Tactile experience does not ameliorate age-related reductions in sensory function.

UNLABELLED: BACKGROUND/STUDY CONTEXT: Sensory function degrades with age, with well-established reductions in tactile spatial acuity, vibrotactile sensitivity, and thermosensation, to name but three aspects of perception. Such age-related losses might be partially stemmed by ongoing experience with tasks requiring high levels of manual dexterity or analogous tactile expertise; individuals who are highly expert in skills that have a fundamental tactile component can show improved tactile function as compared with nonexperts. METHODS: Eighty individuals (17 males, 63 females) in the 18-58 age range were assessed on their tactile experience, as measured by self-assessment on a variety of tasks and competencies, each of which required a high level of skill with the hands. Tactile sensory performance, manual dexterity ("haptic efficiency"), and the subjective response to tactile stimulation were quantified. RESULTS: Degradation in tactile sensory acuity with age was confirmed, but no strong evidence was found for variations in acuity contingent on the tactile expertise of participants. In contrast to the performance measures, differences in tactile experience were associated with differences in the subjective response to touch. Greater tactile experience was associated with the provision of richer descriptions of textured materials manipulated with the digits. CONCLUSION: The range of tactile experience reported in a convenience sample of the population was apparently insufficient to preserve sensory function during aging.

Effect of hydration on the tactile and thermal sensitivity of the lip.

The vermilion lip is a body site particularly susceptible to water loss. Therefore, the role of hydration in tactile perception at the lip was investigated. A series of measures of tactile performance and response were obtained from 22 female subjects, namely: (1) the subjective assessment of lip feel, (2) tactile sensitivity, (3) spatial acuity, (4) thermal sensitivity, and (5) the subjective assessment of thermal stimulation. These measures were obtained from lips in their natural (untreated) state, and lips that had been treated using a hydrating preparation. The preparation altered the subjective feel of the lips consistent with the treatment increasing lip hydration and compliance. Hydrated lips showed greater sensitivity to light touch, and there was a trend toward the lip's thermal sensitivity being altered consistent with the lip treatment having a physical cooling effect. Spatial acuity was unaltered by the state of lip hydration. The sensitivity changes on hydration were proposed to have mechanical basis.

Perception of fluids with diverse rheology applied to the underarm versus forearm skin.

Little is known about the tactile-perceptual structure of fluids. Therefore, ten fluids with diverse, characterized rheologies were rated by 16 females, on 27 sensory attributes (e.g., "slippery") and 14 emotional attributes (e.g., "enjoyable") via five-point categorical scales. Fluids were assessed against the volar forearm and underarm, sites that commonly experience contact with fluids during the use of personal care products. Application of fluids was either by the participant to their own body ("self-applied") or by the experimenter to the participant's body ("experimenter-applied"). Separate factor analyses of the sensory and emotional attributes for different body sites and modes of touch suggested approximately the same factorial structure in each case. Four general sensory factors emerged, labeled Lubricating, Textured, Silken, and Viscous, and two emotional factors, Comfortable and Arousing. These factors resembled those from equivalent work that used solid materials as stimuli, emphasizing that despite the differences in perceptual structure between fluid-coated and dry, solid surfaces, different body sites, and modes of touch influence the perception of fluid and dry stimuli similarly. As expected, fluids varied widely in how they scored on the factors. Site-wise differences were found, whereby stimuli assessed against the forearm were rated as more Lubricating, less Textured, more Silken, and more Comfortable than they were against the underarm. Self-applied touch was less Comfortable than experimenter-applied. The physical and perceptual were linked insofar as greater measured viscosity at low shear rates was associated with perceptions of cold and wet, whereas at high shear rates, greater viscosity was associated with greater perceived thickness.

Perceptual and neural response to affective tactile texture stimulation in adults with autism spectrum disorders.

