Independent psychophysical measurement of experimental modulations in the somatotopy of cutaneous heat-pain stimuli

Distortions of the body image have been repeatedly reported for various clinical conditions, but direct experimental analyses of the perceptual changes involved are still scarce. In addition, most experimental studies rely on cerebral activation patterns to assess neuroplastic changes in central representation, although the relationship between cerebral topography and the topology of the perceptual space is not clear. This study examines whether the direct psychophysical mapping approach we introduced recently (Trojan et al., Brain Res 2006;1120:106–113) is capable of tracking perceptual distortions in the somatotopic representation of heat-pain stimuli. Eleven healthy participants indicated the perceived positions of CO₂ laser stimuli, repetitively presented to the dorsal forearm, with a 3D tracking system in two consecutive sessions, separated by the topical application of capsaicin cream. In line with earlier reports, we expected that the resulting individual perceptual maps (i.e., one-dimensional projections of the perceived positions onto the forearm surface) would be subject to modulation through the altered sensory input, to be measured in terms of altered topological parameters. We found that the topology and metrics of the somatotopic representation were well preserved in the second session, but that the perceptual map was compressed to a smaller range in 9 out of 11 participants. By providing dimensional measures of perceptual representations, perceptual maps constitute an independent, genuinely psychological complement to the topography of cortical activations measured with neuroimaging methods. In addition, we expect them to be useful in diagnosing pathological changes in body perception accompanying chronic pain and other disorders.     

Body Site Variation of Cool Perception Thresholds,with Observations on Paradoxical Heat

Thresholds for the perception of coolness and heat pain were determined in sessions that randomly intermixed temperature increases and decreases. Four body sites were tested bilaterally: thenar eminence of the hand, plantar surface of the foot, dorsolateral forearm, and lateral calf. Coolness thresholds were lowest for the hand, intermediate for the forearm, and highest for the leg and foot. Laterality differences were not statistically significant.

In 34% of the sessions, subjects did not consistently report cool or cold sensations with detectable temperatue decreases. When they did not report cool or cold, they most often reported heat or pain, thus exhibiting the phenomenon of “paradoxical heat”. There were significantly more paradoxical heat responses when cooling stimuli were intermixed with painfully hot stimuli than when they were intermixed with only warm stimuli.

There was no significant correlation observed between thresholds for coolness and heat pain, either across body sites or across subjects at any single body site. This result implies that the various factors relevant to thermal sensitivity (i.e., thermal properties of the epidermis, innervation density) are differentially important for cool versus heat pain perception.     

Cerebral Evoked Potential Correlates in Forced-paced Tasks

CEREBRAL evoked potentials can be monitored by averaging scalp records in subjects performing psychological tasks. The waveform is affected not only by the physical features of the sensory stimulus but also by cognitive and motivational parameters^1–7. These can be manipulated through verbal instructions given to the subject and several studies have shown that a slow positive component of about 300 ms peak latency (P₃₀₀) can be elicited by stimuli to which perceptual significance is attached^2,5–8. We have examined the evoked potential correlates of sensory overload in forced-paced auditory tasks and find that the cerebral “decision” potential can reveal intermittency in the perceptual channel.     

FLAVOR PROPERTIES OF PLAIN SOYMILK*

A trained sensory panel was used to (1) establish terminology for describing flavor attributes of a wide range of “fresh” and processed soymilks (SMs); and (2) test the lexicon and describe the flavor properties of a wide range (n = 32) of plain SM samples. Twenty‐eight attributes were identified in the SMs studied. However, findings indicate that the main differences are a consequence largely of the presence of certain attributes that are either infrequently present or unique to a specific product. Thus, sensory evaluation of SM needs to include a review of samples to ensure that all attributes are documented prior to evaluation, or use a method that allows the addition of attributes during testing.     

