Effects of context on sweet and bitter tastes: Unrelated to sensitivity to PROP (6-npropylthiouracil)

In a double-shifting context paradigm, subjects gave magnitude estimates of the perceived intensity of qualitatively dissimilar taste substances (saccharin and quinine, sucrose and quinine) or qualitatively similar ones (saccharin and sucrose), with each pair of substances taking on different contextual sets of concentrations in different sessions. The dissimilar pairs produced substantial differential effects of context (e.g., a particular concentration of saccharin or sucrose was judged more intense than a particular quinine in one contextual setting, less intense in another), but the similar pair did not. This result accords with the hypothesis that differential context effects depend on qualitative similarity. Contrary to expectations, however, the magnitude of the context effect did not differ in tasters and nontasters of the bitter substance 6-n-propylthiouracil (PROP), groups previously shown to differ in sensitivity to bitterness in saccharin. Similarity judgments suggest that saccharin and sucrose were qualitatively alike for ail subjects, regardless of sensitivity to PROP.     

Effects of context on sweet and bitter tastes: unrelated to sensitivity to PROP (6-n-propylthiouracil).

In a double-shifting context paradigm, subjects gave magnitude estimates of the perceived intensity of qualitatively dissimilar taste substances (saccharin and quinine, sucrose and quinine) or qualitatively similar ones (saccharin and sucrose), with each pair of substances taking on different contextual sets of concentrations in different sessions. The dissimilar pairs produced substantial differential effects of context (e.g., a particular concentration of saccharin or sucrose was judged more intense than a particular quinine in one contextual setting, less intense in another), but the similar pair did not. This result accords with the hypothesis that differential context effects depend on qualitative similarity. Contrary to expectations, however, the magnitude of the context effect did not differ in tasters and nontasters of the bitter substance 6-n-propylthiouracil (PROP), groups previously shown to differ in sensitivity to bitterness in saccharin. Similarity judgments suggest that saccharin and sucrose were qualitatively alike for all subjects, regardless of sensitivity to PROP.     

On the cross-modal perception of intensity

Are cross-modality matches based on absolute equivalences between the intensities of perceptual experiences in different senses, or are they based on relative positions within the respective sets of stimuli? To help answer this question, we conducted a series of three experiments; in each the levels of stimulus magnitude in one modality stayed constant while the levels in the other changed from session to session. Results obtained by two methods--magnitude matching and cross-modal difference estimation--agreed in revealing the following: First, the cross-modality matches seem to represent in all cases a compromise between absolute equivalence and relative (contextual) comparison, the compromise being about 50-50 for both auditory loudness versus vibratory loudness and auditory loudness versus visual brightness, but more nearly, though not wholly, absolute for perceived auditory duration versus visual duration. Second, individual variations abounded, with some subjects evidencing totally absolute matching, others totally relative matching (with little consistency, however, between tasks or between comparisons of different pairs of modalities). Third, the judgments of cross-modal difference were consistent with a model of linear subtraction, and in the case of loudness, the underlying scale was roughly compatible with Stevens's sone scale. Finally, a model designed to describe sequential dependencies in response can account for at least part of the context-induced changes in cross-modal equivalence.     

The slippery context effect in psychophysics: intensive, extensive, and qualitative continua.

When subjects gave magnitude estimates of 500- and 2500-Hz tones at various SPLs, they judged a 500-Hz tone of 60 dB to be as loud as a 2500-Hz tone of 57 dB in one context (low SPLs at 500 Hz, high SPLs at 2500 Hz), but as loud as a 2500-Hz tone at 40 dB in another context (high SPLs at 500 Hz, low at 2500 Hz) (Marks, 1988). Such shifts in matches derived from judgments of multidimensionally varying stimuli are termed slippery context effects. The present set of seven experiments showed that slippery effects were absent from judgments of pitch of tones at different loudnesses, duration of tones at different pitches, and length of lines at different colors, though a small effect emerged in judgments of duration of tones and lights. Slippery context effects were substantial when subjects gave magnitude estimates of loudness of 500- and 2500-Hz tones under conditions in which the pitch at each trial either was cued visually beforehand or could be known through the regular stimulus sequence, and with instructions to make absolute magnitude estimates. The results are consistent with the view that slippery context effects occur automatically and "preattentively."     

