Fast responses to neglected targets in visual search reflect pre-attentive processes: an exploration of response times in visual neglect

Computer-based assessment of unilateral spatial neglect: A systematic review

Background

To date, no gold standard exists for the assessment of unilateral spatial neglect (USN), a common post-stroke cognitive impairment, with limited sensitivity provided by currently used clinical assessments. Extensive research has shown that computer-based (CB) assessment can be more sensitive, but these have not been adopted by stroke services yet.

Objective

We conducted a systematic review providing an overview of existing CB tests for USN to identify knowledge gaps and positive/negative aspects of different methods. This review also investigated the benefits and barriers of introducing CB assessment tasks to clinical settings and explored practical implications for optimizing future designs.

Methodology

We included studies that investigated the efficacy of CB neglect assessment tasks compared to conventional methods in detecting USN for adults with brain damage. Study identification was conducted through electronic database searches (e.g., Scopus), using keywords and standardized terms combinations, without date limitation (last search: 08/06/2022). Literature review and study selection were based on prespecified inclusion criteria. The quality of studies was assessed with the quality assessment of diagnostic accuracy studies tool (Quadas-2). Data synthesis included a narrative synthesis, a table summarizing the evidence, and vote counting analysis based on a direction of effect plot.

Results

A total of 28 studies met the eligibility criteria and were included in the review. According to our results, 13/28 studies explored CB versions of conventional tasks, 11/28 involved visual search tasks, and 5/28 other types of tasks. The vote counting analysis revealed that 17/28 studies found CB tasks had either equal or higher sensitivity than conventional methods and positive correlation with conventional methods (15/28 studies). Finally, 20/28 studies showed CB tasks effectively detected patients with USN within different patient groups and control groups (17/28).

Conclusions

The findings of this review provide practical implications for the implementation of CB assessment in the future, offering important information to enhance a variety of methodological issues. The study adds to our understanding of using CB tasks for USN assessment, exploring their efficacy and benefits compared to conventional methods, and considers their adoption in clinical environments.

Human field of regard, field of view, and attention bias

BACKGROUND AND OBJECTIVE

Human field of regard (FOR) is an important concept that should be considered along with field of view (FOV) for people with/without handicaps, but previous studies have neglected this aspect of human perception. In the current study, we suggest and test a new virtual reality (VR) software with which to evaluate individual's detection abilities in the human FOR.

METHODS

We conducted measurements of human FOV, FOR, and FOR with visual cue (FOR-cue), and we evaluated healthy adults' responses in a first experiment. Participants were asked to detect targets on a head-mounted display (HMD) as quickly as possible in three conditions: (a) FOV: the head rotation doesn't change the view of the screen in the HMD; (b) FOR: the head rotation changes the view of the screen in the HMD; and (c) FOR-cue: same with the FOR condition but an endogenous visual cue indicating the direction of stimulus. To address the need to increase the number of trials in the FOR condition, we also conducted a second experiment with new samples and four times of trial numbers.

RESULTS

The participants' detection time results indicated that the FOV condition was faster than the FOR-cue and FOR conditions, and the FOR-cue was faster than the FOR condition. Interestingly, we found a unique characteristic in the FOR conditions that did not exist in the FOV condition: The target responses were faster for the left side than the right side. The results of the second experiment were consistent with the first, and head motion trajectory analysis showed that participants had more movement toward the left side than the right side in the early parts of each trial.

CONCLUSIONS

In this study, we suggested a new virtual reality (VR) evaluation technique and measured the human searching pattern in the FOR condition. We found a unique left-side attention bias in the FOR condition, and discussed implication of these results and potential attention bias factors. We believe this work is an important foundation for interactive 3D UI design, and we hope it will help people who have FOR handicaps.

