Visual and Proprioceptive Adaptation of Arm Position in a Virtual Environment

The authors examined the resolution of a discrepancy between visual and proprioceptive estimates of arm position in 10 participants. The participants fixed their right shoulder at 0°, 30°, or 60° of transverse adduction while they viewed a video on a head-mounted display that showed their right arm extended in front of the trunk for 30 min. The perceived arm position more closely approached the seen arm position on the display as the difference between the actual and visually displayed arm positions increased. In the extreme case of a 90° discrepancy, the seen arm position on the display was very gradually perceived as approaching the actual arm position. The magnitude of changes in sensory estimates was larger for proprioception (20%) than for vision (< 10%).     

Human responses to various conditions of water temperature

Skin-surface temperatures on thehuman hand were obtained immediately following six exposure times ranging from 5 to 60 sec. for water temperatures varying in 5° increments from 10° to 40°C. The surface of the skin was found to respond rapidly and regularly to both the temperature and time of exposure. In a second study 30 Ss exposed a hand for 5 or 30 sec. to water temperatures ranging from 10° to 45°C. and made ratings on scales of pain and comfort as well as attaching a verbal label (cold, cool, tepid, etc.) to each experience. The experience of cold became more intense over these time intervals while the experience of warmth became less, and with the threshold constant taken into account the sensations of pain and discomfort were found to follow a psychophysical power law. The usefulness of these sorts of data for interpreting the effects of noxious stimuli in basic learning studies is discussed.     

Sex differences in pain and thermal sensitivity: the role of body size

Sex differences in heat-pain and thermal sensitivity were investigated in 32 women (20 to 60 years of age) and 32 men (17 to 63 years of age) who had no somatosensory impairments. Pain thresholds were measured with stimuli of two different durations (phasic and tonic). Warmth and cold thresholds were assessed as indices of thermal sensitivity. Stimulation was applied to the hand and to the foot by an apparatus containing a Peltier thermode. There were no sex differences in heat-pain thresholds. Women had significantly lower warmth thresholds than men (more pronounced on the foot than on the hand), but similar cold thresholds. Measures of body size (weight, height) correlated much more strongly with thermal than with pain sensitivity, and helped to explain the sex difference in the warmth threshold. A reduction of sex differences to body-measure differences appears likely, but could not be demonstrated unequivocally.     

Cutaneous saltation within and across arms: A new measure of the saltation illusion in somatosensation

A new objective procedure was used to measure the strength of cutaneous saltation, in order to clarify current debates about the nature of this illusion. Three taps were presented successively to three possible forearm locations. Participants attended to the middle location and reported whether a tap was perceived there. When all stimuli were delivered to the same arm and intertap intervals were short, participants were unable to distinguish real and illusory stimuli at the middle location. When both arms were stimulated, location judgments on one arm were shifted toward a tap subsequently delivered to the other arm. These results challenge the view that saltation is a purely attentional phenomenon, but they are inconsistent with the idea that this illusion is produced in the primary somatosensory cortex.     

Cutaneous saltation within and across arms: a new measure of the saltation illusion in somatosensation

A new objective procedure was used to measure the strength of cutaneous saltation, in order to clarify current debates about the nature of this illusion. Three taps were presented successively to three possible forearm locations. Participants attended to the middle location and reported whether a tap was perceived there. When all stimuli were delivered to the same arm and intertap intervals were short, participants were unable to distinguish real and illusory stimuli at the middle location. When both arms were stimulated, location judgments on one arm were shifted toward a tap subsequently delivered to the other arm. These results challenge the view that saltation is a purely attentional phenomenon, but they are inconsistent with the idea that this illusion is produced in the primary somatosensory cortex.     

Effects of preparatory information about sensations, threat of pain, and attention on cold pressor distress.

Pain experience is conceptualized as a combination of stimulus sensations (e.g., aching) and emotional distress. In Experiment 1, less distress was reported to cold pressor stimulation by subjects first told about stimulus sensations than by subjects who were uninformed or were told about symptoms of bodily arousal (e.g., tension). Adding a pain warning to sensation information blocked distress reduction, presumably by eliciting an emotional interpretation of the stimulus. In Experiment 2, subjects attending only to hand sensations reported less distress than subjects attending to their bodies. This decrease in the power of the stimulus to provoke emotion is presumably mediated by a schema of hand sensations formed by attention. In Experiment 3, subjects attending to hand sensations early in the immersion and distracting themselves later reported the same low levels of distress as did subjects who attended to hand sensations throughout. Subjects distracted throughout and subjects attending to hand sensations later showed no distress reduction. Therefore, stimulus schematization must precede distress reduction. Implications for distress control are discussed.     

