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LINGUIST List 24.98

Wed Jan 09 2013

Review: Computational Linguistics; Historical Linguistics; Linguistic Theories; Text/Corpus Linguistics: Steels (2012)

Editor for this issue: Rajiv Rao <rajivlinguistlist.org>

Date: 09-Jan-2013
From: Nick Moore <nick.moorelycos.com>
Subject: Experiments in Cultural Language Evolution
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Book announced at http://linguistlist.org/issues/23/23-1182.html

Editor: Luc Steels
Title: Experiments in Cultural Language Evolution
Series Title: Advances in Interaction Studies 3
Publisher: John Benjamins
Year: 2012

Reviewer: Nick Moore, Sheffield Hallam University


The ten papers collected in “Experiments in Cultural Language Evolution”
represent the state-of-the-art of research into simulated multi-agent
interaction. Centered around Luc Steels’ work at the Sony Computer Science
Laboratory, Paris, this volume represents the culmination of more than a
decade of work dedicated to uncovering the practicalities of language
evolution in a social setting. The book is divided into three sections. An
introductory section comprises a Foreword and an Introduction, both by Steels,
that set out the direction and the theoretical framework for the remaining
papers. Part 1 describes experiments in vocabulary evolution and Part 2
details how grammatical features evolve in experiments in the same framework.
Each experiment enhances results gained in previous experiments.

The Foreword places the volume in its historical context by stressing that the
question of language evolution is almost as plagued by speculation today as in
1995, when Steels launched this research project. Because there is no fossil
record and because we cannot allow any modern language to represent languages
as they first emerged, we can only be guided by general principles of
evolution when theorising the evolution of languages. Steels and his team have
since synthesised an approach to language evolution that attempts to simulate
the evolution of language in a cultural context by using computational agents,
typically embodied as robots. The Foreword also summarises each chapter.

Chapter 1, “Self-organization and selection in cultural language evolution” by
Steels, outlines the theoretical framework for the empirical descriptions in
the remaining chapters. Steels demands that any theoretical description of
language evolution be biologically feasible, demonstrate advantage to social
reproduction, and adapt to cultural change. Language in this model is assumed
to be open-ended, distributed, and transmitted non-telepathically. The key
aspects of an evolutionary theory that are applied to language are
fundamentally functional, i.e., Does language succeed in communicating? Agents
apply general strategies that adapt language for optimum expressive adequacy,
cognitive effort, learnability and social conformity. The repeated application
of these strategies to instances of communicative events produces a language
system based on the probability of communicative success. The language system
is the combination of the general cognitive capabilities of routine processing
and meta-analysis. Ready-made responses may be available to a speaker, but
analysis is required to evaluate those responses. Where self-evaluation
indicates a lack of success, a repair is introduced. Repair actions may
require a reframing of the chosen sentence, the selection of an alternative
lexical item, or the creation of a new item or structure. Self-evaluation is
possible because of a routine termed ‘re-entry’ (i.e. a process that matches
the mirror-neuron hypothesis; see Rizzolatti and Craighero, 2004), which
allows the speaker to practice the communicative effect of the chosen sentence
before it is articulated by acting as the hearer in an internal process.

While the language system adapts, constrained by language strategies, language
items emerge through a self-enforcing cumulative process of invention, trial,
and alignment between agents. As with repair, alignment is central to the
self-organising character of language. Alignment is the social enaction of
frequency, such that the communicatively successful use of a language item
increases the likelihood of it being adopted by other agents. This process is
demonstrated throughout the volume in various experiments. To further
strengthen the centrality of self-organisation in language evolution, Steels
also employs the principle of 'structural coupling' (Maturana, 2002), which
facilitates alignment through linguistic transmission due to the structure of
an organism and its interaction with the living, non-living and linguistic
environment, without the need for intention or a central authority.

