The nature of selective attention effects on auditory event-related potentials

The purpose of the research reported here was to examine a number of issues relating to the nature of selective attention effects on auditory event-related potentials (ERPs), namely, to determine the relative contribution of N1 and slow wave (SW) to the early and late components of Nd respectively, where Nd is defined as the negative shift of attended ERPs relative to unattended ERPs; to examine whether individual differences in Nd morphology are related to performance and the strategies that subjects use; and to determine the contribution of changes in the attended and unattended ERPs to Nd. Auditory ERPs were recorded from subjects as they carried out an auditory selective attention task and a visual target detection task. The auditory selective attention task was a multidimensional task in which stimuli varied on location, pitch and duration and in which the subject's task was to pay attention to a particular location/pitch combination and respond whenever they detected a long-duration target tone. In the visual target detection task, subjects were required to respond whenever they detected a colour change in a light-emitting diode which also acted as a fixation point. Auditory ERPs recorded during the visual task were used to provide a measure of exogenous components uncontaminated by differential effects of selective processing of auditory stimuli. The results suggested that early Nd and N1 are independently generated as Nd did not exhibit the contralateral scalp focus typical of N1, and that late Nd is independent of SW. While substantial differences in Nd morphology were observed over subjects, these differences showed no consistent relationships to performance or to task strategies. Comparison of auditory ERPs during active auditory attention with auditory ERPs recorded during the visual control task indicated that there was an early negative shift of the attended ERP, a later negative shift of the attended ERP which had a frontal focus and a later positive shift of the unattended ERP. These results suggest that there are active processes involved in the processing of stimuli from both the attended and unattended source.     

Somatosensory Evoked Potential Changes With a Selective Attention Task

Somatosensory evoked potential (SEP) changes associated with selective attention were investigated. In 16 subjects, SEPs were recorded from five locations while they counted electrical stimuli to one of four randomly stimulated fingers. Sequential SEP events measured included peaks P30 (positivity at 30 msec). P45, N60, P100. N140. P190. N230, P400. Counting was associated with greater P45, P100. P190, N230, and P400 amplitudes; effects were not attributable to eye or tongue activity. Analyses designed to reveal changes associated with two conceptualized “channels” (finger class, hand) showed that the P45, P100, and P190 amplitude increases involved both channels. The P400 effect was limited to the target finger. Channel effects for N60 and N140 amplitudes resulted from decreases localized to the unattended element of one channel, suggesting “inhibition.” Latency effects involved mainly the hand channel; counted hand latencies were shorter for P30, P45, P100 and P190. The findings indicate modifications of both early and late electrocortical events with selective attention, and that changes can be of several kinds. They support the view that attention proceeds in more than one stage.     

Modification of sudden onset auditory ERP by involuntary attention to visual stimuli.

To investigate the cross-modal nature of the exogenous attention system, we studied how involuntary attention in the visual modality affects ERPs elicited by sudden onset of events in the auditory modality. Relatively loud auditory white noise bursts were presented to subjects with random and long inter-trial intervals. The noise bursts were either presented alone, or paired with a visual stimulus with a visual to auditory onset asynchrony of 120 ms. In a third condition, the visual stimuli were shown alone. All three conditions, auditory alone, visual alone, and paired visual/auditory, were randomly inter-mixed and presented with equal probabilities. Subjects were instructed to fixate on a point in front of them without task instructions concerning either the auditory or visual stimuli. ERPs were recorded from 28 scalp sites throughout every experimental session. Compared to ERPs in the auditory alone condition, pairing the auditory noise bursts with the visual stimulus reduced the amplitude of the auditory N100 component at Cz by 40% and the auditory P200/P300 component at Cz by 25%. No significant topographical change was observed in the scalp distributions of the N100 and P200/P300. Our results suggest that involuntary attention to visual stimuli suppresses early sensory (N100) as well as late cognitive (P200/P300) processing of sudden auditory events. The activation of the exogenous attention system by sudden auditory onset can be modified by involuntary visual attention in a cross-model, passive prepulse inhibition paradigm.     

