Effect of Posture Change on Tactile Perception: Impaired Direction Discrimination Performance With Interleaved Fingers (original) (raw)
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Studying One and Two-Finger Perception of Tactile Directional Cues
Lecture Notes in Computer Science, 2016
In this paper, we study the perception of tactile directional cues by one or two fingers, using either the index, middle, or ring finger, or any of their combination. Therefore, we use tactile devices able to stretch the skin of the fingertips in 2 DOF along four directions: horizontal, vertical, and the two diagonals. We measure the recognition rate in each direction, as well as the subjective preference, depending on the (couple of) finger(s) stimulated. Our results show first that using the index and/or middle finger performs significantly better than using the ring finger on both qualitative and quantitative measures. The results when comparing one versus two-finger configurations are more contrasted. The recognition rate of the diagonals is higher when using one finger than two, whereas two fingers enable a better perception of the horizontal direction. These results pave the way to other studies on one versus two-finger perception, and raise methodological considerations for the design of multi-finger tactile devices.
Brain Research, 2006
Crossing the hands over, whether across the body midline or with respect to each other, leads to measurable changes in spatial compatibility, spatial attention, and frequently to a general decrement in discrimination performance for tactile stimuli. The majority of multisensory crossed hands effects, however, have been demonstrated with explicit or implicit spatial discrimination tasks, raising the question of whether non-spatial discrimination tasks also show spatial effects when the hands are crossed. We designed a novel, non-spatial tactile discrimination task to address this issue. Participants made speeded discriminations of single-versus double-pulse vibrotactile targets, while trying to ignore simultaneous visual distractor stimuli, in both hands uncrossed, and hands crossed postures. Tactile discrimination performance was significantly affected by the visual distractors (demonstrating a significant crossmodal congruency effect), and was affected most by visual distractors in the same external location as the tactile target (i.e., spatial modulation), regardless of the posture (uncrossed or crossed) of the hands (i.e., spatial 'remapping' of visual-tactile interactions). Finally, crossing the hands led to a general performance decrement with visual distractors, but not in a control task with unimodal visual or tactile judgements. These results demonstrate, for the first time, significant spatial and postural modulations of crossmodal congruency effects in a non-spatial discrimination task.
Experimental Brain research, 2022
The grating orientation discrimination task (GOT) is a sensitive and reliable measure of tactile spatial resolution, or acuity. We used the GOT in three experiments to investigate the effects of hand posture and hand visibility on spatial acuity. Participant sex and experimental design were also manipulated. Healthy adult participants received brief touches to their index fingertips of grated, domed objects. Their task was to decide whether the gratings ran 'along' or 'across' their finger. Measures of the smallest grating width for which participants could reliably discriminate between orientations were recorded as threshold. Experiment 1 evaluated the effect of two-versus one-interval discrimination, hand used and participant sex. Experiments 2 and 3 evaluated the effects of hand visibility (visible or covered) and hand posture (in front or to the side). Females were better than males; the two-interval task resulted in lower thresholds than the one-interval task; and left and right hand thresholds were not significantly different. Most importantly, while hand visibility did not have a significant effect on the task, thresholds were affected by hand posture-worse when the hand was oriented to the side of the body than in front. These results replicate previously reported effects of sex (or finger size), but failed to replicate the so-called 'visual enhancement of touch' (VET) effect. We also report a meta-analysis of 27 VET studies, finding a significant effect of 'noninformative' vision on tactile perception. Our novel finding is that hand posture affects tactile acuity.
Combined contribution of tactile and proprioceptive feedback to hand movement perception
Here we investigated how the tactile modality is used along with muscle proprioception in hand movement perception, whether these two sensory inputs are centrally integrated and whether they work complementarily or concurrently. The illusory right hand rotations induced in eleven volunteers by a textured disk scrolling under their hand in two directions at three velocities and/or by mechanical vibration applied to their wrist muscles at three frequencies were compared. The kinesthetic illusions were copied by the subjects on-line with their left hand. Results: 1) in all the subjects, tactile stimulation alone induced an illusory hand rotation in the opposite direction to that of the disk, and the velocity of the illusion increased non-linearly with the disk velocity: the highest gain (the illusion velocity to disk velocity ratio) occurred at the slowest disk rotation; 2) adding a consistent roprioceptive stimulus increased the perceptual effects, whereas adding a conflicting proprioceptive stimulus of increasing frequency gradually decreased the tactile illusions and reversed their initial direction; 3) under both consistent and conflicting conditions, only strong proprioceptive stimulation significantly affected the gain of the resulting illusions, whereas the largest gain always occurred at low tactile stimulation levels when the illusory movements were in the same direction as the tactile-induced illusion. Tactile information may equal or even override muscle proprioceptive information in the perception of relatively small, slow hand movements. These two somatosensory inputs may be integrated complementarily, depending on their respective relevance to the task of accurately perceiving one's own hand movements.