The key issue for Steels is to provide empirical evidence for the theoretical
framework sketched here. Contemporary evolutionary linguistic processes, such
as creolisation, can shed light on how language evolves, as can placing
linguistically-competent subjects into a context where new language must be
invented to complete a communicative task. However, Steels and his
collaborators choose to model evolutionary processes computationally and
robotically, using embodied agents to enact language games. Throughout the
volume, robots engage in: acquisition experiments, where one linguistically
competent robot passes on a linguistic system to another robot with a pidgin
version of the language, through tutoring, although neither robot knows which
has the full version; emergent experiments, where both robot agents, using the
strategies described above, collaborate to converge on a non-predetermined
stable linguistic system; and reconstruction experiments, where strategies are
varied by agents to simulate known linguistic evolution. The remaining
chapters describe these experiments for selected vocabulary (Part 1) and
grammatical (Part 2) features.

Steels and Martin Loetzsch start Part 1 with the simplest language game: the
naming game. In the “non-grounded” version of this emergent experiment, two
agents share the same viewpoint of a set of objects. The speaker offers a name
for an object, to which the hearer points. If the hearer matches the speaker’s
object, a new round is played. However, a number of repairs may occur. The
speaker may identify an object with no known name, in which case it has to
invent one. The hearer may not know the word, so it guesses the object. If the
guess is correct, the new word is remembered, but if it is incorrect, the
speaker points out the object, and the new word is remembered. If the hearer
knows a different word for the same object, scores are given to the different
words so that, through usage, agents converge on agreed words. Thus, in one
experiment, twelve words for five objects after 50 games become five to six
words, on average, after 200 games. In the “grounded” version of the game, the
agents are mobile and may see the same objects from different angles.
Identifying objects through luminance, yellow/blue and red/green scores, x and
y coordinates, and height and width measurements, agents store prototypes of
objects which they then collaborate to name with other agents, using similar
strategies and repairs as in the previous game. Aggregate results produce
close to 100% communicative success after 1,000 games producing 20 terms after
18 views of 10 objects. Adding the ability to both track moved objects and
update prototype models results in about 90% success with 11 terms from 1,500
games after 16 views of 10 objects. That is, these two learning heuristics
produce far less ambiguity and synonymy.

In “Language Strategies for Color”, Joris Bleys engages robot agents in naming
games for colour, thereby accounting for how categories emerge from a natural
spectrum. Agents carry out the same language games as in the previous
experiment, but here the objects are distinguishable only by colour. Robot
agents use a learning strategy that adjusts, rather than replaces, the current
prototypical colour towards the speaker’s use of the colour word whenever
communication is unsuccessful. Using English words based on scores for
brightness, red/green and yellow/blue scores, robot agents score about 83%
communicative success, matching baseline or target scores set by human agents.
In an emergent experiment using only hue (or brightness), robot agents achieve
about 72% success. To make the experiments more closely match natural
language, Bleys also investigates graded membership of colour categories (e.g.
“only slightly”, “somewhat” or “very” red). In a reconstruction experiment,
robot agents produce words that were “qualitatively similar” (p.74) to their
human counterparts in baseline data. Similarly, in acquisition experiments,
robot agents demonstrate communicative success at rates marginally below
humans. An emergent experiment for colour produces almost 95% communicative
success with little variance for 5 words after about 15,00 games. The
impressive results for graded membership demonstrate another important aspect
of these evolutionary experiments: language strategies adapt to give selective
advantage. In this case, graded membership of colours allows a higher rate of
success than brightness-only or hue-and-brightness systems.