Neural dynamics of neglected targets in patients with right hemisphere damage

We studied the neural correlates of target omissions in five patients with right hemisphere damage and varying signs of left spatial neglect. Benefiting from the high temporal resolution of magneto-encephalography, we directly compared brain regional synchrony events of detected and omitted left-sided targets. Results showed that before stimulus presentation, a low beta synchronization activity was specifically increased within left frontal areas before pathological response omissions of left-sided targets. In the same pre-stimulus period, there were no such beta oscillations when patients correctly detected the target, or when no target was presented. Our findings emphasize the importance of neural activity during the pre-stimulus period on subsequent stimulus processing, and highlight the consequences of episodic interruptions of large-scale interhemispheric networks on target detection. Furthermore, our data suggest that prefrontal activity is not necessarily beneficial to target detection, but can be detrimental to it.

Extracting the mean size across the visual field in patients with mild, chronic unilateral neglect

Previous studies suggest that normal vision pools information from groups of objects in a display to extract statistical summaries (e.g., mean size). Here we explored whether patients with mild, chronic left neglect were able to extract statistical summaries on the right and left sides of space in a typical manner. We tested four patients using a visual search task and varied the mean size of a group of circles within the display. On each trial, a single circle first appeared in the center of the screen (the target). This circle varied in size from trial to trial. Then a multi-item display appeared with circles of various sizes grouped together either on the left or right side of the display. The instructions were to search the circles and determine whether the target was present or not. The circles were always accompanied by a group of task-irrelevant triangles that appeared on the opposite side of the display. On half the trials, the mean size of the circles was the size of the target. On the other half the mean size was different from the target. The patients were not told that this was the case, and no explicit report of the statistics was required. The results showed that when the targets were absent patients produced more false alarms to the mean than non-mean size when the circles were on the left (neglected) side of the display. This finding demonstrates that statistical information was implicitly extracted from the left group of circles. However, summary statistics on the right side were not limited to the circles. Rather it appears that participants pooled the distractors with the target circles, yielding a skewed statistical summary on the right side. These findings are discussed as they relate to statistical summary processing, visual search and segregation of right and left items in patients with mild, chronic unilateral neglect.

The countervailing forces of binding and selection in vision

Evidence indicates that when one feature of an object is specifically attended, other task-irrelevant features of that object also receive enhanced processing, presumably as a result of automatic binding processes. On the other hand, evidence also shows that attention can be selectively biased in favor of processing one feature at the expense of processing others. Thus, binding invokes combinatorial processing of related features whereas selective attention emphasizes differential processing. We hypothesized that binding and selective feature-based attention depend on a common resource and therefore might show interference effects. The current study tested this by manipulating binding demands while human participants directed their attention to the color or motion of moving random dot stimuli. Response time measures showed that effects of biased attention were reduced when binding demands were increased. This finding supports the thesis that binding relies, at least in part, upon the same mechanisms invoked by preparatory biasing of selective attention.

The effect of stimulus duration and motor response in hemispatial neglect during a visual search task

Patients with hemispatial neglect exhibit a myriad of profound deficits. A hallmark of this syndrome is the patients' absence of awareness of items located in their contralesional space. Many studies, however, have demonstrated that neglect patients exhibit some level of processing of these neglected items. It has been suggested that unconscious processing of neglected information may manifest as a fast denial. This theory of fast denial proposes that neglected stimuli are detected in the same way as non-neglected stimuli, but without overt awareness. We evaluated the fast denial theory by conducting two separate visual search task experiments, each differing by the duration of stimulus presentation. Specifically, in Experiment 1 each stimulus remained in the participants' visual field until a response was made. In Experiment 2 each stimulus was presented for only a brief duration. We further evaluated the fast denial theory by comparing verbal to motor task responses in each experiment. Overall, our results from both experiments and tasks showed no evidence for the presence of implicit knowledge of neglected stimuli. Instead, patients with neglect responded the same when they neglected stimuli as when they correctly reported stimulus absence. These findings thus cast doubt on the concept of the fast denial theory and its consequent implications for non-conscious processing. Importantly, our study demonstrated that the only behavior affected was during conscious detection of ipsilesional stimuli. Specifically, patients were slower to detect stimuli in Experiment 1 compared to Experiment 2, suggesting a duration effect occurred during conscious processing of information. Additionally, reaction time and accuracy were similar when reporting verbally versus motorically. These results provide new insights into the perceptual deficits associated with neglect and further support other work that falsifies the fast denial account of non-conscious processing in hemispatial visual neglect.

