Contextual effects in difference judgments

Manipulating stimulus spacing, stimulus frequency, or stimulus range usually affects intensity judgments. In six experiments, I investigated the locus of analogues of these contextual effects in a “difference” estimation task. When all stimuli elicited the same taste quality, stimulus distribution affected the scale values only when water was included in the stimulus set (Experiments 1–3). When the subjective ranges of two taste qualities were manipulated, different scale values were obtained for the separate qualities in the two conditions (Experiment 4). Manipulation of the expected response distribution did not affect the scale values or the responses (Experiments 5–6). It is concluded that shifts in stimulus distributions or stimulus ranges result in shifts in subjective scale values. The contextual effects can be interpreted as relative shifts of a number of gustatory continua, with water lying on a separate continuum. Proposed is a model for context-dependent judgments, consisting of four stages: stimulus classification, stimulus placement, continuum placement, and continuum projection.     

Sweetness suppression in fructose/citric acid mixtures: A study of contextual effects

Twoexperiments investigated whether stimulus context affects ratings for mixtures of dissimilartasting substances (fructose/citric acid) to the same degree that it affects ratings for unmixed substances (fructose). In Experiment 1, replacing mixtures by equisweet unmixed fructose solutions produced virtually no response shifts. The proportion of mixtures in the stimulus set affected only slightly the degree of mixture suppression inferred from the responses. In Experiment 2, both the stimulus type (mixed or unmixed) and the stimulus distribution (positively versus negatively skewed) affected the responses. Several factors that determine the impact of contextual changes are identified: (a) the stage in stimulus processing affected—that of representation on the internal continuum or that of response selection; (b) the size and sources of variation in the affected process; and (c) the degree to which a stimulus is perceptually integrated in the context. In the present study, the sweetness of fructose/citric acid mixtures was largely, but not completely, integrated with the sweetness of unmixed fructose solutions. It is suggested that increased stimulus complexity makes mixture ratings more susceptible to contextual shifts. An analysis relating the size of the contextual shift to the degree of response variability suggests that response-selection processes are more important in determining the responses for unmixed stimuli than they are in determining the responses for mixtures.     

Contextual and sequential effects on judgments of sweetness intensity.

Presenting stimuli from skewed concentration distributions affects mean responses on category scales. However, if the number of categories on the response scale is increased, the degree of separation between the mean responses obtained for a positively as opposed to a negatively skewed concentration distribution diminishes. The present study investigates the effect of skewed concentration distributions upon ratings on a line scale and compares it to the context effect found for a 7-point category scale. In addition, sequential dependencies between consecutive stimuli and responses are investigated in order to assess their relevance in taste-intensity scaling studies. The context effects are similar for the 7-point category scale and for the line scale. The analyses of sequential effects show that both preceding responses and preceding stimuli affect current responses. However, since these two factors work in opposite directions, only a small contrast effect from the previous stimulus is significant in an overall analysis. The present study shows that even though the overall sequential effects between consecutive stimuli and responses are small, the effect of experimental context may be considerable. Since subjective context is established at the beginning of a session and sequential dependencies operate throughout the whole session, it is argued that contextual and sequential effects are only indirectly related.     

Both perceptual and conceptual factors influence taste-odor and taste-taste interactions

Observers are often asked to make intensity judgments for a sensory attribute of a stimulus that is embedded in a background of “irrelevant” stimulusdimensions. Under some circumstances, these background dimensions of the stimulus can influence intensity judgments for the target attribute. For example, judgments of sweetness can be influenced by the other taste or-odor qualities of a solution (Frank & Byram, 1988; Kamen et al., 1961). Experiments 1 and 2 assessed the influence of stimulus context, instructional set, and reference stimuli on cross-quality interactions in mixtures of chemosensory stimuli. Experiment 1 demonstrated that odor-induced changes in sweetness judgments were dramatically influenced when subjects rated multiple attributes of the stimulus as compared with when they judged sweetness alone. Several odorants enhanced sweetness when sweetness alone was judged, while sweetness was suppressed for these same stimuli when total-intensity ratings were broken down into ratings for the sweetness, saltiness, sourness, bitterness, and fruitiness of each solution. Experiment 2 demonstrated a similar pattern of results when bitterness was the target taste. In addition, Experiment 2 showed that the instructional effects applied to both taste-odorand taste-taste mixtures. It was concluded that the taste enhancement and suppression observed for taste-odor and taste-taste mixtures are influenced by (1) instructional sets which influence subjects’ concepts of attribute categories, and (2) the perceptual similarities among the quality dimensions of the stimulus.     

