The face-sensitivity of the n170 component

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Attention modulates the processing of emotional expression triggered by foveal faces

To investigate whether the processing of emotional expression for faces presented within foveal vision is modulated by spatial attention, event-related potentials (ERPs) were recorded in response to stimulus arrays containing one fearful or neutral face at fixation, which was flanked by a pair of peripheral bilateral lines. When attention was focused on the central face, an enhanced positivity was elicited by fearful as compared to neutral faces. This effect started at 160 ms post-stimulus, and remained present for the remainder of the 700 ms analysis interval. When attention was directed away from the face towards the line pair, the initial phase of this emotional positivity remained present, but emotional expression effects beyond 220 ms post-stimulus were completely eliminated. These results demonstrate that when faces are presented foveally, the initial rapid stage of emotional expression processing is unaffected by attention. In contrast, attentional task instructions are effective in inhibiting later, more controlled stages of expression analysis

Why the item will remain the unit of attentional selection in visual search

Hulleman & Olivers reject item-based serial models of visual search, and suggest that items are processed equally and globally during each fixation period. However, neuroscientific studies have shown that attentional biases can emerge in parallel but in a spatially selective item-based fashion. Even within a parallel architecture for visual search, the item remains the critical unit of selection

Shifts of attention in the early blind: an ERP study of attentional control processes in the absence of visual spatial information

To investigate the role of visual spatial information in the control of spatial attention, event-related brain potentials (ERPs) were recorded during a tactile attention task for a group of totally blind participants who were either congenitally blind or had lost vision during infancy, and for an age-matched, sighted control group who performed the task in the dark. Participants had to shift attention to the left or right hand (as indicated by an auditory cue presented at the start of each trial) in order to detect infrequent tactile targets delivered to this hand. Effects of tactile attention on the processing of tactile events, as reflected by attentional modulations of somatosensory ERPs to tactile stimuli, were very similar for early blind and sighted participants, suggesting that the capacity to selectively process tactile information from one hand versus the other does not differ systematically between the blind and the sighted. ERPs measured during the cue–target interval revealed an anterior directing attention negativity (ADAN) that was present for the early blind group as well as for the sighted control group. In contrast, the subsequent posterior late direction attention negativity (LDAP) was absent in both groups. These results suggest that these two components reflect functionally distinct attentional control mechanisms which differ in their dependence on the availability of visually coded representations of external space

Lateralized delay period activity marks the focus of spatial attention in working memory: evidence from somatosensory event-related brain potentials

The short-term retention of sensory information in working memory (WM) is known to be associated with a sustained enhancement of neural activity. What remains controversial is whether this neural trace indicates the sustained storage of information or the allocation of attention. To evaluate the storage and attention accounts, we examined sustained tactile contralateral delay activity (tCDA component) of the event-related potential. The tCDA manifests over somatosensory cortex contralateral to task-relevant tactile information during stimulus retention. Two tactile sample sets (S1, S2) were presented sequentially, separated by 1.5 s. Each set comprised two stimuli, one per hand. Human participants memorized the location of one task-relevant stimulus per sample set and judged whether one of these locations was stimulated again at memory test. The two relevant pulses were unpredictably located on the same hand (stay trials) or on different hands (shift trials). Initially, tCDA components emerged contralateral to the relevant S1 pulse. Sequential loading of WM enhanced the tCDA after S2 was presented on stay trials. On shift trials, the tCDA's polarity reversed after S2 presentation, resulting in delay activity that was now contralateral to the task-relevant S2 pulse. The disappearance of a lateralized neural trace for the relevant S1 pulse did not impair memory accuracy for this stimulus on shift trials. These results contradict the storage account and suggest that delay period activity indicates the sustained engagement of an attention-based rehearsal mechanism. In conclusion, somatosensory delay period activity marks the current focus of attention in tactile WM

The guidance of spatial attention during visual search for colour combinations and colour configurations

Representations of target-defining features (attentional templates) guide the selection of target objects in visual search. We used behavioural and electrophysiological measures to investigate how such search templates control the allocation of attention in search tasks where targets are defined by the combination of two colours or by a specific spatial configuration of these colours. Target displays were preceded by spatially uninformative cue displays that contained items in one or both target-defining colours. Experiments 1 and 2 demonstrated that, during search for colour combinations, attention is initially allocated independently and in parallel to all objects with target-matching colours, but is then rapidly withdrawn from objects that only have one of the two target colours. In Experiment 3, targets were defined by a particular spatial configuration of two colours, and could be accompanied by nontarget objects with a different configuration of the same colours. Attentional guidance processes were unable to distinguish between these two types of objects. Both attracted attention equally when they appeared in a cue display, and both received parallel focal-attentional processing and were encoded into working memory when they were presented in the same target display. Results demonstrate that attention can be guided simultaneously by multiple features from the same dimension, but that these guidance processes have no access to the spatial-configural properties of target objects. They suggest that attentional templates do not represent target objects in an integrated pictorial fashion, but contain separate representations of target-defining features

Independent attention mechanisms control the activation of tactile and visual working memory representations

