Prism adaptation reverses the local processing bias in patients with right temporo-parietal junction lesions

Investigating premotor reaching biases after prism adaptation

Prism adaptation (PA) is both a visuomotor learning task and potential treatment for spatial neglect after stroke. While PA's aftereffects can improve neglect symptoms, therapeutic benefits vary across individuals, possibly due to differences in neglect subtypes. Neglect symptoms can be described along an information processing pathway, yielding perceptual (input) and premotor (output) neglect subtypes. There is some evidence that PA mainly benefits persons with premotor neglect. We investigated whether PA modulates the premotor stage of information processing by examining whether PA could induce a premotor bias in healthy adults. We measured perceptual and premotor biases using a speeded reach task that compares the initiation time of leftward and rightward reaches to lateralized targets from different hand start positions. Using a randomized mixed experimental design, 30 right-handed healthy adults completed this speeded reach task before and after either left-shifting (n = 15) or right-shifting (n = 15) PA. As hypothesized, left-shifting PA speeded initiation time specifically for reaches in the rightward direction, regardless of target location (p = .02, ηp2 = .18), suggesting that PA induced a premotor bias in the direction of the prism aftereffect. These findings have implications for PA's underlying mechanisms, which can inform visuomotor learning theories and PA's use as a treatment for spatial neglect.

Electrophysiological effects of smartphone notifications on cognitive control following a brief mindfulness induction

Smartphone use is nearly ubiquitous, with 93% of adults among economically developed countries, including the United States, Canada, Israel, and South Korea owning a smartphone (Taylor & Silver, 2019). Multiple studies have demonstrated the distracting effects of smartphone notifications on behavioral measures of cognition. Fewer studies have examined the effects of notifications on neural activity underlying higher-level cognitive processes or behavioral inductions to reduce smartphone-related distraction. Using EEG spectral frequency power densities, we assessed the effects of smartphone notifications (vs. control trials) on engagement of attentional shifting processes involved in cognitive control during a Navon Letter visual oddball task. Participants were randomly assigned to a brief mindfulness induction (N = 44) or a neutral narration control condition (N = 43). Overall, participants had lower theta-band power, but higher alpha- and beta-band power densities on target letter trials preceded by smartphone notifications. Additionally, participants in the mindfulness (vs. control) condition had a larger attention shifting oddball assessed via theta power density and theta/beta ratio (TBR) values-reflecting increased engagement of cognitive control-particularly on smartphone notification (vs. control) trials. Altogether, these results provide evidence supporting the idea that smartphone notifications can decrease activity of neural correlates of cognitive control, and offer the promise of a brief mindfulness induction to buffer against the effects of smartphone notifications on cognitive control. The findings indicate a need for further research on mindfulness inductiosn as a means to reduce potential distraction caused by smartphones.

Zooming in on abnormal local and global processing biases after stroke: Frequency, lateralization, and associations with cognitive functions

OBJECTIVES

The 'attentional spotlight' can be adjusted depending on the task requirements, resulting in processing information at either the local or global level. Stroke can lead to local or global processing biases, or the inability to simultaneously attend both levels. In this study, we assessed the (1) prevalence of abnormal local and global biases following stroke, (2) differences between left- and right-sided brain damaged patients, and (3) relations between local and global interference, the ability to attend local and global levels simultaneously, and lateralized attention, search organization, search speed, visuo-construction, executive functioning, and verbal (working) memory.

METHODS

Stroke patients admitted for inpatient rehabilitation completed directed (N = 192 total; N = 46 left-sided/N = 48 right-sided lesion) and divided (N = 258 total; N = 67 left-sided/N = 66 right-sided lesion) local-global processing tasks, as well as a conventional neuropsychological assessment. Processing biases and interference effects were separately computed for directed and divided tasks.

RESULTS

On the local-global tasks, 7.8-10.9% of patients showed an abnormal local bias and 6.3-8.3% an abnormal global bias for directed attention, and 5.4-10.1% an abnormal local bias and 6.6-15.9% an abnormal global bias for divided attention. There was no significant difference between patients with left- and right-sided brain damage. There was a moderate positive relation between local interference and search speed, and a small positive relation between global interference and neglect.

CONCLUSIONS

Abnormal local and global biases can occur after stroke and might relate to a range of cognitive functions. A specific bias might require a different approach in assessment, psycho-education, and treatment.

The Effect of Cognitive Style on Individual Differences in Prismatic Adaptation: A Pilot Study

Prism adaptation (PA) is a well-known and widely used technique for rehabilitating unilateral spatial neglect and studying sensory-motor plasticity. However, there is conflicting evidence in the literature regarding its effectiveness which may arise from differences in the type of prisms used, clinical characteristics of the patients, and the procedure used in training. Individual differences may play a role in PA effectiveness in rehabilitating neglect, affecting both its development and its effects. Field-dependent/independent cognitive style is a pervasive characteristic of individual functioning, affecting how environmental information is processed. Here, we tested the hypothesis that cognitive style plays a role in PA efficacy by submitting to a protocol of prism adaptation to 38 health participants, who were classified as field-dependent (FD, N = 19) or field-independent (FI, N = 19), by using the Embedded Figure Test. Results show that during the exposure phase, FI individuals needed a lesser number of pointing movements to reduce the deviation error than FD individuals. However, there are no differences in the extinction of sensory-motor and cognitive after-effects. These results suggest that prismatic adaptation is affected by individuals' cognitive style since FI individuals will need fewer trials to reach adaptation and this could explain why using this rehabilitation technique with a unique, standard protocol is not always effective.

