Visual size processing in spatial neglect

Evidence from the use of the landmark task and from two size-matching tasks shows that many patients with left-sided neglect systematically under-perceive visual extent in leftward parts of space. This perceptual distortion of size serves to explain the occurrence of rightward line-bisection errors in most neglect patients. One possibility is that attentional biases of a chronic nature might underlie these perceptual changes seen in neglect patients. But contrary to this idea, we have found that attentional cueing in the landmark task causes changes in neglect patients exactly opposite to those seen in healthy subjects. The distortions of size perception seen in neglect could instead be caused by a high-level alteration of visual processing rather than by an attentional bias. In order to explore which visual stream of cortical processing might be compromised in such a disorder, we have begun to examine neglect patients on visuomotor as well as perceptual tasks. We have found clear evidence in one patient for intact grip scaling for object size in the neglected half of space, despite gross perceptual underestimations of the same objects. This result suggests that neglect can occur without major disruption of the dorsal stream, and may result instead from damage to a cortical system whose predominant visual input comes from the ventral stream.     

Dissociable coordinate frames of unilateral spatial neglect: "viewer-centered" neglect

Detailed analyses of reading and nonlexical tasks by three patients with unilateral spatial neglect (USN) secondary to stroke indicate that the USN in each of these patients affects the left side (contralateral to brain damage) of the viewer, with respect to the viewer's head, mid-sagittal plane of the body, or line of sight. In one case, the neglect was further specified as concerning the left side of the viewer's line of sight (the left half of her residual visual field). Thus, the frame of reference of USN in these three cases appears to have viewer-centered (in at least one case, specifically retinotopic) coordinates. The performance of these patients is contrasted to that of other patients in the literature whose USN appears to have a frame of reference with stimulus-centered or object-centered coordinates. These results are interpreted within a model of visual processing (adapted from Marr, 1980 and others) with at least three coordinate frames. It is argued that USN can affect one or more of these coordinate frames independently.     

Perceptual and premotor components of unilateral auditory neglect

Recent investigations have distinguished between ophthalmokinetic and melokinetic factors of unilateral neglect. The aim of our study was to investigate the possible dissociation between melokinetic (premotor) and perceptual factors, avoiding any overt oculokinetic components. We asked four blindfolded left neglect patients to set a dichotic sound in central position, by moving a handle controlling the difference of intensity between the sounds delivered to the left and to the right ears. Two conflicting conditions were used. In the congruent condition, the sound moved in the same direction as the hand movement; in the noncongruent condition, it moved in the opposite direction. One patient performed as if suffering from melokinetic neglect, and another as if suffering from perceptual neglect. The behavior of the other two subjects did not lend itself to a clearcut interpretation.     

Auditory sustained attention is a marker of unilateral spatial neglect

The relationships between performance on a non-spatially-lateralized measure of sustained attention and spatial bias on tests sensitive to unilateral neglect were considered in a group of 44 patients with right hemisphere lesions following stroke. As predicted from earlier studies showing a strong association between unilateral spatial neglect and sustained attention, performance on a brief and monotonous tone-counting measure formed a significant predictor of spatial bias across a variety of measures of unilateral visual neglect. This study provides further evidence for a very close link between two attentional systems hitherto regarded as being quite separate, namely a spatial attention system implicated in unilateral neglect and a sustained attention system. A close connection between these two systems was predicted by Posner, who argued that the right hemisphere-dominant sustained attention system provides a strong modulatory influence on the functioning of the lateralized posterior attention system.     

Effects of attention and unilateral neglect on auditory stream segregation.

Two pairs of experiments studied the effects of attention and of unilateral neglect on auditory streaming. The first pair showed that the build up of auditory streaming in normal participants is greatly reduced or absent when they attend to a competing task in the contralateral ear. It was concluded that the effective build up of streaming depends on attention. The second pair showed that patients with an attentional deficit toward the left side of space (unilateral neglect) show less stream segregation of tone sequences presented to their left than to their right ears. Streaming in their right ears was similar to that for stimuli presented to either ear of healthy and of brain-damaged controls, who showed no across-ear asymmetry. This result is consistent with an effect of attention on streaming, constrains the neural sites involved, and reveals a qualitative difference between the perception of left- and right-sided sounds by neglect patients. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Impaired orienting of attention in left unilateral neglect: A componential analysis.

