EXTINCTION DURING TIME CONTROLLED DIRECT RETINAL STIMULATION AFTER RECOVERY FROM RIGHT HEMISPHERIC STROKE

The temporal variables of extinction in two patients with right hemisp heric stroke and two normal controls were studied using a scanning las er ophthalmoscope (SLO). This instrument enabled eye movements to be c ontrolled for by projecting time controlled stimuli directly on to the retina. Both patients had recovered from their stroke (four months an d five years) and seemed clinically normal. At 50 ms, patient 1 exting uished one of two stimuli on seven of 40 double simultaneous stimulati on (DSS) trials (five left, two right) and patient 2 extinguished the left stimulus on every DSS trial. At 100 ms, patient 1 performed almos t perfectly, whereas patient 2 extinguished on 30% of the DSS trials ( 10 left, two right). At 200 ms, patient 2 performed perfectly. Neither of the controls showed extinction to DSS at any presentation time. Th us detecting DSS was time dependent in the patients but not the normal subjects. These data support the theory that recovery from neglect af ter right hemispheric damage may be mediated by the left hemisphere.