Language evolution seminar

Speakers: Christine Cuskley, Molly Flaherty and Marieke Schouwstra (University of Edinburgh)

Christine Cuskley: Alien symbols for alien language: iterated learning in a unique, novel signal space

Abstract: Studies in iterated learning of artificial ‘alien’ languages show that structure in language can arise from the process of cultural transmission (Kirby, Cornish, & Smith, 2008). Structure can accumulate not only in iterated artificial language learning (ALL) tasks, but also in iterated sequence learning tasks which are not explicitly linguistic (e.g., they contain no meanings, and do not use linguistic stimuli). Meaningless sequences of colours become more structured and more learnable over time (Cornish, Smith, & Kirby, 2013), reproduction of rhythmic sequences results in increased structure, learnability, and emergence of 'musical universals' (Ravignani, Delgado, & Kirby, 2016), and transmission of slide whistles can result increased structure (Verhoef, Kirby, & Boer, 2014). Where signals are mapped onto meanings, the relationships between these two spaces can have significant effects on the resulting structure (Little, Erylmaz, & Boer, 2017). While the signals and modalities with which iterated learning studies are conducted have expanded considerably in recent years, how properties of signal spaces interact with biases of learners in the emergence of structure is relatively under-studied.

To further investigate the effect of signal space on the evolution of structure and learnability, we used a completely novel set of graphical symbols called Ferros: a set of 137 abstract graphemes created using ferrofluid ink and visually unlike e.g., Roman orthography. To articulate in Ferro, participants move in a virtual two dimensional palette which produces a different symbol depending on their location within a square. The space is structured along two axes corresponding to the number of contours and nodes in each Ferro. Much like the phonetic space of consonants, distance between Ferros encodes similarity, but the forms are discrete. Ferros are signals which are entirely foreign to participants, who have to learn not only to use the apparatus which produces Ferros, but also what the relevant features of Ferros are.

The Ferro palette was used in an iterated sequence copying task involving hundreds of participants: each participant had three minutes to copy as many 3-character Ferro sequences as they could. Each sequence faded slowly after presentation, providing an additional pressure for quick reproduction. Participants were confined to producing three characters (i.e., sequences could not vary in length), and were provided with feedback on accuracy at each trial.

The initial sequences were pseudo-random, consisting of graphemes with either large articulation spaces in the palette or small, specific articulation spaces. Overall, 672 sequences were produced across 76 chains, each chain being between 5 and 10 generations. Reproduction error was measured as mean Euclidean distance in the palette from the target sequence to the produced sequence, and examined using a linear mixed effects model with generation and articulation space size as fixed effects.

Inclusion of generation and articulation space size improved the model fit significantly over a null model (χ2 = 4.53, p = 0.03). Error was higher overall in chains which started with small articulation spaces (β = 0.1, SE= 0.04, t = 2.5), indicating that participants found these harder to reproduce. Error decreased over generations in the small articulation space condition (β = -0.018, SE = 0.006, t = −3.035), but there was no such effect of generation for sequences which started with large articulation spaces.

Error decreased despite an overall retention of high sequence entropy: in other words, most sequences retained three different characters throughout a chain. The size of the area of the articulation space of a particular Ferro grapheme was significantly correlated with copying accuracy, and sequences in small articulation chains moved towards the larger articulation spaces over time, suggesting that larger articulation spaces make for greater ease of articulation.

The current study shows transmission can lead to increased learnability even in a completely novel signal system that participants have to learn from scratch in the process of transmission. In this case, the biases which drive increased learnability seem to derive primarily from the shape of the signal space: articulation area of a particular Ferro correlates significantly with its learnability (operationalised as reproduction error), and sequences gravitated towards larger articulation spaces over ‘time’. The shape of the space was perhaps especially influential in the current task because participants had no prior experience with Ferros, and so had fewer (or less influential) prior biases relative to other iterated learning tasks, particularly those that utilise non-words and leverage existing linguistic knowledge. This has potential implications for the co-evolution of language and speech: constraints of the signal space may be more influential in early stages of emergence as ‘speakers’ are not only reproducing utterances, but also learning how to manipulate a novel signal space. This study shows that the Ferro palette has broad applications in language evolution research as a system of truly ‘alien’ symbols to study ‘alien’ language learning, emergence, and evolution.

