Integrated Perceptual Decisions Rely on Parallel Evidence Accumulation.

The ability to make accurate and timely decisions, such as judging when it is safe to cross the road, is the foundation of adaptive behavior. While the computational and neural processes supporting simple decisions on isolated stimuli have been well characterized, decision-making in the real world often requires integration of discrete sensory events over time and space. Most previous experimental work on perceptual decision-making has focused on tasks that involve only a single, task-relevant source of sensory input. It remains unclear, therefore, how such integrative decisions are regulated computationally. Here we used psychophysics, electroencephalography, and computational modeling to understand how the human brain combines visual motion signals across space in the service of a single, integrated decision. To that purpose, we presented two random-dot kinematograms in the left and the right visual hemifields. Coherent motion signals were shown briefly and concurrently in each location, and healthy adult human participants of both sexes reported the average of the two motion signals. We directly tested competing predictions arising from influential serial and parallel accounts of visual processing. Using a biologically plausible model of motion filtering, we found evidence in favor of parallel integration as the fundamental computational mechanism regulating integrated perceptual decisions.

Evaluation of upper limb perception after stroke with the new Affected Limb Perception Questionnaire (ALPQ): a study protocol.

BACKGROUND: Following a stroke, patients may suffer from alterations in the perception of their own body due to an acquired deficit in body representations. While such changes may impact their quality of life as well as recovery, they are not systematically assessed in clinical practice. This study aims at providing a better understanding of the rate, evolution, and impact on recovery of upper limb (UL) body perceptions (BPs) alterations following stroke. In addition, we will investigate associations among BPs alterations items, their associations with the sensorimotor functions, UL activity, damages in brain structure and connectivity. METHODS: We developed a new tool named ALPQ (for Affected Limb Perception Questionnaire) to address the present study objectives. It assesses subjective alterations in the perception of the affected UL following stroke, by measuring several dimensions, namely: anosognosia for hemiplegia, anosodiaphoria for hemiplegia, hemiasomatognosia, somatoparaphrenia, personification of the affected limb, illusion of modification of physical characteristics (temperature, weight, length), illusory movements, super- or undernumerary limb, UL disconnection, misoplegia, and involuntary movement. This study combines a cross-sectional and longitudinal design. The completed data sample will include a minimum of 60 acute and 100 sub-acute stroke patients. When possible, patients are followed up to the chronic stage. Complementary evaluations are administered to assess patients' sensorimotor and cognitive functions as well as UL activity, and brain lesions will be analysed. DISCUSSION: This study will provide a better understanding of BPs alterations following stroke: their rate and evolution, as well as their associations with sensorimotor deficit, cognitive profile and UL activity, brain lesions and recovery. Ultimately, the results could support the personalization of rehabilitation strategy according to patients' UL perception to maximize their recovery. STUDY REGISTRATION: The protocol for this study has been pre-registered on the Open Science Framework on July the 7th, 2021: https://osf.io/p6v7f .

Task relevance effects in electrophysiological brain activity: early, but not first.

A current controversy surrounds the question whether high-level features of a stimulus such as its relevance to the current task may affect early attentional processes. According to one view abruptly appearing stimuli gain priority during an initial feedforward processing stage and therefore capture attention even if they are irrelevant to the task. Alternatively, only stimuli that share a relevant property with the target may capture attention of the observer. Here, we used high-density EEG to test whether task relevance may modulate early feedforward brain activity, or whether it only becomes effective once the physical characteristics of the stimulus have been processed. We manipulated task relevance and visual saliency of distracters presented left or right of an upcoming central target. We found that only the relevance of distracters had an effect on manual reaction times to the target. However, the analysis of electrocortical activity revealed three discrete processing stages during which pure effects of distracter saliency (~80-160 ms), followed by an interaction between saliency and relevance (~130-240 ms) and finally pure effects of relevance (~230-370 ms) were observed. Electrical sources of early saliency effects and later relevance effects were localized in the posterior parietal cortex, predominantly over the right hemisphere. These findings support the view that during the initial feedforward stage only physical (bottom-up) factors determine cortical responses to visual stimuli, while top-down effects interfere at later processing stages.

Exploring the world with Bálint syndrome: biased bottom-up guidance of gaze by local saliency differences.