Tactile directional sensibility: peripheral neural mechanisms in man
Brain Research, 2000
Tactile directional sensibility, i.e. the ability to tell the direction of an object's motion across the skin, is an easily observed sensory function that is highly sensitive to disturbances of the somatosensory system. Based on previous psychophysical experiments on healthy subjects it was concluded that directional sensibility depends on two kinds of information from cutaneous mechanoreceptors; spatio-temporal information and information about friction-induced changes in skin stretch. In the present study responses to similar probe movements as in the psychophysical experiments were recorded from human single mechanoreceptors in the forearm skin. All slowly adapting type 2 (SA2) units were spontaneously active, and with increasing force of friction their discharge rates were modified by probe movements at increasing distances from the Ruffini end-organ, reflecting the high stretch-sensitivity of these units. Slowly adapting type 1 (SA1) and field units responded to the moving probe within well-defined skin areas directly overlying the individual receptor terminals, and compared to the SA2 units their response properties were less dependent on the force of friction. The results suggest that SA1 and field units have the capacity to signal spatio-temporal information, whereas a population of SA2 units have the capacity to signal direction-specific information about changes in lateral skin stretch.
Back-to-front: Improved tactile discrimination performance in the space you cannot see
Neuroscience Letters, 2006
We investigated any differences in people's ability to reconstruct the appropriate spatiotemporal ordering of multiple tactile stimuli, when presented in frontal space (a region where visual inputs tend to dominate) versus in the space behind the back (a region of space that we rarely see) in professional piano players and in non-musicians. Even though tactile temporal order judgments were much better in the musicians overall, both groups showed a much reduced crossed-hands deficit when their hands were crossed behind their backs rather than at the front. These results suggest that because of differences in the availability of visual input, the spatiotemporal representation of non-visual stimuli in front versus rear space is different.
Directional biases in whole hand motion perception revealed by mid-air tactile stimulation
2020
Human machine interfaces are increasingly designed to reduce our reliance on the dominantly used senses of vision and audition. Many emerging technologies are attempting to convey complex spatiotemporal information via tactile percepts shown to be effective in the visual domain, such as shape and motion. Despite the intuitive appeal of touch as a method of feedback, we do not know to what extent the hand can substitute for the retina in this way. Here we ask whether the tactile system can be used to perceive complex whole hand motion stimuli, and whether it exhibits the same kind of established perceptual biases as reported in the visual domain. Using ultrasound stimulation, we were able to project complex moving dot percepts onto the palm in mid-air, over 30cm above an emitter device. We generated dot kinetogram stimuli involving motion in three different directional axes (‘Horizontal’, ‘Vertical’, and ‘Oblique’) on the ventral surface of the hand. We found clear evidence that part...
Relative finger position influences whether you can localize tactile stimuli
Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale, 2011
To investigate whether the relative positions of the Wngers inXuence tactile localization, participants were asked to localize tactile stimuli applied to their Wngertips. We measured the location and rate of errors for three Wnger conWgurations: Wngers stretched out and together so that they are touching each other, Wngers stretched out and spread apart maximally and Wngers stretched out with the two hands on top of each other so that the Wngers are interwoven. When the Wngers contact each other, it is likely that the error rate to the adjacent Wngers will be higher than when the Wngers are spread apart. In particular, we reasoned that localization would probably improve when the Wngers are spread. We aimed at assessing whether such adjacency was measured in external coordinates (taking proprioception into account) or on the body (in skin coordinates). The results conWrmed that the error rate was lower when the Wngers were spread. However, there was no decrease in error rate to neighbouring Wngertips in the Wngers spread condition in comparison with the Wngers together condition. In an additional experiment, we showed that the lower error rate when the Wngers were spread was not related to the continuous tactile input from the neighbouring Wngers when the Wngers were together. The current results suggest that information from proprioception is taken into account in perceiving the location of a stimulus on one of the Wngertips.
Spatial Modulation of Tactile Temporal-Order Judgments
Perception, 2005
We report a series of three experiments designed to examine the effect of posture on tactile temporal processing. Observers reported which of two tactile stimuli, presented to the left and right index fingers (experiments 1 – 3; or thumb, experiment 3), was perceived first while adopting one of two postures—hands-close (adjacent, but not touching) or hands-far (1 m apart)—in the dark. Just-noticeable differences were significantly smaller in the hands-far posture across all three experiments. In the first two experiments we compared hand versus foot responses and found equivalent advantages for the hands-far posture. In the final experiment the stimuli were presented to either the same or different digit on each hand (index finger or thumb) and we found that only when the same digit on each hand was stimulated was there an advantage for the hands-far posture. The finding that temporal precision was better with greater distance contradicts predictions based on attention-switching mod...
Anisotropic distortion in the perceived orientation of stimuli on the arm
Scientific Reports
Mechanoreceptors on the skin are heterogeneously distributed, and the sampling of neural signals in the brain can vary depending on the part of the body. Therefore, it can be challenging for the brain to consistently represent stimuli applied to different body sites. Here, we report an example of a regional perceptual distortion of the tactile space. We used a piezoelectric braille display to examine shape perception on the volar surface of the arm and to compare it to that on the palm. We found that the orientation of perceived stimuli on the arm was distorted in certain areas. In particular, an inwardly-inclined line shape was perceived as being more inwardly-inclined than it actually was. On the other hand, an outwardly-inclined line was perceived accurately. When the same stimuli were applied to the palm, this anisotropic bias was not observed. We also found that changing the posture of the arm changed the angle at which this anisotropic distortion occurred, suggesting the influ...