SEMANTIC PROCESSING IN THE NEGLECTED VISUAL-FIELD - EVIDENCE FROM A LEXICAL DECISION TASK

The present study examined the possibility of a dissociation between visual information processing and conscious awareness of that processing in patients with unilateral visual neglect. Implicit processing of visual information was measured in the context of a semantic priming task (Experiment 1) in which patients made lexical decisions to centrally located targets following the presentation of lateralised picture primes. Like normal controls, patients with unilateral neglect showed equivalent priming when related picture primes were presented to the left or to the right visual field. This contrasts with the performance of a patient with a dense left hemianopia without neglect who did not show priming from the affected field. To contrast performance on the implicit task with that on a task requiring explicit awareness of visual information, Experiment 2 used a delayed discrimination task, in which patients had to match a lateralised target to one of two centrally presented alternatives. As expected, patients with neglect, as well as a hemianopic patient, had marked difficulty in discriminating targets presented in the left visual field. The dissociation between processing of meaning and conscious awareness of this information is difficult to reconcile with theories of neglect that imply a complete interruption in the early processing of sensory information. Rather, current models should accommodate the possibility that neglect reflects only a partial disruption in the formation of visual representations. Alternatively, neglect can be conceptualised as a disorder in accessing these representations intentionally.