Psychophysical Isolation of the Modality Responsible for Detecting Multimodal Stimuli: A Chemosensory Example Hisanori Nagata, Pamela Dalton, Nadine Doolittle, and Paul A. S. Breslin Monell Chemical Senses Center Multiple sense modalities can be stimulated conjointly by a physically complex item, such as a predator, and also by a physically solitary stimulus that acts on multiple receptor classes. As a prime example of this latter group, l-menthol from mint stimulates taste, smell, and several somatosensory submodalities. In 6 experiments that used a variety of psychometric techniques, the authors experimentally isolated the modality by which l-menthol is detected in the upper airways (the nose and mouth). Interestingly, absolute detection in both the nasal and oral cavities was based on olfaction and not stinging, cooling, or taste. These experiments illustrate how the sensory modality responsible for detecting a multimodal or multisensory stimulus can be psychophysically isolated. The ability to simultaneously use multiple sensory inputs to perceive the external environment is an adaptive characteristic of most vertebrates. Many real world entities, such as foods, preda- tors, and even conspecific animals, are physically complex stim- uli— emitting sounds, reflecting light, and releasing chemicals into the air. Physically simple stimuli, such as chemicals, may also stimulate multiple sensory systems and subsystems. To wit, recent evidence within the chemical senses suggests that traditional bitter-tasting compounds activate somatosensory neurons (Finger et al., 2003; Liu & Simon, 1998), thermal stimuli induce taste sensations (Cruz & Green, 2000), astringent compounds (alum) elicit taste sensations (Breslin, Gilmore, Beauchamp, & Green, 1993), and a large majority of olfactory stimuli elicit irritation in the nose (Cometto-Mun ˜iz & Cain, 1995) and possibly pharynx. Under these circumstances, it is very difficult to know which sense modality is responsible for detection of the stimulus or object, especially when qualitative information is lacking, as is often the case at absolute detection (Stevens, 1995, 1997). There are even individual stimuli that will stimulate several sensory systems si- multaneously, including, taste, smell, pain, tactile, and thermal sensations. The principal flavor in mint, l-menthol, is a prototyp- ical example of this type of stimulus. That a single physical stimulus may have multimodal action is a widely accepted idea. To this point, l-menthol is widely used as both a chemical cooling agent and as a counterirritant, that is, an analgesic, for intrinsic irritation (e.g., from oral and pharyngeal epithelia and from muscle). In the upper airways, l-menthol can elicit sensations using three different modalities: somatosensation (cooling, irritation, tingling, etc.), olfaction (minty), and gustation (bitter). Regarding menthol, complex sensory and perceptual in- teractions take place within the chemesthetic modality (Cliff & Green, 1993, 1996; Green, 1985), from the activation of submo- dalities such as irritation (burning, prickling, stinging, itching, etc.) to thermal effects (cooling, warming) and tactile effects (buzzing, tingling, tickling, numbing, etc.). In addition to stimulating odor and taste, menthol elicits stinging, numbing, touch, and a cooling sensation, which can inhibit the perception of warmth (Green, 1986, 1992). Humans experience l-menthol most commonly in the upper airways in the form of lozenges, chewing gums, cigarettes, tooth- pastes, and mouth washes. Humans can detect the presence of l-menthol in both the nasal and oral cavities; however, the relative sensitivity of each of these regions and the modality by which absolute detection of menthol occurs has not been well established. Thus, as a prototypical example of a compound that stimulates multiple sensory modalities, menthol could be detected using any of these sensory systems in either the nose or mouth. To illustrate this point, we conducted six experiments to psy- chophysically isolate the sensory modality responsible for the absolute detection of l-menthol. In Experiment 1, absolute detec- tion thresholds were measured in the nasal cavity for l-menthol in polyethylene glycol (PEG) 200. Oral detection thresholds with aqueous solutions were collected with and without nose clips to determine the effect of retronasal olfaction on oral thresholds (Experiments 2, 3A, and 3B). Volatile compounds do not flow retronasally into the nasal cavity when the nares are pinched close. Thus, when one’s nares are pinched in an oral detection threshold paradigm, oral sensations can be effectively isolated from nasal sensations. Because intranasal chemosensation can be based on either olfactory or somatosensory detection, we took advantage of the fact that an olfactory sensation cannot be localized, or even lateralized in humans (Kobal, Van Toller, & Hummel, 1989), and collected intranasal lateralization thresholds to identify whether nasal detection is olfactory or somatosensory based (Experiments 4 and 5). Experiments 3A, 3B, 4, and 5 attempted to refine the possible modalities responsible for the oral and nasal detection of l-menthol. Specifically, we asked whether oral thresholds were Hisanori Nagata, Pamela Dalton, Nadine Doolittle, and Paul A. S. Breslin, Monell Chemical Senses Center, Philadelphia, Pennsylvania. This research was supported by National Institutes of Health (NIH) Grant RO1DC03704 to Pamela Dalton and NIH Grant DC02995 to Paul A. S. Breslin. We thank Ines Rodriguez and Jeanmarie Diamond for their assistance with laboratory work and Barry Green for his advice regarding olfactory lateralization techniques. Correspondence concerning this article should be addressed to Paul A. S. Breslin, Monell Chemical Senses Center, 3500 Market Street, Phil- adelphia, PA 19104. E-mail: breslin@monell.org Journal of Experimental Psychology: Copyright 2005 by the American Psychological Association Human Perception and Performance 2005, Vol. 31, No. 1, 101–109 0096-1523/05/$12.00 DOI: 10.1037/0096-1523.31.1.101 101