Tactile Targets Research Articles

SII and the fronto-parietal areas are involved in visually cued tactile top-down spatial attention

Visual cue-oriented, tactile top-down attention (vTA) has been well investigated behaviorally. However, vTA-related brain activation remains unclear, and whether SI (primary somatosensory cortex) or SII (secondary somatosensory cortex) is modulated by the top-down process of tactile cognition remains particularly controversial. We used the Posner paradigm in which a visual spatial cue directed attention to a tactile target [tactile spatial attention (TS) task]. The TS is compared with a visual nonspatially cued, tactile attention task [tactile neutral attention (TN) task]. The behavioral results showed no significant differences between the TS and TN tasks. However, we considered the possibility that the visual spatial hint affected the TS neural network. Brain-imaging data showed that the inferior parietal lobe was activated more during the TS task than during the TN task. Furthermore, we present evidence to support SII modulation by top-down processing during the TS task.

Neural correlates of endogenous attention, exogenous attention and inhibition of return in touch.

Selective attention helps process the myriad of information constantly touching our body. Both endogenous and exogenous mechanisms are relied upon to effectively process this information; however, it is unclear how they relate in the sense of touch. In three tasks we contrasted endogenous and exogenous event-related potential (ERP) and behavioural effects. Unilateral tactile cues were followed by a tactile target at the same or opposite hand. Clear behavioural effects showed facilitation of expected targets both when the cue predicted targets at the same (endogenous predictive task) and opposite hand (endogenous counter-predictive task), and these effects also correlated with ERP effects of endogenous attention. In an exogenous task, where the cue was non-informative, inhibition of return (IOR) was observed. The electrophysiological results demonstrated early effects of exogenous attention followed by later endogenous attention modulations. These effects were independent in both the endogenous predictive and exogenous tasks. However, voluntarily directing attention away from a cued body part influenced the early exogenous marker (N80). This suggests that the two mechanisms are interdependent, at least when the task requires more demanding shifts of attention. The early marker of exogenous tactile attention, the N80, was not directly related to IOR, which may suggest that exogenous attention and IOR are not necessarily two sides of the same coin. This study adds valuable new insight into how we process and select information presented to our body, showing both independent and interdependent effects of endogenous and exogenous attention in touch.

Response speed advantage for vision does not extend to touch in early deaf adults

Early deaf adults typically respond faster than hearing controls when performing a speeded simple detection on visual targets. Whether this response time advantage can generalise to another intact modality (touch) or it is instead specific to visual processing remained unexplored. We tested eight early deaf adults and twelve hearing controls in a simple detection task, with visual or tactile targets delivered on the arms and occupying the same locations in external space. Catch trials were included in the experimental paradigm. Results revealed a response time advantage in deaf adults compared to hearing controls, selectively for visual targets. This advantage did not extend to touch. The number of anticipation errors was negligible and comparable in both groups. The present findings strengthen the notion that response time advantage in deaf adults emerges as a consequence of changes specific to visual processing. They also exclude the involvement of sensory-unspecific cognitive mechanisms in this improvement (e.g. increased impulsivity in initiation of response, longer-lasting sustained attention or higher motivation to perform the task). Finally, they provide initial evidence that the intact sensory modalities can reorganise independently from each other following early auditory deprivation.

When vision influences the invisible distractor: Tactile response compatibility effects require vision.

Research on the nature of crossmodal interactions between vision and touch has shown that even task-irrelevant visual information can support the processing of tactile targets. In the present study, we implemented a tactile variant of the Eriksen flanker task to investigate the influences of vision on the processing of tactile distractors. In particular, we analyzed whether the size of the flanker effect at the level of perceptual congruency and at the level of response compatibility would differ as a function of the availability of vision (Experiments 1 and 2). Tactile distractors were processed up to the level of response selection only if visual information was provided (i.e., no flanker effects were observed at the level of response compatibility for blindfolded participants). In Experiment 3, we manipulated whether the part of the body receiving the tactile target or distractor was visible, while the other body part was occluded from view. Flanker effects at the level of response compatibility were observed in both conditions, meaning that vision of either the body part receiving the tactile target or the body part receiving the tactile distractor was sufficient to further the processing of tactile distractors from the level of perceptual congruency to the level of response selection. Taken together, these results suggest that vision modulates tactile distractor processing because it results in the processing of tactile distractors up to the level of response selection.

