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LANGUAGE AND THE MIRROR SYSTEM:A PERCEPTION/ACTION BASED APPROACH TO
COMMUNICATIVE DEVELOPMENT
Michael A. ARBIB*1, Erhan OZTOP2, Patricia ZUKOW-GOLDRING3
1Computer Science, Neuroscience and USC Brain Project,

University of Southern California, USA
2JST-ICORP Computational Brain Project ATR, Computational Neuroscience

Laboratories, Kyoto, Japan
3 Department of Linguistics, University of Southern California, USA

ABSTRACTIn answering "What are the sources from outside the self that inform what thechild knows?", our basic idea is that a shared understanding of action
grounds what individuals know in common. In particular, we root the
ontogeny of language in the progression from action and gesture to speech or
signed language. What then might the evolutionary path to language and theontogeny of language in the child have in common? We can characterize thesource of the emergence of language in both as arising from perceiving andacting, leading to gesture, and eventually to speech or signed language.
Rizzolatti & Arbib (1998) argue that the brain mechanisms underlying humanlanguage abilities evolved from our non-human primate ancestors' ability tolink self-generated actions and the similar actions of others. On this view,communicative gestures emerged eventually from a shared understandingthat actions one makes oneself are indeed similar to those made byconspecifics. Thus, what the self knows can be enriched by an understandingof the actions and aims of others, and vice versa. From this view, the origins
of language reside in behaviors not originally related to communication.
That is, this common understanding of action sequences may provide the"missing link" to language. A corollary of this, not always sufficiently
stressed, is that the full pattern of communication and understanding rests on
a far richer set of brain functions than the core "mirror system for grasping"said to be shared by monkey and human. We report here on the early stagesof a research program designed to integrate empirical cross-cultural studies
of infant communicative development (Zukow, 1990; Zukow-Goldring, 1996,
1997, 2001) with a computational approach to the mirror system in monkey,
human and robot (Oztop & Arbib, 2002). We stress that mirror neurons are
not innate but instead correspond to a repertoire of learned actions andlearned methods for recognizing those actions. Our aim is an integrated viewof how perceiving and acting ground the emergence of language. Our effort
is to integrate analysis of the influences of the environment and, in particular,of the ways in which caregivers attune the child to that environment ("whatthe head is inside of" [Mace, 1977]) with the study of the neural mechanismsthat can learn from these attunements ("what is in the head"). We seek to*

Corresponding address:
E-mail: arbib@usc.edu, erhan@atr.jp, zukow@usc.edu

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©Romanian Association of Cognitive Sciencesdelineate what children might "know" from birth, and the interplay ofperceptual processes with action that might allow them to come to know"what everyone else already knows", including word meaning.
KEY-WORDS: mirror system, language, communication, perception/action

A mirror system primer
In this section we review data on the monkey brain and our own modelingthereof to provide the substrate of basic action recognition mechanisms that we
believe lie at the core of both phylogenetic and ontogenetic accounts of thedevelopment of language capabilities. The neurophysiological findings of the
Sakata group on parietal cortex (Taira, Mine, Georgeopoulos, Murata, & Sakata,1990) and the Rizzolatti group on premotor cortex (Rizzolatti et al., 1988) indicatethat parietal area AIP (the Anterior Intra-Parietal sulcus) and ventral premotor area
F5 in monkey form key elements in a cortical circuit which transforms visual
information on intrinsic properties of objects into hand movements that allow theanimal to grasp the objects appropriately (see Jeannerod, Arbib, Rizzolatti, &Sakata, 1995 for a review.) Other studies lead us to postulate that the storage andadministration of sequences of manual actions (inhibiting extraneous actions, while
priming imminent actions) is carried out by the portion of the supplementary motor
area (SMA) known as pre-SMA and the basal ganglia, respectively, which
cooperate in the phasing in and out of appropriate F5 activity as a given task
unfolds.
Motor information is transferred from F5 to the primary motor cortex(denoted F1 or M1), to which F5 is directly connected, as well as to various
subcortical centers for movement execution. For example, neurons located in area
F5 discharge during active hand and/or mouth movements (di Pellegrino, Fadiga,
Fogassi, Gallese, & Rizzolatti, 1992; Rizzolatti, Fadiga, Gallese, & Fogassi, 1996a;
Gallese, Fadiga, Fogassi, & Rizzolatti, 1996). Moreover, discharge in most F5
neurons correlates with an action rather than with the individual movements thatform it, so that one may classify F5 neurons into various categories corresponding
to the action associated with their discharge. The most common are:"grasping-with-the-hand"
neurons,"grasping-with-the-hand-and-the-mouth"
neurons, "holding" neurons, "manipulating" neurons, and "tearing" neurons.
The FARS model (Fagg & Arbib, 1998) makes clear certain conceptualissues that will be crucial at later stages of the argument. It provides acomputational account of what we shall call the canonical system, centered on the
AIP ! F5 pathway, showing how it can account for basic phenomena of grasping.
Our basic view is that AIP cells encode (by a population code whose details arebeyond the present discussion) “affordances” for grasping from the visual stream
and sends (neural codes for) these on to area F5. Affordances (Gibson, 1979) areproperties of the object relevant for action, in this case to grasping. In other words,
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vision here provides perceptual information on how to interact with an object,rather than categorizing the object or determining its identity.
The FARS model posits a crucial role for IT (inferotemporal cortex) andPFC (prefrontal cortex) in modulating F5’s selection of an affordance. Here, thedorsal stream (from primary visual cortex to parietal cortex) carries among otherthings the information needed for AIP to detect that different parts of the object canbe grasped in different ways, thus extracting affordances for the grasp system
which (according to the FARS model) are then passed on to F5 where a selection
must be made for the actual grasp. However, Figure 1 shows “FARS Modificato”
in which PFC affects affordance selection in AIP rather than F5. This change isbased on anatomical studies (Rizzolatti & Luppino, 2001, 2003). The point is thatthe dorsal stream does not know "what" the object is, it can only see the object
as a set of possible affordances. The ventral stream (from primary visual cortex to

Figure 1. “FARS Modificato”: The original FARS diagram (Fagg & Arbib, 1998) is here
modified to show PFC acting on AIP rather than F5. The idea is that AIP does not “know”
the identity of the object, but can only extract affordances (opportunities for grasping forthe object consider as an unidentified solid); prefrontal cortex uses the IT identification of
the object, in concert with task analysis and working memory, to help AIP select theappropriate action from its “menu”.

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©Romanian Association of Cognitive Sciencesinferotemporal cortex), by contrast, is able to recognize what the object is. This
information is passed to prefrontal cortex which can then, on the basis of thecurrent goals of the organism and recognition of the nature of the object, bias F5 tochoose the affordance appropriate to the task at hand. In particular, the FARS
model represents the way in which F5 may accept signals from areas F6(pre-SMA), 46 (dorsolateral prefrontal cortex), and F2 (dorsal premotor cortex) to
respond to task constraints, working memory, and instruction stimuli, respectively(see Fagg and Arbib 1988 for more details).
Further neurophysiological study of F5 revealed something unexpected – aclass of F5 neurons that discharged not only when the monkey grasped ormanipulated objects, but also when the monkey observed the experimenter make agesture similar to the one that, when actively performed by the monkey, involved
activity of the neuron. Neurons with this property are called "mirror neurons"(Gallese et al., 1996). Movements yielding mirror neuron activity when made by
the experimenter include placing objects on or taking objects from a table, grasping
food, or manipulating objects. Mirror neurons, in order to be visually triggered,require an interaction between the agent of the action and the object of it. The
simple presentation of objects, even when held by hand, does not evoke mirror
neuron discharge. Mirror neurons require a specific action – whether observed or
self-executed – to be triggered. The majority of them respond selectively in relation
to one type of action (e.g., grasping). This congruence can be extremely strict with,for example, the effective motor action (e.g., a precision grip) coinciding with theaction that, when seen, triggers the neuron. For other neurons the congruence isbroader. For them the motor requirement (e.g., precision grip) is usually stricter
than the visual (any type of hand grasping, but not other actions). All mirror
neurons show visual generalization. They fire when the instrument of the observed
action (usually a hand) is large or small, far from or close to the monkey. They also
fire even when the action instrument has shapes as different as those of a human ormonkey hand. A few neurons respond even when the object is grasped by themouth
However, not all F5 neurons respond to action observation. We thus
distinguish mirror neurons, which are active both when the monkey performs
certain actions and when the monkey observes them performed by others, fromcanonical neurons in F5. Canonical F5 neurons are active when the monkey
observes an object and acts upon it, but not when the monkey observes actions
performed by others. Mirror neurons receive input from the PF region of parietal
cortex encoding observations of arm and hand movements. This is in contrast withthe canonical F5 neurons that receive object-related input from AIP. It is the
canonical neurons, with their input from AIP, that are modeled in the FARS model.
In summary, the properties of mirror neurons suggest that area F5 is endowed withan observation/execution matching system: When the monkey observes a motor act
that resembles one in its movement repertoire, a neural code for this action is
automatically retrieved. This code consists in the activation of a subset, the mirror

