Biomedical subjects

M Eimer

Publications and source records attributed to M Eimer.

At least 37 records · Page 2Linked to original sources

PubMed2000

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.

Adult↗

PubMed1999

Prosopagnosia and structural encoding of faces: evidence from event-related potentials.

Event-related brain potentials (ERPs) were recorded in response to unfamiliar faces and to houses from a severely prosopagnosic patient (PHD) and 24 control subjects. For all control subjects, faces elicited an enhanced negativity at lateral temporal electrodes (N170). This component was absent for PHD. Comparable results were obtained in response to inverted faces and houses. A selective deficit in face recognition is therefore reflected by abnormalities in ERP components specific to faces. As PHD was shown to have substantial deficits on tasks requiring the structural analysis of faces, these findings are consistent with the view that the N170 reflects processes involved in the structural encoding of faces, and may be a measure of selective impairments in the analysis of face components.

Adult↗

PubMed1999

On the relation between brain potentials and the awareness of voluntary movements.

We investigated the relation between neural events and the perceived time of voluntary actions or the perceived time of initiating those actions using the method of Libet. No differences were found in either movement-related potentials or perceived time of motor events between a fixed movement condition, where subjects made voluntary movements of a single finger in each block, and a free movement condition, in which subjects chose whether to respond with the left or the right index finger on each trial. We next calculated both the readiness potential (RP) and lateralised readiness potential (LRP) for trials with early and late times of awareness. The RP tended to occur later on trials with early awareness of movement initiation than on trials with late awareness, ruling out the RP as a cause of our awareness of movement initiation. However, the LRP occurred significantly earlier on trials with early awareness than on trials with late awareness, suggesting that the processes underlying the LRP may cause our awareness of movement initiation.

Adult↗

PubMed1999

Facilitatory and inhibitory effects of masked prime stimuli on motor activation and behavioural performance.

Three experiments investigated the impact of information provided by masked stimuli on motor activation. Masked primes were presented prior to target stimuli and these primes were identical to the target on compatible trials, identical to the target mapped to the opposite response on incompatible trials and task-irrelevant on neutral trials. A previous study [Eimer, M., & Schlaghecken, F. (1998). Effects of masked stimuli on motor activation: Behavioural and electrophysiological evidence. Journal of Experimental Psychology: Human Perception and Performance, 24, 1737-1747] found performance costs for compatible trials and benefits for incompatible trials. Experiment 1 showed that these effects are not due to 'perceptual repetition blindness'. Experiments 2 and 3 obtained evidence for an initial response facilitation triggered by the primes that was followed by inhibition. With short intervals between prime presentation and response execution, performance benefits were found for compatible trials and these turned into costs at longer intervals. It is argued that an early response facilitation mediated by direct perceptuo-motor links is subsequently inhibited by a central mechanism operating to prevent behaviour from being controlled by irrelevant information.

Adult↗

PubMed1999

Can attention be directed to opposite locations in different modalities? An ERP study.

OBJECTIVES: An event-related brain potential (ERP) study investigated whether spatially selective processing in vision and audition is controlled by a single supramodal system or by independent modality-specific systems. METHODS: Event-related brain potentials were recorded in response to visual and auditory stimuli at attended and unattended locations. In the 'Attend Same' condition, attention was directed to a single location in both modalities, while in the 'Attend Opposite' condition, visual and auditory attention had to be directed into opposite directions. RESULTS: Sensory-specific effects of attention on visual and auditory ERPs reflecting attentional modulations of perceptual processing were obtained in the 'Attend Same' condition, but not the 'Attend Opposite' condition. Beyond 200 ms post-stimulus, attentional ERP effects were also found in the 'Attend Opposite' condition. CONCLUSION: Results are inconsistent with the view that spatially selective processing is controlled by independent modality-specific systems. Effects of spatial attention on visual and auditory perceptual processing are closely linked, suggesting the existence of a supramodal attentional control system. At post-perceptual levels, attentional control may be more flexible.

Adult↗

PubMed1999

Attending to quadrants and ring-shaped regions: ERP effects of visual attention in different spatial selection tasks.

Attentional modulations of event-related brain potentials (ERPs) were measured when subjects were cued to attend to a visual quadrant or to a ring-shaped region of visual space to detect infrequently presented targets within the attended region. Spatial attention directed to quadrants was reflected in modulations of sensory-evoked P1 and N1 components at lateral posterior sites and enhanced negativities (Nds) at midline electrodes that started around 150 ms poststimulus. When attention was directed to ring-shaped regions, no modulations of P1 and N1 amplitudes were found, and Nd effects observed at midline electrodes were delayed by about 50 ms. These findings indicate that behavioral effects observed both when attention is directed to contiguous regions and to general areas of visual space may be caused by different underlying processes. Intraperceptual "sensory gating" mechanisms operating in a way suggested by the notion of an attentional "zoom-lens" may be responsible for the selection of single regions, quadrants, or hemifields. When relevant regions are more complex, spatial selectivity will affect primarily postperceptual processes.

Adult↗

PubMed1998

Does the face-specific N170 component reflect the activity of a specialized eye processor?

