Distractor interference in hemianopic patients

There are two main neural pathways in human vision: the geniculostriate and the
retinotectal pathway. Because the geniculostriate pathway is dominant in
humans, people with lesions of this pathway are blind in the hemifield
contralateral to the lesion and can not see even salient signals
('hemianopia'). Some residual visual processing might be possible however
(*blindsight*) (Weiskrantz, 1986).

In a study of Rafal et al (Rafal, Smith, Cohen, & Brennan, 1990) it was shown
that distractors in the blind field of three hemianopic patients increased
saccade latencies to a target in the intact field. An increase in saccade
latency in the presence of an irrelevant distractor is a typical finding in eye
movement research.
Neurophysiological research has revealed that the Superior Colliculus (SC)
plays an important role in this effect. The finding of a remote distractor
effect of a *blind* distractor might therefore reflect processing of visual
input in the retinotectal pathway from the retina to the SC.

The conclusions of Rafal et al. were questioned by a recent study by Walker et
al. (Walker, Mannan, Maurer, Pambakian, & Kennard, 2000) who showed that
saccade latency was not affected by visual distractors within the blind field.

The current study further investigates residual vision in hemianopics by using
a new measure of distractor interference on saccadic eye movements. Previous
research with healthy participants has indicated that irrelevant distractors
evoke saccade trajectory deviations away from their location (Van der Stigchel,
Meeter, & Theeuwes, in press). Similar to the remote distractor effect, these
saccade trajectories deviations are claimed to be a reflection of the
competition between saccade goals in the SC.

Similar to the previous studies investigating the interference evoked by
*blind* distractors, we will present irrelevant distractors in the blind part
of the visual field and record eye movement responses to targets in the intact
visual field. The influence of the distractor will be examined by looking at
saccade trajectory deviations.

By using an eyetracker, eye movements to objects in the intact visual field
will be recorded. Simultaneously distractors willen be presented in the blind
field. We will investigate the influence of distractors on the eye movement.

Minimal burden and risk