A W MacRae

University of Birmingham, Birmingham, England, United Kingdom

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Publications (13)30.42 Total impact

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    ABSTRACT: In a test of theoretical predictions made by MacRae and Falahee (1993), trained assessors evaluated water samples which sometimes contained 10−5 mg/l of trichloroanisole, using three different procedures. Compared with the blue-book method of single-sample assessment, providing a reference sample identified to the assessor as being odour-free increased the proportion of responses reporting an odour. This decreased the number of odorous samples missed. Although this outcome may be valuable in itself, discrimination between odorous and odour-free samples was not really enhanced since ‘false alarms’ increased correspondingly. Incorporating additional, different odours into the sequence of samples and giving knowledge of results when these were judged, dramatically improved performance — the rates both of missing trichloroanisole and of mistakenly attributing odour to odour-free samples were halved.
    Water Science & Technology 01/1999; 40(6):149-152. · 1.21 Impact Factor
  • M. Falahee, A. W. MacRae
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    ABSTRACT: Twenty untrained assessors took part in repeated similarity sorting and preference ranking tasks on five separate occasions. The same three drinking water types were assessed on each trial, and the sample set to be assessed included duplicate and blended samples. A satisfactory level of agreement between assessors' responses for each testing session was obtained, indicating that these tasks can be consistently performed by untrained assessors. Multidimensional scaling of the grouping and ranking data produced reliable and interpretable solutions (although a vector model of the preference data was not satisfactory). Duplicate pairs of samples were grouped together and different water types were spatially separated in the resulting configurations. The position of blended samples in relation to the water types of which they were comprised was also often interpretable. It is concluded that simple sorting and ranking procedures can be efficient methods for the collection of consistent sensory data from untrained consumers on qualitative variation among drinking waters, and that multidimensional scaling can provide a valid model of such data.
    Food Quality and Preference 09/1997; 8(5):389-394. · 2.73 Impact Factor
  • J Greaney, A W MacRae
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    ABSTRACT: Two experiments evaluated the properties of polygon displays and bar graphs as fault indicator for systems with many parameters. A modified visual search paradigm was used to test the effectiveness of different display configurations to be check-read for the presence of abnormal ('target') readings. Whether the task was to detect the occurrence of a single abnormal (off-limits) parameter or count the number of abnormal parameters, both displays yielded response times and error rates that were independent of the total number (from 4 to 16) of displayed parameters. When the task was fault detection, the subjects performed equally well with both types of displays. When the task was counting the number of abnormalities, performance with the bar graph was independent of the number of abnormalities but performance with the polygon display was poorer overall and deteriorated with larger numbers of abnormalities. The results contradict either the proximity-compatibility hypothesis of Wickens or the traditional classification of polygons and bar graphs as typical integral and separable displays, respectively. The results are best characterized in terms of the similarity relations between and among 'target' and 'nontarget' parameters.
    Acta Psychologica 03/1997; 95(2):165-79. · 2.26 Impact Factor
  • A. W. MacRae, M. Falahee
    Food Quality and Preference 07/1996; 7(3):308-308. · 2.73 Impact Factor
  • A.W. MacRae
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    ABSTRACT: The Thurstone-Ura model of triangle and 3AFC judgements explains the greater statistical power of 3AFC tests compared with triangular tests, but its mathematical expression is abstract. However, if the subjective differences among samples are represented on isometric co-ordinates, it is possible to express a Thurstone model of the triangle and 3AFC tasks as a bivariate normal distribution divided into segments by straight lines representing optimal decision rules. The triangle and 3AFC have different optimal decision rules and hence different segment shapes, which account for the tests' different relationships between sensory acuity and the probability of making a correct response. The isometric representation makes the same predictions of these relationships as more abstract formulations but is much easier to represent graphically and to explain to non-specialists.
    Food Quality and Preference 01/1995; · 2.73 Impact Factor
  • A.W. MacRae
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    ABSTRACT: One of the major advantages of the triangle test to set against its low statistical power is its potential for revealing discriminable sensory differences when the nature of the difference is unknown. That makes it an attractive tool for seeking assurance that there is no sensory difference between samples (after a process change, for instance). Mere absence of significant difference is completely inadequate to give that reassurance and power analysis is much better. However, power analysis requires three somewhat arbitrary parameter values to be selected in advance. An alternative approach based on exact binomial confidence intervals is described which needs only a single parameter, comparable to the alpha level in a test of significance, to be specified. It is shown that the amount of data usually envisaged for seeking reassurance about lack of difference is much too small to do the task adequately.
    Food Quality and Preference 01/1995; · 2.73 Impact Factor
  • T Hughes, A W MacRae
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    ABSTRACT: Polygon displays compress information that would otherwise be conveyed by separate indicators into a single display in which each reading is represented by the distance of a polygon vertex from its center. The effect on detection of fault states of varying the number of polygon vertices from 4 to 20 in a display presented peripherally around a dynamic, simulated flight display was studied. Presence of the dynamic task reduced both speed and accuracy of response to the polygon display but did not significantly affect the pattern of response to differing numbers of vertices. All measures of performance were better with larger numbers of vertices. If the vertices are processed serially, more vertices require more processing time. Therefore, the result argues for holistic processing and implies that such information integration is beneficial to human performance in fault detection.
