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Associative sequence learning (ASL) is a
neuroscientific
Neuroscience is the scientific study of the nervous system (the brain, spinal cord, and peripheral nervous system), its functions, and its disorders. It is a multidisciplinary science that combines physiology, anatomy, molecular biology, ...
theory that attempts to explain how
mirror neuron
A mirror neuron is a neuron that fires both when an animal acts and when the animal observes the same action performed by another. Thus, the neuron "mirrors" the behavior of the other, as though the observer were itself acting. Mirror neurons a ...
s are able to match observed and performed actions, and how individuals (adults, children, animals) are able to imitate body movements. The theory was proposed by
Cecilia Heyes
Cecilia Heyes (born 6 March 1960) is a British psychologist who studies the evolution of the human mind. She is a Senior Research Fellow in Theoretical Life Sciences at All Souls College, and a Professor of Psychology at the University of Oxford ...
in 2000. (For reviews see). A conceptually similar model proposed by
Christian Keysers
Christian Keysers is a French and German neuroscientist.
Education and career
He finished his school education at the European School, Munich and studied psychology and biology at the University of Konstanz, the Ruhr University Bochum, Univers ...
and David Perrett, based on what we know about the neural properties of mirror neurons and spike-timing-dependent plasticity is the Hebbian learning account of mirror neurons.Keysers, C., & Perrett, D.I. (2004). Demystifying social cognition: a Hebbian perspective. Trends in Cognitive Sciences, 8, 501–507
Its central principle is that associations between sensory and motor representations are acquired ontogenetically (i.e. acquired during development), as a result of correlated sensorimotor experience. Consider the example of an actor clenching their fist. In this situation the activation of the motor representation (the motor plan to clench fist) is often paired with the corresponding perceptual representation (the sight of a closed fist). Heyes proposes that, over time, a bidirectional associative link is formed such that activation of one representation excites the other. Put simply, as a consequence of paired 'doing' and 'seeing' links are established which allow action observation to prime action execution.
In the above example, correlated sensorimotor experience is provided by self-observation. However, this cannot explain the development of sensorimotor associations for so-called 'perceptually opaque' actions. These are actions which cannot be observed by the actor, and include
facial expression
Facial expression is the motion and positioning of the muscles beneath the skin of the face. These movements convey the emotional state of an individual to observers and are a form of nonverbal communication. They are a primary means of conveying ...
s, and whole body actions (e.g. a
tennis serve
A serve (or, more formally, a service) in tennis is a shot to start a point (tennis), point. A player will hit the ball with a racquet so it will fall into the diagonally opposite service box without being stopped by the net. Normally players be ...
). Heyes proposes two other sources of sensorimotor experience to account for the emergence of associations for opaque actions; experience mediated by mirror reflections, and the experience of being imitated by others. When an actor smiles in the mirror, his reflection smiles back. Consequently, a motor representation ("smile") is paired with the corresponding sensory representation (the sight of a smiling face). Similarly, there is considerable evidence that parents imitate young infants.Malatesta, C. Z., & Haviland, J. M. (1982). Learning display rules: The socialization of emotion expression in infancy. Child Development, 53, 991–1003. Thus when an infant 'stumbles across' the motor plan to frown, this may be paired with the sight of a parent's frowning face.
Other sources of correlated sensorimotor experience may also include synchronous action (in dance and sports contexts where actors are executing and observing similar actions) and acquired equivalence experience (where an action excites a visual representation, via a shared auditory representation).
A further defining characteristic of the ASL model is its claim that the development of sensorimotor links is mediated by the same mechanisms of
associative learning
Learning is the process of acquiring new understanding, knowledge, behaviors, skills, values, attitudes, and preferences. The ability to learn is possessed by humans, non-human animals, and some machines; there is also evidence for some kin ...
that produce
Pavlovian conditioning
Classical conditioning (also respondent conditioning and Pavlovian conditioning) is a behavioral procedure in which a biologically potent stimulus (e.g. food, a puff of air on the eye, a potential rival) is paired with a neutral stimulus (e.g. ...
