“IT’S ALL RIGHT”. Multimodal rightward spatial bias modified by age and praxis

The general goal of the present work was to study whether spatial perceptual asymmetry initially observed in linguistic dichotic listening studies is related to the linguistic nature of the stimuli and/or is modality-specific, as well as to investigate whether the spatial perceptual/attentional asymmetry changes as a function of age and sensory deficit via praxis. Several dichotic listening studies with linguistic stimuli have shown that the inherent perceptual right ear advantage (REA), which presumably results from the left lateralized linguistic functions (bottom-up processes), can be modified with executive functions (top-down control). Executive functions mature slowly during childhood, are well developed in adulthood, and decline as a function of ageing. In Study I, the purpose was to investigate with a cross-sectional experiment from a lifespan perspective the age-related changes in top-down control of REA for linguistic stimuli in dichotic listening with a forced-attention paradigm (DL). In Study II, the aim was to determine whether the REA is linguistic-stimulus-specific or not, and whether the lifespan changes in perceptual asymmetry observed in dichotic listening would exist also in auditory spatial attention tasks that put load on attentional control. In Study III, using visual spatial attention tasks, mimicking the auditory tasks applied in Study II, it was investigated whether or not the stimulus-non-specific rightward spatial bias found in auditory modality is a multimodal phenomenon. Finally, as it has been suggested that the absence of visual input in blind participants leads to improved auditory spatial perceptual and cognitive skills, the aim in Study IV was to determine, whether blindness modifies the ear advantage in DL. Altogether 180-190 right-handed participants between 5 and 79 years of age were studied in Studies I to III, and in Study IV the performance of 14 blind individuals was compared with that of 129 normally sighted individuals. The results showed that only rightward spatial bias was observed in tasks with intensive attentional load, independent of the type of stimuli (linguistic vs. non-linguistic) or the modality (auditory vs. visual). This multimodal rightward spatial bias probably results from a complex interaction of asymmetrical perceptual, attentional, and/or motor mechanisms. Most importantly, the strength of the rightward spatial bias changed as a function of age and augmented praxis due to sensory deficit. The efficiency of the performance in spatial attention tasks and the ability to overcome the rightward spatial bias increased during childhood, was at its best in young adulthood, and decreased as a function of ageing. Between the ages of 5 and 11 years probably at first develops movement and impulse control, followed by the gradual development of abilities to inhibit distractions and disengage attention. The errors especially in bilateral stimulus conditions suggest that a mild phenomenon resembling extinction can be observed throughout the lifespan, but especially the ability to distribute attention to multiple targets simultaneously decreases in the course of ageing. Blindness enhances the processing of auditory bilateral linguistic stimuli, the ability to overcome a stimulus-driven laterality effect related to speech sound perception, and the ability to direct attention to an appropriate spatial location. It was concluded that the ability to voluntarily suppress and inhibit the multimodal rightward spatial bias changes as a function of age and praxis due to sensory deficit and probably reflects the developmental level of executive functions.

Étude de l'attention spatiale en condition d'interférence émotionnelle chez les enfants avec un trouble autistique

Le déficit social, incluant la perturbation du traitement du regard et des émotions, est au cœur de l’autisme. Des études ont montré que les visages de peur provoquent une orientation rapide et involontaire de l’attention spatiale vers leur emplacement chez les individus à développement typique. De plus, ceux-ci détectent plus rapidement et plus efficacement les visages avec un regard direct (vs regard dévié). La présente étude vise à explorer l’effet de l’émotion de peur et de la direction du regard (direct vs dévié) sur l’attention spatiale chez les enfants autistes à l’aide d’une tâche d’attention spatiale implicite. Six enfants avec un trouble autistique (TA) ont participé à cette étude. Les participants doivent détecter l’apparition d’une cible à gauche ou à droite d’un écran. L’apparition de la cible est précédée d’une amorce (paire de visages peur/neutre avec regard direct/dévié). La cible peut être présentée soit dans le même champ visuel que l’amorce émotionnellement chargée (condition valide), soit dans le champ visuel opposé (condition invalide). Nos résultats montrent que les amorces avec un visage de peur (vs les amorces avec un visage neutre) provoquent un effet d’interférence au niveau comportemental et divergent l’attention de leur emplacement chez les enfants avec un TA.

