Electrocortical and ocular indices of attention to fearful and neutral faces presented under high and low working memory load

Working memory load reduces the late positive potential (LPP), consistent with the notion that functional activation of the DLPFC attenuates neural indices of sustained attention. Visual attention also modulates the LPP. In the present study, we sought to determine whether working memory load might exert its influence on ERPs by reducing fixations to arousing picture regions. We simultaneously recorded eye-tracking and EEG while participants performed a working memory task interspersed with the presentation of task-irrelevant fearful and neutral faces. As expected, fearful compared to neutral faces elicited larger N170 and LPP amplitudes; in addition, working memory load reduced the N170 and the LPP. Participants made more fixations to arousing regions of neutral faces and faces presented under high working memory load. Therefore, working memory load did not induce avoidance of arousing picture regions and visual attention cannot explain load effects on the N170 and LPP.     

Electrocortical and ocular indices of attention to fearful and neutral faces presented under high and low working memory load

Working memory load reduces the late positive potential (LPP), consistent with the notion that functional activation of the DLPFC attenuates neural indices of sustained attention. Visual attention also modulates the LPP. In the present study, we sought to determine whether working memory load might exert its influence on ERPs by reducing fixations to arousing picture regions. We simultaneously recorded eye-tracking and EEG while participants performed a working memory task interspersed with the presentation of task-irrelevant fearful and neutral faces. As expected, fearful compared to neutral faces elicited larger N170 and LPP amplitudes; in addition, working memory load reduced the N170 and the LPP. Participants made more fixations to arousing regions of neutral faces and faces presented under high working memory load. Therefore, working memory load did not induce avoidance of arousing picture regions and visual attention cannot explain load effects on the N170 and LPP.     

Distraction in a continuous-stimulation detection task

Event-related potential (ERP) correlates of distraction are usually investigated in the oddball paradigm following a discrete, trial-by-trial stimulation protocol. In this design, participants perform a discrimination task while oddball stimuli deviate in a task-irrelevant stimulus feature. In our experiment, participants detected gaps in a continuous tone while infrequent frequency glides served as distracting events.Glides preceding a gap by 150 ms delayed the response to the gap and elicited the ERP sequence of N1, probably MMN, P3a, and reorienting negativity, suggesting that these responses reflect distraction-related processes which are neither task- nor stimulation-specific.When participants watched a silent movie and the auditory stimulation was task-irrelevant, glides preceding a gap by 150 ms enhanced the amplitude of the gap-elicited N1. However, when the auditory stimulation was task-relevant, the gap-elicited N1 was attenuated. These results show that the glides drew attention away from the ongoing task, both from watching the silent movie and from detecting gaps.     

Behind the scenes: How visual memory load biases selective attention during processing of visual streams

We recorded ERPs to investigate whether the visual memory load can bias visual selective attention. Participants memorized one or four letters and then responded to memory‐matching letters presented in a relevant color while ignoring distractor letters or letters in an irrelevant color. Stimuli in the relevant color elicited larger frontal selection positivities (FSP) and occipital selection negativities (OSN) compared to irrelevant color stimuli. Only distractors elicited a larger FSP in the high than in the low memory load task. Memory load prolonged the OSN for all letters. Response mapping complexity was also modulated but did not affect the FSP and OSN. Together, the FSP data suggest that high memory load increased distractability. The OSN data suggest that memory load sustained attention to letters in a relevant color until working memory processing was completed, independently of whether the letters were in working memory or not.     