Can’t touch this: The first-person perspective provides privileged access to predictions of sensory action outcomes.

Previous studies have shown that viewing others in pain activates cortical somatosensory processing areas and facilitates the detection of tactile targets. It has been suggested that such shared representations have evolved to enable us to better understand the actions and intentions of others. If this is the case, the effects of observing others in pain should be obtained from a range of viewing perspectives. Therefore, the current study examined the behavioral effects of observed grasps of painful and nonpainful objects from both a first- and third-person perspective. In the first-person perspective, a participant was faster to detect a tactile target delivered to their own hand when viewing painful grasping actions, compared with all nonpainful actions. However, this effect was not revealed in the third-person perspective. The combination of action and object information to predict the painful consequences of another person's actions when viewed from the first-person perspective, but not the third-person perspective, argues against a mechanism ostensibly evolved to understand the actions of others.

Vision affects tactile target and distractor processing even when space is task-irrelevant

The human brain is adapted to integrate the information from multiple sensory modalities into coherent, robust representations of the objects and events in the external world. A large body of empirical research has demonstrated the ubiquitous nature of the interactions that take place between vision and touch, with the former typically dominating over the latter. Many studies have investigated the influence of visual stimuli on the processing of tactile stimuli (and vice versa). Other studies, meanwhile, have investigated the effect of directing a participant’s gaze either toward or else away from the body-part receiving the target tactile stimulation. Other studies, by contrast, have compared performance in those conditions in which the participant’s eyes have been open versus closed. We start by reviewing the research that has been published to date demonstrating the influence of vision on the processing of tactile targets, that is, on those stimuli that have to be attended or responded to. We outline that many – but not all – of the visuotactile interactions that have been observed to date may be attributable to the direction of spatial attention. We then move on to focus on the crossmodal influence of vision, as well as of the direction of gaze, on the processing of tactile distractors. We highlight the results of those studies demonstrating the influence of vision, rather than gaze direction (i.e., the direction of overt spatial attention), on tactile distractor processing (e.g., tactile variants of the negative-priming or flanker task). The conclusion is that no matter how vision of a tactile distractor is engaged, the result would appear to be the same, namely that tactile distractors are processed more thoroughly.

Gaze-dependent spatial updating of tactile targets in a localization task

There is concurrent evidence that visual reach targets are represented with respect to gaze. For tactile reach targets, we previously showed that an effector movement leads to a shift from a gaze-independent to a gaze-dependent reference frame. Here we aimed to unravel the influence of effector movement (gaze shift) on the reference frame of tactile stimuli using a spatial localization task (yes/no paradigm). We assessed how gaze direction (fixation left/right) alters the perceived spatial location (point of subjective equality) of sequentially presented tactile standard and visual comparison stimuli while effector movement (gaze fixed/shifted) and stimulus order (vis-tac/tac-vis) were varied. In the fixed-gaze condition, subjects maintained gaze at the fixation site throughout the trial. In the shifted-gaze condition, they foveated the first stimulus, then made a saccade toward the fixation site where they held gaze while the second stimulus appeared. Only when an effector movement occurred after the encoding of the tactile stimulus (shifted-gaze, tac-vis), gaze similarly influenced the perceived location of the tactile and the visual stimulus. In contrast, when gaze was fixed or a gaze shift occurred before encoding of the tactile stimulus, gaze differentially affected the perceived spatial relation of the tactile and the visual stimulus suggesting gaze-dependent coding of only one of the two stimuli. Consistent with previous findings this implies that visual stimuli vary with gaze irrespective of whether gaze is fixed or shifted. However, a gaze-dependent representation of tactile stimuli seems to critically depend on an effector movement (gaze shift) after tactile encoding triggering spatial updating of tactile targets in a gaze-dependent reference frame. Together with our recent findings on tactile reaching, the present results imply similar underlying reference frames for tactile spatial perception and action.

