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Biomedical subjects

Martin Eimer

Publications and source records attributed to Martin Eimer.

At least 19 recordsLinked to original sources
PubMed2006

Covert manual response preparation triggers attentional modulations of visual but not auditory processing.

OBJECTIVE: We investigated whether covert unimanual response preparation triggers attention shifts, as postulated by the premotor theory of attention, and whether these result in spatially specific modulations of visual and auditory processing. METHODS: Visual response cues instructed participants to prepare to lift their left or right index finger in response to a subsequent target stimulus. Irrelevant visual or auditory probes were delivered to the left or right hand during the response preparation interval. ERPs were measured time-locked to cue onset, and time-locked to probe stimulus onset. RESULTS: Lateralised ERP components triggered during covert response preparation (ADAN, LDAP) were similar to components previously found during attention shifts. N1 components were enhanced to visual probes delivered adjacent to the cued response relative to those delivered to the opposite hand. Auditory probe ERPs were unaffected by manual response preparation. CONCLUSIONS: Shifts of spatial attention that are triggered during covert unimanual response preparation result in spatially specific modulations of visual but not auditory processing. SIGNIFICANCE: Results support the claim of the premotor theory that the preparation of manual responses is associated with attention shifts. However, such shifts are not based on purely supramodal processes, as they result in a modality-specific pattern of sensory modulations.

Adult↗
PubMed2006

Manual response preparation and saccade programming are linked to attention shifts: ERP evidence for covert attentional orienting and spatially specific modulations of visual processing.

The premotor theory of attention claims that attentional shifts are triggered during response programming, regardless of which response modality is involved. To investigate this claim, event-related brain potentials (ERPs) were recorded while participants covertly prepared a left or right response, as indicated by a precue presented at the beginning of each trial. Cues signalled a left or right eye movement in the saccade task, and a left or right manual response in the manual task. The cued response had to be executed or withheld following the presentation of a Go/Nogo stimulus. Although there were systematic differences between ERPs triggered during covert manual and saccade preparation, lateralised ERP components sensitive to the direction of a cued response were very similar for both tasks, and also similar to the components previously found during cued shifts of endogenous spatial attention. This is consistent with the claim that the control of attention and of covert response preparation are closely linked. N1 components triggered by task-irrelevant visual probes presented during the covert response preparation interval were enhanced when these probes were presented close to cued response hand in the manual task, and at the saccade target location in the saccade task. This demonstrates that both manual and saccade preparation result in spatially specific modulations of visual processing, in line with the predictions of the premotor theory.

Adolescent↗
PubMed2006

Cortico-cortical interactions in spatial attention: A combined ERP/TMS study.

To gain insight into the neural basis of visual attention, we combined transcranial magnetic stimulation (TMS) and event-related potentials (ERPs) during a visual search task. Single-pulse TMS over right posterior parietal cortex (rPPC) delayed response times to targets during conjunction search, and this behavioral effect had a direct ERP correlate. The early phase of the N2pc component that reflects the focusing of attention onto target locations in a search display was eliminated over the right hemisphere when TMS was applied there but was present when TMS was delivered to a control site (vertex). This finding demonstrates that rPPC TMS interferes with attentional selectivity in remote visual areas.

Adult↗
PubMed2005

Attention modulates the processing of emotional expression triggered by foveal faces.

To investigate whether the processing of emotional expression for faces presented within foveal vision is modulated by spatial attention, event-related potentials (ERPs) were recorded in response to stimulus arrays containing one fearful or neutral face at fixation, which was flanked by a pair of peripheral bilateral lines. When attention was focused on the central face, an enhanced positivity was elicited by fearful as compared to neutral faces. This effect started at 160 ms post-stimulus, and remained present for the remainder of the 700 ms analysis interval. When attention was directed away from the face towards the line pair, the initial phase of this emotional positivity remained present, but emotional expression effects beyond 220 ms post-stimulus were completely eliminated. These results demonstrate that when faces are presented foveally, the initial rapid stage of emotional expression processing is unaffected by attention. In contrast, attentional task instructions are effective in inhibiting later, more controlled stages of expression analysis.

Adolescent↗
PubMed2005

The role of spatial frequency information for ERP components sensitive to faces and emotional facial expression.

To investigate the impact of spatial frequency on emotional facial expression analysis, ERPs were recorded in response to low spatial frequency (LSF), high spatial frequency (HSF), and unfiltered broad spatial frequency (BSF) faces with fearful or neutral expressions, houses, and chairs. In line with previous findings, BSF fearful facial expressions elicited a greater frontal positivity than BSF neutral facial expressions, starting at about 150 ms after stimulus onset. In contrast, this emotional expression effect was absent for HSF and LSF faces. Given that some brain regions involved in emotion processing, such as amygdala and connected structures, are selectively tuned to LSF visual inputs, these data suggest that ERP effects of emotional facial expression do not directly reflect activity in these regions. It is argued that higher order neocortical brain systems are involved in the generation of emotion-specific waveform modulations. The face-sensitive N170 component was neither affected by emotional facial expression nor by spatial frequency information.

