Spatial features of vibrotactile masking effects on airpuff-elicited sensations in the human hand

It was recently shown that the cutaneous sensitivity to airpuffs is decreased by a low-frequency vibrotactile masker in the hairy skin, and by a low-frequency but especially by a high-frequency masker in the glabrous skin. In the current study, the spatial features of this masking effect were determined in four healthy human subjects, using a reaction time paradigm. The masking effect decreased monotonically with increasing interstimulus distance, and identically in longitudinal and transverse (i.e., lateral) directions in the palm or dorsal surface of the hand. The masking effect was stronger in the glabrous than in the hairy skin, especially in the fingers. In the glabrous skin, the spread of masking effect produced by a high-frequency masker was more extensive than that produced by a low-frequency masker. The mechanical spread of high-frequency vibration was less extensive than that of low-frequency vibration in the skin. In the glabrous skin, a masker applied to the tip of the finger produced a stronger masking effect on sensations in the base of the finger than when the masker was located at the base and the test stimulus was located at the tip. It is concluded that mechanical spread of vibration in the skin is of minor importance in explaining the masking effects. Different peripheral neural mechanisms underlie the airpuff-elicited sensations in the hairy and glabrous skin. The afferent inhibitory mechanisms are stronger for signals coming from the glabrous skin of the fingers than for signals coming from the hairy skin. Furthermore, the peripheral innervation density and size of the cortical representational areas may be of importance in determining the magnitude of the masking effect.     

Attenuation of vibrotactile spatial summation.

Masked and quiet thresholds at several frequencies of vibratory stimuli were measured as a function of contactor area. The test site was the left index finger; the masking site was the left little finger. The quiet threshold data were consistent with previous investigations: Low-frequency stimuli showed no spatial summation, whereas high-frequency stimuli did. In the presence of a masker, spatial summation was reduced or eliminated for high-frequency stimuli, i.e., the masked threshold was, under some conditions, independent of contactor area. Low-frequency stimuli continued to show no spatial summation in the presence of a masker. The attenuation of spatial summation appears to be a direct function of the intensity of the masking stimulus. Additional measurements with the left thenar eminence as the test site showed that spatial summation could be attenuated by a masker placed on a contralateral body site. The implications of the results for quantifying the effectiveness of a masking stimulus, for the duplex mechanoreceptor hypothesis, and for the nature of spatial summation on the skin are discussed.     

Hearing Sensitivity to Shifts of Rippled-Spectrum Sound Signals in Masking Noise

The goal of the study was to enlarge knowledge of discrimination of complex sound signals by the auditory system in masking noise. For that, influence of masking noise on detection of shift of rippled spectrum was studied in normal listeners. The signal was a shift of ripple phase within a 0.5-oct wide rippled spectrum centered at 2 kHz. The ripples were frequency-proportional (throughout the band, ripple spacing was a constant proportion of the ripple center frequency). Simultaneous masker was a 0.5-oct noise below-, on-, or above the signal band. Both the low-frequency (center frequency 1 kHz) and on-frequency (the same center frequency as for the signal) maskers increased the thresholds for detecting ripple phase shift. However, the threshold dependence on the masker level was different for these two maskers. For the on-frequency masker, the masking effect primarily depended on the masker/signal ratio: the threshold steeply increased at a ratio of 5 dB, and no shift was detectable at a ratio of 10 dB. For the low-frequency masker, the masking effect primarily depended on the masker level: the threshold increased at a masker level of 80 dB SPL, and no shift was detectable at a masker level of 90 dB (for a signal level of 50 dB) or 100 dB (for a signal level of 80 dB). The high-frequency masker had little effect. The data were successfully simulated using an excitation-pattern model. In this model, the effect of the on-frequency masker appeared to be primarily due to a decrease of ripple depth. The effect of the low-frequency masker appeared due to widening of the auditory filters at high sound levels.     