Event-related brain potentials (ERPs) to intact faces and to faces without eyes were compared to ERPs elicited by houses to find out whether the face-specific N170 component reflects the activity of a cortical eye processor. When compared to houses, face stimuli elicited a posterior negativity (N170) and a frontocentral positivity. N170 amplitude was not affected by the presence or absence of eyes, but N170 was delayed in response to faces without eyes. It is concluded that the N170 is not directly related to the activity of cortical regions sensitive to the presence of eyes, and is more likely to reflect processes involved in the structural encoding of face components.

Adult↗

PubMed1998

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.

Acoustic Stimulation↗

PubMed1998

Effects of masked stimuli on motor activation: behavioral and electrophysiological evidence.

Three experiments investigated the influence of unperceived events on response activation. Masked primers were presented before a target. On compatible trials, primes and targets were identical; on incompatible trials, opposite responses were assigned to them. Forced-choice performance indicated that prime identification was prevented by the masking procedure, but overt performance and motor activation as mirrored by the lateralized readiness potential (LRP) were systematically influenced by the prime. The direction of these effects was unexpected: Performance costs for compatible and performance benefits for incompatible trials were obtained relative to a neutral trial condition. The LRP revealed a sequential pattern of motor activation. A partial activation of the response corresponding to the prime was followed by a reverse activation pattern. It is argued that these effects primarily reflect an inhibition of the response initially triggered by the prime.

Adult↗

PubMed1997

Uninformative symbolic cues may bias visual-spatial attention: behavioral and electrophysiological evidence.

Event-related brain potentials and response latencies were measured in an experiment where centrally presented arrow cues were followed by left or right visual target stimuli. In one condition, target location was indicated by the cues with 75% validity. In another condition, the precues were uninformative with respect to target location. Faster response times and larger negativities in the ERPs at midline electrodes were measured for targets at cued locations following informative cues, but also with uninformative precues. This indicates that visual-spatial attention may be biased involuntarily by central symbolic precues.

Adult↗

PubMed1997

An event-related potential (ERP) study of transient and sustained visual attention to color and form.

Event-related potential (ERP) effects of transient and sustained non-spatial visual attention were investigated in an experiment where subjects were instructed to attend to the color or form of visual stimuli in order to detect infrequently presented targets with the relevant feature. The to-be-attended feature was either varied in a trial-by-trial fashion (transient attention) or was kept constant for an entire experimental block (sustained attention). Both transient and sustained attention resulted in a larger negativity for attended as compared to unattended stimuli between 200 and 300 ms post-stimulus. This effect was more pronounced for sustained attention than for transient attention and larger for attention to color than for attention directed to stimulus form. In the sustained, but not in the transient attention condition, color attention resulted in larger positivities for attended stimuli between 150 and 200 ms and in the P3 time range. These effects are interpreted as evidence for the existence of non-spatial attentional selection processes that are more effective under sustained than under transient attention conditions and are different from processes of visual-spatial attention. Moreover, the results indicate a special status for sustained attention to stimulus color.

Adult↗

PubMed1997

Attentional selection and attentional gradients: an alternative method for studying transient visual-spatial attention.

In two experiments, I employed an alternative method for studying transient visual-spatial attention. Instead of using precues, attention was manipulated by presenting most stimuli sequentially at predictable locations. In Experiment 1, most stimuli appeared in a regular clockwise or counterclockwise order, but some were separated by one or both visual meridians from the expected location. In Experiment 2, most stimuli were presented successively along the horizontal meridian, and some stimuli were separated by one, two, or three positions from the expected location. Faster response times and larger posterior P1 and N1 components as well as enhanced negativities at midline electrodes were found for expected-location than for unexpected-location stimuli. These effects were partially modulated by the distance of unexpected stimuli from the current focus of attention, suggesting the existence of attentional gradients. Moreover, the data suggest that the direction of previous attentional shifts and the visual meridians play an important role for spatial attention.

Adult↗

PubMed1996

Effects of lateralized cues on the processing of lateralized auditory stimuli.

We examined the influence of auditory spatial cues on the processing of subsequently presented lateralized auditory target stimuli. In three experiments, effects of the position of the cue on event-related potentials (ERPs) and reaction times (RTs) to the target, which could occur at the same or at a different position to the cue, were examined. In Experiments I and II, stimulus-pairs were delivered via loudspeakers 13 degrees to the right or left of fixation. The cue was task-irrelevant in the sense that it never required a response, whereas the target was task-relevant. In Experiment I, the cue was not informative about the position of the succeeding target, that is, the target was presented at the same or at a different position to the cue with equal probability. In Experiment II, the cue predicted a target with high validity, occurring at the position opposite to the cue. In both experiments, the ERPs to targets presented at the same position as the preceding cue were negatively modulated compared with the ERPs to targets presented at a different position. This negative difference (Nd) between the ERPs to same and different position stimuli occurring between 200-300 ms relative to target onset was also obtained in situations where no overt behavior was required. Effects of cue position on RTs to the target were only observed in Experiment II, being shorter for validly predicted targets. These Nd effects either reflect refractoriness of location-specific exogeneous ERP components or involuntary attentional selection. In order to decide between these alternatives, a third experiment was performed, in which stimulus-pairs were presented via headphones to the left and right ear in attend and ignore condition. An Nd effect was obtained in the attend condition only. The absence of Nd effects in the ignore condition suggests that the Nd obtained in attend condition cannot completely be explained by refractoriness of exogeneous ERP components and thus reflects attentional processes.

