Anxiety sensitivity and auditory perception of heartbeat.

Anxiety sensitivity (AS) is the fear of sensations associated with autonomic arousal. AS has been associated with the development and maintenance of panic disorder. Given that panic patients often rate cardiac symptoms as the most fear-provoking feature of a panic attack, AS individuals may be especially responsive to cardiac stimuli. Consequently, we developed a signal-in-white-noise detection paradigm to examine the strategies that high and low AS individuals use to detect and discriminate normal and abnormal heartbeat sounds. Compared to low AS individuals, high AS individuals demonstrated a greater propensity to report the presence of normal, but not abnormal, heartbeat sounds. High and low AS individuals did not differ in their ability to perceive normal heartbeat sounds against a background of white noise; however, high AS individuals consistently demonstrated lower ability to discriminate abnormal heartbeats from background noise and between abnormal and normal heartbeats. AS was characterized by an elevated false alarm rate across all tasks. These results suggest that heartbeat sounds may be fear-relevant cues for AS individuals, and may affect their attention and perception in tasks involving threat signals.

Valid across-group comparisons with labeled scales: the gLMS versus magnitude matching.

Labeled scales are commonly used for across-group comparisons. The labels consist of adjective/adverb intensity descriptors (e.g., "very strong"). The relative distances among descriptors are essentially constant but the absolute perceived intensities they denote vary with the domain to which they are applied (e.g., a "very strong" rose odor is weaker than a "very strong" headache), as if descriptors were printed on an elastic ruler that compresses or expands to fit the domain of interest. Variation in individual experience also causes the elastic ruler to compress or expand. Taste varies genetically: supertasters perceive the most intense tastes; nontasters, the weakest; and medium tasters, intermediate tastes. Taste intensity descriptors on conventional-labeled scales denote different absolute perceived intensities to the three groups making comparisons across the groups invalid. Magnitude matching provides valid comparisons by asking subjects to express tastes relative to a standard not related to taste (e.g., supertasters match tastes to louder sounds than do nontasters). Borrowing the logic of magnitude matching, we constructed a labeled scale using descriptors unrelated to taste. We reasoned that expressing tastes on a scale labeled in terms of all sensory experience might work. We generalized an existing scale, the Labeled Magnitude Scale (LMS), by placing the label "strongest imaginable sensation of any kind" at the top. One hundred subjects rated tastes and tones using the generalized LMS (gLMS) and magnitude matching. The two methods produced similar results suggesting that the gLMS is valid for taste comparisons across nontasters, medium tasters, and supertasters.

Chemosensory context effects: role of perceived similarity and neural commonality.

Seven experiments investigated how stimulus context affects judgements of the magnitude of chemosensory stimuli. In each experiment, subjects gave magnitude estimates of the intensity of several concentrations of two substances, with the contextual set of concentrations varying across experimental conditions. Different experiments used different pairs of substances, which could be tastants (sucrose or NaCl) that were sipped, odorants (orange or vanillin) that were sipped (i.e. presented retronasally) or the same odorants sniffed (i.e. presented orthonasally). Varying the stimulus context affected the judgements differentially when the two substances were compositionally different (sucrose and NaCl; sucrose and orange; sucrose and vanillin) but not when they were the same (vanillin or orange presented orally and nasally). Judgements of qualitative similarity of the same pairs of substances, obtained in a separate experiment, failed to predict accurately the pattern of differential context effects. Taken together, the results suggest that differential effects of context relate only indirectly to perceptual dissimilarity per se but may primarily reflect the result of stimulus-specific adaptation-like processes.

Cross-modal interaction between vision and touch: the role of synesthetic correspondence.

At each moment, we experience a melange of information arriving at several senses, and often we focus on inputs from one modality and 'reject' inputs from another. Does input from a rejected sensory modality modulate one's ability to make decisions about information from a selected one? When the modalities are vision and hearing, the answer is "yes", suggesting that vision and hearing interact. In the present study, we asked whether similar interactions characterize vision and touch. As with vision and hearing, results obtained in a selective attention task show cross-modal interactions between vision and touch that depend on the synesthetic relationship between the stimulus combinations. These results imply that similar mechanisms may govern cross-modal interactions across sensory modalities.