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neurons, of the F5 neurons which discharge when the observed act is executed by
the monkey itself.
Most analyses of the monkey have focused on the idea of a limited"hard-wired" repertoire of basic grasps, such as the precision pinch and the powergrasp. However, in this article we emphasize that the child – and so, presumably,
the monkey – must learn even the most basic grasps, as well as learn to detect theaffordances for which they are appropriate. Thus, development entails cycles ofperceiving and acting that engender new skills as children notice how thecapabilities of the body relate to affordances of the environment. The basic
capabilities are then extended through learning:
1) Developing a further set of useful grasps (extending the repertoire ofactions for canonical F5 neurons);
2) Observing new affordances that match with the new grasps (extending therepertoire of AIP neurons);
3) Learning the relation between the self's grasping of an object and that ofothers grasping (linking F5 mirror neurons with the appropriate visual
preprocessing and F5 canonical neurons to match the re-presentations ofself-generated actions with similarly goal-oriented actions executed byothers).
An interesting anecdote from the Rizzolatti laboratory (unpublished) issuggestive for further analysis: When a monkey first sees the experimenter grasp a
raisin using a pair of pliers, his mirror neurons will not fire. However, after manysuch experiences, the monkey's mirror neurons encoding precision grip will fire
when he sees the pliers used to grasp a raisin – the initially novel performance has
been characterized as a familiar action.
The notion that a mirror system might exist in humans was tested by two
brain imaging experiments (Rizzolatti et al., 1996b; Grafton, Arbib, Fadiga, &Rizzolatti, 1996). The two experiments differed in many aspects, but bothcompared brain activation when subjects observed the experimenter grasping a 3-D
object against activation when subjects simply observed the object. Grasp
observation significantly activated the superior temporal sulcus (STS), the inferiorparietal lobule, and the inferior frontal gyrus (area 45). All activations were in theleft hemisphere. The last area is of especial interest since areas 44 and 45 in thehuman left hemisphere constitute Broca's area, a major component of the humanbrain's language mechanisms. Although there is no dataset yet that shows the sameactivated voxels for grasping execution and grasping observation in Broca's area,such data certainly contribute to the growing body of indirect evidence that there isa mirror system for grasping in Broca's area.
Moreover, F5 in the monkey is generally considered (analysis by Massimo
Matelli in Rizzolatti and Arbib 1998) to be the homologue of Broca's area inhumans, i.e., it can be argued that these areas of monkey and human brain are
related to the same region of the common ancestor. Thus, the cortical areas active
during action recognition in humans and monkeys correspond very well. Taken
together, human and monkey data indicate that in primates there is a fundamental
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system for action recognition: we argue that individuals recognize actions made byothers because the neural pattern elicited in their premotor areas (in a broad sense)
during action observation is similar to a part of that internally generated to producethat action. This system in humans is circumscribed to the left hemisphere. This
provides the basis for the: Mirror System Hypothesis (Rizzolatti & Arbib, 1998;
Arbib, 2002, 2005): The brain mechanisms crucial to human language in Broca's
area evolved from our non-human primate ancestors' mirror system for grasping
which provides the ability to link self-generated actions and the similar actions ofothers. The Mirror System Hypothesis offers a neural "missing link" for the viewthat manual gesture preceded speech in the evolution of human symbolic
communication, and provides a foundation for the parity property of language,
namely that what a message means to the sender will be, in general, approximatedby what it means to the receiver.
Imitation and attention: affordances and effectivities
The ability to imitate has profound implications for learning andcommunication as well as playing a crucial role in attempts to build upon the
mirror system hypothesis (Arbib, Billard, Iacoboni, & Oztop, 2000; Iacoboni et al.,1999). Our concern is to understand how imitation, especially assisted imitation,
contributes to communicative development.
The empirical literature documents that monkeys do not imitate (Bard &Russell, 1999). Chimpanzees imitate the actions of others in the wild (Quiatt &Itani, 1994), but learn much more complex actions with objects when raised byhumans (Tomasello, Savage-Rumbaugh, & Kruger, 1993) but the pace and extent
of their imitation is very limited with respect to that of humans. Indeed, the vast
majority of human children do imitate, albeit to varying degrees at different ages
and for behaviors that differ in modality and complexity of content (Nadel &Butterworth, 1999; Eckerman, 1993). But such imitation requires the ability to map
the body of the other onto the body of the self, and generate movements which insome sense correspond. If a child know that she is herself like the other (e.g., thecaregiver) she may learn to do what the other does to achieve similar benefits or
avoid risks. But can such an individual spontaneously or after a delay imitate justany "developmentally appropriate" behavior observed without assistance? We
argue, probably not.
Assisted imitation may pave the way to language
Most research investigating the development and implications of imitation
focuses on what the child knows, rather than how on the child comes to know.
Accounting for these achievements usually takes the form of proposing somecombination of cognitive precursors, socio-pragmatic knowledge, or maturing
modules hypothesized to be necessary for the activity (Meltzoff & Moore, 1995,
1999; Tomasello, Kruger, & Ratner, 1993; Uzgiris, 1991, 1999). This literature
documents the age at which the average child can observe someone else's action
and repeat it accurately either promptly or after a delay. In our opinion, this bodyof research underestimates sources of the infants' accomplishments located in the
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©Romanian Association of Cognitive Sciencescaregiving environment. Informed by an integrative view of action and perception,
we offer a somewhat different perspective that also suggests how imitation may
foster the emergence of language.
Greenfield (1972) observed that children imitate those actions that areentering their repertoire. Why might these particular actions be ripe for imitationand not others? Are the children's imitations usually autonomous accomplishments
or do they have a robust history of assistance from others? In answer, we provide
evidence that caregivers invite infants to imitate. On those occasions, caregivers
both direct attention (Adamson & Bakeman, 1984; Tomasello, 1988;
ZukowGoldring, 1989, 1990, 1997) to aspects of the ongoing events and tutor actions to"achieve consensus" (Zukow-Goldring, 1996, 2001). These interactional
opportunities give infants crucial practice in (and a refining of) what to notice anddo, and when to do it. Further, when demonstrating an activity, the caregiver marks
the child's subsequent suitable attempts to imitate with speech and gestures ofapproval or may elaborate the ongoing activity, whereas repeated and revised
messages, dropping the current activity, or remarking on the child's lack of interest
follow inadequate responses. These interactions also may be central tocommunicative development. In particular, engaging in these activities may
provide the means to grasp important prerequisites that underlie communicatingwith language. These basics include knowing that words have an instrumental
effect on the receiver of a message (Braunwald, 1978; Braunwald & Brislin, 1979),
that words refer (Bates, 1976; Schlesinger, 1982, Zukow-Goldring, 1997,
Zukow-Goldring & Rader, 2001), and that coparticipants share or negotiate acommon understanding of ongoing events (Macbeth, 1994; Moerman, 1988;
Zukow-Goldring, 1990, 1997).
Our normal experience is highly multi-sensory, not restricted to the limited
perceptual input of, say, a video clip. Indeed, Stoffregen and Bardy (2001) haveargued that "multisensory perception is not merely the primary type of perception;
it's the only type of perception". In fact, caregivers and children detect “thesomething that something is happening to” as well as "the something that ishappening" through vision, touch, sound, taste, and touch (Michaels & Carello,
1981; Zukow-Goldring, 1997). Especially relevant to this idea is the young infant's
known ability to detect regularities or invariants in the continuous stream ofperceptual information (Bahrick & Pickens, 1994).
We have already mentioned J. J. Gibson's notion of affordances, andembrace his proposal that creatures detect the perceptual structure that specifies theunchanging invariant aspects of ongoing events as well as the structure specifying
transformation and change. However, when we don our "neuroscience hats", wemust note that what Gibson calls direct perception involves subtle processing of
retinal signals by specific brain mechanisms that make the various invariants
available for further processing as a basis for action and perception. Gibson
claimed that people act to perceive and perceive to act, and much of our work in
brain theory (e.g., Arbib, 1989) has stressed action-oriented perception and theaction-perception cycle (see also Neisser 1976). The classic example is that as we
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walk across a room we see more and that more that we see tells us which surfaces
will support our walking, what objects block our way and so on. We now add thenotion of effectivities to the notion of affordances (Shaw & Turvey, 1981; Turvey,
Shaw, Reed, & Mace, 1981): acting itself is informed by what the body can do(effectivities expand as an individual gains skill participating in new activities) as
well as by what the environment affords for action.
However, the child at first lacks the ability to detect by observation alone
how the body relates to the physical layout and to the furniture of the world, except
for the most rudimentary actions. In this regard, our empirical studies ofcommunicative development (Zukow-Goldring, 1996, 2001) have stressed, in
addition, that during interaction, the perceiving and acting of one person
continuously affects the perceiving and acting of the other. We thus propose thatcaregiver practices guide the infant to perceive possibilities for action(Zukow-Goldring, 1997, 2001; Zukow-Goldring & Ferko, 1994). Our point is not
to deny that children can learn certain things for themselves by trial-and-error.
Clearly the physical environment or layout affects us and we surely affect it
continuously, but we stress too the mutuality of the person and the social
environment. That is, by directing the child's attention to its own effectivities inrelation to affordances in the environment, the caregiver greatly narrows the search
space for learning, and consequently enhances the speed and extent of learning.
Further, these caregiver practices or methods may educate infants to notice that the
infant is "like the other" through interactions that explicitly foreground thecorrespondence between the effectivities of the infant-actor's body and that of the
caregiver. In any novice-expert interaction, whether infant and caregiver or student
and teacher, the perceiving and acting of one person continuously informs that ofother interactional partners.
Educating attention: from being a body to becoming a cultural being"like the other"
What do infants have to learn about the world in order to communicate
about what’s happening? Infants must learn the most basic things (even about),e.g., taking a bath, eating with utensils, walking. During mundane activities, infants
must detect and participate in assembling the structure and organization of
everyday events before they can communicate with others about these events. Outof the unceasing perceptual flow, which is quite unlike the highly edited cuts ofmost movies, caregivers continuously educate attention to aspects of ongoing
events. This assistance guides infants to notice key elements of what persists andwhat changes. Caregiver gestures make perceptual structure prominent throughtranslational movements that often occlude other information in a scene. In thesame vein, placing objects close to the child’s face ensures attention and theinescapability of details (Zukow-Goldring, 1997).
Caregivers embody or put infants through the motions of activities as well
as direct attention to the similarity of the one's own body to those of others, to therelation of the body to specific objects and animate beings, and to what these246 2005 • Cogniţie, Creier, Comportament
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objects and animate beings afford for action and interaction. In contrast, manystudies and theories assume that children know and/or learn autonomously how
their bodies move in space and in relation to animate and inanimate things (Piaget,
1962, Thelen & Smith, 1994), and thus do not explore what experiences mightunderlie eventual adept performance. We thus stress again the role of the caregiverin directing attention to effectivities as well as affordances – the two sides of themirror system. These interactive sequences eventually invite imitation.
Caregivers talk about what they are doing as they do it. Often children
initially misunderstand these actions and spoken gestures, in part, because words
cannot explain unless the child already knows what the words means. Given thesecircumstances, how is consensus achieved as the child becomes an adept memberof the community? Our approach integrates perception, the building of action, andthe meaning of words, despite the fact that many studies of language acquisition
assume that gestures entail ambiguity of reference (Markman, 1989; Schlesinger,1982). These authors rely on Quine's classic essay (1960) in which he discussed theambiguity of reference entailed in, say, speaking about and pointing to a rabbit. But
caregivers tend to focus attention with precision. They do not simply say anunfamiliar word (such as Quine's gavagai) while pointing. Instead, caregivers may
rub a rabbit's fur while saying, “fur”; trace the topography of its ears while saying,“ear”, stroke the entire rabbit or rotate the whole animal when saying, “rabbit”, etc.
(Zukow-Goldring, 1990, 1996; Reed, 1993). Successful teaching entails marking
the correspondence between what is said and what is happening.
In what follows, we shall illustrate the findings from a number of studies of
infant development with some qualitative examples (Zukow-Goldring, 1996, 1997,
2001). The final section will use our modeling of the development of grasping andthe grasp-related mirror neuron to advance our understanding on how the mirror
system grounds imitation as a core component of communicative and linguistic
development within an action/perception framework.
The naturalistic experiments
Infants are immersed in talk: some directed to them, some to others, someto prohibit action, some to direct attention to something new or when the child does
not understand an utterance. We argue that at early stages of communicative
development, learning that words mean and what they mean entails having anembodied understanding of the organization and structure of relevant aspects ofdaily life. Concomitantly, the child must notice that others mark the relation
between what is said and what is happening, and how they do so. To support thisview, we summarize key results from a series of naturalistic experiments we
conducted to clarify how children come to comprehend initially misunderstoodmessages (Zukow-Goldring, 1996, 2001). In these studies we tested the following
hypotheses:
1. Providing a child with more perceptual structure will assist caregiver andchild to achieve the consensus needed for communication, including,where appropriate, explicit guidance of the child's movements.
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2. Additional or more specific verbal information will not enhance
understanding when no basis for that understanding has yet been
embodied.
The studies reported illuminate how a human child learns about the world.
Of course, we are not denying the utility of verbal instruction for older children.
Rather, our purpose is to illustrate how the fundamental link between perception
and action provides the information upon which communication can build. It is aseparate study to understand the later "bootstrapping" that occurs when words cantake a far greater role in advancing what the child knows.

