An event-related brain potential study of cross-modal links in spatial attention between vision and touch

Event-related potential (ERP) evidence for the existence of cross-modal links in endogenous spatial attention between vision and touch was obtained in an experiment where participants had to detect tactile or visual targets on the attended side and to ignore the irrelevant modality and stimuli on the unattended side. For visual ERPs, attentional modulations of occipital P1 and N1 components were present when attention was directed both within vision and within touch, indicating that links in spatial attention from touch to vision can affect early stages of visual processing. For somatosensory ERPs, attentional negativities starting around 140 ms poststimulus were present at midline and lateral central electrodes when touch was relevant. No attentional somatosensory ERP modulations were present when vision was relevant and tactile stimuli could be entirely ignored. However, in another task condition where responses were also required to infrequent tactile targets regardless of their location, visual-spatial attention modulated somatosensory ERPs. Unlike vision, touch apparently can be decoupled from attentional orienting within another modality unless it is potentially relevant.     

Crossmodal links in spatial attention are mediated by supramodal control processes: evidence from event-related potentials

Crossmodal links in spatial attention were studied in an experiment where participants had to detect peripheral tactile or visual targets on the attended side, while ignoring all stimuli on the unattended side and in the currently irrelevant modality. Both relevant locations and relevant modalities were specified on a trial-by-trial basis by auditory precues. Spatial orienting in the cue-target interval was reflected in anterior negativities and occipital positivities contralateral to the cued side, either when vision or touch was cued as relevant. These effects resembled previously reported ERP modulations during shifts of visual attention, implicating supramodal mechanisms in the control of spatial attention and demonstrating their independence of cue modality. Early effects of spatial attention on somatosensory and visual ERPs were of equivalent size for currently relevant and irrelevant modalities. Results support the idea that crossmodal links in spatial attention are mediated by supramodal control mechanisms.     

Cross-modal links in endogenous spatial attention are mediated by common external locations: evidence from event-related brain potentials

Recent behavioural and event-related potential (ERP) studies reported cross-modal links in spatial attention between vision, audition and touch. Such links could reflect differences in hemispheric-activation levels associated with spatial attention to one side, or more abstract spatial reference-frames mediating selectivity across modalities. To distinguish these hypotheses, ERPs were recorded to lateral tactile stimuli, plus visual (experiment 1) or auditory stimuli (experiment 2), while participants attended to the left or right hand to detect infrequent tactile targets, and ignored other modalities. In separate blocks, hands were either in a crossed or uncrossed posture. With uncrossed hands, visual stimuli on the tactually attended side elicited enhanced N1 and P2 components at occipital sites, and an enhanced negativity at midline electrodes, reflecting cross-modal links in spatial attention from touch to vision. Auditory stimuli at tactually attended locations elicited an enhanced negativity overlapping with the N1 component, reflecting cross-modal links from touch to audition. An analogous pattern of results arose for crossed hands, with tactile attention enhancing auditory or visual responses on the side where the attended hand now lay (i.e. in the opposite visual or auditory hemifield to that enhanced by attending the same hand when uncrossed). This suggests that cross-modal attentional links are not determined by hemispheric projections, but by common external locations. Unexpectedly, somatosensory ERPs were strongly affected by hand posture in both experiments, with attentional effects delayed and smaller for crossed hands. This may reflect the combined influence of anatomical and external spatial codes within the tactile modality, while cross-modal links depend only on the latter codes. Electronic Publication     

ERP investigation of transient attentional selection of single and multiple locations within touch

Mechanisms underlying pure tactile attentional selection were investigated. Tactile imperative stimuli were preceded by symbolic tactile cues directing attention to the left or right (directional cues), or to both hands (non-directional cues). Comparison of ERP waveforms on directional and non-directional cue trials showed that attentional modulations at N140 and P200 components reflect mainly enhancement of stimuli at the attended, while longer latency modulations reflect mainly suppression of processing of stimuli at the unattended location. This pattern of results differs from analogous studies involving other modalities suggesting that different mechanisms underlie pure tactile attention. Furthermore, ERP waveforms on non-directional cue trials were enhanced in comparison to directional cue trials at the P100 component and at longer latencies, indicating that tactile attentional mechanisms may differ when attending to one compared to multiple locations.     

