Several attention-related wave forms in auditory areas: a topographic study

Attention to audiovisual speech shapes neural processing through feedback-feedforward loops between different nodes of the speech network

Selective attention-related top-down modulation plays a significant role in separating relevant speech from irrelevant background speech when vocal attributes separating concurrent speakers are small and continuously evolving. Electrophysiological studies have shown that such top-down modulation enhances neural tracking of attended speech. Yet, the specific cortical regions involved remain unclear due to the limited spatial resolution of most electrophysiological techniques. To overcome such limitations, we collected both electroencephalography (EEG) (high temporal resolution) and functional magnetic resonance imaging (fMRI) (high spatial resolution), while human participants selectively attended to speakers in audiovisual scenes containing overlapping cocktail party speech. To utilise the advantages of the respective techniques, we analysed neural tracking of speech using the EEG data and performed representational dissimilarity-based EEG-fMRI fusion. We observed that attention enhanced neural tracking and modulated EEG correlates throughout the latencies studied. Further, attention-related enhancement of neural tracking fluctuated in predictable temporal profiles. We discuss how such temporal dynamics could arise from a combination of interactions between attention and prediction as well as plastic properties of the auditory cortex. EEG-fMRI fusion revealed attention-related iterative feedforward-feedback loops between hierarchically organised nodes of the ventral auditory object related processing stream. Our findings support models where attention facilitates dynamic neural changes in the auditory cortex, ultimately aiding discrimination of relevant sounds from irrelevant ones while conserving neural resources.

A multi-step blind source separation approach for the attenuation of artifacts in mobile high-density electroencephalography data

Objective.Electroencephalography (EEG) is a widely used technique to address research questions about brain functioning, from controlled laboratorial conditions to naturalistic environments. However, EEG data are affected by biological (e.g. ocular, myogenic) and non-biological (e.g. movement-related) artifacts, which-depending on their extent-may limit the interpretability of the study results. Blind source separation (BSS) approaches have demonstrated to be particularly promising for the attenuation of artifacts in high-density EEG (hdEEG) data. Previous EEG artifact removal studies suggested that it may not be optimal to use the same BSS method for different kinds of artifacts.Approach.In this study, we developed a novel multi-step BSS approach to optimize the attenuation of ocular, movement-related and myogenic artifacts from hdEEG data. For validation purposes, we used hdEEG data collected in a group of healthy participants in standing, slow-walking and fast-walking conditions. During part of the experiment, a series of tone bursts were used to evoke auditory responses. We quantified event-related potentials (ERPs) using hdEEG signals collected during an auditory stimulation, as well as the event-related desynchronization (ERD) by contrasting hdEEG signals collected in walking and standing conditions, without auditory stimulation. We compared the results obtained in terms of auditory ERP and motor-related ERD using the proposed multi-step BSS approach, with respect to two classically used single-step BSS approaches.Main results. The use of our approach yielded the lowest residual noise in the hdEEG data, and permitted to retrieve stronger and more reliable modulations of neural activity than alternative solutions. Overall, our study confirmed that the performance of BSS-based artifact removal can be improved by using specific BSS methods and parameters for different kinds of artifacts.Significance.Our technological solution supports a wider use of hdEEG-based source imaging in movement and rehabilitation studies, and contributes to the further development of mobile brain/body imaging applications.

Endogenous Covert Spatial Orienting in Audition Cost-Benefit Analyses of Reaction Times and Event related Potentials

The present study examines mechanisms of endogenous covert spatial orienting in audition as revealed by event-related brain potentials (ERPs) and reaction times (RTs). In one experimental condition, subjects were instructed to respond to any target tone irrespective of whether it was presented in a valid (spatially predictive cue), neutral (uninformative cue), or invalid (misleading cue) trial. In another experimental condition, only target tones presented at a cued position required a response—that is, subjects could completely ignore tones presented at the uncued ear. Cue validity had an effect on RT, which consisted in benefits for valid trials and in costs for invalid trials relative to the RTs in neutral trials. There were also distinct ERP effects of cue validity in the 100–300 msec time range. These ERP effects were enlarged in the condition in which uncued tones could be ignored. The effects of cue validity on RTs and ERPs demonstrated covert orienting in audition both for stimuli requiring an overt response and also for stimuli that did not require a behavioural response. It is argued that this attentional selection is located at intermediate stages of information processing, rather than at peripheral stages such as basic sensory-specific processing or response selection.

