Cognitive task to differentiate between visual field deficit and neglect

Neglect patients are able to process visual stimuli even if they do not have an overt perception of them. Indeed, since first studies at the end of 80 s lot of works demonstrated the presence of an implicit information processing, specifically part of them focused on the presence of a semantic activation effect due to the onset of a prime (either word or picture) in neglected space. This kind of effect was not found in patient with visual field deficits. Actually hemianopia determines a variable reduction of visual field width and a consequent partial blindness for the patient. Even though there are different neuroanatomical substrates between neglect and hemianopia, we know that clinical examination (including neuropsychological assessment) may provide confounding results. Not so many studies tried to disentangle neglect from hemianopia even using an implicit information processing task to discriminate. In our previous works we hypothesized that a prime-word in the neglected field should determine a semantic activation effect differently for what expected by prime in hemianopic field. We discussed a single case patient with bilateral brain lesion causing both left neglect and right hemianopia. Our results confirmed a strong repetition priming effect only when prime occurred in neglect hemifield. In this work we will describe the performance of 8 patients with a unilateral brain lesion which causes the presence of left visual neglect or left homonymous hemianopia. The experimental procedure was identical to those one described in our previous work. The patients were required to press the space-bar when the target word belonged to a living category after a prime word onset on six different possible positions of the monitor. We collect data on a small group of patients but our first results have confirmed the hypothesis concerning semantic activation in the space affected by neglect but not in hemianopic field. This test gives than promising results as a tool for differential diagnosis, even if it requires minimal levels of attention to be executed.