MethodSubjects: Five Euro-American families and six Latino families with an
infant of 6 months were followed monthly through the one-word period.
Data: We collected twenty-minute monthly videos of naturalistic
interaction at home, field notes, diaries and check lists of lexical development, as
well as interviews following each video-taping session to ascertain the caregiver's
interpretation of ongoing events and of the infant’s utterances.
We selected situations in which caregivers directed infants to noticespecific elements, relations, or events over the myriad other possibilities available.
This collection of attention-directing interactions included all instances ofperceptual imperatives expressed by caregivers, such as look!/¡mira!, listen!/¡oye!,and so on, as well as the accompanying gestures, and the gestures alone as well as
the infants' subsequent actions. Zukow-Goldring noticed this set of perceptual
imperatives when doing field-work in Mexico (1981-1982). They occurredmassively. Caregivers constantly said, ¡Mira!/Look!. While we do not claim there
is a Mira neuron, the use of perceptual imperatives may help draw the child's
attention to the gestures that co-occur with them. These gestures may, in turn,provide specific support for imitation by directing attention to the perceptual
information (in touch, smell, taste, vision, movement, and hearing) that lays thegroundwork for knowing that the self is like others. Thus, this ability opens up the
possibility of learning the actions that others display. A key issue then is todetermine the relative importance for the young child of verbal messages versus
gestures that educate attention and action. The distinction here is between words
that provide explicit instructions, such as Peel the orange!, and the pairing ofperceptual imperatives like ¡mira! and gestures that direct the child to attend to theactions of the caregiver. Our conclusion will be that explicit verbal instructions are
ineffective in the early stages. During these early stages children notice thoseaffordances and effectivities that provide the referents for the initial developmentof their lexicon.
Perceptual structure: targets of attention
Caregiver messages combine gestures with targets of attention throughout
the prelinguistic and one-word periods. In messages caregivers express what
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persists and changes as events coalesce and disperse. The targets vary in semantic
complexity. The first three levels of caregiver messages that we have observedroughly parallel the three levels of semantic development described by Greenfieldand Smith (1976) and Zukow, Reilly, and Greenfield (1982). Level I includes
occasions when the caregiver might present a nondynamic object or animate being
in the child's line of sight, such as showing a toy or pointing to a person or animal
while saying, Look at the duck/Grandpa!. Level II consists of messages expressing
an object or animate being undergoing some change through action (Look, pushthem) or in which a state or attribute is asserted about someone or something (Lookat the little doll.). For Level III caregivers talk about more complex relations
involving location (patch of dirt), instruments (eating utensils, crayons), part/whole
relations (hair/head), possession (my, your), quantity (several of something), classmembership (another something), concatenations (stacking objects that share acommon surface), nestings (embedding one thing in another), such as saying, Look,
put the bead in the pail!. Messages at Level IV express the relation between events(Look, take your ball to your brother, so he can put it away.). These targets ofattention embody structural and transformational invariants in the environment
across space/time. Caregiver messages in both cultures communicate perceptual
structure and/or semantic functions that are a step or two ahead of those expressed
in infants' speech (Zukow-Goldring, 1997).
Attention-Directing Gestures: Infant-CaregiverNo
GestureEmbodyShow