Pre-target neural oscillations predict variability in the detection of small pitch changes

Pitch discrimination is important for language or music processing. Previous studies indicate that auditory perception depends on pre-target neural activity. However, so far the pre-target electrophysiological conditions which enable the detection of small pitch changes are not well studied, but might yield important insights into pitch-processing. We used magnetoencephalography (MEG) source imaging to reveal the pre-target effects of successful auditory detection of small pitch deviations from a sequence of standard tones. Participants heard a sequence of four pure tones and had to determine whether the last target tone was different or identical to the first three standard sounds. We found that successful pitch change detection could be predicted from the amplitude of theta (4-8 Hz) oscillatory activity in the right inferior frontal gyrus (IFG) as well as beta (12-30 Hz) oscillatory activity in the right auditory cortex. These findings confirm and extend evidence for the involvement of theta as well as beta-band activity in auditory perception.

Source localization of an event-related potential marker of executive attention following mild traumatic brain injury

Recent research suggests that intact performance on an executive attention task after mild traumatic brain injury (mTBI) reflects functional adaptation within neural networks, rather than recovery of premorbid modes of information processing. However, it is unclear whether this compensation includes the recruitment of alternative neural processing resources. The current study used source localization analysis to determine the location and timing of activated brain areas involved in the generation of an event-related potential (ERP) component marker of executive attention in 10 adults with mTBI and in 10 matched healthy controls. In both groups the cerebral sources of the late processing negativity component of the ERP waveform elicited during the Paced Auditory Serial Addition Task were localized to the left ventrolateral prefrontal cortex and right dorsal anterior cingulate cortex. Timing of the dipole moments was consistent with previous reports of the relative contributions of subregions of the frontal cortex critically involved in aspects of executive attention control. Finally, whereas abnormal intensity of ERP activation has recently been related to the achievement of normal levels of performance after mTBI, abnormal sources of cerebral activation do not appear to be a feature of the compensatory response.

Musical Meter Modulates the Allocation of Attention across Time

Dynamic attending theory predicts that attention is allocated hierarchically across time during processing of hierarchical rhythmic structures such as musical meter. ERP research demonstrates that attention to a moment in time modulates early auditory processing as evidenced by the amplitude of the first negative peak (N1) approximately 100 msec after sound onset. ERPs elicited by tones presented at times of high and low metric strength in short melodies were compared to test the hypothesis that hierarchically structured rhythms direct attention in a manner that modulates early perceptual processing. A more negative N1 was observed for metrically strong beats compared with metrically weak beats; this result provides electrophysiological evidence that hierarchical rhythms direct attention to metrically strong times during engaged listening. The N1 effect was observed only on fast tempo trials, suggesting that listeners more consistently invoke selective processing based on hierarchical rhythms when sounds are presented rapidly. The N1 effect was not modulated by musical expertise, indicating that the allocation of attention to metrically strong times is not dependent on extensive training. Additionally, changes in P2 amplitude and a late negativity were associated with metric strength under some conditions, indicating that multiple cognitive processes are associated with metric perception.