A confusion matrix for the study of taste perception.

Taste stimulus identification was studied in order to more thoroughly examine human taste perception. Ten replicates of an array of 10 taste stimuli--NaCl, KCl, Na glutamate, quinine. HCl, citric acid, sucrose, aspartame, and NaCl-sucrose, acid-sucrose, and quinine-sucrose mixtures--were presented to normal subjects for identification from a list of corresponding stimulus names. Because perceptually similar substances are confused in identification tasks, the result was a taste confusion matrix. Consistency of identification for the 10 stimuli (T10) and for each stimulus pair (T2) was quantified with measures derived from information theory. Forty-two untrained subjects made an average of 57.4% correct identifications. An average T10 of 2.25 of the maximum 3.32 bits and an average T2 of 0.84 of a maximum 1.0 bit of information were transmitted. In a second experiment, 40 trained subjects performed better than 20 untrained subjects. The results suggested that the identification procedure may best be used to assess taste function following 1-2 training replicates. The patterns of taste confusion indicate that the 10 stimuli resemble one another to varying extents, yet each can be considered perceptually unique.

Haptic perception of linear extent.

The perception of linear extent in haptic touch appears to be anisotropic, in that haptically perceived extents can depend on the spatial orientation and location of the object and, thus, on the direction of exploratory motion. Experiments 1 and 2 quantified how the haptic perception of linear extent depended on the type of motion (radial or tangential to the body) when subjects explored different stimulus objects (raised lines or solid blocks) varying in length and in relative spatial location. Relatively narrow, shallow, raised lines were judged to be longer, by magnitude estimation, than solid blocks. Consistent with earlier reports, stimuli explored with radial arm motions were judged to be longer than identical stimuli explored with tangential motions; this difference did not depend consistently on the lateral position of the stimulus object, the direction of movement (toward or away from the body), or the distance of the hand from the body but did depend slightly on the angular position of the shoulder. Experiment 3 showed that the radial-tangential effect could be explained by temporal differences in exploratory movements, implying that the apparent anisotropy is not intrinsic to the structure of haptic space.

Taste confusions following gymnemic acid rinse.

The effect of a gymnemic acid (GA) rinse, which simulated a sweet-taste deficit, was measured on human taste perception and identification. Taste ratings showed that GA reduced the intensities of sucrose and aspartame to 14% of pre-rinse levels; over the recovery interval of 30 min, these values increased linearly to 63% of the pre-rinse levels. Repeated presentations of a set of 10 stimuli (five primarily or partly sweet--sucrose, aspartame, and NaCl-sucrose, acid-sucrose and quinine-sucrose mixtures; and five nonsweet--NaCl, KCl, Na glutamate (MSG), quinine HCl and citric acid) for identification following water and GA rinses produced 'taste confusion matrices' (TCMs). Correct identification of the sweet-tasting stimuli was reduced by 23% in presentations closely following the GA rinse, an effect that dissipated with time. Most misidentifications involved sucrose and mixtures containing sucrose. In a second TCM experiment, GA was presented frequently within each session to maintain the sweet taste deficit, which revealed itself as specific confusions. Rinsing with GA impaired discriminability of sweet-nonsweet pairs of stimuli but enhanced discriminability of the aspartame-(NaCl-sucrose) pair. GA had no effect on discriminability of nonsweet stimulus pairs. The results suggest that specific error patterns in the TCM could be used to identify quality-specific taste disorders.

Haptic form perception: relative salience of local and global features.

When we examine objects haptically, do we weight their local and global features as we do visually, or do we place relatively greater emphasis on local shape? In Experiment 1, subjects made either haptic or visual comparisons of pairs of geometric objects (from a set of 16) differing in local and global shape. Relative to other objects, those with comparable global shape but different local features were judged less similar by touch than by vision. Separate groups of subjects explored the same objects while wearing either thick gloves (to discourage contour-following) or splinted gloves (to prevent enclosure). Ratings of similarity were comparable in these two conditions, suggesting that neither exploratory procedure was necessary, by itself, for the extraction of either local or global shape. In Experiment 2, haptic exploration time was restricted to 1, 4, 8, or 16 sec. Limiting exploration time affected relative similarity in objects differing in their local but not their global shape. Together, the findings indicate that the hepatic system initially weights local features more heavily than global ones, that this differential weighting decreases over time, and that neither contour-following nor enclosure is exclusively associated with the differential emphasis on local versus global features.