Task-Related Changes in Functional Properties of the Human Brain Network Underlying Attentional Control

Previous studies have demonstrated task-related changes in brain activation and inter-regional connectivity but the temporal dynamics of functional properties of the brain during task execution is still unclear. In the present study, we investigated task-related changes in functional properties of the human brain network by applying graph-theoretical analysis to magnetoencephalography (MEG). Subjects performed a cue-target attention task in which a visual cue informed them of the direction of focus for incoming auditory or tactile target stimuli, but not the sensory modality. We analyzed the MEG signal in the cue-target interval to examine network properties during attentional control. Cluster-based non-parametric permutation tests with the Monte-Carlo method showed that in the cue-target interval, beta activity was desynchronized in the sensori-motor region including premotor and posterior parietal regions in the hemisphere contralateral to the attended side. Graph-theoretical analysis revealed that, in beta frequency, global hubs were found around the sensori-motor and prefrontal regions, and functional segregation over the entire network was decreased during attentional control compared to the baseline. Thus, network measures revealed task-related temporal changes in functional properties of the human brain network, leading to the understanding of how the brain dynamically responds to task execution as a network.

Biomimetic tactile target acquisition, tracking and capture

Good performance in unstructured/uncertain environments is an ongoing problem in robotics; in biology, it is an everyday observation. Here, we model a particular biological system—hunting in the Etruscan shrew—as a case study in biomimetic robot design. These shrews strike rapidly and accurately after gathering very limited sensory information from their whiskers; we attempt to mimic this performance by using model-based simultaneous discrimination and localisation of a ‘prey’ robot (i.e. by using strong priors to make sense of limited sensory data), building on our existing low-level models of attention and appetitive behaviour in small mammals. We report performance that is comparable, given the spatial and temporal scale differences, to shrew performance, and discuss what this study reveals about biomimetic robot design in general.

Object-Guided Spatial Selection in Touch Without Concurrent Changes in the Perceived Location of the Hands

In an endogenous cueing paradigm with central visual cues, observers made speeded responses to tactile targets at the hands, which were either close together or far apart, and holding either two separate objects or one common object between them. When the hands were far apart, the response time costs associated with attending to the wrong hand were reduced when attention had to be shifted along one object jointly held by both hands compared to when it was shifted over the same distance but across separate objects. Similar reductions in attentional costs were observed when the hands were placed closer together, suggesting that processing at one hand is less prioritized over that at another when the hands can be "grouped" by virtue of arising from the same spatial location or from the same object. Probes of perceived hand locations throughout the task showed that holding a common object decreased attentional separability without decreasing the perceived separation between the hands. Our findings suggest that tactile events at the hands may be represented in a spatial framework that flexibly adapts to (object-guided) attentional demands, while their relative coordinates are simultaneously preserved.

The Crossmodal Congruency Task as a Means to Obtain an Objective Behavioral Measure in the Rubber Hand Illusion Paradigm

The rubber hand illusion (RHI) is a popular experimental paradigm. Participants view touch on an artificial rubber hand while the participants' own hidden hand is touched. If the viewed and felt touches are given at the same time then this is sufficient to induce the compelling experience that the rubber hand is one's own hand. The RHI can be used to investigate exactly how the brain constructs distinct body representations for one's own body. Such representations are crucial for successful interactions with the external world. To obtain a subjective measure of the RHI, researchers typically ask participants to rate statements such as "I felt as if the rubber hand were my hand". Here we demonstrate how the crossmodal congruency task can be used to obtain an objective behavioral measure within this paradigm. The variant of the crossmodal congruency task we employ involves the presentation of tactile targets and visual distractors. Targets and distractors are spatially congruent (i.e. same finger) on some trials and incongruent (i.e. different finger) on others. The difference in performance between incongruent and congruent trials - the crossmodal congruency effect (CCE) - indexes multisensory interactions. Importantly, the CCE is modulated both by viewing a hand as well as the synchrony of viewed and felt touch which are both crucial factors for the RHI. The use of the crossmodal congruency task within the RHI paradigm has several advantages. It is a simple behavioral measure which can be repeated many times and which can be obtained during the illusion while participants view the artificial hand. Furthermore, this measure is not susceptible to observer and experimenter biases. The combination of the RHI paradigm with the crossmodal congruency task allows in particular for the investigation of multisensory processes which are critical for modulations of body representations as in the RHI.