Multistability in perception: binding sensory modalities, an overview

This special issue presents research concerning multistable perception in different sensory modalities. Multistability occurs when a single physical stimulus produces alternations between different subjective percepts. Multistability was first described for vision, where it occurs, for example, when different stimuli are presented to the two eyes or for certain ambiguous figures. It has since been described for other sensory modalities, including audition, touch and olfaction. The key features of multistability are: (i) stimuli have more than one plausible perceptual organization; (ii) these organizations are not compatible with each other. We argue here that most if not all cases of multistability are based on competition in selecting and binding stimulus information. Binding refers to the process whereby the different attributes of objects in the environment, as represented in the sensory array, are bound together within our perceptual systems, to provide a coherent interpretation of the world around us. We argue that multistability can be used as a method for studying binding processes within and across sensory modalities. We emphasize this theme while presenting an outline of the papers in this issue. We end with some thoughts about open directions and avenues for further research.     

Age and Sex-Based Differences in the Use of Prey Sensory Cues in Wolf Spiders (Araneae: Lycosidae)

Differences in foraging patterns mediated by sensory cues were examined between adult and juvenile male and female wolf spiders (Schizocosa rovneri; Lycosidae). Patch residence time for thirty-one spiders were tested among juveniles and adults in artificial foraging patches. Patches varied in sensory information provided by live prey (crickets) as follows: visual stimuli alone; vibratory stimuli alone; visual and vibratory stimuli together; and control (no stimuli). Spiders moved between patches for one hour, but could not feed. Adult Schizocosa rovneri use primarily visual information to determine patch residence time, but juveniles use vibratory cues as well. Significant age and sex-based differences in the use of sensory cues suggest that observed divergent foraging strategies are partly due to the use of different perceptual cues in prey detection.     

Factors contributing to the integration of textural qualities: Evidence from virtual surfaces

Two experiments involving indirect touch were carried out to explore the relationships among perceptual dimensions of haptically examined surfaces. Subjects in both experiments used a stylus to evaluate the properties of virtual surfaces created by a force-feedback device; four surface properties (resistance to normal force, coefficient of friction, texture scale, and vibration amplitude) were manipulated in various combinations. In Experiment 1, the extent to which there was a one-to-one relationship between specific stimulus properties and perceptual qualities (“perceptual separability”) was evaluated. A substantial failure of separability was demonstrated, with friction tending to be more separable from the other properties than they were from one another. The pattern of results suggests that the amount of measured separability depends crucially on the way stimulus properties are defined (e.g., force versus displacement). In Experiment 2, surfaces with known perceptual properties were used to study the metric(s) of the relevant perceptual space. By specifying the perceptual, rather than the stimulus, coordinates of the surfaces, it was possible to bypass issues of perceptual separability. For surfaces of equal friction, a Euclidean metric captured the results (r²?=?0.75) more effectively than a city-block metric did; neither metric did well when differences in friction were involved. The fact that—unlike stickiness—hardness, roughness, and perceived vibration intensity are all increasing functions of surface-normal forces may facilitate their integration into a Euclidean space, in both direct (Hollins M, Bensmaïa S, Karlof K, Young F, . Individual differences in perceptual space for tactile textures: Evidence from multidimensional scaling. Percept Psychophys 62:1534–1544.) and indirect touch.     

Perception of the tactile texture of raised-dot patterns: A multidimensional analysis

An ALSCAL multidimensional scaling analysis in Euclidean space revealed that three orthogonal perceptual dimensions can account for the judged tactile dissimilarities of raised-dot patterns. Through magnitude estimates of various perceptual attributes, it was determined that the three dimensions consist of blur, roughness, and clarity. The only effect that selective adaptation of the Pacinian (P) channel had was to change the perceptual clarity of the raised dots against their background. Adaptation of the P channel with a 20?dB SL 250?Hz stimulus enhanced clarity. As indicated by magnitude estimates, adaptation of the P channel by the 250?Hz stimulus had no effect on the perceived roughness of the dot pattern but did cause the individual dots of the textured pattern to feel smoother. When the observer was required to estimate magnitude “overall roughness” defined as a combination of dot-pattern roughness and individual-dot roughness, adaptation of the P channel affected perceived roughness by reducing it. Taken as a whole, the results are consistent with the hypothesis that the NP channels and the P channel jointly influence the perception of textured surfaces.     