Comparison and reliability of three goniometric methods for measuring forearm supination and pronation.

Active supination and pronation range of motion of the right forearm by 10 men and 21 women were measured with a goniometer using three methods. For Method One the moveable arm was aligned with a pencil held in the hand; for Method Two the moveable arm was placed over the anterior and posterior surface of the distal forearm for supination and pronation, respectively; and for Method Three the moveable arm was aligned parallel with a visualized line connecting the distal ulna and radius. Supination range of motion was greatest for Method One, followed by Methods Three and Two, respectively. Pronation range for Method One was less than for the two other methods. Intraclass correlation coefficients ranged from .81 to .97 for three trials within the test session and from .86 to .96 between the test and a 1-hr. retest session for both actions using all three methods. Method One was the most reliable but appeared invalid for measuring supination because of movements of the 4th and 5th metacarpal bones. Methods Two and Three appeared appropriate for clinical application but not interchangeable.     

Part‐based representations of the body in early childhood: evidence from perceived distortions of tactile space across limb boundaries

Studies show that touch in adults is referenced to a representation of the body that is structured topologically according to body parts; the perceived distance between two stimuli crossing over a body part boundary is elongated relative to the perceived distance between two stimuli presented within one body part category. Here we investigate this influence of body parts on tactile space perception in children of 5, 6 and 7 years of age. We presented children with pairs of tactile stimuli on the left hand/arm, either within the hand, within the forearm, or over the wrist. With their eyes closed children were asked to adjust the distance between the thumb and forefinger of their right hand to represent the felt distance between the two tactile stimuli. Like adults, the children perceived the distance between two stimuli that cross the body part boundary to be further apart than those that were presented within the hand or arm. They also perceive tactile distance to be greater on the hand than the arm which is the first observation of Weber's illusion in young children. We propose that a topological mode of body representation is particularly advantageous during early life given that body part categories remain constant while the metric proportions of the body change substantially as the child grows.     

Pain modulation during drives through cold and hot virtual environments.

Evidence exists that virtual worlds reduce pain perception by providing distraction. However, there is no experimental study to show that the type of world used in virtual reality (VR) distraction influences pain perception. Therefore, we investigated whether pain triggered by heat or cold stimuli is modulated by "warm "or "cold " virtual environments and whether virtual worlds reduce pain perception more than does static picture presentation. We expected that cold worlds would reduce pain perception from heat stimuli, while warm environments would reduce pain perception from cold stimuli. Additionally, both virtual worlds should reduce pain perception in general. Heat and cold pain stimuli thresholds were assessed outside VR in 48 volunteers in a balanced crossover design. Participants completed three 4-minute assessment periods: virtual "walks " through (1) a winter and (2) an autumn landscape and static exposure to (3) a neutral landscape. During each period, five heat stimuli or three cold stimuli were delivered via a thermode on the participant's arm, and affective and sensory pain perceptions were rated. Then the thermode was changed to the other arm, and the procedure was repeated with the opposite pain stimuli (heat or cold). We found that both warm and cold virtual environments reduced pain intensity and unpleasantness for heat and cold pain stimuli when compared to the control condition. Since participants wore a head-mounted display (HMD) in both the control condition and VR, we concluded that the distracting value of virtual environments is not explained solely by excluding perception of the real world. Although VR reduced pain unpleasantness, we found no difference in efficacy between the types of virtual world used for each pain stimulus.     

Perceptual Estimates of Motor Skill Proficiency Are Constrained by the Stability of Coordination Patterns

This study demonstrated that motor skill proficiency ratings are constrained by the same order parameter dynamics that constrain action production and action perception processes. Participants produced rhythmic actions simulated by an animated stick figure of the human arm. The primary finding was that participants’ proficiency ratings covaried most with relative phase (φ) variability compared to mean relative phase. In-phase (φ = 0°) was produced with the least variability and received the highest proficiency rating, whereas the patterns φ = ±150° were attempted with the most variability and received the lowest proficiency ratings. A temporal delay in attempting to produce the animated pattern had a large impact on produced relative phase, yet had little impact on the proficiency ratings. Proprioceptive processes provide individuals information on motor skill proficiency. The lead or lag motion of the hand to forearm segment of the animated arm was identified consistently through visual processes and revealed asymmetries in the mapping of visual input to motor output. The results are consistent with concepts from the dynamic pattern theory of coordination and are discussed with regard to relative phase as an informational variable that constraints the perception-action system across many levels.     

