Stimulus- and Response-locked Posterior Contralateral Negativity Bisect Cognitive Operations in Visual Search.

We explored the flow of information during visual search by examining activity indexing visual attention (N2pc) and the subsequent processing of the selected objects in visual short-term memory (SPCN) time-locked to stimulus presentation and to the motor response. We measured event-related activity at posterior sites (PO7/PO8) for 96 participants during a simple visual search task. A response-locked posterior contralateral negativity (RLpcN) was observed with a scalp distribution similar to that of the N2pc and SPCN. The RLpcN was compared with the stimulus-locked activity (N2pc and SPCN) across experimental manipulations (targets were either closer or farther from fixation in visual space, and the response was either more frequent [75%] or less frequent [25%]) and across response speeds (EEG data were separated into tertiles by RT both within-subjects and between-subjects). The leading edge and early portion of the RLpcN appeared to reflect the initial deployment of attention (N2pc), whereas the later portion (up to peak amplitude) reflected subsequent processing of visual information (SPCN). SPCN and RLpcN also had similar modulations in amplitude for both analyses. Moreover, whereas very small N2pc and SPCN onset latency differences were observed when data were separated into tertiles by RT, there were large onset differences for the RLpcN, with earlier RLpcN onsets for longer RTs, suggesting that RT variance is in large determined by processing after the initial deployment of attention. The results show how we can bisect processing responsible for variations in RT relative to the onset of visual spatial attention.

A MEG study of the neural substrates of semantic processing in semantic variant primary progressive aphasia.

Despite a well-documented pattern of semantic impairment, the patterns of brain activation during semantic processing in semantic variant primary progressive aphasia (svPPA) still remain poorly understood. In the current study, one svPPA patient (EC) and six elderly controls carried out a general-level semantic categorization task while their brain activity was recorded using magnetoencephalography (MEG). Despite similar behavioral performance, EC showed hyperactivation of the left inferior temporal gyrus (ITG) and right anterior temporal lobe (ATL) relative to controls. This suggests that periatrophic regions within the ATL region may support preserved semantic abilities in svPPA.

Inability to suppress salient distractors predicts low visual working memory capacity.

According to contemporary accounts of visual working memory (vWM), the ability to efficiently filter relevant from irrelevant information contributes to an individual's overall vWM capacity. Although there is mounting evidence for this hypothesis, very little is known about the precise filtering mechanism responsible for controlling access to vWM and for differentiating low- and high-capacity individuals. Theoretically, the inefficient filtering observed in low-capacity individuals might be specifically linked to problems enhancing relevant items, suppressing irrelevant items, or both. To find out, we recorded neurophysiological activity associated with attentional selection and active suppression during a competitive visual search task. We show that high-capacity individuals actively suppress salient distractors, whereas low-capacity individuals are unable to suppress salient distractors in time to prevent those items from capturing attention. These results demonstrate that individual differences in vWM capacity are associated with the timing of a specific attentional control operation that suppresses processing of salient but irrelevant visual objects and restricts their access to higher stages of visual processing.

On the Role of the Inferior Intraparietal Sulcus in Visual Working Memory for Lateralized Single-feature Objects.

A consolidated practice in cognitive neuroscience is to explore the properties of human visual working memory through the analysis of electromagnetic signals using cued change detection tasks. Under these conditions, EEG/MEG activity increments in the posterior parietal cortex scaling with the number of memoranda are often reported in the hemisphere contralateral to the objects' position in the memory array. This highly replicable finding clashes with several reported failures to observe compatible hemodynamic activity modulations using fMRI or fNIRS in comparable tasks. Here, we reconcile this apparent discrepancy by acquiring fMRI data on healthy participants and employing a cluster analysis to group voxels in the posterior parietal cortex based on their functional response. The analysis identified two distinct subpopulations of voxels in the intraparietal sulcus (IPS) showing a consistent functional response among participants. One subpopulation, located in the superior IPS, showed a bilateral response to the number of objects coded in visual working memory. A different subpopulation, located in the inferior IPS, showed an increased unilateral response when the objects were displayed contralaterally. The results suggest that a cluster of neurons in the inferior IPS is a candidate source of electromagnetic contralateral responses to working memory load in cued change detection tasks.

Backward masking interrupts spatial attention, slows downstream processing, and limits conscious perception.

