Endpoints and viewpoints on spatial neglect

In this issue of the Journal of Neuropsychology, Abe and Ishiai (2022) report an experiment designed to probe the subjective experience of line bisection in neglect. A re-analysis of their data can also offer insights into how best to characterise neglect performance for this and other tasks. We show that sensitive measures of neglect can be obtained by quantifying the difference in the influence (or ‘weighting’) that each endpoint has on the response. The right endpoint is dramatically more influential than the left in people with neglect performing line bisection and endpoint reproduction tasks. This supports the view that neglect may limit the ability to simultaneously represent two locations, so that the response is determined primarily with respect to the right endpoint. We also discuss Abe and Ishiai's conclusion that bisection responses in neglect are accompanied by the subjective experience of a complete line extending equally to either side of the chosen midpoint.     

Learning spatial sequences in unilateral neglect

Brain-damaged patients with unilateral spatial neglect ignore aspects of the world located on the side opposite their lesion. In the present study we examined the performance of unilateral neglect patients (UN) on an SRT task in which a hybrid repeating sequence (21313) was used. We analyzed the patients' performance for each location separately as a function of the target's location in the trial preceding the response. The UN patients were severely limited in their learning of the sequence when compared to normal controls. In particular, they appeared to learn unique associations (21 and 13) but not ambiguous ones (31 and 32). We discuss two possible explanations for this phenomenon. The first is that UN patients show a deficit similar to that of normal subjects in dual task situations. The second is that the learning deficit is unique to spatial processing impairments of UN patients and is not directly related to research with normal population. We outline future research that may distinguish between these two explanations.     

Enactivism,other minds,and mental disorders

Although enactive approaches to cognition vary in terms of their character and scope, all endorse several core claims. The first is that cognition is tied to action. The second is that cognition is composed of more than just in-the-head processes; cognitive activities are (at least partially) externalized via features of our embodiment and in our ecological dealings with the people and things around us. I appeal to these two enactive claims to consider a view called “direct social perception” (DSP): the idea that we can sometimes perceive features of other minds directly in the character of their embodiment and environmental interactions. I argue that if DSP is true, we can probably also perceive certain features of mental disorders as well. I draw upon the developmental psychologist Daniel Stern’s notion of “forms of vitality”—largely overlooked in these debates—to develop this idea, and I use autism as a case study. I argue further that an enactive approach to DSP can clarify some ways we play a regulative role in shaping the temporal and phenomenal character of the disorder in question, and it may therefore have practical significance for both the clinical and therapeutic encounter.

     

Eye movements and bisection behavior in spatial neglect syndrome: representational biases induced by the segment length and spatial dislocation of the stimulus

The present study explored behavioral and eye-movement measures in unilateral neglect patients in response to online bisection task (unfilled gap line). Two different tasks supported the bisection performance, a pointing and a grasping strategy. It was explored whether these different strategies may influence subjects' behavioral and eye-movement measures in response to different segment features: segment length (from shorter to longer) and segment spatial dislocation (from right to left spatial location). Consistent spatial biases were found for both bisection responses, fixation count, and duration, as well as for the first fixation count in case of pointing task. An "extreme-left" gradient effect was suggested and discussed, with patients' behavioral and eye measures more impaired. On the contrary, the patients' performance overlaps with the controls' one in case a grasping task. The direct link of visual pointing and grasping strategy, respectively, with the two cortical ventral and dorsal pathways was adduced to explain our results.     

Eye movements and bisection behavior in spatial neglect syndrome: representational biases induced by the segment length and spatial dislocation of the stimulus

The present study explored behavioral and eye-movement measures in unilateral neglect patients in response to online bisection task (unfilled gap line). Two different tasks supported the bisection performance, a pointing and a grasping strategy. It was explored whether these different strategies may influence subjects’ behavioral and eye-movement measures in response to different segment features: segment length (from shorter to longer) and segment spatial dislocation (from right to left spatial location). Consistent spatial biases were found for both bisection responses, fixation count, and duration, as well as for the first fixation count in case of pointing task. An “extreme-left” gradient effect was suggested and discussed, with patients’ behavioral and eye measures more impaired. On the contrary, the patients’ performance overlaps with the controls’ one in case a grasping task. The direct link of visual pointing and grasping strategy, respectively, with the two cortical ventral and dorsal pathways was adduced to explain our results.     

Spatial cognition: evidence from visual neglect

Recent work on human attention and representational systems has benefited from a growing interplay between research on normal attention and neuropsychological disorders such as visual neglect. Research over the past 30 years has convincingly shown that, far from being a unitary condition, neglect is a protean disorder whose symptoms can selectively affect different sensory modalities, cognitive processes, spatial domains and coordinate systems. These clinical findings, together with those of functional neuroimaging, have increased knowledge about the anatomical and functional architecture of normal subsystems involved in spatial cognition. We provide a selective overview of how recent investigations of visual neglect are beginning to elucidate the underlying structure of spatial processes and mental representations.     