Demonstrate

Point

Look

Figure 2. Attention-Directing Gestures

Five gestures that direct attention often accompany caregivers' verbal
messages (Figure 2). These gestures encompass varying degrees of other- to selfregulation of attention to the effectivities of the body and the affordances of theenvironment.
Embody: a caregiver puts an infant through the motions of some activity(e.g., the caregiver takes the child’s hand, using it to press down a lever as he says,¡por abajo!/ down!). The child already "knows" the movement, but this is a new
way to match or fit the effectivity of the hand/arm movement to the affordance ofan object.
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Show: caregivers regulate the infant's line of sight with a translationalmotion or perform some action using a familiar bodily effectivity to introduce a
new possibility for action with an unfamiliar object or affordance. For instance, thecaregiver looms an object toward the infant, saying, gwow-wow/wow-wow whilelooming a puppy or pushes a button on a new toy, saying, ¡empújalo!/push it!.
Demonstration: an infant is invited to act/imitate through action and/or
speech (¿Y tu? or You do it!). The infant who watches closely must detect or pickup in the perceptual flow a familiar coupling of effectivity and affordance to be
duplicated. For example, the caregiver may synchronize rhythmically retracting
fingers of an upright palm with saying, adiocito/bye-bye when catching gaze andsmiling. Alternately, an infant may be asked to pretend to avoid the sharp spines ofa prickly-pear while the caregiver mimes approaching and pulling away from thefruit's surface, saying, ¡espinoso!/prickly!.
Point: the infant must detect where a gesture's trajectory through spaceconverges with some target of attention (the caregiver pointing to and saying,p'acá/over here).
Whereas adults take following a point for granted, infants must learn totrace its projected trajectory through time/space. As the infant develops, caregivers
gradually increase the difficulty and shift the burden of tracing the trajectory fromthe caregiver to the infant. This work suggests a developmental sequence in which
the caregivers of younger infants frequently point-tap a proximal target of attention
with an index finger, thereby tracing the entire trajectory (point-tap a lever). Next
caregivers often point to objects or animate beings close at hand. Learning tofollow distal points to a target across the room or in a large, open area outside
appears near the end of the second year. Caregivers may trace the entire trajectoryfrom the corner of the child's eye across a busy environment (a kitchen full ofpeople) to an indistinct target (clothing spattered with beaten egg white) or may
throw a small object, such as a rock or seed pod, to trace the trajectory thateventually intersects the place where the target can be found. These preliminary
results document that learning to follow a point is another ability that is not asolitary achievement, but one in which caregivers educate attention.
Look: no gestures accompany the caregiver's speech. Instead, only the
caregiver's words and gaze direct the infant to correlate attention with that of the
caregiver.
Our longitudinal data suggest that caregivers of less advanced infants (notnecessarily younger infants) embody and show most frequently, shifting todemonstrations, points, and eventually looks as the infant develops(Zukow-Goldring, 1997).
Consensus: We determined whether or not caregivers treated their infants'
responses to each message in a sequence as adequate or not. Action or speech
indicating approval or embellishing the ongoing activity followed acceptableattempts, whereas inadequate responses were followed by repeated and revised
messages, terminating the current activity, or noticing the child's lack of interest.

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Perceptual Structure: We scored each message in a sequence after the
initial one as providing or failing to offer additional perceptual structure. (Forfurther detail, see Zukow-Goldring, 1996, 2001).
Linguistic Specificity: We assessed each sequence, message by message,
for increases or decreases in linguistic specificity. Linguistic messages in ensuingturns can contain more or less explicit expression of nouns and verbs andpreviously ellipted lexical items. For instance, when adding linguistic specificity,
the caregiver might say, Peel it! and then You peel the orange! Caregivers also can
express less specificity in subsequent messages, e.g., Peel it! followed by Do it!.
Qualitative examples: assisted imitation
The caregiver demonstrates the action(s) and then gives the infant a chanceto act. Quite often the infant's attempt is inadequate. Caregivers take care toarrange the physical layout, so that the configuration in space of caregiver, infant,and object(s) makes them suitably aligned in space so that action is within reach. In
addition, optimal proximity makes perceptually prominent what the object or some
aspect of it affords for action. Frequently the caregiver embodies the infant, so thatthe child can perceive the relation of his or her body in terms of posture, motor
actions, rhythm as it changes over time to accomplish the action or action
sequence.
In the following examples, the infants' unsuccessful attempts at "delayed"
imitation with toys and a food item display some familiarity with the culturally
relevant use of these objects. The three examples below focus mainly on: (1)tutoring effectivities and affordances to learn to concatenate objects (Pop Beads);(2) learning a sequence of actions to consummate an activity (Vibrating Toy); and(3) illustrating that more explicit verbal messages do not usually disambiguate
initially misunderstood messages at this early level of lexical development; rather,
providing more perceptual structure allows mother and daughter to achieveconsensus (Orange Peeling). Even though these objects and their uses are notentirely novel, what is required to imitate apparently is. That is, the ability to notice
the relevant affordances and coordinate them with particular effectivities that arenecessary to accomplish these tasks is not available to the infant without assistance.
Their fragmentary, flawed attempts to imitate actions observed in the past elicit
very careful and elaborate tutoring on the part of the caregivers to direct attention
to relevant affordances and effectivities. Going further, we need to understand how
picking-up the perceptual information that the caregiver is completing an action
can provide the basis for detecting the affordances that will guide children in theirattempts to imitate that action.
Pop beads (13 months): caregiver tutoring of effectivities and affordances
when concatenating beads
Pop beads, easily graspable by infants and toddlers, have affordances thatallow concatenation. Play with this toy consists of (a) orienting toward each otherthe parts of each bead that afford concatenation (the dual complements ofIunie 2005 • Cogniţie, Creier, Comportament

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protrusion and opening), (ii) moving the appropriately oriented beads toward eachother on a converging path, and (iii) applying enough force when the parts meet toembed the protrusion of one in the opening of the other.

Figure 3. Pop Beads.

