encountered information by making an intact image of the object in memory which might also help with recall [Paivio 2007].
Main finding of the experiment was that congruent objects were rated as more pleasant (1.75) than incongruent (0.47), or odorless ones (0.66). This is in line with previous research [Rantala et al. 2019]. This finding also supports the research by Flavián et al. [2021] in that congruent scents increase affective reactions in VR experiences more than incongruent or odorless scents. Odor stability on the other hand did not have any effect on valence.
The object-odor pairs that were congruent might be more pleasant than incongruent pairs because participants smelled what they expected to smell. When seeing a lemon object, a lemon-like odor is expected. The object-odor pairs that were incongruent, were surprising and did not fit any mental models, and might have therefore been considered unpleasant. For example, mushroom was expected to smell mushroom-like, but instead it smelled like lemon. Odorless objects were probably considered more neutral than odorous ones, and therefore evoked only mildly pleasant emotions.
There were statistically nonsignificant trends towards incongruent objects causing higher ratings of arousal than congruent or odorless ones. Odorless ones were rated as slightly relaxing. Also, dynamic objects trended towards higher arousal than static ones.
This would support previous studies in that adding odors to objects makes them more arousing [Bensafi et al. 2002], and especially incongruent ones induce the highest arousal ratings [Rantala et al. 2019]. The surprising element of unmatching visual and olfactory cues might lead to greater arousal. When it comes to dynamic odors, the increased arousal might be due to two things. First, as the highest intensity level was only present in the dynamic condition, the stronger odor intensity in itself might have affected arousal. Second, adding dynamic intensity change increases the amount of information to be processed when interacting with an odorous object, which in turn might increase arousal.
The average arousal and valence ratings were quite neutral, ranging from -1 to 1, except the valence of congruent objects. The olfactory stimulus was probably not strong enough to cause any stronger emotional reactions.
The experiment had some limitations. First, the number of participants was low.
The planned number of participants (30) was not achieved due to the COVID-19 situation, as many possible participants might have been too scared to come to the experiment. The nonsignificant trends might have turned significant with the planned number of participants, and it would be beneficial to continue the experiment to see if this would be true and to find out if there indeed are any effects of odor intensity change on recall accuracy.
Second, there was no objective measurement of the intensity change, the three levels were only tested on human nose. Therefore, there may have been slight differences between participants due to, for example, unwanted evaporation of odorants. Using only three levels is also not an adequate replication of real-world odor intensity changes, as real objects emit odors at a relatively constant pace and when the object is brought closer to the nose, the intensity increases smoothly without jumping from one level to the next.
The current experiment can pave way for future research on odorous virtual environments. Especially the intensity change of odors would need closer examination.
Questions remain such as how important changing intensity is for successful virtual experiences in the first place, in other words, does it increase affective reactions and memories in a VR setting. And if it does, how accurately and similar to real life it should be done.