The orienting of attention during eye and hand movements: ERP evidence for similar frame of reference but different spatially specific modulations of tactile processing

To investigate which frames of reference guide shifts of attention triggered during eye and hand movement preparation and the specificity of their effects on somatosensory processing, we recorded event-related brain potentials (ERPs) in a Go/Nogo task where a cue indicated to prepare an eye movement toward - or a hand movement with - the left or right hand. Before the imperative stimulus, a tactile probe was presented to one hand. Spatially selective modulations of tactile processing were more sustained for hand than eye movements, indicating stronger attentional modulations for the modality of the effector's sensory organ. Importantly, attentional modulations of somatosensory processing as well as lateralized ERP components in the preparation interval were virtually identical under uncrossed and crossed hands conditions, suggesting that shifts of attention triggered during hand and eye movement preparation are guided by a common external reference frame.     

Early posterior ERP components do not reflect the control of attentional shifts toward expected peripheral events

Previous experiments investigating ERP correlates of anticipatory attention shifts triggered by central symbolic cues have identified a contralateral "early directing attention negativity," which was assumed to be generated by processes involved in the control of spatial orienting. Here we demonstrate that this component is not directly linked to the control of attentional shifts, but instead reflects the selection of task-relevant aspects of cue stimuli. In contrast, later ERP components triggered during covert attentional shifts are insensitive to physical cue attributes, and thus appear to be genuine electrophysiological correlates of covert attentional control mechanisms.     

Lateralized irrelevant speech alters visuospatial selective attention mechanisms

Recent studies indicate that the coordination of spatial attention across modalities may in part be mediated by a supramodal attentional system. We try to extend the concept of a supramodal system and hypothesized that involuntary modulations of auditory attentional processes by irrelevant speech signals influence visuospatial attention, suggesting crossmodal links between vision and speech. In order to test this we recorded event-related brain potentials (ERPs) of 12 healthy subjects in a visuospatial selective attention task. The task to identify target stimuli appearing at lateral visual field locations caused the expected enhancements of the early P1 and N1 ERP components to attended visual stimuli. Understandable and ununderstandable task irrelevant speech was presented either at the visually attended position or in the opposite visual field location. Speech contralateral to unattended visual stimuli led to a decreased N1 amplitude. This effect was stronger for understandable speech. Thus, speech influences the allocation of visual spatial attention if it is presented in the unattended location. The results suggest crossmodal links of speech and visuospatial attention mechanisms at a very early stage of human perception.     

Covert attention in touch: behavioral and ERP evidence for costs and benefits

To investigate the mechanism underlying tactile spatial attention, reaction times (RTs) and event-related potentials (ERPs) were recorded in response to mechanical stimuli delivered to the hands. At the start of each trial cues indicated either the correct (valid) or incorrect (invalid) tactile stimulus location or were uninformative (neutral). RT costs (suppression of invalid compared to neutral trials) were found to be larger than benefits (enhancement of valid compared to neutral trials). ERPs showed that costs and benefits contribute equally to attentional modulations of the somatosensory N140 component, whereas these were largely due to costs at longer latencies. These results differ from the pattern of attentional ERP modulations previously found for vision and audition, where costs precede benefits, and therefore suggest that the mechanisms of attentional selectivity in touch might be different from attentional processes in other modalities.     