A registered re-examination of the effects of leftward prism adaptation on landmark judgements in healthy people

It has long been known that active adaptation to a shift of the visual field, caused by laterally-displacing prisms, induces short-term sensorimotor aftereffects. More recent evidence suggests that prism adaptation may also stimulate higher-level changes in spatial cognition, which can modify the spatial biases of healthy people. The first reported, and most replicated, higher-level aftereffect is a rightward shift in the point of subjective equality (PSE) for a perceptual bisection task (the landmark task), following adaptation to leftward prisms. A recent meta-analysis suggests that this visuospatial aftereffect should be robustly induced by an extended period of adaptation to strong leftward prisms (15°, ∼26.8 prism dioptres). However, we have been unable to replicate this effect, suggesting that the effect size estimated from prior literature might be over-optimistic. This Registered Report compared visuospatial aftereffects on the landmark task for a 15° leftward prism adaptation group (n = 102) against a sham-adaptation control group (n = 102). The effect size for the comparison was Cohen's d = .27, 95% CI [-.01, .55], which did not pass the criterion set for significance. A Bayesian analysis indicated that the data were more than 4.1 times as likely under the null than under an informed experimental hypothesis. Exploratory analyses showed no evidence for a rightward shift of landmark judgements in the prism group considered alone, and no relationship between sensorimotor and visuospatial aftereffects. We further found no support for previous suggestions that visuospatial aftereffects are modulated by a person's baseline bias (leftward or rightward) for the landmark task. Null findings are also presented for a preliminary group of 62 participants adapted to 15° leftward prisms, and an additional group of 29 participants adapted to 10° leftward prisms. We do not rule out the possibility that leftward prisms might induce higher-level visuospatial aftereffects in healthy people, but we should be more sceptical about this claim.

The hidden cost of a smartphone: The effects of smartphone notifications on cognitive control from a behavioral and electrophysiological perspective

Since their release in 2007, smartphones and their use have seemingly become a fundamental aspect of life in western society. Prior literature has suggested a link between mobile technology use and lower levels of cognitive control when people engage in a cognitively demanding task. This effect is more evident for people who report higher levels of smartphone use. The current study examined the effects of smartphones notifications on cognitive control and attention. Participants completed the Navon Letter paradigm which paired visual (frequent and rare target letters) and auditory (smartphone and control sounds) stimuli. We found that overall, participants responded slower on trials paired with smartphone notification (vs. control) sounds. They also demonstrated larger overall N2 ERP and a larger N2 oddball effect on trials paired with smartphone (vs. control) sounds, suggesting that people generally exhibited greater levels of cognitive control on the smartphone trials. In addition, people with higher smartphone addiction proneness showed lower P2 ERP on trials with the smartphone (vs. control) sounds, suggesting lower attentional engagement. These results add to the debate on the effects of smartphones on cognition. Limitations and future directions are discussed.

Global and local priming in a multi-modal context

Perceptual information can be processed at many different scales, from featural details to entire scenes. Attentional selection of different scales has been studied using hierarchical stimuli, with research elucidating a variety of biases in local and global attentional selection (due to, e.g., stimulus properties, brain injury, and experience). In this study, the emphasis is on biases produced through recent experience, or level-specific priming effects, which have been demonstrated within both the visual and auditory modalities. Namely, when individuals attend to local information, they are subsequently biased to attend locally (and similarly so with global attention). Here, these level-specific priming effects are investigated in a multi-modal context to determine whether cross-modal interactions occur between visual and auditory modalities during hierarchical processing. Specifically, the study addresses if attentional selection of local or global information in the visual modality subsequently biases auditory attentional selection to that level, and vice versa (i.e., level-priming). Though expected identity priming effects emerged in the study, no cross-modal level-priming effects manifested. Furthermore, the multi-modal context eliminated the well-established within-modality level-specific priming effects. Thus, though the study does reveal a multi-modal effect, it was not a level-based effect. Instead, paradoxically, the multi-modal context eliminated attentional scope biases (i.e., level-priming) within uni-modal transitions. In other words, when visual and auditory information are equally likely require attention, no persistence emerges for processing local or global information over time, even within a single modality.

Attention upturned: Bias toward and away from the affected side of the body and near space in a case of complex regional pain syndrome

