Effects of passive and active movement on vibrotactile detection thresholds of the Pacinian channel and forward masking

Abstract

We investigated the gating effect of passive and active movement on the vibrotactile detection thresholds of the Pacinian (P) psychophysical channel and forward masking. Previous work on gating mostly used electrocutaneous stimulation and did not allow focusing on tactile submodalities. Ten healthy adults participated in our study. Passive movement was achieved by swinging a platform, on which the participant’s stimulated hand was attached, manually by a trained operator. The root-mean-square value of the movement speed was kept in a narrow range (slow: 10–20?cm/s, fast: 50–60?cm/s). Active movement was performed by the participant him-/herself using the same apparatus. The tactile stimuli consisted of 250-Hz sinusoidal mechanical vibrations, which were generated by a shaker mounted on the movement platform and applied to the middle fingertip. In the forward-masking experiments, a high-level masking stimulus preceded the test stimulus. Each movement condition was tested separately in a two-interval forced-choice detection task. Both passive and active movement caused a robust gating effect, that is, elevation of thresholds, in the fast speed range. Statistically significant change of thresholds was not found in slow movement conditions. Passive movement yielded higher thresholds than those measured during active movement, but this could not be confirmed statistically. On the other hand, the effect of forward masking was approximately constant as the movement condition varied. These results imply that gating depends on both peripheral and central factors in the P channel. Active movement may have some facilitatory role and produce less gating. Additionally, the results support the hypothesis regarding a critical speed for gating, which may be relevant for daily situations involving vibrations transmitted through grasped objects and for manual exploration.     

Age- and sex-related changes in vibrotactile sensitivity of hand and face in neurotypical adults

Abstract

Sensory perception decreases with age, and is altered as a function of sex. Very little is known about the age- and sex-related changes in vibrotactile detection thresholds (VDTs) of the face relative to the glabrous hand. This study utilized a single-interval up/down (SIUD) adaptive procedure to estimate the VDT for mechanical stimuli presented at 5, 10, 50, 150, 250, and 300?Hz at two sites on the face, including the right non-glabrous surface of the oral angle and the right lower lip vermilion; and on the hand on the glabrous surface of the distal phalanx of the right dominant index finger. Eighteen right-handed healthy younger adults and 18 right-handed healthy older adults participated in this study. VDTs were significantly different between the three stimulus sites (p?<?0.0001), and dependent on stimulus frequency (p?<?0.0001) and the sex of the participants (p?<?0.005). VDTs were significantly higher for older adults when compared to younger adults for the finger stimulation condition (p?<?0.05). There were significant differences (p?<?0.05) in cheek and lower lip VDTs between male and female subjects. Difference in the VDTs between the three stimulation sites is presumed to reflect the unique typing and distribution of mechanoreceptors in the face and hand. Age-related differences in finger skin sensitivity are likely due to changes in the physical structure of skin, changes in the number and morphology of the mechanoreceptors, differences in the functional use of the hand, and its central representation. Sex-related differences in the VDTs may be due to the differences in tissue conformation and thickness, mechanoreceptor densities, skin hydration, or temperature characteristics.     

Thresholds of microwave-evoked warmth sensations in human skin

We measured thresholds for microwave-evoked skin sensations of warmth at frequencies of 2.45, 7.5, 10, 35, and 94 GHz. In the same subjects, thresholds of warmth evoked by infrared radiation (IR) were also measured for comparison. Detection thresholds were measured on the skin in the middle of the back in 15 adult male human subjects at all microwave (MW) frequencies and with IR. Long duration (10-s), large area (327-cm²) stimuli were used to minimize any differential effects of temporal or spatial summation. Sensitivity increased monotonically with frequency throughout the range of microwave frequencies tested. The threshold at 94 GHz (4.5 ± 0.6 mW/cm²) was more than an order of magnitude less than at 2.45 GHz (63.1 ± 6.7 mW/cm²), and it was comparable to the threshold for IR (5.34 ± 1.07 mW/cm²). Bioelectromagnetics 18:403–409, 1997. © 1997 Wiley-Liss, Inc.     