Processing linguistic and perceptual dimensions of speech: interactions in speeded classification.

Performance on selective-attention and divided-attention tasks shows strong and consistent interactions when participants rapidly classify auditory stimuli whose linguistic and perceptual dimensions (the words low vs. high, low and high pitch, low and high position in space) share common labels. Compared with baseline performance, response times were greater when one or two irrelevant dimensions varied (Garner interference) and when combinations of attributes were incongruent rather than congruent (congruence effects). Performance depended only on the congruence relationships between the relevant dimension and each of the irrelevant dimensions and not on the congruence relationships between the irrelevant dimensions themselves. In selective attention, an additive multidimensional model accounts well for the patterns of both Garner interference and congruence effects.

Perceptual and linguistic interactions in speeded classification: tests of the semantic coding hypothesis.

We tested the semantic coding hypothesis, which states that cross-modal interactions observed in speeded classification tasks arise after perceptual information is recoded into an abstract format common to perceptual and linguistic systems. Using a speeded classification task, we first confirmed the presence of congruence interactions between auditory pitch and visual lightness and observed Garner-type interference with nonlinguistic (perceptual) stimuli (low-frequency and high-frequency tones, black and white squares). Subsequently, we found that modifying the visual stimuli by (a) making them lexical (related words) or (b) reducing their compactness or figural 'goodness' altered congruence effects and Garner interference. The results are consistent with the semantic coding hypothesis, but only in part, and suggest the need for additional assumptions regarding the role of perceptual organization in cross-modal dimensional interactions.

A multimodal assessment of sensory thresholds in aging.

Young and elderly subjects yielded forced-choice detection thresholds in each of seven sensory tasks: (1) taste of sodium chloride, (2) smell of butanol, (3) cooling, (4) low-frequency vibrotaction, (5) high-frequency vibrotaction, (6) low-frequency hearing, and (7) high-frequency hearing. Average scores across these tasks nearly perfectly separated the 22 elderly from the 15 young subjects. For individual modalities, however, separation between the groups varied from complete (high-frequency touch) to negligible (low-frequency hearing). Scores on the Boston Picture Naming Test and especially the Wechsler Logical Memory Test correlated strongly with average threshold score (Pearson r = .80) and moderately with scores on individual modalities. This sensory-cognitive link is not caused, as might be supposed, by diminishing age-related capacity to handle the detection task, because the very same task resulted in negligible age effect (low-frequency hearing) and large effect (high-frequency hearing) in the same subjects.

Attention and the detectability of weak taste stimuli.

Subjects detected weak solutions of sucrose or citric acid under conditions in which attention was directed toward one of the tastants or the other. Detection thresholds were measured using an adaptive, forced-choice procedure, with a three-down one-up rule, which computer simulations suggest should be more reliable than the popular two-down one-up rule. The thresholds were modestly but systematically lower for attended tastants than for unattended ones. Similar results have been reported in other sense modalities, including vision (greater sensitivity to stimuli presented to attended versus unattended spatial locations) and hearing (greater sensitivity to stimuli presented at attended versus unattended sound frequencies). Taken together, the findings are consistent with a general hypothesis regarding attention in sensory systems: gains or losses in detectability occur when a central attentional mechanism (or, conceivably, a preattentive mechanism) selectively and preferentially monitors signals arising from particular subsets of peripheral neural inputs.

Circle size and diameter tilt: a new look at integrality and separability.