Electrophysiological correlates of spatial orienting towards angry faces: a source localization study

The goal of this study was to examine behavioral and electrophysiological correlates of involuntary orienting toward rapidly presented angry faces in non-anxious, healthy adults using a dot-probe task in conjunction with high-density event-related potentials and a distributed source localization technique. Consistent with previous studies, participants showed hypervigilance toward angry faces, as indexed by facilitated response time for validly cued probes following angry faces and an enhanced P1 component. An opposite pattern was found for happy faces suggesting that attention was directed toward the relatively more threatening stimuli within the visual field (neutral faces). Source localization of the P1 effect for angry faces indicated increased activity within the anterior cingulate cortex, possibly reflecting conflict experienced during invalidly cued trials. No modulation of the early C1 component was found for affect or spatial attention. Furthermore, the face-sensitive N170 was not modulated by emotional expression. Results suggest that the earliest modulation of spatial attention by face stimuli is manifested in the P1 component, and provide insights about mechanisms underlying attentional orienting toward cues of threat and social disapproval.

Manual response preparation and saccade programming are linked to attention shifts: ERP evidence for covert attentional orienting and spatially specific modulations of visual processing

The premotor theory of attention claims that attentional shifts are triggered during response programming, regardless of which response modality is involved. To investigate this claim, event-related brain potentials (ERPs) were recorded while participants covertly prepared a left or right response, as indicated by a precue presented at the beginning of each trial. Cues signalled a left or right eye movement in the saccade task, and a left or right manual response in the manual task. The cued response had to be executed or withheld following the presentation of a Go/Nogo stimulus. Although there were systematic differences between ERPs triggered during covert manual and saccade preparation, lateralised ERP components sensitive to the direction of a cued response were very similar for both tasks, and also similar to the components previously found during cued shifts of endogenous spatial attention. This is consistent with the claim that the control of attention and of covert response preparation are closely linked. N1 components triggered by task-irrelevant visual probes presented during the covert response preparation interval were enhanced when these probes were presented close to cued response hand in the manual task, and at the saccade target location in the saccade task. This demonstrates that both manual and saccade preparation result in spatially specific modulations of visual processing, in line with the predictions of the premotor theory.

Direct evidence for attention-dependent influences of the frontal eye-fields on feature-responsive visual cortex

Voluntary selective attention can prioritize different features in a visual scene. The frontal eye-fields (FEF) are one potential source of such feature-specific top-down signals, but causal evidence for influences on visual cortex (as was shown for "spatial" attention) has remained elusive. Here, we show that transcranial magnetic stimulation (TMS) applied to right FEF increased the blood oxygen level-dependent (BOLD) signals in visual areas processing "target feature" but not in "distracter feature"-processing regions. TMS-induced BOLD signals increase in motion-responsive visual cortex (MT+) when motion was attended in a display with moving dots superimposed on face stimuli, but in face-responsive fusiform area (FFA) when faces were attended to. These TMS effects on BOLD signal in both regions were negatively related to performance (on the motion task), supporting the behavioral relevance of this pathway. Our findings provide new causal evidence for the human FEF in the control of nonspatial "feature"-based attention, mediated by dynamic influences on feature-specific visual cortex that vary with the currently attended property.

Automatic attention lateral asymmetry in visual discrimination tasks

There is evidence that automatic visual attention favors the right side. This study investigated whether this lateral asymmetry interacts with the right hemisphere dominance for visual location processing and left hemisphere dominance for visual shape processing. Volunteers were tested in a location discrimination task and a shape discrimination task. The target stimuli (S2) could occur in the left or right hemifield. They were preceded by an ipsilateral, contralateral or bilateral prime stimulus (S1). The attentional effect produced by the right S1 was larger than that produced by the left S1. This lateral asymmetry was similar between the two tasks suggesting that the hemispheric asymmetries of visual mechanisms do not contribute to it. The finding that it was basically due to a longer reaction time to the left S2 than to the right S2 for the contralateral S1 condition suggests that the inhibitory component of attention is laterally asymmetric.

Absence of placeholders abolishes exogenous attention effect in a peripheral cueing procedure

Most studies of exogenous visuospatial attention use placeholders indicating the regions where the stimuli appear on the screen. Preliminary results from our laboratory provided evidence that the attentional effect is more frequently observed when placeholders are used in these experimental procedures. Four experiments were carried out. Experiment 1 aimed at confirming the finding that the attentional effect of a spatially non-informative cue (S1) observed in the presence of placeholders disappears in their absence. The results confirmed this finding. Experiments 2, 3, and 4 examined several possible processes that could explain this finding. Experiment 2 investigated if the contribution of a faster disengagement of attention from the cued location or a stronger forward masking could explain the absence of attentional effect when no placeholders were used. Experiment 3 investigated if increased difficulty in discrimination of the target (S2) from S1 would favor the appearance of the attentional effect in the absence of placeholders. Experiment 4 investigated if an insufficient focusing of attention towards the cued location could explain the absence of attentional effect when no placeholders were used. The results of the three experiments indicated that placeholders act by reducing the discriminability of the S2. This would presumably lead to the adoption of an attentional set that favors the mobilization of attention by the S1