The infant, Angela, begins by pressing a block lacking the appropriate
affordances and a pop bead together. She displays an understanding thatcompleting the task requires two small graspable objects and the application ofsome force to bring them together (Figure 3, PB1). Her behavior provides noevidence that she knows that a set of objects with specific parts must come252 2005 • Cogniţie, Creier, Comportament
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together, nor that they must sustain an orientation as they meet along a converging
path. Her mother, Cecilia, provides perceptual information to Angela, graduallyforegrounding the affordances of the objects and the effectivities of the bodyrequired to put the beads together. At first, Cecilia provides a bit of both,
point-touching the opening on one bead (but not the protrusion in the other) as she
directs attention to an affordance (PB2) and then reorients another bead (PB3),
enacting a movement that aligns the beads on the same converging path.
Lacking at this point, however, is information displaying the path itself or
the force required to push the converging objects together. After an unsuccessfulattempt by Angela, Cecilia shows her what the body must do to move the beads
along a path with the required orientation as she pushes the protrusion into the
opening with appropriate force (PB4). The infant remains unable to put the beads
together (PB5) The mother then more elaborately provides perceptual information
as she slowly point-touches both the affordances of protrusion (PB6) and opening(PB7), followed by demonstrating the effectivities required for connecting and thendisconnecting of the beads (PB8). As the infant watches more intently, Cecilia
eventually invites Angela to imitate, "¿A ver, tu?/Let's see, you (do it)?". She
assists her daughter's imitation by partially demonstrating what to do by orienting
a bead opening toward Angela, making the protrusion easy to see on the second,and holding it in a fixed position (affordances for action) (PB9). Angela moves thebead along the appropriate path (PB10), but she misorients her bead as the beads
touch one another (PB11). Cecilia reorients hers to place it back on a converging
path. The realignment makes prominent just where Cecilia should push in her bead.
As the infant pushes in the protruding end of her bead, the mother pushes from the
opposite direction with enough force to link the beads (PB12).
In this case, the caregiver's gestures gradually provided increments inperceptual information that guided the infant to concatenate two objects.
Eventually, the caregiver simplified the task by holding an appropriately oriented
bead as a fixed target. This assistance allowed the child to bring her slightly
misoriented bead (i) along a path toward her mother's (ii). Angela pushed her beadagainst the other (ii), while her mother subtly reoriented her bead (i) and provided acomplimentary push. Notwithstanding Angela's noteworthy improvement on thisoccasion, bringing together two hands, each grasping a properly oriented object,
was not within her "reach". Nor could she by herself apply enough force to connect
her beads. It is possible that embodying Angela, putting her through the motions,might have drawn maximal attention to the coordination of the affordances of thebeads and the effectivities of the body required to consummate this activity. The
point is that the young child cannot simply observe a complex activity and imitate
it. Much tutoring is required to build a repertoire on which “true” imitation (if such
exists!) can take place.
Vibrating toy (14.5 months) - caregiver and "toy" tutoring of a sequence ofactions
This infant, Elsa, and her mother, Kathy, engage in a familiar routine witha reindeer toy that has a hidden affordance, a spring inside the toy to which a string
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is attached. Family members had played this "game" with Elsa quite frequently
during the prior eleven months. However, she had never attempted to imitate theothers. In this routine, when the caregiver pulls on a ring that protrudes from theback of the toy, the string unwinds. Releasing the ring/string at the apex of its
extension retracts the string so quickly that the toy vibrates strongly accompanied
by a loud pulsing noise. Elsa expresses delight when she feels the vibrating toy
placed on her stomach. Elsa, however, cannot make the toy vibrate by herself. This
"game" entails a sequence of actions: (i) someone grasps the string by the ring, (ii)the string unwinds as it is pulled and (iii) retracts within the toy as the tension on
the string lessens. Finally, (iv) someone places the reindeer toy on the infant's
stomach. In this example, we place more emphasis on the sequence of actions thanon the briefly noted affordances and effectivities that mother and toy makeperceptually available. For conciseness sake, we have abbreviated this sequence,omitting repetitions and variations leading to the child's final adept enactment of
this activity.
Elsa, sitting in front of her mother, turns to give her mother, Kathy, the toythat she wants her to animate (Figure 4, R1).
Kathy pulls the string out by the ring (R2), releases the string and places
the vibrating toy on Elsa's stomach (R3). When Elsa wants her mother to continue,
Kathy says, You do it!, as she partially demonstrates by orienting the back of the
toy toward Elsa, making the ring for pulling (affordance) prominent and within theinfant's reach. The infant grasps the ring (R4). The mother embodies by holding
Elsa's hand and the toy steady as she pulls the toy away from them, presumably so
the infant can feel the tension (affordance) as the string unwinds (R5). The spring
attached to the string embodies Elsa by pulling her hand back toward the toy (R6).
Subsequently, the infant pulls the string out herself (R7) and holds on as the springembodies by retracting the string back into the toy (R8). At this point, the toy
vibrates weakly, if at all. A few seconds later, Elsa pulls the string so quickly andfully out, that the tension on the string embodies her by snapping the ring from her
fingers. This adept use of her body when pulling the string forcefully (effectivity)
allows her quite serendipitously to experience how to take advantage of thevibratory properties of the toy (affordance). Note that her arm recoils from theforce moving quickly away from its former position, while the hand holding thestrongly vibrating toy moves far in the opposite direction (R9). Within seconds,
Elsa first pulls and lets go of the string and then places the base of the toy on her
stomach to best perceive the vibrations as she expresses evident joy (R10).
Note the free building up of a sequence, as the child understands each newelement. Both caregiver and toy educate Elsa's attention to new affordances and therefining of her actions (effectivities) to fill in the gap between grasping the ring andfeeling the vibration of the toy on her stomach. Elsa experiences bodily the tensionof the string unwinding as her mother pulls the toy away from her and as the spring
hidden in the toy that controls the string retracts as the string appears anddisappears. Pulling the string out is within Elsa's grasp. However, the accidental
snapping back (letting go) of the string at the apex of its path and at its highest
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Figure 4. Vibrating Toy

tension made evident the relation between the effectivity of releasing the string andthe ensuing affordance of the toy's vibrations. By the second attempt, Elsa hadplaced the toy to bring the most enjoyment. Within the next several minutes, shechanged her grasp from a finger crooked through the ring to a pincer grip, could
pull the string with both right and left hands, and attempted to give her doll thesame experience. Although she knew "that" the toy held potential for vibrating, she
did not know "how" to make it happen until she received very careful tutoring. This
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educating of attention and action contrasts sharply with the effort it takes to tutor
the attention and action of monkeys as well as autistic children (Fogassi, personalcommunication; Nadel, Guérini, Pezé, & Rivet, 1999).
Orange peeling (16 months) - caregiver tutoring "when actions speak
louder than words"
Peeling an orange with the hand entails penetrating the peel (both zest andpith), grasping the pulled away edge in a pincer grip, pulling the peel away fromthe flesh, and separating that portion of the peel from the fruit. Tearing off a pieceof peel may involve yanking it away or, if the zest is tough, rotating the wrist at a
90 degree angle from the fruit. Thus, what to an adult seems like a single action
must for the child be learned as a sequence of grasps and directed actions.
In the first vignette, the infant, who is quite fond of oranges, has seen thempeeled and wants to do so herself but cannot. She scratches quite ineffectually at
the surface of the peel, but does not know how to remove it. Angela needs hermother's help to learn the actions that go into peeling an orange. However,increasingly explicit verbal messages (Let’s see. Peel it! You peel! Take it off like
this, look!) coordinated with a variety of points, ranging from a subtle head point toproximal points of hand and index finger, do not communicate just how to peel anorange. In contrast, embodying the child provides the missing perceptual
information (Figure 5A, Vignette 1) regarding how effectivities of her body and theaffordances of the orange continuously inform one another. The mother's hands
shadow and guide those of the child as together they each support the orange with
one hand and pull off the peel with the other together. Embodying the infant
provides her with perceptual information in vision, touch, and movement that she islike her mother (the other). (For more detail, see Zukow-Goldring, 2001.).
In the second vignette (Figure 5B), Cecilia partially demonstrates bypulling the peel nearly free of the orange. Angela easily removes that bit of peeling.
In vignette three (Figure 5C), Cecilia ups the ante by lifting the peel just asmall distance away from the flesh. In the third frame below the mother mimes
what she says, Duro duro duro! Fuerte fuerte fuerte!/Hard hard hard! Forcefully
forcefully forcefully! However, she provides perceptual information for bothmanner of action (hard, forcefully) and trajectory (a change in direction of about
ninety degrees) in gesture, but only for manner in speech. Note that trajectory is theinformation that helps solve the problem, illustrating when and that gestures"speak" louder than words (Kendon, 2002). Although Angela changes the directionof her pulling about 45 degrees (compare frames 2 and 5), Cecilia helps by
showing how to pull away the peel at a more extreme angle.

