Nobuyuki Sakai

The effect of order of dwells on the first dwell gaze bias for eventually chosen items

The relationship between choice and eye movement has gained marked interest. The gaze bias effect, i.e., the tendency to look longer at items that are eventually chosen, has been shown to occur in the first dwell (initial cohesion of fixations for an item). In the two-alternative forced-choice (2AFC) paradigm, participants would look at one of the items first (defined as first look; FL), and they would then move and look at another item (second look; SL). This study investigated how the order in which the chosen items were looked at modulates the first dwell gaze bias effect. Participants were asked to assert their preferences and perceptual 2AFC decisions about human faces (Experiment 1) and daily consumer products (Experiment 2), while their eye movements were recorded. The results showed that the first dwell gaze bias was found only when the eventually chosen item was looked at after another one; the chosen item was looked at for longer as compared to the not-chosen item in the SL, but not in the FL. These results indicate that participants actively allocate more time to looking at a subsequently chosen item only after they perceive both items in the SL. Therefore, the selective encoding seems to occur in the early comparison stage of visual decision making, and not in the initial encoding stage. These findings provide insight into the relationship between choice and eye movement.

Enhancement of Saltiness Perception by Monosodium Glutamate Taste and Soy Sauce Odor: A Near-Infrared Spectroscopy Study

Abstract Previous studies have reported that the umami taste of monosodium l-glutamate (MSG) and salty-smelling odors (e.g., soy sauce, bacon, sardines) enhance the perception of saltiness. This study aimed to investigate the neural basis of the enhancement of saltiness in human participants using functional near-infrared spectroscopy (fNIRS). University students who had passed a taste panel test participated in this study. Sodium chloride solutions were presented with or without either 0.10% MSG or the odor of soy sauce. The participants were asked to drink a cup of the stimulus and to evaluate only saltiness intensity in Experiment 1, as well as other sensory qualities in Experiment 2, and temporal brain activity was measured using fNIRS. In Experiment 3, the participants were asked to evaluate saltiness intensity using the time-intensity (TI) method, and the response of the parotid salivary glands was measured using fNIRS. The fNIRS data showed that the added MSG and soy sauce enhanced the hemodynamic response in temporal brain regions, including the frontal operculum, but no effect on the hemodynamic salivary responses was detected. These results indicate that the perceived enhancement of saltiness occurs in the brain region that is involved in central gustatory processing. Furthermore, the results of the sensory evaluations suggest that enhancement of saltiness by the addition of MSG is mainly based on fusion of the salty-like property of MSG and saltiness of NaCl, whereas enhancement by the addition of soy sauce odor is mainly based on modulation of the temporal dynamics of saltiness perception.

Higher-order conditioning of taste-odor learning in rats: Evidence for the association between emotional aspects of gustatory information and olfactory information

Previous studies have shown that rats prefer an odor paired with saccharin solution to an odor paired with quinine solution (taste-odor learning). However, it remains unclear whether the odors are associated with the emotional (i.e., positive and/or negative hedonics) or qualitative (i.e., sweetness and/or bitterness) aspects of gustatory information. This study aimed to examine this question using higher-order conditioning paradigms: second-order conditioning (SOC) and sensory preconditioning (SPC). Adult Wistar rats were divided into SOC and SPC groups. Food flavors, purchased from a Japanese market, such as melon (0.05%), lemon (0.1%), vanilla (0.1%), and almond (0.1%), were randomly used as odors A, B, C, and D for each rat. The SOC group was exposed to 0.005M saccharin solutions with odor A and 0.02M quinine solutions with odor C in the first 5days of learning. Additionally, they were exposed to water with a mixture of odors A and B, and water with a mixture of odors C and D in the next 5days of learning. The order of these two learning sessions was reversed in the SPC group. We hypothesized that if odor was associated with the emotional, or qualitative, aspects of gustatory information, the SOC, or SPC groups, respectively, would prefer odor B to odor D. Our results showed that the SOC group preferred odor B to odor D, whereas the SPC group did not show any such preference. This suggests that odors may be primarily associated with emotion evoked by gustation in taste-odor learning.

Psychological and physiological bases of umami taste perception as related to nutrition

Abstract Eating behavior is an important factor that can affect human nutrition status both under- and overnutrition. Human eating behavior is influenced by physiological and psychological inputs. Maslow’s Motivation Theory that consists of five stages can be used to explain human eating behavior due to the physiological and psychological effects. Physiologically, basic senses in the gustatory system and visceral sense in the gastrointestinal system signal to different parts of brain to function on hunger, satiety, food memory, and palatability, which mainly involves human survival and safety. In more developed societies, psychological inputs from social norm, status, and recognition can be equally or even more influential to human eating behavior than the physiological ones. In order to solve the nutrition problems, several researches were performed in humans and animals on foods and food ingredients as well as their physiological and psychological mechanisms. Foods containing natural or added umami tastant were found to have effect on food palatability and satiety via the sensations from mouth and viscera. Therefore, umami tastant should be beneficial in solving both ends of nutrition problems. The decayed gustatory system of elderly people can be aroused by umami tastant, which consequently increases their appetite. Umami tastant can physiologically signal for satiety, which is useful for controlling caloric intake. Sodium content can be reduced by 35% at the same salty taste by mixing low-concentrated sodium chloride solution with umami tastant, MSG. Washoku is an ideal menu due to its low calorie and rich in umami tastant.