Concurrent Tactile Stimulation Research Articles

Multisensory visuo-tactile context learning enhances the guidance of unisensory visual search

Does multisensory distractor-target context learning enhance visual search over and above unisensory learning? To address this, we had participants perform a visual search task under both uni- and multisensory conditions. Search arrays consisted of one Gabor target that differed from three homogeneous distractors in orientation; participants had to discriminate the target’s orientation. In the multisensory session, additional tactile (vibration-pattern) stimulation was delivered to two fingers of each hand, with the odd-one-out tactile target and the distractors co-located with the corresponding visual items in half the trials; the other half presented the visual array only. In both sessions, the visual target was embedded within identical (repeated) spatial arrangements of distractors in half of the trials. The results revealed faster response times to targets in repeated versus non-repeated arrays, evidencing ‘contextual cueing’. This effect was enhanced in the multisensory session—importantly, even when the visual arrays presented without concurrent tactile stimulation. Drift–diffusion modeling confirmed that contextual cueing increased the rate at which task-relevant information was accumulated, as well as decreasing the amount of evidence required for a response decision. Importantly, multisensory learning selectively enhanced the evidence-accumulation rate, expediting target detection even when the context memories were triggered by visual stimuli alone.

Vibro-Tactile Enhancement of Speech Intelligibility in Multi-talker Noise for Simulated Cochlear Implant Listening.

Many cochlear implant (CI) users achieve excellent speech understanding in acoustically quiet conditions but most perform poorly in the presence of background noise. An important contributor to this poor speech-in-noise performance is the limited transmission of low-frequency sound information through CIs. Recent work has suggested that tactile presentation of this low-frequency sound information could be used to improve speech-in-noise performance for CI users. Building on this work, we investigated whether vibro-tactile stimulation can improve speech intelligibility in multi-talker noise. The signal used for tactile stimulation was derived from the speech-in-noise using a computationally inexpensive algorithm. Eight normal-hearing participants listened to CI simulated speech-in-noise both with and without concurrent tactile stimulation of their fingertip. Participants' speech recognition performance was assessed before and after a training regime, which took place over 3 consecutive days and totaled around 30 min of exposure to CI-simulated speech-in-noise with concurrent tactile stimulation. Tactile stimulation was found to improve the intelligibility of speech in multi-talker noise, and this improvement was found to increase in size after training. Presentation of such tactile stimulation could be achieved by a compact, portable device and offer an inexpensive and noninvasive means for improving speech-in-noise performance in CI users.

Crossmodal Classification of Mu Rhythm Activity during Action Observation and Execution Suggests Specificity to Somatosensory Features of Actions.

The alpha mu rhythm (8-13 Hz) has been considered to reflect mirror neuron activity because it is attenuated by both action observation and action execution. The putative link between mirror neuron system activity and the mu rhythm has been used to study the involvement of the mirror system in a wide range of socio-cognitive processes and clinical disorders. However, previous research has failed to convincingly demonstrate the specificity of the mu rhythm, meaning that it is unclear whether the mu rhythm reflects mirror neuron activity. It also remains unclear whether mu rhythm suppression during action observation reflects the processing of motor or tactile information. In an attempt to assess the validity of the mu rhythm as a measure of mirror neuron activity, we used crossmodal pattern classification to assess the specificity of EEG mu rhythm response to action varying in terms of action type (whole-hand or precision grip), concurrent tactile stimulation (stimulation or no stimulation), or object use (transitive or intransitive actions) in 20 human participants. The main results reveal that above-chance crossmodal classification of mu rhythm activity was obtained in the central channels for tactile stimulation and action transitivity but not for action type. Furthermore, traditional univariate analyses applied to the same data were insensitive to differences between conditions. By calling into question the relationship between mirror system activity and the mu rhythm, these results have important implications for the use and interpretation of mu rhythm activity.SIGNIFICANCE STATEMENT The central alpha mu rhythm oscillation is a widely used measure of the human mirror neuron system that has been used to make important claims concerning cognitive functioning in health and in disease. Here, we used a novel multivariate analytical approach to show that crossmodal EEG mu rhythm responses primarily index the somatosensory features of actions, suggesting that the mu rhythm is not a valid measure of mirror neuron activity. Results may lead to the revision of the conclusions of many previous studies using this measure, and to the transition toward a theory of mu rhythm function that is more consistent with current models of sensory processing in the self and in others.