Autism spectrum disorders (ASD) are associated with differences in sensory sensitivity and affective response to sensory stimuli, the neural basis of which is still largely unknown. We used psychophysics and functional magnetic resonance imaging (fMRI) to investigate responses to somatosensory stimulation with three textured surfaces that spanned a range of roughness and pleasantness in a sample of adults with ASD and a control group. While psychophysical ratings of roughness and pleasantness were largely similar across the two groups, the ASD group gave pleasant and unpleasant textures more extreme average ratings than did controls. In addition, their ratings for a neutral texture were more variable than controls, indicating they are less consistent in evaluating a stimulus that is affectively ambiguous. Changes in brain blood oxygenation level-dependent (BOLD) signal in response to stimulation with these textures differed substantially between the groups, with the ASD group exhibiting diminished responses compared to the control group, particularly for pleasant and neutral textures. For the most unpleasant texture, the ASD group exhibited greater BOLD response than controls in affective somatosensory processing areas such as the posterior cingulate cortex and the insula. The amplitude of response in the insula in response to the unpleasant texture was positively correlated with social impairment as measured by the Autism Diagnostic Interview-Revised (ADI-R). These results suggest that people with ASD tend to show diminished response to pleasant and neutral stimuli, and exaggerated limbic responses to unpleasant stimuli, which may contribute to diminished social reward associated with touch, perpetuating social withdrawal, and aberrant social development.

Tactile and thermal detection thresholds of the scalp skin.

The tactile and thermal sensitivity of diverse regions of the human body have been documented extensively, with one exception being the scalp. Additionally, sensory changes may accompany the hair loss from the scalp in androgen-related alopecia (ARA), but formal quantitative sensory testing (QST) has not been reported in respect of this. Therefore, light touch detection thresholds were obtained at nine scalp sites and one forehead site, using Semmes-Weinstein filaments (Von Frey hairs), and for warming and cooling from skin baseline temperature, using 28 and 256 mm(2) thermodes. Affective, thermal, and nociceptive sensations experienced at thermal detection threshold were quantified. Thirty-two male participants were recruited, 10 of whom had normal hair coverage, 12 of whom had shaved scalp but with potentially normal hair coverage, and 10 of whom exhibited ARA to some extent. The scalp was relatively insensitive to tactile and thermal stimulation at all tested sites, especially so along the midline and near the apex of the skull. Threshold level warm stimuli were rated less pleasant, the less sensitive the test site. After correction for age-related changes in sensitivity, bald scalp sites were found more sensitive to cooling than the same sites when shaved, consistent with prior informal reports of increased sensitivity for some scalp sensations in ARA. QST on hair-covered sites was subject to methodological issues that render such testing non-ideal, such as bias in measurement of resting skin temperatures, and the near impossibility of delivering filament stimuli to the scalp skin without disturbing neighboring hairs.

The development and validation of sensory and emotional scales of touch perception.

No comprehensive language exists that describes the experience of touch. Three experiments were conducted to take steps toward establishing a touch lexicon. In Experiment I, 49 participants rated how well 262 adjectives described sensory, emotional and evaluative aspects of touch. In Experiment II, participants rated pairwise dissimilarities of the most descriptive words of the set. Multidimensional scaling (MDS) solutions representing semantic-perceptual spaces underlying the words resulted in a touch perception task (TPT) consisting of 26 'sensory' attributes (e.g., bumpiness) and 14 'emotional' attributes (e.g., pleasurable). In Experiment III, 40 participants used the TPT to rate unseen textured materials that were moved actively or received passively against the index fingerpad, volar forearm, and two underarm sites. MDS confirmed similar semantic-perceptual structures in Experiments II and III. Factor analysis of Experiment III data decomposed the sensory attribute ratings into factors labeled Roughness, Slip, Pile and Firmness, and the emotional attribute ratings into Comfort and Arousal factors. Factor scores varied among materials and sites. Greater intensity of sensory and emotional responses were reported when participants passively, as opposed to actively, received stimuli. The sensitivity of the TPT in identifying body site and mode of touch-related perceptual differences affirms the validity and utility of this novel linguistic/perceptual tool.

Quantitative assessment of pleasant touch.

The hedonic attributes of tactile stimulation are important to one's quality of life, yet they have rarely been studied scientifically. The earliest experimental investigations suggested soft and smooth materials as pleasant, those that were stiff, rough, or coarse as unpleasant. More recent studies conducted by the authors and described herein obtained ratings of pleasantness of different textured materials stroked across the skin of multiple body sites at controlled velocities and forces of application. Statistically significant interactions between materials, sites, velocities, forces and subject sex attest to the complexity of the percept. Less pleasant percepts arose from stimuli that were rougher. However, the difficulty in making further general statements regarding hedonic touch raises questions as to whether the body surface can be mapped affectively in a meaningful manner with a single stimulus and indeed whether pleasantness-to-touch can be viewed as a unidimensional construct.