Guidance of visual attention from working memory contents depends on stimulus attributes

Recent work shows that items maintained in working memory could guide the orienting of attention in visual search, demonstrating an interesting interaction between working memory and attention. For such guidance effect, some studies emphasize the importance of search task type: for fixed-target search, task-irrelevant memory items stay inside the attentional focus and guides attention; for varied-target search, these items stay outside attentional focus and do not guide attention. With two experiments, we showed that stimulus attribute of items held in working memory can play an important role in attentional guidance. The first behavioral experiment duplicated a previous fixed-target search paradigm demonstrating robust guidance effect but failed to find such effect when the stimuli was simply changed from colored shapes to complex artificial shapes. The second event-related potential experiment duplicated a previous varied-target search paradigm that used complex shapes but did not observe any guidance effect. A clear guidance effect was found when we changed the stimuli to colored shapes. The results suggest that attentional guidance from working memory depends on stimulus attributes of the items held in working memory. When effective attribute is used, task-irrelevant items that stay outside the attentional focus are still able to guide attention.     

Surprise? Early visual novelty processing is not modulated by attention

This study investigated the influence of direction of attention on the early detection of visual novelty, as indexed by the anterior N2. The anterior N2 was measured in young subjects (n=32) under an attend and an ignore condition. Subjects were presented standard, target/rare, and perceptually novel visual stimuli under both conditions, but under the ignore condition, attention was directed toward an auditory n-back task. The size of the anterior N2 to novel stimuli did not differ between conditions and was significantly larger than the anterior N2 to all other stimulus types. Furthermore, under the ignore condition, the anterior N2 to visual novel stimuli was not affected by the level of difficulty of the auditory n-back task (3-back vs. 2-back). Our findings suggest that the early processing of visual novelty, as measured by the size of the anterior N2, is not strongly modulated by direction of attention.     

人脑对视觉信息变化的处理过程的事件相关电位研究

目的:采用256导联事件相关电位技术和低分辨率电磁图的方法,研究人脑对视觉信息变化的处理过程.方法:12名健康志愿者参与试验.视觉刺激为同时具有颜色和形状2种特征的图形.先后呈现的2张图片(S1和S2)组成一个刺激对并分为4种类型:S1和S2的颜色、形状均相同;S1和S2的颜色相同,形状不同;S1和S2的颜色不同,形状相同;S1和S2的颜色、形状均不同.受试者分别完成注意颜色和注意形状2个任务.结果:①S2呈现后135 ms～165 ms,3种变化的刺激对引出了变化相关正波(change-related positivity,CRP).低分辨率电磁图(low-resolution electromagnetic tomography,LORETA)分析显示CRP的发生源是枕叶舌回、楔叶.②235 ms～275 ms时间窗内,无变化和无关变化状态引出了N200,右侧颞叶梭状回、颞中回和海马旁回是该成分的发生源.③240 ms～320 ms时间窗内,所有变化的刺激对均引出了N270,前扣带回和双侧杏仁核是N270的发生源.结论:人脑对视觉信息变化的处理过程可分为3个阶段:CRP所代表的可能是人脑对视觉信息变化的早期处理阶段;N200所反映的可能是人脑对无关信息变化的主动忽略阶段;N270可能代表高级处理阶段.     

Maintenance of tactile short-term memory for locations is mediated by spatial attention

According to the attention-based rehearsal hypothesis, maintenance of spatial information is mediated by covert orienting towards memorized locations. In a somatosensory memory task, participants simultaneously received bilateral pairs of mechanical sample pulses. For each hand, sample stimuli were randomly assigned to one of three locations (fingers). A subsequent visual retro-cue determined whether the left or right hand sample was to be memorized. The retro-cue elicited lateralized activity reflecting the location of the relevant sample stimulus. Sensory processing during the retention period was probed by task-irrelevant pulses randomized to locations at the cued and uncued hand. The somatosensory N140 was enhanced for probes delivered to the cued hand, relative to uncued. Probes presented shortly after the retro-cue showed greatest attentional modulations. This suggests that transient contributions from retrospective selection overlapped with the sustained effect of attention-based rehearsal. In conclusion, focal attention shifts within tactile mnemonic content occurred after retro-cues and guided sensory processing during retention.     

