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Caption
Figure 1: Timing of syntactic processing following different strategies. The colored circles refer to the nodes of the syntactic structure that are built at the time point the word in the same color is uttered or heard. A: Colored representation of anticipatory top-down phrase structure building, with nodes counted from the top of the syntactic tree to the word. For example, at “He” orange nodes S, NP and PRP are counted. B: Colored representation of integratory bottom-up phrase structure building, with nodes counted from the bottom of the tree to the top. Only nodes where all of their branching nodes have already been met can be counted at each word. For example, at “He” nodes NP and PRP are counted, while S has a branch that is unaccounted for. The unfolding of node counting over time is shown in the gifs.
Figure 2: Graphical representation of the analysis procedure to relate word-by-word predictors of syntactic processing to brain activity. A: Word-by-word predictors of syntactic complexity were extracted from the constituent structure of the sentence spoken by a participant and listened to by other participants (D). The height of the bars in A represents the number of phrase-structure building operations expected to take place at each word following top-down and bottom-up strategies (e.g. at “so” 3 nodes are counted for top-down, 2 for bottom-up). The weights of the syntactic predictors were convolved with the haemodynamic response function (B) to get predictor timeseries of BOLD activity (brain activity that is usually measured with fMRI) at 1.5 sec resolution (C). These predictors timeseries were then compared to the average brain activity (F) in the speaker or the listener (D) in three regions of interest that have been associated with syntactic processing (BA44, BA45 and left posterior middle temporal gyrus (LpMTG), E).
Figure 3: Estimates for the effect of sentence-onset, sentence-offset, top-down and bottom-up syntactic strategies on brain activity in the three regions of interest. Error bars represent standard error of the mean. The top-down strategy is related to an increase in brain activity similarly in the three regions, while there is a decrease in brain activity in association with the bottom-up parser (e.g. at “bodies” in the example in Fig. 1). In comprehension, instead, brain activity decreases in the LpMTG with more top-down counts, but increases with bottom-up (e.g. at “bodies”). BA45 (or pars triangularis of the left inferior frontal gyrus) is instead sensitive to sentence-onsets and offsets, with increased activity at the end of sentences during listening.
Credit
Laura Giglio
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