Optimization of single electrode tactile codes

The effects of a frequency modulated electrocutaneous signal's (code's) characteristics on the interpretability of the signal were investigated using an electrocutaneous tracking approach. The characteristics investigated include the functional relationship (exponential and hybrid) between an informational signal and the stimulation frequency, the range of stimulation (2–50 Hz and 2–100 Hz), and the impact of pulse width compensation on a code's efficacy. The interpretability of six different single bipolar electrode codes was examined by 30 subjects using a balanced incomplete block experimental design. Codes with exponentially shaped transfer functions resulted in generally lower electrocutaneous tracking errors than codes utilizing hybridshaped transfer functions. Hybrid codes had a transfer function that was linear in the lower frequency range and exponential in the higher frequency range. Codes with a 2–100 Hz frequency range were interpreted better than codes with a 2–50 Hz frequency range. The use of pulse width compensation to maintain a more even level of stimulation intensity had a slightly negative effect on the subjects' abilities to cutaneously track the information signal.     

Effects of training on human tracking of electrocutaneous signals

The effects of training on a person's ability to perceive, interpret and utilize information presented via the tactile sense were examined by using a dual-channel electrocutaneous tracking approach. The electrocutaneous code studied was linear pulse rate encoding of information. The stimulus had a pulse width of 200 μs and a pulse rate between 2 and 50 pulsed per second. Three tracking tasks-visual tracking, onedimensional electrocutaneous tracking and two-dimensional electrocutaneous tracking-were performed by 20 subjects during eight to nine daily training sessions. The effects of this training regimen were found to be highly significant for both electrocutaneous tracking tasks (p<0.00005). The overall average improvement between successive training sessions was 21.6% for one-dimensional electrocutaneous tracking and 22.9% for two-dimensional electrocutaneous tracking. Furthermore, the rate of improvement was fastest during the initial training sessions with a slower rate of improvement seen in most subjects beginning with their fifth session. The cumulative effects of training were also reflected in the lesser amounts of practice and review required by the subjects with each succeeding test session. Results from this study can be used to estimate the amount and rate of improvement that one can expect using a typical training program for tactile sensory aids.     

Relationship between pulse rate and pulse width for a constant-intensity level of electrocutaneous stimulation

The relationship between pulse rate (PR) and pulse width (PW) for a constant level of electrocutaneous stimulation was ascertained using the method of comparative judgments. Twelve volunteer subjects were asked to adjust the PW of a Comparison Stimulus (S₂) until its intensity matched that of a Standard Stimulus (S₁) for which the PW was 200 μs and PR was 10 or 20 pulses per sec (pps). As expected, the experimental results indicate that the PW of a constant-current amplitude pulse train should decrease as its PR increases if a constant level of tactile stimulation intensity is desired. However, PW and PR were not linear-inversely related (p<0.005). Rather, their relationship was best described by a logarithmic equation: log PW=a+b log PR, where PW is in microseconds,a is 2.82,b is −0.412, and PR is between 1 and 100 pps. Utilization of this relationship during electrical stimulation of the skin sense will decouple the intensity component of the tactile sensation from its frequency component, thereby enhancing the potential comfort and clarity of this sensory communication interface.     

Bias and sensitivity in the haptic perception of geometry

Our ability to recognize and manipulate objects relies on our haptic sense of the objects' geometry. But little is known about the acuity of haptic perception compared to other senses like sight and hearing. Here, we determined how accurately humans could sense various geometric features of objects across the workspace. Subjects gripped the handle of a robot arm which was programmed to keep the hand inside a planar region with straight or curved boundaries. With eyes closed, subjects moved the manipulandum along this virtual wall and judged its curvature or direction. We mapped their sensitivity in different parts of the workspace. We also tested subjects' ability to discriminate between boundaries with different degrees of curvature, to sense the rate of change of curvature, and to detect the elongation or flattening of ellipses. We found that subjects' estimates of the curvature of their hand path were close to veridical, and did not change across the workspace though they did vary somewhat with hand path direction. Subjects were less accurate at judging the direction of the hand path in an egocentric frame of reference, and were slightly poorer at discriminating between arcs of different curvature than at detecting absolute curvature. They also consistently mistook flattened ellipses and paths of decreasing curvature (inward spirals) for circles—and mistook arcs of true circles for arcs of tall ellipses or outward spirals. Nevertheless, the sensitivity of haptic perception compared well with that of spatial vision in other studies. Furthermore, subjects detected curvature and directional deviations much smaller than those that actually arise for most reaching movements. These findings suggest that our haptic sense is acute enough to guide and train motor systems and to form accurate representations of shapes. Electronic Publication     