The experiments in the next two chapters, “Emergent mirror systems for body
language” by Steels and Michael Spranger and “The co-evolution of basic
spatial terms and categories” by Spranger, add complexity to the linguistic
models developed in the previous two chapters by adding verbal and adverbial
options (Steel and Spranger) and prepositional meanings (Spranger). Spranger’s
experimental embodied-robotic subjects achieve 98% communicative success when
reconstructing German spatial terms. Steel and Spranger claim that “It is only
by the full integration of all aspects of language with sophisticated
sensory-motor intelligence that agents were able to arrive at a shared
communicative system that is adequate for the game” (107) of correctly
ordering a fellow robot agent to strike a particular pose. That is,
communicative success is achieved by: grounding the agents in a sensory
experience relative to their own body and its parts; employing a prototypical,
rather than categorical, approach to language; simulating mirror neurons (by
enabling robots to simulate and monitor, without enacting, a motor programme);
and providing feedback loops for the motor system.

Part 1 culminates in the chapter “Multi-dimensional meanings in lexical
formation”, by Pieter Wellens and Loetzsch, which attempts to simulate a more
natural environment for lexical emergence and demonstrate the adaptive
benefits of the strategies adopted in the studies in this volume. The language
games played by robot agents in the preceding chapters all focus on one aspect
of language, but this does not reflect natural language use, when speakers
must select the most suitable linguistic features to distinguish objects. The
most favourable results are obtained when agents use a probability-based
‘Adaptive Strategy’ for word learning, whereby a fuzzy-logic algorithm for
‘best fit’ is used in naming objects as speaker or hearer. In experiments
where 25 agents able to distinguish 16 features per object play 4,000 games
each, totalling 50,000 games over 10 repetitions, the agents achieve 90%
communicative success after 10,000 games, and approach a 98% success rate
after 30,000 games. Another measure, lexicon coherence, which quantifies the
alignment between agents’ lexicons at any time, reaches 0.4 after 10,000 games
and averages only as high as 0.45 on a scale of -1 to +1 after 50,000 games.
This reflects natural language, where high levels of communicative success are
achieved even when agents do not totally agree on word meanings.

Part Two of the book, ‘Emergence of Grammatical Systems’, opens with Remi van
Trijp’s ‘The evolution of case systems for marking event structure’, which
posits three bold hypotheses: 1. “Case evolves because it has selective
advantage for communication” (170); 2. case emerges when a population shares a
‘case strategy’; and 3. “Case markers can be repurposed for a different
language system if the original selective advantages of a case system have
been ‘usurped’ by more dominant, competing systems in the language” (170). In
experiments where one robot agent describes a scene that the two agents have
just watched together, robot agents acquire the case system for German,
although van Trijp rejects the need for 'a priori' grammatical categories.
After 5,000 games, coherence scores are above 0.95, the language system is
highly systematic, and cognitive effort is at a minimum, thus providing
support for the first hypothesis. Moreover, the evolution of the Spanish
personal pronoun system is reconstructed in experiments that provide evidence
for hypotheses 2 and 3 above. As with native speakers, grammatical variation
is accommodated by robot agents who produce language with preferences for
certain structures. Similarly, subsequent experiments demonstrate a paradigm
shift in the population, with preferences moving from one system to another.
In the conclusion, van Trijp is careful to emphasise that these experiments
demonstrate a high level of communicative success using general shared
cognitive strategies – typically, “analogical reasoning or similarity-based
categorization” (202).

In “Emergent functional grammar for space”, Spranger and Steels demonstrate
the selective advantage of grammaticalising spatial relationships over the
solely lexical variant in experiments that reconstruct German and that
self-organise into an emergent system. Crucially, they show how a
semantically-oriented strategy towards grammaticalised spatial relationships
requires less cognitive effort for greater communicative success. Similarly,
Katrien Beuls, Steels and Sebastian Höfer’s experiments into “The emergence of
internal agreement systems” produce results that reduce cognitive effort and
ambiguity by grouping related words into groups or phrases. Kateryna
Gerasymova, Spranger and Beuls investigate the Russian system of Aktionsarten
in “A language strategy for aspect”. Although the Russian system of aspect is
considered complex and elaborate, robot agents are able to reconstruct and
acquire the system, partially aided by the ability to accept holophrases (a
learned combination of words) for later analysis. Robot agents then
demonstrate how an entirely new aspect system can emerge. As in the
experiments by Wellens and Loetzsch, the final chapter ''The emergence of
quantifiers'', by Simon Pauw and Joseph Hilferty, demonstrates the selective
advantage of fuzzy categories by focusing on quantifying expressions.
Experiments in acquisition and formation compare the alternative strategies of
absolute quantification and scalable quantification, resulting in the
conclusion that the more unpredictable the environment, the more likely a
scalable strategy will prevail.


