Discriminations of the A-Not A difference test improved when “A” was familiarized using a brand image

The A-Not A difference test can be used to measure the overall sensory difference of two or more products from a reference product. It is an economically efficient method for difference testing because it is more statistically powerful and less prone to working memory problems than the triangle or duo-trio tests. With the A-Not A test, subjects are required to be familiar with the reference product to stabilize their cognitive decision criteria. An effective familiarization procedure is needed. In the present study, the effects of four different familiarization procedures were investigated: (1) 2-AFCR, (2) no-additional familiarization, (3) repeated tastings of the reference, and (4) repeated tastings of the reference with a brand image provided. Two products were discriminated from a reference using 12 subjects over repeated sessions. Comparisons of the test performances, analyzed with d′ estimates, showed that there was a tendency toward better discrimination when repeated tastings of the reference were accompanied by a brand image.     

Observed discriminability is more variable than predicted by signal detection theory

Food scientists and technologists are interested in how sensitive judges and consumers are to changes in product formulations. Numerous approaches to measuring sensitivity have developed at a rapid rate in the last 25 years, however, the evaluation and assessment of sensory tasks is still ongoing. The current study compared the efficiency of four difference tests (A-Not A, A-Not AR, 2-AFC, 2-AFCR) across three concentrations (difficulty levels) of orange essence. To determine which of the four tasks had the lowest variance in d′, the decision strategy used by the judges first had to be ascertained. Using the rating-scale approach of signal detection theory, four estimates of sensitivity, d′, were obtained for each judge (n = 10) at each of the three difficulty levels, for all four tasks. Results indicate that the majority of judges adopted the β-strategy for the A-Not A and A-Not AR tasks, and the β/τ-strategy for the 2-AFC and 2-AFCR tasks. The A-Not A and A-Not AR tasks produced greater estimates of d′ than the other two tasks, and the A-Not A task exhibited a greater variance in d′ than the other three tasks.     

Comparison of the triangle and a self-defined two alternative forced choice test

The triangle test and the 2-AFC test or paired comparison are commonly used discrimination tests. The 2-AFC is statistically more powerful than the triangle test, but can only be used when the quality of the difference is known (e.g. one sample has added sucrose and is expected to be sweeter). By allowing subjects to define their own criteria for use in the 2-AFC, the procedure might be used when the sensory difference between two samples is not known or easily defined, as is possible during a warm-up protocol. The research reported here investigated a modification of the sometimes extensive warm-up procedure but limited the number of samplings of the preview samples. This modified procedure we describe as a self-defined 2-AFC (SD-2-AFC). This method was compared to the triangle and conventional 2-AFC using four food systems, differing in the magnitude and quality of sensory differences. The AFC tests (including the SD-2-AFC) performed better than the triangle on a statistical basis. However, in some cases the SD-2-AFC produced lower d-prime values indicating lower absolute levels of sensory differentiation. Correlates of poorer discrimination with the SD-2-AFC included miss-identification of the critical attribute (as determined by majority response) or reversal of the direction of the difference during the inspection phase. Results were interpreted in terms of Thurstonian models. No advantage of adding a preview to the triangle or 2-AFC was observed. The overall statistical advantage of the SD-2-AFC suggests it should be considered as an alternative to the triangle test.     

Unspecified duo–trio tests can be as powerful as the specified 2-AFC: Effects of instructions and familiarization procedures on cognitive decision strategies

Using signal detection theory (SDT) and Thurstonian analysis, it has been possible in the food industry to make various business decisions such as reformulations and cost reductions based on the degree of consumer sensory discriminability by applying equivalence/difference testing. To achieve more efficient decision-making, it is important to investigate a theoretically and operationally more powerful consumer discrimination test method. Cognitive decision strategies used in discrimination methods largely determine relative test power and thus are of theoretical and practical significance. The goal of this study was to investigate if test procedures using a constant-ref. duo–trio design enable untrained/naïve subjects to use a powerful 2-AFC strategy. Although previously the constant-ref. duo–trio design showed operational superiority to other unspecified test methods, the ‘comparison of distance’ (COD) strategy which is conventionally assumed for the duo–trio, lacks theorized power. The tested variables included two versions of duo–trio design, different familiarizations, instructions and experimental session designs. Three different iced tea samples were discriminated from a reference by 263 untrained/naïve subjects using 5 different duo–trio test procedures. Results showed that untrained/naïve subjects were able to perform the duo–trio with the reference presented twice, first and middle (DTFM) as a 2-AFC procedure, even with multiple pairs in a block design, after only two reference tastings with the information of the constant-reference. The duo–trio preceded by specified tetrad tests also showed potential as another efficient two-sequence test design. These results suggest that such constant-ref. duo–trio protocols using a 2-AFC strategy can be an alternative to the unspecified triangle and tetrad test.     