Sensory and affective judgments of skin during inter- and intrapersonal touch.

Here we report two experiments that investigated the tactile perception of one's own skin (intrapersonal touch) versus the skin of other individuals (interpersonal touch). In the first experiment, thirteen female participants rated, along four perceptual attributes, the skin of their own palm and volar forearm, then that of several of the other participants. Ratings were made using visual analogue scales for perceived smoothness, softness, stickiness, and pleasantness. One's own skin was rated less pleasant than the skin of others. For both intra- and interpersonal touch, the forearm skin was rated smoother, softer, less sticky and more pleasant than the palmar skin. In the second experiment, ten pairs of female participants rated each other's palm and volar forearm skin, with the skin of the touched individual being assessed before and after the application of skin emollients that alter skin feel. As in the first experiment, the untreated skin of others was rated more pleasant than the participants' own skin, and the forearm versus palm differences were replicated. However, the emollient had generally larger effects on self-assessments than the assessments of others, and the site effect showed greater positive sensory and pleasantness increases for palm versus volar forearm. The disparate results of the two experiments suggest that attention, influenced by the ecological importance of the stimulus, is more important to assessment of touched skin than ownership of the skin or the contribution to self-touch made by the additional receptors in the passively touched skin. In both experiments, the pleasantness of touched skin was associated with the skin's perceived smoothness and softness, with weak trends toward negative associations with its perceived stickiness, consistent with prior research using inanimate surfaces (e.g., textiles and sandpapers).

The effect of oral drying and astringent liquids on the perception of mouth wetness.

A feeling of mouth dryness occurs from actual drying of the oral surfaces or from sampling astringent substances such as polyphenols (e.g., tannins in brewed tea and wine), which bind proline-rich proteins in saliva to reduce its lubricity. Here we investigated the interactions between physical drying and the effect of polyphenols on the subjective state of oral hydration. Twelve subjects rated the perceived wetness/dryness of their mouth using a labeled magnitude scale, after the mouth was dried with air for 35 s, or the subjects waited for an equal period of time during which the mouth was not dried. Subsequently, 1.5 mL volumes of an astringent solution (5 g L(-1) tannic acid in distilled water), distilled drinking water, or a sweet solution (40 g L(-1) sugar in mango tea with no tannins) were introduced into the mouth. After swishing and swallowing, the subject rated the wetness of the mouth for 4.3 min. The liquids were found to differ in their ability to wet the mouth (p<0.0001). The least wet sensations were reported for the astringent solution, on average; however, the differences among liquids were not equally pronounced at all times during the observation period (p<0.02). When the mouth was normally hydrated (i.e., had not been dried), the wetting effectiveness of the three liquids, based on the ratings, differed most greatly immediately after they had been received and swallowed. In contrast, when the mouth was dried, the liquids did not differ at this time. That the astringent solution did not have less wetting effectiveness in the dried mouth was attributed to the absence of precipitable salivary proteins. The findings suggest that the refreshment value of astringent drinks, based on their perceived wetting effectiveness, may vary with the state of oral hydration.

Human cortical representation of oral temperature.

The temperature of foods and fluids is a major factor that determines their pleasantness and acceptability. Studies of nonhuman primates have shown that many neurons in cortical taste areas receive and process not only chemosensory inputs, but oral thermosensory (temperature) inputs as well. We investigated whether changes in oral temperature activate these areas in humans, or middle or posterior insular cortex, the areas most frequently identified for the encoding of temperature information from the human hand. In the fMRI study we identified areas of activation in response to innocuous, temperature-controlled (cooled and warmed, 5, 20 and 50 degrees C) liquid introduced into the mouth. The oral temperature stimuli activated the insular taste cortex (identified by glucose taste stimuli), a part of the somatosensory cortex, the orbitofrontal cortex, the anterior cingulate cortex, and the ventral striatum. Brain regions where activations correlated with the pleasantness ratings of the oral temperature stimuli included the orbitofrontal cortex and pregenual cingulate cortex. We conclude that a network of taste- and reward-responsive regions of the human brain is also activated by intra-oral thermal stimulation, and that the pleasant subjective states elicited by oral thermal stimuli are correlated with the activations in the orbitofrontal cortex and pregenual cingulate cortex. Thus the pleasantness of oral temperature is represented in brain regions shown in previous studies to represent the pleasantness of the taste and flavour of food. Bringing together these different oral representations in the same brain regions may enable particular combinations to influence the pleasantness of foods.

