Papers by Elisa Santandrea
An EEG study of the combined effects of top-down and bottom-up attentional selection under varying task difficulty
This work reports an investigation of the effect of combined top-down and bottom-up attentional c... more This work reports an investigation of the effect of combined top-down and bottom-up attentional control sources, using known attention-related EEG components that are thought to reflect target selection (N2pc) and distractor suppression (PD), in easy and difficult visual search tasks.
Attenzione selettiva e coscienza: un approccio neurobiologico alla studio di meccanismi cerebrali condivisi
Neural basis of visual selective
Attentional modulation along the object-recognition pathway of the cortical visual system of prim... more Attentional modulation along the object-recognition pathway of the cortical visual system of primates has been shown to consist of enhanced representation of the retinal input at a specific location in space, or of objects located anywhere in the visual field which possess a critical object feature. Moreover, selective attention mechanismsallowthevisualsystemtoresolvecompetition amongmultiple objects in a crowded scene in favor of the object that is relevant for the current behavior. Finally, selective attention affects the spontaneous activity of neurons as well as their visually driven responses, and it does so not only by modulating the spiking activity of individual neurons, but also by modulating the degree of coherent firing within the critical neuronal populations. 2010 John Wiley & Sons, Ltd. WIREs Cogn Sci
Capitolo 16: Meccanismi retinici della visione e proiezioni retiniche secondarie
Integrating top-down and bottom-up attention control factors: an EEG study
Journal of Vision, 2021
Compound statistical learning of target selection and distractor suppression
Journal of Vision, 2018
Encoding of reaching and grasping intentions from monkey medial parietal cortex
Journal of Vision, 2018
Investigating the role of the Frontal Eye Field (FEF) and of the Intraparietal Sulcus (IPS) in attentional capture: A TMS study
Journal of Vision, 2018
Scientific Reports, 2019
Addiction is accompanied by attentional biases (AB), wherein drug-related cues grab attention ind... more Addiction is accompanied by attentional biases (AB), wherein drug-related cues grab attention independently of their perceptual salience. AB have emerged in different flavours depending on the experimental approach, and their clinical relevance is still debated. In chronic smokers we sought evidence for dissociable attention abnormalities that may play distinct roles in the clinical manifestations of the disorder. Fifty smokers performed a modified visual probe-task measuring two forms of AB and their temporal dynamics, and data on their personality traits and smoking history/ status were collected. Two fully dissociable AB effects were found: A Global effect, reflecting the overall impact of smoke cues on attention, and a Location-specific effect, indexing the impact of smoke cues on visuospatial orienting. Importantly, the two effects could be neatly separated from one another as they: (i) unfolded with dissimilar temporal dynamics, (ii) were accounted for by different sets of predictors associated with personality traits and smoking history and (iii) were not correlated with one another. Importantly, the relevance of each of these two components in the single individual depends on a complex blend of personality traits and smoking habits, a result that future efforts addressing the clinical relevance of addiction-related AB should take into careful consideration. Efficient behaviour in a busy world crucially depends on visual selective attention, so that limited processing resources can be devoted to task-relevant information while disregarding irrelevant and potentially distracting stimuli. Only objects that are selected by visual attention undergo in-depth processing, access awareness and guide overt behaviour 1,2. Attentional priority, or the probability that a stimulus in the visual field will be selected at a given moment in time, has been traditionally described as depending on two classes of mechanisms 3. On the one hand, bottom-up (or sensory-driven) mechanisms, reflecting low-level sensory-perceptual properties of the input, guide attention automatically towards conspicuous or unexpected stimuli; on the other, top-down (or goal-driven) mechanisms guide attention strategically towards task-relevant information 4. However, growing evidence has recently challenged this dichotomous view, showing that attentional guidance is susceptible to other sources of control, generally attributable to the experience gained in the past with the same stimuli and context, sometimes known as selection history effects 5-8. So, for instance, if the attentional selection of a given stimulus is extensively practiced 9-11 , or is systematically coupled with rewarding outcomes 12-14 , the attentional priority of the stimulus will be increased, irrespectively of its low-level properties (bottom-up information) and of current goals (top-down information). Indeed, studies investigating cognitive abnormalities in addiction (e.g., nicotine addiction) have long shown that individuals who have developed a drug dependence tend to have their attention grabbed by stimuli in the environment that are associated with their substance of abuse 15-21. Such attentional biases (AB) have been described in a large variety of addicted populations 22 and are thought to result from the systematic coupling, which occurs as the addiction develops, between the perceptual and attentional processing of certain visual objects and the effects of the substance of abuse. Despite exerting different pharmacological effects, drugs of
Neuron, 2018
Vision requires perception of both coarse layout and fine details of objects. In this issue of Ne... more Vision requires perception of both coarse layout and fine details of objects. In this issue of Neuron, Lu et al. (2018) describe a possible basis for the latter: neuronal clusters in area V4 coding high-acuity information, despite the tendency along the visual hierarchy to generate global representations of objects.