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Figure 5A. Orange Peeling, Vignette 1: Hand, head, and finger points andincreasingly specific verbal messages do not convey just how child and orange
engage in "you peel it". Cecilia embodies her child to provide the missing
perceptual information.

Figure 5B. Orange Peeling, Vignette 2: Cecilia partially demonstrates by lifting
the peel almost entirely free of the flesh. She invites Angela to join in, saying Aver, estírale/Let's see, pull it. Now, Angela knows how.

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Figure 5C. Orange Peeling, Vignette 3: Cecilia makes the task more difficult,peeling only part way through the pith. Angela cannot tear through the zest.
Cecilia mimes "strong and hard" as well as change in direction. Angela imitates,
but still needs help.

We have argued that ambiguity is the rule, not the exception. Words cannot
explain unless a person already knows what words mean. To understand whatwords mean a person must understand what is happening. Novices do not
automatically understand the organization and structure of daily events. Experts
show them. These qualitative examples emphasize the finding that caregivers work
hard to cultivate their infants’ understanding of ongoing events by providing
perceptual information to disambiguate their initially misunderstood messages.
When there is lack of consensus, providing more perceptual structure tends toresolve misunderstanding, whereas adding specificity to verbal messages did not
reduce ambiguity. Perceptual restructuring of messages following communicative
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breakdowns led to achieving a common understanding whether in Spanish or in
English.
In sum, caregivers establish an understanding of what is happening. They
provide and direct attention to perceptual structure that makes prominent therelations among animate beings, objects and their actions. These dynamic relations
specify the organization and structure of the most mundane daily activities.
Caregivers introduce their infants to new effectivities or bodily capabilities andaffordances for action and interaction on a daily basis. They assist them to linksequences of actions that comprise more and more complex activities. Caregivers
also set aside language training when communication breaks down and, instead,focus on providing the perceptual information that will lead to a consensus. As
caregivers educate attention, infants gradually learn to perceive, act, and know in
culturally relevant ways.
Modeling development

Object recognition
IT
Objectaffordance
extraction(FARS-AIP)

Object features

Visual Cortex

cIPS

H and
shape
recognition& Handm otiondetection
STS

F5canonical

AIP

Object affordance-hand state
association

Motor
program(Grasp)Integrate
temporalassociation

7b

ActionMirrorFeedback recognition

H and-Object
spatial relation
analysis
7a(MirrorN eurons)

Motor
program(Reach)F5mirror

F4

Motor
execution
M1

Objectlocation
MIP/LIP/VIP

Figure 6. The Mirror Neuron System (MNS) Model, which extends the earlier FARS
model. (Oztop and Arbib, 2002)

We have already mentioned the FARS model of the canonical system (Fagg &Arbib, 1998; Figure 1) that shows the importance of object recognition(inferotemporal cortex) and "planning" (prefrontal cortex) in modulating theselection of affordances in the determination of action. Figure 6 provides a glimpse

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©Romanian Association of Cognitive Sciencesof the schemas (functions) involved in the monkey mirror system1. In this section
we first briefly review the elements of Figure 6 and then indicate the stages ofmodeling required to place this system in a developmental perspective. This isfollowed by the briefest review of completed work on modeling fragments of thesestages. This review grounds our analysis of the challenges for future modelingwhich unites these modeling efforts with analysis of the data reviewed above on aperception/action based approach to communicative development, and how these
considerations may provide a developmental counterpart to the Mirror System
Hypothesis (Rizzolatti and Arbib, 1998) on the evolution of brain mechanisms
supportive of language.
First, we look at those elements involved when the monkey itself reaches
for an object. Areas IT and cIPS provide visual input concerning the nature of theobserved object and the position and orientation of the object's surfaces,
respectively, to AIP. The job of AIP is then to extract the affordances the object
offers for grasping. The upper diagonal in Figure 6 corresponds to the basic
pathway AIP → F5canonical → M1 (primary motor cortex) of the FARS model,
but we will not dwell here on the role of PFC in action selection that was soimportant in the FARS model. The lower right diagonal (VIP → F4) completes the"canonical" portion of the MNS model, since motor cortex must not only instruct
the hand muscles how to grasp but also (via various intermediaries) the arm
muscles how to reach, transporting the hand to the object. However, we stress herethat MNS (and the ILGM model described below) are "non-neurophysiological"
models in the sense that we do not formulate separate models for each of thesebrain regions, coupling them in a way which represents the anatomy of the brain,
and decomposing them into neural networks whose structure matches the observed
connectivity of neurons within that region of the given brain. Instead, we simulate
several "schemas", which represent the functional equivalent of the aggregate ofseveral such brain regions without matching their internal structure. Nonetheless,even these models have implications for neurophysiology since they do containpopulations of simulated neurons which correspond well with actual neural
populations of the monkey brain, even when no such "neural matching" need holdfor the simulation that provides their input and output.
The rest of the diagram presents the core elements for the understanding of
the mirror system. As we have seen, mirror neurons do not fire when the monkey
sees the hand movement or the object in isolation – it is the sight of the handmoving appropriately to grasp or otherwise manipulate a seen (or recently seen;
Umilta et al., 2001) object that is required for the mirror neurons attuned to the1

For our present purposes, it is not necessary to pursue the hypotheses on where different schemas
are located in the brain. In this paper, it will be the development of function that is of concern, rather
than where in the brain the neural changes occur that mediate that development. Thus, in what follows
we will use the abbreviations for brain regions without further explanation. For some readers, theabbreviations may just be seen as bizarre labels for the different functions diagrammed in Figure 6.
Those readers wanting to see the abbreviations spelled out, as well as a brief exposition of data related
to the hypothesized linkage of functions to brain structures, are referred to Oztop and Arbib (2002)
and Arbib & Bota (2003).

