We think we figured out the disease mechanism in simultanagnosia (a neuropsychological disease in which the patients see only one object at the time, and are unable to identify large visual scenes). This is a rare but a very invalidating disease: the patients can no longer read or orient themselves in unfamiliar surroundings. I hope my research will help towards better assessment and treatment for these patients. However, I must confess that I did it also for a selfish reason. I find neuropsychological puzzles cool and I think I solved this one.
In brief, simultanagnosia patients cannot see what they are directly looking at. Central and peripheral objects compete for attention and objects in the periphery win this competition. If multiple objects are instead presented in the visual periphery only, the patients are better able to perceive them simultaneously.
An abstract is below:
Abnormal center-periphery gradient in spatial attention in simultanagnosia
Daniela Balslev, Bartholomaeus Odoj, Johannes Rennig, Hans-Otto Karnath
Journal of Cognitive Neuroscience (in press)
Patients suffering from simultanagnosia cannot perceive more than one object at a time. The underlying mechanism is incompletely understood. One hypothesis is that simultanagnosia reflects “tunnel vision”, a constricted attention window around gaze, which precludes the grouping of individual objects. Although this idea has a long history in neuropsychology, the question whether the patients indeed have an abnormal attention gradient around the gaze has so far not been addressed. Here we tested this hypothesis in two simultanagnosia patients with bilateral parieto-occipital lesions and two control groups, with or without brain damage. We assessed the subjects’ ability to discriminate letters presented briefly at fixation with and without a peripheral distractor or in the visual periphery, with or without a foveal distractor. A constricted span of attention around gaze would predict an increased susceptibility to foveated versus peripheral distractors. Contrary to this prediction and unlike both control groups, the patients’ ability to discriminate the target decreased more in the presence of peripheral compared to foveated distractors. Thus the attentional spotlight in simultanagnosia does not fall on foveated objects as previously assumed, but rather abnormally highlights the periphery. Furthermore, we found the same center-periphery gradient in the patients’ ability to recognize multiple objects. They detected multiple, but not single objects more accurately in the periphery than at fixation. These results suggest that an abnormal allocation of attention around the gaze can disrupt the grouping of individual objects into an integrated visual scene