Modulations of early somatosensory ERP components by transient and sustained spatial attention

To investigate when and how spatial attention affects somatosensory processing, event-related brain potentials (ERPs) were recorded in response to mechanical tactile stimuli delivered to the left and right hand while attention was directed to one of these hands. The attended hand either remained constant throughout an experimental block (sustained attention), or was changed across successive trials (transient attention). Attentional modulations of the N140 component and a sustained 'processing negativity' for attended stimuli were observed in both attention conditions. However, attentional effects on earlier somatosensory components differed systematically. Sustained attention resulted in a contralateral negativity overlapping with the N80 component, while transient attention was reflected by a bilateral positivity overlapping with the P100 component. This dissociation indicates that sustained and transient attention affect different somatosensory areas. It is suggested that sustained attention can modulate tactile processing within primary somatosensory cortex (S1), while effects of transient attention are located beyond S1. Overall, results demonstrate that spatial selectivity in touch is mediated by activity modulations in modality-specific somatosensory cortex.     

Pikachurin interaction with dystroglycan is diminished by defective O-mannosyl glycosylation in congenital muscular dystrophy models and rescued by LARGE overexpression

Visuo-tactile integration occurs in a privileged way in peripersonal space, namely when visual and tactile stimuli are in spatial proximity. Here, we investigated whether crossmodal spatial effects (i.e. stronger crossmodal interactions for spatially congruent compared to incongruent visual and tactile stimuli) are also present when visual stimuli presented near the body are indirectly viewed in a mirror, thus appearing in far space. Participants had to attend to one of their hands throughout a block of stimuli in order to detect infrequent tactile target stimuli at that hand while ignoring tactile targets at the unattended hand, all tactile non-target stimuli, and any visual stimuli. Visual stimuli were presented simultaneously with tactile stimuli, in the same (congruent) or opposite (incongruent) hemispace with respect to the tactile stimuli. In one group of participants the visual stimuli were delivered near the participants' hands and were observed as indirect mirror reflections ('mirror' condition), while in the other group these were presented at a distance from the hands ('far' condition). The main finding was that crossmodal spatial modulations of ERPs recorded over and close to somatosensory cortex were present in the 'mirror' condition but not the 'far' condition. That is, ERPs were enhanced in response to tactile stimuli coupled with spatially congruent versus incongruent visual stimuli when the latter were viewed through a mirror. These effects emerged around 190 ms after stimuli onset, and were modulated by the focus of spatial attention. These results provide evidence that visual stimuli observed in far space via a mirror are coded as near-the-body stimuli according to their known rather than to their perceived location. This suggests that crossmodal interactions between vision and touch may be modulated by previous knowledge of reflecting surfaces (i.e. top-down processing).     

Assessing the effect of posture change on tactile inhibition-of-return

If a peripheral target follows an ipsilateral cue with a stimulus-onset-asynchrony (SOA) of 300 ms or more, its detection is delayed compared to a contralateral-cue condition. This phenomena, known as inhibition-of-return (IOR), affects responses to visual, auditory, and tactile stimuli, and is thought to provide an index of exogenous shifts of spatial attention. The present study investigated whether tactile IOR occurs in a somatotopic vs an allocentric frame of reference. In experiment 1, tactile cue and target stimuli were presented to the index and middle fingers of either hand, with the hands positioned in an uncrossed posture (SOA 500 or 1,000 ms). Speeded target detection responses were slowest for targets presented from the cued finger, and were also slower for targets presented to the adjacent finger on the cued hand than to either finger on the uncued hand. The same pattern of results was also reported when the index and middle fingers of the two hands were interleaved on the midline (experiment 2), suggesting that the gradient of tactile IOR surrounding a cued body site is modulated by the somatotopic rather than by the allocentric distance between cue and target.     

Spatial attention affects the processing of tactile and visual stimuli presented at the tip of a tool: an event-related potential study

An event-related potential (ERP) experiment was conducted in order to investigate the nature of any cross-modal links in spatial attention during tool use. Tactile stimuli were delivered from the tip of two sticks, held in either a crossed or an uncrossed tools posture, while visual stimuli were presented along the length of each tool. Participants had to detect tactile deviant stimuli at the end of one stick while trying to ignore all other stimuli. Reliable ERP spatial attention effects to tactile stimuli were observed at early (160–180 ms) and later time epochs (>350 ms) when the tools were uncrossed. Reliable ERP attention effects to visual stimuli presented close to the tip of the tool and close to the hand were also observed in the uncrossed tools condition (time epoch 140–180 ms). These results are consistent with the claim that tool-use results in a shift of visuospatial attention toward the tip of the tool and also to attention being focused by the hand where the touch is felt.     

