Cognitive resource limitations during sentence comprehension in Parkinson's disease

Patients with idiopathic Parkinson's disease (PD) were asked to identify th e agent of the action in orally presented sentences with subject-relative o r object-relative center-embedded clauses while simultaneously performing a secondary task that was less resource-demanding (finger tapping) or more r esource-demanding (recognition span). We found that a subgroup of PD patien ts with impaired sentence comprehension at baseline (no secondary task) did not differ from random in their accuracy understanding all types of senten ces during the more demanding (recognition span) condition and also had dif ficulty understanding the most complex sentences during the less demanding (finger tapping) condition. Control subjects and PD patients without baseli ne sentence comprehension difficulty were random only in their comprehensio n of the most complex sentences under the more demanding (recognition span) secondary task condition. Examination of response latencies for accurately understood sentences revealed only an effect for the type of sentence, and this was equally evident across all groups of subjects and regardless of t he condition under which the sentences were administered. The sensitivity o f PD patients' sentence comprehension accuracy to secondary task resource d emands is most consistent with the hypothesis that limited cognitive resour ces contribute to sentence comprehension difficulty in PD. (C) 2000 Academi c Press.