Oral hydration, parotid salivation and the perceived pleasantness of small water volumes.

Previous studies have suggested that the preference for drinking cold water is increased when the drinker has a dry mouth. In a first experiment, we investigated whether a positive shift in preference would occur for small water volumes (0.75 ml and 1.5 ml) at 8, 16 or 25 degrees C, delivered into a mouth that had been dried using a warmed airflow, versus a normally hydrated mouth. Subjects rated the perceived wetness (or dryness) of their mouth, and the perceived pleasantness (or unpleasantness) of the water samples, using a labeled magnitude scale. Cooler water samples were preferred, and consistent with previous research, this preference was slightly enhanced when the subject's mouth was dried. The coldest water sample led to significantly wetter mouthfeel than the other two less cold samples, consistent with the possibility that the coldest water increased the rate of salivation. However, a second experiment found that although the rate of parotid salivation was increased if the mouth had been dried using a warm airflow, the different water temperatures did not induce different rates of parotid salivation. This indicates that enhanced preference for cold water when the mouth is dry is not invariably based in the reward gained from mouth rewetting via increased parotid saliva flow.

Validation of a handheld display device for an expandable labeled magnitude scale (LMS).

Palmtop computers provide a possible avenue for the convenient collection of subjective ratings from individuals outside of a fixed laboratory setting. One disadvantage of these computers is the small size of their display screens, which may reduce the resolution of responses available as compared with standard display screens. One plausible solution to this problem is to use a scale that expands contingent on an initial response made by the subject, so that the final response is made from a scale with finer resolution. To validate this approach, we compared taste intensity judgments of six sucrose solutions (0.03, 0.06, 0.12, 0.24, 0.48, and 0.96 M), using a labeled magnitude scale either presented in expandable form on a palmtop computer (Palm scale) or in conventional (nonexpandable) form on a standard 17'' PC monitor (PC scale). Twenty-four subjects rated all six sucrose solutions thrice, using both scale types, the different scales being used on different days of testing. The scales led to very similar taste intensity ratings at all but the lowest concentration, which was rated less intense on the Palm scale. The Palm scale was used with slightly less precision than the PC scale for the weakest solution concentrations. In summary, the responses of the two scales were similar enough to validate the use of the expandable scale on the palmtop computer outside the laboratory setting.

Thermally evoked parotid salivation.

Parotid salivation is known to be influenced by the temperature of liquids moved around the mouth. Here we investigated the ability of non-liquid thermal stimuli to change the rate of salivation. Unilateral parotid saliva was collected using a Lashley Cup from 12 normally hydrated subjects. Thermal stimuli were delivered through a copper tube, in which temperature-controlled water flowed, resting statically on the anterior tongue. During separate trials, the tube was 10, 22, or 44 degrees C, or the resting temperature of the tongue (or hypothenar of the hand, the control site). On each trial, the unstimulated salivation rate was first measured for 6 min while the subject remained seated with the mouth closed. Subsequently, salivation was measured for 6 min during application of the thermal stimulus. The tube was then removed for 1-2 min before the next trial. During the trials, subjects repeatedly rated the subjective temperature of the tongue (or hypothenar) and its perceived wetness/dryness. Stimulated salivation, expressed as a proportion of the previously measured unstimulated salivation, differed among body sites and temperatures (P<0.03). A significant increase in salivation was seen only for the 10 degrees C stimulus applied to the tongue. Wetness ratings and salivation rates were positively correlated, albeit weakly. These results demonstrate that temperature-evoked changes in parotid salivation do not require the unique spatiotemporal dynamics of the tongue and jaw movements in wetting the oral mucosa.

Audio-visual simultaneity judgments.