The Effects of Spatial Selective Attention on the Somatosensory Event-Related Potential

Event-related potentials (ERPs) were recorded during a selective attention task involving weak or strong electrical stimuli delivered to the index fingers of the left and right hands. In an attend weak condition, subjects were asked to count the number of weak stimuli (targets) interspersed amongst strong stimuli (standards) delivered to a designated hand, whilst ignoring a similar set of stimuli delivered to the other hand. In an attend strong condition, subjects were asked to count the number of strong targets interspersed amongst weak stimuli. In both conditions, targets and standards occurred with probabilities of .10 and .40 respectively on each hand. Counting weak targets was found to be more difficult than counting strong targets. The latency of the earliest significant effect of selective attention on ERPs to standards was dependent on stimulus intensity: N80 in the case of weak standards, P105 for strong standards. There was no evidence of a later prolonged negative shift in attended standard ERPs. Rather, an enhanced N150 component post-centrally was followed by a prolonged positive shift of attended standard ERPs. This Late positive shift had a similar scalp distribution to the late positive component elicited by attended target stimuli.     

A modified selective attention auditory event-related potential paradigm suitable for the clinical setting

Auditory event-related potentials (ERPs) were recorded without practice sessions using a selective attention ERP paradigm modified from Hillyard et al. (1973) in 20 normal individuals who varied across wide ranges of age and educational background. The results concur with previous findings concerning the effects of selective attention on both the earlier and later phases of the ERP waveform. Attended stimuli elicited a larger N1 deflection compared with unattended stimuli. Processing negativity was also elicited by attended stimuli, but not by unattended stimuli. Mismatch negativity (N2) was evident in waveforms to signals as compared with standards, and a late positivity (P3) followed N2 only in waveforms to attended signals. This paradigm may be appropriate for evaluating suspected attentional dysfunctions in clinical populations.     

Selective Attention in Auditory Processing as Reflected by Event-Related Brain Potentials

Measures of event-related brain potentials (ERPs) have revealed two kinds of selective-attention mechanisms that operate on attended and unattended auditory stimuli. The processing negativity of the ERP reveals a mechanism of intramodal selective attention in the auditory cortex controlled by the frontal cortex. This mechanism selects attended auditory stimuli for further processing when they differ from unattended stimuli in location or tonal frequency. Studies of intermodal selective attention have compared auditory ERPs during auditory and visual attention. At least in part different brain mechanisms may be involved in the selection of auditory stimuli among other auditory stimuli (intramodal selective attention) and in the selection of auditory stimuli among visual stimuli (intermodal selective attention). This is suggested by the results showing that the earlier component of the processing negativity, which is generated in the auditory cortex during intramodal selective attention, differs in scalp distribution from the early attention-related negativity elicited during intermodal selective attention. With respect to the unattended auditory stimuli, ERP studies of selective attention suggest that physical features of these stimuli are extensively processed. This is shown by the mismatch negativity component of the ERP, which is usually elicited by infrequent physical deviations in an auditory stimulus sequence both when this sequence is attended and when it is ignored. This would be impossible if the physical stimulus features were not extensively processed, even in the absence of attention.     

Event-related potentials (ERPs) to hemifield presentations of emotional stimuli: differences between depressed patients and healthy adults in P3 amplitude and asymmetry.