Different patterns of dissociation in unilateral spatial neglect

The aim of this paper is to discuss the issue of dissociations found in unilateral spatial neglect according to the modality of space exploration and the nature of the task. For this purpose we present a reanalysis of the data from a recent paper of Gentilini et al. (1989) comparing visual and blindfolded exploration of a computer keyboard and discuss the performance of a left-brain-damaged patient with right visuospatial neglect and left-sided neglect dyslexia. We conclude that unilateral spatial neglect cannot be interpreted as a disruption of a single attentional mechanism, but rather it reflects impaired attentional mechanisms at several levels of cognitive processing.     

Improving left spatial neglect through music scale playing

The study assessed whether the auditory reference provided by a music scale could improve spatial exploration of a standard musical instrument keyboard in right‐brain‐damaged patients with left spatial neglect. As performing music scales involves the production of predictable successive pitches, the expectation of the subsequent note may facilitate patients to explore a larger extension of space in the left affected side, during the production of music scales from right to left. Eleven right‐brain‐damaged stroke patients with left spatial neglect, 12 patients without neglect, and 12 age‐matched healthy participants played descending scales on a music keyboard. In a counterbalanced design, the participants' exploratory performance was assessed while producing scales in three feedback conditions: With congruent sound, no‐sound, or random sound feedback provided by the keyboard. The number of keys played and the timing of key press were recorded. Spatial exploration by patients with left neglect was superior with congruent sound feedback, compared to both Silence and Random sound conditions. Both the congruent and incongruent sound conditions were associated with a greater deceleration in all groups. The frame provided by the music scale improves exploration of the left side of space, contralateral to the right hemisphere, damaged in patients with left neglect. Performing a scale with congruent sounds may trigger at some extent preserved auditory and spatial multisensory representations of successive sounds, thus influencing the time course of space scanning, and ultimately resulting in a more extensive spatial exploration. These findings offer new perspectives also for the rehabilitation of the disorder.     

Spatial awareness, alertness, and ADHD: the re-emergence of unilateral neglect with time-on-task

Studies examining a relationship between attention deficit hyperactivity disorder (ADHD) and relative visual inattention towards left space have produced inconsistent results. Here, based on previous studies with adult neurological patients who show very severe inattention to the left, we examine whether any spatial bias in ADHD may be modulated by changes in alertness levels. In a single case, we found that inattention to the left--that was intermittently apparent--dramatically increased as a function of time-on-task. No significant changes were observed on the right. The implications for clinical assessment and research design are discussed.     

Pure agraphia and Gerstmann's syndrome as a visuospatial-language dissociation: an experimental case study

A right-handed man suffered a left parieto-occipital cerebral infarction, causing agraphia with Gerstmann's syndrome but without major aphasia, alexia, or apraxia. Oral spelling was superior to written spelling. Experiments were performed involving (1) analysis of errors in writing, (2) tasks of visual imagery, and (3) identifying letters drawn without leaving a visual trace. The results suggest that the agraphia and Gerstmann's syndrome are due to a dissociation of language skills and visuospatial skills caused by a dominant parieto-occipital lesion.     

Self, other and dialogical space in autistic disorders

The authors propose to re-evaluate Tustin's thesis using both the extensive clinical material of a child with an autistic disorder [PDD], and current research on infant development. Beebe's concept of 'interaction structure' that could be inferred from the fi fth month of life using face-to-face research data is used for postulating a dialogic space that would be generated inside such structure, allowing for defi nition of self and other in a relationship. If such space is collapsed, the other would be a threat of annihilation for the self, thus it should be avoided or merged with, which could explain the systematic avoidance of the not-me in autistic states. The authors stress that these ideas are just one alternate model, among several, that seems to be able to explain the patient's deviant development.     

Selective spatial attention and length representation in normal subjects and in patients with unilateral spatial neglect

The aim of this study was to assess whether perceptual representation along the horizontal axis is affected by hemispace position of the stimulus or by orienting attention to one side. Ten control subjects and 10 right brain damaged patients with left unilateral spatial neglect (USN) were asked to bisect lines of five lengths in three space positions (left, center, right) and under three cueing conditions (no cue, left cue, right cue). Normal controls showed significant displacement of bisection opposite to the side of hemispace presentation and toward the side of cueing. USN patients showed a bisection error toward the right end which increased with lines placed in the left hemispace and decreased with lines placed in the right hemispace and when attention was oriented toward the left side. We conclude that (1) In absence of cues normal subjects tend to overestimate the portions of space closer to their body midline; (2) both normal and USN patients tend to overestimate portions of space that they direct their attention to; (3) USN patients' performance without cueing is consistent with an attentional shift toward the right hemispace implying a gradient of overestimation of the right-most portions of space. A common neural substratum for directing attention and space representation can explain these findings.     