Implicit representation and explicit detection of features in patients with hemispatial neglect

Despite profound inattention to the side of space opposite a brain lesion in patients with unilateral neglect, priming studies demonstrate that undetected stimuli are capable of influencing subsequent behaviour. However, the nature of implicit processing of neglected stimuli is poorly understood. In the current study, we examined implicit processing in five patients with neglect using both visual search and priming methods. A psychophysical staircase method varying time of presentation was first used to establish a high (75%) and low (25%) detection probability for targets in both a feature and a conjunction search array. The arrays were then used in a priming task to examine how a difference in the level of overt detection of a feature or a conjunction presented in neglected space influenced subsequent discrimination speed to a single probe presented at fixation. The results showed that priming effects with feature primes were independent of their explicit detection rates (high versus low), but priming effects with conjunction primes reflected the pattern of explicit detection. These findings are discussed as they relate to availability versus accessibility of neglected stimuli.

Visual hemispatial neglect, re-assessed

Increased computer use in clinical settings offers an opportunity to develop new neuropsychological tests that exploit the control computers have over stimulus dimensions and timing. However, before adopting new tools, empirical validation is necessary. In the current study, our aims were twofold: to describe a computerized adaptive procedure with broad potential for neuropsychological investigations, and to demonstrate its implementation in testing for visual hemispatial neglect. Visual search results from adaptive psychophysical procedures are reported from 12 healthy individuals and 23 individuals with unilateral brain injury. Healthy individuals reveal spatially symmetric performance on adaptive search measures. In patients, psychophysical outcomes (as well as those from standard paper-and-pencil search tasks) reveal visual hemispatial neglect. Consistent with previous empirical studies of hemispatial neglect, lateralized impairments in adaptive conjunction search are greater than in adaptive feature search tasks. Furthermore, those with right hemisphere damage show greater lateralized deficits in conjunction search than do those with left hemisphere damage. We argue that adaptive tests, which automatically adjust to each individual's performance level, are efficient methods for both clinical evaluations and neuropsychological investigations and have the potential to detect subtle deficits even in chronic stages, when flagrant clinical signs have frequently resolved.

Cross-modal interactions in time and space: auditory influence on visual attention in hemispatial neglect

Recent studies indicate that auditory tone presentation and auditory alerting can temporarily ameliorate visuospatial attention deficits in patients with unilateral neglect [Frassinetti, F., Pavani, F., & Ladavas, E. Acoustical vision of neglected stimuli: Interaction among spatially converging audiovisual inputs in neglect patients. Journal of Cognitive Neuroscience, 14, 62-69, 2002; Robertson, I. H., Mattingley, J. B., Rorden, C., & Driver, J. Phasic alerting of neglect patients overcomes their spatial deficit in visual awareness. Nature, 395, 169-172, 1998]. The current study investigated proposed mechanisms of cross-modal interaction to determine conditions in which auditory stimulation affects spatial and nonspatially lateralized attention deficits in a patient with hemispatial neglect. In Experiment 1, a target was presented among related distracters (conjunction search) while a tone was presented either bilaterally or in a congruent or incongruent spatial location with respect to the visual target. Whereas the results suggest a benefit of both general alerting and cross-modal spatial integration on visual search efficiency, the most significant improvement occurred when the target and tone were both presented in contralesional space. In Experiment 2, the effect of auditory alerting on selective attention was examined in a rapid serial visual search procedure with visual targets embedded in a stream of distracters presented at central fixation. When two targets were presented without an alerting tone, the patient missed the second target for up to 1000 msec after the first target appeared (a finding known as the "attentional blink" [AB] and, on average, about 400-500 msec in normals). An alerting tone presented at a fixed temporal location significantly reduced the AB in a tone-duration-dependent manner. Experiment 3 examined the effect of cross-modal space on selective attention in an AB paradigm in which T2 occurred randomly to the left or right of T1 with a spatially congruent or incongruent tone. Discrimination of T2 in contralesional space significantly improved when the tone was presented in the same location, and was impaired when the tone was presented on the ipsilesional side. The findings are discussed as they relate to cross-modal interactions and their influence on spatial and nonspatially lateralized attention deficits in neglect.

