Concepts are more than percepts: the case of action verbs

Abstract

Several regions of the posterior-lateral-temporal cortex (PLTC) are reliably recruited when participants read or listen to action verbs, relative to other word and nonword types. This PLTC activation is generally interpreted as reflecting the retrieval of visual-motion features of actions. This interpretation supports the broader theory, that concepts are comprised of sensory-motor features. We investigated an alternative interpretation of the same activations: PLTC activity for action verbs reflects the retrieval of modality-independent representations of event concepts, or the grammatical types associated with them, i.e., verbs. During a functional magnetic resonance imaging scan, participants made semantic-relatedness judgments on word pairs varying in amount of visual-motion information. Replicating previous results, several PLTC regions showed higher responses to words that describe actions versus objects. However, we found that these PLTC regions did not overlap with visual-motion regions. Moreover, their response was higher for verbs than nouns, regardless of visual-motion features. For example, the response of the PLTC is equally high to action verbs (e.g., to run) and mental verbs (e.g., to think), and equally low to animal nouns (e.g., the cat) and inanimate natural kind nouns (e.g., the rock). Thus, PLTC activity for action verbs might reflect the retrieval of event concepts, or the grammatical information associated with verbs. We conclude that concepts are abstracted away from sensory-motor experience and organized according to conceptual properties.

Figure 1.

Motion ratings and neural responses to high-and-low-motion verbs and nouns. A, Motion ratings for high-motion and low-motion verbs and nouns: high-motion verbs (actions), high-motion nouns (animals), low-motion verbs (mental processes), low-motion nouns (inanimate natural kinds). B, Percentage signal change in regions of interest during word comprehension. The lMT+, rMT+, lSTS, and rSTS ROIs were defined based on the localizer experiments (see Materials and Methods for details). The lTPJ, ant lSTS, and ant rSTS were defined based on the action verbs > animal nouns contrast. For the action-verb regions, we display data for high and low-motion words defined orthogonally to the action verbs > animal nouns contrast (see Materials and Methods for details). lMT+ and rMT+, Left and right middle temporal complex, respectively; lSTS and rSTS, left and right superior temporal sulci, respectively; lTPJ, left temporoparietal junction; ant lSTS and rSTS, left and right anterior superior temporal sulcui, respectively. Error bars represent a within-subject standard error of the difference between verbs and nouns.

Figure 2.

Results of the whole-brain analyses for verbs > nouns (pink), biological motion (biological > scrambled motion green), basic motion (motion > luminance, purple), and overlap of biological > scrambled motion and verbs > nouns (yellow). Results are thresholded at p < 0.05 (corrected for multiple comparisons) and displayed on a canonical brain.