Reduced spatial attentional distribution in older adults.

Older adults show decline in visual search performance, but the underlying cause remains unclear. It has been suggested that older adults' altered performance may be related to reduced spatial attention to peripheral visual information compared with younger adults. In this study, 18 younger (M = 21.6 years) and 16 older (M = 69.1 years) participants performed pop-out and serial visual search tasks with variously sized gaze-contingent artificial central scotomas (3°, 5°, or 7° diameter). By occluding central vision, we measured how attention to the periphery was contributing to the search performance. We also tested the effect of target eccentricity on search times and eye movements. We hypothesized that, if attention is reduced primarily in the periphery in older adults, we would observe longer search times for more eccentric targets and with central occlusion. During the pop-out search, older adults showed a steeper decline in search performance with increasing eccentricity and central scotoma size compared with younger adults. In contrast, during the serial search, older adults had longer search times than younger adults overall, independent of target eccentricity and scotoma size. Longer search times were attributed to higher cost-per-item slopes, indicating increased difficulty in simultaneously processing complex symbols made up of separable features in aging, possibly stemming from challenges in spatially binding individual features. Altogether, our findings point to fewer attentional resources of simultaneous visual processing to distribute over space or separable features of objects, consistent with decreased dorsal visual stream functioning in aging.

Toward the characterization of a visual form of developmental dyslexia: Reduced visuo-attentional capacity for processing multiple stimuli made of separable features.

Some dyslexics cannot process multiple letters simultaneously. It has been argued that this reduced visuo-attentional (VA) letter span could result from poor reading ability and experience. Here, moving away from reading context, we showed that dyslexic group exhibited slower visual search than normal readers group for "symbols", defined as graphic stimuli made up of separable visual features, but not for filled objects. Slowness in symbol visual search was explained by reduced VA field and atypical ocular behaviour when processing those letter-like stimuli and was associated with reduced VA letter span and impaired elementary visuo-spatial perception. Such a basic visual search deficit can hardly be attributed to poor reading ability and experience. Moreover, because it is specific to letter-like stimuli (i.e., "symbols"), it can specifically hinder reading acquisition. Symbol visual search can easily be tested in the pre-reading phase, opening up prospects for early risk detection and prevention of VA dyslexia.

Spatial bias in anti-saccade endpoints following bilateral dorsal posterior parietal lesions.

Anti-saccades are eye movements in which the saccade is executed in the opposite direction of a visual target and are often hypometric. Because the visual target and saccade goal are decoupled, it has been suggested that competition between the two locations occurs and needs to be resolved. It has been hypothesized that the hypometria of anti-saccades reflects this spatial competition by revealing a bias towards the visual target. To confirm that this hypometria is not simply due to reduced gain, we tested 10 healthy subjects on three different anti-saccade spatial configuration tasks: 90° away across hemifields, 90° away within the same hemifield and 180° away (classic, diagonally opposite). Specifically, we examined whether saccade endpoints showed evidence for the visual target location's interference with anti-saccade programming and execution processes. Among other neural substrates involved in anti-saccades production, the dorsal posterior parietal cortex (PPC) has been implicated in the spatial inhibition of contralateral visual target. To gain insight into the neural processes involved in spatial competition during anti-saccades, we also tested one patient with a bilateral dorsal PPC lesion. In all spatial configurations, we observed that anti-saccade endpoints demonstrated a spatial bias towards the visual target for all participants, likely due to an incomplete inhibition of the visual target location. This spatial bias was exacerbated in our patient, which suggests that the dorsal PPC contributes to the amalgamation of the two competing spatial representations.

Enhancing reading accuracy through visual search training using symbols.

Children with reading disorders present with inaccurate and/or delayed printed word identification. Regarding visual-attentional processing, printed words are letter strings, and each letter is a symbol made of separable features. Simultaneous processing of separable features has been evidenced to be specifically impaired in visual search tasks using symbols in poor readers as well as in a patient with superior parietal lobules (SPL) lesion. Additionally, activation in the SPL has been shown to be abnormally low in dyslexic readers displaying a reduced span of letter strings processing. This deficit has been assumed to impair visual-attentional sampling of printed words. An experiment conducted with 21 dyslexic children tested the hypothesis that a training program based on visual symbol search may stimulate the SPL, leading to a potential benefit transferred to reading performance. We designed the VisioCogLetters serious game and introduced it at random for one month (10 min every day) between four monthly reading sessions. No training was provided between the other (control) reading sessions. Reading accuracy increased without any speed-accuracy trade-off specifically in the session after training. Moreover, the percentage of improvement correlated with the individual time spent at home on training. These results show that improved visual search skills on symbols can translate into enhanced reading performance, and pave a new avenue for future rehabilitation tools.