The relative spatiotemporal correspondence between sensory events affects multisensory integration across a variety of species; integration is maximal when stimuli in different sensory modalities are presented from approximately the same position at about the same time. In the present study, we investigated the influence of spatial and temporal factors on audio-visual simultaneity perception in humans. Participants made unspeeded simultaneous versus successive discrimination responses to pairs of auditory and visual stimuli presented at varying stimulus onset asynchronies from either the same or different spatial positions using either the method of constant stimuli (Experiments 1 and 2) or psychophysical staircases (Experiment 3). The participants in all three experiments were more likely to report the stimuli as being simultaneous when they originated from the same spatial position than when they came from different positions, demonstrating that the apparent perception of multisensory simultaneity is dependent on the relative spatial position from which stimuli are presented.

Site-dependent and subject-related variations in perioral thermal sensitivity.

The Marstock method of limits was used to obtain thresholds for detection of cooling, warming, cold pain and heat pain for 34 young adults, upon eight spatially matched sites on the left and right sides of the face, the right ventral forearm and the scalp. Male and female subjects were tested by both a male and a female experimenter. Neither the experimenter nor the gender of the subject individually influenced the thresholds. The thermal thresholds varied greatly across facial sites: sixfold and tenfold for cool and warmth, respectively, from the most sensitive sites on the vermilion to the least sensitive facial site, the preauricular skin. Warm thresholds were 68% higher than cool thresholds, on average, and 12% higher on the left compared to the right side of the face. The mean cold pain threshold increased from 21.0 degrees C on the hairy upper lip to 17.8 degrees C on the preauricular skin. Sites on the upper lip were also most sensitive to noxious heat with pain thresholds of 42-43 degrees C. The scalp was notably insensitive to innocuous and noxious changes in temperature. For the sensations of nonpainful cool and warmth, the more sensitive a site, the less the estimates of the thresholds differed between subjects. In contrast, for heat pain, the more sensitive a site, the more the estimates differed between subjects. Subjects who were relatively more sensitive to cool tended to be relatively more sensitive to warmth. Subjects' sensitivities to nonpainful cool and warmth were less predictive of their sensitivities to painful cold and heat, respectively. Short-term within-subject variability increased with the magnitude of the thresholds. The lower the threshold, the more similar were repeated measurements of it, within a 5-25 s period.

Lingual tactile acuity, taste perception, and the density and diameter of fungiform papillae in female subjects.

A growing body of evidence suggests that individuals who differ in taste perception differ in lingual tactile perception. To address this issue, spatial resolution acuity was estimated for 83 young adult females (52 Asians and 31 Caucasians) by their ability to examine with the tongue and identify embossed letters of the alphabet. Ratings of the magnitude of the bitterness of 0.0032M 6-n-propylthiouracil (PROP) were obtained to characterize subjects' taste perception. The density and diameter of fungiform papillae on the anterior tongues of the Asian subjects were measured also. Subjects who rated the bitterness of PROP as very or intensely strong (supertasters) were found to be about 25% more tactually acute than subjects who rated the bitterness as moderate to strong (medium tasters) and twice as acute as subjects who rated it as nondetectable or weak (non-tasters; P<.0001): The threshold heights for letter recognition averaged 2.8, 3.5 and 5.4 mm, respectively, for the Asian subjects and 2.6, 3.2, and 5.1 mm for the Caucasian subjects. The thresholds correlated highly with subjects' ratings of bitterness (rho=-0.84, P<.0001), and for the Asian subjects with the density (rho=-0.84, P<.0001) and diameter (rho=0.66, P<.0001) of fungiform papillae. Mean densities varied from 54.4 cm(-2) (non-tasters) to 106.5 cm(-2) (medium tasters) to 143.7 cm(-2) (supertasters; P<.0001). These findings confirm that individuals who differ in taste (PROP) sensitivity also differ in lingual tactile acuity. Tactile and taste sensitivities covary and reflect individual differences in the density and diameter of fungiform papillae on the anterior tongue.

What role does multisensory integration play in the visuotactile perception of texture?