Working memory (WM) is limited in capacity, but it is controversial whether these capacity limitations are domain-general or are generated independently within separate modality-specific memory systems. These alternative accounts were tested in bimodal visual/tactile WM tasks. In Experiment 1, participants memorized the locations of simultaneously presented task-relevant visual and tactile stimuli. Visual and tactile WM load was manipulated independently (1, 2 or 3 items per modality), and one modality was unpredictably tested after each trial. To track the activation of visual and tactile WM representations during the retention interval, the visual and tactile contralateral delay activity (CDA and tCDA) were measured over visual and somatosensory cortex, respectively. CDA and tCDA amplitudes were selectively affected by WM load in the corresponding (tactile or visual) modality. The CDA parametrically increased when visual load increased from 1 to 2 and to 3 items. The tCDA was enhanced when tactile load increased from 1 to 2 items, and showed no further enhancement for 3 tactile items. Critically, these load effects were strictly modality-specific, as substantiated by Bayesian statistics. Increasing tactile load did not affect the visual CDA, and increasing visual load did not modulate the tCDA. Task performance at memory test was also unaffected by WM load in the other (untested) modality. This was confirmed in a second behavioral experiment where tactile and visual loads were either two or four items, unimodal baseline conditions were included, and participants performed a color change detection task in the visual modality. These results show that WM capacity is not limited by a domain-general mechanism that operates across sensory modalities. They suggest instead that WM storage is mediated by distributed modality-specific control mechanisms that are activated independently and in parallel during multisensory WM

Object-based target templates guide attention during visual search

During visual search, attention is believed to be controlled in a strictly feature-based fashion, without any guidance by object-based target representations. To challenge this received view, we measured electrophysiological markers of attentional selection (N2pc component) and working memory (SPCN) in search tasks where two possible targets were defined by feature conjunctions (e.g., blue circles and green squares). Critically, some search displays also contained nontargets with two target features (incorrect conjunction objects, e.g., blue squares). Because feature-based guidance cannot distinguish these objects from targets, any selective bias for targets will reflect object-based attentional control. In Experiment 1, where search displays always contained only one object with target-matching features, targets and incorrect conjunction objects elicited identical N2pc and SPCN components, demonstrating that attentional guidance was entirely feature-based. In Experiment 2, where targets and incorrect conjunction objects could appear in the same display, clear evidence for object-based attentional control was found. The target N2pc became larger than the N2pc to incorrect conjunction objects from 250 ms post-stimulus, and only targets elicited SPCN components. This demonstrates that after an initial feature-based guidance phase, object-based templates are activated when they are required to distinguish target and nontarget objects. These templates modulate visual processing and control access to working memory, and their activation may coincide with the start of feature integration processes. Results also suggest that while multiple feature templates can be activated concurrently, only a single object-based target template can guide attention at any given time

Response inhibition is linked to emotional devaluation: behavioural and electrophysiological evidence

To study links between the inhibition of motor responses and emotional evaluation, we combined electrophysiological measures of prefrontal response inhibition with behavioural measures of affective evaluation. Participants first performed a Go-Nogo task in response to Asian and Caucasian faces (with race determining their Go or Nogo status), followed by a trustworthiness rating for each face. Faces previously seen as Nogo stimuli were rated as less trustworthy than previous Go stimuli. To study links between the efficiency of response inhibition in the Go-Nogo task and subsequent emotional evaluations, the Nogo N2 component was quantified separately for faces that were later judged to be high versus low in trustworthiness. Nogo N2 amplitudes were larger in response to low-rated as compared to high-rated faces, demonstrating that trial-by-trial variations in the efficiency of response inhibition triggered by Nogo faces, as measured by the Nogo N2 component, co-vary with their subsequent affective evaluation. These results suggest close links between inhibitory processes in top-down motor control and emotional responses

Does contralateral delay activity reflect working memory storage or the current focus of spatial attention within visual working memory?

During the retention of visual information in working memory, event-related brain potentials show a sustained negativity over posterior visual regions contralateral to the side where memorised stimuli were presented. This contralateral delay activity (CDA) is generally believed to be a neural marker of working memory storage. In two experiments, we contrasted this storage account of the CDA with the alternative hypothesis that the CDA reflects the current focus of spatial attention on a subset of memorized items set up during the most recent encoding episode. We employed a sequential loading procedure where participants memorised four task-relevant items that were presented in two successive memory displays (M1 and M2). In both experiments, CDA components were initially elicited contralateral to task-relevant items in M1. Critically, the CDA switched polarity when M2 displays appeared on the opposite side. In line with the attentional activation account, these reversed CDA components exclusively reflected the number of items that were encoded from M2 displays, irrespective of how many M1 items were already held in working memory. On trials where M1 and M2 displays were presented on the same side, and on trials where M2 displays appeared non-laterally, CDA components elicited in the interval after M2 remained sensitive to a residual trace of M1 items, indicating that some activation of previously stored items was maintained across encoding episodes. These results challenge the hypothesis that CDA amplitudes directly reflect the total number of stored objects, and suggest that the CDA is primarily sensitive to the activation of a subset of working memory representations within the current focus of spatial attention