People with Complex Regional Pain Syndrome (CRPS) following limb injury can show neuropsychological symptoms in the absence of observable brain pathologies. These can include sensory changes, distorted body representation, and inattention to their affected limb and its surrounding space, resembling post-stroke hemispatial neglect. The precise nature and mechanisms of these neuropsychological symptoms are unclear, however insights could be gained by testing for dissociations and associations that have been observed in stroke patients. Drawing from clinical and experimental methods for investigating spatial attention bias and related symptoms in stroke patients, we conducted a detailed investigation of neuropsychological symptoms in a woman with CRPS of her left arm who initially presented to us with pronounced inattention to her affected side. The patient showed visual and tactile neglect and extinction on her affected side on confrontation tests, but no attention deficits on "bedside" tests of neglect. On sensitive computer-based measures, attention biases were found in the patient's body and near space (in Temporal Order Judgements), but not far or imagined space (on the Greyscales task and Mental Number Line Bisection). Unique to the current literature, the patient showed a reversal in her Temporal Order Judgement bias across time, from inattention (first and second session) to hyperattention (third session) to her affected side. In contrast, pain and self-reported body representation distortion were similar across the three sessions. The patient had reduced central and peripheral visual acuity, however these deficits were near symmetrical and therefore could not explain her performance on the visual attention tasks. Given that spatial attention bias has been linked to imbalance in relative activation of the two cerebral hemispheres, we administered a Global-Local processing task to test for hemispheric asymmetry. This revealed no difference in global compared to local interference refuting any hemispheric imbalance. Instead, the patient showed impaired performance (compared to controls) on incongruent trials regardless of trial type, consistent with executive impairment. We conclude that spatial attention bias in CRPS can generalize across different sensory modalities and extend beyond the affected limb to the external space around it, independent of any low-level sensory disturbances. This bias is not necessarily directed away from the affected side or stable over time. People with CRPS can also demonstrate more generalized neuropsychological changes in sensory and executive functions. Our observations refute several existing theories about the mechanisms of attention bias in CRPS, and their relationship to pain, and have potential implications for treatment.

Handling or being the concept: An fMRI study on metonymy representations in coverbal gestures

In "Two heads are better than one," "head" stands for people and focuses the message on the intelligence of people. This is an example of figurative language through metonymy, where substituting a whole entity by one of its parts focuses attention on a specific aspect of the entity. Whereas metaphors, another figurative language device, are substitutions based on similarity, metonymy involves substitutions based on associations. Both are figures of speech but are also expressed in coverbal gestures during multimodal communication. The closest neuropsychological studies of metonymy in gestures have been nonlinguistic tool-use, illustrated by the classic apraxic problem of body-part-as-object (BPO, equivalent to an internal metonymy representation of the tool) vs. pantomimed action (external metonymy representation of the absent object/tool). Combining these research domains with concepts in cognitive linguistic research on gestures, we conducted an fMRI study to investigate metonymy resolution in coverbal gestures. Given the greater difficulty in developmental and apraxia studies, perhaps explained by the more complex semantic inferencing involved for external metonymy than for internal metonymy representations, we hypothesized that external metonymy resolution requires greater processing demands and that the neural resources supporting metonymy resolution would modulate regions involved in semantic processing. We found that there are indeed greater activations for external than for internal metonymy resolution in the temporoparietal junction (TPJ). This area is posterior to the lateral temporal regions recruited by metaphor processing. Effective connectivity analysis confirmed our hypothesis that metonymy resolution modulates areas implicated in semantic processing. We interpret our results in an interdisciplinary view of what metonymy in action can reveal about abstract cognition.

Flexible or leaky attention in creative people? Distinct patterns of attention for different types of creative thinking

Creativity has been putatively linked to distinct forms of attention, but which aspects of creativity and which components of attention remains unclear. Two experiments examined how divergent thinking and creative achievement relate to visual attention. In both experiments, participants identified target letters (S or H) within hierarchical stimuli (global letters made of local letters), after being cued to either the local or global level. In Experiment 1, participants identified the targets more quickly following valid cues (80% of trials) than following invalid cues. However, this smaller validity effect was associated with higher divergent thinking, suggesting that divergent thinking was related to quicker overcoming of invalid cues, and thus to flexible attention. Creative achievement was unrelated to the validity effect. Experiment 2 examined whether divergent thinking (or creative achievement) is related to "leaky attention," so that when cued to one level of a stimulus, some information is still processed, or leaks in, from the non-cued level. In this case, the cued stimulus level always contained a target, and the non-cued level was congruent, neutral, or incongruent with the target. Divergent thinking did not relate to stimulus congruency. In contrast, high creative achievement was related to quicker responses to the congruent than to the incongruent stimuli, suggesting that real-world creative achievement is indeed associated with leaky attention, whereas standard laboratory tests of divergent thinking are not. Together, these results elucidate distinct patterns of attention for different measures of creativity. Specifically, creative achievers may have leaky attention, as suggested by previous literature, whereas divergent thinkers have selective yet flexible attention.

Prism Adaptation Alters Electrophysiological Markers of Attentional Processes in the Healthy Brain

Neglect patients typically show a rightward attentional orienting bias and a strong disengagement deficit, such that they are especially slow in responding to left-sided targets after right-sided cues (Posner et al., 1984). Prism adaptation (PA) can reduce diverse debilitating neglect symptoms and it has been hypothesized that PA's effects are so generalized that they might be mediated by attentional mechanisms (Pisella et al., 2006; Redding and Wallace, 2006). In neglect patients, performance on spatial attention tasks improves after rightward-deviating PA (Jacquin-Courtois et al., 2013). In contrast, in healthy subjects, although there is evidence that leftward-deviating PA induces neglect-like performance on some visuospatial tasks, behavioral studies of spatial attention tasks have mostly yielded negative results (Morris et al., 2004; Bultitude et al., 2013). We hypothesized that these negative behavioral findings might reflect the limitations of behavioral measures in healthy subjects. Here we exploited the sensitivity of event-related potentials to test the hypothesis that electrophysiological markers of attentional processes in the healthy human brain are affected by PA. Leftward-deviating PA generated asymmetries in attentional orienting (reflected in the cue-locked N1) and in attentional disengagement for invalidly cued left targets (reflected in the target-locked P1). This is the first electrophysiological demonstration that leftward-deviating PA in healthy subjects mimics attentional patterns typically seen in neglect patients. Significance statement: Prism adaptation (PA) is a promising tool for ameliorating many deficits in neglect patients and inducing neglect-like behavior in healthy subjects. The mechanisms underlying PA's effects are poorly understood but one hypothesis suggests that it acts by modulating attention. To date, however, there has been no successful demonstration of attentional modulation in healthy subjects. We provide the first electrophysiological evidence that PA acts on attention in healthy subjects by mimicking the attentional pattern typically reported in neglect patients: both a rightward attentional orienting bias (reflected in the cue-locked N1) and a deficit in attentional disengagement from the right hemispace (reflected in the target-locked P1). This study makes an important contribution to refining current models of the mechanisms underlying PA's cognitive effects.