Forced Grouping: A new methodology to measure the similarity between products and predefined references

In sensory evaluation, many discrimination tests (e.g. A-Not A, duo-trio, ABX, etc.) aim to detect whether a blind sample matches a predefined reference or not. Such tests require blind samples to either fully match the reference (e.g. A) or not (e.g. Not-A). But in some situations, the samples tested do not match exactly the references used. The question then is: How do the tested samples relate to these references? With the new methodology of Forced Grouping (FG), this question can be answered.The objective of this paper is to detail the methodology of FG and its analysis (including a binomial test, a Thurstonian model, and some tools to evaluate the panel and panellist performance). To illustrate the FG methodology, a total of 30 trained assessors (split into two panels) evaluated the same set of six mixtures of skimmed yoghurt (SY) and full fat quark (FFQ). Reference A consists of 75% SY/ 25% FFQ and reference B consists of 50 SY/50 FFQ, while the other four samples have a ratio in between the two references. The six products were tested in monadic sequence. After familiarization with the references, assessors were asked to associate each of these products to the closest reference, based on taste and mouthfeel separately. Additionally, FG was extended to other sample sets (approx. 40 studies) to generalise the results.The yoghurt samples showed a clear transitioning from reference A to reference B across samples with an increasing proportion of full fat quark within the sample composition. Similar results were obtained for most of the other studies, although some discrepancies were observed in particular for studies including samples with large batch variations, or samples that are very similar overall.FG has shown to be a quick and easy method, which extends our sensory toolbox to new situations where “new” in-between samples are associated to pre-defined references.     

Sensory difference tests for margarine: A comparison of R-Indices derived from ranking and A-Not A methods considering response bias and cognitive strategies

Sensory difference tests were performed between 6 margarine products, a standard vs 5 other products. Three testing protocols were used. The first protocol was simple ranking. The second protocol was the A-Not A method where a single standard was presented beforehand and which could be retasted during testing. The third protocol was the A-Not A method where all products were presented beforehand but could not be retasted during testing. R-Index values were computed for each protocol. Ranking gave the highest R-Index values while the A-Not A method, where only a single standard was presented prior to testing, gave the lowest R-Index values. R-Indices were calculated by averaging indices from individual judges and also by pooling data from all judges. Differences between these computations only occurred for the A-Not A method where all the products were presented prior to testing. Differences were explained in terms of the forced-choice nature of ranking, boundary variance, concept formation and differences in cognitive strategies involving tau and beta-criteria.     

Exploration of a new consumer test method based on metacognitive certainty

Successful product development and marketing necessitate a study of the consumer concept of culture-specific or deep-positioned branded food. In this study, a new consumer test method was designed based on an authenticity test and used as a reference frame for the target concept without an upsetting story. The response format of this method included the metacognitive certainty response following the sensory authenticity response using the A-Not A test procedure. The method was applied to study the concept of goso flavor, as perceived by 91 female consumers with three commercial soymilk products, having each consumer evaluate each product 45 times over three days. The repeated responses of sensory authenticity were analyzed as mean scores and signal detection theory (SDT) d-prime (d′) values of the product difference. From the metacognitive certainty responses after the sensory authenticity response, a new quantitative group measure of d-prime metacognition (d′_MC) was calculated in the SDT context and compared with the other outputs. The measure ranged from negative to positive values, indicating a mismatch to a match for the concept of each product. Data analyses were conducted on both pooled data and segmented data, which was driven from the results of cluster analyses using the mean sensory authenticity scores and SDT C values (estimates of response bias about the concept tested). The results showed that d′_MC of each product corresponded to the mean scores and d′ with the advantage of easy interpretation. Overall, d′_MC can be a useful group measure for studying the consumer concept towards food and beverages.     

Investigation of human flavor perception and discrimination of the fat content in food using DR A-Not A and 3-AFC methods

Food Science and Biotechnology - This study examined human flavor perception and discrimination of powdered milk samples with various fat contents using two different sensory discrimination...     

Just Noticeable Differences and Weber Fraction of Oral Thickness Perception of Model Beverages

Rheological properties of beverages contribute considerably to texture perception. When developing new beverages, it is important to have knowledge on the smallest differences of viscosity which a consumer can discriminate. Thickness is the sensory attribute most commonly used to describe the viscosity of beverages. The aim of this study was to determine the Just Noticeable Differences (JNDs) of oral thickness perception and the Weber fraction (K) of Newtonian model stimuli (maltodextrin solutions). JNDs were determined using the method of constant stimuli with 5 reference stimuli ranging in viscosity from 10 to 100 mPa?s. JNDs increased with increasing viscosity of the reference stimulus. The Weber fraction (K) for oral thickness perception of model beverages was K = 0.26 for the studied viscosity range. The Weber fraction for oral thickness perception is comparable to Weber fractions reported in literature for perception of kinesthetic food firmness and spreadability, creaminess, sourness, and bitterness perception. This demonstrates that the human sensitivity towards oral discrimination of thickness of liquid stimuli is comparable to the human sensitivity towards discrimination of specific texture properties and specific taste stimuli.     