The Crossmodal Congruency Task as a Means to Obtain an Objective Behavioral Measure in the Rubber Hand Illusion Paradigm

The rubber hand illusion (RHI) is a popular experimental paradigm. Participants view touch on an artificial rubber hand while the participants' own hidden hand is touched. If the viewed and felt touches are given at the same time then this is sufficient to induce the compelling experience that the rubber hand is one's own hand. The RHI can be used to investigate exactly how the brain constructs distinct body representations for one's own body. Such representations are crucial for successful interactions with the external world. To obtain a subjective measure of the RHI, researchers typically ask participants to rate statements such as "I felt as if the rubber hand were my hand". Here we demonstrate how the crossmodal congruency task can be used to obtain an objective behavioral measure within this paradigm.The variant of the crossmodal congruency task we employ involves the presentation of tactile targets and visual distractors. Targets and distractors are spatially congruent (i.e. same finger) on some trials and incongruent (i.e. different finger) on others. The difference in performance between incongruent and congruent trials - the crossmodal congruency effect (CCE) - indexes multisensory interactions. Importantly, the CCE is modulated both by viewing a hand as well as the synchrony of viewed and felt touch which are both crucial factors for the RHI.The use of the crossmodal congruency task within the RHI paradigm has several advantages. It is a simple behavioral measure which can be repeated many times and which can be obtained during the illusion while participants view the artificial hand. Furthermore, this measure is not susceptible to observer and experimenter biases. The combination of the RHI paradigm with the crossmodal congruency task allows in particular for the investigation of multisensory processes which are critical for modulations of body representations as in the RHI.

Anticipation Increases Tactile Stimulus Processing in the Ipsilateral Primary Somatosensory Cortex

Stimulus anticipation improves perception. To account for this improvement, we investigated how stimulus processing is altered by anticipation. In contrast to a large body of previous work, we employed a demanding perceptual task and investigated sensory responses that occur beyond early evoked activity in contralateral primary sensory areas: Stimulus-induced modulations of neural oscillations. For this, we recorded magnetoencephalography in 19 humans while they performed a cued tactile identification task involving the identification of either a proximal or a distal stimulation on the fingertips. We varied the cue-target interval between 0 and 1000 ms such that tactile targets occurred at various degrees of anticipation. This allowed us to investigate the influence of anticipation on stimulus processing in a parametric fashion. We observed that anticipation increases the stimulus-induced response (suppression of beta-band oscillations) originating from the ipsilateral primary somatosensory cortex. This occurs in the period in which the tactile memory trace is analyzed and is correlated with the anticipation-induced improvement in tactile perception. We propose that this ipsilateral response indicates distributed processing across bilateral primary sensory cortices, of which the extent increases with anticipation. This constitutes a new and potentially important mechanism contributing to perception and its improvement following anticipation.