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given action to fire. This requires schemas for the recognition of both the shape ofthe hand and analysis of its motion (ascribed in the figure to STS), and for analysisof the relation of these hand parameters to the location and affordance of the object(7a and 7b in the figure). In the MNS model (Oztop and Arbib, 2002), the "handstate" was accordingly defined as a vector whose components represented the
movement of the wrist relative to the location of the object and of the hand shape
relative to the affordances of the object.
Learning in the mirror system
Oztop and Arbib (2002) showed that an artificial neural network
corresponding to 7b → F5mirror could be trained to recognize the grasp type fromthe hand state trajectory, with correct classification often being achieved wellbefore the hand reached the object. The situation simulated was that of training
mirror neurons for grasps already in the repertoire of the simulated monkey. Moreprecisely, we assume that the neural equivalent of a grasp being in the monkey's
repertoire is that there is a pattern of activity in the F5 canonical neurons thatcommands that grasp. During training, then, the output of the F5canonical neurons,
acting as a code for the grasp being executed by the monkey at that time, was usedas the training signal for the F5mirror neurons. As a result of this training, theappropriate mirror neurons can fire in response to the hand state trajectory evenwhen the trajectory is not accompanied by F5canonical firing – and thus the F5
mirror neurons are prepared to respond to hand state trajectories even when thehand is of the "other" rather than the "self".
In other words, the simulated F5 mirror system could learn to produce theneural code for a grasp even when the F5 canonical neurons were silent, correctlyclassifying the encoding of the hand state trajectory (the object-hand relation
encoded by 7a and the hand motion information encoded by STS) that it received
after recoding by 7b, with this recoding being itself dependent on learning. This
provides "action recognition" because the hand state is defined in such a way thatthe relevant data can be based on the movement of any hand, whether that of self orother, relative to the object. Of course, what makes the modeling worthwhile wasthat the trained network responded not only to the training set trajectory (theobject-hand relation encoded by 7a and the hand motion information encoded bySTS) that it received after recoding by 7b, with this recoding being itself dependent
on learning), but also exhibited interesting responses to novel hand-object
relationships. Despite the use of a non-physiological neural network, simulations
with the model revealed a range of putative properties of mirror neurons thatsuggest new neurophysiological experiments. To close this discussion of MNS, we
stress that although it was constructed as a model of the development of mirror
neurons in the monkey, we believe that it serves equally well as a model of thedevelopment of mirror neurons in the human infant. A major theme of the future
modeling that this article delineates, then, is to clarify which aspects of humandevelopment are generic for primates, and which are specific to the human
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repertoire. As we shall now see, further work is required to understand how it is,for example, that an infant appears to understand the hand actions of a parent
preparing to feed him long before the infant can feed himself – the infant
anticipates and opens his mouth before the spoon arrives.
Learning to grasp
The MNS model makes the crucial assumption that the grasps which themirror system comes to recognize are already in the (monkey or human) infant's
repertoire. But this raises the question of how grasps entered the repertoire. To
simplify somewhat, there are two answers: (i) Children explore their environment
and as their initially inept arm and hand movements successfully contact objects,
they learn to reliably reproduce the successful grasps, with the repertoire being
tuned through further experience. (ii) With more or less help from caregivers,
infants come to recognize certain novel actions in terms of similarities anddifferences from movements already in their repertoires and on this basis learn toproduce some version of these novel actions for themselves. In terms of Figure 6,
we might say that if MNS were augmented to have a population of mirror neurons
which could acquire population codes for observed actions not yet in the repertoireof self-actions, then in case (ii) the mirror neurons would provide training for thecanonical neurons, reversing the information flow see in the MNSI model. We notethat this raises the further possibility that the infant may come to recognize
movements that are not only not within the repertoire but which never come to bewithin the repertoire. In this case, the cumulative development of action
recognition may proceed to increase the breadth and subtlety of the range ofactions that are recognizable but cannot be performed by children. These
considerations will prove especially important for our further work on thephylogeny and ontology of language, and make clear why that work goes under theslogan "Beyond the Mirror" to emphasize that the functionality common to monkey
F5 mirror neurons and human Broca's area will be a small part, no matter how
crucial, of the final analysis. However, for the present paper, we limit ourselves to
two further accounts,(a) the description of two views of a completed models for autonomous grasp
development, and(b) a high-level view of prospects for modeling the learning of new actions withthe assistance of a caregiver.
Our first view of the model of how the infant or monkey learns to grasp, ILGM,
the Learning to Grasp Model (Oztop, Bradley and Arbib, 2004; see Oztop, Arbib
and Bradley, 2005, for further exposition) takes seriously the claim that this basicstage is common to monkey and human infants, and uses as its database what is
known about how human infants develop grasping skills. From the first, an infant
learns its own possibilities for action in the environment, and the affordances ofobjects, through exploratory behavior. By 2-3 months, infants start exploring theirbodies as they move in the environment, they babble and touch themselves and also
start to stare at their hands (Bayley 1969). Infants progress from a crude ability ofreaching at birth to finer reaching and further grasping ability around four months
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©Romanian Association of Cognitive Sciencesof age. Infants learn to overcome problems associated with reaching and graspingby interactive searching (von Hofsten 1993; Berthier, Clifton, Gullapalli, McCall,& Robin, 1996).The precision grasp appears around 12-18 months of age (Berthier,
Clifton, McCall, & Robin, 1999). To grasp successfully infants have to learn how
to control their arms and, further, to match the abilities of their limbs withaffordances presented by the environment (Bernstein 1967; Gibson, E. J., 1969;
Gibson, J. J., 1988; Thelen 2000). At first, the poorly controlled arm, trunk andpostural movements make it very difficult for the young infant to generateconsistent feedback to form stable links between perceptual and motor schemas.
However, Rochat and Morgan (1995) have shown that infants are aware of avariety of visual, proprioceptive and haptic consequences of their limb movements.
The child's grasping can be affected by haptic cues by 4 months (Newell 1986),
while infants as young as 5 months may abort their reaches if vision of the hand isremoved (Lasky 1977). All this yields a well established set of grasps, including
the precision grip, with preshaping to visual affordances by 12-18 months of age(Berthier et al. 1999).
ILGM models the discovery of grasps that match the affordances presented
by the objects in the environment. The advent of voluntary grasping of objects is
preceded by several weeks in which the infant engages in arm movements andfisted swipes in the presence of visible objects (von Hofsten 1984). An infant, once
contacting an object, will occasionally try to grasp it (Clifton, Muir, Ashmead, &Clarkson, 1993). Normal infants very quickly (in a few weeks) acquire the ability
to habituate and sculpt hand movements in the presence of a palmar stimulus –cutaneous reflexes initially aid or increase the probability in securing grasp of an
object and then come to selectively use them to assist their movements. By aroundseven moths the infant is able to stabilize the grasp (Clifton et al. 1993). However,infants do not readily demonstrate control over fractionated finger movements
before the end of the first year, even though fractionated finger movements may
occur spontaneously and much earlier in the noise of random movements – we may
speak of "motor babbling", comparing it to the infant's (vocal) babbling whichcontains many sounds that will later emerge in purposeful language. Adults
preshape the hand during hand transport, e.g., adjusting the distance between the
thumb and other fingers according to the size of the object. In contrast, before ninemonths of age, infants adjust their grasps after touching the object, lacking
anticipation of the orientation and size of the object (Rosenbaum 1991). This holds
even though infants younger than nine months old are physically able to vary theirgrip size, for they can spread their fingers farther apart once they have felt a large
object (von Hofsten and Ronnqvist 1988). Newell (1986) identified rudimentary
hand shaping after contact starting at 4 to 6 months, whereas 7 to 8 month olds did
not appear to need contact to initiate shaping. Von Hofsten and Ronnqvist (1988)
found that children would start shaping the hand midreach by 9-13 mos. It appears
that in early infancy the fractionated control of fingers is mainly driven bysomatosensory feedback. Newell (1986) find that the older infants’ visuallyprogrammed and younger infants’ haptically adjusted grasp configurations are very
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similar. This strongly suggests that the earlier haptic grasping phase serves to train
the visual grasp planning circuits in the infant brain.
Such data constrained the design of ILGM, and enabled us to evaluate its
relevance to infant learning through explicit comparisons. The model interacts with
its environment (plans and executes grasp actions) and observes the consequencesof its actions (grasp feedback) and modifies its internal parameters (corresponding
to neural connections) in such a way that certain patterns (grasp plans) are selected
and refined amongst many other possibilities. The Learning to Grasp Model(ILGM) models development in two stages. The first stage is the period wheninfants are unable to incorporate object affordance into grasp plans while thesecond phase is when infants start incorporating object information into grasps.
ILGM has been analyzed via simulation experiments that predict behavioral
responses which allow us to make comparisons where experimental data isavailable. When no data are available, we produce useful predictions that can beexperimentally tested.

Virtual Finger
Layer
ObjectAffordance(Size, Axis,
Position)

Wrist Rotations
Layer

Motor Cortex

SpinalCord

Parietal Cortex
Hand Position
Layer

Premotor Cortex

Somatosensory
cortexReinforcement Signal

Grasp
Evaluation

Figure 7. The structure of the Infant Learning to Grasp Model. The individual
layers are trained based on somatosensory feedback.

