Hemifield Of Patients Research Articles

Ipsilesional perceptual deficits in hemispatial neglect: Case reports

Hemispatial neglect, usually after right hemisphere lesions, is characterized by contralesional deficits in attention and perception. However, little is known about impairments of perceptual processing in the ipsilesional region of visual space (the right visual field for right hemisphere lesions). In two right hemisphere neglect patients, we used a metacontrast masking paradigm to characterize systematic spatial and temporal visual processing deficits in the ipsilesional right visual field. The presence of a visual mask caused the neglect patients to miss targets in ipsilesional space, even when a mask was presented as long as 1.5 sec after the target and in a different spatial position. These prolonged and spatially extended masking effects were not measured in age-matched healthy controls or in two control patients with hemianopsia but without neglect. The results show that perceptual processing is distorted and delayed in a region of the visual field that has been thought to be unaffected – the ipsilesional hemifield in patients with neglect.

P 155. Serial anodal tDCS over V1 induces long-term effects on colour discrimination in V4 measured in the unimpaired hemifield of patients with occipital stroke

Question Little is known about the impact of tDCS on higher level visual functions such as colour perception. Previous studies have primarily investigated the effects of anodal and cathodal direct current stimulation over the occipital cortex on basic visual functions (Antal and Paulus, 2008). In a recent single-session tDCS study in healthy young subjects, anodal stimulation was ineffective in transiently improving red/green discrimination (Costa, 2012). One possible explanation for this may be a ceiling effect of red/green discrimination in the healthy visual system. Given the high degree of plasticity in the sensory cortices of adults (Fahle and Poggie, 2002) we examined whether serial anodal tDCS can induce long-lasting improvements in colour discrimination in the unimpaired visual hemifield of patients with occipital stroke. Materials and methods Twelve chronic stroke patients with unilateral visual cortex lesions (mean age 54.0years, 5 male) participated in a within-subject, sham-controlled, double-blind study. MRI-registered anodal(1.5mA, 20min.)or sham tDCS was applied on 5 consecutive days above the ipsilesional calcarine sulcus. Campimetric testing of age matched colour discrimination was performed in the unaffected hemifield before and after each stimulation session and at 14-and 28-day follow-up. After a 14-day interval, an identical stimulation block with the other stimulation parameter was performed. The visual task was a forced choice task involving binocular detection of red circular stimuli, presented for 200ms in one visual field quadrant at 5° offset from fixation against a green background. Results The age matched overall deviation of colour discrimination was entered in a 2-way ANOVA. In order to control for assumable learning effects, a covariate was added to the ANOVA model. The repeated measures ANOVA attained significance for the factor stimulation ( p =0.004) (stimulation∗learning: p =0.006). The factor time reached significance by trend ( p =0.065) (time∗learning: p =0.181).No significant interaction was revealed for the factor stimulation∗time (stimulation∗time∗learning).Due to a positive learning effect post hoc tests were performed within the first block. No significant difference was seen between the baselines of anodal and sham conditions ( p =0.21).In the anodal condition colour discrimination improved compared to sham on day 5 ( p =0.045) and at two ( p =0.066) and four week ( p =0.041) follow-up. Conclusion Long-term modulation in colour perception following serial anodal tDCS may represent evidence of inducible long-term plasticity in distantly connected components of the visual system (V1 and V4) in patients with occipital stroke measured in the unimpaired hemifield. This builds on studies describing the immediate effects of tDCS in the visual system in healthy volunteers. The temporal dynamics of serial anodal tDCS seem to interact with learning processes, and may yield potential support for neuroplastic adaptation processes following cerebral lesions. Future studies should examine the long-term outcomes and dynamics of tDCS-induced neuromodulation.

Spatial and non-spatial aspects of neglect

Spatial and non-spatial aspects of neglect

Passive Auditory Stimulation Improves Vision in Hemianopia

Techniques employed in rehabilitation of visual field disorders such as hemianopia are usually based on either visual or audio-visual stimulation and patients have to perform a training task. Here we present results from a completely different, novel approach that was based on passive unimodal auditory stimulation. Ten patients with either left or right-sided pure hemianopia (without neglect) received one hour of unilateral passive auditory stimulation on either their anopic or their intact side by application of repetitive trains of sound pulses emitted simultaneously via two loudspeakers. Immediately before and after passive auditory stimulation as well as after a period of recovery, patients completed a simple visual task requiring detection of light flashes presented along the horizontal plane in total darkness. The results showed that one-time passive auditory stimulation on the side of the blind, but not of the intact, hemifield of patients with hemianopia induced an improvement in visual detections by almost 100% within 30 min after passive auditory stimulation. This enhancement in performance was reversible and was reduced to baseline 1.5 h later. A non-significant trend of a shift of the visual field border toward the blind hemifield was obtained after passive auditory stimulation. These results are compatible with the view that passive auditory stimulation elicited some activation of the residual visual pathways, which are known to be multisensory and may also be sensitive to unimodal auditory stimuli as were used here.Trial Registration DRKS00003577

Multifocal pupillary light response fields in normal subjects and patients with visual field defects

The optimal conditions for recording focal pupillary light responses with a multifocal stimulation technique were determined, and the technique was applied to normal subjects and patients with visual field defects. Thirty-seven hexagonal stimuli were presented on a TV monitor with a visual field of 40° diameter under a constant background illumination. Using a slow (4.7 Hz) m-sequence, reliable focal responses were obtained in both normal subjects and patients. The pupillary field and visual field were well correlated in patients with retinal diseases, but the correlation was not strong in patients with optic-nerve diseases. Pupillary light responses were reduced in the blind hemifield in patients with post-geniculate lesions. These results indicate that the multifocal stimulation technique can be used clinically to obtain a pupillary field for objective visual field testing.

Contrast Sensitivity Loss in The Neglected Hemifield

Contrast sensitivity to gratings of various spatial frequencies displayed in the left and right visual hemifield was measured in a group of ten right brain-damaged patients with unilateral visuospatial neglect. Two groups of ten left brain-damaged (LBD) and ten right brain-damaged (RBD) patients without neglect served as controls. All patients had normal visual fields according to standard clinical procedure. Stimuli were patches of sinusoidal gratings of 1, 2, 4 and 8 c/deg spatial frequency. The patches subtended 6 deg and were displayed at 3 deg of eccentricity. A two-alternative forced-choice technique was employed. Results showed a reduction in contrast sensitivity for stimuli presented to the contralesional hemifield with respect to the ipsilesional hemifield in patients with neglect. No difference in contrast sensitivity between hemifields was found for LBD and RBD groups. These findings indicate a basic visual impairment in the contralesional hemifield in patients with neglect.