Tactile perception of roughness: raised-dot spacing,density and disposition

Recently, we showed that tactile speed estimates are modified by the spatial parameters of moving raised-dot surfaces, specifically dot spacing but not dot disposition (regular, irregular) or density. The purpose of this study was to determine the extent to which tactile roughness perception resembles tactile speed with respect to its dependence and/or independence of the spatial properties of raised-dot surfaces. Subjects scaled the roughness of surfaces displaced under the finger. Dot spacing (centre-to-centre) ranged from 1.5 to 8.5 mm in the direction of the scan (longitudinal). Mean dot density varied from 2.2 to 46.2 dots/cm². Dot disposition was varied: repeating rows (periodic) or quasi-random (non-periodic). In the first experiment (n = 8), the periodic and non-periodic surfaces were matched for mean dot density. Roughness showed a monotonic increase with 1/dot density, but non-periodic surfaces were judged to be smoother than the periodic surfaces. Subjective equality was obtained when the data were re-expressed relative to longitudinal SP. In the second experiment (n = 7), the periodic and non-periodic surfaces were matched for longitudinal dot spacing. Perceptual equivalence was observed when the results were plotted relative to dot spacing, but not 1/dot density. Dot spacing in the orthogonal direction (transverse) was excluded as a contributing factor. Thus, as found for tactile speed scaling, roughness is critically dependent on longitudinal dot spacing, but independent of dot disposition and dot density (over much of the tested range). These results provide a set of predictions to identify cortical neurones that play critical roles in roughness appreciation.     

电触觉的皮肤神经机理仿真及实验验证

触觉学已经在很多领域得到应用,如遥控机器人、手术机器人、假肢、娱乐交互界面以及虚拟现实技术等,以此来增强人对机器或者虚拟物体的操作性。电触觉是现在主要的触觉再现措施,即通过改变恒流/恒压电脉冲的频率、脉宽、强度以及脉冲方向等因素,让人产生不同的触觉感。首先通过人体皮肤神经的建模推导出激励函数,并进行仿真研究,通过改变施加在电刺激阵列的电脉冲方向和强度,设计能分别刺激皮下3种刺激感受器（Meissner触觉小体、Merkel触盘、Pancinian环层小体）的实验范式,同时进行了心理物理学实验。10位受试者参加了实验,对食指进行电触觉刺激。正脉冲时采用不同频率（10、30、70、90 Hz）的电脉冲进行刺激,让受试者产生不同级别的振动感;负脉冲时采用不同脉宽（150、200、250、300 μs）的电脉冲进行刺激,让受试者产生不同级别的压力感。受试者对振动和压力的感觉强度进行主观判断。统计结果表明,该模型下的实验模式能够使触觉强度分级平均识别率高达80%以上,同时可通过对刺激电极分布以及电流大小的分析,找到最佳的刺激模式,保证最佳的触觉再现。     

Temporal properties of the visual detectability of moving spatial white noise

Summary We obtained movement detection thresholds for two-dimensional random speck-patterns (Julesz patterns) homogeneously moving over the whole target field (5.21×5.31 degrees of visual angle). We alternated between two uncorrelated but otherwise similar patterns, one moving with velocity v₁, the other with velocity v₂, such that each pattern was on for T ms. We masked this pattern (signal) with spatio-temporal white noise (snow). The total r.m.s. contrast was kept constant, whereas the ratio of the r.m.s. contrasts of signal and noise was varied. The square of this ratio was designated SNR.At low SNR values the pattern was not perceptually different from the snow alone. At high SNR values the subject detected spatio-temporal correlation (e.g., movement). In these experiments we determined the threshold SNR values as a measure of the detectability of spatio-temporal correlation as a function of the parameters T, v₁ and v₂.When v₁ and v₂ were sufficiently dissimilar one of three percepts occurred: for very large T the alternation could be followed, for very small T two transparent, simultaneously moving sheets of noise-pattern with different velocities could be seen. For intermediate T-values no systematic movement at all could be observed. At these T-values the threshold SNR was maximal. This critical T-value decreased with increasing velocity.We found that it was possible to have more than one percept of uniform smooth movement at a single location in the visual field if these movements had velocity vectors with an angular difference of at least 30 deg or if their magnitudes differed by at least a factor of 4.Supported in part by the Netherlands Organization for the Advancement of Pure Research (Z.W.O.)     

Studies on the perception of taste: Do primaries exist?

