Target Omissions Research Articles

Algorithm for the Weak Target Joint Detection and Ambiguity Resolution Based on Ambiguity Matrix

The looking-down mode of space airship bistatic radars faces complex sea–land clutter, and the mode of wide-range surveillance and the over-sight detection of the satellite platform generates a low SNR and range–Doppler ambiguity. The method traditionally used involves the transmission of multiple Pulse Repetition Frequencies (PRFs) and correlating them to solve the ambiguity. However, with a low SNR, the traditional disambiguation fails due to the large number of false alarms and target omissions. In order to solve this problem, a new algorithm for multi-target joint detection and range–Doppler disambiguation based on an ambiguity matrix is presented. Firstly, all possible state values corresponding to the ambiguous sequence are filled into the ambiguity matrix one by one. Secondly, the state values in the matrix cell are divided into several groups of subsequences according to the PRF. By disambiguating multiple sets of subsequences, performing subsequence fusion, and then undertaking point aggregation, the targets can be effectively detected in scenarios with a strong clutter rate, the false alarms can be suppressed, and the disambiguation of the range and Doppler is completed. The simulation shows that the proposed algorithm has the strong ability to detect targets and perform ambiguity resolution in the scenario of a multi-target and multi-false alarm.

UK exceptional case driving application outcomes in post-stroke homonymous hemianopia: results from a clinical study

Purpose We report results in relation to returning to driving in the UK under the exceptional cases rule for visual field loss. Methods The Hemianopia Adaptation Study is a prospective clinical study recruiting adult stroke survivors with new onset homonymous hemianopia. The mobility assessment course (MAC) was used to measure navigational scanning. Car drivers were offered a 1-year post-stroke assessment to consider referral for driving assessment. Results Of 144 participants, 51 were eligible for driving assessment, with 13 (25.4%) accepting appointment for UK Driving and Vehicle Licensing Agency (DVLA) referral. A statistically significant difference in gender and baseline Barthel (stroke severity) scores was found between those requesting referral and those declining (p = 0.046; p < 0.001). MAC outcomes were significantly different, with those referred having a lower percentage of target omissions (9.0%) and faster mean course completion time (46.0 s), than those not referred (28.3%/72.5 s) (p = 0.006/p < 0.001). Twelve of the 13 referred were offered a driving assessment by the DVLA. All 12 passed and returned to driving. Conclusions It is possible for individuals with post-stroke homonymous hemianopia to return to driving, where exceptional cases criteria are met. There is evidence to support use of the MAC as a clinical measurement of adaptation. IMPLICATIONS FOR REHABILITATION Individuals with post-stroke homonymous hemianopia should be fully informed regarding driving regulations that can differ between countries and sometimes different states within a country, as well as provided with the support and opportunity to consider a return to driving if appropriate. Professionals providing care within the stroke multi-disciplinary team should be aware that it is possible for patients with homonymous hemianopia to return to driving, when exceptional cases criteria are met. The mobility assessment course (MAC) should be considered as a clinical measurement of adaptation in homonymous hemianopia. A cut-off score of ≤25% omissions on MAC could be employed to determine those likely to adapt to hemianopia long-term and potentially return to driving.

Adaptation to post-stroke homonymous hemianopia – a prospective longitudinal cohort study to identify predictive factors of the adaptation process

Purpose To determine any factors that predict how an individual will adapt to post-stroke hemianopic visual field loss, with close monitoring of the adaptation process from an early stage. Materials and methods The Hemianopia Adaptation Study (HAST) is a prospective observational longitudinal cohort clinical study. Adult stroke survivors (n = 144) with new onset homonymous hemianopia were monitored using standardised mobility assessment course (MAC) as the primary outcome measure of adaptation. Results Several baseline variables were found to be good predictors of adaptation. Three variables were associated with adaptation status at 12-weeks post-stroke: inferior % visual field, % total MAC omissions, and MAC completion time (seconds). Baseline measurements of these variables can predict the adaptation at 12 weeks with moderate to high accuracy (area under ROC curve, 0.82, 95% CI 0.74–0.90). A cut-off score of ≤25% target omissions is suggested to predict which individuals are likely to adapt by 12-weeks post-stroke following gold standard care. Conclusions Adaptation to hemianopia is a personal journey with several factors being important for prediction of its presence, including MAC outcomes and extent of inferior visual field loss. A clinical recommendation is made for inclusion of the MAC as part of a functional assessment for hemianopia. Implications for rehabilitation The mobility assessment course (MAC) should be considered as an assessment of mobility/scanning in the rehabilitation of patients with homonymous hemianopia. A cut-off score of ≤25% omissions on MAC could be employed to determine those likely to adapt to hemianopia long-term. Targeted support and therapy for patients with significant visual loss in the inferior visual field area should be considered.