The effectiveness of different sweeteners in suppressing citric acid sourness

The exact mechanism that causes taste suppression in a perceptually heterogeneous mixture, and the locus of that mechanism, are as yet unknown. The present study was designed to explore the idea that mixture suppression is a perceptual phenomenon and not the result of physical, chemical, or receptor-substance interactions. An investigation was carried out as to whether perceptually similar taste stimuli give rise to the same sensory interactions when mixed with a substance of a different taste quality. In the first study, five different sweeteners (sucrose, fructose, aspartame, saccharin, and sorbitol) were matched in perceived sweetness intensity, in order to obtain five perceptually similar stimuli. Every equisweet sweetener concentration was mixed with each of four citric acid concentrations. In a second study, the sourness-suppressing effects of two sweeteners, sucrose and aspartame, were compared at four different concentration levels. Sourness scale values of unmixed citric acid, the unmixed sweeteners, and the citric acid/sweetener mixtures were assessed with a functional measurement approach in combination with a two-stimulus procedure. The equisweet sweeteners were equally effective in suppressing the perceived sourness intensity of citric acid over the concentration range used. The side tastes of the sweeteners, if present, did not have a substantial effect on the degree of sourness suppression.     

Determinants of cumulative successive contrast in saltiness intensity judgments

When all stimuli elicit the same taste quality, solutions preceded by a high concentration level are judged to be significantly less intense than solutions preceded by a low concentration level. After repetitious stimulation with a different tasting stimulus, the intensity of the present stimulus is overestimated. This phenomenon is called “successive contrast.” In the present study, the cumulative effects of three identical stimuli on the saltiness ratings for a test stimulus are investigated. The preceding stimuli are manipulated with regard to taste quality, saltiness intensity, total taste intensity, and complexity. Whether the size of the cumulative contrast effect is associated with the degree of dissimilarity between preceding stimuli and test stimulus, or with the saltiness or total taste intensity of the preceding stimuli, is investigated. The size of the contrast effect depends on the type of preceding stimulus, its intensity, and the type of test stimulus. No association was found with judgments of the degree of dissimilarity between the preceding stimuli and the test stimulus. For nonsalty preceding stimuli, the contrast effects are independent of concentration level. When the preceding stimuli taste at least partly salty, the total intensity appears to determine the size of the contrast for an unmixed salty test stimulus.     

Method of stimulation, mouth movements, concentration, and viscosity: effects on the degree of taste adaptation

Although sensory adaptation, the gradual loss of sensation during prolonged stimulation, has been demonstrated in laboratory taste experiments, a comparable loss of taste intensity is not experienced in real-life eating situations. This discrepancy may be due to differences in the proximal stimuli or to differences in the ways the taste receptors are stimulated. In two experiments, the effects of four potentially relevant variables were investigated: stimulus intensity, stimulus viscosity, mouth movements, and presentation method. During the initial seconds of stimulation, adaptation to the weakest of the two solutions was faster. Although more viscous stimuli were less sweet, viscosity as such did not affect adaptation rate, nor did mouth movements. Among the three presentation methods, a sucrose-soaked filter paper on the tongue produced more adaptation than either sipping the solution or flowing it over the tongue. This suggests that even mouth movements far more subtle than those still present in the no-movement condition of a sip-and-spit experiment can disrupt the adaptation process.     

Visualising fragrances through colours: the mediating role of emotions

To facilitate communication about fragrances, one can use the colours people tend to associate with their smells. We investigated to what extent odour-colour correspondences for fine fragrances can be accounted for by underlying emotional associations. Odour-colour matches and degree-of-fit judgments revealed that odours were matched to colours non-randomly. Matching colours differed mainly on blackness (brightness), and less on chromaticness (saturation) and hue. Furthermore, we found a consistent negative relationship between odour-colour degree-of-fit ratings and the difference between the odour scores and the colour scores on one of the emotion dimensions (pleasure). This suggests that emotional associations may partly underlie odour-colour correspondences.     

The perceived importance of sensory modalities in product usage: a study of self-reports

Although popular belief holds that vision dominates human experience, this does not necessarily imply that people regard vision as the most important sensory modality during the interaction with every product. Instead, the relative importance of the different modalities is likely to depend on the type of product and on the task performed. In Study 1, respondents reported how important they found vision, audition, touch, taste, and smell during the use of 45 different products. In Study 2, the respondents answered a similar question for the evaluation of the safety, ease of use, and enjoyment experienced for 15 products. Importance ratings for the sensory modalities differed considerably between the products. Differences due to the types of evaluations were smaller. Averaged over products and evaluation types, vision was the most important sensory modality for product evaluations, followed by touch, smell, audition, and taste. However, for about half of the individual products, the importance ratings for vision were lower than for one of the other modalities. These findings are in line with the view that vision is regarded the dominant modality, because it plays an important part in many and an irrelevant part in virtually no product experiences.