Semantic processing and orthographic specificity in hemispatial neglect.

Two sets of experiments, each consisting of a semantic priming task and a discrimination task, investigated the proceedings of lexical information in the neglected visual field. In the semantic priming task, subjects made lexical decisions to target words preceded by lateralized word primes; in the discrimination task, they indicated which of two words corresponded to a target word presented to the left visual field (LVF) or right visual field (RVF). The first set of experiments indicated that although patients were unable to discriminate words presented in the LVF, they showed significant priming when LVF primes were followed by semantically related targets compared to unrelated targets. The second set of experiments further examined the nature of this priming effect by comparing priming in a condition in which primes were semantically related to the target word (e.g., TEA-CUP) and a condition in which primes were unrelated to the target word, but orthographically similar to a related prime (e.g., PEA-CUP). This experiment replicated the previously established semantic priming effects and demonstrated significant negative priming for targets preceded by LVF primes that were orthographically similar to a semantically related word. Again, patients performed at chance in the forced-choice discrimination task when targets were presented in the LVF These findings indicate that semantic processing of neglected lexical information is based on fully specified perceptual and orthographic information. A lateral inhibitory mechanism is proposed that maximizes the probability, albeit unsuccessfully, that neglected orthographic information will reach awareness.