Functional Properties of Slowly Adapting Mechanoreceptors in Cat Footpad Skin

The functional properties of slowly adapting (SA) afferent fibers innervating cat footpad skin were examined. Measurements were taken of receptive field area; spontaneous activity (< 1 impulse/sec); the slope of the stimulus-response curve for steady indentations up to 2 mm in amplitude; variability of the interimpulse intervals, as measured by the coefficient of variation of time interval histograms; decay of the response to steady indentation; and sensitivity to sinusoidal vibration (most sensitive at 5-10 Hz). Where comparable tests were performed on glabrous and hairy skin SA fibers, the functional properties of those in glabrous skin more closely resembled SAI fibers than SAII fibers. Additional results from glabrous skin SA fibers suggest that it is distortion of the nerve endings rather than steady indentation or compression that leads to a brisk response. On the measures described above, there appeared to be only one functional class of SA fiber innervating the cat footpad skin.     

Independent responses of Pacinian and Non-Pacinian systems with hand-transmitted vibration detected from masked thresholds

This study was designed to identify psychophysical channels responsible for the detection of hand-transmitted vibration. Perception thresholds for vibration (16, 31.5, 63 and 125?Hz sinusoidal for 600?ms) at the distal phalanx of the middle finger and the whole hand were determined with and without simultaneous masking stimuli (1/3 octave bandwidth Gaussian random vibration centered on either 16?Hz or 125?Hz for 3000?ms, varying in magnitude 0 to 30?dB above threshold). At all frequencies from 16 to 125?Hz, absolute thresholds for the hand were significantly lower than those for the finger. Changes in threshold as a function of masker level were used to estimate the thresholds of three psychophysical channels (i.e. P, NP I, and NP II channels). Increased vibrotactile sensitivity of the hand compared to the finger seems to be not entirely due to increased spatial summation via the Pacinian system (P channel); non-Pacinian system (NP I and NP II channels) also contributed to perception. Differing transmission of vibration between the hand and the finger may have also influenced the thresholds.     

Independent responses of Pacinian and Non-Pacinian systems with hand-transmitted vibration detected from masked thresholds

This study was designed to identify psychophysical channels responsible for the detection of hand-transmitted vibration. Perception thresholds for vibration (16, 31.5, 63 and 125 Hz sinusoidal for 600 ms) at the distal phalanx of the middle finger and the whole hand were determined with and without simultaneous masking stimuli (1/3 octave bandwidth Gaussian random vibration centered on either 16 Hz or 125 Hz for 3000 ms, varying in magnitude 0 to 30 dB above threshold). At all frequencies from 16 to 125 Hz, absolute thresholds for the hand were significantly lower than those for the finger. Changes in threshold as a function of masker level were used to estimate the thresholds of three psychophysical channels (i.e. P, NP I, and NP II channels). Increased vibrotactile sensitivity of the hand compared to the finger seems to be not entirely due to increased spatial summation via the Pacinian system (P channel); non-Pacinian system (NP I and NP II channels) also contributed to perception. Differing transmission of vibration between the hand and the finger may have also influenced the thresholds.     

The neural dependency of Merkel cell development in the rat: the touch domes and foot pads contrasted

We have used the quinacrine labeling technique and electron microscopy to study the development of the Merkel cell population in the skin of the rat and how this is affected by denervation produced at birth and at various times thereafter. An unexpected difference was found between the Merkel cells of glabrous and hairy skin. In the paw pads of rats aged 1 day or older the Merkel cells differentiated normally and survived quantitatively in the absence of their nerves. In the touch domes however, denervation at 1-4 days prevented the differentiation of the normal Merkel cell population and led to the disappearance of all or most of the Merkel cells that were already present. The Merkel cells in touch domes of the lower leg were affected by denervation like those of the back skin, differing strikingly from the Merkel cells of the footpads, even though the hairy skin of the leg and the glabrous skin of the foot are innervated by the same anatomical nerve. In adult rats, axons regenerating to denervated paws reinnervated epidermal Merkel cells of the pads and restored essentially normal mechanosensitivity to them; thus the Merkel cells of mammalian glabrous skin, like their counterparts in the wholly glabrous skin of lower vertebrates (S. A. Scott, E. Cooper, and J. Diamond, 1981, Proc. R. Soc. London B211, 455-470; K. M. Mearow and J. Diamond, 1988, Neuroscience 26, 695-708), can act as targets for ingrowing nerves. However, even though the differentiation of Merkel cells in hairy skin is nerve dependent, they probably have in common with the Merkel cells of glabrous skin the role of acting as final targets for nerves during development and regeneration.     