Underlying mechanisms of the P3a task-difficulty effect

In three-stimulus oddball studies, even typical deviant stimuli elicited a large P3a event-related brain potential (ERP) when target/standard discrimination was difficult. To investigate the underlying mechanisms, the effects of task difficulty on early deviant-related ERPs were assessed. Four visual stimuli defined by an orthogonal combination of task-relevant size (nontarget 80%, target 20%) and task-irrelevant luminance (standard 80%, deviant 20%) were presented randomly, where two task difficulties (easy, difficult) were defined by target/nontarget discriminability. An increase in task difficulty enhanced P3a as well as a posterior negativity (change-related negativity) and an anterior positivity (frontal positivity) elicited by deviant nontarget stimuli. These results suggest that attentional modulation of refractoriness-based rareness detection and an attention-triggering process underlie the P3a task-difficulty effect.     

Contralateral delay activity tracks the storage of visually presented letters and words

Electrophysiological studies have demonstrated that the maintenance of items in visual working memory (VWM) is indexed by the contralateral delay activity (CDA), which increases in amplitude as the number of objects to remember increases, plateauing at VWM capacity. Previous work has primarily utilized simple visual items, such as colored squares or picture stimuli. Despite the frequent use of verbal stimuli in seminal investigations of visual attention and memory, it is unknown whether temporary storage of letters and words also elicit a typical load‐sensitive CDA. Given their close associations with language and phonological codes, it is possible that participants store these stimuli phonologically, and not visually. Participants completed a standard visual change‐detection task while their ERPs were recorded. Experiment 1 compared the CDA elicited by colored squares compared to uppercase consonants, and Experiment 2 compared the CDA elicited by words compared to colored bars. Behavioral accuracy of change detection decreased with increasing set size for colored squares, letters, and words. We found that a capacity‐limited CDA was present for colored squares, letters, and word arrays, suggesting that the visual codes for letters and words were maintained in VWM, despite the potential for transfer to verbal working memory. These results suggest that, despite their verbal associations, letters and words elicit the electrophysiological marker of VWM encoding and storage.     

Neural fate of ignored stimuli: dissociable effects of perceptual and working memory load

Observers commonly experience functional blindness to unattended visual events, and this problem has fuelled an intense debate concerning the fate of unattended visual information in neural processing. Here we used functional magnetic resonance imaging (fMRI) to demonstrate that the type of task that a human subject engages in determines the way in which ignored visual background stimuli are processed in parahippocampal cortex. Increasing the perceptual difficulty of a foveal target task attenuated processing of task-irrelevant background scenes, whereas increasing the number of objects held in working memory did not have this effect. These dissociable effects of perceptual and working memory load clarify how task-irrelevant, unattended stimuli are processed in category-selective areas in human ventral visual cortex.     

Age and novelty: event-related potentials to visual stimuli within an auditory oddball--visual detection task.

Age-related change of event-related potentials to novel visual stimuli was investigated while participants attended to both auditory and visual stimulation. Meaningful but irrelevant pictures (novel stimuli) were presented to younger (mean=21.8, range=18-26 years) and older (mean=70.0, range=60-78) participants (10 in each group). The participants were performing an auditory oddball task and counting silently the changes of a visually presented letter. In the younger group novel stimuli elicited a posterior positivity in the 220-255 ms range. This component habituated to the repetition of the same picture. In the older group this component had longer latency, and did not habituate. A later positivity had shorter latency and larger amplitude in the younger group, but this positivity was preceded by a negative component (N2b) only in the elderly. Results show decreased sensitivity to the content of the visual stimuli in an earlier stage of novelty processing in the elderly, and the age-related slowing of both orientation-related and task-related processes.     