Perceived range, perceived velocity, and perceived duration of the body rotating in the frontal plane

We investigated perceived range, perceived velocity, and perceived duration of the body rotating in the frontal plane (in roll). Specifically, to examine how shear to the otoliths in the inner ears and tactile pressure to the trunk affect judgments of range and velocity, in two experiments, we manipulated rotating range (30°–160°), rotating velocity (1.8°/sec to 9.6°/sec), mean tilt of the body (?60°, 0°, and 60°), and exposure to the visual vertical. Thirty-three normal or blindfolded participants made verbal judgments of range, velocity, and duration for each combination of these factors. The exponents of the power functions fitted to these judgments were, as a first approximation, .94, .61, and .84 for range, velocity, and duration, respectively, and perceived velocity was proportional to the ratio of perceived range to perceived duration (r = .91). These results suggest that the vestibular and somatosensory inputs are effective on judgments of range, but less so on judgments of velocity, and that perceived velocity may be determined as a ratio of perceived range to perceived duration. In addition, we found that (1) when the range the body has traveled is constant, the perceived range increases as the objective velocity decreases (proprioceptive τ effect); (2) self-motion through the tilted roll sometimes enlarges perceived range and perceived duration but reduces perceived velocity; and (3) the exposure to the visual vertical reduces variability of judgments for range and velocity and also reduces perceived range and perceived velocity of self-motion within a small range through the vertical roll.     

Spatial summation of chemical irritation and itch produced by topical application of capsaicin

The effect of increasing the total area of stimulation on the sensations of irritation produced by topical application of capsaicin was studied in two experiments. In the first experiment, stimulus area was varied by changing the size of filter paper disks on which capsaicin was delivered to the skin of the forearm. Subjects rated the intensity and quality of the cutaneous sensations over a 15-min period. Increasing stimulus area by a factor of 15 resulted in a relatively modest increase in the peak perceived intensity of irritation, a shortening of the latency to the onset of irritation, and shifts in the frequency of reports of sensations of itching and stinging/pricking. However, itch was the most frequently reported sensation regardless of stimulus size. In Experiment 2, stimulus area was manipulated by varying the number of stimuli applied to the skin. Despite a smaller difference in total stimulus areas (9-fold vs. 15-fold), the difference in perceived irritation was more pronounced than it was in Experiment 1 and reached statistical significance. It is therefore concluded that spatial summation does occur in the afferent system or systems responsible for the perception of capsaicin on the skin. This result is consistent with previous reports of summation at the threshold for heat pain and constitutes new information about the spatial integration of pruritic stimulation.     

Magnitude scales for cold pressor pain

Subjects in two experiments immersed a hand and forearm in ice water (cold pressor test) for 60 sec and gave magnitude estimates of pain every 5 sec. Forty subjects immersed an arm for three trials in Experiment 1, and 60 subjects immersed an arm for two trials in Experiment 2. Linear, power, or additive constant functions fitted the data almost equally well. Exponents of the two-constant power function differed from those of the additive constant function. Individual differences in exponents were marked, but various psychological manipulations aimed at reducing pain failed to affect the exponents. The utility of power functions to describe cold pressor pain has yet to be determined.     

Three-space inference from two-space stimulation

Oblique contours sloping at 30° with respect to the horizontal were presented alone, in combination to form chevrons, or with a vertical line to form arrowhead or Y patterns; they were projected onto a screen in the frontal parallel plane and viewed from positions that gave viewing angles of 90° (normal to the screen’s surface), 53°, or 34°. The perceived orientation of the contours, as assessed by a movable arm that the subjects set to be parallel to the obliques, changed monotonically as a function of viewing angle. The change was as great for single obliques as for combinations of obliques within the chevron, arrowhead, and Y patterns. The results of Experiment 1 were extended in Experiment 2, in which obliques at 30° and 50° with respect to the horizontal were presented singly or in combination as chevron patterns. It is argued that the results of both experiments indicate that single two-space oblique lines are immediately interpreted as lying in three-space and that the changes in perceived orientation are a consequence of this perceptual inference.     

