Smell and 3D Haptic Shapes

Some research in recent years has focused on olfactory perception and how it is highly affected by participation of crossmodal and multisensory perception. An important role in crossmodal interaction has the subject bias to naming the odor, or to represent it in an odor mental imagery, even if the task does not require it. However, although the effect of crossmodal interaction in smell is going to be well investigated, little attention has been paid to facilitation expressed by haptic interaction with a manipulation of the odorous object's shape. Aim of this work is to investigate the interaction and haptic facilitation in a smell task. Ten healthy subjects (25y.o. ± 5 SD), non-smokers, were trained to haptic manipulation of 3D models and olfactory stimulation in a black case. To avoid effects such as color or different textures of the odorous objects models were 3D printed with a monotone blue with rough texture. The smells were selections from five representative types of categorical spatial dimension on the odors (i.e., Cinnamaldheyde, Citral, Hexanal, Phenethyl Alcohol, Acetophenone, Eucalyptol, Carvone, 1 octen-3-ol, Isoamyl Acetate). 9 odors were presented in crossmodal haptic mode (OH), and 27 odors were presented in visual condition (OV). Subsequently, an odor-visual recognition task was arranged during an EEG recording, to investigate ERP components. The subject had to press the Left button if his predominant recognition had been codified through OV or Right button if it had been codified as OH. After the EEG recording, the subject had to perform an odor span task and fill a VAS on 3 dimensions: familiar, arousing and pleasantness. The effects of OV and OH condition and lateralization of N200 and P3b were assessed via linear mixed-effects models that allows controlling the variance related to random factors without any data aggregation. Models were estimated with the lme4 package in R whereas F-tests were computed with the Satterthwaite's degrees of freedom approximation. We found that latencies and amplitudes of N200 increased in the OH condition (F=11.04 p<0.001, F=3.38 p<0.05, respectively), with a significant two-way interaction odor x left-sided lateralization (F=6.32, p<0.001). Significant effects were particularly observed in left occipital, left parietal, and left temporal areas. Concerning P3b, the omnibus test revealed a significant effect of the lateralization (F=4.11, p<0.05) with amplitudes increasing in left and right occipital and parietal areas as well as in Cpz and Pz. The effects of the OH condition were also confirmed by the behavioral data. Subject’s Odor Span was 5, and was linked only to OH condition. The VAS indicated that stimuli assessed in the crossmodal condition were evaluated more pleasant and familiar with respect to the control condition. These results suggest that haptic, comparing visual interaction, can highly affect odor recognition.