Is that a belt or a snake? Object attentional selection affects the early stages of visual sensory processing

Top-Down Modulation of Early Visual Processing in V1: Dissociable Neurophysiological Effects of Spatial Attention, Attentional Load and Task-Relevance

Until today, there is an ongoing discussion if attention processes interact with the information processing stream already at the level of the C1, the earliest visual electrophysiological response of the cortex. We used two highly powered experiments (each N = 52) and examined the effects of task relevance, spatial attention, and attentional load on individual C1 amplitudes for the upper or lower visual hemifield. Bayesian models revealed evidence for the absence of load effects but substantial modulations by task-relevance and spatial attention. When the C1-eliciting stimulus was a task-irrelevant, interfering distracter, we observed increased C1 amplitudes for spatially unattended stimuli. For spatially attended stimuli, different effects of task-relevance for the two experiments were found. Follow-up exploratory single-trial analyses revealed that subtle but systematic deviations from the eye-gaze position at stimulus onset between conditions substantially influenced the effects of attention and task relevance on C1 amplitudes, especially for the upper visual field. For the subsequent P1 component, attentional modulations were clearly expressed and remained unaffected by these deviations. Collectively, these results suggest that spatial attention, unlike load or task relevance, can exert dissociable top-down modulatory effects at the C1 and P1 levels.

Scalp-recorded N40 visual evoked potential: Sensory and attentional properties

N40 is a well-known component of evoked potentials with respect to the auditory and somatosensory modality but not much recognized with regard to the visual modality. To be detected with event-related potentials (ERPs), it requires an optimal signal-to-noise ratio. To investigate the nature of visual N40, we recorded EEG/ERP signals from 20 participants. Each of them was presented with 1800 spatial frequency gratings of 0.75, 1.5, 3 and 6 c/deg. Data were collected from 128 sites while participants were engaged in both passive viewing and attention conditions. N40 (30-55 ms) was modulated by alertness and selective attention; in fact, it was larger to targets than irrelevant and passively viewed spatial frequency gratings. Its strongest intracranial sources were the bilateral thalamic nuclei of pulvinar, according to swLORETA. The active network included precuneus, insula and inferior parietal lobule. An N80 component (60-90 ms) was also identified, which was larger to targets than irrelevant/passive stimuli and more negative to high than low spatial frequencies. In contrast, N40 was not sensitive to spatial frequency per se, nor did it show a polarity inversion as a function of spatial frequency. Attention, alertness and spatial frequency effects were also found for the later components P1, N2 and P300. The attentional effects increased in magnitude over time. The data showed that ERPs can pick up the earliest synchronized activity, deriving in part from thalamic nuclei, before the visual information has actually reached the occipital cortex.

Memorisation and implicit perceptual learning are enhanced for preferred musical intervals and chords

Is it true that we learn better what we like? Current neuroaesthetic and neurocomputational models of aesthetic appreciation postulate the existence of a correlation between aesthetic appreciation and learning. However, even though aesthetic appreciation has been associated with attentional enhancements, systematic evidence demonstrating its influence on learning processes is still lacking. Here, in two experiments, we investigated the relationship between aesthetic preferences for consonance versus dissonance and the memorisation of musical intervals and chords. In Experiment 1, 60 participants were first asked to memorise and evaluate arpeggiated triad chords (memorisation phase), then, following a distraction task, chords’ memorisation accuracy was measured (recognition phase). Memorisation resulted to be significantly enhanced for subjectively preferred as compared with non-preferred chords. To explore the possible neural mechanisms underlying these results, we performed an EEG study, directed to investigate implicit perceptual learning dynamics (Experiment 2). Through an auditory mismatch detection paradigm, electrophysiological responses to standard/deviant intervals were recorded, while participants were asked to evaluate the beauty of the intervals. We found a significant trial-by-trial correlation between subjective aesthetic judgements and single trial amplitude fluctuations of the ERP attention-related N1 component. Moreover, implicit perceptual learning, expressed by larger mismatch detection responses, was enhanced for more appreciated intervals. Altogether, our results showed the existence of a relationship between aesthetic appreciation and implicit learning dynamics as well as higher-order learning processes, such as memorisation. This finding might suggest possible future applications in different research domains such as teaching and rehabilitation of memory and attentional deficits.