Pupil dilation during orienting of attention and conscious detection of visual targets in patients with left spatial neglect

Right Brain-Damaged patients (RBD) with left spatial neglect (N+), are characterised by deficits in orienting and re-orienting attention to stimuli in the contralesional left side of space. In a recent ERPs study with visual stimuli (Lasaponara et al., 2018) we have pointed out that the pathological attentional bias of N+ is matched with exaggerated novelty reaction and contextual updating of targets in the right ipsilesional space and reduced novelty reaction and contextual updating of targets in the left contralesional space. To characterise further the attentional performance of N+, here we measured Pupil Dilation (PDil), which is a reliable marker of noradrenergic-locus coeruleus activity and response to unexpected events/rewards. Compared to Neutral and Valid targets, N+ patients displayed a pathological reduction of PDil in response to infrequent Invalid targets in the left side of space, while in Healthy Controls (HC) and RBD without neglect (N-) the same targets enhanced PDil with respect to Neutral and frequent Valid targets. Invalid targets in the right side of space enhanced PDil in all experimental groups. Interestingly, both N- and N+ showed a consistent number of target omissions both in the left and right side of space. With respect to seen targets, N- showed reduced PDil in response to unseen targets both in the left and right side of space. In contrast, N+ had reduced PDil in response to unseen targets in the left side of space though not in the right side, where seen and unseen targets evoked comparable levels of PDil. These results disclose, for the first time, the PDil correlates of spatial attention in left spatial neglect and suggest that the pathological attentional bias suffered by N+ might enhance the autonomic responses reflected in PDil to unseen ipsilesional stimuli. This enhancement can contribute to biasing contextual updating and predictive coding of stimuli in the ipsilesional space, thus worsening the pathological attentional bias of N+.

Using Mobile Electroencephalography and Actigraphy to Diagnose Attention-Deficit/Hyperactivity Disorder: Case-Control Comparison Study.

BackgroundChildren with attention-deficit/hyperactivity disorder (ADHD), a neurobehavioral disorder, display behaviors of inattention, hyperactivity, or impulsivity, which can affect their ability to learn and establish proper family and social relationships. Various tools are currently used by child and adolescent psychiatric clinics to diagnose, evaluate, and collect information and data. The tools allow professional physicians to assess if patients need further treatment, following a thorough and careful clinical diagnosis process.ObjectiveWe aim to determine potential indicators extracted from a mobile electroencephalography (EEG) device (Mindset; NeuroSky) and an actigraph (MotionWatch 8; CamNtech) and to validate them for diagnosis of ADHD. The 3 indicators are (1) attention, measured by the EEG; (2) meditation, measured by the EEG; and (3) activity, measured by the actigraph.MethodsA total of 63 participants were recruited. The case group comprised 40 boys and 9 girls, while the control group comprised 5 boys and 9 girls. The groups were age matched. The test was divided into 3 stages—pretest, in-test, and posttest—with a testing duration of 20 minutes each. We used correlation analysis, repeated measures analysis of variance, and regression analysis to investigate which indicators can be used for ADHD diagnosis.ResultsWith the EEG indicators, the analysis results show a significant correlation of attention with both hit reaction time (RT) interstimulus interval (ISI) change (r=–0.368; P=.003) and hit standard error (SE) ISI change (r=–0.336; P=.007). This indicates that the higher the attention of the participants, the smaller both the hit RT change and the hit SE ISI change. With the actigraph indicator, confidence index (r=0.352; P=.005), omissions (r=0.322; P=.01), hit RT SE (r=0.393; P=.001), and variability (r=0.351; P=.005) were significant. This indicates that the higher the activity amounts, the higher the impulsive behavior of the participants and the more target omissions in the continuous performance test (CPT). The results show that the participants with ADHD present a significant difference in activity amounts (P<0.001). The actigraph outperforms the EEG in screening ADHD.ConclusionsWhen the participants with ADHD are stimulated under restricted conditions, they will present different amounts of activity than in unrestricted conditions due to participants’ inability to exercise control over their concentration. This finding could be a new electronic physiological biomarker of ADHD. An actigraph can be used to detect the amount of activity exhibited and to help physicians diagnose the disorder in order to develop more objective, rapid auxiliary diagnostic tools.