Investigative Opthalmology & Visual Science, 2018
The purpose of the research was to elucidate the role of folic acid (B 9) deficiency in the devel... more The purpose of the research was to elucidate the role of folic acid (B 9) deficiency in the development of nutritional optic neuritis and to characterize the neurophysiological consequences of optic nerve degeneration in the cortical visual system. METHODS. A combined behavioral and electrophysiological approach was applied to study luminance contrast sensitivity in two macaque monkeys affected by nutritional optic neuritis and in two healthy monkeys for comparison. For one monkey, a follow-up approach was applied to compare visual performance before onset of optic neuropathy, during the disease, and after treatment. RESULTS. Optic nerve degeneration developed as a consequence of insufficient dietary intake of folic acid in two exemplars of macaque monkeys. The degeneration resulted in markedly reduced luminance contrast sensitivity as assessed behaviorally. In one monkey, we also measured visual activity in response to varying contrast at the level of single neurons in the cortical visual system and found a striking reduction in contrast sensitivity, as well as a marked increase in the latency of neuronal responses. Prolonged daily folate supplementation resulted in a significant recovery of function. CONCLUSIONS. Folic acid deficiency per se can lead to the development of optic nerve degeneration in otherwise healthy adult animals. The optic nerve degeneration strongly affects contrast sensitivity and leads to a distinct reduction in the strength and velocity of the incoming signal to cortical visual areas of the macaque brain, without directly affecting excitability and functional properties of cortical neurons.
Modulating attentional capture via Transcranial Magnetic Stimulation (TMS) of right TPJ
Journal of Vision, 2019
The Journal of Neuroscience, 2019
In visual search, the presence of a salient, yet task-irrelevant, distractor in the stimulus arra... more In visual search, the presence of a salient, yet task-irrelevant, distractor in the stimulus array interferes with target selection and slows down performance. Neuroimaging data point to a key role of the frontoparietal dorsal attention network in dealing with visual distractors; however, the respective roles of different nodes within the network and their hemispheric specialization are still unresolved. Here, we used transcranial magnetic stimulation (TMS) to evaluate the causal role of two key regions of the dorsal attention network in resisting attentional capture by a salient singleton distractor: the frontal eye field (FEF) and the cortex within the intraparietal sulcus (IPS). The task of the participants (male/female human volunteers) was to discriminate the pointing direction of a target arrow while ignoring a task-irrelevant salient distractor. Immediately after stimulus onset, triple-pulse 10 Hz TMS was delivered either to IPS or FEF on either side of the brain. Results indicated that TMS over the right FEF significantly reduced the behavioral cost engendered by the salient distractor relative to left FEF stimulation. No such effect was obtained with stimulation of IPS on either side of brain. Interestingly, this FEF-dependent reduction in distractor interference interacted with the contingent trial history, being maximal when no distractor was present on the previous trial relative to when there was one. Our results provide direct causal evidence that the right FEF houses key mechanisms for distractor filtering, pointing to a pivotal role of the frontal cortex of the right hemisphere in limiting interference from an irrelevant but attention-grabbing stimulus.