Hemispheric Asymmetry in Visual Processing: An ERP Study on Spatial Frequency Gratings

A hemispheric asymmetry for the processing of global versus local visual information is known. In this study, we investigated the existence of a hemispheric asymmetry for the visual processing of low versus high spatial frequency gratings. The event-related potentials were recorded in a group of healthy right-handed volunteers from 30 scalp sites. Six types of stimuli (1.5, 3 and 6 c/deg gratings) were randomly flashed 180 times in the left and right upper hemifields. The stimulus duration was 80 ms, and the interstimulus interval (ISI) ranged between 850 and 1000 ms. Participants paid attention and responded to targets based on their spatial frequency and location. The C1 and P1 visual responses, as well as a later selection negativity and a P300 component of event-related potentials (ERPs), were quantified and subjected to repeated-measure analyses of variance (ANOVAs). Overall, the performance was faster for the right visual field (RVF), thus suggesting a left hemispheric advantage for the attentional selection of local elements. Similarly, the analysis of the mean area amplitude of the C1 (60–110 ms) sensory response showed a stronger attentional effect (F+L+ vs. F−L+) at the left occipital areas, thus suggesting the sensory nature of this hemispheric asymmetry.

Interindividual differences in brain dynamics of early visual processes: Impact on score accuracy in the mental rotation task

Interindividual variations in the ability to perform visuospatial mental transformations have been investigated extensively, in particular through mental rotation tasks. However, the impact of early visual processes on performance has been largely ignored. To clarify this issue, we explored the time-course of early visual processing (from 0 to 450 ms poststimulus) using event-related potentials topographic analyses. The main findings demonstrated a significant link between early attentional processes and accuracy scores occurring more than five seconds later, as well as a strong association between spatial covariance and microstate topographies exhibiting substantial gender differences. More specifically, the results indicated that, in a classical mental rotation task, the male brain expends more time processing visual-spatial information resulting in a longer bilateral positive potential at posterior-occipital sites. In comparison, the female brain initiates earlier processing of non-spatial information resulting in a faster transition from a bilateral positive potential of posterior-occipital sites to a negative potential at central-frontal sites. These findings illustrate how a more complete utilization of the spatiotemporal information contained in EEG recordings can provide important insights about the impact of early visual processes on interindividual differences, particularly across gender, and thus shed new light on alternate cognitive strategies.

Early Attentional Modulation by Working Memory Training in Young Adult ADHD Patients during a Risky Decision-Making Task

Background: Working memory (WM) deficits and impaired decision making are among the characteristic symptoms of patients affected by attention deficit/hyperactivity disorder (ADHD). The inattention associated with the disorder is likely to be due to functional deficits of the neural networks inhibiting irrelevant sensory input. In the presence of unnecessary information, a good decisional process is impaired and ADHD patients tend to take risky decisions. This study is aimed to test the hypothesis that the level of difficulty of a WM training (WMT) is affecting the top-down modulation of the attentional processes in a probabilistic gambling task. Methods: Event-related potentials (ERP) triggered by the choice of the amount wagered in the gambling task were recorded, before and after WMT with a the dual n-back task, in young ADHD adults and matched controls. For each group of participants, randomly assigned individuals were requested to perform WMT with a fixed baseline level of difficulty. The remaining participants were trained with a performance-dependent adaptive n-level of difficulty. Results: We compared the ERP recordings before and after 20 days of WMT in each subgroup. The analysis was focused on the time windows with at least three recording sites showing differences before and after training, after Bonferroni correction ( p < 0.05 ). In ADHD, the P1 wave component was selectively affected at frontal sites and its shape was recovered close to controls' only after adaptive training. In controls, the strongest contrast was observed at parietal level with a left hemispheric dominance at latencies near 900 ms, more after baseline than after adaptive training. Conclusion: Partial restoration of early selective attentional processes in ADHD patients might occur after WMT with a high cognitive load. Modified frontal sites' activities might constitute a neural marker of this effect in a gambling task. In controls, conversely, an increase in late parietal negativity might rather be a marker of an increase in transfer effects to fluid intelligence.

False Recognition in Short-Term Memory - Age-Differences in Confidence

Compared to young adults, older adults are more susceptible to endorse false memories as genuine and exhibit higher confidence in their decisions to do so. While most studies to date have addressed this phenomenon in the context of episodic memory, the literature on age-differences in false recognition during short-term memory (STM) is scarce. Hence, the present study investigated age-related differences in the rate of false alarms (FA) and subsequent confidence judgments in STM. Thirty-three young and thirty-three older adults performed a visual short-term recognition memory task. In each trial, participants encoded a single abstract object, then made a "same" or "different" decision on a subsequent test, followed by a confidence judgment. We found significant age-related differences in performance as measured by the sensitivity index (d'), but not in the rate of FAs. Older adults were more confident in their erroneous recognition decisions than younger adults. The results are discussed in the context of age-differences in monitoring and associative processes.