Emotion and goal-directed behavior: ERP evidence on cognitive and emotional conflict

Cognitive control supports goal-directed behavior by resolving conflict among opposing action tendencies. Emotion can trigger cognitive control processes, thus speeding up conflict processing when the target dimension of stimuli is emotional. However, it is unclear what role emotionality of the target dimension plays in the processing of emotional conflict (e.g. in irony). In two EEG experiments, we compared the influence of emotional valence of the target (emotional, neutral) in cognitive and emotional conflict processing. To maximally approximate real-life communication, we used audiovisual stimuli. Participants either categorized spoken vowels (cognitive conflict) or their emotional valence (emotional conflict), while visual information was congruent or incongruent. Emotional target dimension facilitated both cognitive and emotional conflict processing, as shown in a reduced reaction time conflict effect. In contrast, the N100 in the event-related potentials showed a conflict-specific reversal: the conflict effect was larger for emotional compared with neutral trials in cognitive conflict and smaller in emotional conflict. Additionally, domain-general conflict effects were observed in the P200 and N200 responses. The current findings confirm that emotions have a strong influence on cognitive and emotional conflict processing. They also highlight the complexity and heterogeneity of the interaction of emotion with different types of conflict.

Attention and prediction in human audition: a lesson from cognitive psychophysiology

Attention is a hypothetical mechanism in the service of perception that facilitates the processing of relevant information and inhibits the processing of irrelevant information. Prediction is a hypothetical mechanism in the service of perception that considers prior information when interpreting the sensorial input. Although both (attention and prediction) aid perception, they are rarely considered together. Auditory attention typically yields enhanced brain activity, whereas auditory prediction often results in attenuated brain responses. However, when strongly predicted sounds are omitted, brain responses to silence resemble those elicited by sounds. Studies jointly investigating attention and prediction revealed that these different mechanisms may interact, e.g. attention may magnify the processing differences between predicted and unpredicted sounds. Following the predictive coding theory, we suggest that prediction relates to predictions sent down from predictive models housed in higher levels of the processing hierarchy to lower levels and attention refers to gain modulation of the prediction error signal sent up to the higher level. As predictions encode contents and confidence in the sensory data, and as gain can be modulated by the intention of the listener and by the predictability of the input, various possibilities for interactions between attention and prediction can be unfolded. From this perspective, the traditional distinction between bottom-up/exogenous and top-down/endogenous driven attention can be revisited and the classic concepts of attentional gain and attentional trace can be integrated.

Attention effects on the processing of task-relevant and task-irrelevant speech sounds and letters

We used event-related brain potentials (ERPs) to study effects of selective attention on the processing of attended and unattended spoken syllables and letters. Participants were presented with syllables randomly occurring in the left or right ear and spoken by different voices and with a concurrent foveal stream of consonant letters written in darker or lighter fonts. During auditory phonological (A_P) and non-phonological tasks, they responded to syllables in a designated ear starting with a vowel and spoken by female voices, respectively. These syllables occurred infrequently among standard syllables starting with a consonant and spoken by male voices. During visual phonological and non-phonological tasks, they responded to consonant letters with names starting with a vowel and to letters written in dark fonts, respectively. These letters occurred infrequently among standard letters with names starting with a consonant and written in light fonts. To examine genuine effects of attention and task on ERPs not overlapped by ERPs associated with target processing or deviance detection, these effects were studied only in ERPs to auditory and visual standards. During selective listening to syllables in a designated ear, ERPs to the attended syllables were negatively displaced during both phonological and non-phonological auditory tasks. Selective attention to letters elicited an early negative displacement and a subsequent positive displacement (Pd) of ERPs to attended letters being larger during the visual phonological than non-phonological task suggesting a higher demand for attention during the visual phonological task. Active suppression of unattended speech during the A_P and non-phonological tasks and during the visual phonological tasks was suggested by a rejection positivity (RP) to unattended syllables. We also found evidence for suppression of the processing of task-irrelevant visual stimuli in visual ERPs during auditory tasks involving left-ear syllables.

