Task-dependent and task-independent neurovascular responses to syntactic processing

Abstract

The neural basis for syntactic processing was studied using event-related fMRI to determine the locations of BOLD signal increases in the contrast of syntactically complex sentences with center-embedded, object-extracted relative clauses and syntactically simple sentences with right-branching, subject-extracted relative clauses in a group of 15 participants in three tasks. In a sentence verification task, participants saw a target sentence in one of these two syntactic forms, followed by a probe in a simple active form, and determined whether the probe expressed a proposition in the target. In a plausibility judgment task, participants determined whether a sentence in one of these two syntactic forms was plausible or implausible. Finally, in a non-word detection task, participants determined whether a sentence in one of these two syntactic forms contained only real words or a non-word. BOLD signal associated with the syntactic contrast increased in the left posterior inferior frontal gyrus in non-word detection and in a widespread set of areas in the other two tasks. We conclude that the BOLD activity in the left posterior inferior frontal gyrus reflects syntactic processing independent of concurrent cognitive operations and the more widespread areas of activation reflect the use of strategies and the use of the products of syntactic processing to accomplish tasks.

Fig. 1

Accuracy and RTs for different sentence conditions in verification, plausibility judgment (plausible sentences) and non-word detection (sentences with real words). SO: subject object structure; OS: object subject structure. Incongruent: order of animacy of noun phrases biases against syntactically determined meaning; congruent: order of animacy of noun phrases biases towards syntactically determined meaning.

Fig. 2

Mean RT for correct responses in non-word detection for sentences containing non-words, showing increased RTs as a function of non-word location and longer RTs for object- than for subject- extracted sentences with non-words at the position of the embedded verb (V1).

Fig. 3

Histogram of RTs for responses in non-word detection. Top panels: subject-extracted sentences. Blue: sentences with real words; red: sentences with non-words. Bottom panels: object-extracted sentences. Pink: sentences with real words; green: sentences with non-words.

Fig. 4

Areas of BOLD signal differences between stimuli in the verification task. Color overlays represent p-values of the contrast such that the color threshold (red) corresponds to p = .01 and ceilings (yellow) at p = .001. Blue overlays represent areas in which BOLD signal was reduced. Each area has a minimum area of 200 mm² and a false-positive p < .05. The number label for each cluster corresponds to the cluster with the number contrast in Table 2 Left top: early TR interval (6–12 sec post-stimulus onset), SO–OS contrast. Left bottom: early TR interval (6–12 sec post-stimulus onset), false–true contrast. Right top: late TR interval (12–18 sec post-stimulus onset), SO–OS contrast. Right bottom: late TR interval (12–18 sec post-stimulus onset), false–true contrast.

Fig. 5

Areas of BOLD signal differences between plausible stimuli in the plausibility judgment task. Color overlays represent p-values as in Fig. 4. The number label for each cluster corresponds to the cluster with the number contrast in Table 3. Left panel: SO–OS contrast for sentences in which noun animacy order biases towards the meaning of the sentence (“congruent” stimuli). Right panel: SO–OS contrast for sentences in which noun animacy order biases against the meaning of the sentence (“incongruent” stimuli).

Fig. 6

Areas of BOLD signal differences between SO and OS sentences containing real words in which noun animacy order biases against the meaning of the sentence (“incongruent” stimuli) in the non-word judgment task. Color overlays represent p-values as in Fig. 4. The number label for each cluster corresponds to the cluster with the number contrast in Table 4.