Pre-saccadic attention relies more on suppression than does covert attention.

During covert and pre-saccadic attentional shifts, it is unclear how facilitation and suppression processes interact for target selection. A recent countermanding task pointed to greater suppression at unattended locations during trials with saccades compared to trials without saccades (i.e., fixation and successful stop trials), whereas target facilitation did not differ. It is unknown whether this finding is restricted to countermanding paradigms that involve inhibitory processes. To test this, we adapted Gaspelin and colleagues (2015)'s attention capture task where, within the same block, one location was primed with frequent line discrimination trials, and all locations were occasionally probed using letters report trials. Participants also performed a baseline condition without priming. We tested 15 participants and examined how performance at non-primed locations was affected by covert versus pre-saccadic attention in blocks of four or six items, as well as by position from the primed location and timing from saccade onset. For both attention conditions, letter report at non-primed locations was worse compared to baseline, demonstrating suppression, and letter report at primed location was better, demonstrating facilitation. In saccades trials, letter report was better at primed locations and worse at non-primed locations compared to fixation trials. The timing of this additional pre-saccadic suppression differed from saccadic suppression. In both attention conditions, suppression was greater when primed and non-primed locations were within the same hemifield or in diagonal opposite quadrants. These results confirmed that attention preceding saccade execution suppressed non-primed locations to a larger extent than covert attention, with the same spatial quadrant effect.

Role of the Dorsal Posterior Parietal Cortex in the Accurate Perception of Object Magnitude in Peripheral Vision.

Following superior parietal lobule and intraparietal sulcus (SPL-IPS) damage, optic ataxia patients underestimate the distance of objects in the ataxic visual field such that they produce hypometric pointing errors. The metrics of these pointing errors relative to visual target eccentricity fit the cortical magnification of central vision. The SPL-IPS would therefore implement an active "peripheral magnification" to match the real metrics of the environment for accurate action. We further hypothesized that this active compensation of the central magnification by the SPL-IPS contributes to actual object' size perception in peripheral vision. Three optic ataxia patients and 10 age-matched controls were assessed in comparing the thickness of two rectangles flashed simultaneously, one in central and another in peripheral vision. The bilateral optic ataxia patient exhibited exaggerated underestimation bias and uncertainty compared to the control group in both visual fields. The two unilateral optic ataxia patients exhibited a pathological asymmetry between visual fields: size perception performance was affected in their contralesional peripheral visual field compared to their healthy side. These results demonstrate that the SPL-IPS contributes to accurate size perception in peripheral vision.

Impaired Spatial Inhibition Processes for Interhemispheric Anti-saccades following Dorsal Posterior Parietal Lesions.

Anti-saccades are eye movements that require inhibition to stop the automatic saccade to the visual target and to perform instead a saccade in the opposite direction. The inhibitory processes underlying anti-saccades have been primarily associated with frontal cortex areas for their role in executive control. Impaired performance in anti-saccades has also been associated with the parietal cortex, but its role in inhibitory processes remains unclear. Here, we tested the assumption that the dorsal parietal cortex contributes to spatial inhibition processes of contralateral visual target. We measured anti-saccade performance in 2 unilateral optic ataxia patients and 15 age-matched controls. Participants performed 90 degree (across and within visual fields) and 180 degree inversion anti-saccades, as well as pro-saccades. The main result was that our patients took longer to inhibit visually guided saccades when the visual target was presented in the ataxic hemifield and the task required a saccade across hemifields. This was observed through anti-saccades latencies and error rates. These deficits show the crucial role of the dorsal posterior parietal cortex in spatial inhibition of contralateral visual target representations to plan an accurate anti-saccade toward the ipsilesional side.

Attentional limits in visual search with and without dorsal parietal dysfunction: space-based window or object-based span?