Although each paper has different authors, the volume exhibits both a
remarkable sense of consistency and a clear sense of progression from one
chapter to the next. The research reveals a sense of direction shared by
Steels and the other contributors that is laid out in Chapter One. In fact, it
is advisable to read Chapter One again after examining the results of later
experiments, in order to fully appreciate the significance of the bold
approach taken by this team of researchers.

The greatest danger of depending on functional explanations to support a
hypothesis is that evidence can only be interpreted as supporting an inert
status quo. Fortunately, Steels and colleagues avoid this theoretical blind
alley by incorporating the dynamics of alignment and the explanations and
mechanisms for linguistic change. For instance, in van Trijp’s chapter,
experimental evidence provides support for the hypothesis that the advantages
provided by grammatical case in Spanish have been replaced by other
grammatical features, freeing case markers to function in new ways. Perhaps my
only concern with some of the papers in the volume is that there is an
over-reliance on formal, rather than functional models of language. While some
functional models may be difficult to model computationally, there are
solutions, such as Halliday and Matthiessen (1999), which may provide the
research team with grammatical models more aligned with the
non-representational approach to language that is central to the research
reported here.

This book and other experiments by the same team provide empirical evidence
for the emergence of language based on evolutionary principles, on what we
currently understand about brain structure and organisation (e.g. Edelman
1999; 2004) and, significantly, without the need for language-specific
acquisition strategies; in all of the experiments here, the learning
strategies employed are general cognitive strategies rather than
language-specific. The experiments repeatedly demonstrate that: language can
emerge without a priori conditions; current language systems can be aligned
within a community through structural coupling; known developments in language
can be modelled in embodied robotic agents with simulated mirror neurons; and
language functions probabilistically, not categorically. I am unaware of any
other series of falsifiable experiments that provide verifiable evidence to
counter these conclusions, despite many theoretical claims to the contrary.
Consequently, this volume should be of value to anyone interested in language
evolution, in the application of natural languages to robotic agents, and in
general linguistic theory.


Edelman, G.M. 1999. Building a picture of the brain. Annals of the New York
Academy of Sciences 882 June 1999, p.68-89

Edelman, G.M. 2004. Wider Than the Sky - The Phenomenal Gift of Consciousness.
New Haven: Yale University Press

Halliday, M.A.K. and Matthiessen, C.M.I.M. 1999. Construing Experience through
Meaning: A Language-based Approach to Cognition. London: Continuum

Maturana Romesin, H. 2002. Autopoiesis, Structural coupling and cognition: A
history of these and other notions in the biology of cognition. Cybernetics
and Human Knowing 9(4), pp.5-34

Rizzolatti, G. and Craighero, L. 2004. The Mirror-Neuron system. Annual Review
of Neuroscience 27, pp.169-92

About the Reviewer:
Nick Moore has worked in Brazil, Oman, Turkey, the UAE and the UK with
students and teachers of English as a foreign language, English for specific
and academic purposes, and linguistics. His PhD in applied linguistics from
the University of Liverpool addressed information structure in written
English. His other research interests include systemic functional linguistics,
corpus linguistics, theories of embodiment, lexis and skills in language
teaching, and reading programs. He is the co-editor of 'READ', maintains a
blog on language, linguistics and learning at najmoore.blogspot.com and has
recently joined the TESOL unit at Sheffield Hallam University.
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