The slippery context effect in psychophysics: Intensive,extensive, and qualitative continua

When subjects gave magnitude estimates of 500- and 2500-Hz tones at various SPLs, they judged a 500-Hz tone of 60 dB to be as loud as a 2500-Hz tone of 57 dB in one context (low SPLs at 500 Hz, high SPLs at 2500 Hz), but as loud as a 2500-Hz tone at 40 dB in another context (high SPLs at 500 Hz, low at 2500 Hz) (Marks, 1988). Such shifts in matches derived from judgments of multi-dimensionally varying stimuli are termedslippery context effects. The present set of seven experiments showed that slippery effects were absent from judgments of pitch of tones at different loudnesses, duration of tones at different pitches, and length of lines at different colors, though a small effect emerged in judgments of duration of tones and lights. Slippery context effects were substantial when subjects gave magnitude estimates of loudness of 500- and 2500-Hz tones under conditions in which the pitch at each trial either was cued visually beforehand or could be known through the regular stimulus sequence, and with instructions to make absolute magnitude estimates. The results are consistent with the view that slippery context effects occur automatically and “preattentively.”     

Intensity scales for pure tastes and for taste mixtures

In four series of studies, taste intensities of sour, bitter, sweet, and salt were measured by number matching (magnitude estimation), and by noise matching. The two procedures agreed in their estimates of the power-function exponent for each taste. Representative exponents obtained from the studies are 1.0 to 1.1 for sour and bitter and 1.3 to 1.5 for sweet and salt. In a second set of studies each taste was judged against three or more background levels of a second taste. The results suggest that the power-function exponent is unaffected when a second taste is present in the solution. Whether the intercept changes in taste mixtures was not determined in these experiments.     

The influence of cognitive set on performance and arousal under different noise loads

Three groups of 12 subjects each performed a mental arithmetic task while exposed to continuous white noise in two experimental sessions. In Session I, each group was exposed to a different noise level [56, 72.5, or 85dB(A)], whereas in Session II all had the medium [72.5 dB(A)] intensity. Arithmetic performance deteriorated with increasing noise intensity in Session I, and in Session II each group retained its position relative to the other two groups. Thus, the higher the noise intensity in the first session, the poorer the performance in the second session. These results suggest that the motivation and energy mobilized in Session II were determined by the cognitive set adopted to meet the demands of Session I. Arousal level, as measured by adrenaline excretion and heart rate, was higher during both experimental sessions than in a control session. The rise in adrenaline output was of the same magnitude regardless of the intensity of the noise, which indicates that the subjects adjusted to the increase in total load by slowing down their performance rather than by raising their energy mobilization. Heart rate rose in response to changes in noise level in Session II relative to Session I, regardless of the direction of the change.     

Context effects,reliability, and internal consistency of intermodal joint scaling

Context effects, intraindividual variability, and internal consistency of intermodal joint scaling with magnitude estimation (“magnitude matching”) were studied by instructing 12 subjects to judge the three pairs of odor intensity, loudness, and brightness on a common scale of perceived intensity as well as to judge odor intensity separately (unimodal magnitude estimation). Significant context effects were found by comparing odor intensity judgments obtained by separate versus intermodal joint scaling as well as across different modalities (loudness vs. brightness) in joint scaling. But no such effects were found for loudness or brightness when compared across modality of joint scaling. Intraindividual variability in the estimates imply about equal reliability in intermodal joint scaling and separate scaling. Good internal consistency was found, indicating that subjects are successful in expressing perceived intensities of different modalities on a common scale.     