The skin of primates. XXX. The skin of the woolly monkey. (Lagothrix lagotricha)

The anatomical and histochemical features of the skin of the woolly monkey are intermediate between those of the Cercopithecoidea and the Pithecoidea. The animal has a prehensile tail, the glabrous, friction surface of which is similar to that of the fingers. The epidermis is heavily pigmented. The dermal vascularization is relatively well-developed and similar to that of the skin of the Cercopithecoidea. Hair follicles grow in groups of 4 to 15, as in the skin of the Pithecoidea. In the hairy skin, eccrine sweat glands occur only in the tail and genitalia. The woolly monkey, like the green monkey, possesses only acetylcholinesterase-containing nerve fibers around its eccrine sweat glands.     

Body Site Variation of Heat Pain Sensitivity

Thirty-two healthy human subjects provided thresholds for the perception of slight and moderate heat pain. Four body sites were tested bilaterally: thenar eminence of the hand, plantar surface of the foot, dorsolateral forearm, and lateral calf. Thresholds for the glabrous skin of the hand and foot were significantly greater than thresholds for the hairy skin of the arm and leg, the average difference being 1.3°c. Laterality was not a statistically significant factor. Thresholds increased progressively over 2–4 weeks of repeated testing, resulting in values averaging 0.6°c higher in the later sessions. The difference between moderate and slight pain thresholds averaged 1.1°c, and was consistent across body sites and with repeated testing.

The threshold values were normally distributed across subjects. Considerable intersubject variability was observed for both slight and moderate pain thresholds, more so on glabrous than on hairy skin sites. In comparison, the distribution of right-left difference values was narrower, demonstrating less intrasubject versus intersubject variability.

The highly significant difference in thresholds between glabrous and hairy skin sites demonstrates the importance of skin type for heat pain sensitivity. In contrast, there was no significant difference in heat pain sensitivity between comparable sites on the upper versus lower extremities, or between left and right sides.     

Compressive Nonlinearity in the Auditory System: Manifestation in the Action of Complex Sound Signals

In psychophysical experiments on humans, a cochlear compression was revealed by comparing onfrequency and low-frequency masking in the conditions of discrimination of complex spectra of sound signals. It has been established that, with an increase in the level of the masker, the limit of the discriminable density of the spectrum ripples decreases. It was noted that when the signal level increased, the on-frequency masker level at threshold grew proportionally to the level of the signal, whereas the low-frequency masker level grew much more slowly, indicating the compression of the signal, which was not affected by lateral suppression and off-frequency listening.     

持续与间断噪声前掩蔽条件下小鼠下丘神经元的不同反应模式

有关听中枢神经元纯音前掩蔽效应的神经表征已进行了大量研究,但是,噪声前掩蔽尤其是间断噪声前掩蔽效应的神经表征却鲜有报道。本研究观察了自由声场条件下,昆明小鼠下丘神经元在持续与间断噪声前掩蔽条件下对纯音探测声的反应。共记录到96个下丘神经元,测量了其中51个神经元在不同声刺激条件下的强度一放电率函数。结果显示,掩蔽声强度分布较广（探测声阈下21dB至阈上19dB之间）。在将近一半的神经元中,间断噪声的前掩蔽效应比持续噪声强（Ⅰ型,45．10％,P〈0．001）,但也有少数神经元其间断噪声的掩蔽效应较持续噪声的弱（Ⅲ型,17．65％,P〈0．001）,部分神经元无显著性差异（Ⅱ型,37．25％,P〉0．05）。无论Ⅰ型还是Ⅲ型神经元,持续噪声和间断噪声均在探测声强度较低时产生较强的抑制效应,随着探测声强度的升高,抑制效应逐渐降低（P〈0．001）;同时,持续噪声和间断噪声之间前掩蔽效应差异亦不复存在（P〉0．05）。此外,当掩蔽声由持续噪声换为间断噪声后,部分Ⅰ型神经元掩蔽时相的类型发生转变,其中最主要的转变为由前期抑制转变为均衡抑制（53．85％,7／13）。对下丘神经元声反应的时间域以及强度域,持续与间断噪声具有分化性前掩蔽效应,提示噪声前掩蔽并非简单的神经元发放压抑源,某些主动性神经调制机制可能参与了噪声条件下时相声信息的编码过程。     