The spatial representation of time

Numerosi studi mostrano che gli intervalli temporali sono rappresentati attraverso un codice spaziale che si estende da sinistra verso destra, dove gli intervalli brevi sono rappresentati a sinistra rispetto a quelli lunghi. Inoltre tale disposizione spaziale del tempo può essere influenzata dalla manipolazione dell’attenzione-spaziale. La presente tesi si inserisce nel dibattito attuale sulla relazione tra rappresentazione spaziale del tempo e attenzione-spaziale attraverso l’uso di una tecnica che modula l’attenzione-spaziale, ovvero, l’Adattamento Prismatico (AP). La prima parte è dedicata ai meccanismi sottostanti tale relazione. Abbiamo mostrato che spostando l’attenzione-spaziale con AP, verso un lato dello spazio, si ottiene una distorsione della rappresentazione di intervalli temporali, in accordo con il lato dello spostamento attenzionale. Questo avviene sia con stimoli visivi, sia con stimoli uditivi, nonostante la modalità uditiva non sia direttamente coinvolta nella procedura visuo-motoria di AP. Questo risultato ci ha suggerito che il codice spaziale utilizzato per rappresentare il tempo, è un meccanismo centrale che viene influenzato ad alti livelli della cognizione spaziale. La tesi prosegue con l’indagine delle aree corticali che mediano l’interazione spazio-tempo, attraverso metodi neuropsicologici, neurofisiologici e di neuroimmagine. In particolare abbiamo evidenziato che, le aree localizzate nell’emisfero destro, sono cruciali per l’elaborazione del tempo, mentre le aree localizzate nell’emisfero sinistro sono cruciali ai fini della procedura di AP e affinché AP abbia effetto sugli intervalli temporali. Infine, la tesi, è dedicata allo studio dei disturbi della rappresentazione spaziale del tempo. I risultati ci indicano che un deficit di attenzione-spaziale, dopo danno emisferico destro, provoca un deficit di rappresentazione spaziale del tempo, che si riflette negativamente sulla vita quotidiana dei pazienti. Particolarmente interessanti sono i risultati ottenuti mediante AP. Un trattamento con AP, efficace nel ridurre il deficit di attenzione-spaziale, riduce anche il deficit di rappresentazione spaziale del tempo, migliorando la qualità di vita dei pazienti.

The role of medial parieto occipital cortex in visuospatial attention and reach planning: electrophysiological studies in human and non-human primates

We usually perform actions in a dynamic environment and changes in the location of a target for an upcoming action require both covert shifts of attention and motor planning update. In this study we tested whether, similarly to oculomotor areas that provide signals for overt and covert attention shifts, covert attention shifts modulate activity in cortical area V6A, which provides a bridge between visual signals and arm-motor control. We performed single cell recordings in monkeys trained to fixate straight-ahead while shifting attention outward to a peripheral cue and inward again to the fixation point. We found that neurons in V6A are influenced by spatial attention demonstrating that visual, motor, and attentional responses can occur in combination in single neurons of V6A. This modulation in an area primarily involved in visuo-motor transformation for reaching suggests that also reach-related regions could directly contribute in the shifts of spatial attention necessary to plan and control goal-directed arm movements. Moreover, to test whether V6A is causally involved in these processes, we have performed a human study using on-line repetitive transcranial magnetic stimulation over the putative human V6A (pV6A) during an attention and a reaching task requiring covert shifts of attention and reaching movements towards cued targets in space. We demonstrate that the pV6A is causally involved in attention reorienting to target detection and that this process interferes with the execution of reaching movements towards unattended targets. The current findings suggest the direct involvement of the action-related dorso-medial visual stream in attentional processes, and a more specific role of V6A in attention reorienting. Therefore, we propose that attention signals are used by the V6A to rapidly update the current motor plan or the ongoing action when a behaviorally relevant object unexpectedly appears at an unattended location.

Spatial biases during mental arithmetic: evidence from eye movements on a blank screen

While the influence of spatial-numerical associations in number categorization tasks has been well established, their role in mental arithmetic is less clear. It has been hypothesized that mental addition leads to rightward and upward shifts of spatial attention (along the “mental number line”), whereas subtraction leads to leftward and downward shifts. We addressed this hypothesis by analyzing spontaneous eye movements during mental arithmetic. Participants solved verbally presented arithmetic problems (e.g., 2 + 7, 8–3) aloud while looking at a blank screen. We found that eye movements reflected spatial biases in the ongoing mental operation: Gaze position shifted more upward when participants solved addition compared to subtraction problems, and the horizontal gaze position was partly determined by the magnitude of the operands. Interestingly, the difference between addition and subtraction trials was driven by the operator (plus vs. minus) but was not influenced by the computational process. Thus, our results do not support the idea of a mental movement toward the solution during arithmetic but indicate a semantic association between operation and space.