Adult↗
PubMed2005

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.

Adult↗
PubMed2005

Vision and gaze direction modulate tactile processing in somatosensory cortex: evidence from event-related brain potentials.

Several behavioural studies have shown that directing one's gaze at a body part reduces detection speed and enhances discrimination of tactile stimuli at that location. We investigated how vision of a body part stimulated and manipulations of gaze direction affect tactile processing. Participants' gaze was directed to one of their hands, with vision of this hand either available or prevented in different experiments. They had to detect infrequent tactile targets among non-targets. Somatosensory event-related brain potentials were recorded in response to stimulation of the hand towards which gaze was directed (G+ trials) and in response to stimulation of the other hand (G- trials). When vision (V+) of the hand gaze was directed at was available (G+V+), an early positivity overlapping with the P45 and N 80 component was observed for G+V+ trials relative to G-V- trials. In contrast, when the hands were occluded from view (V-), an enhanced N 140 component followed by a late negativity was observed for G+V- as compared to G-V- trials. It is suggested that vision of the body part stimulated can modulate processing in primary somatosensory cortex (S1), while effects of gaze direction in the absence of vision of the body part touched are located in higher order somatosensory areas. Such effects of vision and gaze on tactile processing may be mediated by pathways from multimodal brain regions to somatosensory cortex.

Adult↗
PubMed2005

Covert manual response preparation triggers attentional shifts: ERP evidence for the premotor theory of attention.

The premotor theory of attention claims that the preparation of goal-directed action and shifts of attention are closely linked, because they are controlled by shared sensorymotor mechanisms. Until now, support for this theory has come primarily from studies demonstrating links between saccade programming and attention shifts. The present event-related brain potential (ERP) study demonstrated that attentional orienting processes are also elicited during the covert preparation of unimanual responses. ERPs were recorded in the interval between a visual response-hand selection cue and a subsequent visual Go/Nogo signal when participants prepared to lift their left or right index finger. Lateralised ERP components elicited during response preparation were very similar to components previously observed during instructed endogenous attention shifts, indicating that analogous attentional orienting processes are activated in both cases. Somatosensory ERP components (P90, N140) were enhanced when task-irrelevant tactile probes were delivered during response preparation to the hand involved in an anticipated response, even when probes were presented well in advance of response execution. These results suggest that attentional shifts are triggered during unimanual response preparation, as predicted by the premotor theory. This link between manual response programming and attention is consistent with the hypothesis that common mechanisms are involved in the control of attention and action.

Adult↗
PubMed2005

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.

Adult↗
PubMed2005

Electrophysiological correlates of change detection.

To identify electrophysiological correlates of change detection, event-related brain potentials (ERPs) were recorded while participants monitored displays containing four faces in order to detect a face identity change across successive displays. Successful change detection was mirrored by an N2pc component at posterior electrodes contralateral to the side of a change, suggesting close links between conscious change detection and attention. ERPs on undetected-change trials differed from detected-change and no-change trials. We suggest that short-latency ERP differences between these trial types reflect trial-by-trial fluctuations in advance task preparation, whereas differences in the P3 time range are due to variations in the duration of perceptual and decision-related processing. Overall, these findings demonstrate that ERPs are a useful tool for dissociating processes underlying change blindness and change detection.

Adult↗
PubMed2005

Cutaneous saltation within and across arms: a new measure of the saltation illusion in somatosensation.

A new objective procedure was used to measure the strength of cutaneous saltation, in order to clarify current debates about the nature of this illusion. Three taps were presented successively to three possible forearm locations. Participants attended to the middle location and reported whether a tap was perceived there. When all stimuli were delivered to the same arm and intertap intervals were short, participants were unable to distinguish real and illusory stimuli at the middle location. When both arms were stimulated, location judgments on one arm were shifted toward a tap subsequently delivered to the other arm. These results challenge the view that saltation is a purely attentional phenomenon, but they are inconsistent with the idea that this illusion is produced in the primary somatosensory cortex.

Adult↗
PubMed2004

The attentional selection of spatial and non-spatial attributes in touch: ERP evidence for parallel and independent processes.

To investigate the functional relationship between spatial and non-spatial attentional selectivity in somatosensory processing, event-related potentials (ERPs) were recorded to mechanical tactile stimuli, which were delivered to the right or left hand, and were low or high in frequency (Experiment 1), or soft or strong in intensity (Experiment 2). Participants' task was to attend to a specific combination of one stimulus location and one non-spatial attribute. Spatial attention was reflected in enhanced N140 components followed by a sustained attentional negativity. ERP effects of non-spatial attention (enhanced negativities to the attended frequency or intensity) were observed in the same latency range, suggesting that the attentional selection of relevant spatial and non-spatial attributes occurs in parallel. Most importantly, ERP correlates of attention directed to stimulus frequency and intensity were unaffected by the current focus of spatial attention. In contrast to vision, where the selective processing of non-spatial attributes is hierarchically dependent on selection by location, but similar to auditory attention, spatial and non-spatial attentional selectivity appear to operate independently in touch.

