Biomedical subjects

Steve Guest

Publications and source records attributed to Steve Guest.

10 recordsLinked to original sources

PubMed2006

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.

Adult↗

PubMed2006

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.

Adult↗

PubMed2006

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.

Adult↗

PubMed2005

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.

Adult↗

PubMed2003

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.

Adult↗

PubMed2003

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.

Adolescent↗

PubMed2003

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.

Adolescent↗

PubMed2002

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.

Adult↗

PubMed2002

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.

Classification↗

PubMedDate not supplied

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.

Adult↗