Beitrag einzelner parameter zum wahrnehumungsgemäßen unterschied von zusammengesetzten reizen bei der honigbiene

The perceptual difference between stimuli can be regarded as distance within the perceptual space of the bee. The author used this assumption to determine the specific distance function, on the basis of which the differences in the individual perceptual parameters constituted the perceptual difference between the complex stimulus and the reference stimulus. The perceptual differences can be deduced only indirectly from the choice frequency. Consequently, it was necessary to establish a “calibration curve”, to deduce quantitatively the perceptual difference from the choice frequency. The resulting hyperbolic curves for the parameters “brightness” and “size” were almost identical (Fig. 2). The perceptual difference between the complex stimulus and the reference stimulus is greater than one would expect in an Euclidean space. Rather it is the sum of the distances along the perceptual parameters which compose the complex stimulus (Fig. 3). Thus, the bee determines the perceived difference of composite stimuli which affect the perceptual parameters “brightness” and “size” in terms of the city-blockmetric.     

The caudal ganglion of the leech,with particular reference to homologues of segmental touch receptors

The caudal ganglion of the leech, which provides sensory and motor innervation to the posterior sucker, represents the fusion of seven embryonic segmental ganglia. Although fused, each of the seven contributing ganglia (“subganglia”) of the caudal ganglion can be distinguished morphologically and functionally. The roots from each subganglion carry the axons of mechanoreceptors homologous to “touch” cells found in the segmental ganglia and the subesophageal compound ganglion. The receptive fields supplied by the touch cells of the caudal ganglion are uniquely arranged and reveal the modified segmentation of the circular posterior sucker. Extensive overlap of sensory innervation occurs between adjacent segments of the sucker, beyond the overlap characteristic of the homologous cells of body segments. It thus appears that the touch receptors of the caudal ganglion are less restricted than receptors of the segmental ganglia with regard to their territories of innervation. The caudal ganglion has additional unique properties that establish it as a distinct integrative center of the leech CNS.     

Multisensory learning: from experimental psychology to animal training

Abstract

Stimuli and events that animals have to learn about in both their natural environments and in modern environments, such as our homes and farms, are often “multisensory,” i.e., they usually occur in more than one sensory modality. There are studies in humans and animals showing that stimuli that are multisensory are learned more quickly than stimuli presented in just a single sensory modality. My aim is to highlight how animals can combine information from several sensory modalities simultaneously, and show how using multisensory stimuli in training can enhance an animal's ability to learn new behaviors.     

Evidence for a protein tether involved in somatic touch

The gating of ion channels by mechanical force underlies the sense of touch and pain. The mode of gating of mechanosensitive ion channels in vertebrate touch receptors is unknown. Here we show that the presence of a protein link is necessary for the gating of mechanosensitive currents in all low‐threshold mechanoreceptors and some nociceptors of the dorsal root ganglia (DRG). Using TEM, we demonstrate that a protein filament with of length ～100 nm is synthesized by sensory neurons and may link mechanosensitive ion channels in sensory neurons to the extracellular matrix. Brief treatment of sensory neurons with non‐specific and site‐specific endopeptidases destroys the protein tether and abolishes mechanosensitive currents in sensory neurons without affecting electrical excitability. Protease‐sensitive tethers are also required for touch‐receptor function in vivo. Thus, unlike the majority of nociceptors, cutaneous mechanoreceptors require a distinct protein tether to transduce mechanical stimuli.     

“Gift Giving” by Wild Bottle nose Dolphins (Tursiops sp.) to Humans at a Wild Dolphin Provisioning Program,Tangalooma, Australia

