FRONTAL LESIONS INCREASE POST-TARGET INTERFERENCE IN RAPID STIMULUS STREAMS

We examined the effects of frontal lesions on the attentional processe s surrounding the discrimination of target stimuli by comparing patien ts with frontal excisions, patients with temporal excisions and contro ls on target-letter identification in rapid visual streams. Subjects w ere asked to look at streams of 18-26 letters presented centrally at r ates of 6, 8, or 10 letters/sec and to name the two white target lette rs (T1 and T2) embedded among black letters in each stream. The two ta rget letters were separated by either 0, 2, 4, or 6 black letters. Nor mals and temporals correctly reported T1 at all rates, they showed the expected T2 identification errors peaking 300 msec after T1 at high r ate and little T2 interference at lower rates. However, frontals showe d T2 interference at the two lower rates and were unable to identify T 1 at high rate. The effects observed suggest that an inertia of target discrimination processes contributes to the frontal attention deficit s. Copyright (C) 1996 Elsevier Science Ltd.