From gaze shifts to set shifts: Using eye-tracking during sentence -picture matching to link deficits in language comprehension and cognition in Parkinson's disease.

摘要

The dopamine deficit underlying Parkinson's disease (PD) causes not only characteristic motor symptoms but cognitive deficits. PD impairs performance on off-line sentence comprehension tasks. However, such tasks give limited insight into the mechanism that causes the deficit. On-line tasks on which PD patients have been tested require participants to divide their attention, so their results may be compromised by patients' deficits in executive function. I obtained on-line data by tracking participants' eye movements as they did an "off-line" task without undue cognitive demands---sentence-picture matching. Participants listened to sentences containing relative clauses in center-embedded or sentence-final position and verbs in active or passive voice. One picture could be ruled out at each of three sentence positions: the transitive verb, the verb's object, and the terminal adjective. (For example, on hearing The queen was kicking the cook who was fat, participants could eliminate a picture of a cook kicking a queen---the verb distracter---on comprehending kicking; a queen kicking a judge on comprehending cook; and a fat queen kicking a thin cook on comprehending fat.) In Passive trials, young participants initially looked toward the verb distracter, showing a bias toward taking the subject noun as the agent. Subsequently they showed rapid reductions in looks to distracters as they were ruled out. Nondemented patients with mild to moderate PD showed increased error rates on sentences with center-embedded clauses or passive verbs. Patients with higher error rates were correspondingly slower to reject the verb distracter in Center trials. These patients also evinced on-line difficulty with processing final relative clauses; however, there was no corresponding off-line deficit (perhaps because they used heuristics to correctly attach the adjective). Comprehension errors correlated with errors on a non-linguistic set-shifting task. These results indicate that PD impairs comprehension by altering inhibitory-excitatory processes common to language and other aspects of cognition. PD patients also exhibited an exaggerated agent-first bias, suggesting that PD might overactivate prepotent, automatic aspects of sentence processing. Consistent with this hypothesis, patients with slower comprehension response times launched reflexive saccades with faster latencies, indicating overactivation of automatic motor behavior.