Local and global attention are mapped retinotopically in human occipital cortex

Clinical evidence suggests that control mechanisms for local and global attention are lateralized in the temporal–parietal cortex. However, in the human occipital (visual) cortex, the evidence for lateralized local/global attention is controversial. To clarify this matter, we used functional MRI to map activity in the human occipital cortex, during local and global attention, with sustained visual fixation. Data were analyzed in a flattened cortical format, relative to maps of retinotopy and spatial frequency peak tuning. Neither local nor global attention was lateralized in the occipital cortex. Instead, local attention and global attention appear to be special cases of visual spatial attention, which are mapped consistently with the maps of retinotopy and spatial frequency tuning, in multiple visual cortical areas.

Event-related brain potentials in the study of visual selective attention

Event-related brain potentials (ERPs) provide high-resolution measures of the time course of neuronal activity patterns associated with perceptual and cognitive processes. New techniques for ERP source analysis and comparisons with data from blood-flow neuroimaging studies enable improved localization of cortical activity during visual selective attention. ERP modulations during spatial attention point toward a mechanism of gain control over information flow in extrastriate visual cortical pathways, starting about 80 ms after stimulus onset. Paying attention to nonspatial features such as color, motion, or shape is manifested by qualitatively different ERP patterns in multiple cortical areas that begin with latencies of 100–150 ms. The processing of nonspatial features seems to be contingent upon the prior selection of location, consistent with early selection theories of attention and with the hypothesis that spatial attention is “special.”

Selective attention to stimulus location modulates the steady-state visual evoked potential.

Steady-state visual evoked potentials (SSVEPs) were recorded from the scalp of human subjects who were cued to attend to a rapid sequence of alphanumeric characters presented to one visual half-field while ignoring a concurrent sequence of characters in the opposite half-field. These two-character sequences were each superimposed upon a small square background that was flickered at a rate of 8.6 Hz in one half-field and 12 Hz in the other half-field. The amplitude of the frequency-coded SSVEP elicited by either of the task-irrelevant flickering backgrounds was significantly enlarged when attention was focused upon the character sequence at the same location. This amplitude enhancement with attention was most prominent over occipital-temporal scalp areas of the right cerebral hemisphere regardless of the visual field of stimulation. These findings indicate that the SSVEP reflects an enhancement of neural responses to all stimuli that fall within the "spotlight" of spatial attention, whether or not the stimuli are task-relevant. Recordings of the SSVEP provide a new approach for studying the neural mechanisms and functional properties of selective attention to multi-element visual displays.

Event-related potential effects of object repetition depend on attention and part-whole configuration

The effects of spatial attention and part-whole configuration on recognition of repeated objects were investigated with behavioral and event-related potential (ERP) measures. Short-term repetition effects were measured for probe objects as a function of whether a preceding prime object was shown as an intact image or coarsely scrambled (split into two halves) and whether or not it had been attended during the prime display. In line with previous behavioral experiments, priming effects were observed from both intact and split primes for attended objects, but only from intact (repeated same-view) objects when they were unattended. These behavioral results were reflected in ERP waveforms at occipital-temporal locations as more negative-going deflections for repeated items in the time window between 220 and 300 ms after probe onset (N250r). Attended intact images showed generally more enhanced repetition effects than split ones. Unattended images showed repetition effects only when presented in an intact configuration, and this finding was limited to the right-hemisphere electrodes. Repetition effects in earlier (before 200 ms) time-windows were limited to attended conditions at occipito-temporal sites (N1), a component linked to the encoding of object structure, while repetition effects at central locations during the same time window (P150) were found only from objects repeated in the same intact configuration—both previously attended and unattended probe objects. The data indicate that view-generalization is mediated by a combination of analytic (part-based) representations and automatic view-dependent representations.

Attentional modulation of visual cortex activity following right parietal damage in humans

Pathological inattention following parietal damage causes perceptual impairments for visual stimuli in the contralesional hemifield. Here we used functional magnetic resonance imaging (fMRI) to examine visual cortex activity in parietal patients as they performed a spatial attention task. Righthemisphere patients and healthy controls viewed counterphasing checkerboards in which coloured targets appeared briefly within the contralesional and ipsilesional hemifields. In separate fMRI runs participants focused their attention covertiy on the left or right hemifield, or on both hemifields concurrentiy. They were required to detect coloured targets that appeared briefly within the attended hemifield(s), and to withhold responses to distractor stimuli. Neural activit}' was significantly attenuated in early visual areas within the damaged hemisphere. Crucially, although attention significantiy modulated early visual activit}' within the intact (left) hemisphere, there was relatively littie modulation of activity within the affected hemisphere. Our findings suggest that parietal lesions alter early cortical responses to contralesional visual inputs.