Emotionally negative pictures increase attention to a subsequent auditory stimulus

Emotionally negative stimuli serve as a mechanism of biological preparedness to enhance attention. We hypothesized that emotionally negative stimuli would also serve as motivational priming to increase attention resources for subsequent stimuli. To that end, we tested 11 participants in a dual sensory modality task, wherein emotionally negative pictures were contrasted with emotionally neutral pictures and each picture was followed 600 ms later by a tone in an auditory oddball paradigm. Each trial began with a picture displayed for 200 ms; half of the trials began with an emotionally negative picture and half of the trials began with an emotionally neutral picture; 600 ms following picture presentation, the participants heard either an oddball tone or a standard tone. At the end of each trial (picture followed by tone), the participants categorized, with a button press, the picture and tone combination. As expected, and consistent with previous studies, we found an enhanced visual late positive potential (latency range = 300-700 ms) to the negative picture stimuli. We further found that compared to neutral pictures, negative pictures resulted in early attention and orienting effects to subsequent tones (measured through an enhanced N1 and N2) and sustained attention effects only to the subsequent oddball tones (measured through late processing negativity, latency range = 400-700 ms). Number pad responses to both the picture and tone category showed the shortest response latencies and greatest percentage of correct picture-tone categorization on the negative picture followed by oddball tone trials. Consistent with previous work on natural selective attention, our results support the idea that emotional stimuli can alter attention resource allocation. This finding has broad implications for human attention and performance as it specifically shows the conditions in which an emotionally negative stimulus can result in extended stimulus evaluation.     

Examining task-dependencies of different attentional processes as reflected in the P3a and reorienting negativity components of the human event-related brain potential

Unexpected changes in task-irrelevant auditory stimuli are capable to distract processing of task-relevant visual information. This effect is accompanied by the elicitation of event-related potential (ERP) components associated with attentional orientation, i.e. P3a and reorienting negativity (RON). In the present study we varied the demands of a visual task in order to test whether the RON component -- as an index of attentional reorientation after distraction -- is confined to a semantic task requiring working memory. In two ERP experiments we applied an auditory-visual distraction paradigm in which subjects were instructed to discriminate visual stimuli preceded by a task-irrelevant sound, this being either a standard tone (600 Hz, 88%) or a deviant tone (660 Hz, 12%). The visual stimuli were numbers which had to be judged on basis of a semantic (odd or even) or physical feature (either size or colour). As expected, deviance related ERP components namely the mismatch negativity (MMN), P3a, and RON were elicited. Importantly, the RON was affected by the variation of the task: within the semantic task an early RON and within the physical task a late RON was obtained. These results suggest that the RON component reflects two functionally distinct processes of attentional allocation after distraction: refocusing on task-relevant information on the working memory level, and general reorientation of attention, e.g. preparation for the upcoming task.     

The role of inhibition for working memory processes: ERP evidence from a short‐term storage task

Human working memory is the central unit for short‐term storage of information. In addition to the selection and adequate storage of relevant information, the suppression of irrelevant stimuli from the environment seems to be of importance for working memory processes. To learn more about the interplay of information uptake and inhibition of irrelevant information, the present study used ERP measures and a short‐term storage and retrieval task, in which pairs of either numbers or letters had to be compared. Random sequences of four stimuli (two numbers and two letters) were presented, with either the numbers or the letters being relevant for comparison. The analysis of ERPs to each of the four stimuli indicated more pronounced P2 and P3b amplitudes for relevant than irrelevant stimuli. In contrast, the N2 (reflecting inhibitory control) was only elicited by irrelevant stimuli. Moreover, the N2 amplitude of the second irrelevant stimulus was associated with behavioral performance, indicating the importance of inhibition of task‐irrelevant stimuli for working memory processes. In sum, the findings demonstrate the role of cognitive control mechanisms for protecting relevant contents in working memory against irrelevant information.     