Beyond the Sensorimotor Plasticity: Cognitive Expansion of Prism Adaptation in Healthy Individuals

Sensorimotor plasticity allows us to maintain an efficient motor behavior in reaction to environmental changes. One of the classical models for the study of sensorimotor plasticity is prism adaptation. It consists of pointing to visual targets while wearing prismatic lenses that shift the visual field laterally. The conditions of the development of the plasticity and the sensorimotor after-effects have been extensively studied for more than a century. However, the interest taken in this phenomenon was considerably increased since the demonstration of neglect rehabilitation following prism adaptation by Rossetti et al. (1998). Mirror effects, i.e., simulation of neglect in healthy individuals, were observed for the first time by Colent et al. (2000). The present review focuses on the expansion of prism adaptation to cognitive functions in healthy individuals during the last 15 years. Cognitive after-effects have been shown in numerous tasks even in those that are not intrinsically spatial in nature. Altogether, these results suggest the existence of a strong link between low-level sensorimotor plasticity and high-level cognitive functions and raise important questions about the mechanisms involved in producing unexpected cognitive effects following prism adaptation. Implications for the functional mechanisms and neuroanatomical network of prism adaptation are discussed to explain how sensorimotor plasticity may affect cognitive processes.

Spatial and temporal dynamics of visual search tasks distinguish subtypes of unilateral spatial neglect: Comparison of two cases with viewer-centered and stimulus-centered neglect

We developed a computerised test to evaluate unilateral spatial neglect (USN) using a touchscreen display, and estimated the spatial and temporal patterns of visual search in USN patients. The results between a viewer-centered USN patient and a stimulus-centered USN patient were compared. Two right-brain-damaged patients with USN, a patient without USN, and 16 healthy subjects performed a simple cancellation test, the circle test, a visuomotor search test, and a visual search test. According to the results of the circle test, one USN patient had stimulus-centered neglect and a one had viewer-centered neglect. The spatial and temporal patterns of these two USN patients were compared. The spatial and temporal patterns of cancellation were different in the stimulus-centered USN patient and the viewer-centered USN patient. The viewer-centered USN patient completed the simple cancellation task, but paused when transferring from the right side to the left side of the display. Unexpectedly, this patient did not exhibit rightward attention bias on the visuomotor and visual search tests, but the stimulus-centered USN patient did. The computer-based assessment system provided information on the dynamic visual search strategy of patients with USN. The spatial and temporal pattern of cancellation and visual search were different across the two patients with different subtypes of neglect.

Ready, set, point: the effects of alertness on prism adaptation in healthy adults

Prism adaptation (PA) is a promising rehabilitation technique for visuo-spatial neglect, an attention disorder that is characterized by spatial attention deficits (i.e., deficits in orienting). PA involves visuo-motor adaptation to rightward shifting prism goggles. Following goggle removal, this adaptation results in leftward shifts in visuo-motor aiming and amelioration of spatial neglect. Even though some studies clearly support the beneficial effects of PA for spatial neglect, not all studies find benefits, thus it remains unclear how PA effects could be improved. Taking advantage of the known interactions between orienting and alerting reported in the attention literature (i.e., alerting enhances orienting function; e.g., Ishigami and Klein in J Individ Differ 30:220-237. doi: 10.1027/1614-0001.30.4.220 , 2009, in J Neurosci Methods 190:117-28. doi: 10.1016/j.jneumeth.2010.04.019 , 2010; Robertson et al. in Nature 395:169-72. doi: 10.1038/25993 , 1998), we examined the effects of alerting tones on PA with healthy young and older adults. We found that the effects of alerting on PA with young adults were negative, while there was a positive effect with older adults, specifically on a visuo-motor outcome task. Thus, enhancement of PA effects by alerting may be age specific and task specific. Therefore, we can conclude that while the impact of alerting tones is not always positive, further research in patients with neglect may be warranted.

