Categorisation of ‘perceptual’ and ‘premotor’ neglect patients across different tasks: is there strong evidence for a dichotomy?
Introduction
Over the past 15 years there has been an increasing recognition that neglect is not a unitary phenomenon, i.e. that there are different types see [27]. According to Heilman and co-workers [16] many patients suffer from ‘directional hypokinesia’, a symptom in which they are reluctant and slow to initiate a movement in the direction contralateral to their brain lesion. Heilman and Valenstein [15] have argued that this symptom could explain both the occurrence and the nature of the rightward error that neglect patients typically show when asked to bisect a line in the centre [3], [12], [31], [34]. However, Bisiach et al. [4] realised that in any test of line bisection ‘premotor’ and ‘perceptual’ biases are confounded so that a patient might bisect a line to the right of centre because of a failure to direct the action (directional hypokinesia) and/or because of an attentional failure. In their study, the authors pitted these two factors directly against each other by asking their participants to position a pointer in the centre of a line either directly (congruent condition) or indirectly (incongruent condition) so that positioning the pointer in one direction actually required a movement in the opposite direction. As expected their patients bisected consistently to the right when moving the pointer directly. However, patients varied considerably in the extent to which there was still a rightward error when a leftward movement had to occur. This reduction in the bisection error could be taken as an index of the premotor bias that contributed to the line bisection error in the first place.
Tegnér and Levander [35] published a similar experiment, using a line cancellation task which patients where asked to perform under mirror-viewing and normal conditions. In the mirror condition, 10 out of the 18 patients tested continued to delete stimuli on the visual right only (motoric left), their behaviour seemingly controlled by the perceptual field rather than a premotor bias. Four patients, however, cancelled lines on the right only (their visual left), a behaviour pattern compatible with premotor neglect.
Nico [32] published a study in which Tegnér and Levander’s technique and a line cancellation task performed on an overhead projector where directly compared. One of the problems of the mirror task is that the two halves of the mirror are joined in the midline, a feature which interferes with the presentation of the stimuli and makes it impossible to use with the Line Bisection Task, as it would give the patients an inescapable clue with regard to the true centre of the line presented. Direct comparison of the two techniques was found to produce similar results although interestingly, Nico could not find even one premotor patient among the 22 neglect patients tested.
Milner et al. devised a very simple way of distinguishing between the two broad factors assumed to cause the right line bisection errors [25], [26]. They argued that if such errors are due to a perceptual distortion, possibly as the result of an attentional and/or representational failure, then a centrally pre-bisected line (landmark) should appear to the patient to be leftwardly bisected. However, if there is no such distortion but instead a premotor bias to respond rightwardly, then the same task should elicit a predominance of rightward-pointing responses when asked to ‘point to the end nearer to the bisection mark’. Harvey et al. [14] found exactly this pattern: out of their eight patients, seven pointed predominantly towards the left in the landmark test, indicating a perceptual bias whereas one patient pointed predominantly towards the right, indicating a premotor bias.
Associated with the investigation of perceptual versus premotor neglect is the debate whether either type can be associated with a distinct lesion location in the brain. Mesulam [23], [24] proposed that premotor neglect might be correlated with anterior lesions, whereas more posterior lesions might cause perceptual neglect. This dichotomy has generally been supported in a range of studies [4], [6], [7], [8], [9], [35], [18]. Other studies, however, have produced more ambiguous results [1], [14] or even contrary findings [6], [21].
The obvious question that now arises is whether the dichotomies reported in these experiments are consistent across the varying techniques. That is, would the patients that were classified as say premotor in Bisiach et al.’s Pulley Device Task [4] because they showed a reduced rightward error in the incongruent condition have also shown this in the line bisection version of Nico et al.’s [32] Overhead Task, and indeed have produced more rightward-pointing biases in Milner and colleagues’ [25], [26] Landmark Task? Are all these techniques tapping the taxonomic distinction in the same way or are the task demands too heterogeneous to allow a consistent categorisation across tasks? Numerous studies have already shown that there can be dissociations between line bisection and the line cancellation tasks in neglect patients [1], [10], [13], [19], [29]. However, within Line Bisection Tasks, it seems reasonable to expect that a patient should be classified similarly across the varying techniques.