The idea that there are four primary tastes is basic to almost all research in gustation. Although this concept guides the formulation and interpretation of studies of taste psychophysics, as well as studies of taste stimuli, receptors, and neural organization, there is a surprising absence of studies designed to determine if this quadripartite view of taste is correct. The present group of three studies is designed to ask this question on a psychophysical level, comparing the taste data with combinations of tones, which appear to remain separate; subjects are asked: (a) whether tastes and tones—including mixtures—are perceived as singular or more-than-one, (b) whether increasing the number of components in a mixture (tastes or tones) results in increases in the perceived complexity, and (c) whether stimuli (tastes or tones) remain identifiable in mixtures with other stimuli. In all three experiments, it appears that the individual tones remained distinct and unaltered in combinations. Taste stimuli combined very differently from tones, in ways that suggested that the original components lost their identity, and sensations other than those in the original components (e.g., “primary tastes”) were synthesized. From this it follows that taste is composed of many sensations, not just the “primary four”.     

Spatial properties of the visual detectability of moving spatial white noise

Summary We determined the spatial parameters that describe the visual detection of spatio-temporal correlation in moving two-dimensional noise patterns. The target field (5.21×5.31 deg of visual angle) was divided into horizontal stripes of equal width D. Adjacent bars alternately contained noise patterns moving with velocity v₁ and v₂. We varied D, v₁ and v₂.Roughly three different percepts occurred. If the stripes were very broad the different movements in alternate stripes were perceived together with the division of the field into stripes. If the stripes were very narrow the division into stripes was not seen, but the moving noise patterns with velocities v₁ and v₂ were perceived as transparent sheets moving through each other. For intermediate stripe widths the target field looked incoherent and the subject was not clear about the percept. In this region the subject found it difficult and sometimes impossible to discriminate these patterns from a completely uncorrelated spatiotemporal white noise pattern (snow).To quantify the detectability, the patterns were masked with snow (spatio-temporal white noise). The r.m.s. contrast of the total stimulus was kept at a constant value, whereas the subject set the signal-to-noise ratio (SNR) to a threshold value. At certain barwidths the thresholds reached a maximum value. These critical barwidths depended on the velocities v₁ and v₂.These critical barwidths were interpreted in terms of a simple general model for the detection of spatiotemporal correlation. In these terms the span of the elementary correlators rose monotonically with the velocity to which the correlator is most sensitive.Supported in part by the Netherlands Organization for the Advancement of Pure Research (Z.W.O.)     

Effect of reduced cutaneous cues on motion perception and postural control

To investigate whether the sensory perception could be a more direct assessment of sensory deficit as oppose to the postural performance, we examined the effect of reduced cutaneous cues on motion perception and motion control. The subject was translated in a mediolateral direction with a single sinusoidal acceleration at a stimulus frequency of 0.25 Hz with a peak acceleration magnitude ranging from 0.25 to 8 mG in the dark. Two different plantar cutaneous conditions were provided: the control condition (barefoot) and the reduced cutaneous condition (foot on a spongy surface). For each foot-sole sensory condition, the subject completed six sets of 33 randomly ordered translation stimuli. After each translational stimulus, the subject reported their perceived direction of motion by pressing a hand-held button. The center of pressure (COP) and joint kinematics of the quiet stance were also measured. The results showed a significant increase in perception threshold as well as COP variation in the anteroposterior direction in the reduced cutaneous cue trials. However, a non-significant increase in COP in the mediolateral direction was shown. Multivariate covariance analysis of joint kinematics showed changes in postural coordination, such as increased reliance on hip strategy under reduced cutaneous cues condition, that have not been differentiated by univariate measures. The observed discrepancy in the significance of the contribution of plantar cutaneous cues to the detection threshold and the COP variation implies that the ‘perception’ could provide more direct and sensitive assessment of the sensory degradation than the ‘action’.     

On the singularity of taste sensations: What is a taste primary?

It is commonly accepted that there are four primary tastes. This conceptualization is notable for its simplicity and usefulness in guiding research and organizing data in the stimulus, receptor, neural and psychophysical aspects of taste. But however strongly defended or widely used, the concept of a primary taste remains undefined, especially in the psychophysical sense. The present research sets forth and tests one psychophysical defining property of a taste primary, that it should appear singular, and remain singular when mixed with other tastes; i.e., several singular tastes, when mixed, should remain separate and distinct. It is shown that mixtures are often judged to be as singular as their separate components, indicating synthesis of new tastes different from the components, and thus the existence of more than the few primary tastes.     

