Neuroscience Letters 411 (2007) 6–10 Investigations on multimodal sensory integration: Texture, taste, and ortho- and retronasal olfactory stimuli in concert Johannes H.F. Bult a,b,∗ , Rene A. de Wijk a,b , Thomas Hummel c a Wageningen Centre of food Science, Wageningen, The Netherlands b Centre for Innovative Consumer Studies, Wageningen University and Research Centre, P.O. Box 17, 6700 AA Wageningen, The Netherlands c Smell and Taste Clinic, Department of Otorhinolaryngology, University of Dresden Medical School, Dresden, Germany Received 22 June 2006; received in revised form 11 September 2006; accepted 18 September 2006 Abstract Perceptual interactions between odour and oral texture were explored in a study in which a cream odour was presented ortho- or retronasally at well-defined moments whilst milk-like foods with different viscosities, produced by adding a thickener, were present in the mouth. Gaseous (odour) and liquid (texture) pulses were presented using a specially-developed computer-controlled system of air-dilution olfactometry and pumps. Odour pulses, lasting 2s, were presented either during a 3-s period in which a liquid filled the oral cavity, during a 3-s period in which the liquid was manipulated orally or during the swallowing of the liquid. Subjects rated the intensity of overall flavour, thickness and creaminess. Perceived flavour intensity was reduced with increasing viscosity of the liquid, irrespective of whether or not the odour was presented ortho- or retronasally. The odour stimulus increased the intensities of thickness and creaminess, but only when the odour was presented retronasally that is as if the odour would have originated from the liquid. Furthermore, this enhancement was most pronounced when odours coincided with swallowing, less pronounced when odours coincided with oral manipulation and absent when presented during mouth filling. The results suggest that cross-modal interactions are the rule rather than the exception, provided that multi-modal sensory integration has occurred. © 2006 Elsevier Ireland Ltd. All rights reserved. Keywords: Multimodal interaction; Odour; Flavour; Oral texture; Stimulus congruency Human perception of food flavour and texture during consump- tion involves taste, mouth feel, vision, olfaction, trigeminal stimulation and auditory signals that contribute to the total appre- ciation of a food product. In their contribution to perception of the food, these different sensory modalities may interact in a non-linear way [11]. One such cross-modal phenomenon is the influence of texture on the odour of a food product: increas- ing viscosity is consistently found to reduce odour intensity. This effect has been interpreted solely in thermodynamic terms resulting from the lower volatile mobility at the food–air inter- face [20]. However, more recent findings suggest that these interactions occur in the central nervous system since aroma sup- pression by increased viscosities also occurs when nasal volatile concentrations remain unaffected [6,15,27,28]. In addition to texture-odour interactions, perceptual taste- odour interactions have also been demonstrated in numerous psychophysical studies. At threshold levels, odours may enhance ∗ Tel.: +31 317 475274; fax: +31 317 475347. E-mail address: harold.bult@wur.nl (J.H.F. Bult). taste intensity and tastes may enhance odour intensity [7]. At supra-threshold levels, this mutual interaction occurs consis- tently only when the odour and taste qualities are congruent, i.e., when combinations have been experienced before such as a sweet taste presented together with strawberry odour [12]. Apparently, qualitative congruence between stimulus modal- ities allows for the occurrence of multi-modal sensory inte- gration (MSI), i.e., the blending of distinct sensory modalities into a unitary percept. In this case, odours may be confused with tastes [8,26]. Evidence for the existence of multi-modal cortical response patterns was presented by Small et al. [24] who demonstrated that specific brain areas were activated in a super-additive fashion by familiar taste–odour combinations (e.g., sweet–vanilla) but not by unfamiliar combinations (e.g., salty–vanilla). Orthonasal olfactory perception occurs during odour sniff- ing and allows a person to assess the quality of the food before consuming it. Studies on aroma release from liquids and semi- solids have shown that swallowing determines, to a large extent, the retronasal aroma release [29]. Videofluorescopy measure- ments showed the formation of a thin layer of food product on 0304-3940/$ – see front matter © 2006 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.neulet.2006.09.036