Olfactory Imagery and Emotions: Neuroscientific Evidence
Stevenson and Case (2005) define olfactory imagery as “being able to experience the sensation of smell when an appropriate stimulus is absent.” Olfactory imagery is a form of odor presentation in addition to actual odors. In some cases, odors associated w
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ciated with an odor are further rated on the dimensions of familiarity, pleasantness and intensity on a 7-point scale. Stimuli with mean ratings of 5.5 were included in the pleasant odor category, and mean ratings below 2.5 were categorized as unpleasant. Agreement of 85% or above is required for inclusion in the stimuli. Eighty images, encompassing 30 each for pleasant and unpleasant odor and 20 for no odor associations, were included in the final stimuli set. Study design and participants This is a 3 (associated odor valence: neutral vs. pleasant vs. unpleasant) × 2 (tasks: view vs. olfactory mental imagery) within subject × 2 (sense of smell: normal vs. hyperosmics) mixed design study. Undergraduates and graduate students at a Midwestern university are recruited for participation in the study. Twenty participants are recruited for each of two groups based on sensitivity to smell, resulting in a total of 40 participants. These groups include participants with a normal sense of smell and hyperosmics, who are sensitive to smell. The individual difference groups are prescreened with a self-reported question which asks them to select the category that best characterizes their sense of smell: normal, sensitive to smell, decreased sense of smell or no sense of smell. Procedures and scales There are two tasks in this study, the passive view task and imagery task. In the passive view task, participants are asked to passively view the images. In the second task, the participants are instructed to perform olfactory mental imagery where they mentally form images of the odor associated with the object presented in the image. Each picture is presented on the screen for 1500ms. Thirty trials for each odor valence category (pleasant vs. unpleasant) are presented in random order along with 20 trials in the control condition. A total of 80 trials are presented in two blocks of 40 trials for each task. RESULTS AND DISCUSSION ERP results in emotion studies are interpreted and analyzed based on two primary parameters of emotions (Hajcak et al. 2012): 1) direction (movement toward or away from a stimulus) and 2) intensity (strength, speed or vigor of the movement). Based on the assumption of automaticity of emotions is associated with the unconscious formation of emotions, ERP methods have gain a lot of attention as a means for objective measurement of emotions. Late positive potential (LPP) is commonly identified as a midline centroparietal occurring after 300ms and may last up to 1500ms. LPP has been used to study emotion-relevant stimuli compared to neutral stimuli (Lang, Bradley and Cuthbert 1998). The initial analyses include data collected from 11 participants. These individuals self-reported themselves as normal. We analyzed LPP at the electrode site Pz, in the window of 500 to 700ms. Our results show that in the “view” condition, unpleasant odor-associated pictures appear to generate a higher level of LPP compared to pleasant and neutral (Fig. 1a). This is also present in the “imagery” condition (Fig.1b). Directly comparing the
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