Clock drawing in spatial neglect: A comprehensive analysis of clock perimeter, placement, and accuracy

Clock drawings produced by right-brain-damaged (RBD) individuals with spatial neglect often contain an abundance of empty space on the left while numbers and hands are placed on the right. However, the clock perimeter is rarely compromised in neglect patients' drawings. By analysing clock drawings produced by 71 RBD and 40 healthy adults, this study investigated whether the geometric characteristics of the clock perimeter reveal novel insights to understanding spatial neglect. Neglect participants drew smaller clocks than either healthy or non-neglect RBD participants. While healthy participants' clock perimeter was close to circular, RBD participants drew radially extended ellipses. The mechanisms for these phenomena were investigated by examining the relation between clock-drawing characteristics and performance on six subtests of the Behavioral Inattention Test (BIT). The findings indicated that the clock shape was independent of any BIT subtest or the drawing placement on the test sheet and that the clock size was significantly predicted by one BIT subtest: the poorer the figure and shape copying, the smaller the clock perimeter. Further analyses revealed that in all participants, clocks decreased in size as they were placed farther from the centre of the paper. However, even when neglect participants placed their clocks towards the centre of the page, they were smaller than those produced by healthy or non-neglect RBD participants. These results suggest a neglect-specific reduction in the subjectively available workspace for graphic production from memory, consistent with the hypothesis that neglect patients are impaired in the ability to enlarge the attentional aperture.     

Attention,spatial representation,and visual neglect: simulating emergent attention and spatial memory in the selective attention for identification model (SAIM)

The selective attention for identification model (SAIM) is presented. This uses a spatial window to select visual information for recognition, binding parts to objects and generating translation-invariant recognition. The model provides a qualitative account of both normal and disordered attention. Simulations of normal attention demonstrate 2-object costs and effects of object familiarity on selection, global precedence, spatial cueing, and inhibition of return. When lesioned, SAIM demonstrated either view- or object-centered neglect or spatial extinction, depending on the type and extent of lesion. The model provides a framework to unify (a) object- and space-based theories of normal selection, (b) dissociations within the syndrome of unilateral neglect, and (c) attentional and representational accounts of neglect.     

Lateral specialization in unilateral spatial neglect: a cognitive robotics model

In this paper, we present the experimental results of an embodied cognitive robotic approach for modelling the human cognitive deficit known as unilateral spatial neglect (USN). To this end, we introduce an artificial neural network architecture designed and trained to control the spatial attentional focus of the iCub robotic platform. Like the human brain, the architecture is divided into two hemispheres and it incorporates bio-inspired plasticity mechanisms, which allow the development of the phenomenon of the specialization of the right hemisphere for spatial attention. In this study, we validate the model by replicating a previous experiment with human patients affected by the USN and numerical results show that the robot mimics the behaviours previously exhibited by humans. We also simulated recovery after the damage to compare the performance of each of the two hemispheres as additional validation of the model. Finally, we highlight some possible advantages of modelling cognitive dysfunctions of the human brain by means of robotic platforms, which can supplement traditional approaches for studying spatial impairments in humans.     

Spatial breakdown in spatial construction: evidence from eye fixations in children with Williams syndrome

We investigated the role of executive and spatial representational processes in impaired performance of block construction tasks by children with Williams syndrome (WS), a rare genetic defect that results in severely impaired spatial cognition. In Experiment 1, we examined performance in two kinds of block construction tasks, Simple Puzzles, in which block faces contained a single color, and Complex, in which some block faces contained an arrangement of two colors. WS and control children were comparable in their ability to solve simple puzzles, and showed similar eye-fixation patterns, suggesting that basic executive processes were intact. However, WS children were severely impaired in their ability to solve complex puzzles. In these puzzles, WS children fixated the complex puzzle models and checked their partial solutions less often than normal children, but they were comparable in their ability to detect errors in their copies and almost exclusively made repairs to copies that were, in fact, incorrect. We conjecture that the abnormal fixation patterns were a consequence of impoverished spatial representations, rather than a cause of it. This conjecture was tested in Experiment 2, where we examined children's capacity to match and place individual blocks without engaging the complex executive processes required to carry out a complete puzzle solution. We found serious deficiency among WS children in both aspects of spatial representation. Moreover, estimates of the errors in representing the identity and location of model blocks derived from Experiment 2 provided a good account of the observed errors in the block construction task of Experiment 1.