Assessment of spatial attention after brain damage with a dynamic reaction time test

Lateralized spatial biases after brain damage are commonly assessed using batteries of paper-and-pencil tests. These tests hardly allow quantification of performance in different locations in space, and they tend to lose sensitivity along the course of recovery. We tested the dynamic Starry Night Test (SNT), a novel computerized test measuring reaction time and detection accuracy for visual target stimuli in a dynamic background, in 32 inpatients with right hemisphere stroke (RHS), 16 patients with left hemisphere stroke (LHS), and 9 healthy controls. As a group, only the RHS patients were significantly slower to respond to contralesional targets. Individually, 21 (66%) RHS patients and 5 (31%) LHS patients showed statistically significant contralateral deficits. In a number of RHS patients the SNT was more sensitive to the ipsilesional bias of spatial attention than the Behavioral Inattention Test (BIT), a standardized paper-and-pencil test battery of unilateral spatial neglect. Two illustrative case reports show that the dynamic SNT, but not the BIT, was sensitive to the spatial deficit in recovered patients, one of whom was involved in repeated car accidents. The SNT overcomes serious shortcomings of paper-and-pencil tests of unilateral neglect. It provides a simple quantitative tool for monitoring the natural and treatment-induced recovery of patients.

Crossing the midline: reducing attentional deficits via interhemispheric interactions

Patients with unilateral neglect and extinction show a profound lack of awareness of stimuli presented contralateral to their lesion. However, many processes of perception are intact and contralesional stimuli seem to reach a high level of representation, perceptual and semantic. Some of these processes can work to decrease the magnitude of the attentional deficit. Here, we examine two of these intact processes, feature detection and perceptual grouping. First, we demonstrate that feature detection occurs in parallel in the contralesional visual fields of neglect and extinction patients. Second, we attempt to dissociate the influence of perceptual contours across the vertical meridian from the presence of an object or higher-level perceptual unit (or group) that may be created by these contours. We find that connections across the midline affect attentional deficits independently of the objects they may create. This suggests that several effects of grouping on neglect and extinction may be mediated by long-range cortical interactions that arise from connections across the vertical meridian.

Perception of biological motion in parietal patients

Three unilateral parietal patients were tested on their perception of biological motion, a special case of form-from-motion. Two patients had the lesion in the right, and one in the left parietal area. All patients could easily perform a classical form-from-motion task [Neuron 32 (2001) 985], but they were severely impaired in a visual search task using biological motion sequences. In particular, the left parietal patient showed a more severe loss. He was unable to identify even a single item. Overall our patients seemed to perform differently from the classical motion-blind patients described in the literature [Visual Cognition 3 (1996) 363; Eur. J. Neurol. 9 (2002) 463; Visual Neurosci. 5 (1990) 353] whose lesions included the visual cortical area V5. Since our patients' low-level motion mechanisms are preserved, we suggest that the perception of biological motion relies on a high-level description of dynamic patterns [Cognition 80 (2001) 47], a mechanism that is impaired in parietal lobe patients. We discuss our results at the light of the recent theories suggesting that biological motion is performed by visual associative areas outside the classical motion pathways and that it is an active process dependent on attentional resources [Cognition 80 (2001) 47].