Costs and benefits of tool-use on the perception of reachable space

Previous studies have shown that using a tool modifies in a short time-scale both near-body space perception and arm-length representation in the body schema. However, to date no research has specifically investigated the effect of tool-use on an action-related perceptual task. We report here a study assessing the effect of tool-use on the perception of reachable space for perceptual estimates made in reference to either the tool or the hand. Using the tool on distal objects resulted in an extension of perceived reachable space with the tool and reduced the variability of reachability estimates. Tool use also extended perceived reachable space with the hand, but with a concomitant increase of the variability of reachability estimates. These findings suggest that tool incorporation into the represented arm following tool-use improves the anticipation of action possibilities with the tool, while hand representation becomes less accurate.     

Spatial localization of warmth

This study explored the ability to localize warmth sensations produced by radiant stimulation of the forearm. The subject’s task was to state on which side of a tactile reference line warmth was perceived. Percentage correct improved with increasing intensity of the radiation, as well as with increasing distance from the reference line. There appears to be an inverse relation between the ability to make spatial judgments and the degree of spatial summation. At low levels of stimulation, intensity and area both contribute heavily to the magnitude of a warmth sensation and spatial localization is poor; but with increasing level, area contributes less and less to sensation and localization is better.     

Role of gravitational cues in the haptic perception of orientation

The haptic perception of vertical, horizontal, +45°-oblique, and +135°-oblique orientations was studied in adults. The purpose was to establish whether the gravitational cues provided by the scanning arm—hand system were involved in the haptic oblique effect (lower performances in oblique orientations than in vertical—horizontal ones) and more generally in the haptic coding of orientation. The magnitude of these cues was manipulated by changing gravity constraints, and their variability was manipulated by changing the planes in which the task was performed (horizontal, frontal, and sagittal). In Experiment 1, only the horizontal plane was tested, either with the forearm resting on the disk supporting the rod (“supported forearm” condition) or with the forearm unsupported in the air. In the latter case, antigravitational forces were elicited during scanning. The oblique effect was present in the “unsupported” condition and was absent in the “supported” condition. In Experiment 2, the three planes were tested, either in a “natural” or in a “lightened forearm” condition in which the gravitational cues were reduced by lightening the subject’s forearm. The magnitude of the oblique effect was lower in the “lightened” condition than in the “natural” one, and there was no plane effect. In Experiment 3, the subject’s forearm was loaded with either a 500- or a 1,000-g bracelet, or it was not loaded. The oblique effect was the same in the three conditions, and the plane effect (lower performances in the horizontal plane than in the frontal and sagittal ones) was present only when the forearm was loaded. Taken together, these results suggested that gravitational cues may play a role in haptic coding of orientation, although the effects of decreasing or increasing these cues are not symmetrical.     

How skin and object temperature influence touch sensation

Twenty subjects made magnitude estimations of the apparent heaviness of metallic stimulators of various masses and temperatures (cold, neutral, and warm). The stimulators were placed on the forearm at normal skin temperature (about 33°C), at elevated skin temperature (38°C), and at lowered skin temperature (25°C). Under neutral conditions, we replicated earlier studies: cold objects felt considerably heavier than neutral ones, warm objects somewhat heavier than neutral objects. Warming the skin essentially obliterated the intensifying effect of the warm objects but left unaltered the intensifying effect of the cold objects. Cooling the aim also essentially obliterated the intensifying effect of warm objects. It also diminished, but far from eliminated, the intensifying effect of cold objects. Cold intensification of touch sensation is a large and robust phenomenon and, unlike warm intensification, appears to characterize all body regions.     

Psychophysical features of the transition from pure heat perception to heat pain perception

The psychophysical features of the transition from the pure heat to the heat pain range were studied in 25 healthy subjects (mean age 28.8 years). Thirty short heat stimuli from ?1.6° C to + 1.6° C relative to the pain threshold were applied to the thenar of the left hand with an apparatus containing a Peltier thermode (nine different temperatures at 0.4°C intervals). The subjects rated the sensation intensity on a visual analogue scale. The resulting stimulus/sensation intensity relations could be explained equally well (same goodness of fit) by a model with a power function (PF) and by a model with two linear regression lines (TLR), one for stimulus intensities below and one for those above the pain threshold and intersecting at the pain threshold. The slopes of the TLR model were significantly larger above the pain threshold than below it. The PF model produced exponents between 1.8 and 1.9. We conclude that to describe the transition area, it is sufficient to use simple linear models for both the pure heat and the heat pain ranges.