Depression may involve dysfunction of right parietotemporal cortex, a region activated during perception of affective stimuli. To further test this hypothesis, event-related brain potentials (ERPs) were measured in a paradigm previously shown to produce ERP asymmetries to affective stimuli over parietal sites in healthy adults. Pictures of patients with dermatological diseases showing disordered or healed facial areas before (negative) or after (neutral) surgical treatment were briefly exposed for 250 ms to either the left or right hemifield. ERPs of 30 unmedicated, unipolar depressed patients and 16 healthy adults, all right-handed, were recorded from 30 electrodes. A principal components analysis extracted factors which closely corresponded to distinctive ERP components previously reported for this task (N1, N2, early P3, late P3, slow wave). Significant effects of emotional content, i.e. enhanced amplitudes to negative than neutral stimuli, were found for early and late P3. Control subjects showed significant hemispheric asymmetries of emotional processing for late P3 (peak latency 460 ms), with the largest emotional content effects over the right parietal region. In striking contrast to control subjects, depressed patients did not show an increase in late P3 for negative compared to neutral stimuli over either hemisphere and had smaller late P3 amplitude than control subjects. Patients did, however, show larger early P3 (peak latency 330 ms) to negative than neutral stimuli. Results suggest intact early discrimination but abnormal late appraisal of affective content in depression, which may arise from selective inhibition of right parietal regions integral for perceiving and evaluating emotional stimuli.     

Prepulse effects as a function of cortical projection system

A putative gating mechanism reduces startle blink, midline scalp potentials beginning with P50, and perceived loudness of startling stimuli. Tactile prestimuli were paired with auditory startle stimuli to determine if: (1) P50 inhibition is due to an extrinsic mechanism, (2) pairing differentially affects potentials reflecting modality specific and nonspecific system activity, and (3) crossmodal pairing modifies perceptual magnitudes of both pair members. Stimuli were presented alone and in pairs separated by 60 or 360 ms. Event-related potentials (ERPs) were recorded from midline and lateral sites; EMG was recorded from several facial and scalp muscles. Pairing reduced blink, and midline P50, N100 and P200 amplitudes; reductions were greater at the longer interval. P30 was largely unaffected by pairing. Pairing also differentially affected lateral N100 components reflecting later activity in specific and nonspecific systems. Results show that prestimulus inhibition of ERPs is not due to intrinsic refractoriness and that pairing differentially affects ERPs associated with modality specific and nonspecific projection systems.     

Intermodal selective attention: Evidence for processing in tonotopic auditory fields

Auditory event-related brain potentials (ERPs) were recorded for 250- and 4,000-Hz tone bursts in an intermodal selective attention task. Tonotopic changes were evident in the scalp distribution of the rising phase of the auditory N1 (mean peak latency 116 ms); the N1 was more frontally distributed following the 4,000-Hz than following the 250-Hz tone bursts, and it included a contralateral P90 component that was absent following 250-Hz tones. ERPs related to intermodal selective attention were isolated as negative and positive auditory difference waves (Nd_a and Pd_as). Neither the Nd_a nor the Pd_a showed changes in distribution with tone frequency, but both showed Ear × Frequency changes in distribution. ERPs for deviant tones included mismatch negativities (MMNs) and, in attend auditory conditions, N2b and P3 components. These components did not change in scalp distribution with tone frequency. One possible explanation is that tonotopic displacements of ERP distributions on the scalp surface depend on angular displacements in generator fields on gyral convexities. The results are consistent with the possibility that auditory processing radiates outward with increasing latency from tonotopic fields on Heschl's gyri to more gyrus-free regions of the planun temporale and anterior superior temporal plane.     

An ERP study of visual spatial attention and letter target detection for isoluminant and nonisoluminant stimuli

The event-related potential (ERP) effects of visual spatial attention and letter target detection for stimuli presented against a (nonisoluminant) dark background or against an isoluminant grey background were investigated. The goal was to study how the perceptual variable of luminance would influence early ERP reflections of selective attention. Such effects could further substantiate the claim that selective attention operates at the level of early perceptual processing and could provide evidence regarding the role of different visual routes in selective attention. Isoluminance increased the peak latency of the early ERP deflections (NP80, PI, and NI) by 40–50 ms. The ERP effects of spatial attention. consisting of PI and NI amplitude enhancements, were similarly delayed by isoluminance. supporting the idea that early selective processing is strongly dependent on bottom-up perceptual processing. P300 latency and reaction time were delayed by 70–75 ms, the additional delay probably reflecting that isoluminance affected decision processes in addition to perceptual processes. Isoluminance left the scalp topographies of the early ERP deflections largely unaffected, although a slight shift of the NI topography in the isoluminant condition toward more inferior lateral posterior regions of the scalp could have reflected an increased contribution from ventral (occipitotemporal) brain areas. Relative to nontarget letters, targels presented at both attended and unattended spatial positions elicited an early contralaterally dominant lateral occipitotemporal negativity (N2pc). This ERP component is proposed to reflect an early, partly automatic process of template matching, consistent with indications from spatiotemporal dipole modelling that the N2pc was generated in inferior occipitotemporal brain regions.     