The attentional blink (AB) is a difficulty in correctly processing a target when it follows one or more other targets after a short delay. When no backward mask is presented after the last critical target, there is no or little behavioral AB deficit. The mask plays an important role in limiting conscious access to target information. In this electrophysiological study, we tested the impact of masking on the deployment and engagement of attention by measuring the N2pc and P3 components in an RSVP paradigm. We found that the presence of a mask in an AB paradigm reduced the amplitude of the N2pc, P3a, and P3b components. In addition to reducing encoding in memory, masking also reduced the effectiveness of the deployment and engagement of attention on the last target. We discuss the role of these findings in the context of current masking, consciousness, and AB models.

The attentional blink impairs detection and delays encoding of visual information: evidence from human electrophysiology.

This article explores the time course of the functional interplay between detection and encoding stages of information processing in the brain and the role they play in conscious visual perception. We employed a multitarget rapid serial visual presentation (RSVP) approach and examined the electrophysiological P3 component elicited by a target terminating an RSVP sequence. Target-locked P3 activity was detected both at frontal and parietal recording sites and an independent component analysis confirmed the presence of two distinct P3 components. The posterior P3b varied with intertarget lag, with diminished amplitude and postponed latency at short relative to long lags-an electroencephalographic signature of the attentional blink (AB). Under analogous conditions, the anterior P3a was also reduced in amplitude but did not vary in latency. Collectively, the results provide an electrophysiological record of the interaction between frontal and posterior components linked to detection (P3a) and encoding (P3b) of visual information. Our findings suggest that, although the AB delays target encoding into working memory, it does not slow down detection of a target but instead reduces the efficacy of this process. A functional characterization of P3a in attentive tasks is discussed with reference to current models of the AB phenomenon.

Theta oscillations linked to auditory informativeness and context disambiguation.

Accurate predictions and the processing of prediction error signals can be important for efficient interaction with the auditory environment. In a reanalysis of data from Simal et al . (2021), who found that informative tones elicited increased N1 and P2 event-related potential components, we sought to identify electrophysiological indicators in the time-frequency domain associated with disambiguation of the hearing context and prediction of forthcoming stimulation. Participants heard two isochronous sequences of pure tones separated by a silent retention interval. A sequence could contain one, three, or five tones. Fifteen participants heard the three load conditions randomly intermixed. In this case, when sequence length was unknown, the second and fourth tone during encoding contained information allowing the prediction of another tone. Other participants heard the sequences blocked by sequence length, and the second and fourth tone of the sequences provided no new information (and hence were not informative). We used wavelet analysis and Hilbert transform methods to analyse the oscillatory activity related to tone informativeness. We found a significant increase in theta (4-7 Hz) amplitude following a tone that was informative and allowed prediction, in comparison with a tone that carried no predictive information. Previous work suggests increased theta amplitude is linked with task switching and an increase in cognitive control. We suggest informative tones recruit higher-level control processes involved in prediction of upcoming auditory events.

Pitch discrimination without awareness in congenital amusia: evidence from event-related potentials.

Congenital amusia is a lifelong disorder characterized by a difficulty in perceiving and producing music despite normal intelligence and hearing. Behavioral data have indicated that it originates from a deficit in fine-grained pitch discrimination, and is expressed by the absence of a P3b event-related brain response for pitch differences smaller than a semitone and a bigger N2b-P3b brain response for large pitch differences as compared to controls. However, it is still unclear why the amusic brain overreacts to large pitch changes. Furthermore, another electrophysiological study indicates that the amusic brain can respond to changes in melodies as small as a quarter-tone, without awareness, by exhibiting a normal mismatch negativity (MMN) brain response. Here, we re-examine the event-related N2b-P3b components with the aim to clarify the cause of the larger amplitude observed by Peretz, Brattico, and Tervaniemi (2005), by experimentally matching the number of deviants presented to the controls according to the number of deviants detected by amusics. We also re-examine the MMN component as well as the N1 in an acoustical context to investigate further the pitch discrimination deficit underlying congenital amusia. In two separate conditions, namely ignore and attend, we measured the MMN, the N1, the N2b and the P3b to tones that deviated by an eight of a tone (25 cents) or whole tone (200 cents) from a repeated standard tone. The results show a normal MMN, a seemingly normal N1, a normal P3b for the 200 cents pitch deviance, and no P3b for the small 25 cents pitch differences in amusics. These results indicate that the amusic brain responds to small pitch differences at a pre-attentive level of perception, but is unable to detect consciously those same pitch deviances at a later attentive level. The results are consistent with previous MRI and fMRI studies indicating that the auditory cortex of amusic individuals is functioning normally.