Adult↗
PubMed2004

Effects of hand posture on preparatory control processes and sensory modulations in tactile-spatial attention.

OBJECTIVE: Event-related brain potentials (ERPs) were measured to investigate spatial coordinate systems involved in the control of preparatory tactile-spatial orienting, and in subsequent attentional modulations of somatosensory processing. METHODS: On each trial, a visual precue directed attention to the left or right hand, where infrequent tactile targets had to be detected. Hands were positioned either close together or wide apart. ERPs were recorded in the cue-target interval and in response to attended and unattended tactile non-targets. RESULTS: A frontal anterior directing attention negativity (ADAN) and a posterior late directing attention positivity (LDAP) were elicited in the cue-target interval contralateral to the direction of an attentional shift. The ADAN was unaffected by hand posture, but the LDAP was attenuated when hands were close together. N140 amplitudes were enhanced in response to tactile stimuli presented to the attended hand, and this effect was more pronounced when hands were wide apart. CONCLUSIONS: ADAN and LDAP are linked to separable anterior and posterior attentional control systems, which use coordinate systems based on somatotopic and external space, respectively. Effects of spatial attention on somatosensory stimulus processing are affected by variations in body posture. SIGNIFICANCE: Our results demonstrate that representations of body locations in external space play a central role in the control of tactile attention.

Adult↗
PubMed2004

ERP evidence for cross-modal audiovisual effects of endogenous spatial attention within hemifields.

Previous ERP studies have uncovered cross-modal interactions in endogenous spatial attention. Directing attention to one side to judge stimuli from one particular modality can modulate early modality-specific ERP components not only for that modality, but also for other currently irrelevant modalities. However, past studies could not determine whether the spatial focus of attention in the task-irrelevant secondary modality was similar to the primary modality, or was instead diffuse across one hemifield. Here, auditory or visual stimuli could appear at any one of four locations (two on each side). In different blocks, subjects judged stimuli at only one of these four locations, for an auditory (Experiment 1) or visual (Experiment 2) task. Early attentional modulations of visual and auditory ERPs were found for stimuli at the currently relevant location, compared with those at the irrelevant location within the same hemifield, thus demonstrating within-hemifield tuning of spatial attention. Crucially, this was found not only for the currently relevant modality, but also for the currently irrelevant modality. Moreover, these within-hemifield attention effects were statistically equivalent regardless of the task relevance of the modality, for both the auditory and visual ERP data. These results demonstrate that within-hemifield spatial attention for one task-relevant modality can transfer cross-modally to a task-irrelevant modality, consistent with spatial selection at a multimodal level of representation.

Acoustic Stimulation↗
PubMed2004

Masked prime stimuli can bias "free" choices between response alternatives.

Stimuli presented below the threshold of awareness can systematically influence choice responses determined by the instructed stimulus-response (S-R) mapping (task set). In this study, we investigated whether such stimuli will also bias a free choice between two response alternatives under conditions in which this choice subjectively appears to be internally generated and free. Participants had to respond to targets preceded by masked arrow primes. Left-pointing and right-pointing arrow targets required left or right responses, whereas randomly interspersed "free-choice" targets indicated that the participants were free to choose either response. Although masked primes could not be consciously discriminated, they systematically affected not only performance to arrow targets, but also the free choice between response alternatives. This demonstrates that apparently "free" choices are not immune to nonconsciously triggered biases. However, in blocks in which no specific S-R mapping was imposed, masked primes did not affect free-choice performance, indicating that these effects are not automatic but are determined by currently active task sets.

Adolescent↗
PubMed2003

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.

Adult↗
PubMed2003

Response facilitation and inhibition in subliminal priming.

The research reviewed in this article has investigated with behavioural, electrophysiological, and functional imaging methods how subliminally presented masked prime stimuli affect response-related processes. An initial response activation triggered by these primes was found to be followed by an inhibition of this response tendency, provided that the initial activation was strong enough to exceed an 'inhibition threshold'. This biphasic pattern is assumed to reflect the presence of self-inhibitory circuits in motor control. In contrast to endogenous response inhibition, observed when response-relevant signals are consciously perceived, this exogenous mode of response inhibition appears to be mediated by corticostriate rather than by prefrontal mechanisms. Overall, results demonstrate that inhibitory mechanisms are involved in the control of response processes, even when motor activations are triggered by stimuli that are not accessible to conscious awareness.

Dominance, Cerebral↗