The details of the model are beyond the scope of the present review but withreference to Figure 7 we note that the crucial element of the model is the built-in
grasp evaluation mechanism which uses kinesthetic information to evaluate that theextent to which a successful contact with the object is made as a result of theinfant's initially more or less random contact with an object and consequent
grasping. The "better" the resultant grasp, the greater the reinforcement signal thatmakes the premotor network more likely to generate the grasp again. As a result,
through time the system becomes less likely to produce a random grasp and more
likely to produce one from its repertoire of successful grasps. Five comments about
this simulation:

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©Romanian Association of Cognitive Sciences• It requires not only the simulation of neural networks for the "premotor
cortex" shown in Figure 7 but also the simulation of an arm and hand sothat the simulation can compute data about the contact between hand andobject needed for grasp evaluation.
• ILGM models how the child may discover grasps through "motor
babbling", having already acquired the ability to project the hand in thegeneral direction of an object and make an uncoordinated swipe at theobject. Learning is driven by "the joy of grasping", as signaled by the grasp
evaluation, not by any explicit training signal.
• In this round of modeling, we have assumed that affordance information isalready encoded in the brain. An immediate goal for further modeling is tounderstand how the activity of AIP might itself be shaped by experience, as
it comes to recognize and encode those visual features of objects local tothe part of the object where a successful grasp has taken place, with thosevisual features becoming cross-indexed to the kinesthetic features of theassociated grasp.
• Even this takes us only as far as finding a stable grasp appropriate to theobserved affordance of the object. This says nothing of the adaptive valueof a grasp or the context (dependent on object and task) in which it will be
used. This returns us to the loop via IT and PFC in the FARS model of
Figure 1, showing how other parts of the brain complement the canonicaland mirror neurons of F5 in placing a grasp in "semantic context".
• The ILGM model is non-neurophysiological, designed to explain thedevelopment of the infant's behavior, rather than analyze the changes inneural activity that might be observed in the monkey.
We close by noting that ILGM says nothing about the mirror system –rather it shows how the infant brain may acquire the basic repertoire of grasps that"gets the mirror neurons started" along the lines delineated in the MNS model (andits future, more neurophysiologically realistic, variants). Our task in the rest of thisarticle is to give a prospectus for future modeling of the learning of new actions
with the assistance of a caregiver, once the basic motor repertoire and mirror
system for that repertoire are in place.
Imitation and attention: challenges for future modeling
Our Naturalistic Experiments delineated some of the ways in which
imitation, especially assisted imitation, contributes to communicative development.
From a neuroscience perspective, the present sections will summarize some of ourobservations in terms of the future modeling they suggest along with aneoGibsonian view of child development. (A challenge we have set ourselves is to
unpackage aspects of our naturalistic and computational approaches that do not at
first converge.) But first we note two major deficiencies in the MNS model
overview of Figure 6 and the related modeling which we have just outlined:(a) In each of our present models, the input to the model is already focused on
the task at hand: visual input solely concerning the object for the FARS
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©Romanian Association of Cognitive Sciencesmodel; visual input solely concerning the object and the one hand for the
MNS model; and visual input concerning object affordances plus
somatosensory input related to the success of the grasp for the ILGM model.
Clearly, models that address the naturalistic experiments must encompass awider range of sensory data concerning a range of objects and information
about the body of the child, the behavior of the caregiver, and interactions
between child and caregiver. We must then model the attentional processesof the child, seeking to explain why certain caregiver behaviors are more
effective than others in focusing the attention of the child on relevant
affordances and effectivities. On the one hand, such new elements provide amajor challenge for future modeling. On the other hand, they will pay off ingreatly improved efficiency in learning, since the successful focusing ofattention by the caregiver means that the child's "search space" is limited to
the neighborhood of successful grasps and manipulations, rather thaninvolving a time-consuming trial-and-error process that includes many
configurations far removed from those required for successful completion of
the task.
(b) Both neurophysiological studies of the mirror system and the above
modeling get as far as recognizing the similarity of actions whether
conducted by the self or another. As already noted, we seek to model not
only how movements within the child's repertoire become recognizable
even when performed by others, but also how the movements performed byothers may become, not only recognizable but imitatable and thus added tothe child's repertoire. However, this still ignores the question of agency:
What information allows the child to know whose hand it is that acts? Goingfurther, we need to understand how picking-up the perceptual informationthat specifies that the caregiver is completing an action can provide the basis
for detecting the affordances that will guide children in their attempts toimitate that action. In any case, we reiterate that successful imitation
requires attention to the pattern of regularities in the other's behavior (which
involves the relation of the agent to other agents and to objects). Thisrequires not only the concern with attention outlined in (a) but also
recognition that "perceiving regularities" is always a function of what thechild already knows. At any time, the child can recognize those actions thatshare regularities with ones in its repertoire. If the difference between the
known action and the desired action is "perceivable" then the child canquickly detect the "new" affordance that will guide the ensuing movement,
adding the new motion to its repertoire. Otherwise, a time-consuming
process of trial-and-error is required to gradually shape a successful action.
(c) At a more technical level, the "biomechanical" model of the arm and handmust be refined to allow compliant motion, e.g., the motion of fingers
conforming to the affordances of an object rather than being
preprogrammed to match those affordances. Reliance on compliance isanother important factor in reducing the search space.
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©Romanian Association of Cognitive Sciences(d) Similarly, the emphasis must shift from single actions to sequences ofactions, where the shaping of action and the transition from one action to thenext depends crucially on the response of objects in the environment tomanipulation. In the vibrating toy, it is the toy that determines how far out
the ring can be pulled, and the child learns that the resistance of the fully
extended string is the signal to release the ring. This dimension of the
proposed work will build upon and extend studies of the role of the
supplementary motor area and basal ganglia in sequential behavior (e.g.,
Dominey, Arbib, & Joseph, 1995; Bischoff-Grethe, Crowley, & Arbib,
2003). However, most of the modeling here has focused on how a sequence
may be learned as the result of many, many repetitions. This is certainly
appropriate for analysis of certain aspects of the child's behavior and evenadult skills may require much practice to be honed, though this process oftuning, as distinct from assemblage, may place more emphasis on the
cerebellum than on the basal ganglia. However - and the vibrating toy is acase in point - there are cases where the process of learning is extremely
rapid, and may be characterized as "sequence editing", with an unsuccessful
element A of a sequence being replaced by a successful element B within atrial or two once that success is recognized.
Earlier, we countered Quine’s “gavagai” argument by noting thatcaregivers can direct attention to the desired referent - they may rub a rabbit's fur
while saying “fur”; trace the topography of its ears while saying “ear”, and so on.
Rather than outline here specific models for building language atop the basic
structure of action recognition and imitation, we simply stress again themultimodality of perception. That is, crucial to this achievement is the child's
ability to detect the higher-order perceptual regularities that mark thecorrespondence between the caregiver's utterance and the ongoing action to which
he is attending (Zukow-Goldring, 1997; Zukow-Goldring & Rader, 2001).
Evidence that suggests the evolutionary origins of this ability comes from Gallese(2001). He has found that mirror neurons can be activated by the sound thatco-occurs with the action. For example, since there is no reason to believe that
there is any a priori neural linkage between the sight and sound of, say, breaking apeanut, there is every reason to believe that detecting these regularities can beextended to sounds that co-occur with the action, as distinct from the sounds for theaction itself. This sets the goal for extending the modeling of the mirror systemfrom hand movements to speech gestures. Of course, as the mirror system
hypothesis suggests, this requires many developments that extend the mirror
system of the monkey-human ancestor to support not only imitation of hand
movements but more general forms of pantomime, leading on to sequences ofmanual signs and then to protospeech as the control systems for protosign extend tothe comprehension and control of intentional patterns of vocalization.
All this is in the context of understanding how the methods of the caregivercorrespond to the expanding capabilities of the child. Often developmental
researchers and scholars study affective, motor, perceptual and cognitive
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©Romanian Association of Cognitive Sciencesdevelopment separately. Caregivers do not. During the prelinguistic and one-wordperiods, caregivers prepare infants to imitate by assisting them "to see what to do"
before they can "do what they see" others doing. Day-in and day-out, they cultivate
imitation within mundane daily activities with gestures. They animate and direct
their infants' attention to their own and others' bodily movements as well as making
prominent what the environment offers for action. Thus, this investigation suggeststhat caregiver practices are crucial to the development of the important "like theother" phenomenon (cf. Meltzoff and Moore, 1999).
Humans who eventually learn/understand that the self is "like the other"cultivate abilities in their young that contribute to imitating, tutoring,
communicating, and representing events. The mirror system offers a means toclarify in what manner human and nonhuman primates understand what they seeother conspecifics and other primates doing, what abilities and perceptual
information underlie learning to do what they see others do, and much more.
♣

This paper expands upon an earlier version whose abstract was prepared for discussion at theconference on "Perspectives On Imitation: From Cognitive Neuroscience to Social Science", 23-26
May 2002, Royaumont Abbey, France.

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