In six experiments using the speeded classification paradigm, we provide evidence that the ostensibly "separable" dimensions of size and orientation can produce patterns of either separability or asymmetric configurality, depending on the spatial arrangement of the stimuli. In all experiments, subjects classified large or small circles containing a single line in one of two possible orientations. When the line touched the circle's perimeter, thereby defining the diameter of the circle (Experiments 1-4), asymmetric configurality obtained: Variations in size interfered with classification by orientation, but variations in orientation did not interfere with classification by size, and redundancy gain was weak or absent. When the lines fell completely within (i.e., did not touch) the circles (Experiments 5 and 6), the results were consistent with separability: There was neither redundancy gain nor interference. Taken together, the results add to the growing body of evidence that classification of specific dimensional pairs as separable or integral may be less feasible than identifying the more general conditions that increase or decrease the psychological salience of dimensional structures and facilitate or interfere with selection of optimal processing strategies.

Focused attention and the detectability of weak gustatory stimuli. Empirical measurement and computer simulations.

Attentional processes can modulate the detectability of weak stimuli; for example, the detectability of visual or auditory signals can depend on whether attention is allocated to the appropriate spatial location (vision) or acoustic frequency (hearing). Earlier attempts in the first author's laboratory to find analogous effects of focused attention on the detectability of taste stimuli were equivocal, in part it seems because human gustatory sensitivity can fluctuate substantially over time, a serious problem when using procedures that track sensitivity (d') to a constant stimulus concentration. To circumvent this problem, we adopted an adaptive psychophysical procedure, the transformed up-down method, using a 3-down/1-up rule to determine how the threshold to detect weak concentrations of sucrose and citric acid depended on whether the stimulus presented in a given two-alternative, forced-choice trial was expected or unexpected. The results showed threshold sensitivity to be slightly but consistently poorer when the test stimulus was unexpected (e.g., sucrose presented when citric acid was expected) than it was when the test stimulus was expected (e.g., sucrose presented when sucrose was expected). In this attentional paradigm, the unexpected stimulus must perforce be presented on only a small fraction of the trials. In selecting a procedure, we chose a 3-down/1-up adaptive rule rather than the more popular 2-down/1-up rule, a choice that turned out to be in line with results of Monte Carlo computer simulations. These simulations suggest that across a wide range of conditions (starting stimulus concentrations, step sizes), the variability in threshold measurements can be smaller with a 3-down/1-up rule than with a 2-down/1-up rule, even when the total number of trials is the same and not very great.

Haptic underestimation of angular extent.

To what extent can individuals accurately estimate the angle between two surfaces through touch alone, and how does tactile judgment compare to visual judgment? Subjects' ability to estimate angle size for a variety of haptic and visual stimuli was examined in a series of nine experiments. Triangular wooden blocks and raised contour outlines comprising different angles and radii of curvature at the apex were used in experiments 1-4 and it was found that subjects consistently underestimated angular extent relative to visual baselines and that the degree of underestimation was inversely related to the actual size of the angle. Angle estimates also increased with increasing radius of curvature when actual angle size was held constant. In contrast, experiments 5-8 showed that subjects did not underestimate angular extent when asked to perform a haptic-visual match to a computerized visual image; this outcome suggests that visual input may 'recalibrate' the haptic system's internal metric for estimating angle. The basis of this cross-modal interaction was investigated in experiment 9 by varying the nature and extent of visual cues available in haptic estimation tasks. The addition of visual-spatial cues did not significantly reduce the magnitude of haptic underestimation. The experiments as a whole indicate that haptic underestimations of angle occur in a number of different stimulus contexts, but leave open the question of exactly what type of visual information may serve to recalibrate touch in this regard.

Differential effects of stimulus context on perceived length: implications for the horizontal-vertical illusion.

Six experiments examined orientation-specific effects of stimulus context on the visual perception of horizontal and vertical lengths: Using a paired-comparison method, Experiments 1-5 showed that the probability of judging a given vertical line to be longer than a given horizontal line was relatively great when the stimulus set comprised relatively long horizontals and short verticals, and relatively small when the stimulus set comprised short horizontals with long verticals. To the extent that stimulus context exerts orientation-specific effects on perceived length, it thereby modulates the degree to which verticals appear longer than physically equivalent horizontals: the horizontal-vertical illusion (HVI). Under various contextual conditions, the HVI was as small as 3% (horizontals had to be 3% greater than verticals to be perceived as equally long) and as great as 15%, equaling about 12% in a "neutral" context. In Experiment 6, subjects judged the absolute physical length of each stimulus, and the results indicated that stimulus context acted largely by decreasing perceived lengths. The results are consistent with the hypothesis that differential effects of context reflect a process of stimulus-specific perceptual attenuation.