The effects of cross-modal manipulations of attention on the detection of vibrotactile stimuli in humans

Although it is well known that attention to a visual or auditory stimulus can enhance its perception, less is known concerning the effects of attention on the perception of natural tactile stimuli. The present study was conducted to examine the magnitude of the effect of cross-modal manipulations of attention in human subjects on the detection of weak, low-frequency vibrotactile stimuli delivered to the glabrous skin of the finger pad of the right index finger via an Optacon. Three suprathreshold vibrotactile arrays (40 Hz), varying in the number of activated pegs and hence the area of skin stimulated, were used. Subjects were trained to detect the occurrence of vibrotactile or visual stimuli and to respond by pressing a foot pedal as quickly as possible thereafter. Two instructional lights were used to cue the subjects as to which stimulus modality they should attend, in three experimental conditions. In the first cue condition, the forthcoming stimulus modality was indicated by the illumination of its associated light. In the second cue condition, both instructional lights were illuminated, and the subjects were asked to divide their attention equally between the two modalities. In the third cue condition, the stimulus modality was falsely indicated by the illumination of the cue not associated with the stimulus to be presented. Reaction times (RTs) were calculated for each trial. For each modality, tactile and visual, the RTs varied significantly with the cue condition, with the mean RT changing in a graded manner across the experimental conditions (being shortest for the correctly cued condition, intermediate for the neutrally cued condition, and longest for the incorrectly cued condition.(ABSTRACT TRUNCATED AT 250 WORDS)     

Origin of the human hand

A means of determining the phylogenetic implications of similarities between the hands of man and non-human primates is proposed. The only traits shared by man and non-human primates accepted as evidence of our ancestral hand structure and functions are those which are incompatible or out of keeping with current behavior of the human hand. They may be assumed to remain only as relics of adaptations to former habits of locomotion and feeding. The relics found through this analysis are all traits that are present in the apes (some of them only in African apes) and probably related to functions of the hand in suspension of the body, fist-walking, and knuckle-walking. The presence of these traits in man implies that human ancestors similarly used the hand to suspend the body in the trees and to support it on the back of the flexed fingers.     

Study on the transient characteristic in the human visual system using masking experiments

In this paper the visual masking effect is interpreted on the basis of the transient characteristic in two dimensional neuronal networks. The study investigates the suitability of the effect for use as a measurement method. It is shown that the stimulus distribution in space can be scanned at different points in time and that various dynamic characteristic values of the system can be measured.This paper was supported by the DFG with grant no. Se 251/13; Prof. W. von Seelen was in charge of the project     

典型山区生态系统服务对居民福祉影响的空间差异及动态特征——以川西山区为例

明确山区生态系统服务对居民福祉的局域空间影响是开展生态系统可持续管理决策的重要基础,对助推山区人地协调发展具有积极促进作用。基于2000、2005、2010和2015年4期土地利用数据和社会经济数据,以西部典型山区川西为案例,采用生态系统服务价值当量评估法和人类福祉框架构建指数评估模型,通过地理加权回归（GWR）探析生态系统服务对县域居民福祉的空间驱动特征与动态变化,识别影响福祉的主导生态系统服务因子。结果表明：（1）川西山区居民福祉呈同质集聚,空间依赖关系逐步减弱,"高-高"与"低-低"集聚在南北分异明显。（2）全域上生态系统服务因子对居民福祉具有显著负向影响,阻滞效应趋于减缓。（3）局域空间上影响系数具有方向和程度异性,西部减量效应明显,阿坝州和凉山州东北部增量效应显著,敏感程度从东南向西北梯次递减,负向敏感性强于正向敏感性,空间差异随时间变化趋于缩小。（4）供给与文化服务是影响川西山区居民福祉的关键生态系统服务,主控区域随时间变化在川西东北部和西部交替。山区生态资源红利释放应以新发展理念为导向,通过生态文明建设、生态经济提质、资源有偿使用和生态补偿制度设计助推生态资源价值创造与转换,实现山区可持续发展。     

The effect of masking in the human subject on the solving of a visual-spatial task

Images of two fragments of regular geometrical figures (square, triangle etc.) have been presented to 58 healthy persons successively with intervals of 20, 80, 120 and 380 ms. The subject must compare these fragments mentally, decide whether they form the standard figure and press a button by the right or left hand according to the instruction. At presentation of both fragments in one visual field, left or right, the number of correct responses is greater when they form the figure. The greater the interstimulus intervals, the greater the number of correct responses to stimuli forming and not forming the standard figure. At presentation of fragments in different visual fields, the number of correct decisions is the same, independently from forming the standard figure. The reaction time is shorter when exposing fragments forming the figure, independently from the way of their presentation; with prolongation of interstimulus intervals the reaction time decreases in all cases. The number of correct decisions is greater and the reaction time is shorter when the stimuli are presented in different visual fields.     

Cutaneous ligaments of the human hand

A topographical study concerning the cutaneous ligaments of adult as well as human fetal hands was performed. In order to be able to preserve the cutaneous ligaments in their entirety two different methods, a careful dissection and a new histological technique, have been employed. The results of these methods are compared and the detailed topography of the different cutaneous ligaments is clarified. In addition to topographical details, the functional co-operation of the ligaments especially in regard to their clinical relevance is reported.     