A transfer of technology from engineering: use of ROC curves from signal detection theory to investigate information processing in the brain during sensory difference testing

This article reviews a beneficial effect of technology transfer from Electrical Engineering to Food Sensory Science. Specifically, it reviews the recent adoption in Food Sensory Science of the receiver operating characteristic (ROC) curve, a tool that is incorporated in the theory of signal detection. Its use allows the information processing that takes place in the brain during sensory difference testing to be studied and understood. The review deals with how Signal Detection Theory, also called Thurstonian modeling, led to the adoption of a more sophisticated way of analyzing the data from sensory difference tests, by introducing the signal-to-noise ratio, d', as a fundamental measure of perceived small sensory differences. Generally, the method of computation of d' is a simple matter for some of the better known difference tests like the triangle, duo-trio and 2-AFC. However, there are occasions when these tests are not appropriate and other tests like the same-different and the A Not-A test are more suitable. Yet, for these, it is necessary to understand how the brain processes information during the test before d' can be computed. It is for this task that the ROC curve has a particular use.     

Investigation of the effect of within-trial retasting and comparison of the dual-pair, same-different and triangle paradigms

The performance on three protocols (same–different, triangle, dual–pair) was compared under two conditions: with and without sample retasting permitted. Allowing sample retasting was investigated as a means of improving the discrimination power of sensory discrimination methods. This improvement is predicted by the sensory sampling model or SESAM [Juslin, P., & Olsson, H. (1997). Thurstonian and Brunswikian origins of uncertainty in judgment: a sampling model of confidence in sensory discrimination. Psychological Review, 104, 344–366.]. Sixteen judges took part in the experiment which involved non-carbonated orange flavored beverages. No significant difference was observed among the three protocols' d′ values in either the retasting and no retasting conditions but there was a trend for the same–different to be more sensitive than the other two procedures. Such a trend would depend on the effects of stimulus presentation order and memory. Yet, since the same–different test is statistically more powerful, it is a preferable choice over the triangle, duo–trio and dual–pair tests. Also, retasting brought significant improvement for all tests over the no retasting condition as predicted by SESAM. This was illustrated by significantly larger d′ values. A further analysis indicated that when subjects were allowed to, but chose not to retaste, they performed better than when they chose to retaste the samples. Data involving sureness judgments in the same-different test provided an explanation on such a ‘discrepancy’. Therefore, it appears that sample retasting, when possible, should be allowed, but not required, in order to improve sensory discrimination among products.     

Corroborating the 2-AFC and 2-AC Thurstonian models using both a model system and sparkling water

Two experiments were conducted to investigate the suitability of the Thurstonian models for the 2-AFC (2-alternative forced choice) and 2-AC protocols (2-AFC test with a “no difference” option). The Thurstonian approach predicts that if the same subjects and products are used, the degree of difference measured between the products (d^′) should be the same. Experiment I tested this prediction using solutions with different salt concentration. The average d^′ values for the 2-AFC and 2-AC were found to be 1.66 and 1.54, respectively, and were not significantly different (t-test, p=0.46). This indicated the suitability of the models for a taste stimulus. Experiment II used a trigeminal stimulus: sparkling water with different CO₂ levels as a food system. Three levels of carbonation were used and all three possible pairs of samples were compared. The d^′ values measured for the 2-AFC and 2-AC for each pair of products were: pair 1––1.7 and 1.7; pair 2––0.8 and 0.7; pair 3––1.2 and 1.0. For each pair of products, no significant difference was observed between the d^′ of each protocol (t-tests, p=0.65, 0.20, 0.30, respectively), giving further support to the Thurstonian models of these paradigms and indicating their robustness.     

Consumer acceptance measurement focusing on a specified sensory attribute of products: Can the attribute-specified degree of satisfaction-difference (DOSD) method replace hedonic scaling?