Difficulty suppressing visual distraction while dual tasking.

Human beings must often perform multiple tasks concurrently or in rapid succession. Laboratory research has revealed striking limitations in the ability to dual task by asking participants to identify two target objects that are inserted into a rapid stream of irrelevant items. Under a variety of conditions, identification of the second target (T2) is impaired for a short period of time following presentation of the first target (T1). Several theories have been developed to account for this "attentional blink" (AB), but none makes a specific prediction about how processing of T1 might impact an observer's ability to ignore a salient distractor that accompanies T2. Using event-related potentials (ERPs) to track target and distractor processing, we show that healthy young adults are capable of suppressing a salient visual-search distractor (D2) while dual tasking (as measured by the PD component, which has been associated with suppression) but struggle to do so shortly after the appearance of T1. In fact, the impairment was more severe for distractor processing than it was for target processing (as measured by the N2pc component). Whereas, the T2-elicited N2pc was merely delayed during the AB, the distractor PD was reduced in magnitude and was found to be statistically absent. We conclude that the inhibitory control processes that are typically engaged to prevent distraction are unavailable while an observer is busy processing a target that appeared earlier.

On the automaticity of semantic processing during task switching.

There is growing evidence that processes formerly believed to be automatic are, in fact, strongly modulated by top-down influences. The purpose of the present work was to investigate how cognitive control can affect the purported automaticity of word processing by examining the impact of task switching on semantic processing using the ERP technique. In the context of the psychological refractory period dual-task paradigm, two experiments contrasted the context-sensitive N400 ERP elicited by the second of two target words under conditions that involved either a task switch or no-task switch. Although the N400 was not affected by SOA in the absence of switching, it was strongly attenuated at short SOAs when the psychological refractory period procedure involved a switch from a perceptual to a semantic task (Experiment 1) or a switch between two different semantic tasks (Experiment 2). These findings suggest that semantic processing cannot be performed in parallel with task switching and illustrate limitations in the ability of the cognitive system to adapt flexibly to the dynamically changing challenges of the environment according to task demands and behavioral goals.

On target selection as reflected by posterior ERP components in feature-guided visual search.

The N2pc event-related potential is a widely studied ERP component that reflects the covert deployment of visuo-spatial attention to target stimuli displayed laterally relative to fixation. Recently, an analogous ERP component, named N2pcb, has been proposed as a marker of the deployment of visuo-spatial attention to targets displayed on the vertical midline. Two studies that investigated the N2pcb component found analogous results, using however two different algorithms to compute the amplitude of N2pcb. One study subtracted the ipsilateral activity elicited by a lateral target from the bilateral activity elicited by a target displayed on the vertical midline, whereas the other study subtracted the bilateral activity elicited by target-absent displays from the bilateral activity elicited by a target displayed on the vertical midline. Here we show both algorithms estimate properly the N2pc as well as the N2pcb components. In addition, we explored whether the singleton detection positivity (SDP) component, a posterior bilateral positivity temporally concomitant to N2pc recently reported in studies using singleton search, could be observed in the present study in which a target was defined by a combination of features. Given that such component was indeed found using feature search, we named this component posterior processing positivity (PPP), and showed that bilateral activity elicited by target-absent displays is an adequate baseline for its correct isolation.

A bilateral SPCN is elicited by to-be-memorized visual stimuli displayed along the vertical midline.

We recently showed that deploying attention to target stimuli displayed along the vertical meridian elicits a bilateral N2pc, that we labeled N2pcb (Psychophysiology). Here we investigated whether a different component, the sustained posterior contralateral negativity (SPCN), shows the same property when a varying number of visual stimuli are displayed either laterally or on the vertical meridian. We displayed one or two cues that designated candidate targets to be detected in a search array that was displayed after a retention interval. The cues were either on the horizontal meridian or on the vertical meridian. When the cues were on the horizontal meridian, we observed an N2pc followed by an SPCN in their classic form, as negativity increments contralateral to the cues. As expected, SPCN amplitude was greater when two cues had to be memorized than when only one cue had to be memorized. When the cues were on the vertical meridian, we observed an N2pcb followed by a bilateral SPCN (or SPCNb). Critically, like SPCN, SPCNb amplitude was greater when two cues had to be memorized than when only one cue had to be memorized. A series of additional parametrical and topographical comparisons between N2pcb and SPCNb revealed similarities but also some important differences between these two components that we interpreted as evidence for their distinct neural sources.

