IMPROVEMENT OF TRIANGLE TEST DATA BY USE OF INCENTIVES

The objectives of this study were to determine the distribution of the sensory panelists' ability to detect differences and to improve the triangle test by minimizing unnecessary guessing. The triangle test was modified to include the use of economic incentives through which panelists voluntarily revealed their ability to detect differences. Panelists were asked to estimate their ability to detect differences and the probability of identifying the odd sample in a triangle test. They were then organized into three ability groups according to their responses. Double triangle tests, followed by triangle tests with economic incentives, were used to evaluate a cereal product and a beverage. The ability to detect differences was modeled as a probability, and the distribution of panelists was estimated. The economic incentives test was more effective when used with the beverage in which differences were less difficult to detect. We found that the economic incentive test discouraged the panelists from guessing unnecessarily, thus increasing the motivation of the panelists to detect differences, and allowing researchers to determine the distribution of discrimination ability.     

SOME ISSUES IN THE DESIGN AND ANALYSIS OF SENSORY DATA: REVISITED

Sensory experimental data whether collected via the consumer or via the laboratory population have many characteristics in common. Among the more important characteristics are that they are relative, skewed, and difficult to replicate. These characteristics result from the use of human beings as instruments to measure multivariate stimuli as opposed to the use of a mechanical instrument. The use of human beings as instruments presents several problems in the design and analysis of sensory/consumer studies. In the clinical/medical applications of sensory evaluation, we have used people both as the experimental unit (panelists/subjects) and as the instrument (judges) to measure panelists’ responses. Thus it is my belief that sensory data are the most difficult scientific data to statistically analyze and interpret. Unfortunately, limited theoretical work has been done to tackle the resulting problems. These problems include the comparison of responses obtained from independent populations (monadic design), sample size estimation with special reference to time-dependent responses, analysis of degree of difference data, the invariance property of rating scales, effect of correlated errors in observations, and the use of laboratory panels to predict results from a consumer panel. Some solutions to these problems have been provided by experience. My purpose here is to discuss each of these problems in greater detail and offer some possible scientific solutions.     

Root architecture and hydraulic conductance in nutrient deprived Pistacia lentiscus L. seedlings

Plants respond to low nutrient availability by modifying root morphology and root system topology. Root responses to nitrogen (N) and phosphorus (P) limitation may affect plant capacity to withstand water stress. But studies on the effect of nutrient availability on plant ability to uptake and transport water are scarce. In this study, we assess the effect of nitrogen and phosphorus limitation on root morphology and root system topology in Pistacia lentiscus L seedlings, a common Mediterranean shrub, and relate these changes to hydraulic conductivity of the whole root system. Nitrogen and phosphorus deprivation had no effect on root biomass, but root systems were more branched in nutrient limited seedlings. Total root length was higher in seedlings subjected to phosphorus deprivation. Root hydraulic conductance decreased in nutrient-deprived seedlings, and was related to the number of root junctions but not to other architectural traits. Our study shows that changes in nutrient availability affect seedling water use by modifying root architecture. Changes in nutrient availability should be taken into account when evaluating seedling response to drought.     

Limiting response alternatives in time-intensity scaling: an examination of the halo-dumping effect

Time-related measurements pose some challenges to psychophysicsand to applied sensory testing methods including control ofpsychological biases which have been found in single-point scaling.This research examined enhancement of ratings when responsealternatives were limited in time-intensity scaling tasks usingrepeated category ratings. Panelists rated a pseudo-beveragecontaining sweetener and flavor and one with sweetener onlyover a 90-s period. The aromatic flavor caused an increase insweetness intensity and especially so when the panelists werelimited to sweetness responses only. The odor-induced enhancementof sweetness was smaller when panelists were given both flavorand sweetness response options than when the panelists weregiven only a sweetness scale. Prior use of both scales in aprevious experimental session did not lessen the halo-dumpingenhancement effect. In one study, sweetness ratings of sucrosealone were depressed when the additional scale for flavor wasprovided, perhaps due to inappropriate partitioning of responses.     