Quality-specific effects of aging on the human taste system

Elderly persons are known to have elevated taste thresholds, with those for bitter more affected by age, for example, than those for sweet. Do analogous quality-specific effects occur at suprathreshold levels? Young (mean age = 20.3 years, SD = 2.99) and elderly (mean age = 72.5 years, SD = 4.58) subjects made magnitude estimates of sweetness, bitterness, sourness, and saltiness for the unmixed components sucrose, caffeine, citric acid, and NaCl at three concentration levels for each. They also made magnitude estimates of the separate taste qualities in two-component mixtures of sucrose with each of the other three qualities, at various levels of the two components in each mixture. Magnitude estimates of taste intensity were interweaved with magnitude estimates of the heaviness of six weights, which subjects were to judge on the same subjective intensity scale: This is the calibration feature of the method of magnitude matching, and permits the comparison of elderly and young subjects on the absolute intensity of tastes. When unmixed components were judged, elderly subjects found the characteristic tastes of caffeine and citric acid less intense than, but those of sucrose and NaCl as intense as, younger subjects did. In judging mixtures, the elderly found bitterness, but not the other three qualities, less intense than did the young subjects.     

Choice, experience, and the generalized matching law

Five pigeons were exposed to different pairs of concurrent variable-interval, variable-interval schedules on nine experimental conditions of 30 sessions each. For every session, the parameters of the generalized matching equation were computed for the first five, six, seven, eight, and nine experimental conditions. The exponent a, both for response and time distribution, tended to decrease with increases in number of experimental conditions and to increase with number of sessions per condition, but values of k (bias) varied unsystematically. When the subjects were exposed to five new pairs of schedules, with 55 sessions per condition, the findings were confirmed. Data from the literature on the generalized matching law suggest that the variability of exponent values may be explained in part by the use of naive or experienced subjects in different investigations and by the variability in number of experimental conditions and in number of sessions per condition.     

A further parallel between selective adaptation and contrast

It is generally believed that selective adaptation effects in speech perception are due to a reduction in sensitivity of auditory feature detectors. Recent evidence suggest that these effects may derive instead from contrast. In a further test of the contrast hypothesis, we conducted two experiments each involving both adaptation and contrast sessions with matching stimulus sets. During the adaptation sessions of Experiment 1, subjects identified two series of velar stimuli varying in voice onset time, [ga]-[kha] and [gi]-[khi], before and after adaptation with of the following stimuli: [ga], [kha], [gi], and [khi]. In the contrast session, subjects identified either of two ambiguous test items (drawn from near the phonetic boundaries of the [ga]-[kha] and the [gi]-[khi] series) following a single presentation of [ga], [kha], [gi], or [khi]. For both the adaptation and contrast sessions, (a) the [--a] test items were more greatly affected (in a contrast direction) by the [--a] than by the [--i] adaptor/context stimuli, and (b) the [--i] test items were not differentially affected by the [--1] and [--i] adaptor/context stimuli. An analogous design was used in Experiment 2, except that the stimulus sets varied in pitch rather than vowel quality. For both the adaptation and contrast sessions, the test items were not differentially affected by the pitch of the adaptor/context stimulus. These parallel results provide further evidence that adaptation effects are actually a form of contrast.     

THE CONTINGENCY OF PERCEPTUAL PROCESSING: Context Modifies Equal-Loudness Relations

Abstract –The relative loudnesses of tones that differ in sound frequency can depend strongly on the stimulus context, that is, on the set of intensity levels m the stimulus ensemble Using a new paradigm, called matching in scaling, this investigation sought to confirm that context modifies loudness relations per se, and not, for example, only overt responses To this end, two experiments revealed that changes in stimulus context differentially affect direct comparisons of loudness of 500-Hz and 2,500-Hz tones, as well as numerical judgments of individual tones—when loudness matches and scaling judgments alike are obtained in the same experimental sessions These contingent effects vary dynamically over time as a function of the recent stimulus history A third experiment revealed analogous effects in a simple matching paradigm, with no numerical judgments at all These findings support the contention that basic properties of loudness perception—grounded in auditory processes often considered "low level"—nevertheless can be deeply contextual     