The effects of the activation of hostile and non-hostile schemas on intent attribution processes in non-aggressive individuals: An ERP study.

We investigated the influences of hostile and non-hostile schemas activations in non-aggressive individuals on their intent attribution processes in various social contexts. 38 non-aggressive participants were randomly assigned to one of two groups, one primed with negative words, to be conditioned as temporarily hostile (TH), and the other with positive words, be conditioned as temporarily non-hostile (TNH). They were asked to read social scenarios composed of positive or negative behaviors of others whose intentions are ambiguous followed by a disambiguation of others' real intentions (hostile vs non-hostile) behind their behaviors. Neural activity related to spontaneous intent attribution processes was measured using electroencephalography (EEG). The results showed that when non-hostile intentions were revealed following ambiguous-negative behaviors of others, the N400 effect was observed only in the TH group. Similarly, when hostile intentions were revealed following ambiguous-positive behaviors of others, the N400 effect was observed only in the TNH group. In other words, non-aggressive individuals were led to attribute either hostile or non-hostile intentions to the same ambiguous behaviors of others depending on which concepts or thoughts (hostile vs non hostile) were activated and accessible in memory by priming at the time of social interactions.

Signal informativeness for sequence structure modulates human auditory cortical responses.

We observed how information about the structure of tone sequences modulates cortical responses in the context of a standard short-term memory (STM) task. Participants heard two sequences of one, three, or five tones (203 ms on, 203 ms off) interspersed by a silent interval (2 s) and decided whether the sequences were the same or different. In experiment 1, sequence length was randomized between trials. During the first sequence, the amplitude of the auditory P2 was larger for the second tone in trials with three tones, and for the second and fourth tone in trials with five tones. We hypothesize the increase in P2 reflected a dynamic disambiguation process because these tones were predictive of a sequence longer than one or three tones. This hypothesis was supported by the absence of P2 amplitude modulation during the second sequence (when sequence length was known). In experiment 2, we blocked trials by sequence length to ensure the effects were not caused by some process related to encoding in STM. There was no P2 amplitude modulation in either the first or second sequences. Thus, tones 2 and 4 had a larger amplitude only when they provided new information about the length of the current tone sequence. To some extent, the auditory N1 also showed those modulations. Independent Component Analysis of the ERPs provided evidence the modulations in P2 amplitude could originate in auditory cortex. These results suggest a rapid dynamic adaptation of auditory cortical responses based on the local informativeness of auditory signals.

Electrophysiological evidence of low salience distractor interference during visual search.

Visual search displays often include distractors of lesser salience in addition to a target and one or more salient distractors. We investigated low salience distractor effects on the N2pc, an ERP component indexing the deployment of attention, and the Ptc, a component purported to reflect attentional disengagement. We hypothesized that salient distractors pull the attentional focus away from the target, which could lead to increased attentional processing of low salience distractors close to the target and salient distractor. Participants looked for a colored inverted T during a visual search task while ignoring an L of the same color at a fixed distance on an imaginary circle around fixation. There were four conditions: no additional gray (low salience) distractors, two additional gray distractors between color items, two additional gray distractors just outside the area delimited by the colored items, and four additional gray distractors inside and outside the attended region. The gray distractors impacted N2pc and Ptc amplitude and latency, indicating an effect of gray distractors on attentional processing. Also, additional gray distractors led to increasingly more deviation of the N2pc and Ptc waveforms from the baseline offered by the condition with no additional gray distractors. When we increased the difficulty to individuate the target, we observed more displacement of lateralized activity from the N2pc to the Ptc time window. We argue that distractor-related modulations likely result from increased variance in the latency of attentional engagement activity to the target instead of distractor inhibition or attentional disengagement.

Differential engagement of attention and visual working memory in the representation and evaluation of the number of relevant targets and their spatial relations: Evidence from the N2pc and SPCN.

We examined the role of attention and visual working memory in the evaluation of the number of target stimuli as well as their relative spatial position using the N2pc and the SPCN. Participants performed two tasks: a simple counting task in which they had to determine if a visual display contained one or two coloured items among grey fillers and one in which they had to identify a specific relation between two coloured items. The same stimuli were used for both tasks. Each task was designed to permit an easier evaluation of either the same-coloured or differently-coloured stimuli. We predicted a greater involvement of attention and visual working memory for more difficult stimulus-task pairings. The results confirmed these predictions and suggest that visuospatial configurations that require more time to evaluate induce a greater (and presumably longer) involvement of attention and visual working memory.