A TEST OF THE CRITICAL ASSUMPTION OF THE SENSORY BIAS MODEL FOR THE EVOLUTION OF FEMALE MATING PREFERENCE USING NEURAL NETWORKS

The sensory bias model for the evolution of mating preferences states that mating preferences evolve as correlated responses to selection on nonmating behaviors sharing a common sensory system. The critical assumption is that pleiotropy creates genetic correlations that affect the response to selection. I simulated selection on populations of neural networks to test this. First, I selected for various combinations of foraging and mating preferences. Sensory bias predicts that populations with preferences for like-colored objects (red food and red mates) should evolve more readily than preferences for differently colored objects (red food and blue mates). Here, I found no evidence for sensory bias. The responses to selection on foraging and mating preferences were independent of one another. Second, I selected on foraging preferences alone and asked whether there were correlated responses for increased mating preferences for like-colored mates. Here, I found modest evidence for sensory bias. Selection for a particular foraging preference resulted in increased mating preference for similarly colored mates. However, the correlated responses were small and inconsistent. Selection on foraging preferences alone may affect initial levels of mating preferences, but these correlations did not constrain the joint evolution of foraging and mating preferences in these simulations.     

Sodium deprivation alters neural responses to gustatory stimuli

The effects of sodium deprivation for 10 d, a period sufficient to induce sodium appetite, on gustatory nerve discharges in rats were determined. Chorda tympani responses to concentration series of sodium chloride, sucrose, hydrochloric acid, and quinine hydrochloride were recorded and analyzed without the experimenter knowing the animal's deprivation condition. After deprivation, both whole nerve and single nerve fiber responses to sodium chloride were smaller; NaCl-best fibers, those more responsive to sodium chloride than to sucrose, hydrochloric acid, or quinine, were most affected. Thresholds had not changed; however, slopes of the stimulus-response functions for sodium chloride were lowered. Comparable changes in responses to the other stimuli did not occur. These results were discussed with respect to a possible relationship between changes in sodium chloride responsivity and changes in sodium intake, differences between methods of inducing sodium appetite, coding of taste quality and intensity, and mechanisms which might effect the responsivity change.     

PERFORMANCE ASSESSMENT OF SENSORY PANELISTS

The replication variance of individual stimulus evaluations and scale utilization across a panelist's stimulus profile are simultaneously employed to develop statistics for assessing performance of panelists. The approach provides opportunities for comparison of panelists to each other, determination of attributes for which panelist confusion is observed, isolation of stimuli presenting unstable properties, and engagement of influence weights (based on relative precision) in subsequent analyses of data. Although the methodology has been developed for applications involving sensory panelists, the statistical concepts may be extended to other data collection scenarios involving replicated determinations from bounded quantitative measurement scales.     

EVALUATION AND APPLICATIONS OF ODOR PROFILING

An odor profiling procedure was developed based on the ASTM odor profiling method. This modified procedure involved using approximately twenty panelists. Panel sessions and data collection were controlled by computer. The results obtained by this panel compared favorably to results obtained by the ASTM panel for which 150 panelists evaluated each compound, indicating that a small panel can be used to produce replicable results. Statistical methods of finding similarities and dissimilarities among compounds using profile data are discussed and compared to results from a multidimensional scaling (MDS) study in which degrees of differences among compounds were judged directly. These results indicate that profile data can be used to define and map the degree of similarity/dissimilarity among compounds, as well as to define the sensory dimensions on which these compounds differ. The use of factor analysis to study the underlying sensory dimensions of the odor space is also discussed. It is hoped that this type of research will lead to a better understanding of the underlying dimensions used to describe odorants.     