The role of the right temporoparietal junction in attention and social interaction as revealed by ALE meta-analysis

The right temporoparietal junction (rTPJ) is frequently associated with different capacities that to shift attention to unexpected stimuli (reorienting of attention) and to understand others' (false) mental state [theory of mind (ToM), typically represented by false belief tasks]. Competing hypotheses either suggest the rTPJ representing a unitary region involved in separate cognitive functions or consisting of subregions subserving distinct processes. We conducted activation likelihood estimation (ALE) meta-analyses to test these hypotheses. A conjunction analysis across ALE meta-analyses delineating regions consistently recruited by reorienting of attention and false belief studies revealed the anterior rTPJ, suggesting an overarching role of this specific region. Moreover, the anatomical difference analysis unravelled the posterior rTPJ as higher converging in false belief compared with reorienting of attention tasks. This supports the concept of an exclusive role of the posterior rTPJ in the social domain. These results were complemented by meta-analytic connectivity mapping (MACM) and resting-state functional connectivity (RSFC) analysis to investigate whole-brain connectivity patterns in task-constrained and task-free brain states. This allowed for detailing the functional separation of the anterior and posterior rTPJ. The combination of MACM and RSFC mapping showed that the posterior rTPJ has connectivity patterns with typical ToM regions, whereas the anterior part of rTPJ co-activates with the attentional network. Taken together, our data suggest that rTPJ contains two functionally fractionated subregions: while posterior rTPJ seems exclusively involved in the social domain, anterior rTPJ is involved in both, attention and ToM, conceivably indicating an attentional shifting role of this region.

Adaptation to leftward-shifting prisms enhances local processing in healthy individuals

In healthy individuals, adaptation to left-shifting prisms has been shown to simulate the symptoms of hemispatial neglect, including a reduction in global processing that approximates the local bias observed in neglect patients. The current study tested whether leftward prism adaptation can more specifically enhance local processing abilities. In three experiments, the impact of local and global processing was assessed through tasks that measure susceptibility to illusions that are known to be driven by local or global contextual effects. Susceptibility to the rod-and-frame illusion - an illusion disproportionately driven by both local and global effects depending on frame size - was measured before and after adaptation to left- and right-shifting prisms. A significant increase in rod-and-frame susceptibility was found for the left-shifting prism group, suggesting that adaptation caused an increase in local processing effects. The results of a second experiment confirmed that leftward prism adaptation enhances local processing, as assessed with susceptibility to the simultaneous-tilt illusion. A final experiment employed a more specific measure of the global effect typically associated with the rod-and-frame illusion, and found that although the global effect was somewhat diminished after leftward prism adaptation, the trend failed to reach significance (p=.078). Rightward prism adaptation had no significant effects on performance in any of the experiments. Combined, these findings indicate that leftward prism adaptation in healthy individuals can simulate the local processing bias of neglect patients primarily through an increased sensitivity to local visual cues, and confirm that prism adaptation not only modulates lateral shifts of attention, but also prompts shifts from one level of processing to another.

Prism adaptation in the healthy brain: the shift in line bisection judgments is long lasting and fluctuates

Rightward prism adaptation has been shown to ameliorate visuospatial biases in right brain-damaged patients with neglect, and a single session of prism adaptation can lead to improvements that last up to several hours. Leftward prism adaptation in neurologically healthy individuals induces neglect-like biases in visuospatial tasks. The duration of these effects in healthy individuals, typically assumed to be ephemeral, has never been investigated. Here we assessed the time-course of the adaptation-induced modifications in a classical perceptual line bisection task that was repeatedly administered for approximately 40min after a single session of adaptation to either a leftward or rightward prismatic deviation. Consistent with previous reports, only adaptation to leftward-deviating prisms induced a visuospatial shift on perceptual line bisection judgments. The typical pattern of pseudoneglect was counteracted by a rightward shift in midline judgments, which became significant between 5 and 10 min after adaptation, fluctuated between being significant or not several times in the 40 min following adaptation, and was present as late as 35 min. In contrast, the sensorimotor aftereffect was present immediately after adaptation to both rightward and leftward deviating prisms, decayed initially then remained stable until 40 min. These results demonstrate that both the sensorimotor and visuospatial effects last for at least 35 min, but that the visuospatial shift needs time to fully develop and fluctuates. By showing that the effects of prism adaptation in the undamaged brain are not ephemeral, these findings reveal the presence of another, so-far neglected dimension in the domain of the cognitive effects induced by prism adaptation, namely time. The prolonged duration of the induced visuospatial shift, previously considered to be a feature of prism adaptation unique to brain-damaged subjects, also applies to the normal brain.

Novel insights in the rehabilitation of neglect

Visuospatial neglect due to right hemisphere damage, usually a stroke, is a major cause of disability, impairing the ability to perform a whole range of everyday life activities. Conventional and long-established methods for the rehabilitation of neglect like visual scanning training, optokinetic stimulation, or limb activation training have produced positive results, with varying degrees of generalization to (un)trained tasks, lasting from several minutes up to various months after training. Nevertheless, some promising novel approaches to the remediation of left visuospatial neglect have emerged in the last decade. These new therapy methods can be broadly classified into four categories. First, non-invasive brain stimulation techniques by means of transcranial magnetic stimulation (TMS) or transcranial direct current stimulation (tDCS), after a period of mainly diagnostic utilization, are increasingly applied as neurorehabilitative tools. Second, two classes of drugs, dopaminergic and noradrenergic, have been investigated for their potential effectiveness in rehabilitating neglect. Third, prism adaptation treatment has been shown to improve several neglect symptoms consistently, sometimes during longer periods of time. Finally, virtual reality technologies hold new opportunities for the development of effective training techniques for neglect. They provide realistic, rich, and highly controllable training environments. In this paper the degree of effectiveness and the evidence gathered to support the therapeutic claims of these new approaches is reviewed and discussed. The conclusion is that for all these approaches there still is insufficient unbiased evidence to support their effectiveness. Further neglect rehabilitation research should focus on the maintenance of therapy results over time, on a more functional evaluation of treatment effects, on the design and execution of true replication studies and on the exploration of optimal combinations of treatments.