Adult↗

PubMed1996

The N2pc component as an indicator of attentional selectivity.

Event-related potentials (ERPs) were recorded during visual discrimination tasks in which stimulus arrays were presented that contained one lateral target and 3 (experiment 1) or one (experiments 2 and 3) non-targets. In experiments 1 and 2, targets differed from non-targets with respect to their form or their color. In experiment 3, word pairs were presented, with targets differing from non-targets with respect to their content. Subjects were required to respond to the identity of the target. In all experiments, an enhanced negativity was elicited at posterior electrodes contralateral to the location of the target. In the form discrimination tasks, this effect was present in the N1, N2, and P3 time intervals. In the color discrimination tasks, it was confined to the N2 time range. In the word discrimination task (experiment 3), this effect could only be observed over the left posterior hemisphere. It is argued that these lateralized negativities reflect the N2pc component that is assumed to indicate attentional filtering processes during visual search tasks. The present results extend this assumption by showing that this component is also elicited when targets are presented together with just one non-target item. It is argued that the N2pc may reflect the attentional selection of task-relevant stimuli.

Adult↗

PubMed1996

Explicit and implicit learning of event sequences: evidence from event-related brain potentials.

Event-related brain potentials (ERPs) were recorded during a serial reaction time (RT) task, where single deviant items seldom (Experiment 1) or frequently (Experiment 2) replaced 1 item of a repeatedly presented 10-item standard sequence. Acquisition of sequence knowledge was reflected in faster RTs for standard as compared with deviant items and in an enhanced negativity (N2 component) of the ERP for deviant items. Effects were larger for participants showing explicit knowledge in their verbal reports and in a recognition test. The lateralized readiness potential indicated that correct responses were activated with shorter latencies after training. For deviant items, participants with explicit knowledge showed an initial activation of the incorrect but expected response. These findings suggest that the acquisition of explicit and implicit knowledge is reflected in different electrophysiological correlates and that sequence learning may involve the anticipatory preparation of responses.

Adolescent↗

PubMed1996

ERP modulations indicate the selective processing of visual stimuli as a result of transient and sustained spatial attention.

Two experiments investigated selective processing as a result of transient and sustained visual-spatial attention. In Experiment 1, attention was cued on a trial-by-trial basis and event-related brain potentials were measured to stimuli preceded by valid, invalid, or neutral symbolic precues. Trial validity had only small effects on posterior P1 and N1 components. At midline electrodes, an enhanced negativity for valid as compared with invalid trials was present, which appeared to reflect initial processing costs for invalid trials followed by an additional processing benefit for valid trials. Experiment 2 investigated whether these effects are specific for transient spatial attention by comparing transient and sustained attention conditions. No indication of early processing costs was found in the latter case.

Adult↗

PubMed1995

The location of preceding stimuli affects selective processing in a sustained attention situation.

Event-related potentials (ERPs) were recorded to visual and auditory stimuli in a situation where subjects were required to attend selectively to the left or right side for an entire experimental block and to detect occasional target stimuli at attended locations. Stimuli were presented randomly at attended and unattended locations. In exp. 1, visual and auditory stimuli were presented in separate blocks, while in exp. 2, they were presented together and subjects had to detect visual targets at attended locations. Stimuli at attended positions elicited enlarged sensory-evoked potentials and an enhanced negativity at midline electrodes as compared with unattended stimuli. The latter effect was, however, modulated by the location of the preceding stimulus. At frontocentral electrodes, it was larger for stimuli that were preceded by stimuli at the contralateral side as compared with stimuli preceded by stimuli at the same location. It is argued that this effect may be due to a different amount of processing required for the preceding stimulus. When the predecessor is at a to-be-attended location, it has to processed more intensively which may interfere with the processing of the next stimulus.

Acoustic Stimulation↗

PubMed1995

Event-related potential correlates of transient attention shifts to color and location.

Effects of selectively attending to specific combinations of stimulus location and color were measured by means of event-related brain potentials in a trial-by-trial cueing paradigm. A symbolic precue was presented at the beginning of each trial indicating the response-relevant position and color of an upcoming imperative stimulus. Responses were required to infrequent target stimuli of the relevant color appearing at the cued location. Stimuli at attended locations elicited enhanced posterior N1/components as well as enhanced negativities at midline electrodes. No P1 enhancement was found for stimuli at the attended location. Attended color stimuli elicited a broad negativity starting about 220 ms that tended to be larger for stimuli presented at attended locations. These results show that transient attention shifts to non-spatial features like color are reflected by event-related potential (ERP) effects comparable to the effects measured under sustained attention conditions. Transient spatial attention yields earlier and larger ERP effects than transient attention to color and may modulate the ERP effects of non-spatial attention.

Adult↗