Is baldness a thermoregulatory adaptive process?

In 100 adult men the area of the face and neck where beard was growing was measured and compared to that of glabrous skin on the forehead and calvaria. In the population as a whole, forehead area was found to be proportional to bearded area. Forehead and calvaria sweat rate was measured on 10 baldheaded male subjects and compared with that of 10 hairy control subjects during mild hyperthermia. Bald skin was found to sweat more than twice as much as hairy skin. In the light of these results the hypothesis that baldness is a thermoregulatory adaptative process is proposed.     

Restoration of sensation to the hand by a free neurovascular flap from the first web space of the foot.

A neurovascular free flap from the first web space of the foot was used successfully in two patients for replacement of glabrous skin of the hand and fingers. The potential advantages of this flap are that (1) it may be used to replace large defects of glabrous skin, (2) it provides a rich vascular supply to the periphery of the hand, and (3) the sensation achieved approaches the normal for the intact glabrous skin of the hand.     

Frequency-dependent herbivory by a leaf beetle,Phaedon brassicae,on hairy and glabrous plants of Arabidopsis halleri subsp. gemmifera

Frequency-dependent prey choice by natural enemies may influence the coexistence of multiple prey types, but little is known about whether frequency-dependent foraging choice occurs in herbivory on plants showing resistance polymorphism within a single population. Here we examined frequency-dependent foraging by a crucifer-feeding leaf beetle, Phaedon brassicae, on trichome-producing (hairy) and trichomeless (glabrous) plants coexisting within a natural population of the perennial herb Arabidopsis halleri subsp. gemmifera. Larvae of P. brassicae fed on hairy leaves showed slower growth than those fed on glabrous leaves. Although adult beetles consumed similar amounts of leaves when they were fed either hairy or glabrous leaves in no-choice conditions, our choice experiment showed that adult beetles fed at less than the proportionally expected level on hairy leaves compared to glabrous leaves when the hairy leaves were less or equally abundant. Both types of leaves were consumed at the proportionally expected levels when the hairy leaves were more abundant than the glabrous leaves. In a natural population, the leaf damage on the hairy plants was negatively correlated with the local proportion of the glabrous plants in a 1-m diameter patch across 2 years, while correlations between the leaf damage on the glabrous plants and their proportion differed between the 2 years. Additionally, we found five glucosinolates in leaves of A. halleri, but their accumulation did not differ between hairy and glabrous plants. Our experimental results indicate that hairy plants incur less herbivory by P. brassicae when glabrous plants are abundant. The field pattern provides evidence suggestive of frequency-dependent herbivory acting on hairy plants. The present study highlights one of the putative mechanisms of maintaining plant resistance polymorphism.     

Evidence that adaptation of suppression cannot account for auditory enhancement or enhanced forward masking.

Delaying the onset of a signal relative to the onset of a simultaneous notched masker often improves the ability of listeners to 'hear out' the signal at both threshold and suprathreshold levels. Viemeister & Bacon (J. acoust. Soc. Am., 71, 1502-1507 (1982)) suggested that such auditory enhancement effects could be accounted for if the suppression produced by the masker on the signal frequency adapted, thereby releasing the signal from suppression. In support of their hypothesis, Viemeister & Bacon reported that a masker preceded by an enhancer having no component at the signal frequency produced more forward masking than did the masker by itself. Here evidence is provided from five new experiments showing that adaptation of psychophysical two-tone suppression is inadequate to account either for auditory enhancement effects or for the enhanced forward masking demonstrated by Viemeister & Bacon.     