Analysis of cortical shape in children with simplex autism

We used surface-based morphometry to test for differences in cortical shape between children with simplex autism (n = 34, mean age 11.4 years) and typical children (n = 32, mean age 11.3 years). This entailed testing for group differences in sulcal depth and in 3D coordinates after registering cortical midthickness surfaces to an atlas target using 2 independent registration methods. We identified bilateral differences in sulcal depth in restricted portions of the anterior-insula and frontal-operculum (aI/fO) and in the temporoparietal junction (TPJ). The aI/fO depth differences are associated with and likely to be caused by a shape difference in the inferior frontal gyrus in children with simplex autism. Comparisons of average midthickness surfaces of children with simplex autism and those of typical children suggest that the significant sulcal depth differences represent local peaks in a larger pattern of regional differences that are below statistical significance when using coordinate-based analysis methods. Cortical regions that are statistically significant before correction for multiple measures are peaks of more extended, albeit subtle regional differences that may guide hypothesis generation for studies using other imaging modalities.

Prism adaptation does not alter configural processing of faces

Patients with hemispatial neglect (‘neglect’) following a brain lesion show difficulty responding or orienting to objects and events on the left side of space. Substantial evidence supports the use of a sensorimotor training technique called prism adaptation as a treatment for neglect. Reaching for visual targets viewed through prismatic lenses that induce a rightward shift in the visual image results in a leftward recalibration of reaching movements that is accompanied by a reduction of symptoms in patients with neglect. The understanding of prism adaptation has also been advanced through studies of healthy participants, in whom adaptation to leftward prismatic shifts results in temporary neglect-like performance. Interestingly, prism adaptation can also alter aspects of non-lateralised spatial attention. We previously demonstrated that prism adaptation alters the extent to which neglect patients and healthy participants process local features versus global configurations of visual stimuli. Since deficits in non-lateralised spatial attention are thought to contribute to the severity of neglect symptoms, it is possible that the effect of prism adaptation on these deficits contributes to its efficacy. This study examines the pervasiveness of the effects of prism adaptation on perception by examining the effect of prism adaptation on configural face processing using a composite face task. The composite face task is a persuasive demonstration of the automatic global-level processing of faces: the top and bottom halves of two familiar faces form a seemingly new, unknown face when viewed together. Participants identified the top or bottom halves of composite faces before and after prism adaptation. Sensorimotor adaptation was confirmed by significant pointing aftereffect, however there was no significant change in the extent to which the irrelevant face half interfered with processing. The results support the proposal that the therapeutic effects of prism adaptation are limited to dorsal stream processing.

Coupling acoustic feedback to eye movements to reduce spatial neglect

BACKGROUND

A typical consequence of right hemispheric brain lesions is spatial neglect. Patients with spatial neglect suffer from a variety of neglect phenomena and related disorders, including a sustained shift of the horizontal eye-in-head position toward the affected hemisphere. The aim of this study was to investigate benefits of a method of coupling eye movement to an acoustic feedback.

METHODS

Seven outpatients of the Department of Neurology, Medical University of Vienna, with a chronic spatial neglect following a brain lesion took part in the study. The participants underwent a neuropsychological assessment of spatial neglect at baseline after 10 and 15 training sessions and a follow-up after 3 months. Therapy sessions included training of the saccadic and the pursuit eye movement with the help of acoustic feedback.

RESULTS

There were significant improvements of performance in visual exploration, reading, reaction times, and the total score of the conventional subtest of the Behavioral Inattention Test and decreased symptoms of anosognosia. The results stayed stable over a period of 3 months.

CONCLUSION

Coupling eye movements to acoustic feedback seemed to be a suitable training method to improve visual exploration, reading, and awareness of patients with visual neglect.

Short-term attentional perseveration associated with real-life creative achievement

There are at least two competing hypotheses of how attention interacts with creative cognition, although they are not mutually exclusive. The first hypothesis is that highly creative people are particularly flexible at switching their attention - that is, they adaptively shift focus among different attentional levels using cognitive control. The second, less common, view is that creative people exhibit attentional persistence, or an ability for sustained attention. We suggest these two views need not be competing, as they may both operate, but on different time scales or on different components of creativity. In the present study we examined the role of attention in real-world creative achievement and in divergent thinking. In Experiment 1 participants with high and low real-world creative achievements identified whether the stimulus contained letters S or H within hierarchically constructed letters (e.g., large S made of small Es - global level; large E made up of small Ss - local level), which were presented in blocks of eight trials per level. In Experiment 2 participants with high, medium, and low creative achievements identified the same stimulus letters, but in blocks of five, seven, and nine trials per level. Results from both experiments indicated that people with high creative achievements made significantly more errors on trials in which they had to switch the level of attention, even after controlling for general intelligence. In Experiment 2, divergent thinking was also assessed, but it was not related to switching cost. Results from both experiments demonstrate that real-world creative acts relate to increased levels of attentional persistence, even if it comes with the cost of perseveration in certain circumstances.