ABSTRACT

While there is increasing interest in the impact of animal interactions upon children's wellbeing and attitudes, there has been less attention paid to the specific characteristics of the animals that attract and engage children. We used a within-subjects design to explore how differences in animal features (such as their animacy, size, and texture) impacted upon pre-school children's social and emotional responses. This study examined pre-schoolers' interactions with two animal-like robots (Teksta and Scoozie), two insect types (stick insects and hissing cockroaches) and a dog (Teasel, a West Highland Terrier). Nineteen preschool participants aged 35–57 months were videoed while interacting with the experimenter, a peer, and each stimulus (presented individually). We used both verbal and nonverbal behaviors to evaluate interactions and emotional responses to the stimuli and found that these two measures could be incongruent, highlighting the need for systematic approaches to evaluating children's interactions with animals. We categorized the content of children's dialogues in relation to psychological and biological attributes of each stimulus and their distinctions between living and non-living stimuli; the majority of comments were biological, with psychological terms largely reserved for the dog and mammal-like robot only. Comments relating to living qualities revealed ambiguity towards attributes that denote differences between living and non-living creatures. We used a range of nonverbal measures, including willingness to approach and touch stimuli, rates of self-touching, facial expressions of emotion, and touch to others. Insects (hissing cockroaches and stick insects) received the most negative verbal and nonverbal responses. The mammal-like robot (rounded, fluffy body shape, large eyes, and sympathetic sounds) was viewed much more positively than its metallic counterpart, as was the real dog. We propose that these interactions provide information on how children perceive animals and a platform for the examination of human socio-emotional and cognitive development more generally. The children engaged in social referencing to the adult experimenter rather than familiar peers when uncertain about the stimuli presented, suggesting that caregivers have a primary role in shaping children's responses to animals.     

Tactile sensitivity of normal and autistic children

Many children with autistic spectrum disorders have unusual reactions to certain sensory stimuli. These reactions vary along a hyper- to hypo-responsivity continuum. For example, some children overreact to weak sensory input, but others do not respond negatively to even strong stimuli. It is typically assumed that this deviant responsivity is linked to sensitivity, although the particular stage of sensory processing affected is not known. Psychophysical vibrotactile thresholds of six male children (age: 8–12) who were diagnosed to have autistic spectrum disorders and six normal male children (age: 7–11) were measured by using a two-alternative forced-choice task. The tactile stimuli were sinusoidal displacements and they were applied on the terminal phalanx of the left middle finger of each subject. By using a forward-masking paradigm, 40- and 250-Hz thresholds of the Pacinian tactile channel and 40-Hz threshold of the Non-Pacinian I tactile channel were determined. There was no significant difference between the thresholds of autistic and normal children, and the autistic children had the same detection and masking mechanisms as the normal children. The sensory responsivity of each subject was tested by clinical questionnaires, which showed again no difference between the two subject groups. Furthermore, no significant correlations could be found between the questionnaire data and the psychophysical thresholds. However, there was a high correlation between the data from the tactile and emotional subsets of the questionnaires. These results support the hypothesis that the hyper- and hypo-responsivity to touch, which is sometimes observed in autistic spectrum disorders, is not a perceptual sensory problem, but may probably be emotional in origin.     

Comparing sensibility for touch,cold, and warmth in different skin areas

The primary objective of this pilot study was to assess if the magnitude estimation of suprathreshold brushing, warmth (40?°C), and cold (25?°C) stimuli of the skin over the dorsum of the hand and the dorsum of the foot are comparable to the perceived intensity for the same stimuli applied to the skin over any of the following areas: forehead, m. trapezius, m. deltoideus, thoracic back, and lumbar back, respectively. Thirty-two subjects aged 18–64 years were included. Participants were examined by two physicians on two different occasions, 1–58 days apart. Participants rated the magnitude of the perceived sensation of each stimulus on an 11-point numerical rating scale (NRS) 0–10, where 0 was anchored to “no sensation at all for touch/cold/warmth” and 10 anchored to “the most intense imaginable non-painful sensation of touch/cold/warmth”. The criterion for sensory equivalence for one modality was arbitrarily considered satisfactory if two regions had the same numerical rating ±1 point in at least 85% of the individuals. Based on the pre-study criteria for sensory equivalence applied in this study only one area was found to be equivalent to the foot skin for the percept of brushing, that is, the skin over the deltoid muscle and one area for the hand, that is, the skin over the forehead. We failed to find any area with equivalent sensitivity to the hand or the foot for the cold or warm stimuli.