Attention to natural auditory signals

The challenge of understanding how the brain processes natural signals is compounded by the fact that such signals are often tied closely to specific natural behaviors and natural environments. This added complexity is especially true for auditory communication signals that can carry information at multiple hierarchical levels, and often occur in the context of other competing communication signals. Selective attention provides a mechanism to focus processing resources on specific components of auditory signals, and simultaneously suppress responses to unwanted signals or noise. Although selective auditory attention has been well-studied behaviorally, very little is known about how selective auditory attention shapes the processing on natural auditory signals, and how the mechanisms of auditory attention are implemented in single neurons or neural circuits. Here we review the role of selective attention in modulating auditory responses to complex natural stimuli in humans. We then suggest how the current understanding can be applied to the study of selective auditory attention in the context natural signal processing at the level of single neurons and populations in animal models amenable to invasive neuroscience techniques. This article is part of a Special Issue entitled "Communication Sounds and the Brain: New Directions and Perspectives".

The interaction between attention and motor prediction. An ERP study

Performing a voluntary action involves the anticipation of the intended effect of that action. Interaction with the environment also requires the allocation of attention. However, the effects of attention upon motor predictive processes remain unclear. Here we use a novel paradigm to investigate attention and motor prediction orthogonally. In an acquisition phase, high and low tones were associated with left and right key presses. In the following test phase, tones were presented at random and participants attended to only one ear whilst ignoring tones presented in the unattended ear. In the test phase a tone could therefore be presented at the attended or unattended ear, as well as being congruent or incongruent with prior action-effect learning. We demonstrated early and late effects of attention as well as a later independent motor prediction effect with a larger P3a for incongruent tones. Interestingly, we demonstrated an intermediate interaction, showing an action-effect negativity (NAE) for tones which were unattended, whilst no motor prediction effect was found for attended tones. This interaction pattern suggests that attention and motor prediction are not opposing processes but can both operate to modulate prediction, providing valuable new insight into the relationship between attention and the effects of motor prediction.

The ups and downs of temporal orienting: a review of auditory temporal orienting studies and a model associating the heterogeneous findings on the auditory N1 with opposite effects of attention and prediction

The temporal orienting of attention refers to the process of focusing (neural) resources on a particular time point in order to boost the processing of and the responding to sensory events. Temporal attention is manipulated by varying the task-relevance of events at different time points or by inducing expectations that an event occurs at a particular time point. Notably, the electrophysiological correlates of these manipulations at early processing stages are not identical: Auditory studies operationalizing temporal attention through task-relevance consistently found enhancements of early, sensory processing, as shown in the N1 component of the auditory event-related potential (ERP). By contrast, previous work on temporal orienting based on expectations showed mixed results: early, sensory processing was either enhanced or attenuated or not affected at all. In the present work, I will review existing findings on temporal orienting with a special focus on the auditory modality and present a working model to reconcile the previously heterogeneous results. Specifically, I will suggest that when expectations are used to manipulate attention, this will lead both to an orienting of attention and to the generation of precise predictions about the upcoming event. Attention and prediction are assumed to have opposite effects on early auditory processing, with temporal attention increasing and temporal predictions decreasing the associated ERP correlate, the auditory N1. The heterogeneous findings of studies manipulating temporal orienting by inducing expectations may thus be the consequence of differences in the relative contribution of attention and prediction processes. The model's predictions will be discussed in the context of a functional interpretation of the auditory N1 as an attention call signal, as presented in a recent model on auditory processing.

The N1-suppression effect for self-initiated sounds is independent of attention

BACKGROUND

If we initiate a sound by our own motor behavior, the N1 component of the auditory event-related brain potential (ERP) that the sound elicits is attenuated compared to the N1 elicited by the same sound when it is initiated externally. It has been suggested that this N1 suppression results from an internal predictive mechanism that is in the service of discriminating the sensory consequences of one's own actions from other sensory input. As the N1-suppression effect is becoming a popular approach to investigate predictive processing in cognitive and social neuroscience, it is important to exclude an alternative interpretation not related to prediction. According to the attentional account, the N1 suppression is due to a difference in the allocation of attention between self- and externally-initiated sounds. To test this hypothesis, we manipulated the allocation of attention to the sounds in different blocks: Attention was directed either to the sounds, to the own motor acts or to visual stimuli. If attention causes the N1-suppression effect, then manipulating attention should affect the effect for self-initiated sounds.