Bálint syndrome is a combination of severe deficits affecting spatial attention, visuo-motor control and oculomotor function. While the severe restriction of attention (simultanagnosia) and impairments of visually guided reaching have been extensively studied, oculomotor apraxia has received comparatively little attention. The main explanatory hypothesis of oculomotor apraxia is that it is a direct consequence of the severe restriction of attention. Here, we examined in a patient with Bálint syndrome to what extent local image features such as luminance and contrast predict whether a region will be fixated or not. During the viewing of natural photographs, the patient made saccades of very small amplitude, but showed strongly increased fixation duration. In addition, the horizontal and vertical range of fixations was severely restrained compared to control subjects. When analysing the local feature content at fixation, we found that central fixations of the patient contained less local luminance and contrast than fixations of controls while he made fixations to peripheral image regions with disproportionately high luminance and contrast. These findings suggest that while our patient gazes at central regions irrespective of their local feature content, he only looks to the periphery when his gaze is captured by particularly conspicuous features. We propose that oculomotor apraxia in Bálint syndrome reflects a combination of biased representations within a parietal priority map and increased fixational activity due to biased interactions within the oculomotor network.

Sharpening of peripersonal space during the COVID-19 pandemic.

Our social world has been transformed by the COVID-19 pandemic. Beyond the direct impact of the pandemic on physical health, the social distancing measures implemented worldwide to slow down disease transmission have dramatically impacted social interactions1,2. These measures, including orders to stay at home and to maintain a social distance of at least 2 meters, have been essential to limit the spread of the disease, but they have had severe costs for humans as social animals2. Right before and right after the adoption of the most stringent measures in Switzerland in Spring 2020, we were conducting a series of experiments to measure the representation of the so-called peripersonal space - the space immediately surrounding our body, where we normally interact with objects and other individuals3. We found that the introduction of social distancing measures led to a reduction in the extent of the peripersonal space and enhanced its segregation between individuals, as if the presence of others in close space would activate an implicit form of freezing response.

Neuropsychological Outcomes after Surgery for Olfactory Groove Meningiomas.

BACKGROUND: In recent years, several studies have reported abnormal pre- and postoperative neuropsychological functioning in patients with meningiomas located in the prefrontal cortex (notably the ventromedial region). In the case of olfactory groove meningiomas, the tumor is in direct contact with the inferior aspect of the prefrontal cortex, a cortical region with crucial roles in decision-making, cognition and memory functions, potentially negatively impacting neuropsychological functions. MATERIALS AND METHODS: We retrospectively compared pre- and post-operative neuropsychological testing of 17 patients undergoing surgical removal of olfactory groove meningiomas in our institution between January 2013 and December 2018. Neuropsychological results were obtained from the patients' medical history and normalized as z-scores of their respective cognitive functions. RESULTS: Assessment of cognitive follow-up showed an important heterogeneity among patients. Pre-operative cognitive impairment was observed in most patients, particularly in cognitive flexibility (mean z-score: -1.35). Immediate post-operative cognitive status showed an overall impairment in all domains of cognition, significant for the domains of attention (p = 0.0273) and flexibility (p = 0.0234) and almost significant for the domain of language (p = 0.0547). The late follow-up at one year showed a trend towards general improvement, although attention and flexibility remained impaired. DISCUSSION: Olfactory groove meningiomas impact pre-frontal cortex cognitive functions, particularly in the domain of cognitive flexibility. After an initial postoperative worsening, patients tended to improve in most aspects after one year, aside from cognitive flexibility and attention.

The Dorsal Frontoparietal Network: A Core System for Emulated Action.

The dorsal frontoparietal network (dFPN) of the human brain assumes a puzzling variety of functions, including motor planning and imagery, mental rotation, spatial attention, and working memory. How can a single network engage in such a diversity of roles? We propose that cognitive computations relying on the dFPN can be pinned down to a core function underlying offline motor planning: action emulation. Emulation creates a dynamic representation of abstract movement kinematics, sustains the internal manipulation of this representation, and ensures its maintenance over short time periods. Based on these fundamental characteristics, the dFPN has evolved from a pure motor control network into a domain-general system supporting various cognitive and motor functions.

Electrophysiological correlates of visual binding errors after bilateral parietal damage.

Illusory conjunctions (e.g. the confusion between the shape of one stimulus with the color of another stimulus) are the most dramatic expression of binding failures in vision. Under brief exposure or when attention is diverted illusory conjunctions may be observed in healthy participants, but they only represent a real-life problem for patients with parietal damage. However, it is unclear whether such failures reflect the impairment of early or late stages of visual processing. Here, we examined the time-course of visual processing using evoked potential measures in a patient with bilateral damage to the posterior parietal cortex presenting prominent binding failures. The patient was asked to identify colored letters that were briefly flashed to the left or right hemifield. When only one item was presented she adequately identified color or shape of left and right letters. In contrast, when presentation was bilateral she either identified the correct right shape-color combination and missed the item in the left hemifield (extinction) or combined incorrectly the right shape with the left color (illusory conjunction). Evoked potential analyses revealed a specific electrophysiological signature of illusory conjunctions, starting ∼105ms after stimulus onset over the right frontal cortex. These findings indicate that binding errors reflect failures of early stages of attentional filtering relying on the integrity of the posterior parietal cortex.