ERP indices of auditory selective attention in aging and Parkinson's disease

In the present study, we compared the performance of normal subjects in three age groups and of medicated Parkinson's disease patients on auditory selective attention processes. Two tone sequences were dichotically presented. Subjects responded to deviant tones in the attended location. Event-related potentials (ERPs) were recorded from nine scalp electrodes. The old group showed significant decline in hit rate, increase in N1 amplitude, and reduction in P3a, P3b, target negativity, and mismatch negativity amplitude. The amplitude and duration of late Nd increased with age, reflecting modulation of both attended and unattended standard ERPs. Although the middle group showed a similar pattern of ERP changes, the effects were generally nonsignificant. The Parkinson's disease group showed little further disruption of behavioral or ERP measures. However, Parkinson's disease affected late Nd in the direction opposite of that of aging, reflecting differential modulation of unattended standard positivity.     

Short latency cerebral response evoked by painful electrical stimulation applied to the human sigmoid colon and to the convergent referred somatic pain area

Background. The brain-gut interaction is important for the understanding of pain mechanisms related to gastroenterological diseases. Unfortunately little is known about the early cerebral events related to the processing of gut-evoked pain. The aims of this human study were (1) to investigate the early-evoked brain potentials (EPs) to painful sigmoid colon stimulation and (2) to evaluate the EPs evoked from the convergent referred skin pain area after this area was induced by the painful gut stimulation. The background for the second aim was to evaluate whether the convergent input between somatic and visceral structures could induce detectable short-term cortical reorganization. Methods. Eleven subjects (nine men) participated; the mean age was 39.5±11.9 years. The gut-evoked EPs (recorded from 31 scalp sites) were evoked by electrical stimulation 30 cm from the anal verge by a modified biopsy forceps, inserted through a sigmoidoscope. The painful gut stimulation elicited a characteristic pain pattern referred to the abdomen. The short latency somatosensory evoked potentials were evoked from the skin inside and outside the referred pain area elicited by gut stimulation. A total of 750 electrical stimuli were delivered to the gut at slight painful stimulus intensity and 500 stimuli were delivered to the skin. Results. Short-latency EPs to electrical gut stimulation with an onset of 50–60 ms could be recorded. The gut EP topography revealed three consecutive positive peaks (P63, P101, P145) towards the frontal area. Centroparietal negativities (N128 and N222) were found, which were followed by two central positivities (P269 and P352). The somatic and gut evoked EPs differed in morphology and topography, but the EPs to skin stimulation inside and outside the gut-evoked referred pain area did not differ significantly. Conclusion. Short latency (50–60 ms) EPs to painful electrical sigmoid colon stimulation were demonstrated, reflecting an early cortical processing of sensory input from the sigmoid colon. The early cortical processing of somatic input from experimentally evoked visceral referred pain areas did not cause any detectable short-term cortical reorganization.     