    Human Factors The Journal of the Human Factors and Ergonomics Society 01/1995; 36(4):645-51. · 1.29 Impact Factor
  • Marie Falahee, A.W. MacRae
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    ABSTRACT: Two non-quantitative, non-descriptive procedures, similarity sorting and preference ranking, were used to compare the tastes of 13 different water types. Each procedure was conducted with a different set of completely untrained assessors. A total of 25 assessors took part in the sorting procedure and 87 in the ranking procedure. After multidimensional scaling there was good agreement between the spatial configurations of sample types given by the two procedures. In both configurations there was distinct clustering of the different water types. Bottled and untreated waters were preferred to distilled and tap waters by the majority of the assessors. Carbon filtration did not appear to make a large improvement to the acceptability of tap and distilled waters, but did alter the character of tap water as perceived by the assessors. It is concluded that the procedures and analyses are efficient and economical methods of obtaining detailed information about sensory differences among water types and the perception of water quality and are suitable for use with untrained assessors and large numbers of sample types.
    Food Quality and Preference 01/1995; · 2.73 Impact Factor
  • A. W. MacRae, M. Falahee
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    ABSTRACT: Threshold models indicate that the best way to improve the effectiveness of sensory screening of water at the point of production is to give assessors sensory training, but we argue that it is likely to be ineffective. The notion of sensory threshold has been displaced in psychophysics by signal-detection models which assume that the assessor is uncertain on every trial, but makes an unconscious decision about the presence or absence of the attribute. The decision can be influenced by many factors other than the strength of the attribute and the sensitivity of the assessor Taking account of possible changes in response criterion as well as in sensory sensitivity indicates a quite different way of improving sensory screening by attempting to counteract vigilance decrement and the effects of relative judgement. This approach indicates that, rather than trying to increase the sensitivity of assessors, we should aim to prevent shifts in response criterion and the transmission of errors from one sample to the next. A method that has proved successful with industrial inspection and military watchkeeping is to add artificial ‘signals’ to those being assessed and give the assessors immediate feedback on their success in judging them.
    Food Quality and Preference 01/1995; 6(2):69-74. · 2.73 Impact Factor
  • Source
    E N Geelhoed, A W MacRae, D M Ennis
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    ABSTRACT: Earlier data showed that subjects presented with two samples of distilled water and one of tap water were significantly more consistent in choosing the tap water as preferred than in identifying it as the odd sample in the set. The results were sometimes interpreted as demonstrating greater sensitivity for hedonic judgments than for oddity judgments. They are now shown to be explained by the statistical properties of the decision rules followed in different judgment tasks. In a new experiment, oddity and preference judgements were obtained in a replication of the original task with extra conditions. In two of the new conditions, the decision structure of a preference task was the same as that for the oddity task; in these conditions, performance was no better than with explicit oddity responses. The Thurstone-Ura model of triangle judgments proposed by Frijters predicts the results as an outcome of the greater statistical power of three-alternative forced choice tests compared with triangular tests. An excellent fit to all the data is given by a model wherein all subjects have the same d' for the difference between the water types but 25% of them prefer distilled water to tap water.
    Perception & Psychophysics 05/1994; 55(4):473-7. · 1.37 Impact Factor
  • A W MacRae, E N Geelhoed
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    ABSTRACT: Subjects presented with sets of three samples, two of distilled water and one of tap water, were significantly more consistent in choosing the tap water as preferable than they were in identifying it as the odd sample in the set. The result is opposite to the prediction of high-threshold models of sensory discrimination, which say that if a difference is not noticed, preferences will be random, whereas if a difference is noticed, preferences may still be in either direction. The result can be quantitatively explained by a model advanced by Frijters to explain an analogous anomaly found with the triangle test used in the food industry. Applying his model to the observed proportions yields essentially equivalent estimates of sensory difference (d' = 1.5, approximately) from the two tasks, and a direction of preference almost unanimously in favor of the tap water that was used. Since the model predicts that the proportion of subjects choosing the odd item will depart further from chance in the preference task than in the oddity task, the former has greater power to reject the null hypothesis of no sensory difference if one exists and if preference is overwhelmingly in one direction.
    Perception & Psychophysics 03/1992; 51(2):179-81. · 1.37 Impact Factor
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    ABSTRACT: The odours of five carbonyls: heptanone, octanone, octenal, nonenal and decadienal, and two mixtures of each ketone with each aldehyde, giving 17 sample types in all, were compared using two non-quantitative, non-descriptive procedures: sorting and the method of triads. Each procedure was conducted with a different set of eight completely untrained assessors. After non-metric, multi-dimensional scaling the two procedures gave similar groupings of odours which also agreed well with results obtained previously using only eleven sample types and a much larger number of very experienced assessors. The ketones and aldehydes clustered at opposite poles of the diagrams with the mixtures lying between the positions of their components. It is concluded that the procedures are suitable for use with untrained assessors and large numbers of sample types and the results are robust, especially in the case of the sorting procedure.
    Chemical Senses 01/1992; 17:119-125. · 3.28 Impact Factor
  • A. W. MacRae, P. Howgate, E. Geelhoed
    Chemical Senses 01/1990; 15(6):691-699. · 3.28 Impact Factor