Attentional resource and distribution are specifically impaired in simultanagnosia, and also in the visuo-attentional form of developmental dyslexia. Both clinical conditions are conceived as a limitation of simultaneous visual processing after superior parietal lobule (SPL) dysfunction (review in Valdois et al., 2019). However, a reduced space-based attentional window (i.e. a limited visual eccentricity at which the target object can be identified, Khan et al. 2016) has been demonstrated in simultanagnosia versus a reduced object-based span (i.e. a limited number of objects processed at each fixation, Bosse et al., 2007) in developmental dyslexia. In healthy individuals, the cost in reaction times per item in serial search tasks suggests that a group of objects is processed simultaneously at a time, but this group is also undefined and depends on the visual complexity of the task. Healthy individuals and a patient with simultanagnosia performed serial search tasks involving either symbols (made of separable features) or objects made of non-separable features, and with distractors that were either all identical or all dissimilar. We used a moving window paradigm to determine whether the task was performed with a "working space" versus a "working span" limitation in control group and in patient with bilateral SPL damage. We found that healthy individuals performed search in a color task comprising non-separable feature objects and dissimilar distractors with a limited space-based attentional window; this attentional window, as well as the mean saccade amplitude used to displace it across the visual display, were independent of set size, thus inconsistent with an object-based attentional span. In the symbol task comprising a feature-absent search in which all feature-present distractors were dissimilar, we observed that mean saccade amplitude decreased with set size and that search performance could not be mimicked by a moving window of a single diameter; instead participants seemed to process a fixed number of symbols at a time (object-based span). Following bilateral SPL lesions, patient IG demonstrated a similar space-based search process in the color search task with a normal attentional window. In contrast, her cost-per-item in the symbol task increased dramatically, demonstrating a clear deficit of simultaneous object perception. These results confirmed the specific contribution of the SPL to the visual processing of multiple objects made of separable features (like letters), and more dramatically when they are all different, which explains the specific difficulty for a reading beginner in case of SPL dysfunction.

Post-saccadic changes disrupt attended pre-saccadic object memory.

Trans-saccadic memory consists of keeping track of objects' locations and features across saccades; pre-saccadic information is remembered and compared with post-saccadic information. It has been shown to have limited resources and involve attention with respect to the selection of objects and features. In support, a previous study showed that recognition of distinct post-saccadic objects in the visual scene is impaired when pre-saccadic objects are relevant and thus already encoded in memory (Poth, Herwig, Schneider, 2015). Here, we investigated the inverse (i.e. how the memory of pre-saccadic objects is affected by abrupt but irrelevant changes in the post-saccadic visual scene). We also modulated the amount of attention to the relevant pre-saccadic object by having participants either make a saccade to it or elsewhere and observed that pre-saccadic attentional facilitation affected how much post-saccadic changes disrupted trans-saccadic memory of pre-saccadic objects. Participants identified a flashed symbol (d, b, p, or q, among distracters), at one of six placeholders (figures "8") arranged in circle around fixation while planning a saccade to one of them. They reported the identity of the symbol after the saccade. We changed the post-saccadic scene in Experiment one by removing the entire scene, only the placeholder where the pre-saccadic symbol was presented, or all other placeholders except this one. We observed reduced identification performance when only the saccade-target placeholder disappeared after the saccade. In Experiment two, we changed one placeholder location (inward/outward shift or rotation re. saccade vector) after the saccade and observed that identification performance decreased with increased shift/rotation of the saccade-target placeholder. We conclude that pre-saccadic memory is disrupted by abrupt attention-capturing post-saccadic changes of visual scene, particularly when these changes involve the object prioritized by being the goal of a saccade. These findings support the notion that limited trans-saccadic memory resources are disrupted when object correspondence at saccadic goal is broken through removal or location change.

[Neurodevelopmental disorders modify neurodegenerative diseases: a medical history to screen in memory clinic]. / Les troubles neurodéveloppementaux miment ou influencent les pathologies neurodégénératives : prise en compte des antécédents neurodéveloppementaux en consultation mémoire.

Neurodevelopmental disorders are frequent in the general population and are often lifelong conditions despite sometimes being masked by conscious or unconscious compensation and avoidance mechanisms. These conditions are often unknown or underestimated in adults, even when diagnosed in childhood. Neurodevelopmental disorders share similarities with and frequently interact in a complex way with neurodegenerative disorders. Considering these aspects during memory clinic assessments can provide a new perspective on lifelong neurocognitive trajectories. Assessing both neurodevelopmental and neurodegenerative dimensions is challenging but should improve diagnostic accuracy. It is therefore necessary to understand the lifelong specific neurocognitive trajectory of each patient in order to develop personalized and focused cognitive medicine and care.

The posterior parietal cortex processes visuo-spatial and extra-retinal information for saccadic remapping: A case study.