A thermal model for human thresholds of microwave-evoked warmth sensations

Human thresholds for skin sensations of warmth were measured at frequencies from 2.45 to 94 GHz. By solving the one-dimensional bioheat equation, we calculated the temperature increase at the skin surface or at a depth of 175 μm at incident power levels corresponding to the observed thresholds. The thermal analysis suggests that the thresholds correspond to a localized temperature increase of about 0.07 °C at and near the surface of the skin. We also found that, even at the highest frequency of irradiation, the depth at which the temperature receptors are located is not a relevant parameter, as long as it is within 0.3 mm of the surface. Over the time range of the simulation, the results of the thermal model are insensitive to blood flow, but sensitive to thermal conduction; and this sensitivity increases strongly with frequency. We conclude with an analysis of the effect of thermal conduction on surface temperature rise, which becomes a dominant factor at microwave frequencies over 10 GHz. Bioelectromagnetics 18:578–583, 1997. © 1997 Wiley-Liss, Inc.     

The effects of heat-induced pain on the detectability,discriminability, and sensation magnitude of vibrotactile stimuli

The effects of heat-induced pain on absolute thresholds, sensation magnitudes and amplitude-difference thresholds were measured at 10 and 100 Hz. Consistent with previous results, heat-induced pain elevated the absolute thresholds by approximately 8.0 dB and lessened the magnitudes of tactile sensations during pain as compared to the non-painful condition. In contrast to these effects, the discriminability of change in the intensity of the vibrotactile stimuli was unaffected by the presence of pain indicating that the effect of pain on tactile sensations is more likely due to sensory rather than cognitive processes (i.e., attention) and that the mechanisms underlying tactile sensitivity as compared to discriminability are different.     

The effects of heat-induced pain on the detectability, discriminability, and sensation magnitude of vibrotactile stimuli

The effects of heat-induced pain on absolute thresholds, sensation magnitudes and amplitude-difference thresholds were measured at 10 and 100 Hz. Consistent with previous results, heat-induced pain elevated the absolute thresholds by approximately 8.0 dB and lessened the magnitudes of tactile sensations during pain as compared to the non-painful condition. In contrast to these effects, the discriminability of change in the intensity of the vibrotactile stimuli was unaffected by the presence of pain indicating that the effect of pain on tactile sensations is more likely due to sensory rather than cognitive processes (i.e., attention) and that the mechanisms underlying tactile sensitivity as compared to discriminability are different.     

Contrast adaptation and contrast masking in human vision.

After a preliminary study of visual evoked potentials (VEPS) to a test grating seen in the presence of masks at different orientations, psychophysical data are presented showing the effects of adaptation and of masking on thresholds for detecting the same test grating. The test is a vertical grating of spatial frequency 2 cycles per degree; adapting and masking gratings differ from the test either in orientation or in spatial frequency. The effects of adaptation and masking are explained by a single mechanism model that assumes: (i) adaptation and masking both alter the contrast response (or transducer) function of the mechanism that detects the test; (ii) masks, but not adaptors, stimulate the mechanism that detects the test; and (iii) a test is detectable when it raises response level by a constant amount. The model incorporates two distinct tuning functions, a broad adaptive contrast function and a narrow effective contrast function. It accounts adequately for all the data, including the location and size of the facilitative dip found in some masking functions, the constant slopes of the threshold elevation segments of adaptation functions and the varying slopes of masking functions. It also predicts the sometimes surprising joint effects of adaptation followed by masking and of two masks operating simultaneously.     

A peripheral neural correlate of the human fungiform papillae salty, insipid sensations

Neurophysiological research in several different laboratorieshas revealed the existence of a Na-, Li-specific peripheraltaste system in mammalian herbivores and omnivores, but notcarnivores. The presence or absence of this system is readilydetectable in the behavior of the animals towards NaCl solutions.It is proposed that the human has an identical system, and thatactivity within this system is largely, but not entirely, responsiblefor the elicitation of the human sensations of salty and insipid.Under normal conditions, neurons in this system display highlevels of spontaneous activity due largely to salivary Na. Solutionswith Na exceeding the salivary Na level will excite the neuronsand be perceived as salty. Solutions with Na levels less thanthat of the saliva will inhibit the neurons and be perceivedas insipid. The existence of this system in humans is attestedby the fact that human behavior towards NaCl is similar to thatseen in the rat and sheep. The stimuli eliciting the human saltysensations are, in most respects, similar to those active inthe animal experiments with one exception: KCl, the chloridesalt most inactive on animals, elicits a fairly strong saltysensory component. To partially resolve this discordance, itis suggested that the human salty sensation is the result ofhigher order neural activity that involves another peripheraltaste system.