RESULTS

We found N1 suppression in all conditions. The N1 per se was affected by attention, but there was no interaction between attention and self-initiation effects. This implies that self-initiation N1 effects are not caused by attention.

CONCLUSIONS

The present results support the assumption that the N1-suppression effect for self-initiated sounds indicates the operation of an internal predictive mechanism. Furthermore, while attention had an influence on the N1a, N1b, and N1c components, the N1-suppression effect was confined to the N1b and N1c subcomponents suggesting that the major contribution to the auditory N1-suppression effect is circumscribed to late N1 components.

The N1 effect of temporal attention is independent of sound location and intensity: implications for possible mechanisms of temporal attention

It has been repeatedly shown that the auditory N1 is enhanced for sounds presented at an attended time point. The present study investigated the underlying mechanisms using a temporal cuing paradigm. In each trial, an auditory cue indicated at which time point a second sound could be relevant for response selection. Crucially, in addition to temporal attention, two physical sound features with known effects on the sensory N1 were manipulated: location and intensity. Positive evidence for conjoint effects of attention and location or attention and intensity would corroborate the notion that the sensory N1 was modulated by temporal attention, thus supporting a gain mechanism. However, the N1 effect of temporal attention was not similarly lateralized as the sensory N1, and, moreover, it was independent of sound intensity. Thus, the present results do not provide compelling evidence that temporal attention involves an increase in sensory gain.

The role of attention in auditory information processing as revealed by event-related potentials and other brain measures of cognitive function

This article examines the role of attention and automaticity in auditory processing as revealed by event-related potential (ERP) research. An ERP component called the mismatch negativity, generated by the brain's automatic response to changes in repetitive auditory input, reveals that physical features of auditory stimuli are fully processed whether or not they are attended. It also suggests that there exist precise neuronal representations of the physical features of recent auditory stimuli, perhaps the traces underlying acoustic sensory (“echoic”) memory. A mechanism of passive attention switching in response to changes in repetitive input is also implicated.

Conscious perception of discrete acoustic stimuli might be mediated by some of the mechanisms underlying another ERP component (NI), one sensitive to stimulus onset and offset. Frequent passive attentional shifts might accountforthe effect cognitive psychologists describe as “the breakthrough of the unattended” (Broadbent 1982), that is, that even unattended stimuli may be semantically processed, without assuming automatic semantic processing or late selection in selective attention.

The processing negativity supports the early-selection theory and may arise from a mechanism for selectively attending to stimuli defined by certain features. This stimulus selection occurs in the form ofa matching process in which each input is compared with the “attentional trace,” a voluntarily maintained representation of the task-relevant features of the stimulus to be attended. The attentional mechanism described might underlie the stimulus-set mode of attention proposed by Broadbent. Finally, a model of automatic and attentional processing in audition is proposed that is based mainly on the aforementioned ERP components and some other physiological measures.

ERP evidence of early cross-modal links between auditory selective attention and visuo-spatial memory

Previous dual-task research pairing complex visual tasks involving non-spatial cognitive processes during dichotic listening have shown effects on the late component (Ndl) of the negative difference selective attention waveform but no effects on the early (Nde) response suggesting that the Ndl, but not the Nde, is affected by non-spatial processing in a dual-task. Thus to further explore the nature of this dissociation and whether the Nd waveform is affected by spatial processing; fourteen adult participants performed auditory dichotic listening in conjunction with visuo-spatial memory in a cross-modal dual-task paradigm. The results showed that the visuo-spatial memory task decreased both the Nde and Ndl waveforms, and also attenuated P300 and increased its latency. This pattern of results suggests that: (1) the Nde reflects a memory trace that is shared with vision when the information is spatial in nature, and (2) P300 latency appears to be influenced by the discriminability of stimuli underlying the Nde and Ndl memory trace.