Beauty in mind: Aesthetic appreciation correlates with perceptual facilitation and attentional amplification

Neuroaesthetic research suggests that aesthetic appreciation results from the interaction between the object perceptual features and the perceiver's sensory processing dynamics. In the present study, we investigated the relationship between aesthetic appreciation and attentional modulation at a behavioural and psychophysiological level. In a first experiment, fifty-eight healthy participants performed a visual search task with abstract stimuli containing more or less natural spatial frequencies and subsequently were asked to give an aesthetic evaluation of the images. The results evidenced that response times were faster for more appreciated stimuli. In a second experiment, we recorded visual evoked potentials (VEPs) during exposure to the same stimuli. The results showed, only for more appreciated images, an enhancement in C1 and N1, P3 and N4 VEP components. Moreover, we found increased attention-related occipital alpha desynchronization for more appreciated images. We interpret these data as indicative of the existence of a correlation between aesthetic appreciation and perceptual processing enhancement, both at a behavioural and at a neurophysiological level.

Electrophysiological evidence of perceived sexual attractiveness for human female bodies varying in waist-to-hip ratio

The dynamics of brain activation reflecting attractiveness in humans are unclear. Among the different features affecting attractiveness of the female body, the waist-to-hip ratio (WHR) is considered to be crucial. To date, however, no event-related potential (ERP) study has addressed the question of its associated pattern of brain activation. We carried out two different experiments: (a) a behavioural study, to judge the level of attractiveness of female realistic models depicting 4 different WHRs (0.6, 0.7, 0.8, 0.9) with and without clothes; (b) an EEG paradigm, to record brain activity while participants (heterosexual men and women) viewed these same models. Behavioural results showed that WHRs of 0.7 were considered more attractive than the others. ERP analyses revealed a different pattern of activation for male and female viewers. The 0.7 ratio elicited greater positivity at the P1 level in male viewers but not females. Naked bodies increased the N190 in both groups and peaked earlier for the 0.7 ratio in the male viewers. Finally, the late positive component (LPC) was found to be greater in male than in female viewers and was globally more marked for naked bodies as well as WHRs of 0.7 in both groups of viewers. These results provide the first electrophysiological evidence of specific time periods linked to the processing of a body feature denoting attractiveness and therefore playing a role in mate choice.

Endogenous attention to object features modulates the ERP C1 component

Converging neuroimaging and electrophysiological evidence supports the notion that selective attention can modulate neural activity not only in V1 (BA17)-as early as 40-60 ms post-stimulus-but also at the subcortical level (thalamic lateral geniculate nucleus, LGN). V1 modulation has been documented both in space-based and (especially) object-based selection conditions, most of all in endogenous orienting paradigms. It seems then that an attentional modulation of the ERP C1 response-reflecting V1 modulation-would not be especially favoured by exogenous cuing as far as object-based attention is concerned.

Women are better at seeing faces where there are none: an ERP study of face pareidolia

Event-related potentials (ERPs) were recorded in 26 right-handed students while they detected pictures of animals intermixed with those of familiar objects, faces and faces-in-things (FITs). The face-specific N170 ERP component over the right hemisphere was larger in response to faces and FITs than to objects. The vertex positive potential (VPP) showed a difference in FIT encoding processes between males and females at frontal sites; while for men, the FIT stimuli elicited a VPP of intermediate amplitude (between that for faces and objects), for women, there was no difference in VPP responses to faces or FITs, suggesting a marked anthropomorphization of objects in women. SwLORETA source reconstructions carried out to estimate the intracortical generators of ERPs in the 150-190 ms time window showed how, in the female brain, FIT perception was associated with the activation of brain areas involved in the affective processing of faces (right STS, BA22; posterior cingulate cortex, BA22; and orbitofrontal cortex, BA10) in addition to regions linked to shape processing (left cuneus, BA18/30). Conversely, in the men, the activation of occipito/parietal regions was prevalent, with a considerably smaller activation of BA10. The data suggest that the female brain is more inclined to anthropomorphize perfectly real objects compared to the male brain.

Emotional Reactivity to Visual Content as Revealed by ERP Component Clustering

Abstract. In the study, the neural basis of emotional reactivity was investigated. Reactivity was operationalized as the impact of emotional pictures on the self-reported ongoing affective state. It was used to divide the subjects into high- and low-responders groups. Independent sources of brain activity were identified, localized with the DIPFIT method, and clustered across subjects to analyse the visual evoked potentials to affective pictures. Four of the identified clusters revealed effects of reactivity. The earliest two started about 120 ms from the stimulus onset and were located in the occipital lobe and the right temporoparietal junction. Another two with a latency of 200 ms were found in the orbitofrontal and the right dorsolateral cortices. Additionally, differences in pre-stimulus alpha level over the visual cortex were observed between the groups. The attentional modulation of perceptual processes is proposed as an early source of emotional reactivity, which forms an automatic mechanism of affective control. The role of top-down processes in affective appraisal and, finally, the experience of ongoing emotional states is also discussed.