Visual object separation resolves competitive interactions in somatosensory cortex evoked signals during concurrent vibrotactile stimulation of the left and right hand

We investigated the effect of visual separation of left and right hemispaces within peripersonal space to sustained tactile spatial attention processing and showed that visually perceived object separation weakened the competitive interaction for concurrent vibrotactile stimulation to two hands. Participants received concurrent vibrotactile stimulation at different frequencies on two hands (right: 20Hz; left: 24Hz) for 4500ms to elicit steady-state somatosensory evoked potentials (SSSEPs). They attended to one of the stimulated hands and reacted to rare transient events embedded in the attended ongoing stream. Behavioral and neurophysiological results reveal that separation of spatial representation of tactile event locations could facilitate bilateral tactile spatial selection in sustained attention processing. Visual separation by a gap between hands increased the magnitude of attentional gain in SSSEPs compared to the situation when no gap was present. Results suggest that visual separation resolved the competition between concurrent tactile stimulation on two hands.

Re-examining overlap between tactile and visual motion responses within hMT + and STS

Here, we examine overlap between tactile and visual motion BOLD responses within the human MT+ complex. Although several studies have reported tactile responses overlapping with hMT+, many used group average analyses, leaving it unclear whether these responses were restricted to subregions of hMT+. Moreover, previous studies either employed a tactile task or passive stimulation, leaving it unclear whether or not tactile responses in hMT+ are simply the consequence of visual imagery. Here, we carried out a replication of one of the classic papers finding tactile responses in hMT+. We mapped MT and MST in individual subjects using visual field localizers. We then examined responses to tactile motion on the arm, either presented passively or in the presence of a visual task performed at fixation designed to minimize visualization of the concurrent tactile stimulation. To our surprise, without a visual task, we found only weak tactile motion responses in MT (6% of voxels showing tactile responses) and MST (2% of voxels). With an unrelated visual task designed to withdraw attention from the tactile modality, responses in MST were reduced to almost nothing (<1% regions). Consistent with previous results, we did observe tactile responses in STS regions superior and anterior to hMT+. Despite the lack of individual overlap, group-averaged responses produced strong spurious overlap between tactile and visual motion responses within hMT+ that resembled those observed in previous studies. The weak nature of tactile responses in hMT+ (and their abolition by withdrawal of attention) suggests that hMT+ may not serve as a supramodal motion processing module.

Extending peripersonal space representation without tool-use: evidence from a combined behavioral-computational approach.

Stimuli from different sensory modalities occurring on or close to the body are integrated in a multisensory representation of the space surrounding the body, i.e., peripersonal space (PPS). PPS dynamically modifies depending on experience, e.g., it extends after using a tool to reach far objects. However, the neural mechanism underlying PPS plasticity after tool use is largely unknown. Here we use a combined computational-behavioral approach to propose and test a possible mechanism accounting for PPS extension. We first present a neural network model simulating audio-tactile representation in the PPS around one hand. Simulation experiments showed that our model reproduced the main property of PPS neurons, i.e., selective multisensory response for stimuli occurring close to the hand. We used the neural network model to simulate the effects of a tool-use training. In terms of sensory inputs, tool use was conceptualized as a concurrent tactile stimulation from the hand, due to holding the tool, and an auditory stimulation from the far space, due to tool-mediated action. Results showed that after exposure to those inputs, PPS neurons responded also to multisensory stimuli far from the hand. The model thus suggests that synchronous pairing of tactile hand stimulation and auditory stimulation from the far space is sufficient to extend PPS, such as after tool-use. Such prediction was confirmed by a behavioral experiment, where we used an audio-tactile interaction paradigm to measure the boundaries of PPS representation. We found that PPS extended after synchronous tactile-hand stimulation and auditory-far stimulation in a group of healthy volunteers. Control experiments both in simulation and behavioral settings showed that the same amount of tactile and auditory inputs administered out of synchrony did not change PPS representation. We conclude by proposing a simple, biological-plausible model to explain plasticity in PPS representation after tool-use, which is supported by computational and behavioral data.