The effect of force and conformance on tactile intensive and spatial sensitivity

The effect of force on intensive and spatial processing was examined with three measures of tactile sensitivity. One of the measures based on intensive cues is the smooth-grooved (SM/GV) task, and the two other measures based on spatial cues are the grating orientation and gap detection tasks. Measures were made at two locations that vary in sensitivity and in the density of innervation of the primary afferent fibers, the right index fingerpad and the palmar surface of the proximal phalanx (fingerbase). At each location, psychometric functions were generated for each of the three measures for two forces (50 and 200 g). The results indicated that increasing force led to marked improvement on the task that relied on intensive cues; however, on the tasks that relied on spatial cues, force had no effect on performance. Biomechanical measures were made of the depth to which the skin invades the grooves of the contactors (conformance) at the two test sites, with the two forces, and with different groove widths. Conformance was found to be a joint function of force and groove width. Further, performance on the SM/GV task could be predicted by the amount of conformance. The psychophysical results are consistent with the view that increasing conformance increases neural activity in the primary afferent fibers, and that this increase in neural activity improves SM/GV performance, but has little effect on the quality of the spatial image.     

Visual motion perception from stimulation of the human medial parieto-occipital cortex

Summary Visual phenomena evoked by direct electrical stimulation of extrastriate cortex were observed in 30 epileptic patients as part of a presurgical investigation. An incremental sequence of low-level bipolar stimulation trains was delivered at medial and lateral pairs of contacts of stereotaxically-implanted multilead intracerebral electrodes in parietal, occipital and posterior temporal regions. Diffusion of stimulus afterdischarges was monitored by electrodes in temporal and frontal lobes and by the non-stimulated contacts of the stimulated electrode. Localized stimulations evoked few visual phenomena. The strongest anatomo-perceptual correlation was found for stimulation in the medial parieto-occipital fissure which evoked visual motion phenomena in all three patients stimulated in that region. The evoked motion perceptions were not associated with eye movements or any particular localization of the epileptic focus. These perceptions were only evoked once outside of the medial PO region at the 61 sites examined. The results suggest that the medial parieto-occipital region is closely linked to the human visual motion processing system.     

Comparison of sensory gating to mismatch negativity and self-reported perceptual phenomena in healthy adults

To better understand the possible functional significance of electrophysiological sensory gating measures, response suppression of midlatency auditory event related potential (ERP) components was compared to the mismatch negativity (MMN) and to self-rated indices of stimulus filtering and passive attention-switching phenomena in an age-restricted sample of healthy adults. P1 sensory gating, measured during a paired-click paradigm, was correlated with MMN amplitude, measured during an acoustic oddball paradigm (intensity deviation). Also, individuals that exhibited less robust P1 suppression endorsed higher rates of "perceptual modulation" difficulties, whereas component N1 suppression was more closely related to "over-inclusion" of irrelevant sounds into the focus of attention. These findings suggest that the ERP components investigated are not redundant, but correspond to distinct-possibly related-pre-attentive processing systems.     

Vergence effects on the perception of motion-in-depth

When the eyes follow a target that is moving directly towards the head they make a vergence eye movement. Accurate perception of the target's motion requires adequate compensation for the movements of the eyes. The experiments in this paper address the issue of how well the visual system compensates for vergence eye movements when viewing moving targets. We show that there are small but consistent biases across observers: When the eyes follow a target that is moving in depth, it is typically perceived as slower than when the eyes are kept stationary. We also analysed the eye movements that were made by observers. We found that there are considerable differences between observers and between trials, but we did not find evidence that the gains and phase lags of the eye movements were related to psychophysical performance.     

正常青年人视觉、听觉诱发的ERP的比较

对３５例正常青年人同时进行视觉、听觉不同刺激模式检测到的事件相关电位（ＥＲＰ）进行比较分析，发现不同刺激模式诱发出的ＥＲＰ各波的潜伏期、波幅均不相同。本文对其原因和不同年龄的Ｐ３波在颅顶有不同的分布部位以及其中一些Ｐ３波电位值两半球不对称性的机理进行了初步探讨。     

Measurement precision of a portable instrument to assess vibrotactile perception threshold

Summary The objective of the present study was to evaluate the reliability of a modified version of the commercially available Biothesiometer, and to examine vibrotactile perception thresholds with respect to age and gender. A standardized protocol for measuring vibrotactile perception threshold was administered to 80 subjects, once a week over 4 weeks. Inter-session variability was stable (analysis of variance for repeated measures; P>0.05) and correlations were high (Pearson's: 0.87r0.90; P0.001). For sites on both hands and feet, there was a significant increase with age (0.19r ²0.52; P0.001). Five factor analysis of variance model showed that vibrotactile perception threshold was significantly different with stimulus site, age category and gender; no differences were observed with alcohol consumption or smoking status. The findings indicate that the measurements from this device are highly reproducible and sensitive to expected threshold differences with age and gender. The authors attribute this to technical improvements of the original apparatus, rigid adherence to test protocol and maintenance of standard conditions. This type of instrument would be useful in assessing vibrotactile perception loss in occupational health studies.     