Theta-band functional connectivity in the dorsal fronto-parietal network predicts goal-directed attention.

Functional imaging studies have identified a dorsal fronto-parietal network whose activity reflects shifts of attention in space and is sensitive to the behavioural relevance of stimuli. In patients with severe deficits of spatial attention this network is often structurally preserved. Here, we show that resting-state EEG functional connectivity in the dorsal fronto-parietal network predicts impaired goal-directed processing in stroke patients with spatial attention deficits. Eleven right-hemisphere damaged patients with different degrees of contralesional spatial deficits and sixteen age-matched healthy controls performed a visuo-spatial task which required them to react to a central target while ignoring task-relevant distracters presented left or right of fixation. Unlike controls, performance of patients was not modulated by the goal-relevance of peripheral distracters. Compared to controls patients showed a significant decrease in theta-band connectivity between the right dorsolateral prefrontal cortex and the right superior parietal region. Moreover, in both groups we observed a significant correlation between fronto-parietal connectivity and the behavioural effect of distracter relevance. These findings indicate that fronto-parietal functional connectivity is impaired in patients with spatial attention deficits and predicts effects of goal-relevant information on target processing.

The role of visual saliency for the allocation of attention: Evidence from spatial neglect and hemianopia.

Visual scanning and exploration of natural scenes not only depends on specific objects, but also on local features. Models of spatial attention propose that features such as orientation or colour are processed pre-attentively and in parallel. According to these models attention interferes at a later stage, where features are combined into a representation of visual saliency. Saliency is a good predictor of ocular fixations during scanning of static pictures. Here, we tested whether fixations of patients with left spatial neglect, hemianopia, or both can be predicted based on local image content. Participants were asked to freely scan natural images while saccades and ocular fixations were registered. Hemianopic patients produced a similar distribution of fixations and relied similarly on picture saliency as healthy controls. In contrast, neglect patients looked to image regions with increased saliency and higher local orientation and intensity thresholds on the neglected side of space. The reliance on increased saliency during visual exploration was predicted by damage to subcortical regions interconnecting the inferior parietal and lateral premotor cortex. These findings suggest that spatial neglect leads to a combined attentive and pre-attentive deficit in the processing of saliency and feature information.

Spatial neglect and the neural coding of attentional priority.

The concept of attentional priority plays an increasingly important role in theoretical interpretations of the neurophysiological mechanisms underlying attentional selection. A priority map is a feature-independent, spatiotopic representation of the environment that combines stimulus-driven information with goal-related signals. It emerges from the functional properties of parietal brain regions involved in spatial attention and saccade programming on the one hand, and reaching or grasping movements on the other hand. Here, we explore the value of this concept for the understanding of neuropsychological deficits of attention such as spatial extinction and neglect. We argue that these conditions reflect spatially graded, multisensory deficits affecting a processing level at which stimulus-driven and goal-driven signals interact. These attributes of neglect and extinction agree with the functional characteristics of attentional priority and suggest that components of both disorders can be understood as manifestations of damage or dysfunction affecting the parietal priority map.

Visual search in spatial neglect studied with a preview paradigm.

Impaired visual search is a hallmark of spatial neglect. When searching for an unique feature (e.g., color) neglect patients often show only slight visual field asymmetries. In contrast, when the target is defined by a combination of features (e.g., color and form) they exhibit a severe deficit of contralesional search. This finding suggests a selective impairment of the serial deployment of spatial attention. Here, we examined this deficit with a preview paradigm. Neglect patients searched for a target defined by the conjunction of shape and color, presented together with varying numbers of distracters. The presentation time was varied such that on some trials participants previewed the target together with same-shape/different-color distracters, for 300 or 600 ms prior to the appearance of additional different-shape/same-color distracters. On the remaining trials the target and all distracters were shown simultaneously. Healthy participants exhibited a serial search strategy only when all items were presented simultaneously, whereas in both preview conditions a pop-out effect was observed. Neglect patients showed a similar pattern when the target was presented in the right hemifield. In contrast, when searching for a target in the left hemifield they showed serial search in the no-preview condition, as well as with a preview of 300 ms, and partly even at 600 ms. A control experiment suggested that the failure to fully benefit from item preview was probably independent of accurate perception of time. Our results, when viewed in the context of existing literature, lead us to conclude that the visual search deficit in neglect reflects two additive factors: a biased representation of attentional priority in favor of ipsilesional information and exaggerated capture of attention by ipsilesional abrupt onsets.