A specific attribute can play an important role in determining consumers’ perceived quality and acceptance of a product. Kim, van Hout, Dessirier, and Lee (2018) proposed a new affective method, the degree of satisfaction-difference (DOSD) method, to study consumer acceptance in terms of overall satisfaction with products. In the present study, this DOSD method was further developed to assess satisfaction for a specified attribute of products rather than overall satisfaction, and this modification is referred to as the attribute-specified DOSD method. To test its applicability, 11 bouillon products (including a reference product) varying in viscosity were used as stimuli. Satisfaction with the perceived mouthfeel thickness, which is a viscosity-related sensory attribute, was evaluated with the attribute-specified DOSD method and with a 10-point category scale for overall liking as the control method. Two groups of consumers performed either the attribute-specified DOSD method or hedonic scaling over two repeated sessions. Results showed that the satisfaction patterns of the attribute-specified DOSD method were similar to those of the hedonic scaling across products, confirming that the mouthfeel thickness was a determinant of consumer acceptance for bouillon products. Examining the test reliability in terms of consistency of consumers’ responses for the same stimulus in different sessions, both groups showed consistent results. The subjects who performed the attribute-specified DOSD method were also segmented based on the degree of satisfaction with the reference product. Here, each consumer sensory segment showed different patterns on satisfaction with other test products. These findings demonstrate the potential of the attribute-specified DOSD method for measuring the consumer responses to the level/quality of an important attribute/dimension and highlight its usefulness for consumer sensory segmentation.     

Affective discrimination methodology: Determination and use of a consumer-relevant sensory difference for food quality maintenance

To achieve more efficient decision making for many business objectives including reformulations and processing changes in the food industry, the important questions become 1) what is the best way to measure consumer discrimination and 2) how much discrimination is meaningful in consumer preference that can be used as a business action standard for food quality maintenance. The purpose of the present paper was to develop a consumer sensory discrimination methodology using affective reference framing to provide more accurate information on both questions. For such affective methods, two versions of repeated duo–trio tests using the preferred sample as reference were implemented: Affective group I—each of 8 repeated duo–trio tests was preceded by a paired-preference test; and Affective group II—a paired-preference test was performed before each of the two sub-sessions consisted of 6 repeated duo–trio tests and the preferred sample was used as a constant-reference during the sub-session. The discrimination performance of these tests was compared to the analytical balanced-reference duo–trio test. Results indicated that for affective group I only, it was possible to identify the ‘affective discriminators’ who showed genuine preference for one product over another and their sensory discrimination in the affective method was significantly higher than in the analytical method. It suggested that this affective method is a desirable consumer sensory methodology that can reveal insightful consumer-relevant sensory differences by comparing sensory discriminations between the so-called ‘affective discriminators’ and ‘affective non-discriminators’.     

Investigating more powerful discrimination tests with consumers: effects of memory and response bias

Two experiments were conducted to investigate the sensitivity of four discrimination methods when they were performed by consumers. In Experiment I, the influence of memory in the duo-trio method was studied. Three versions of the duo-trio method with different memory requirements were considered. Calculated d′ values indicated a higher sensitivity for the duo-trio with the reference tasted between the two test samples (DTM), illustrating the importance of memory in sensory discrimination testing. In Experiment 2, four discrimination tests were compared: the triangle, the DTM, the same–different and the dual-pair tests. The dual-pair test was predicted to increase the d′ value of the same–different test by eliminating the large response bias variations between consumers. Results indicated no significant differences in d′ among the protocols. Thus the dual-pair method was not able to improve the sample discrimination ability of the same–different test.     

Effects of Order of Tasting in Sensory Difference Tests Using Apple Juice Stimuli: Development of a New Model

ABSTRACT:  3-AFC discrimination tests between 2 confusable versions of apple juice were performed using a variety of interstimulus rinsing regimes, to investigate the effects of order of tasting on difference test sensitivity. The results were compared to predictions from the sequential sensitivity analysis (SSA) model and the conditional stimulus (CS) model, which have been developed to account for differences in model systems. These models did not account for the data for this beverage system. A new model was developed. This took a Thurstonian/signal detection approach but included new elements. It considered the gradual build-up of adaptation effects that would be encountered as a judge proceeded through a 3-AFC test with a relatively strong flavored food system. It further considered cognitive contrast effects, which had not been considered in the prior models. The model was named the sequential perception analysis (SPA) model and it accounted for the data found with the apple juice stimuli. The predictions of the model were precise enough to account for differences between individual triads, which the former models had not been able to do.     

The double discrimination methods

Theoretical aspects of the double discrimination methods are investigated in this paper. The main aspects involve statistical models, test powers, Thurstonian d′ s and variance of d′ s for the methods. The double discrimination methods can be treated under the same framework as the conventional discrimination methods, i.e. under the same binomial model but with different parameters. The double discrimination methods possess lower guessing probabilities and higher test powers than the conventional discrimination methods. The relationship between the double methods and the conventional methods in Thurstonian d′ s and variances of d′ s are derived in the paper. The tables of critical values for tests and the table of sample sizes required to reach 0.8 test power for the double two-alternative forced choice (the double 2-AFC), the double three-alternative forced choice (the double 3-AFC), the double triangular and the double duo-trio methods are given.