Toward a universal decoder of linguistic meaning from brain activation.
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ABSTRACT:
SUBMITTER: Pereira F
PROVIDER: S-EPMC5840373 | biostudies-literature | 2018 Mar
REPOSITORIES: biostudies-literature
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Project description:The brain is thought to combine linguistic knowledge of words and nonlinguistic knowledge of their referents to encode sentence meaning. However, functional neuroimaging studies aiming at decoding language meaning from neural activity have mostly relied on distributional models of word semantics, which are based on patterns of word co-occurrence in text corpora. Here, we present initial evidence that modeling nonlinguistic "experiential" knowledge contributes to decoding neural representations of sentence meaning. We model attributes of peoples' sensory, motor, social, emotional, and cognitive experiences with words using behavioral ratings. We demonstrate that fMRI activation elicited in sentence reading is more accurately decoded when this experiential attribute model is integrated with a text-based model than when either model is applied in isolation (participants were 5 males and 9 females). Our decoding approach exploits a representation-similarity-based framework, which benefits from being parameter free, while performing at accuracy levels comparable with those from parameter fitting approaches, such as ridge regression. We find that the text-based model contributes particularly to the decoding of sentences containing linguistically oriented "abstract" words and reveal tentative evidence that the experiential model improves decoding of more concrete sentences. Finally, we introduce a cross-participant decoding method to estimate an upper bound on model-based decoding accuracy. We demonstrate that a substantial fraction of neural signal remains unexplained, and leverage this gap to pinpoint characteristics of weakly decoded sentences and hence identify model weaknesses to guide future model development.SIGNIFICANCE STATEMENT Language gives humans the unique ability to communicate about historical events, theoretical concepts, and fiction. Although words are learned through language and defined by their relations to other words in dictionaries, our understanding of word meaning presumably draws heavily on our nonlinguistic sensory, motor, interoceptive, and emotional experiences with words and their referents. Behavioral experiments lend support to the intuition that word meaning integrates aspects of linguistic and nonlinguistic "experiential" knowledge. However, behavioral measures do not provide a window on how meaning is represented in the brain and tend to necessitate artificial experimental paradigms. We present a model-based approach that reveals early evidence that experiential and linguistically acquired knowledge can be detected in brain activity elicited in reading natural sentences.
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Project description:BackgroundLinguists and psychologists have explained the remarkable similarities in the orderings of linguistic elements across languages by suggesting that our inborn ability for language makes available certain innately wired primitives. Different types of adjectives, adverbs, and other elements in the functional spine are considered to occupy fixed positions via innate hierarchies that determine orderings such as A>B>C, banning other permutations (*B>C>A). The goal of this research is to tap into the nature and rigidity of such hierarchies by comparing what happens when people process orderings that either comply with them or violate them.MethodN = 170 neurotypical, adult speakers completed a timed forced choice task that featured stimuli showing a combination of two adjectives and a Spelke-object (e.g., 'I bought a square black table'). Two types of responses were collected: (i) acceptability judgments on a 3-point Likert scale that featured the options 'correct', 'neither correct nor wrong', and 'wrong' and (ii) reaction times. The task featured three conditions: 1. size adjective > nationality adjective, 2. color adjective > shape adjective, 3. subjective comment adjective > material adjective. Each condition had two orders. In the congruent order, the adjective pair was ordered in agreement with what is traditionally accepted as dictated by the universal hierarchy. In the incongruent order, the ordering was reversed, thus the hierarchy was violated.ResultsIn the first experiment, the results of n = 140 monolinguals showed that across conditions, both congruent and incongruent orders were generally accepted as correct. For 2/3 conditions, the difference in acceptability ratings between congruent and incongruent orders did not reach statistical significance. Using time as a window to processing, reaction times showed that incongruent orders do not take longer to process than congruent ones, as should be the case if the former were treated as being licensed under some type of special condition (e.g., contrastive focus) that reverses the unmarked order and legitimizes the violation of the hierarchy. In the second experiment, the results of n = 30 bidialectals, tested in both language varieties, corroborated the findings of the first experiment.ConclusionsOur findings do not provide evidence for an innate hierarchy for adjective ordering that imposes one rigid, unmarked order. We discuss the importance of notions such as subjectivity and inherentness, and show that for some conditions, not only is there no evidence for a hard constraint that bans incongruent orders, but even simple preferences of congruent orders over incongruent ones are hard to discern. Capturing the bigger picture, given that both the hierarchies and their legit permutations have been described as innate, our results reduce the amount of primitives that are cast as innate, eventually offering a deflationist approach to human linguistic cognition.
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