Previous research has shown that vision and touch are both effective at many roughness discrimination tasks; however, there is no evidence that using both senses simultaneously improves discrimination performance. We investigated the nature of this failure to integrate multisensory inputs, using three varieties of forced-choice discrimination tasks. In Experiment 1, visual, tactile and bimodal roughness discriminations were made between pairs of fabric stimuli. Bimodal discriminations were typically performed with a sensitivity somewhere between that observed for the unimodal presentations. In Experiment 2, a similar design was used except that during the stimulus presentation, one interval contained a unimodal (vision or touch) stimulus, the other interval a bimodal stimulus presentation. Bias toward the bimodal interval would indicate an increase in the magnitude of perceived roughness for such presentations. No such bias was found. In Experiment 3, participants made single-interval, bimodal discriminations, determining whether a rough stimulus was presented to touch, to vision, to both modalities, or to neither modality. The improved performance seen for the dual-target vs. single-target presentations was best modelled as arising from a trialwise division of attention between vision and touch. Overall, these results suggest that vision and touch act as independent sources of roughness information, where the necessity to divide attention across both modalities reduces the discriminative ability in (or information available from) each of these individual modalities.

Tactile dominance in speeded discrimination of textures.

When assessing the roughness of textures, no single sensory modality universally dominates perception. Instead, the task and stimuli critically determine to what extent a given sense is favoured. We report a visuotactile texture assessment experiment, consisting of the speeded discrimination of roughened textile samples, in the presence of a congruent or an incongruent textile distractor. When discriminating between samples, visual assessment of textile roughness was modulated by incongruous tactile distractors, but not vice versa, even when visual distractors were more discriminable than tactile targets. This asymmetry in interference suggests that 'modality appropriateness' is not purely a function of the discriminative ability of a sensory modality, but that ecological validity may play a role in determining the more 'appropriate' sense for a given task. Results are discussed in relation to the claim that the assessment of textiles is more ecologically suited to touch than to vision.

Audiotactile interactions in roughness perception.

The sounds produced when we touch textured surfaces frequently provide information regarding the structure of those surfaces. It has recently been demonstrated that the perception of the texture of the hands can be modified simply by manipulating the frequency content of such touch-related sounds. We investigated whether similar auditory manipulations change people's perception of the roughness of abrasive surfaces (experiment 1). Participants were required to make speeded, forced-choice discrimination responses regarding the roughness of a series of abrasive samples which they touched briefly. Analysis of discrimination errors verified that tactile roughness perception was modulated by the frequency content of the auditory feedback. Specifically, attenuating high frequencies led to a bias towards an increased perception of tactile smoothness. In experiment 2, we replicated the rubbing-hands manipulation of previous experimenters while participants rated either the perceived roughness or wetness of their hands. The wetness scale data replicated the results in the literature, while the roughness scale data replicated the result from experiment 1. A final experiment showed that delaying the auditory feedback from the hand-rubbing reduced the magnitude of this parchment-skin illusion. These experiments demonstrate the dramatic effect that auditory frequency manipulations can have on the perceived tactile roughness and moistness of surfaces, and are consistent with the proposal that different auditory perceptual dimensions may have varying salience for different surfaces.

The effect of name category and discriminability on the search characteristics of colour sets.

Within (and between) cultures, people tend to agree on which parts of colour space are easiest to name and what the names for these regions are. Therefore it is likely that the manipulation of ease of naming (nameability) of colours should change performance in tasks where categorisation by colour name is important. More specifically? highly 'nameable' colour sets should lead to better performance than metrically equivalent but less categorically distinct sets, when the task requires categorisation. This hypothesis was investigated by testing observers on a name-based task, the naming and subsequent identification by name of colour sets with up to sixteen members. These sets were designed to be easy to name (nameable), maximally discriminable, or matched discriminable. The first were derived from previously generated data, the second by a standard algorithm to space colours widely in colour space, and the latter by closely matching their metric characteristics to those of an easy-to-name colour set. This final condition was metrically (but not categorically) equivalent to the nameable set. It was found that sets designed to be nameable did indeed lead to superior performance as measured by response times, confidence ratings, and response accuracy. Perceptual colour similarity, measured by a AE metric, did not predict errors. Nameability may thus be a valid, manipulable, aspect of sets of colours, and one which is not otherwise duplicated in the metric characteristics of such sets.