Neural dynamics of attending and ignoring in human auditory cortex

Studies in all sensory modalities have demonstrated amplification of early brain responses to attended signals, but less is known about the processes by which listeners selectively ignore stimuli. Here we use MEG and a new paradigm to dissociate the effects of selectively attending, and ignoring in time. Two different tasks were performed successively on the same acoustic stimuli: triplets of tones (A, B, C) with noise-bursts interspersed between the triplets. In the COMPARE task subjects were instructed to respond when tones A and C were of same frequency. In the PASSIVE task they were instructed to respond as fast as possible to noise-bursts. COMPARE requires attending to A and C and actively ignoring tone B, but PASSIVE involves neither attending to nor ignoring the tones. The data were analyzed separately for frontal and auditory-cortical channels to independently address attentional effects on low-level sensory versus putative control processing. We observe the earliest attend/ignore effects as early as 100 ms post-stimulus onset in auditory cortex. These appear to be generated by modulation of exogenous (stimulus-driven) sensory evoked activity. Specifically related to ignoring, we demonstrate that active-ignoring-induced input inhibition involves early selection. We identified a sequence of early (<200 ms post-onset) auditory cortical effects, comprised of onset response attenuation and the emergence of an inhibitory response, and provide new, direct evidence that listeners actively ignoring a sound can reduce their stimulus related activity in auditory cortex by 100 ms after onset when this is required to execute specific behavioral objectives.

Auditory target detection is affected by implicit temporal and spatial expectations

Mechanisms of implicit spatial and temporal orienting were investigated by using a moving auditory stimulus. Expectations were set up implicitly, using the information inherent in the movement of a sound, directing attention to a specific moment in time with respect to a specific location. There were four conditions of expectation: temporal and spatial expectation; temporal expectation only; spatial expectation only; and no expectation. Event-related brain potentials were recorded while participants performed a go/no-go task, set up by anticipation of the reappearance of a target tone through a white noise band. Results showed that (1) temporal expectations alone speeded reaction time and increased response accuracy; and (2) implicit temporal expectations alone independently enhanced target detection at early processing stages, prior to motor response. This was reflected at stages of perceptual analysis, indexed by P1 and N1 components, as well as in task-related stages indexed by N2; and (3) spatial expectations had an effect at later response-related processing stages but only in combination with temporal expectations, indexed by the P3 component. Thus, the results, in addition to indicating a primary role for temporal orienting in audition, suggest that multiple mechanisms of attention interact in different phases of auditory target detection. Our results are consistent with the view from vision research that spatial and temporal attentional control is based on the activity of partly overlapping, and partly functionally specialized neural networks.

Load effects in auditory selective attention: evidence for distinct facilitation and inhibition mechanisms

It is unknown whether facilitation and inhibition of stimulus processing represent one or two mechanisms in auditory attention. We performed electrophysiological experiments in humans to address these two competing hypothesis. Participants performed an attention task under low or high memory load. Facilitation and inhibition were measured by recording electrophysiological responses to attended and ignored sounds and comparing them to responses to these same sounds when attention was considered to be equally distributed towards all sounds. We observed two late frontally distributed components: a negative one in response to attended sounds, and a positive one to ignored sounds. These two frontally distributed responses had distinct timing and scalp topographies and were differentially affected by memory load. Taken together these results provide evidence that attention-mediated top-down control reflects the activity of distinct facilitation and inhibition mechanisms.

Dynamics of cortical responses to tone pairs in relation to task difficulty: a MEG study

We investigated the effect of task difficulty on the dynamics of auditory cortical responses. Whole-scalp magnetoencephalographic (MEG) signals were recorded while subjects performed a same/different frequency discrimination task on equiprobable tone pairs applied in blocks of five, which were separated by a 10 s intertrial interval. Task difficulty was manipulated by the interpair frequency difference. The manipulation of task difficulty affected the amplitude of the N100m response to the first tone and the latency of the N100m response to the second tone in each pair. The N100m responses were smaller and peaked significantly later in the difficult than in the easy condition. The later processing field (PF) responses were longer in duration in the difficult condition. In both conditions, the duration of the PF response was negatively correlated with the subject's performance in the task, and was longer in the less successful subjects. The PF response may thus reflect the subjects' effort to resolve the task. The N100m and the PF responses did not differ between the tone pairs along the five-pair trial as a function of task difficulty, suggesting that changes in response along the five-pair trial are not easily affected by high-level manipulations.