Molly Flaherty, Marieke Schouwstra (joint paper with Susan Goldin-Meadow): Do we see word order patterns from silent gesture studies in a new natural language?

Abstract: Typological analysis clearly shows that the world’s languages are not evenly distributed among all logically possible patterns. Of the six possible orderings of Subject (S), Object (O), and Verb (V), SOV and SVO orders are vastly overrepresented in the world’s languages. Studies on the emergence of word order regularities in silent gesture by hearing non-signers (e.g., Goldin-Meadow, et al., 2008; Gibson et al., 2013) overwhelmingly find evidence for SOV ordering. Based on this type of evidence, it has been proposed that SOV ordering is the most basic ordering from which all other orders emerged. However, semantic properties of the meanings to be conveyed also influence word order in silent gesture. For instance, for intensional events (in which the object is possibly non-existent or dependent on the action; e.g., ‘man thinks of guitar’, ‘woman builds house’) a cross-linguistic preference for SVO was found (Schouwstra & de Swart, 2014). Recent work finds that meaning-dependent word order patterns typical of silent gesture disappear under the influence of interaction (Christensen et al., 2016) and cultural transmission (Schouwstra et al., 2016), in favor of more consistent word order usage. However, in these studies, word order usage never becomes completely regular.

Here we investigate whether traces of the SOV/SVO pattern found in silent gesture can be observed in a new natural language: Nicaraguan Sign Language. This sign language, one of the youngest languages known to science, was born in the late 1970s with the founding of a new school for special education. Though instruction was in Spanish, students soon began to communicate with one another manually. As succeeding cohorts of students learn NSL, the language itself is changing rapidly. Though somewhat variable, NSL word order is strongly verb-final and predominantly SOV (Flaherty, 2014). However, these data are based exclusively on analysis of extensional events. If NSL word order is also influenced by semantic properties of the utterance’s intended meaning, we would expect to see deviation from this SOV patterning. Participants viewed a series of events depicting eight extensional events (i.e. woman pop bubble) and eight intensional events (i.e. woman blow bubble) involving the same object. Participants were asked to describe what they saw to a peer. Twenty-six NSL signers participated. All signers were exposed to NSL before age 7, upon school entry between the early 1980s and early 2000s.

When we analyzed SOV and SVO strings (which accounted for only 39% of strings with 1 verb and 2 arguments), we did not observe the pattern typical of silent gesture: SOV was dominant for both extensional and intensional events, and very few SVO strings were observed (13 total, 10 for intensional events). NSL’s preference for verb-finalness (Flaherty, 2014) may not have allowed the SVO pattern to emerge. However, NSL signers tend to provide more detail than silent gesturers. As a result, many NSL strings were longer than strings observed in silent gesture. When we took into account all strings (including those with several verbs) and asked whether the Object preceded or followed target the Verb, we found more utterances with VO sub-strings (as opposed to OV) for intensional events than for extensional events (Fig 1). A logit mixed effects regression (with event type as fixed effect and random effects for item and signer) confirmed that strings containing VO were uncommon for extensional events (β=-2.9, SE=0.40, p<0.001), but significantly more likely for intensional events (β=1.8, SE=0.45, p<0.001). Thus, objects of intensional verbs are more likely to follow those verbs than are objects of extensionals not only in silent gesture, but also in an emerging sign language.

In this study, we find evidence for lab-documented word order preferences in an emergent natural language: objects precede verbs for extensional events, but follow verbs for intensional events. However, this word order pattern is manifested differently in Nicaraguan Sign because it interacts with NSL’s language-internal constraint for verb finalness. A combination of lab and field-based methodologies made this finding possible: without laboratory results, we would not have looked at a wider semantic range of events in the field; without field data, we would not have discovered the interaction between VO ordering preference and existing natural language constraints.

Contact

Seminars are organised by the Centre for Language Evolution

Svenja Wagner

Centre for Language Evolution