Douglas K. Bemis

Simple Composition: A Magnetoencephalography Investigation into the Comprehension of Minimal Linguistic Phrases

The expressive power of language lies in its ability to construct an infinite array of ideas out of a finite set of pieces. Surprisingly, few neurolinguistic investigations probe the basic processes that constitute the foundation of this ability, choosing instead to focus on relatively complex combinatorial operations. Contrastingly, in the present work, we investigate the neural circuits underlying simple linguistic composition, such as required by the minimal phrase “red boat.” Using magnetoencephalography, we examined activity in humans generated at the visual presentation of target nouns, such as “boat,” and varied the combinatorial operations induced by its surrounding context. Nouns in minimal compositional contexts (“red boat”) were compared with those appearing in matched non-compositional contexts, such as after an unpronounceable consonant string (“xkq boat”) or within a list (“cup, boat”). Source analysis did not implicate traditional language areas (inferior frontal gyrus, posterior temporal regions) in such basic composition. Instead, we found increased combinatorial-related activity in the left anterior temporal lobe (LATL) and ventromedial prefrontal cortex (vmPFC). These regions have been linked previously to syntactic (LATL) and semantic (vmPFC) combinatorial processing in more complex linguistic contexts. Thus, we suggest that these regions play a role in basic syntactic and semantic composition, respectively. Importantly, the temporal ordering of the effects, in which LATL activity (∼225 ms) precedes vmPFC activity (∼400 ms), is consistent with many processing models that posit syntactic composition before semantic composition during the construction of linguistic representations.

Basic Linguistic Composition Recruits the Left Anterior Temporal Lobe and Left Angular Gyrus During Both Listening and Reading

Language is experienced primarily through one of two mediums--spoken words and written text. Although substantially different in form, these two linguistic vehicles possess similar powers of expression. Consequently, one goal for the cognitive neuroscience of language is to determine where, if anywhere, along the neural path from sensory stimulation to ultimate comprehension these two processing streams converge. In the present study, we investigate the relationship between basic combinatorial operations in both reading and listening. Using magnetoencephalography, we measured neural activity elicited by the comprehension of simple adjective-noun phrases (red boat) using the same linguistic materials and tasks in both modalities. The present paradigm deviates from previous cross-modality studies by investigating only basic combinatorial mechanisms--specifically, those evoked by the construction of simple adjective-noun phrases. Our results indicate that both modalities rely upon shared neural mechanisms localized to the left anterior temporal lobe (lATL) and left angular gyrus (lAG) during such processing. Furthermore, we found that combinatorial mechanisms subserved by these regions are deployed in the same temporal order within each modality, with lATL activity preceding lAG activity. Modality-specific combinatorial effects were identified during initial perceptual processing, suggesting top-down modulation of low-level mechanisms even during basic composition.

Stepwise acquisition of vocal combinatorial capacity in songbirds and human infants

Human language, as well as birdsong, relies on the ability to arrange vocal elements in new sequences. However, little is known about the ontogenetic origin of this capacity. Here we track the development of vocal combinatorial capacity in three species of vocal learners, combining an experimental approach in zebra finches (Taeniopygia guttata) with an analysis of natural development of vocal transitions in Bengalese finches (Lonchura striata domestica) and pre-lingual human infants. We find a common, stepwise pattern of acquiring vocal transitions across species. In our first study, juvenile zebra finches were trained to perform one song and then the training target was altered, prompting the birds to swap syllable order, or insert a new syllable into a string. All birds solved these permutation tasks in a series of steps, gradually approximating the target sequence by acquiring new pairwise syllable transitions, sometimes too slowly to accomplish the task fully. Similarly, in the more complex songs of Bengalese finches, branching points and bidirectional transitions in song syntax were acquired in a stepwise fashion, starting from a more restrictive set of vocal transitions. The babbling of pre-lingual human infants showed a similar pattern: instead of a single developmental shift from reduplicated to variegated babbling (that is, from repetitive to diverse sequences), we observed multiple shifts, where each new syllable type slowly acquired a diversity of pairwise transitions, asynchronously over development. Collectively, these results point to a common generative process that is conserved across species, suggesting that the long-noted gap between perceptual versus motor combinatorial capabilities in human infants may arise partly from the challenges in constructing new pairwise vocal transitions.