Remembrance of sounds past: memory and psychophysical scaling

What is the role of long-term memories of previous stimulus-response mappings, and of previous sensory and perceptual experiences generally, in psychophysical scaling judgments? I conducted four experiments in an attempt to provide some preliminary answers to this question. In each experiment, subjects made judgments of the loudness of sounds on 3 successive days. Stimulus intensities were drawn randomly from the same set on Days 1 and 3 but from a different set, either all 12 dB higher or all 12 dB lower, on Day 2. Four different types of psychophysical scaling judgments were studied: category judgment without an experimenter-induced identification function, ratio magnitude estimation with a variable standard, absolute magnitude estimation, and cross-modality matching. The first two methods required completely relative judgment, the last two completely absolute judgment. Data from all methods reveal profound effects of stimulus-response mappings experienced on previous days (long-term memory) and immediately previous stimuli and responses (short-term memory) on responses to current stimuli. Responses were typically a compromise between absolute and relative judgment. Individual differences were dramatic.     

The effects of context change on long-term habituation of the orienting response in humans

Four experiments examined the effects of context change (Experiments 1-3) and context extinction (Experiment 4) on long-term habituation of the skin conductance response. In all experiments, subjects received 15 presentations of a target stimulus in each of two sessions. In Experiment 1 (N=60) there was a 15-min interval between training and test sessions. This interval was extended to 24 hours in Experiments 2 (N=60) and 3 (N=60). The experimental treatment in each of these studies involved a change in context between the two training sessions. None of the experiments provided evidence of context dependency in measures of long-term habituation. In Experiment 4 (N=60) experimental subjects received a period of context extinction during which they remained in the laboratory environment between two series of habituation trials. Again, however, there was no evidence that long-term habituation was contextually mediated. Thus, the results fail uniformly to support theories that argue that long-term habituation is context-dependent.     

Concurrent schedules: reinforcer magnitude effects

Five pigeons were trained on pairs of concurrent variable-interval schedules in a switching-key procedure. The arranged overall rate of reinforcement was constant in all conditions, and the reinforcer-magnitude ratios obtained from the two alternatives were varied over five levels. Each condition remained in effect for 65 sessions and the last 50 sessions of data from each condition were analyzed. At a molar level of analysis, preference was described well by a version of the generalized matching law, consistent with previous reports. More local analyses showed that recently obtained reinforcers had small measurable effects on current preference, with the most recently obtained reinforcer having a substantially larger effect. Larger reinforcers resulted in larger and longer preference pulses, and a small preference was maintained for the larger-magnitude alternative even after long inter-reinforcer intervals. These results are consistent with the notion that the variables controlling choice have both short- and long-term effects. Moreover, they suggest that control by reinforcer magnitude is exerted in a manner similar to control by reinforcer frequency. Lower sensitivities when reinforcer magnitude is varied are likely to be due to equal frequencies of different sized preference pulses, whereas higher sensitivities when reinforcer rates are varied might result from changes in the frequencies of different sized preference pulses.     

Determinants of subjective contour: Bourdon illusions and "unbending" effects

Wenderoth and O'Connor (1987b) reported that, although matches to the straight edge of two triangles placed apex to apex revealed an apparent bending in the direction of the chevron formed by the hypotenuse pair (the Bourdon effect), no perceptual unbending of the bent chevron occurred. Using subjective contour figures, Walker and Shank (1988b) found large and approximately equal bending and unbending effects, consistent with two theories that they proposed. In Experiment 1, using adjustable chevron matching and subjective contours, we found that Bourdon effects, equivalent in magnitude to those reported by Walker and Shank, were 4-5 times larger than unbending effects. In Experiment 2, we used a variation of Walker and Shank's measurement technique, in which subjects selected a matching angle from a graded series. We obtained Bourdon effects similar to those in Experiment 1, but much larger unbending effects. Nevertheless, Bourdon effects were significantly larger than unbending effects in one set of data; and in another, Bourdon test means were larger than unbending test means. In both data sets, there was a large and significant pretest bending effect, which enhanced the magnitude of unbending test minus pretest scores. These results were consistent with our theory but not the theories of Walker and Shank. The variance of unbending test matches, 3-4 times that of Bourdon test matches, reflected the task difficulty. We propose that subjective obtuse angle contraction that exceeds real obtuse angle contraction explains the fact that unbending effects are larger in subjective than in real contours.     