The experiments reported were designed to address exactly this issue. By directly comparing the Pulley Device [4], Overhead [32] and Landmark Tasks [25], [26] we hoped to address whether all these different attempts do indeed classify individual neglect patients in the same way. Moreover, we wanted to investigate the relationship between lesion location and their association to perceptual and premotor neglect within and across tasks.
Section snippets
Patients and participants
Twelve right hemisphere-lesioned patients [seven male, five female; ranging in age from 62 to 79 years (mean age=73.4; S.D.=4.84)] with hemispatial neglect and three control groups [12 patients with right-hemisphere damage (five men, seven women; age range 54–82 years (mean=73.3; S.D.=8.06), 12 patients with left-hemisphere damage (nine male, three female; age range 60–82 years, mean=69.8; S.D.=6.34) and 13 healthy volunteers (eight male, five female; age ranging from 63 to 75 years (mean=70.8;
Classification
The mean performance and standard deviation of each patient for each of the three tasks are listed in Table 3 and can be compared to the average performance of the control groups. In Fig. 1, Fig. 2, we plotted the performance of each patient in the congruent conditions against their performance in the incongruent conditions. Similarly, in Fig. 3 each patients’ line bisection performance was plotted against their leftward-pointing behaviour (in %). Categorical classification of the patients is
Discussion
The main aim of the present study was to investigate whether the Overhead (Task 1, adapted from Nico [32]), Pulley Device (Task 2, adapted from Bisiach et al. [4]) and Landmark Tasks (Task 3, adapted from Milner et al. [25]) categorised the same set of patients in the same way.
As in the previously reported studies, it was found that most patients could be classified into either the premotor or perceptual category in each task, however, no consistent categorisation emerged across the three
Acknowledgements
We would like to thank all the participants for their co-operation. This research was supported by a Wellcome Trust grant awarded to M. Harvey (no.: 050184/Z). T. Krämer-McCaffery was funded by the Deutscher Akademischer Austauschdienst (DAAD).
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2018, Handbook of Clinical NeurologyCitation Excerpt :Furthermore, the same patient may show different patterns of input, perceptual, and attentional, compared with output, premotor, intentional spatial neglect in cancellation or line bisection tasks (Adair et al., 1998; Na et al., 1998). Finally, even within the same task, such as line bisection, different techniques for assessing the perceptual and premotor patterns of impairment may result in different classifications of patients’ deficit (Harvey et al., 2002; Harvey, 2004; Harvey and Olk, 2004). In these tasks patients are asked to draw a copy of a figure presented in front of them, or to draw it from memory, to a verbal command.
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2015, NeuropsychologiaCitation Excerpt :However, this rightward shift only appears to develop into an absolute rightward bias for overt bisection. This pattern suggests important functional differences between bisection and landmark tasks, consistent with dissociations between these tasks reported both in neuropsychological patients (e.g., Harvey et al., 2002; Ishiai et al., 1998) and healthy adults (e.g., Varnava et al., 2013). The meta-analysis of Jewell and McCourt (2000) found much larger effect sizes for pseudoneglect measured using landmark than manual (overt) bisection.
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2012, Brain ResearchCitation Excerpt :In contrast, neglect patients with perceptual biases indicate the left end of the line is closest to the transection mark, suggesting some form of perceptual compression of that end of the line (Harvey et al., 1995). Interestingly, the few studies that have examined the relationship between bisection and landmark task performance have only observed weak correlations (Harvey et al., 1995, 2002; Luh, 1995; Michel et al., 2003; Milner et al., 1992, 1993; Rueckert et al., 2002; for one exception in neglect patients, see Pitzalis et al., 2001). Mattingley et al. (1994) developed a novel paradigm to address perceptual biases in neglect in the absence of a motor response.