Grounding the cognitive neuroscience of semantics in linguistic theory

The mission of cognitive neuroscience is to represent the interaction of cognitive science and neuroscience: cognitive models of the mind guide a neuroscientific investigation of the brain bases of mental processes. In this endeavour, a cognitive model is crucial as without it, the cognitive neuroscientist does not know what to look for in the brain, what the nature of the relevant representations might be, or how the different components of a process might interact with each other. In the cognitive neuroscience of language, the interaction of theoretical models and brain research has, however, been far from ideal, especially when it comes to the study of meaning at the sentence level. Although theoretical semantics has a long history in linguistics and thus offers detailed and comprehensive models of the nature of semantic representations, these theories have had minimal impact on the brain investigation of semantic processing. In this article, we outline what a theoretically grounded cognitive neuroscience of semantics might look like and summarise our own findings regarding the neural bases of semantic composition, the basic combinatory operation that builds the complex meanings of natural language.

Flexible composition: MEG evidence for the deployment of basic combinatorial linguistic mechanisms in response to task demands.

The present study investigates whether a minimal manipulation in task demands can induce core linguistic combinatorial mechanisms to extend beyond the bounds of normal grammatical phrases. Using magnetoencephalography, we measured neural activity evoked by the processing of adjective-noun phrases in canonical (red cup) and reversed order (cup red). During a task not requiring composition (verification against a color blob and shape outline), we observed significant combinatorial activity during canonical phrases only – as indexed by minimum norm source activity localized to the left anterior temporal lobe at 200–250 ms(cf. [1], [2]). When combinatorial task demands were introduced (by simply combining the blob and outline into a single colored shape) we observed significant combinatorial activity during reversed sequences as well. These results demonstrate the first direct evidence that basic linguistic combinatorial mechanisms can be deployed outside of normal grammatical expressions in response to task demands, independent of changes in lexical or attentional factors.

Combination Across Domains: An MEG Investigation into the Relationship between Mathematical, Pictorial, and Linguistic Processing.

Debates surrounding the evolution of language often hinge upon its relationship to cognition more generally and many investigations have attempted to demark the boundary between the two. Though results from these studies suggest that language may recruit domain-general mechanisms during certain types of complex processing, the domain-generality of basic combinatorial mechanisms that lie at the core of linguistic processing is still unknown. Our previous work (Bemis and Pylkkänen, 2011, 2012) used magnetoencephalography to isolate neural activity associated with the simple composition of an adjective and a noun (“red boat”) and found increased activity during this processing localized to the left anterior temporal lobe (lATL), ventro-medial prefrontal cortex (vmPFC), and left angular gyrus (lAG). The present study explores the domain-generality of these effects and their associated combinatorial mechanisms through two parallel non-linguistic combinatorial tasks designed to be as minimal and natural as the linguistic paradigm. In the first task, we used pictures of colored shapes to elicit combinatorial conceptual processing similar to that evoked by the linguistic expressions and find increased activity again localized to the vmPFC during combinatorial processing. This result suggests that a domain-general semantic combinatorial mechanism operates during basic linguistic composition, and that activity generated by its processing localizes to the vmPFC. In the second task, we recorded neural activity as subjects performed simple addition between two small numerals. Consistent with a wide array of recent results, we find no effects related to basic addition that coincide with our linguistic effects and instead find increased activity localized to the intraparietal sulcus. This result suggests that the scope of the previously identified linguistic effects is restricted to compositional operations and does not extend generally to all tasks that are merely similar in form.

Prediction is no panacea: the key to language is in the unexpected.

For action systems, the critical task is to predict what will happen next. In language, however, the critical task is not to predict the next auditory event but to extract meaning. Reducing language to an action system, and putting prediction at center, mistakenly marginalizes our core capacity to communicate the novel and unpredictable.

The Cambridge Handbook of Biolinguistics: Grounding the cognitive neuroscience of semantics in linguistic theory

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