Rehabilitation of spatial neglect by prism adaptation: a peculiar expansion of sensorimotor after-effects to spatial cognition

Unilateral neglect is a neurological condition responsible for many debilitating effects on everyday life, poor functional recovery, and decreased ability to benefit from treatment. Prism adaptation (PA) to a right lateral displacement of the visual field is classically known to directionally bias visuo-motor and sensory-motor correspondences. One longstanding issue about this visuo-motor plasticity is about its specificity to the exposure condition. In contrast to very poor transfer to unexposed effectors classically described in healthy subjects, therapeutic results obtained in neglect patients suggested that PA can generate unexpected "expansion". Prism adaptation affects numerous levels of neglect symptomatology, suggesting that its effects somehow expand to unexposed sensory, motor and cognitive systems. The available body of evidence in support for this expansion raises important questions about the mechanisms involved in producing unexpected cognitive effects following a simple and moderate visuo-motor adaptation. We further develop here the idea that prism adaptation expansion to spatial cognition involves a cerebello-cortical network and review support for this model. Building on the basic, therapeutical and pathophysiological knowledge accumulated over the last 15 years, we also provide guidelines for the optimal use of prism adaptation in the clinic. Although further research and clinical trials are required to precisely define the ideal regime for routine applications, the current state of the art allows us to outline practical recommendations for therapeutical use of prisms.

Prism adaptation for spatial neglect after stroke: translational practice gaps

Spatial neglect increases hospital morbidity and costs in around 50% of the 795,000 people per year in the USA who survive stroke, and an urgent need exists to reduce the care burden of this condition. However, effective acute treatment for neglect has been elusive. In this article, we review 48 studies of a treatment of intense neuroscience interest: prism adaptation training. Due to its effects on spatial motor 'aiming', prism adaptation training may act to reduce neglect-related disability. However, research failed, first, to suggest methods to identify the 50-75% of patients who respond to treatment; second, to measure short-term and long-term outcomes in both mechanism-specific and functionally valid ways; third, to confirm treatment utility during the critical first 8 weeks poststroke; and last, to base treatment protocols on systematic dose-response data. Thus, considerable investment in prism adaptation research has not yet touched the fundamentals needed for clinical implementation. We suggest improved standards and better spatial motor models for further research, so as to clarify when, how and for whom prism adaptation should be applied.

Terminal, but not concurrent prism exposure produces perceptual aftereffects in healthy young adults

A short period of prism adaptation (PA) has been shown to reduce spatial neglect symptoms. Recent evidence suggests that the positive effects of PA might be restricted to visually guided actions, with PA having little effect on perception. However, the majority of studies have adopted a concurrent exposure technique that fosters the development of a change in felt arm position (proprioceptive straight ahead, PSA). Few studies have used terminal exposure that promotes a change in the perceived visual direction (visual straight ahead, VSA). The positive effects of PA might appear to be primarily action based because studies have adopted an exposure technique that promotes a change in proprioception. Here, we compare the effects of the two exposure types on a perceptual and a manual line bisection task in healthy young adults. Before and after seven minutes of exposure to leftward displacing prisms we measured performance on two line bisection tasks (manual and perceptual) and perceived straight ahead (PSA and VSA). During the exposure period participants made pointing movements while the view of their pointing arm was either (i) restricted to the second half of the pointing movement (concurrent exposure) or (ii) restricted to the final part of the pointing movement (terminal exposure). In line with the previous research, concurrent exposure produced a large shift in PSA and a shift on the manual line bisection task. Interestingly, terminal exposure produced a large shift in VSA and a shift in performance on the perceptual line bisection task. Our results shed light on the underlying mechanisms of prism-induced neglect recovery and help to address an apparent discrepancy within the literature.

Prism adaptation alters spatial remapping in healthy individuals: evidence from double-step saccades

The visual system is able to represent and integrate large amounts of information as we move our gaze across a scene. This process, called spatial remapping, enables the construction of a stable representation of our visual environment despite constantly changing retinal images. Converging evidence implicates the parietal lobes in this process, with the right hemisphere having a dominant role. Indeed, lesions to the right parietal lobe (e.g., leading to hemispatial neglect) frequently result in deficits in spatial remapping. Research has demonstrated that recalibrating visual, proprioceptive and motor reference frames using prism adaptation ameliorates neglect symptoms and induces neglect-like performance in healthy people - one example of the capacity for rapid neural plasticity in response to new sensory demands. Because of the influence of prism adaptation on parietal functions, the present research investigates whether prism adaptation alters spatial remapping in healthy individuals. To this end twenty-eight undergraduates completed blocks of a double-step saccade (DSS) task after sham adaptation and adaptation to leftward- or rightward-shifting prisms. The results were consistent with an impairment in spatial remapping for left visual field targets following adaptation to leftward-shifting prisms. These results suggest that temporarily realigning spatial representations using sensory-motor adaptation alters right-hemisphere remapping processes in healthy individuals. The implications for the possible mechanisms of the amelioration of hemispatial neglect after prism adaptation are discussed.