Memory for pure tone sequences without contour.

We presented pure tones interspersed with white noise sounds to disrupt contour perception in an acoustic short-term memory (ASTM) experiment during which we recorded the electroencephalogram. The memory set consisted of seven stimuli, 0, 1, 2, 3, or 4 of which were to-be-remembered tones. We estimated each participant׳s capacity, K, for each set size and measured the amplitude of the SAN (sustained anterior negativity, an ERP related to acoustic short-term memory). We correlated their K slopes with their SAN amplitude slopes as a function of set size, and found a significant link between performance and the SAN: a larger increase in SAN amplitude was linked with a larger number of stimuli maintained in ASTM. The SAN decreased in amplitude in the later portion of the silent retention interval, but the correlation between the SAN and capacity remained strong. These results show the SAN is not an index of contour but rather an index of the maintenance of individual objects in STM. This article is part of a Special Issue entitled SI: Auditory working memory.

Enhanced frontal activation underlies sparing from the attentional blink: Evidence from human electrophysiology.

Using the ERP method, we examined the processing operations elicited by stimuli that appear within the same temporal attention window. Forty subjects searched for letter targets among digit distractors displayed in rapid serial visual presentation (RSVP). ERPs were examined under conditions where a single target was embedded among distractors and compared to those recorded when two consecutive targets were embedded among distractors. Standard and independent component analyses revealed two temporally and topographically distinct ERP responses, a midfrontal P3a component peaking at about 300 ms followed by a midparietal P3b component peaking at about 450 ms. With minimal latency variations, the frontal P3a was amplified when elicited by two consecutive targets relative to a single target. The parietal P3b response was also amplified when elicited by two consecutive targets compared to a single target but, in contrast to P3a, it was also associated with a substantially longer time course. These results provide evidence for the involvement of frontal brain regions in the close-to-concurrent selection of two consecutive targets displayed in RSVP, and of posterior brain regions in the serial encoding of targets in visual working memory. The present findings are discussed in relation to current models of temporal gating of attention and the attentional blink effect.

On the costs of lag-1 sparing.

The attentional blink (AB) is a dual-target, rapid serial visual presentation (RSVP) deficit thought to represent a failure of perceptual awareness that reflects the dynamics of temporal attention. However, second target (T2) report is typically unimpaired when the targets appear within 150 ms of one another (i.e., lag-1 sparing). In addition, this sparing can be extended if more targets appear sequentially. It is thought that sequential targets are processed in the same attentional window. Here, we investigated the fate of targets processed in these windows and, specifically, the consequence for subsequent targets when an item at lag-1 is reported versus missed. The results demonstrated that target encoding in attentional windows has an all-or-none influence on subsequent item report: When comparing two- and three-target (T1 and T2 not separated by distractors) RSVP streams, there was no difference in AB magnitude for the final target when either T2 or T1 was missed in the three-target condition, but both of these conditions had significantly smaller blinks than those observed when T1 and T2 were accurately reported. A comparison of our results to a computational model of temporal attention demonstrates how structural limitations on the rate of encoding affect perception, even during sparing.

Colour-specific differences in attentional deployment for equiluminant pop-out colours: evidence from lateralised potentials.

We investigated how target colour affected behavioural and electrophysiological results in a visual search task. Perceptual and attentional mechanisms were tracked using the N2pc component of the event-related potential and other lateralised components. Four colours (red, green, blue, or yellow) were calibrated for each participant for luminance through heterochromatic flicker photometry and equated to the luminance of grey distracters. Each visual display contained 10 circles, 1 colored and 9 grey, each of which contained an oriented line segment. The task required deploying attention to the colored circle, which was either in the left or right visual hemifield. Three lateralised ERP components relative to the side of the lateral coloured circle were examined: a posterior contralateral positivity (Ppc) prior to N2pc, the N2pc, reflecting the deployment of visual spatial attention, and a temporal and contralateral positivity (Ptc) following N2pc. Red or blue stimuli, as compared to green or yellow, had an earlier N2pc. Both the Ppc and Ptc had higher amplitudes to red stimuli, suggesting particular selectivity for red. The results suggest that attention may be deployed to red and blue more quickly than to other colours and suggests special caution when designing ERP experiments involving stimuli in different colours, even when all colours are equiluminant.