Tactile Modulation of Emotional Speech Samples

Traditionally only speech communicates emotions via mobile phone. However, in daily communication the sense of touch mediates emotional information during conversation. The present aim was to study if tactile stimulation affects emotional ratings of speech when measured with scales of pleasantness, arousal, approachability, and dominance. In the Experiment 1 participants rated speech-only and speech-tactile stimuli. The tactile signal mimicked the amplitude changes of the speech. In the Experiment 2 the aim was to study whether the way the tactile signal was produced affected the ratings. The tactile signal either mimicked the amplitude changes of the speech sample in question, or the amplitude changes of another speech sample. Also, concurrent static vibration was included. The results showed that the speech-tactile stimuli were rated as more arousing and dominant than the speech-only stimuli. The speech-only stimuli were rated as more approachable than the speech-tactile stimuli, but only in the Experiment 1. Variations in tactile stimulation also affected the ratings. When the tactile stimulation was static vibration the speech-tactile stimuli were rated as more arousing than when the concurrent tactile stimulation was mimicking speech samples. The results suggest that tactile stimulation offers new ways of modulating and enriching the interpretation of speech.

When does perception facilitate or interfere with conceptual processing? The effect of attentional modulation.

Conceptual processing relies on the perceptual system, and, as such, perception affects conception. Many studies have demonstrated perceptual-conceptual interference, where perceptual stimulation in a particular modality leads to slower and/or less accurate conceptual processing of information from the same modality (e.g., Kaschak et al., 2005, 2006; Vermeulen et al., 2008). However, many other studies have demonstrated perceptual-conceptual facilitation, where perceptual stimulation leads to faster and/or more accurate conceptual processing in the same modality (Kaschak et al., 2006; van Dantzig et al., 2008; Connell et al., 2012; Connell and Lynott, in preparation). At first glance, this apparent discrepancy seems like a serious problem for accounts of simulation-based concepts. Such theories hold that offline representations—that is, representations of objects and events that are not in the current environment (Wilson, 2002)—are functionally comprised of partial replays (i.e., simulations) of the neural activation captured during perceptual, motor, affective, and other experience (Barsalou, 1999, 2008; Glenberg and Gallese, 2012; Connell and Lynott, submitted). If conceptual representations therefore require modality-specific perceptual simulation, then why do they not consistently interact with perception? Why does perceptual stimulation sometimes impair and sometimes facilitate conceptual processing? One account proposed that the difference lies in whether perceptual stimulation is concurrent with the conceptual task or precedes it, and whether or not the perceptual stimulus can be easily integrated into the simulation required by the conceptual task (Kaschak et al., 2005). According to this account, interference occurs when a concurrent perceptual stimulus cannot be integrated into the simulation required by the conceptual task. For example, Kaschak and colleagues argued that an upward-scrolling visual display could not be easily integrated with the sentence The cat climbed the tree, and hence interfered with its simulation. Facilitation occurs when a perceptual stimulus can be easily integrated into a simulation, regardless of whether the perceptual and conceptual components of the trial are presented concurrently or sequentially. For example, an image of a car would facilitate understanding a sentence like The car approached you. However, this account cannot easily explain later findings. For example, concurrent tactile stimulation, in the form of vibrations to the palms and fingers, facilitates people's ability to judge the size of manipulable objects (Connell et al., 2012). Vibrotactile stimulation seems at least as distant from object representations of wallets and keys as upward-scrolling lines are from a cat climbing a tree. Yet, even though both perceptual stimuli appear “nonintegratible,” the former produced facilitation and the latter interference.