The effect of category learning on visual attention and visual representation

Subordinate‐level category learning recruits neural resources associated with perceptual expertise, including the N250 component of the ERP, a posterolateral negative wave maximal between 230 and 330 ms. The N250 is a relatively late visual ERP and could plausibly be driven by attention to the features of categorized objects. Indeed, it has a latency and scalp distribution similar to the selection negativity (SN), an ERP component long known to be sensitive to attentional selection of target features. To clarify sensitivity of the N250 to attention and to more generally investigate the effect of category learning on attentional modulation of learned features, we independently manipulated subordinate‐level category learning and target detection in a speeded paradigm designed to optimally elicit the SN and accompanying frontal selection positivity (FSP). Participants first practiced categorizing a set of artificial animal stimuli and then performed a speeded target detection task on trained and untrained stimuli while ERPs were recorded. SN and FSP were roughly linearly related to the number of target features in the stimulus. Trained stimuli elicited a significantly larger N250 than untrained stimuli. The SN and N250 effects were additive, with all levels of target similarity equally affected by training, and had different time courses. Training had little effect on the FSP. The results suggest that (a) the N250 and SN have different sources, and (b) at the very least, the learning‐induced N250 indexes a different attentional subprocess from the target‐induced SN and could be driven by a different cognitive process altogether.     

Effects of stimulus intensity increase on short-latency somatosensory evoked potentials: Application of polynomial curvature coefficients

Summary We assessed the influence of increasing stimulus intensity from motor threshold to pain threshold on short latency somatosensory evoked potentials recorded over the parietal and frontal scalp in 14 subjects during median nerve stimulation at the wrist. We used the curvature polynomial coefficient to evaluate alterations of the main components. The N20 and P27 curvature coefficients are not modified. The change of the N30 curvature coefficient is the result of shortened P45 latency. The increase of N60 curvature coefficient shows a great interindividual variability, probably due to a central amplification and synchronization or to involvement of nerve fibres with different excitability.     

Effects of pain-related anxiety on components of the pain event-related potential

The aim of this study was to investigate whether components of pain event-related potentials (ERPs) are modulated by anxiety. Pain ERPs in response to electrical stimulation were collected from 14 healthy individuals in a neutral condition and a condition where pain-related anxiety was induced. The amplitude of the N140 component of the ERP was found to be larger in the anxiety condition than the neutral condition. Arousal, as indicated by alpha power, did not differ between conditions. Differences in valence and focused attention to the painful stimuli may account for the increases in the N140 in the anxiety condition.     

Attention‐dependent sound offset‐related brain potentials

When performing sensory tasks, knowing the potentially occurring goal‐relevant and irrelevant stimulus events allows the establishment of selective attention sets, which result in enhanced sensory processing of goal‐relevant events. In the auditory modality, such enhancements are reflected in the increased amplitude of the N1 ERP elicited by the onsets of task‐relevant sounds. It has been recently suggested that ERPs to task‐relevant sound offsets are similarly enhanced in a tone‐focused state in comparison to a distracted one. The goal of the present study was to explore the influence of attention on ERPs elicited by sound offsets. ERPs elicited by tones in a duration‐discrimination task were compared to ERPs elicited by the same tones in not‐tone‐focused attentional setting. Tone offsets elicited a consistent, attention‐dependent biphasic (positive‐negative—P1‐N1) ERP waveform for tone durations ranging from 150 to 450 ms. The evidence, however, did not support the notion that the offset‐related ERPs reflected an offset‐specific attention set: The offset‐related ERPs elicited in a duration‐discrimination condition (in which offsets were task relevant) did not significantly differ from those elicited in a pitch‐discrimination condition (in which the offsets were task irrelevant). Although an N2 reflecting the processing of offsets in task‐related terms contributed to the observed waveform, this contribution was separable from the offset‐related P1 and N1. The results demonstrate that when tones are attended, offset‐related ERPs may substantially overlap endogenous ERP activity in the postoffset interval irrespective of tone duration, and attention differences may cause ERP differences in such postoffset intervals.     