. Crucially, Heyes therefore proposes that the development of sensorimotor associations is not only sensitive to temporal contiguity (the extent to which activation of sensory and motor representations are close together in time) but also to contingency (the extent to which activation of one representation is predictive of the other). This is a crucial feature of the ASL model as it explains why actors do not acquire spurious sensorimotor associations. Consider the example of two interactants, one of whom is scratching his ear when his colleague sneezes. Learning-based models which do not stipulate a sensitivity to contingency predict that the motor plan for ear-scratching ought to become associated with the visual representation of sneezing! However, ASL predicts that no association will develop because the act of ear-scratching is not predictive of the sight of sneezing – in other words there is no sensorimotor ''contingency''. The Hebbian learning account of the emergence of mirror neurons also emphasizes the importance of contingency, as it is known that the
synaptic plasticity
In neuroscience, synaptic plasticity is the ability of synapses to Chemical synapse#Synaptic strength, strengthen or weaken over time, in response to increases or decreases in their activity. Since memory, memories are postulated to be represent ...
that underlies Hebbian learning is known to depend on contingency.
Evidence
Neuroimaging
Neuroimaging is the use of quantitative (computational) techniques to study the neuroanatomy, structure and function of the central nervous system, developed as an objective way of scientifically studying the healthy human brain in a non-invasive ...
studies suggest that the human mirror system is sensitive to sensorimotor experience. Specifically, it appears that mirror system activation is greater when an observer has related motor expertise.Calvo-Merino, B., Glaser, D. E., Grezes, J., Passingham, R. E., & Haggard, P. (2005). Action observation and acquired motor skills: an fMRI study with expert dancers. Cerebral Cortex, 15, 1243–1249.Calvo-Merino, B., Grezes, J., Glaser, D. E., Passingham, R. E., & Haggard, P. (2006). Seeing or doing? Influence of visual and motor familiarity in action observation. Current Biology, 16, 1905–1910. For example, a stronger fMRI response was observed in classic mirror areas (premotor, parietal and posterior
superior temporal sulcus
The superior temporal sulcus (STS) is the sulcus separating the superior temporal gyrus from the middle temporal gyrus, in the temporal lobe of the mammalian brain. A sulcus (plural sulci) is a deep groove that curves into the largest part of ...
) when ballet experts observed ballet sequences, than when they viewed matched capoeira stimuli. The fact that mirror system activation is sensitive to sensorimotor expertise, provides a strong indication that the properties of mirror neurons are acquired through learning.
Heyes and colleagues have also shown that a number of imitative effects, thought to be mediated by the mirror system, may be reversed through periods of 'counter-mirror' sensorimotor training. For example, humans are typically quicker at making imitative responses relative to comparable non-imitative responses. This effect is widely believed to be a product of the human mirror system: Action observation is thought to excite a subset of the premotor neurons responsible for the execution of an action, thus priming execution of the matching response. However, following periods of training during which the execution of one action (e.g. hand open) is paired with the observation of another action (e.g. hand close) the reaction time advantage for imitative responses may be abolished. Similar counter-mirror training has also been shown to reverse classic mirror system effects observed with
transcranial magnetic stimulation
Transcranial magnetic stimulation (TMS) is a noninvasive neurostimulation technique in which a changing magnetic field is used to induce an electric current in a targeted area of the brain through electromagnetic induction. A device called a st ...
(TMS) and
functional imaging
Functional imaging (or physiological imaging) is a medical imaging technique of detecting or measuring changes in metabolism, blood flow, regional chemical composition, and absorption.
As opposed to structural imaging, functional imaging center ...
Catmur, C., Gillmeister, H., Bird, G., Liepelt, R., Brass, M. & Heyes, C. (2008) Through the looking glass: counter-mirror activation following incompatible sensorimotor learning. European Journal of Neuroscience, 28(6), 1208–1215 paradigms.
As predicted by associative learning theory, and therefore by the ASL model, this learning is sensitive to sensorimotor contingency (i.e. the degree to which excitation of one representation predicts the excitation of the other). When there is no contingency between sensory and motor representations; for example, when action execution is equally likely both in the presence and absence of the counter-mirror visual stimulus, little or no learning is observed.Cook, R., Press, C., Dickinson, A. & Heyes, C. M. (2010) Acquisition of automatic imitation is sensitive to sensorimotor contingency. Journal of Experimental Psychology: Human Perception and Performance, 36(4), 840–852.
See also
*
Mirror neuron
A mirror neuron is a neuron that fires both when an animal acts and when the animal observes the same action performed by another. Thus, the neuron "mirrors" the behavior of the other, as though the observer were itself acting. Mirror neurons a ...