Optimally collecting information and controlling behaviour require that we constantly scan our visual environment through eye movements. How the dynamic interaction between short-lived retinal images and extra-retinal signals of eye motion results in our subjective experience of visual stability remains a major issue in Cognitive Neuroscience. The present study aimed to assess and determine the nature of the contribution of the posterior parietal cortex (PPC) to the saccadic remapping mechanisms which contribute to such perceptual visual constancy. Perceptual responses in transsaccadic visual localization tasks were measured in a patient presenting with a PPC lesion and manifesting optic ataxia in the left hemifield with no neglect. Two perceptual localization tasks, each with versus without an intervening saccade, were used: the saccadic suppression of displacement (SSD) task (Ostendorf, Liebermann, & Ploner, 2010) and the peri-saccadic flash localization (LOC) task (Zimmerman & Lappe, 2010). Compared to a group of age-matched healthy subjects, the patient showed a specific pattern of perceptual deficits in the ataxic (left) hemifield. First, a significant impairment occurred in the stationary eye conditions, attesting for an alteration of visuo-spatial encoding. Second, in the saccade conditions, an additional perceptual deficit (an error of ~5° along the saccade direction) was observed in both tasks and mainly in conditions where extra-retinal signals are thought to be critically involved, revealing a constant underestimation by extra-retinal signals of the saccade size, despite preserved saccade accuracy. These findings highlight a crucial role of the PPC in saccadic remapping processes underlying perceptual visual constancy and provide empirical evidence for models such as Ziesche and Hamker's (2014).

Bálint syndrome.

This chapter starts by reviewing the various interpretations of Bálint syndrome over time. We then develop a novel integrative view in which we propose that the various symptoms, historically reported and labeled by various authors, result from a core mislocalization deficit. This idea is in accordance with our previous proposal that the core deficit of Bálint syndrome is attentional (Pisella et al., 2009, 2013, 2017) since covert attention improves spatial resolution in visual periphery (Yeshurun and Carrasco, 1998); a deficit of covert attention would thus increase spatial uncertainty and thereby impair both visual object identification and visuomotor accuracy. In peripheral vision, we perceive the intrinsic characteristics of the perceptual elements surrounding us, but not their precise localization (Rosenholtz et al., 2012a,b), such that without covert attention we cannot organize them to their respective and recognizable objects; this explains why perceptual symptoms (simultanagnosia, neglect) could result from visual mislocalization. The visuomotor symptoms (optic ataxia) can be accounted for by both visual and proprioceptive mislocalizations in an oculocentric reference frame, leading to field and hand effects, respectively. This new pathophysiological account is presented along with a model of posterior parietal cortex organization in which the superior part is devoted to covert attention, while the right inferior part is involved in visual remapping. When the right inferior parietal cortex is damaged, additional representational mislocalizations across saccades worsen the clinical picture of peripheral mislocalizations due to an impairment of covert attention.

Movement drift in optic ataxia reveals deficits in hand state estimation in oculocentric coordinates.

When vision is removed, limb position has been shown to progressively drift during repetitive arm movements. The posterior parietal cortex (PPC) is known to be involved in the processing of multisensory information, the formation of internal hand estimate, and online motor control. Here, we compared hand position drift between healthy controls and 2 patients with PPC damage to gain insight into the mechanisms underlying movement drift and investigate the possible role of the PPC in this process. To do so, we asked participants to perform back-and-forth movements between 2 targets, in the dark and under different gaze fixation conditions. Each individual participant consistently drifted to the same end position for a given hand and gaze condition. We found that the final drift distance was related to small systematic errors made on the very first trial in the dark, with an approximate 3.5 fold increase in magnitude. Furthermore, PPC damage resulted in greater movement drift in patients when the unseen hand was in the contralesional oculocentric space and also when the target was located in the lower visual field. We conclude that the PPC is involved in the proprioceptive representation of hand position in oculocentric coordinates used for reach planning and motor control. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Elementary visuospatial perception deficit in children with neurodevelopmental disorders.

AIM: To assess the prevalence of elementary visuospatial perception (EVSP) deficit in children with neurodevelopmental disorders. METHOD: Using a screening test designed and validated to measure dorsal EVSP ability, 168 children (122 males, 46 females; mean age 10y [SD 1y 10mo], range 4y 8mo-16y 4mo) diagnosed with developmental coordination disorder (DCD), specific learning disorder (SLD), attention-deficit/hyperactivity disorder (ADHD), and/or oral language disorder were compared with a group of 184 typically developing children. We also tested 14 children with binocular vision dysfunction and no neurodevelopmental disorder. RESULTS: Children with SLD scored below the interquartile range of typically developing children as frequently (59%) as children with DCD, but only 5% were severely impaired (i.e. scored as outliers). Children with DCD were the most severely impaired (22% of outliers), even more so when they exhibited a co-occuring disorder. Children with language disorder and those with binocular vision dysfunction scored similarly to the group of typically developing children. INTERPRETATION: These results confirm the importance of assessing EVSP in the clinical evaluation of children with neurodevelopmental disorders, in particular those presenting with DCD or SLD. What this paper adds More than half of children with developmental coordination disorder (DCD) scored below the normal interquartile range on the elementary visuospatial perception (EVSP) test. More than half of children with specific learning disorder (SLD) scored below the normal interquartile range on the EVSP test. Twenty-two percent of children with DCD performed as outliers on the EVSP test. Children with language disorder and those with binocular vision dysfunction scored similarly to typically developing children.