Thermal taste, PROP responsiveness, and perception of oral sensations

Differences between 6-n-propylthiouracil (PROP) taster groups have long been the focus of studies on individual variation in perception of oral sensation. Recently, "thermal taste" was described, the phenomenon whereby some individuals perceive "phantom" taste sensations after thermal stimulation of small areas of the tongue. As with PROP taster status (PTS), thermal taster status (TTS) has been proposed as a proxy for general responsiveness to oral stimuli. Here we examined the influence of PTS and TTS, independently, on the perceived intensity of sweet, sour, salty, bitter, astringent, and metallic stimuli, and temperature on heating or cooling the tongue. Interactions between PTS and TTS were also examined, and fungiform papillae (FP) density and salivary flow rate (SFR) were determined. Both PTS and TTS were associated with perceived stimulus intensities. PROP super-tasters (pSTs) rated all oral stimuli as more intense than PROP non-tasters (pNTs). Thermal tasters (TTs) gave higher logged ratings than thermal non-tasters (TnTs) for all oral sensations including temperature, with the exception of metallic flavour (at low concentration) and PROP. Examination of ETA-squared values showed that PTS had a greater effect on perceived intensities than did TTS for most sensations. No PTSTTS interaction was found for any oral stimuli. In contrast with PTS, TTS was not associated with FP density, and neither PTS nor TTS were associated with SFR. We conclude that pSTs and TTs possess greater responsiveness across a range of taste and trigeminal stimuli and concentrations.     

The role of human extra-striate visual areas V5/MT and V2/V3 in the perception of the direction of global motion: a transcranial magnetic stimulation study

Several published single case studies reveal a double dissociation between the effects of brain damage in separate extra-striate cortical visual areas on the perception of global visual motion defined by a difference in luminance (first-order motion) versus motion defined by a difference in contrast (second-order motion). In particular, the medial extrastriate cortical region V2/V3 seems to be crucial for the perception of first-order motion, but not for second-order, whereas a lateral and more anterior portion of the cortex close to the temporo–parieto–occipital junction (in the territory of the human motion area hV5/MT⁺) seems to be essential only for the perception of second-order motion. In order to test the hypothesis of a functional specialization of different visual areas for different types of motion, we applied repetitive transcranial magnetic stimulation (rTMS) unilaterally over areas V2/V3, V5/MT, or posterior parietal cortex (PPC) while subjects performed a 2AFC task with first- or second-order global motion displays in the contralateral visual field. Results showed a comparable disruption of the two types of motion, with both rTMS over V2/V3 or over MT/V5, and little or no effect with rTMS over PPC. The results suggest that either the previous psychophysical results with neurological patients are incorrect (highly unlikely) or that the lateral and medial regions are directly connected (as they are in macaque monkeys) such that stimulating one automatically affects the other, in this instance disruptively     

Tactile spatial acuity varies with site and axis in the human upper limb

Historically, beginning with Weber's [E.H. Weber, On the sensitivity of the tactile senses, in: H.E. Ross, D.J. Murray (Eds. and Trans.), E.H. Weber on the Tactile Senses, Erlbaum (UK) Taylor & Francis, Hove, 1996 (Original work published in 1834), pp. 21–136] classical studies, regional variations in the accuracy of localisation of tactile stimuli applied to a limb have been recognised. However, important questions remain concerning both the map of localisation resolution and its neuroscientific basis since methodological confounds have militated against an unambiguous, unified interpretation of the diverse findings. To test the hypotheses that localisation precision on the upper limb varies with site (hand, wrist, forearm) and limb axis (transverse, longitudinal), regional differences in locognosic acuity were quantified in psychophysical experiments. Participants identified the perceived direction (e.g. medial or lateral) relative to a central reference locus of brief tactile test stimuli applied to a cruciform array of loci. Acuity was greater in the transverse than longitudinal axis. This effect probably arises from the asymmetry of receptive fields of upper limb first-order sensory units and their higher-order projection neurons. Additionally, acuity was greater on the dorsal surface at the wrist than either the hand or forearm sites, in the longitudinal axis, supporting an enhancement of resolution at joints (anchor points). This effect may contribute to improved proprioceptive guidance of active wrist movements.