Concurrent visual task effects on evoked and emitted auditory p300 in adolescents

Using an oddball stimulus presentation paradigm, the effects of divided attention on auditory P300s were studied. Auditory attention was either divided or focused, depending on the demands placed on subjects during the performance of a concomitantly presented visual task. Two types of auditory tasks were performed under each of the two auditory attention conditions. In one, subjects responded to infrequently presented high pitched tones (oddball stimuli). In the other they responded to the occasional omission of a stimulus in an otherwise rhythmically presented chain of stimuli. P300s and reaction times were recorded to both the rare tones and the omissions. The Sternberg visual memory task was used to manipulate the subject's auditory attention state. Subjects actively performed the Sternberg task during the divided auditory attention condition, whereas during the focused attention condition they were not required to respond to the visual stimuli. During focused auditory attention, evoked auditory P300s were both larger and faster than their emitted counterparts. During divided attention, auditory P300s were reduced in amplitude but latency was unaffected. Evoked auditory P300s showed evidence of containing P300a as well as P300b components, particularly when attention was shared with the visual task.     

Specific fear modulates attentional selectivity during visual search: Electrophysiological insights from the N2pc

In the present study, we used high‐density EEG during a visual search task to investigate the dynamics of spatial attention to fear‐relevant targets and background stimuli in small animal phobia during a visual search task. Twenty‐five spider fearful (22 females) and 25 healthy nonfearful participants (19 females) were measured, while searching for discrepant objects in visual arrays. Compared to nonfearful participants, s pider fearful individuals showed a more enhanced posterior N2pc to spider (vs. butterfly) targets in an array of flowers. Furthermore, spider fearful participants showed enhanced hypervigilance for all presented stimuli compared to controls as reflected by enhanced N1 amplitudes (160–200 ms). Our findings provide neural evidence for early, enhanced selective spatial attention for fear‐relevant stimuli.     

Visual novel stimuli in an ERP novelty oddball paradigm: effects of familiarity on repetition and recognition memory

The orienting response, the brain's reaction to novel and/or out of context familiar events, is reflected by the novelty P3 of the ERP. Contextually novel events also engender high rates of recognition memory. We examined, under incidental and intentional conditions, the effects of visual symbol familiarity on the novelty P3 recorded during an oddball task and on the parietal episodic memory (EM) effect, an index of recollection. Repetition of familiar, but not unfamiliar, symbols elicited a reduction in the novelty P3. Better recognition performance for the familiar symbols was associated with a robust parietal EM effect, which was absent for the unfamiliar symbols in the incidental task. These data demonstrate that processing of novel events depends on expectation and whether stimuli have preexisting representations in long-term semantic memory.     

Age-dependent changes of auditory evoked potentials--effect of task difficulty

The goal of this study was to evaluate the patterns of age-dependent changes of P3 components of auditory event-related potentials exploring the effects of task difficulty. The participants (age span: 19-68 years, n=55, divided into five age groups) took part in an easy and in a difficult two-tone oddball frequency discrimination task with speed or accuracy instructions, and in a novelty oddball task. The latency of the P3 components increased with aging. While in the easy task a linear P3b latency increase could be seen, in the difficult tasks (difficult frequency discrimination or distracting novel stimuli) an accelerated latency increase was observed for the P3b and P3a. In the two-tone oddball paradigm age had no effect on P3b amplitude, but in the novelty oddball task the amplitude of P3 potentials decreased with age. These results indicate that distracting stimuli increase task demands, and in difficult tasks decay can be observed more easily due to the accumulation of various processing mechanisms characterizing aging.     

Age-related effects of novel visual stimuli in a letter-matching task: an event-related potential study

Younger and older participants (n=8 in each age group) performed a letter-matching task, where they had to respond to identical letters (P=0.15). Task-relevant (target and non-target) letters were presented on two corners of an imagery square, while on the other two corners irrelevant letters were presented. In some trials (P=0.05), pictures of visual objects (novels, unrelated to the matching task) were presented. Reaction times were slower and error rates higher for older adults. The amplitude of the N1 event-related potential component was smaller over anterior locations for the older adults. All target stimuli elicited a late positivity over anterior locations for both age groups, but the late positivity (P3b) was absent over posterior scalp for the older adults. For the younger adults, novel stimuli elicited a large negative component (N2(novel)) that was maximal over the central location. No such activity was observed for older adults. Based on the results, processing of novel stimuli is considered to be compromised in the elderly.