Validation of a simple screening test for elementary visuo-spatial perception deficit.

OBJECTIVE: The reliability and validity of a screening test for a deficit in elementary visuo-spatial perception (EVSP) were evaluated. METHOD: This prospective study collected performance from 210 typically developing individuals and evaluated the internal consistency of the EVSP screening test. Test-retest reliability was examined with 25 individuals. Validity also involved retrospective clinical data collected from 223 non-typically developing children coming to the hospital for outpatient consultation. Since EVSP matures through childhood, we standardized the EVSP screening test scores by age category and performed Pearson correlations with standardized clinical tests scores. RESULTS: Test-retest reliability (intraclass correlation coefficient=0.76) and internal consistency (Cronbach's alpha=0.76) were satisfactory. Construct validity included correlation with the subtests of the Wechsler Intelligence Scale IV (WISC-IV) involving visuo-spatial analysis (Matrix Reasoning and Block Design, P<0.01; Symbol Search and Coding, P<0.05) and was reinforced by the expected non-correlation between the Verbal Comprehension Index and EVSP scoring class. The EVSP scoring class was correlated with Manual dexterity of the M-ABC (P<0.05) and the Working Memory Index (P<0.05) of the WISC-IV including the subtest Arithmetic (P<0.01). CONCLUSION: This screening test is reliable and valid to evaluate EVSP before more complex cognitive or motor assessment.

Spatial and temporal dynamics of presaccadic attentional facilitation before pro- and antisaccades.

The premotor theory of attention and the visual attention model make different predictions about the temporal and spatial allocation of presaccadic attentional facilitation. The current experiment investigated the spatial and temporal dynamics of presaccadic attentional facilitation during pro- and antisaccade planning; we investigated whether attention shifts only to the saccade goal location or to the target location or elsewhere, and when. Participants performed a dual-task paradigm with blocks of either anti- or prosaccades and also discriminated symbols appearing at different locations before saccade onset (measure of attentional allocation). In prosaccades blocks, correct prosaccade discrimination was best at the target location, while during errors, discrimination was best at the location opposite to the target location. This pattern was inversed in antisaccades blocks, although discrimination remained high opposite to the target location. In addition, we took the benefit of a large range of saccadic landing positions and showed that performance across both types of saccades was best at the actual saccade goal location (where the eye will actually land) rather than at the instructed position. Finally, temporal analyses showed that discrimination remained highest at the saccade goal location, from long before to closer to saccade onset, increasing slightly for antisaccades closer to saccade onset. These findings are in line with the premises of the premotor theory of attention, showing that attentional allocation is primarily linked both temporally and spatially to the saccade goal location.

Vibrotactile information improves proprioceptive reaching target localization.

When pointing to parts of our own body (e.g., the opposite index finger), the position of the target is derived from proprioceptive signals. Consistent with the principles of multisensory integration, it has been found that participants better matched the position of their index finger when they also had visual cues about its location. Unlike vision, touch may not provide an additional information about finger position in space, since fingertip tactile information theoretically remains the same irrespective of the postural configuration of the upper limb. However, since tactile and proprioceptive information are ultimately coded within the same population of posterior parietal neurons within high-level spatial representations, we nevertheless hypothesized that additional tactile information could benefit the processing of proprioceptive signals. To investigate the influence of tactile information on proprioceptive localization, we asked 19 participants to reach with the right hand towards the opposite unseen index finger (proprioceptive target). Vibrotactile stimuli were applied to the target index finger prior to movement execution. We found that participants made smaller errors and more consistent reaches following tactile stimulation. These results demonstrate that transient touch provided at the proprioceptive target improves subsequent reaching precision and accuracy. Such improvement was not observed when tactile stimulation was delivered to a distinct body part (the shoulder). This suggests a specific spatial integration of touch and proprioception at the level of high-level cortical body representations, resulting in touch improving position sense.