Sensation individual differences

We have already noted evidence for genetic factors that underlie the preference for and response to caffeine. These factors create a biologically based set of individual difference dimensions that may be modified by experience with the drug. In addition, there is evidence for a number of broader individual difference dimensions that appear to be relevant. These bipolar continua differentiate between subjects who are habitually high in arousal or arousability and those who are habitually low. The factors in question are personality dimensions that theoretically reflect underlying biological continua of arousal or arousability.238 Included among these dimensions are extraversion,58 impulsivity,239240 and sensation-seek-ing.94-241-242 We will take up the first two of these. 

Davidson, R. and Smith, B., Arousal and habituation Differential effects of caffeine, sensation seeking and task difficulty. Personality and Individual Differences 10(1), 111-119, 1989. 

Smith, B., Davidosn, R., Smith, D., Goldstein, H. and Perlstein, W., Sensation seeking and arousal Effects of strong stimulation on electrodermal activation and memory task performance. Personality and Individual Differences 6, 671-679, 1989. 

Individuals may experience a broad array of flavor sensations within one meal or even one food. The interactions among the sensations makes it difficult to separate and quantify individual contributions to tiie flavor experience. An individual stimulus may elicit more than one sensation, and be processed at the recognition and transduction steps by more than one mechanism. In addition, individual differences in sensory responses may provide different assessments of the same event. 

On one hand, as we stiU have the objective of preference mapping, a minimum set of consensual sensations is required. On the other hand, we wanted to preserve the inter-individual differences of perception between the participants. Consequently, our methodological approach has been based on both individual and group sessions. The final list of sensations is composed of terms used by all participants, and terms used by just part of the group. 

Road-holding perceptions are also inflnenced by the driver s anthropometry. In fact, anthropometry has an impact on the driving position, which in turn has an impact on the road-holding sensations. Thns, in addition to inter-individual differences in sensory sensitivity, it is important also to take into account snbjects sizes and weights in such studies. 

Moreover, this methodology, if correctly understood, is quite flexible. Therefore we do not hesitate to adapt the protocol according to the spedlic objectives of the studies. This is the case for the roll and lateral support perception study, where we needed a common minimum set of sensations but wanted to preserve the inter-individual differences of perception between the participants. 

Horvath, P. and Zuckerman, M. 1993. Sensation seeking, risk appraisal and risky behavior. Personality and Individual Differences, 14,41-52. 

Schwebel, D. C., J. Severson, K. K. Ball and M. Rizzo (2006). Individual difference factors in risky driving The roles of anger/hostility, conscientiousness, and sensation-seeking. Accid. Anal. Prev., 38(4), 801-810. 

Several aspects affect the extent and character of taste and smell. People differ considerably in sensitivity and appreciation of smell and taste, and there is lack of a common language to describe smell and taste experiences. A hereditary or genetic factor may cause a variation between individual reactions, eg, phenylthiourea causes a bitter taste sensation which may not be perceptible to certain people whose general abiUty to distinguish other tastes is not noticeably impaired (17). The variation of pH in saUva, which acts as a buffer and the charge carrier for the depolarization of the taste cell, may influence the perception of acidity differently in people (15,18). Enzymes in saUva can cause rapid chemical changes in basic food ingredients, such as proteins and carbohydrates, with variable effects on the individual. 

Whatever the physiology of odor perception may be, the sense of smell is keener than that of taste (22). If flavors are classed into odors and tastes as is common practice in science, it can be calculated that there are probably more than 10 possible sensations of odor and only a few, perhaps five, sensations of taste (13,21,35—37). Just as a hereditary or genetic factor may cause taste variations between individuals toward phenylthiourea, a similar factor may be in operation with odor. The odor of the steroid androsterone, found in many foods and human sweat, may eflcit different responses from different individuals. Some are very sensitive to it and find it unpleasant. To others, who are less sensitive to it, it has a musk or sandalwood-like smell. Approximately 50% of the adults tested cannot detect any odor even at extremely high concentrations. It is befleved that this abiUty is genetically determined (38). 

Certain miscellaneous observations have a bearing on our discussion of differences in taste reactions. For example, it is well recognized in hospitals that, although a barium sulfate emulsion is perfectly tasteless and innocuous to many individuals, to others it is very disagreeable. It would appear that the taste threshold for barium sulfate varies from individual to individual and that this substance is soluble enough to give a sensation of taste to some individuals. 

Severe headaches occurred in an individual exposed to diesel fuel vapor for 10 days (Reidenberg et al. 1964). Anorexia occurred in a man following dermal and/or inhalation exposure to diesel fuel over several weeks (Crisp et al. 1979). Other neurological effects were reported following inhalation of JP-5 vapor in two individuals who had fatigue and coordination and concentration difficulties other effects included headache, apparent intoxication, and anorexia. Effects subsided within 24 hours for one individual and within 4 days for the other (Porter 1990). Sensory impairment did not occur in these individuals. However, experimental data indicate that olfactory fatigue and taste sensation may occur in some individuals after a 15-minute inhalation exposure to 140 mg/m deodorized kerosene vapor (Carpenter et al. 1976). These data suggest that the different types of fuel oils may behave differently under inhalation exposure conditions. The effect of deodorized kerosene may also occur at lower doses, but this cannot be determined from these data. 

The sensation of astringency is felt differently by tasters [86] probably due to differences in individuals saliva in terms of its protein composition [11, 47]. Astringency is also affected by the structure of the phenolic compounds [88], pH [89], the presence of other substances [90-92], and viscosity [11]. In fact it is believed that complex beverages such as wine and beer have subtle sub-qualities of sensorial descriptors related to astringency (soft, grainy, harsh, green, chalky, etc.), that are not perceived in tannin model solutions, which could be due to the presence of other molecules [87]. 

Some authors (Peinado et al. 2004a, 2004b Zea et al. 2007) have grouped aroma compounds in aromatic series based on their aroma descriptors. The overall value for each series is obtained by combining the odour activity value (OAV, which is defined as the ratio of the concentration of a compound to its perception thresholds) of the individual aroma compounds in the series. The combination of individual OAVs in order to calculate the overall value for a series cannot be interpreted as an arithmetic addition of odorant sensations. Some aspects of this classifying scheme can be subject to criticism, but in any case, the scheme is effective for comparing wines obtained with different aging methods inasmuch as the odour series always comprise the same compounds. 

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