Neural mechanisms for generation of tactile interference effects on somatosensory evoked magnetic fields in humans

Objectives: We examined modification of somatosensory evoked fields following electric middle finger stimulation with interference to the same and surrounding digits in 13 subjects.Methods: During electric middle finger stimulation, concurrent tactile stimulation was applied to the middle finger, to the index and ring fingers, and to the thumb and the little finger, individually.Results: The amplitudes of the N20m and the P30m were significantly reduced by the interference to the middle finger, and to the index and ring fingers. The former interference induced more prominent attenuation than the latter. The amplitudes of the P60m did not show significant changes by any kind of the interference.Conclusions: The N20m and the P30m were attenuated according to the cortical distance between electrically and mechanically activated 3b areas. Pyramidal neurons are interconnected by intrinsic horizontal collaterals, even if their representations are segregated. The activation of the intrinsic collaterals induces direct excitation and indirect inhibition (via inhibitory interneurons) to the target pyramidal neurons. The result indicates that the activation of the intrinsic collaterals inhibits, on balance, the postsynaptic pyramidal targets, thereby generating the attenuation of the N20m and P30m.

Influence of concurrent tactile stimulation on somatosensory evoked potentials following posterior tibial nerve stimulation in man

A topographical study was made of SEPs following stimulation of the right posterior tibial nerve at the ankle, with and without concurrent tactile stimulation of the soles of either foot or the palm of the right hand. Effects of the interfering stimulus were best demonstrated by subtracting the wave forms to derive ‘difference’ potentials. The majority of SEP components were significantly attenuated by tactile stimulation of the ipsilateral foot, and the difference wave form was of similar morphology to the control response. Components of opposite polarity peaking at 39 msec were consistent with the field of a cortical generator with dipolar properties, situated in the contralateral hemisphere just posterior to the vertex with the positive poles oriented towards the ipsilateral side. By analogy with median SEP findings, these potentials were believed to originate in the foot region of area 3b where neurones are mainly concerned with cutaneous sensory processing. When the tactile stimulus was applied to the contralateral foot, difference potentials maximally recorded just posterior to the vertex were of smaller amplitude but similar morphology to ipsilateral foot difference components. This suggested the possibility that input from the two lower extremities may converge at cortical or subcortical level, the effect being manifested in the response of certain neurones in area 3b. With both contralateral foot and ipsilateral hand stimulation, other difference potentials were present which suggested that there may be cortical regions responding to combinations of sensory stimuli applied to various parts of the body surface.

Scalp topography of human somatosensory evoked potentials: The effect of interfering tactile stimulation applied to the hand

A detailed topographical analysis of human SEPs in response to median nerve stimulation was performed, with and without concurrent tactile stimulation of the hand. Twenty-eight recording sites on the scalp and neck were referred to earlobe and non-cephalic reference electrodes. The following components were identified in the control wave form: N10, N11, N13, P14, N19, P20, P22, N22, N29, P30 and P44. The interference wave form showed significant attenuation of P14, N19, P20, P22 and N29, while P30 was abolished. N10, N11, N13 and N22 remained unchanged and P44 was enhanced. In the interference wave form there also appeared an N33 component, supplanting P30 over the posterior contralateral quadrant, and a P36 frontally. The pattern of changes was best demonstrated by subtracting the interference from the control response to derive a ‘difference’ wave form. This consisted of ‘P’14, ‘N’19, ‘P’21, ‘P’32 and ‘N’36 components. The last 2 were of large amplitude over the posterior contralateral quadrant and frontal cortex, respectively, and overlapped for at least 10 msec of their duration. The results indicate that the interfering effect occurred at the level of the brain-stem or above. The topography of the difference wave form suggests that the ‘P’32 and ‘N’36 components may be attributable to a generator situated in the posterior bank of the central sulcus (Brodmann's area 3b), concerned with the processing of input from cutaneous mechanoreceptors. It is proposed that the P22 and N22 components of the control and interference wave forms may be due to a generator located at the bottom and in the anterior bank of the central sulcus (area 3a).

Shock-elicited pain and its reduction by concurrent tactile stimulation.

Human affective reactions to nociceptive electrical stimulation were attenuated by application of a tactile stimulus to the shocked site. No alteration was perceived when the same tactile stimulus was applied to a similar contralateral site. These results and a lack of alteration at sensation threshold demonstrate the effect to be more than simple masking and support the Melzack-Wall theory.