Multiple natural language cues assist the processing of hierarchical structure

Trotter, A. S., Frost, R L. A., & Monaghan, P. 

Poster presented at the 15th annual meeting of Psycholinguistics in Flanders. Antwerp: Belgium. May 2016.

The existence of sentences containing hierarchical dependencies is taken as evidence that language is not a finite state system. Whilst phrase structure is necessary in producing these sentences, their comprehension may draw on linear processing. Testing processing of language structures can be controlled in laboratory studies by constructing artificial language fragments and examining participants’ learning of the structures therein. However, hierarchical artificial language structures are difficult to acquire, meaning that measuring their processing is difficult to accomplish. Prior studies have employed nonsense word sequences to determine the learning of hierarchically generated grammatical structures. These may derive from prosodic information: rhythmic cues can indicate structural dependencies at phrasal boundaries, and pitch information can also highlight hierarchical structure, with lower pitch variance within phrases than between phrases. Further, information about similarity within dependencies (e.g., knowing dogs chase cats, and cats meow constrains the meaning of “the cat the dog chases meows”) can promote processing of hierarchically-generated structures. More importantly, the type of process required to comprehend the sentence may then not require phrase structure, but instead may be consistent with finite state operations. Detection of similarity and grouping of material using prosodic information may instead bypass the need for more complex constructions. In the present study, we tested whether participants were able to use prosodic and similarity cues to process the grammatical structure of hierarchical centre embedded structures in an artificial language. Participants listened to sequences of a hierarchical centre embedded language, of the AnBn form (e.g. A1A2B2B1, where A1 and B1 always occur as a dependent pair). 80 participants took part in one of five conditions manipulating the presence of several cues: a baseline condition with no additional cues to the structure; a similarity condition, where dependent pairs shared phonological information; a pitch condition where the pitch change within dependent pairs was smaller than that between pairs; a rhythmic condition, where short pauses intervened at phrasal boundaries; and a condition that combined these cues. In the baseline condition, we found no evidence of learning, consistent with prior literature. Individual cues – particularly the phonological similarity cue – promoted learning in the later stages of training. The combined cues condition, however, processing was facilitated by multiple sources of information in the initial stages of training, before the advantage of individual cues was observed: to the early learner, a wealth of information is beneficial, though with greater expertise, individual cues can be used equally effectively.