Article

Patients with hemispatial neglect are severely impaired in orienting their
attention to contralesional hemispace. Although motion is one of the strongest
attentional cues in humans, it is still unknown how neglect patients visually
explore their moving real-world environment. We therefore recorded eye movements
at bedside in 19 patients with hemispatial neglect following acute right
hemisphere stroke, 14 right-brain damaged patients without neglect and 21 healthy
control subjects. Videos of naturalistic real-world scenes were presented first
in a free viewing condition together with static images, and subsequently in a
visual search condition. We analyzed number and amplitude of saccades, fixation
durations and horizontal fixation distributions. Novel computational tools
allowed us to assess the impact of different scene features (static and dynamic
contrast, colour, brightness) on patients' gaze. Independent of the different
stimulus conditions, neglect patients showed decreased numbers of fixations in
contralesional hemispace (ipsilesional fixation bias) and increased fixation
durations in ipsilesional hemispace (disengagement deficit). However, in videos
left-hemifield fixations of neglect patients landed on regions with particularly
high dynamic contrast. Furthermore, dynamic scenes with few salient objects led
to a significant reduction of the pathological ipsilesional fixation bias. In
visual search, moving targets in the neglected hemifield were more frequently
detected than stationary ones. The top-down influence (search instruction) could
neither reduce the ipsilesional fixation bias nor the impact of bottom-up
features. Our results provide evidence for a strong impact of dynamic bottom-up
features on neglect patients' scanning behaviour. They support the neglect model
of an attentional priority map in the brain being imbalanced towards ipsilesional
hemispace, which can be counterbalanced by strong contralateral motion cues.
Taking into account the lack of top-down control in neglect patients, bottom-up
stimulation with moving real-world stimuli may be a promising candidate for
future neglect rehabilitation schemes.
CI - Copyright (c) 2012 Elsevier Ltd. All rights reserved.

Langue : ANGLAIS