Recalibrating the perception of loudness: interaural transfer.

Previous research, using both magnitude-scaling and direct-comparison methods, has shown the perception of loudness to be contingent on the distribution of tonal stimuli varying in sound frequency as well as SPL: When a low-frequency signal, f1, is presented at low SPLs and a high-frequency signal, f2, at high SPLs, loudness at f1 is great relative that at f2; reversing the association of SPL with frequency reverses the loudness relation. These shifts in relative loudness, recently termed "recalibration" [Marks, J. Exp. Psychol: Hum. Percept. Perf. 20, 382-396 (1994)] [corrected], are consistent with the operation of frequency-specific, fatiguelike processes at f1 and f2. Experiment 1 combined both scaling (magnitude estimation) and matching (direct-comparison) methods and showed that exposing one ear to recalibrating stimuli (500 and 2500 Hz) led to substantial shifts not only in the ipsilateral ear but also in the contralateral ear (albeit smaller ones). Experiment 2 used a selective-exposure procedure and gave similar results. Thus the processes underlying recalibration of loudness appear to involve central mediation; consequently, it is possible that processes of auditory fatigue rely on central as well as peripheral mechanisms.

Visual-auditory interaction in speeded classification: role of stimulus difference.

An experiment examined cross-modal interference and congruence in speeded classification: Subjects had to identify compound (visual-auditory) stimuli as either low or high in spatial position (visual judgment) or low or high in pitch (auditory judgment), in 16 conditions, each of which combined one of four possible pairs of tones, varying in frequency difference, with one of four possible pairs of dots, varying in positional difference. Both classification by position and classification by pitch revealed Garner interference (poorer performance than baseline, with orthogonal variation in the irrelevant dimension) and congruence effects (better performance with congruent than with incongruent stimulus combinations), but pitch classification showed more. Furthermore, the size of the pitch difference strongly affected classification by pitch and less strongly affected classification by position, but the size of the position difference affected neither. The findings are consistent with the view that Garner interference and congruence effects are closely related, perhaps arising from a common source, and suggest that the asymmetries could depend in part on the degree of dimensional overlap between stimuli and responses.

Binaural summation after learning psychophysical functions for loudness.

Do response-related processes affect perceptual processes? Sometimes they may: Algom and Marks (1990) produced different loudness exponents by manipulating stimulus range, and thereby also modified the rules of loudness summation determined by magnitude scaling. The present study manipulated exponents by having a dozen subjects learn prescribed power functions with exponents of 0.3, 0.6, or 1.2 (re sound pressure). Subjects gave magnitude estimates of the loudness of binaural signals during training, and of monaural and binaural signals after training. During training, subjects' responses followed the nominal functions reasonably well. Immediately following training, subjects applied the numeric response scales uniformly to binaural and monaural signals alike; the implicit monaural-binaural loudness matches, and thus the basic rules underlying binaural summation, were unaffected by the exponent learned. Comparison of these results with those of Algom and Marks leads us to conclude that changing stimulus range likely influences underlying perceptual events, whereas "calibrating" a loudness scale through pretraining leaves the perceptual processes unaffected.

"Recalibrating" the auditory system: the perception of loudness.

Listening to relatively intense tones at 1 frequency and weak tones at another makes the latter relatively louder. The auditory system's relative response to low-frequency (f1) and high-frequency (f2) tones depends on the separation between f1 and f2. When f1 and f2 differ little, loudness matches change little with shifts in mean sound pressure levels (SPLs) at each frequency; but when f1 and f2 differ more, matches change markedly, showing how the auditory system "recalibrates" its responses to f1 and f2. The magnitude of recalibration and its frequency bandwidth also depend to a modest degree on the range of SPLs, their mean level, and the experimental paradigm. The representation of loudness reflects the processing and recalibration of multidimensional peripheral inputs within a higher level, context-sensitive (adaptationlike) mechanism. Other perceptual modalities show evidence of analogous mechanisms.