Developmental Evidence for Modality-Dependent P300 Generators: A Normative Study

The behavior of the early and late components of the event-related brain potential (ERP) elicited by auditory and visual stimuli was studied in 40 normal females between the ages of 7 and 20. The ERPs were collected using two different tasks (i.e.,count and reaction time) in an oddball paradigm. Analysis of the early component (i.e., N1, P2, N2) latencies revealed small but significant decreases with age in the visual modality but no change in the auditory modality. Except for the visual N1, early component amplitudes did not change significantly over this age range. The results showed that auditory and visual P300 latencies, but not amplitudes, changed at significantly different rates over this age range. P300 latencies in the auditory modality showed a relatively abrupt change around age 12, after which P300 latencies changed little and were essentially at their adult levels. The latencies of visual P300s showed a much smaller and more steady decrease with age. Thus visual P300 latencies were shorter than auditory P300s in young children but longer than auditory P300s in older children. Significantly different scalp distributions were found for auditory and visual P300s. Although all P300 activity was maximal over parietal scalp, visual P300s were significantly larger than auditory P300s over central and frontal scalp. The developmental differences, combined with the presence of significantly different scalp topographies for auditory and visual P300s, provide convergent evidence that P300 activity is not independent of the modality of the eliciting stimulus.     

Olfactory, auditory, and visual ERPs from single trials: no evidence for habituation.

Event-related potentials (ERPs) using olfactory, auditory, and visual stimuli were recorded from young adults to assess possible component habituation across single trials among modalities. A single-stimulus ERP paradigm was used that employed a 10-min inter-stimulus interval (ISI) to minimize possible sensory adaptation and three stimulus trials for each modality to assess initial habituation effects. The present findings were: (1) P3 amplitude does not habituate appreciably over the initial three trials but may increase from the first to second trial. (2) ERPs from a single-stimulus paradigm with a very long ISI produce significantly correlated component amplitudes for the olfactory, auditory, and visual modalities. (3) P3 amplitude from olfactory stimuli demonstrated scalp topography similar to that for auditory and visual ERPs. These findings suggest that the single-stimulus task using a long ISI produces highly comparable and stable P3 components from olfactory, auditory, and visual stimuli. Application of single-stimulus paradigm to olfactory ERP methods is supported.     

Effects of corollary discharge on event-related potentials during selective attention task in healthy men and women

Corollary discharge is a brain electrical activity associated with self-monitoring, which distinguishes self from others in thoughts or behaviors. Corollary discharge can be non-invasively assessed using event-related potential (ERP) recordings in humans. Previous studies have revealed that the amplitude of the N100 component elicited during an "odd-ball" task is reduced while a healthy subject is vocalizing, which may index the effect of corollary discharge on auditory ERPs. In this study, we attempted to assess the effect of vocalization on ERP components including N100, mismatch negativity (MMN), negative difference wave (Nd), and P300 during a selective attention task in 22 healthy adults. We also evaluated the possible contribution of gender to these effects. N100 amplitudes elicited by unattended standard stimuli were reduced under the vocalization condition compared with those under the baseline condition. However, there were no significant effects of vocalization on MMN, Nd or P300. Moreover, there was no significant effect of gender to the corollary discharge. These results suggest that the effect of corollary discharge on auditory ERPs is limited to the perceptual stage of information processing in healthy men and women.     

Developmental changes in ERPs to visual language stimuli

ERPs to visual language stimuli were recorded in normal children (7-18 years) and adults from Fpz, Fz, Cz, Pz, Oz, F3, F4, C3, C4, P3, P4, T3, T4, T5 and T6. An oddball paradigm was employed with letter discrimination and lexical decision tasks. N2 and P3 latencies decreased significantly with age, N2 until adolescence, P3 until adulthood. The P3 amplitude increased until 11-12 years and then decreased until adulthood. In younger children there was a large frontal negativity and posterior positivity to targets. With increasing age there was a gradual increase in anterior positivity, concomitant with a decrease in posterior positivity. On the Pz and Cz coronal chains P3 was always largest at Pz while P3 was rarely largest at Cz. Asymmetric ERPs over the temporal lobes were recorded in the younger children. These data extend earlier studies by demonstrating variations in ERP scalp topography that occur with age.