Effects of intermodal attention on the auditory steady-state response and the event-related potential

The aim of the present study was to simultaneously measure and compare intermodal attention effects in event-related brain potentials (ERPs) and auditory steady-state responses (ASSRs). For this purpose, 40-Hz amplitude modulated tones and a visual fixation cross were presented concurrently. By means of target detection tasks either on the sounds or on the fixation cross, participants' attention was directed to the respective modality. Attended sounds elicited a negative difference (Nd) in the ERP relative to unattended sounds. Nd was divided into an early and a late part as often observed for intramodal attention. Moreover, attention to the sounds led to a significant enhancement of the ASSR. This modulation of the ASSR by intermodal attention is demonstrated for the first time in the EEG. The present data suggest that ASSRs could provide a useful tool for the investigation of the neural dynamics of intermodal attentional processes.

Selective attention to sound location or pitch studied with event-related brain potentials and magnetic fields

Event-related brain potentials (ERPs) and magnetic fields (ERFs) were used to compare brain activity associated with selective attention to sound location or pitch in humans. Sixteen healthy adults participated in the ERP experiment, and 11 adults in the ERF experiment. In different conditions, the participants focused their attention on a designated sound location or pitch, or pictures presented on a screen, in order to detect target sounds or pictures among the attended stimuli. In the Attend Location condition, the location of sounds varied randomly (left or right), while their pitch (high or low) was kept constant. In the Attend Pitch condition, sounds of varying pitch (high or low) were presented at a constant location (left or right). Consistent with previous ERP results, selective attention to either sound feature produced a negative difference (Nd) between ERPs to attended and unattended sounds. In addition, ERPs showed a more posterior scalp distribution for the location-related Nd than for the pitch-related Nd, suggesting partially different generators for these Nds. The ERF source analyses found no source distribution differences between the pitch-related Ndm (the magnetic counterpart of the Nd) and location-related Ndm in the superior temporal cortex (STC), where the main sources of the Ndm effects are thought to be located. Thus, the ERP scalp distribution differences between the location-related and pitch-related Nd effects may have been caused by activity of areas outside the STC, perhaps in the inferior parietal regions.

Orienting and maintenance of spatial attention in audition and vision: an event-related brain potential study

We examined the effects of orienting and maintenance of attention on performance and event-related brain potentials (ERPs) in audition and vision. Our subjects selectively attended to sounds or pictures in one location (Maintenance of attention) or alternated the focus of their auditory or visual attention between left and right locations (Orienting of attention) in order to detect and press a response button to infrequent targets among the attended stimuli. Reaction times were longer in the Auditory Orienting condition and hit rates were lower and false alarm rates higher in the Visual Orienting condition than in the corresponding Maintenance conditions. Comparison of ERPs to the attended and unattended stimuli in the Auditory and Visual Orienting and Maintenance conditions revealed attention-related modulations of ERPs. In each modality, ERPs to attended stimuli were negatively displaced in relation to unattended stimuli at 100-250 ms from stimulus onset. These negative differences (Nds) showed modality-specific distributions and they were larger over the hemisphere contralateral to the attended sounds and pictures than over the ipsilateral hemisphere. Moreover, the Nd was larger in the Auditory Orienting condition than in the Auditory Maintenance condition, while no such difference was observed in the visual modality. In addition to the Nd, attended visual stimuli elicited a late positive response (LPR) in both Orienting and Maintenance conditions. In contrast to our recent functional magnetic resonance imaging (fMRI) study employing the same experimental paradigm and indicating orienting-related activity in the frontal and parietal cortices, no ERP responses specifically related to orienting were found in either modality.