Prism adaptation differently affects motor-intentional and perceptual-attentional biases in healthy individuals

Prism adaptation (PA) has been shown to affect performance on a variety of spatial tasks in healthy individuals and neglect patients. However, little is still known about the mechanisms through which PA affects spatial cognition. In the present study we tested the effect of PA on the perceptual-attentional "where" and motor-intentional "aiming" spatial systems in healthy individuals. Eighty-four participants performed a line bisection task presented on a computer screen under normal or right-left reversed viewing conditions, which allows for the fractionation of "where" and "aiming" bias components (Schwartz et al., 1997). The task was performed before and after a short period of visuomotor adaptation either to left- or right-shifting prisms, or control goggles fitted with plain glass lenses. Participants demonstrated initial leftward "where" and "aiming" biases, consistent with previous research. Adaptation to left-shifting prisms reduced the leftward motor-intentional "aiming" bias. By contrast, the "aiming" bias was unaffected by adaptation to the right-shifting prisms or control goggles. The leftward "where" bias was also reduced, but this reduction was independent of the direction of the prismatic shift. These results mirror recent findings in neglect patients, who showed a selective amelioration of right motor-intentional "aiming" bias after right prism exposure (Fortis et al., 2009; C.L. Striemer & J. Danckert, 2010). Thus, these findings indicate that prism adaptation primarily affects the motor-intentional "aiming" system in both healthy individuals and neglect patients, and further suggest that improvement in neglect patients after PA may be related to changes in the aiming spatial system.

Recent trends in rehabilitation interventions for visual neglect and anosognosia for hemiplegia following right hemisphere stroke

This article highlights the most recent findings regarding the rehabilitation interventions for the syndromes of visual neglect and anosognosia for hemiplegia that occur following right hemisphere stroke. We review papers published in the past 4 years pertaining to therapeutic approaches for these two syndromes in order to identify the trends in the development of effective interventions. Overall, it appears well recognized that visual neglect syndromes and awareness syndromes frequently co-occur and both include complex, multifaceted impairments leading to significant difficulties in daily life functioning following stroke. Thus, the interventions for these syndromes must be multifaceted in order to address the complex interplay of cognitive-behavioral-emotional components. There appears to be a trend for using combination therapeutic interventions that address these components.

Modulation of non-spatial attention and the global/local processing bias

Amelioration of the rightward spatial attention bias in patients with hemispatial neglect following manipulations of non-spatial attention suggests that spatial attention and mechanisms related to the regulation of attention are interrelated. Studies in normal, healthy subjects have shown similar modulation in spatial bias following tonic and phasic changes in attention suggesting that this interaction is a general mechanism of attention rather than a curiosity of the neglect disorder. The current study examined this attentional interaction to determine if perceptual processes favoring one hemisphere over the other are affected by this relationship. Participants first made rapid discriminations of Navon figures presented at central fixation. As expected, when participants attended to either the local or global dimension, incongruence in the orthogonal dimension resulted in longer reaction times for accurate discrimination compared to congruent trials. However, following a brief (16-min) continuous performance task designed to elicit behaviors associated with greater tonic and phasic alertness, participants showed significantly less local interference when attending the global dimension and more global interference when attending the local dimension on the Navon discrimination task compared to a control task condition. The results indicate that exercising tonic and phasic alertness produces a global processing bias.

Through a prism darkly: re-evaluating prisms and neglect

Many studies have demonstrated that prism adaptation can reduce several symptoms of visual neglect: a disorder in which patients fail to respond to information in contralesional space. The dominant framework to explain these effects proposes that prisms influence higher order visuospatial processes by acting on brain circuits that control spatial attention and perception. However, studies that have directly examined the influence of prisms on perceptual biases inherent to neglect have revealed very few beneficial effects. We propose an alternative explanation whereby many of the beneficial effects of prisms arise via the influence of adaptation on circuits in the dorsal visual stream controlling attention and visuomotor behaviors. We further argue that prisms have little influence on the pervasive perceptual biases that characterize neglect.

Adaptation to leftward-shifting prisms reduces the global processing bias of healthy individuals

When healthy individuals are presented with peripheral figures in which small letters are arranged to form a large letter, they are faster to identify the global- than the local-level information, and have difficulty ignoring global information when identifying the local level. The global reaction time (RT) advantage and global interference effect imply preferential processing of global-level information in the normal brain. This contrasts with the local processing bias demonstrated following lesions to the right temporo-parietal junction (TPJ), such as those that lead to hemispatial neglect (neglect). Recent research from our lab demonstrated that visuo-motor adaptation to rightward-shifting prisms, which ameliorates many leftward performance deficits of neglect patients, improved the local processing bias of patients with right TPJ lesions (Bultitude, Rafal, & List, 2009). Here we demonstrate that adaptation to leftward-shifting prisms, which can induce neglect-like performance in neurologically healthy individuals, also reduces the normal global processing bias. Forty-eight healthy participants were asked to identify the global or local forms of hierarchical figures before and after adaptation to leftward- or rightward-shifting prisms. Prior to prism adaptation, both groups had greater difficulty ignoring irrelevant global information when identifying the local level (global interference) compared to their ability to ignore irrelevant local-level information when identifying the global level (local interference). Participants who adapted to leftward-shifting prisms showed a significant reduction in global interference, but there was no change in the performance of the rightward-shifting Prism Group. These results show, for the first time, that in addition to previously demonstrated effects on lateralised attention, prism adaptation can influence non-lateralised spatial attention in healthy individuals.