Ipsilesional Hemifield Research Articles

Spatial neglect is associated with increased latencies of visual evoked potentials.

We have recorded steady-state visual evoked potentials (VEPs) from patients with vascular damage to their right brain hemispheres, some suffering from unilateral spatial neglect (n = 9), and some not (n = 7). VEPs were recorded in response to sinusoidal gratings of 0.56 cycle/deg contrast-reversed sinusoidally at temporal frequencies from 4-11 Hz. Stimuli were presented either to the left or to the right visual field, or to both. Confirming previous reports, reliable VEPs were recorded from stimuli in the left contralesional hemifield, of comparable amplitude to those of the ipsilesional hemifield and to those of both hemifields of brain damaged patients without neglect. However, analysis of apparent latency derived from phase data showed that the VEPs from the contralesional hemifield were systematically delayed by 30-40 ms compared with those of the ipsilesional hemifield, and compared with both hemifields of the nonneglect groups. This result suggests changes in neural processing in neglect patients.

Can tactile neglect occur at an intra-limb level? Vibrotactile reaction times in patients with right hemisphere damage.

Visual reaction time (RT) studies on patients with right hemisphere (RH) damage have demonstrated that the attentional imbalance to stimuli occupying left and right positions exists even within the "intact" ipsilesional hemifield. The purpose of the present study was to test whether such patients might also exhibit relative left-sided impairments in the tactile modality, where stimuli and responses involve the index and middle fingers of the non-hemiplegic ipsilesional hand. Eight patients with RH damage, and eight matched normal controls, were tested using a vibrotactile choice RT paradigm, with the responding hand held in prone or supine posture, and located either at the body midline, or in left or right hemispace. Patients showed significantly slower RTs with the left than the right finger in both hand postures, a difference which remained constant as a function of the hemispatial location of the responding hand. In the prone posture, patients' left finger RTs were slower than those of controls, who showed no difference between left and right finger RTs, while their right finger RTs were faster than those of controls. In the supine posture, both patients and controls exhibited slower left than right finger RTs, though in controls the left finger disadvantage was attributed to biomechanical rather than attentional factors. Patients also made more errors with left than right finger stimuli, both as failures of detection and as incorrect responses, while controls made fewer errors overall and showed no differences between fingers. These data demonstrate a bias in the distribution of attention to tactile stimuli at an intra-limb level, and suggest that the attentional imbalance created by RH damage may be supramodal.

Can Tactile Neglect Occur at an Intra-Limb Level? Vibrotactile Reaction Times in Patients with Right Hemisphere Damage

Visual reaction time (RT) studies on patients with right hemisphere (RH) damage have demonstrated that the attentional imbalance to stimuli occupying left and right positions exists even within the “intact” ipsilesional hemifield. The purpose of the present study was to test whether such patients might also exhibit relative left-sided impairments in the tactile modality, where stimuli and responses involve the index and middle fingers of the non-hemiplegic ipsilesional hand. Eight patients with RH damage, and eight matched normal controls, were tested using a vibrotactile choice RT paradigm, with the responding hand held in prone or supine posture, and located either at the body midline, or in left or right hemispace. Patients showed significantly slower RTs with the left than the right finger in both hand postures, a difference which remained constant as a function of the hemispatial location of the responding hand. In the prone posture, patients' left finger RTs were slower than those of controls, who showed no difference between left and right finger RTs, while their right finger RTs were faster than those of controls. In the supine posture, both patients and controls exhibited slower left than right finger RTs, though in controls the left finger disadvantage was attributed to biomechanical rather than attentional factors. Patients also made more errors with left than right finger stimuli, both as failures of detection and as incorrect responses, while controls made fewer errors overall and showed no differences between fingers. These data demonstrate a bias in the distribution of attention to tactile stimuli at an intra-limb level, and suggest that the attentional imbalance created by RH damage may be supramodal.

Modulation of the Directional Attention Deficit in Visual Neglect by Hemispatial Factors

Using a visuo-spatial cuing paradigm, Posner and collaborators (Posner, Cohen, & Rafal, 1982; Posner, Walker, Friedrich, & Rafal, 1984) reported that subjects with a parietal lobe lesion have difficulty in disengaging their visual attention from an invalidly precued location in the ipsilesional hemifield when the target they have to respond to is presented in the contralesional field. Later, these authors (Posner, Walker, Friedrich, & Rafal, 1987) proposed that this disengagement deficit is one involving spatial shifts of attention in a contralesional direction, irrespective of the visual hemifield in which the target is presented. This proposal of a directional disengagement deficit along the horizontal axis, present in either hemifield, contrasts with a report by Baynes, Holtzman, & Volpe (1986) showing, in right parietal subjects, a disengagement deficit for shifts of attention along the vertical axis that is only manifest in the contralesional hemifield. In the present report, we assessed the disengagement deficit of a neglect subject along the horizontal and vertical axes. Results show a disengagement deficit restricted to shifts of attention in the contralesional direction (horizontal axis), which is significant only in the contralesional visual hemifield. However, there is a clear trend for a directional disengagement deficit in the ipsilateral field. These observations indicate that the attention deficit present in neglect is directional and is modulated either by hemispatial factors or by the lateral target location in the visual field. On the basis of the present results, it is proposed that the deficit of parietal subjects may best be conceptualized as one of attentional capture for stimuli located on the contralesional side of the current focus of attention rather than one of disengagement.