Twenty-six patients suffering from damage to the right side of the brain, 19 of whom exhibited signs of left neglect, as well as 32 matched controls, ran 3 spatial cuing tasks. Patients were also tested with 2 cancellation tests, a line-bisection test, the copy of a complex drawing, and a visual extinction procedure. Results first showed correlations between extinction and cancellation tests performance on one hand, and between line bisection and copy on the other hand. Second, results demonstrated that an engagement deficit toward contralesional targets appeared to be the most striking feature of neglect, and the engagement score was correlated with the cancellation score and extinction. Most patients with neglect also presented a deficit in disengagement, a deficit of inhibition of return, and probably a deficit of alertness. Deficits in engagement and in disengagement, as well as poor scores in cancellation tests, seemed to be related with posterior cortical and subcortical lesions. Most important, even if an endogenous deficit (frequently related with a thalamic lesion) could aggravate the neglect behavior, neglect syndrome was mainly explained by a deficit of exogenous attention. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Frames of reference in unilateral neglect and visual perception: A computational perspective.

Neurological patients with unilateral neglect fail to orient and respond to stimuli on one side, typically the left. A key research issue is whether neglect is exhibited with respect to the left side of the viewer or of objects. When deficits in attentional allocation depend not merely on an object's location with respect to the viewer but on the object's intrinsic extent, shape, or movement, researchers have inferred that attention must be operating in an object-based frame of reference. Simulations of a view-based connectionist model of spatial attention prove that this inference is not logically necessary: Object-based attentional effects can be obtained without object-based frames. The model thus explains away troublesome phenomena for view-based theories of object recognition. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Prolonged muscular flaccidity: frequency and association with unilateral spatial neglect after stroke

A 21-month-old infant developed coma with hypotonia during a viral infection. Acyl CoA dehydrogenase deficiency was diagnosed on the basis of results of the chromatographic study of organic acids performed on a urine specimen collected during the acute episode. However, other disorders of mitochondrial and fatty acid oxygenation can generate similar symptoms. Emphasis is put on the need for collecting urine specimens in patients who develop alterations in consciousness and hypoglycemia without ketonuria during prolonged fasting or repeated vomiting due to a viral infection. Urine chromatography can suggest which enzyme is defective, although the diagnosis should always be confirmed by a study of fatty acid oxygenation in lymphocytes or fibroblasts.     

Believing what you feel: Using proprioceptive feedback to reduce unilateral neglect.

Unilateral spatial neglect declines when participants reach to grip the center of long metal rods compared with when they point to the perceived center, suggesting that visuomotor control systems are less affected by neglect than other representational systems (I. H. Robertson, D. Nico, & B. Hood, 1995). In this study, 16 participants with unilateral left neglect actually picked up rods, and we predicted short-term improvements in neglect because of induced conflict between a phenomenally symmetrical visual world on the one hand and a proprioceptively conveyed rightward-biased world on the other. With participants serving as their own controls, significant short-term improvements in neglect were found on 2 out of 4 neglect tasks after participants experienced proprioceptive feedback discrepant from the judgments they made on the basis of visual information alone. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Multimodal sensory neglect in rats with radical unilateral posterior isocortical and superior collicular ablations.

In a study with 22 male Long-Evans hooded rats, unilateral posterior decortication resulted in contralateral visual neglect. However, when this lesion was combined with a simultaneous contralateral mid-brain tectal lesion, visual neglect ipsilateral to the cortical ablation and visual responsiveness contralateral to the posterior decortication occurred. Results confirm J. M. Sprague and T. H. Meikle's (1965) findings with cats. Contralateral multimodal sensory neglect followed unilateral superior colliculectomy and was completely independent of the laterality of a simultaneous unilateral posterior decortication. The ipsiversive circling which followed large unilateral tectal lesions may have a sensory basis. Findings are consistent with other recent outcomes which suggest that functions of the optic tectum are broader than has been implied by its classical characterization as a visual integrative mechanism. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

What is line bisection in unilateral spatial neglect? Analysis of perceptual and motor aspects in line bisection tasks

Various methods have been applied to study the physical properties of metal supported bilayer lipid membranes (s-BLM) and large unilamellar liposomes containing biotinylated phospholipids during the binding of IgG modified by avidin. Electrostriction method applied to s-BLM showed that addition of avidin-IgG (A-IgG) complex in a small concentration (0.2 mumol/l) resulted in an approximately twofold decrease of membrane capacitance, C, increase of elasticity modulus in direction perpendicular to the membrane plane, E perpendicular, by 5-20%, increase in intrinsic membrane potential, delta phi m, by approximately 30 mV, and an approximately 5-15% increase of the coefficient of dynamic viscosity, eta. The method of ultrasonic velocimetry showed that addition into the suspension of liposomes of unmodified IgG did not induce any changes in ultrasound velocity, while addition of A-IgG complex in a concentration range of 0-1 mumol/l led to an increase of the velocity number [u]. The plot of changes of [u] versus A-IgG concentration has a tendency to saturate at concentrations above 0.5 mumol/l, which suggests long-range interactions in the membrane induced by strong binding of A-IgG to the biotin sites on the membrane. Probably, this binding leads to a decrease of the coefficient of adiabatic compressibility of liposomes.     

Do we neglect child neglect?