A COMPARISON OF METHODOLOGY APPLIED TO THE SELECTION OF A PANEL FOR SENSORY EVALUATION OF INSTANT COFFEE

Twenty judges performed a variety of chemosensory tasks in order to select the best scores to form a panel for coffee evaluation. An average of correct responses (P%), one-way analysis of variance (ANOVA) and principal components analysis (PCA) were compared. The tests involved: ability to recognize the four basic tastes, identification and matching of odors, taste intensity evaluation and perception of small differences in taste. P% accounted for 71.17 ± 4.34% and 10 of the judges had scores greater than the final average. ANOVA and PCA resulted in 2 different panels consisting of 9 and 12 judges, respectively. The panel was composed by the nine panelists selected by the three methods. The other three panelists that were doubtful could improve to the point of acceptance with additional training. These methods should be used simultaneously to have more security in the acceptance or rejection of panelists.     

EVALUATION OF PANELIST PERFORMANCE IN DESCRIPTIVE PROFILING OF RANCID SAUSAGES: A MULTIVARIATE STUDY

This paper illustrates an application of principal component analysis (PCA), partial least squares regression (PLS) and generalized procrustes analysis (GPA) to evaluate the ability of a trained group of assessors to perceive rancidity in foods. PCA and regression PLS were utilized to determine to which extent sensory attributes capture the information perceived by a trained sensory panel, and if this can be developed into a predictive model for rancidity in sausages. The data were submitted to a GPA to obtain a map of the products for each subject as compared with a consensus products map. Assessors plots for the sensory attributes were also obtained to reveal the dissimilarities between panelists and to explore clustering.     

MATERNAL EFFECTS AT FOUR LEVELS IN SENECIO VULGARIS (ASTERACEAE) GROWN ON A SOIL NUTRIENT GRADIENT

Plants of Senecio vulgaris L. were grown individually within pots to examine effects of maternal soil nutrient level on offspring. Genotypic variability among maternal plants was minimized by using only maternal plants derived from seed of a single inbred line. Significant (P < 0.05) maternal effects of the nutrient gradient were detected at four different levels. Maternal plants grown in lower soil nutrients produced: 1) seeds with lower individual mass; 2) seeds that germinated later; 3) seedling offspring that grew into smaller juvenile plants in nutrient-impoverished soil; and 4) seedling offspring that survived longer in the absence of external nutrients. This last type of maternal effect is reported for the first time in the present study. These data suggest that a compensatory effect of relatively low maternal soil nutrient level may be conferred on the plant's offspring in the form of a “wait and tolerate” strategy through a longer “seedling dormancy” period. This appears to involve a high seedling tolerance threshold level for external nutrient deprivation. To account for these results, we propose two hypotheses based on two different causes of nutrient deprivation, and based on the assumption that if maternal plants experience nutrient deprivation, seedling offspring have a high probability of also experiencing the same cause of nutrient deprivation: 1) Under the “nutrient supply hypothesis,” the wait and tolerate strategy in seedling offspring represents an adaptation to selection factors associated with nutrient deprivation resulting from a low nutrient-supplying power of the environment. 2) Under the “nutrient-depletion hypothesis,” this strategy represents an adaptation to selection factors associated with nutrient depletion by neighbors.     

ESTIMATES OF CARRY-OVER EFFECTS IN TWO-PRODUCT HOME USAGE CONSUMER TESTS

In-house use consumer test data from four studies dealing with three pairs of household products and a pair of antiperspirant products were examined for significant carry-over (product usage order) effects, which would confound the analysis of treatment (product) effects. In each study, two products were compared using a two-period crossover design. One hundred twenty panelists participated in each study. A forced choice preference scale or a 9-point hedonic scale was used to obtain responses from various sensory attributes. In all studies, the estimates of carry-over effects were not significant at the 5% level. Transformation of hedonic scale data into preference dichotomy also gave estimates of carry-over effects which were not significant at the 5% level, but led to a loss of test sensitivity for detecting treatment differences. The authors recommend that all comparative crossover design studies in sensory evaluation be monitored for carry-over effects and that statistically determined sample size should be used to reduce the possibility of obtaining significant carry-over effects.