The neural basis of conceptualizing the same action at different levels of abstraction

Abstract

People can conceptualize the same action (e.g. 'riding a bike') at different levels of abstraction (LOA), where higher LOAs specify the abstract motives that explain why the action is performed (e.g. 'getting exercise'), while lower LOAs specify the concrete steps that indicate how the action is performed (e.g. 'gripping handlebars'). Prior neuroimaging studies have shown that why and how questions about actions differentially activate two cortical networks associated with mental-state reasoning and action representation, respectively; however, it remains unknown whether this is due to the differential demands of the questions per se or to the shifts in LOA those questions produce. We conducted functional magnetic resonance imaging while participants judged pairs of action phrases that varied in LOA and that could be framed either as a why question (Why ride a bike? Get exercise.) or a how question (How to get exercise? Ride a bike.). Question framing (why vs how) had no effect on activity in regions of the two networks. Instead, these regions uniquely tracked parametric variation in LOA, both across and within trials. This suggests that the human capacity to understand actions at different LOA is based in the relative activity of two cortical networks.

Keywords: abstraction; action understanding; concepts; fMRI; semantic memory; social cognition.

Fig. 1.

Experimental design. (A) One of 25 four-level action hierarchies featured in the experimental task. For each four-level hierarchy the action described by a phrase at one level (e.g. ‘make a phone call’) was both a commonly accepted motive for performing the action described by the phrase at the level immediately below it (e.g. ‘dial numbers’) and a commonly accepted means for performing the action described by the phrase at the level immediately above it (e.g. ‘contact a friend’). As shown to the right of the example and described further in the text all phrases were normed on five dimensions used to derive a single factor describing each phrase's level of abstraction (LOA). (B) Structure of one of the trials formed by pairing phrases at contiguous levels of the hierarchy. Trials began with an action phrase embedded in either a why (shown) or how question and concluded with a different action phrase presented as a possible answer. Answer phrases were presented for a maximum duration of 2250 ms. Once the participant responded, the screen was replaced by a fixation cross until the onset of the next trial.

Fig. 2.

Left hemisphere cortical regions reliably modulated by the Why/How contrast in prior work. See Methods and Supplementary Table S2 for further details. TPJ = Temporoparietal Junction; PFC = Prefrontal Cortex; STS = Superior Temporal Sulcus; PCC = Posterior Cingulate Cortex; IPL = Inferior Parietal Lobule; PMC = Premotor Cortex; MTG = Middle Temporal Gyrus.

Fig. 3.

Whole-brain surface renderings of regional activity associated with Trialwise Level of Abstraction (LOA), computed as the mean of the question and answer phrases appearing in each trial. The results in (A) show regions modulated in the categorical High > Low LOA contrast from Model 1, while the results in (B) show regions modulated by the continuous Trialwise LOA parameter from Model 2. Significant clusters were identified in a whole-brain search thresholded at a cluster-level family-wise error rate of 0.05, and their locations are reported in Supplementary Table S3. To provide information about extent and for display purposes only, the cluster-corrected maps were minimally dilated prior to surface rendering.

Fig. 4.

(A) Scatterplot showing the relationship between the Prepotent LOA and the signed Within-Trial Shift in LOA across Why (black markers) and How (white markers) trials. The Prepotent LOA refers to the LOA of the action phrase appearing in the question at the beginning of each trial. The signed within-trial shift in LOA is computed for each trial by subtracting the Prepotent LOA from the LOA of the action phrase appearing in the presented answer. Positive shift trials induced an upward change in LOA, while negative shift trials induced a downward change in LOA. To facilitate comparability, the LOA dimension has been rescaled to 0–1. (B) Regions uniquely associated with the Prepotent LOA parameter when controlling for the signed within-trial shift in LOA. (C) Regions uniquely associated with the signed within-trial shift in LOA parameter. Significant clusters were identified in a whole-brain search thresholded at a cluster-level family-wise error rate of 0.05, and their locations are reported in Supplementary Table S4. To provide information about extent and for display purposes only, the cluster-corrected maps were minimally dilated prior to surface rendering.