Child neglect is a condition in which a major need of the child is not met, regardless of the cause or who is responsible for the condition. Multiple interacting factors at the individual (child and parent), familial, community, and societal levels contribute to child neglect. In typical neglect cases, a caretaker, either deliberately or through extraordinary inattentiveness, permits the child to experience avoidable suffering and/or fails to provide one or more of the components generally deemed essential for developing the child's physical, intellectual, and emotional capacities. Neglect varies in type, severity and chronicity. Both actual and potential harm should be weighed by a physician in considering reporting to child protective services. Outcome data on intervention are lacking, therefore proper intervention should be individualized and the results carefully monitored.     

Visuomotor functions of the lateral pre-motor cortex

Recent studies have provided new insights into the visuomotor functions of the dorsal and ventral regions of the lateral pre-motor cortex. Anatomical and physiological investigations in non-human primates have demonstrated that these regions have differing patterns of cortical connectivity and distinctive neuronal responses. Brain-imaging techniques and lesion studies have begun to probe the functions of homologous regions in humans.     

Controlled Visuomotor Preparation Deficits in Attention-Deficit/Hyperactivity Disorder.

To the best of the authors' knowledge, there are no published reports on visuomotor preparation in attention-deficit/hyperactivity disorder (ADHD). This is unfortunate, because research suggests that ADHD is an output-related deficit, and suboptimal execution of tasks may be the result of incomplete visuomotor preparation. The authors compared 19 children with ADHD with 124 healthy and 120 pathological controls in terms of their performance (speed, speed variability, and accuracy) on the finger precuing test, a test measuring (automatic and controlled) visuomotor preparation. The data implied that children with ADHD have an impaired ability to engage in effortful, controlled visuomotor preparation activities. Fast, automatic response preparation was not affected by ADHD. In addition, children with ADHD showed more variability in overall test performance than other children. No group differences were found in response accuracy. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Quantitative EEG in subcortical neglect

We have analyzed the regulatory roles of the first intron (intron-1) of the bovine beta-casein gene in the bovine beta-casein/CAT expression system using a mouse mammary epithelial cell line, HC11. After a combined treatment of HC11 cells with insulin, dexamethasone and prolactin, the induced expression of p beta c1.8/+ICAT vector including 2 kb intron-1 and 1.8 kb promoter was greatly increased to 23.5 folds, while that of p beta ca.8CAT basic vector with 1.8 kb promoter only, was 6.5. A classical enhancer activity was shown in the 2 kb intron fragment from the experiment in which the orientation and the position of the intron-1 on the vectors were changed. The enhancer activity was largely dependent on the lactogenic hormones, especially prolactin. A stepwise reduction of the inducibility in the 5' to 3' deletion analysis of the intron-1 indicates the existence of several functional elements in the region. In particular, an internal fragment (+1071 to +1490) was important for the prolactin-dependent enhancing activity of the intron-1. These results suggest that several elements in the intron-1 of the bovine beta-casein gene cooperatively interact not only with each other but also with its promoter for hormonal induction.     

Variations in perceptions of child neglect

This study explored the perceptions of the seriousness of specific components of neglect held by mothers from three cultural groups and held by public child welfare workers in two different roles in the Chicago area. It then compared the perceptions of the mothers to those of the workers. The findings suggest that members of minority groups perceive some types of child neglect as more serious than do their Caucasian counterparts, that investigative workers see most types of child neglect as more serious than do service workers, and that workers see all types of child neglect as less serious than do the mothers. Comparisons revealed that various groups perceive the dimensions of neglect differently in terms of their potential harm to the child.     

The judgement of absence in neglect

The usual way of looking at neglect is by investigating how neglect patients fail to detect that something is there. In this study, we look at how neglect patients correctly detect that something is not there. Patients with parietal lesions (11 with and 16 without neglect) and 23 control subjects indicated whether a dot target was or was not present in a geometrical display. While control subjects were consistently (and unexpectedly) faster in the no-dot than in the dot condition, the distinguishing response time pattern of right parietal patients with neglect was not--as one might expect--a relatively longer response time to left vs right targets, but a longer response time to target absence vs presence. This may be due to a serial search or, alternatively, it might result from double-checking for target absence, produced by lowered perceptual confidence. Since this "wariness" about stimulus absence seems to operate in parallel with neglect patients' denial of the deficit, we conclude that the response time pattern observed in this study could be used as a measure of subjective (un)awareness of neglect.     

Exploitation or neglect.

A comparison of lengths of stay for alcoholism treatment in nonpublic and public hospitals indicates that the ratio of median stay was greater in nonpublic hospitals (2:1). While 3 explanations are possible, these results support W. R. Miller and H. K. Hester's (see record 1986-28253-001) contention that financial considerations play a dominant role in patient treatment. (PsycINFO Database Record (c) 2010 APA, all rights reserved)