Individual differences in power functions for a 1-week intersession interval

Two experiments examined correlations of the power function exponents of individual Ss obtained in each of two sessions. Half the Ss for any task performed second sessions immediately after the first, the other half after a week’s delay. In Experiment I, groups of 16 Ss gave magnitude estimations of apparent area, or else of area and loudness. In Experiment II, groups of 16 Ss made cross-modality matches of apparent time duration to area. Significant correlations in all cases indicated consistent and persisting S differences in exponents. The results are related to the findings of other studies of such individual differences.     

Intensity resolution and subjective magnitude in psychophysical scaling

Several successful theories of psychophysical judgment imply that exponents of power functions in scaling tasks should covary with measures of intensity resolution such asd’ in the same tasks, whereas the prevailing metatheory of ideal psychophysical scaling asserts the independence of the two. In a direct test of this relationship, three prominent psychophysical scaling paradigms were studied: category judgment without an identification function, absolute magnitude estimation, and cross-modality matching with light intensity as the response continuum. Separate groups of subjects for each scaling paradigm made repeated judgments of the loudnesses of the pure tones that constituted each of two stimulus ensembles. The narrow- and wide-range ensembles shared six identical stimulus intensities in the middle of each set. Intensity resolution, as measured byd’-like distances, of these physically identical stimuli was significantly worse for the wide-range set for all three methods. Exponents of power functions fitted to geometric mean responses, and in magnitude estimation and cross-modality matching the geometric mean responses themselves, were also significantly smaller in the wide-range condition. The variation of power function exponents, and of psychophysical scale values, for stimulus intensities that were identical in the two stimulus sets with the intensities of other members of the ensembles is inconsistent with the metatheory on which modern psychophysical scaling practice is based, although it is consistent with other useful approaches to measurement of psychological magnitudes.     

Processing of stimulus properties: evidence for dual-task integrality

The conditions under which dual-task integrality can be fostered were assessed in a study in which we manipulated four factors likely to influence the integrality between tasks: intertask redundancy, the spatial proximity of primary and secondary task displays, the degree to which primary and secondary task displays constitute a single object, and the resource demands of the two tasks. The resource allocation policy is inferred from changes in the amplitude of the P300 component of the event-related brain potential. Twelve subjects participated in three experimental sessions in which they performed both single and dual tasks. The primary task was a pursuit step tracking task. The secondary tasks required subjects to discriminate between different intensities or different spatial positions of a stimulus. Task pairs that required the processing of different properties of the same object resulted in better performance than task pairs that required the processing of different objects. Furthermore, these same object task pairs led to a positive relation between primary task difficulty and the resources allocated to secondary task stimuli. Intertask redundancy and the physical proximity of task displays produced similar effects of reduced magnitude.     

Critical bands and mixed-frequency scaling: sequential dependencies, equal-loudness contours, and power function exponents

Stimuli of random intensities and various but predictable frequencies were presented for repeated magnitude estimations on the same scale (mixed-frequency scaling). The frequencies for a particular judgment session were selected so that they lay either inside each other's critical bands or outside them. Contrastive dependencies of current magnitude estimation responses on previous stimuli of a different frequency were significantly affected by whether the two frequencies were inside or outside each other's critical bands, while assimilative dependencies were not. This reinforces the idea that such dependencies are sensory in nature and arise from a different mechanism than do the assimilative dependencies. Mixed-frequency scaling of loudness also gives rise to cross-frequency matching functions from which equal-loudness contours can be calculated. These contours calculated from the present judgments are similar to those produced from other methods, even when they are extrapolated to untested intensities. Power function exponents for loudness scaled in this way are larger for lower frequencies, as has been found in previous studies, and are consistent with the flattening of the calculated equal-loudness contours for low frequencies as intensity increases.