Parietal Oscillations Code Nonvisual Reach Targets Relative to Gaze and Body

Recent blood oxygenation level-dependent (BOLD) imaging work has suggested flexible coding frames for reach targets in human posterior parietal cortex, with a gaze-centered reference frame for visually guided reaches and a body-centered frame for proprioceptive reaches. However, BOLD activity, which reflects overall population activity, is insensitive to heterogeneous responses at the neuronal level and temporal dynamics between neurons. Neurons could synchronize in different frequency bands to form assemblies operating in different reference frames. Here we assessed the reference frames of oscillatory activity in parietal cortex during reach planning to nonvisible tactile stimuli. Under continuous recording of magneto-encephalographic data, subjects fixated either to the left or right of the body midline, while a tactile stimulus was presented to a nonvisible fingertip, located either to the left or right of gaze. After a delay, they had to reach toward the remembered stimulus location with the other hand. Our results show body-centered and gaze-centered reference frames underlying the power modulations in specific frequency bands. Whereas beta-band activity (18-30 Hz) in parietal regions showed body-centered spatial selectivity, the high gamma band (>60 Hz) demonstrated a transient remapping into gaze-centered coordinates in parietal and extrastriate visual areas. This gaze-centered coding was sustained in the low gamma (<60 Hz) and alpha (∼10 Hz) bands. Our results show that oscillating subpopulations encode remembered tactile targets for reaches relative to gaze, even though neither the sensory nor the motor output processes operate in this frame. We discuss these findings in the light of flexible control mechanisms across modalities and effectors.

Lost in vision: ERP correlates of exogenous tactile attention when engaging in a visualtask

Behavioural studies have shown that when engaging in a visual task response facilitation to tactile stimuli at exogenously cued locations is diminished. Here we investigated behavioural and also neural correlates of tactile exogenous attention when participants either watched a visual stream (single task) or also detected targets in the visual stream (dual task). During the visual stream, tactile cues were presented to the left or right hand followed by tactile targets at the same or opposite hand. Behavioural results demonstrated slowed responses to tactile targets at cued locations (i.e., IOR) in the single whilst no attention effect in the dual task. Concurrently recorded EEG revealed multiple stages of tactile processing to be attenuated when engaging in a visual task: First, the amplitude of the cueelicited somatosensory P100 component was suppressed suggesting relative early cross-modality effects in the dual task. Second, correlates of cue-induced attentional control processes showed a reduced late somatosensory negativity (LSN) in the dual compared to the single task suggesting smaller preparatory processes. Finally, early attentional selection correlates of post-target ERPs (N80) were absent in the dual task. This study demonstrated for the first time that engaging in a visual task abolished behavioural IOR in touch. ERP analyses showed that early somatosensory processing as well as specific correlates of tactile attentional orienting and target selection are diminished under visual engagement. Our findings are in line with a supramodal account of attention.

Freezing effect in tactile perception: Sound facilitates tactile identification by enhancing intensity but not duration.

Identification of a visual target can be enhanced by a simultaneously presented high tone embedded in a sequence of low tones. This is called "freezing effect" because it is as if the target display was frozen in time by the tone. Until now, however, it has not been known whether this sound facilitation effect exists for a target with modalities other than vision, such as tactility, and if so, what its underlying mechanism is. We demonstrate, for the first time, an audio-tactile freezing effect (Experiment 1). We use a method of constant stimuli in conjunction with a 2-AFC task to determine the point of subjective equality (PSE) of the duration (Experiment 2A) or intensity (Experiment 2B) of the tactile target. Results do not support the view that a high tone expands the duration of the tactile target, but rather that the tone enhances participants' subjective tactile intensity. When the tactile intensity of the target was increased to match the shift of PSE as in Experiment 2B, this increased intensity indeed improved identification, further suggesting that intensity enhancement is the mechanism (Experiment 3). The perceived tactile intensity enhancement by a sound indicates genuine multisensory integration.

Impact of the spatial congruence of redundant targets on within-modal and cross-modal integration