ERP effects of intermodal attention and cross-modal links in spatial attention

Effects of intermodal attention and of cross-modal links in spatial attention on visual and auditory event-related potentials (ERPs) were investigated in two experiments where participants had to attend to one stimulus modality (audition or vision) to respond to infrequently presented targets whenever these were presented at a relevant location (indicated by a cue). The ERP effects of intermodal attention (measured by comparing the ERPs elicited by visual and auditory stimuli when the respective modality was relevant or irrelevant) were differently distributed in vision and audition, suggesting that intermodal attention operates by a selective modulation of modality-specific areas. Similar ERP effects of spatial attention (measured by comparing the ERPs to stimuli at cued and uncued locations) were elicited at midline electrodes in vision and audition. With one notable exception, these effects were also present when attention was directed within the other modality, suggesting the existence of cross-modal links between vision and audition in the control of transient spatial attention.     

Vision enhances selective attention to body-related information

Viewing ones’ own hands while directing attention to one of the hands leads to earlier attentional modulations of somatosensory processing than when hands are not visible. This effect of vision on tactile-spatial selection could be explained by vision providing additional information about the location of the hands in external space. The present study investigated whether vision of the hands also affected tactile-attentional mechanisms when the relative locations of the hands were irrelevant. Participants silently counted infrequent tactile or auditory deviants in an alternating stream of tactile and auditory stimuli while ignoring stimuli in the other modality, when their hands were either visible or covered from view. Modality-selective attentional modulations of ERPs to tactile stimuli (when touches vs. tones were attended) were already present for the time range of the N80 component when hands were visible, but there were only later modulations (starting at N140) when hands were covered. This suggests that, rather than being restricted to tasks requiring spatial selection between body parts, vision of the hands can facilitate attention toward the body in far more general terms. In contrast to tactile stimuli, attentional modulations of ERPs to auditory stimuli (when tones vs. touches were attended) were not reliably affected by viewing the hands. This suggests that the primary purpose of visual facilitation may be to enhance the processing of body-related information only.     

Spatial tuning of tactile attention modulates visual processing within hemifields: an ERP investigation of crossmodal attention

Recent event-related brain potential (ERP) studies have revealed crossmodal links in spatial attention, but have not yet investigated differences in the spatial tuning of attention between task-relevant and irrelevant modalities. We studied the spatial distribution of attention in vision under conditions where participants were instructed to attend to the left or right-hand in order to detect infrequent targets, and to entirely ignore visual stimuli presented via LEDs at two eccentricities in the left or right hemifield. Hands were located close to two of these four LEDs in different blocks. Visual N1 amplitudes were enhanced when visual stimuli in the cued hemifield were close to the attended hand, relative to visual stimuli presented at the other location on the same side. These within-hemifield attentional modulations of visual processing demonstrate that crossmodal attention is not distributed diffusely across an entire hemifield. The spatial tuning of tactile attention transfers crossmodally to affect vision, consistent with spatial selection at a multimodal level of representation.     

Intermodal spatial attention differs between vision and audition: an event-related potential analysis

Subjects were required to attend to a combination of stimulus modality (vision or audition) and location (left or right). Intermodal attention was measured by comparing event-related potentials (ERPs) to visual and auditory stimuli when the modality was relevant or irrelevant, while intramodal (spatial) attention was measured by comparing ERPs to visual and auditory stimuli presented at relevant and irrelevant spatial locations. Intramodal spatial attention was expressed differently in visual and auditory ERPs. When vision was relevant, spatial attention showed a contralateral enhancement of posterior N1 and P2 components and enhancement of parietal P3. When audition was relevant, spatial attention showed a biphasic fronto-central negativity, starting after around 100 ms. The same effects were also present in ERPs to stimuli that were presented in the irrelevant modality. Thus, spatial attention was not completely modality specific. Intermodal attention effects were also expressed differently in vision and audition. Taken together, the obtained ERP patterns of the present study show that stimulus attributes such as modality and location are processed differently in vision and audition.     