Detection of sonar signals in the presence of pulses of masking noise by the echolocating bat,Eptesicus fuscus

Summary Two big brown bats (Eptesicus fuscus) were trained to report the presence or absence of a virtual sonar target. The bats' sensitivity to transient masking was investigated by adding 5 ms pulses of white noise delayed from 0 to 16 ms relative to the target echo. When signal and masker occurred simultaneously, the bats required a signal energy to noise spectrum level ratio of 35 dB for 50% probability of detection. When the masker was delayed by 2 ms or more there was no significant masking and echo energy could be reduced by 30 dB for the same probability of detection. The average duration of the most energetic sonar signal of each trial was measured to be 1.7 ms and 2.4 ms for the two bats, but a simple relation between detection performance and pulse duration was not found.In a different experiment the masking noise pulses coincided with the echo, and the duration of the masker was varied from 2 to 37.5 ms. The duration of the masker had little or no effect on the probability of detection.The findings are consistent with an aural integration time constant of about 2 ms, which is comparable to the duration of the cries. This is an order of magnitude less than found in backward masking experiments with humans and may be an adaptation to the special constraints of echolocation. The short time of sensitivity to masking may indicate that the broad band clicks of arctiid moths produced as a countermeasure to bat predation are unlikely to function by masking the echo of the moth.Abbreviations SPL sound pressure level - SD standard deviation - SE standard error - BW bandwidth     

Effect of harmonicity on the detection of a signal in a complex masker and on spatial release from masking

The amount of masking of sounds from one source (signals) by sounds from a competing source (maskers) heavily depends on the sound characteristics of the masker and the signal and on their relative spatial location. Numerous studies investigated the ability to detect a signal in a speech or a noise masker or the effect of spatial separation of signal and masker on the amount of masking, but there is a lack of studies investigating the combined effects of many cues on the masking as is typical for natural listening situations. The current study using free-field listening systematically evaluates the combined effects of harmonicity and inharmonicity cues in multi-tone maskers and cues resulting from spatial separation of target signal and masker on the detection of a pure tone in a multi-tone or a noise masker. A linear binaural processing model was implemented to predict the masked thresholds in order to estimate whether the observed thresholds can be accounted for by energetic masking in the auditory periphery or whether other effects are involved. Thresholds were determined for combinations of two target frequencies (1 and 8 kHz), two spatial configurations (masker and target either co-located or spatially separated by 90 degrees azimuth), and five different masker types (four complex multi-tone stimuli, one noise masker). A spatial separation of target and masker resulted in a release from masking for all masker types. The amount of masking significantly depended on the masker type and frequency range. The various harmonic and inharmonic relations between target and masker or between components of the masker resulted in a complex pattern of increased or decreased masked thresholds in comparison to the predicted energetic masking. The results indicate that harmonicity cues affect the detectability of a tonal target in a complex masker.     

Perception of the consequences of self-action is temporally tuned and event driven

It has been proposed that in order to increase the salience of sensations with an external cause, sensations that are predictable based on one's own actions are attenuated [1 and 2]. This may explain why self-imposed tickle [3 and 4] or constant forces [5] are perceived as less intense than the same stimuli externally imposed. Here, subjects used their right index finger to tap a force sensor mounted above their left index finger. When a motor generated a tap on the left finger synchronously with the right tap, simulating contact between the fingers, the perception of force in the left finger was attenuated compared to the same tap experienced during rest. Attenuation gradually reduced as the left tap was either delayed or advanced relative to the active right tap. However, no attenuation was seen to left taps triggered by right-finger movements that stopped above or passed wide of the sensor. We conclude that there is a window of sensory attenuation that is broadly temporally tuned and centered on the time at which the fingers would normally make contact. That is, predictive tactile sensory attenuation is linked to specific external events arising from movement rather than to the movement per se.