The presence and prediction of lateralized inattention 7 years post-stroke.

Lateralized inattention is a typical sign of neglect and related to poor functional outcome. Knowledge of the long-term course of this phenomenon is limited. The purpose of this study was to investigate presence and predictors for signs of lateralized inattention 7 years after stroke. From a cohort of acute ischemic stroke patients, aged 18-69 years (n=297), a consecutive series of 188 survivors without recurrent stroke at follow-up 7 years later were included. Within the first week after stroke onset, stroke severity was assessed according to the Scandinavian Stroke Scale. Target omissions, asymmetry of omissions, and perceptual speed according to Star- and Letter Cancellation Tests were also assessed. Presence of lateralized inattention at the 7-year follow-up was investigated with the Star- and Letter Cancellation Tests and with the neglect item in the National Institutes of Health Stroke Scale. At the follow-up, 22 (11.7%) participants had lateralized inattention and the multivariable regression showed that independent significant baseline predictors were total omissions in target cancellations (P<.001) and inferior baseline performance on visual processing speed (P=.008). About one of ten individuals exhibited signs of lateralized inattention 7 years after stroke. Baseline performance in perceptual processing speed and target omissions independently predicted presence of late signs of lateralized inattention. This is the first time processing speed is recognized as a significant predictor of lateralized inattention several years after the stroke incidence, indicating that the longitudinal course of processing speed following stroke is a critical subject for future research.

Addressing the selective role of distinct prefrontal areas in response suppression: A study with brain tumor patients

The diverging evidence for functional localization of response inhibition within the prefrontal cortex might be justified by the still unclear involvement of other intrinsically related cognitive processes like response selection and sustained attention. In this study, the main aim was to understand whether inhibitory impairments, previously found in patients with both left and right frontal lesions, could be better accounted for by assessing these potentially related cognitive processes. We tested 37 brain tumor patients with left prefrontal, right prefrontal and non-prefrontal lesions and a healthy control group on Go/No-Go and Foreperiod tasks. In both types of tasks inhibitory impairments are likely to cause false alarms, although additionally the former task requires response selection and the latter target detection abilities. Irrespective of the task context, patients with right prefrontal damage showed frequent Go and target omissions, probably due to sustained attention lapses. Left prefrontal patients, on the other hand, showed both Go and target omissions and high false alarm rates to No-Go and warning stimuli, suggesting a decisional rather than an inhibitory impairment. An exploratory whole-brain voxel-based lesion-symptom mapping analysis confirmed the association of left ventrolateral and dorsolateral prefrontal lesions with target discrimination failure, and right ventrolateral and medial prefrontal lesions with target detection failure. Results from this study show how left and right prefrontal areas, which previous research has linked to response inhibition, underlie broader cognitive control processes, particularly involved in response selection and target detection. Based on these findings, we suggest that successful inhibitory control relies on more than one functionally distinct process which, if assessed appropriately, might help us to better understand inhibitory impairments across different pathologies.