An event-related potential study of supramodal attentional control and crossmodal attention effects

We conducted two audiovisual experiments to determine whether event-related potential (ERP) components elicited by attention-directing cues reflect supramodal attentional control. Symbolic visual cues were used to direct attention prior to auditory targets in Experiment 1, and symbolic auditory cues were used to direct attention prior to visual targets in Experiment 2. Different patterns of cue ERPs were found in the two experiments. A frontal negativity called the ADAN was absent in Experiment 2, which indicates that this component does not reflect supramodal attentional control. A posterior positivity called the LDAP was observed in both experiments but was focused more posteriorly over the occipital scalp in Experiment 2. This component appears to reflect multiple processes, including visual processes involved in location marking and target preparation as well as supramodal processes involved in attentional control.     

An ERP study of sustained spatial attention to stimulus eccentricity

Effects of attention on event-related brain potentials (ERPs) were measured when subjects kept sustained attention focused on ring-shaped regions of visual space to detect infrequently presented targets at a given eccentricity. In line with a previous study that employed a trial-by-trial cueing paradigm, no modulations of sensory-evoked P1 and N1 components were found. This suggests that attentional selectivity in complex spatial selection tasks is primarily located at post-perceptual processing levels. Enhanced negativities for attended as compared to unattended stimuli were present between 220 and 380 ms post-stimulus and were followed by an enlarged positivity for attended stimuli in the P3 time range. These effects reflected the distribution of attention in visual space, in part consistent with 'attentional gradient' and 'zoom-lens' models. However, ERPs also suggested the presence of selective mechanisms that exclude irrelevant stimuli located between two simultaneously attended areas.     

Do ERP components triggered during attentional orienting represent supramodal attentional control?

Lateralized ERP components triggered during cued shifts of spatial attention (anterior directing attention negativity [ADAN], late directing attention positivity [LDAP]) have been observed during visual, auditory, and tactile attention tasks, suggesting that these components reflect supramodal attentional control processes. This interpretation has recently been called into question by the finding that the ADAN is absent in response to auditory attention cues. Here we demonstrate that ADAN and LDAP components are reliably elicited in a purely unimodal auditory attention task where auditory cues are followed by auditory imperative stimuli. The fact that the ADAN is not restricted to task contexts where visual or tactile stimuli are relevant is consistent with the hypothesis that this component is linked to supramodal attentional control.     

Attending to the heart is associated with posterior alpha band increase and a reduction in sensitivity to concurrent visual stimuli

Attentional mechanisms have been studied mostly in specific sensory domains, such as auditory, visuospatial, or tactile modalities. In contrast, attention to internal interoceptive visceral targets has only recently begun to be studied, despite its potential importance in emotion, empathy, and self‐awareness. Here, we studied the effects of shifting attention to the heart using a cue‐target detection paradigm during continuous EEG recordings. Subjects were instructed to count either a series of visual stimuli (visual condition) or their own heartbeats (heart condition). Visual checkerboard stimuli were used as attentional probes throughout the task. Consistent with previous findings, attention modulated the amplitude of the heartbeat‐evoked potentials. Directing attention to the heart significantly reduced the visual P1/N1 amplitude evoked by the attentional probe. ERPs locked to the attention‐directing cue revealed a novel frontal positivity around 300 ms postcue. Finally, spectral power in the alpha band over parieto‐occipital regions was higher while attending to the heart—when compared to the visual task—and correlated with subject's performance in the interoceptive task. These results are consistent with a shared, resource‐based attentional mechanism whereby allocating attention to bodily signals can affect early responses to visual stimuli.