Space Exploration with and without the Aid of Vision in Hemisphere-Damaged Patients

Abstract

Space exploration carried out under visual control and in its absence (blindfolded condition) was investigated in 20 RBD patients, 10 LBD patients and 20 normal controls with a modified version of Chedru's test (pressing the keys of a keyboard). Conventional tests for visual hemi-inattention permitted to classify RBD patients in a group with visual neglect (RBD VN+) and a group without visual neglect (RBD VN-). On the visual version of the test both RBD groups showed a preference for pressing the keys ipsilateral to the lesion side, but this tendency was more marked in the RBD VN+ group than in any other brain-damaged group. On the tactile version of the test only RBD VN+ patients showed a gradient favouring the pressing of the ipsilateral half of the keyboard. This ipsilateral preference was, however, significantly less marked than that found when the performance was assisted by vision. No relation between neglect in the blindfolded condition and tactile extinction was found. The nature of space exploration in the absence of vision is discussed and the existence of tactile neglect is questioned.

Visual, proprioceptive and tactile performance in left neglect patients

“…= 0.32; t (11) = 0.04; P > 0.96; see Table 4). This finding is consistent both with previous results [23,26,31,34,49,66] and with the "pseudoneglect" phenomenon originally described by Bowers and Heilman [8]. The length of the line did not significantly affect the position of the subjective middle (see Table 4).…”

“…According to Gentilini and coworkers [26], the increase in ipsilateral responses when key pressing was guided by vision in comparison to the blindfolded condition suggests that incoming sensory stimuli from the ipsilateral side play a role in shifting attention towards it and in enhancing neglect of controlateral space. In fact, although several experiments have shown that attention can be allocated to different parts of the spatial field without overt eye movements (for review see [51]), experiments performed in normals have suggested that eye movements cannot be made without shifting the focus of attention in the same direction (for review see [24]).…”

“…Chedru's conclusion was that the unilateral defect in a manual exploration of space is induced by vision. Using the same protocol, Gentilini and coworkers [26] reported that RBD patients with neglect preferred the right-sided keys, both with and without visual control, although this ipsilateral preference was significantly less marked in the tactile conditions. Our results are also consistent with Villardita's report that patients with left visual spatial neglect do not have impaired tactile exploration on the left side [66].…”

“…As regards the supramodal nature of neglect, the literature shows that when the same left neglect patients are simultaneously submitted to visual and tactile tasks, they often show a strong spatial bias in the visual task which is much less severe in the tactile modality [26,66]. This was the case of bisection protocols in particular.…”

“…In the same way, space-exploration patterns produced under visual control and in its absence (blindfolded conditions) were compared by asking left-brain damaged (LBD) and RBD patients with and without neglect signs to press the keys of a keyboard [26]. Only RBD patients showed a preference for pressing the keys ipsilateral to the lesion, but this tendency was more marked in RBD patients with left neglect (RBDN+) than in RBD patients without left neglect (RBDN−).…”