Although the topic of sensory integration has raised increasing interest, the differing behavioral outcome of combining unisensory versus multisensory inputs has surprisingly only been scarcely investigated. In the present experiment, observers were required to respond as fast as possible to (1) lateralized visual or tactile targets presented alone, (2) double stimulation within the same modality or (3) double stimulation across modalities. Each combination was either delivered within the same hemispace (spatially aligned) or in different hemispaces (spatially misaligned). Results show that the redundancy gains (RG) obtained from the cross-modal conditions were far greater than those obtained from combinations of two visual or two tactile targets. Consistently, we observed that the reaction time distributions of cross-modal targets, but not those of within-modal targets, surpass the predicted reaction time distribution based on the summed probability distributions of each constituent stimulus presented alone. Moreover, we found that the spatial alignment of the targets did not influence the RG obtained in cross-modal conditions, whereas within-modal stimuli produced a greater RG when the targets where delivered in separate hemispaces. These results suggest that within-modal and cross-modal integration are not only distinguishable by the amount of facilitation they produce, but also by the spatial configuration under which this facilitation occurs. Our study strongly supports the notion that estimates of the same event that are more independent produce enhanced integrative gains.

Adverse effects of viewing the hand on tactile-spatial selection between fingers depend on finger posture

Primary somatosensory cortex (S1) is known to rapidly adapt to task demands and to intermodal information (e.g. from vision). Here, we show that also intramodal information (i.e. posture) can affect tactile attentional selection processes and the intermodal effects of vision on those processes at S1 stages of processing. We manipulated the spatial separation between adjacent fingers, that is, thumb and index finger where close, far apart, or touching. Participants directed their attention to either the index finger or thumb to detect infrequent tactile targets at that location while either they saw their fingers or these were covered from view. In line with the previous results, we found that attentional selection affected early somatosensory processing (P45, N80) when fingers were near and this attention effect was abolished when fingers were viewed. When fingers were far or touching, attentional modulations appeared reliably only from the P100, and furthermore, enhanced tactile-spatial selection was found when touching fingers were viewed. Taken together, these results show for the first time a profound effect of finger posture on attentional selection between fingers and its modulations by vision at early cortical stages of processing. They suggest that the adverse effects of vision on tactile attention are not driven by a conflict between the selected information in vision (two fingers) and touch (one finger) and imply that external spatial information (i.e. finger posture) rapidly affects the organisation of primary somatosensory finger representations and that this further affects vision and tactile-spatial selection effects on S1.

The influence of time prediction on modality expectancy

Predicting an upcoming event in time or modality leads to expectancy-based benefits for the predicted time point or modality and to costs for the unpredicted ones. Yet, it is not clear how expectancy to an event in time interacts with expectancy of a particular modality. In our study, participants had to perform a discrimination task (single or double pulse) on visual or tactile targets. An auditory cue (75% of validity) was used to increase expectancy in one or the other modality. We also manipulated the time point (1 or 3 s after the cue) in which the stimulus appeared in a probabilistic way. We found that increasing the temporal expectation reduced the reaction time of valid targets in both, vision and touch, but when the target was presented in the unexpected modality (invalid cue) time predictability induced a cost in reaction time. Therefore the benefit of time expectancy is converted into a cost if the stimulus is presented in the unattended modality, suggesting cross-modal competition in the temporal domain.

ERP investigations into the effects of gaze and spatial attention on the processing of tactile events

Previous research demonstrated that directing one’s gaze at a body part reduces detection speed (e.g., Tipper et al., 1998) and enhances the processing (Forster and Eimer, 2005) of tactile stimuli presented at the gazed location. Interestingly, gaze-dependent modulation of somatosensory evoked potentials (SEPs), are very similar to those observed in previous studies of tactile spatial attention. This might indicate that manipulating gaze direction activates the same mechanisms that are responsible for the covert orienting of spatial attention in touch. To investigate this possibility, gaze direction and sustained tactile attention were orthogonally manipulated in the present study. In different blocks of trials, participants focused their attention on the left or right hand while gazing to the attended or to the unattended hand while they had to respond to infrequent tactile targets presented to the attended hand. Analyses of the SEPs elicited by tactile non-target stimuli demonstrate that gaze and attention influence different stages of tactile processing. While gaze is able to modulate tactile processing already 50 ms after stimulus onset, attentional SEP modulations are only observed beyond 110 ms post-stimulus. This dissociation in the timing and therefore the associated locus of the effects of gaze and attention on somatosensory processing reveals that the effect of gaze on tactile processing is independent of tactile attention.