Agreement processing in control and raising structures. Evidence from sentence production in Spanish

We report the results of a study investigating the production of gender and number agreement between head noun and predicative adjective in Spanish using an elicited-error paradigm with preambles that included either Control or Raising verbs. In order to identify if the subjects of the infinitivals selected by these two verb types are syntactically identical (Movement Theory of Control) or distinct (Theory of Control by PRO or anaphora), the following features in the preambles were manipulated: gender of head noun (Feminine–Masculine), gender and number (Singular–Plural) of local noun, and type of verb (Control–Raising). We analyzed the agreement errors and omissions patterns, as well as response times in the production of the target adjective. The error rate was not different across the two syntactic conditions, but the two verb classes were associated with significantly different number of target omissions. Furthermore, omissions in the Control condition were specifically associated with feminine agreeing adjectives. This pattern was also reflected in the adjective production latency. Taken together, these results undermine the Control by Movement explanation and argue for a Control by PRO analysis of Control constructions.

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.

Brain activation during executive processes in schizophrenia

Schizophrenia patients show some deficits in executive processes (impaired behavioural performance and abnormal brain functioning). The aim of this study is to explore the brain activity of schizophrenia patients during different inhibitory tasks. We used functional magnetic resonance imaging to investigate to investigate the restraint and deletion aspects of inhibition in 19 patients with schizophrenia and 12 normal subjects during the performance of the Hayling and the N-back tasks. The patients demonstrated impaired performance (more errors and longer reaction times) in the Hayling task. Schizophrenia subjects activated the same fronto-parietal network as the control subjects but demonstrated stronger parietal activations. For the N-back task, the deficit shown by the patients was limited to the number of target omissions. The reaction times and the number of false alarms did not differ in the two groups. We interpret this pattern of deficit as an alteration of working memory processes (and unaltered inhibition). Schizophrenia subjects showed higher activations in a fronto-parietal network. Since schizophrenia patients reached normal inhibitory performances in the N-back task and not in the Hayling task, the frontal hyperactivation may reflect an increased effort or a compensatory mechanism that facilitates the performance of executive tasks. During the Hayling task, this frontal hyperactivation was not achieved, and its absence was associated with a performance deficit relative to the performance of normal subjects.

Effects of Graded Levels of Physical Similarity and Density on Visual Selective Attention in Patients With Alzheimer's Disease.

A multitarget visual cancellation test was administered to patients with Alzheimer's disease (AD) and age-matched healthy controls (HC). Attentional loads--physical similarity (number of features shared by target and distractors; 3 levels) and density (number of items per page; 3 levels)--were varied systematically. As physical similarity increased, both groups slowed their search, but whereas the HC group maintained accuracy, the AD group increased commission errors and tended to miss more targets. Increased density yielded slower search and more target omissions in the AD group. Commission errors are additional indicators of higher order attentional deficits, especially in early disease. The findings suggest that patients with AD may rely increasingly on physical features of stimuli during a search, leading to inefficient bottom-up processing strategies.

Just Thinking about Targets Can Aggravate Neglect on Cancellation Tests

While many studies investigate how the visual features of targets influence cancellation performance in neglect, few, if any, even consider that thought processes, such as the use of an algorithm to identify targets, might similarly aggravate neglect. This single-case study of a patient with chronic neglect compared cancellation performance after manipulating (1) ease of visual target identification, (2) the use of an algorithm to identify targets, and (3) the material-specific nature of target cancellation. Neglect severity was defined by the number and location of target omissions. While each manipulation had a differential impact on neglect severity, the novel and interesting finding occurred during the second condition, when a math algorithm was used to identify targets. In this condition, target omissions increased relative to other tests and target cancellations were confined to the right half of the page. This is the first report, to our knowledge, that neglect on cancellation tests can be aggravated by an internal thought process, a math algorithm, as opposed to external manipulations of visual stimuli and procedural characteristics of cancellation tests. An important characteristic of the algorithm used in this study is that it appeared to activate the intact left cerebral hemisphere.

Multi-modal P3 deflation of event-related brain activity in Prader–Willi syndrome

Adults with Prader–Willi syndrome (PWS) and normal controls participated in a cognitive psychophysiology study in which event-related brain activity was recorded in a visual and auditory oddball task. In both tasks, participants were instructed to press a hand key to a target stimulus. All participants had successful task performance but persons with PWS had more target omissions than controls in the visual oddball task. The event-related brain activity in the PWS group revealed an abnormal deflation of the P3 component in both the visual and auditory oddball tasks. The findings support the notion that the auditory modality is more affected than the visual modality and of a short-term memory impairment in persons with PWS.