Inter-response interference contributes to the sequencing deficit in frontal lobe lesions.

In this study we investigated the contribution of inter-response interference to the sequencing deficit in frontal lobe lesions. We examined inter-response interference in choice sequences through the reduction in inter-response interval produced by stimulus preview when compared with sequences performed without preview. If frontal lobe lesions result in a stronger inter-response interference, the facilitative effect of preview on inter-response interval should be attenuated. We compared nine patients with a frontal excision with nine patients with a temporal excision and nine controls in a task requiring rapid keypress responses to each of five letters in a sequence. In the no-preview condition, the five letters were presented one at a time, immediately following the previous response. In the preview condition, the five letters were presented simultaneously before the response sequence. Patients with a frontal lesion showed slower response times than the other groups. In normal subjects and patients with a temporal lesion, stimulus preview produced the expected reduction of inter-response time and the slowing of sequence initiation. In frontal lesions, however, preview did not reduce inter-response time and exacerbated the slowing of sequence initiation. The results indicate that patients with a frontal lobe lesion show increased interference between adjacent responses as well as a sequence initiation problem.