Neural representations of concreteness and concrete concepts are specific to the individual

Different people listening to the same story may converge upon a largely shared interpretation while still developing idiosyncratic experiences atop that shared foundation. What linguistic properties support this individualized experience of natural language? Here, we investigate how the “concrete-abstract” axis — i.e., the extent to which a word is grounded in sensory experience — relates to within- and across-subject variability in the neural representations of language. Leveraging a dataset of human participants of both sexes who each listened to four auditory stories while undergoing functional MRI, we demonstrate that neural representations of “concreteness” are both reliable across stories and relatively unique to individuals, while neural representations of “abstractness” are variable both within individuals and across the population. Using natural language processing tools, we show that concrete words exhibit similar neural representations despite spanning larger distances within a high-dimensional semantic space, which potentially reflects an underlying representational signature of sensory experience — namely, imageability — shared by concrete words but absent from abstract words. Our findings situate the concrete-abstract axis as a core dimension that supports both shared and individualized representations of natural language. Significance Statement The meaning of spoken language is often ambiguous. As a result, people may form different interpretations despite being presented with the same information. What properties of language does the brain leverage to form this diverse, individual experience? Analyses of functional MRI data demonstrated that "concreteness", the extent to which language is related to sensory experience, evoked reliable neural patterns that were unique to individual subjects and allowed us to identify individuals solely based on their neural data. Application of machine learning methods showed that sets of concrete concepts, but not abstract concepts, show stable neural patterns, potentially due to a sensory signature: imageability. Overall, this study characterizes concreteness as a central property supporting the individualized experience of real-world language.