Scientific reports, Jan 2, 2018
Over the years, electrophysiological recordings in macaque monkeys performing visuomotor tasks br... more Over the years, electrophysiological recordings in macaque monkeys performing visuomotor tasks brought about accumulating evidence for the expression of neuronal properties (e.g., selectivity in the visuospatial and somatosensory domains, encoding of visual affordances and motor cues) in the posterior parietal area V6A that characterize it as an ideal neural substrate for online control of prehension. Interestingly, neuroimaging studies suggested a role of putative human V6A also in action preparation; moreover, pre-movement population activity in monkey V6A has been recently shown to convey grip-related information for upcoming grasping. Here we directly test whether macaque V6A neurons encode preparatory signals that effectively differentiate between dissimilar actions before movement. We recorded the activity of single V6A neurons during execution of two visuomotor tasks requiring either reach-to-press or reach-to-grasp movements in different background conditions, and described ...
Every instant of perception depends on a cascade of brain processes calibrated to the history of ... more Every instant of perception depends on a cascade of brain processes calibrated to the history of sensory and decisional events. In the present work, we show that human visual perception is constantly shaped by two contrasting forces, exerted by sensory adaptation and past decisions. In a series of experiments, we used multilevel modelling and cross-validation approaches to investigate the impact of previous stimuli and responses on current errors in adjustment tasks. Our results revealed that each perceptual report is permeated by opposite biases from a hierarchy of serially dependent processes: low-level adaptation repels perception away from previous stimuli; high-level, decisional traces attract perceptual reports toward previous responses. Contrary to recent claims, we demonstrated that positive serial dependence does not result from continuity fields operating at the level of early visual processing, but arises from the inertia of decisional templates. This finding is consisten...
Journal of Cognition, 2018
Independent allocation of attention to eye and hand targets in coordinated eye-hand movements.
Statistical learning of distractor suppression
Journal of Vision, 2017
Journal of Neurophysiology, 2017
We offer an innovative perspective on the interplay between attention and luminance contrast in m... more We offer an innovative perspective on the interplay between attention and luminance contrast in macaque area V4, one in which time becomes a fundamental factor. We place emphasis on the temporal dynamics of attentional effects, pioneering the notion that attention modulates contrast response functions of V4 neurons via the sequential engagement of distinct gain mechanisms. These findings advance understanding of attentional influences on visual processing and help reconcile divergent results in the literature.
Cortex, 2016
Visual selective attention (VSA) optimizes perception and behavioral control by enabling efficien... more Visual selective attention (VSA) optimizes perception and behavioral control by enabling efficient selection of relevant information and filtering of distractors. While focusing resources on task-relevant information helps counteract distraction, dedicated filtering mechanisms have recently been demonstrated, allowing neural systems to implement suitable policies for the suppression of potential interference. Limited evidence is presently available concerning the neural underpinnings of these mechanisms, and whether neural circuitry within the visual cortex might play a causal role in their instantiation, a possibility that we directly tested here. In two related experiments, transcranial magnetic stimulation (TMS) was applied over the lateral occipital cortex of healthy humans at different times during the execution of a behavioral task which entailed varying levels of distractor interference and need for attentional engagement. While earlier TMS boosted target selection, stimulation within a restricted time epoch close to (and in the course of) stimulus presentation engendered selective enhancement of distractor suppression, by affecting the ongoing, reactive instantiation of attentional filtering mechanisms required by specific task conditions. The results attest to a causal role of mid-tier ventral visual areas in distractor filtering and offer insights into the mechanisms through which TMS may have affected ongoing neural activity in the stimulated tissue.
Reward-based plasticity of spatial priority maps: Exploiting inter-subject variability to probe the underlying neurobiology
Cognitive neuroscience, 2016
Recent evidence indicates that the attentional priority of objects and locations is altered by th... more Recent evidence indicates that the attentional priority of objects and locations is altered by the controlled delivery of reward, reflecting reward-based attentional learning. Here, we take an approach hinging on intersubject variability to probe the neurobiological bases of the reward-driven plasticity of spatial priority maps. Specifically, we ask whether an individual's susceptibility to the reward-based treatment can be accounted for by specific predictors, notably personality traits that are linked to reward processing (along with more general personality traits), but also gender. Using a visual search protocol, we show that when different target locations are associated with unequal reward probability, different priorities are acquired by the more rewarded relative to the less rewarded locations. However, while males exhibit the expected pattern of results, with greater priority for locations associated with higher reward, females show an opposite trend. Critically, both t...
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Papers by Elisa Santandrea