Processing of masked and unmasked emotional faces under different attentional conditions: an electrophysiological investigation

In order to investigate the interactions between non-spatial selective attention, awareness and emotion processing, we carried out an ERP study using a backward masking paradigm, in which angry, fearful, happy, and neutral facial expressions were presented, while participants attempted to detect the presence of one or the other category of facial expressions in the different experimental blocks. ERP results showed that negative emotions enhanced an early N170 response over temporal-occipital leads in both masked and unmasked conditions, independently of selective attention. A later effect arising at the P2 was linked to awareness. Finally, selective attention was found to affect the N2 and N3 components over occipito-parietal leads. Our findings reveal that (i) the initial processing of facial expressions arises prior to attention and awareness; (ii) attention and awareness give rise to temporally distinct periods of activation independently of the type of emotion with only a partial degree of overlap; and (iii) selective attention appears to be influenced by the emotional nature of the stimuli, which in turn impinges on unconscious processing at a very early stage. This study confirms previous reports that negative facial expressions can be processed rapidly, in absence of visual awareness and independently of selective attention. On the other hand, attention and awareness may operate in a synergistic way, depending on task demand.

ERP signs of categorical and supra-categorical processing of visual information

BACKGROUND

The aim of the present study was to investigate to what extent shared and distinct brain mechanisms are possibly subserving the processing of visual supra-categorical and categorical knowledge as observed with event-related potentials of the brain. Access time to these knowledge types was also investigated. Picture pairs of animals, objects, and mixed types were presented. Participants were asked to decide whether each pair contained pictures belonging to the same category (either animals or man-made objects) or to different categories by pressing one of two buttons. Response accuracy and reaction times (RTs) were also recorded.

RESULTS

Both ERPs and RTs were grand-averaged separately for the same-different supra-categories and the animal-object categories. Behavioral performance was faster for more endomorphic pairs, i.e., animals vs. objects and same vs. different category pairs. For ERPs, a modulation of the earliest C1 and subsequent P1 responses to the same vs. different supra-category pairs, but not to the animal vs. object category pairs, was found. This finding supports the view that early afferent processing in the striate cortex can be boosted as a by-product of attention allocated to the processing of shapes and basic features that are mismatched, but not to their semantic quintessence, during same-different supra-categorical judgment. Most importantly, the fact that this processing accrual occurred independent of a traditional experimental condition requiring selective attention to a stimulus source out of the various sources addressed makes it conceivable that this processing accrual may arise from the attentional demand deriving from the alternate focusing of visual attention within and across stimulus categorical pairs' basic structural features. Additional posterior ERP reflections of the brain more prominently processing animal category and same-category pairs were observed at the N1 and N2 levels, respectively, as well as at a late positive complex level, overall most likely related to different stages of analysis of the greater endomorphy of these shape groups. Conversely, an enhanced fronto-central and fronto-lateral N2 as well as a centro-parietal N400 to man-made objects and different-category pairs were found, possibly indexing processing of these entities' lower endomorphy and isomorphy at the basic features and semantic levels, respectively.

CONCLUSION

Overall, the present ERP results revealed shared and distinct mechanisms of access to supra-categorical and categorical knowledge in the same way in which shared and distinct neural representations underlie the processing of diverse semantic categories. Additionally, they outlined the serial nature of categorical and supra-categorical representations, indicating the sequential steps of access to these separate knowledge types.

Late electrophysiological modulations of feature-based attention to object shapes

Feature-based attention has been shown to aid object perception. Our previous ERP effects revealed temporally late feature-based modulation in response to objects relative to motion. The aim of the current study was to confirm the timing of feature-based influences on object perception while cueing within the feature dimension of shape. Participants were told to expect either "pillow" or "flower" objects embedded among random white and black lines. Participants more accurately reported the object's main color for valid compared to invalid shapes. ERPs revealed modulation from 252-502 ms, from occipital to frontal electrodes. Our results are consistent with previous findings examining the time course for processing similar stimuli (illusory contours). Our results provide novel insights into how attending to features of higher complexity aids object perception presumably via feed-forward and feedback mechanisms along the visual hierarchy.

Neural pathways conveying novisual information to the visual cortex

The visual cortex has been traditionally considered as a stimulus-driven, unimodal system with a hierarchical organization. However, recent animal and human studies have shown that the visual cortex responds to non-visual stimuli, especially in individuals with visual deprivation congenitally, indicating the supramodal nature of the functional representation in the visual cortex. To understand the neural substrates of the cross-modal processing of the non-visual signals in the visual cortex, we firstly showed the supramodal nature of the visual cortex. We then reviewed how the nonvisual signals reach the visual cortex. Moreover, we discussed if these non-visual pathways are reshaped by early visual deprivation. Finally, the open question about the nature (stimulus-driven or top-down) of non-visual signals is also discussed.