Learning an Embodied Visual Language: Four Imitation Strategies Available to Sign Learners

Abstract

The parts of the body that are used to produce and perceive signed languages (the hands, face, and visual system) differ from those used to produce and perceive spoken languages (the vocal tract and auditory system). In this paper we address two factors that have important consequences for sign language acquisition. First, there are three types of lexical signs: one-handed, two-handed symmetrical, and two-handed asymmetrical. Natural variation in hand dominance in the population leads to varied input to children learning sign. Children must learn that signs are not specified for the right or left hand but for dominant and non-dominant. Second, we posit that children have at least four imitation strategies available for imitating signs: anatomical (Activate the same muscles as the sign model), which could lead learners to inappropriately use their non-dominant hand; mirroring (Produce a mirror image of the modeled sign), which could lead learners to produce lateral movement reversal errors or to use the non-dominant hand; visual matching (Reproduce what you see from your perspective), which could lead learners to produce inward–outward movement and palm orientation reversals; and reversing (Reproduce what the sign model would see from his/her perspective). This last strategy is the only one that always yields correct phonological forms in signed languages. To test our hypotheses, we turn to evidence from typical and atypical hearing and deaf children as well as from typical adults; the data come from studies of both sign acquisition and gesture imitation. Specifically, we posit that all children initially use a visual matching strategy but typical children switch to a mirroring strategy sometime in the second year of life; typical adults tend to use a mirroring strategy in learning signs and imitating gestures. By contrast, children and adults with autism spectrum disorder (ASD) appear to use the visual matching strategy well into childhood or even adulthood. Finally, we present evidence that sign language exposure changes how adults imitate gestures, switching from a mirroring strategy to the correct reversal strategy. These four strategies for imitation do not exist in speech and as such constitute a unique problem for research in language acquisition.

Full text

HYPOTHESIS AND THEORY
published: 30 May 2018
doi: 10.3389/fpsyg.2018.00811
Frontiers in Psychology | www.frontiersin.org 1May 2018 | Volume 9 | Article 811
Edited by:
Marianne Gullberg,
Lund University, Sweden
Reviewed by:
Bencie Woll,
University College London,
United Kingdom
Olga Capirci,
Istituto di Scienze e Tecnologie della
Cognizione (ISTC), Italy
*Correspondence:
Aaron Shield
shielda@miamioh.edu
Specialty section:
This article was submitted to
Language Sciences,
a section of the journal
Frontiers in Psychology
Received: 15 December 2017
Accepted: 07 May 2018
Published: 30 May 2018
Citation:
Shield A and Meier RP (2018) Learning
an Embodied Visual Language: Four
Imitation Strategies Available to Sign
Learners. Front. Psychol. 9:811.
doi: 10.3389/fpsyg.2018.00811
Learning an Embodied Visual
Language: Four Imitation Strategies
Available to Sign Learners
Aaron Shield 1
*and Richard P. Meier 2
1Speech Pathology and Audiology, Miami University, Oxford, OH, United States, 2Linguistics, University of Texas at Austin,
Austin, TX, United States
The parts of the body that are used to produce and perceive signed languages (the
hands, face, and visual system) differ from those used to produce and perceive spoken
languages (the vocal tract and auditory system). In this paper we address two factors that
have important consequences for sign language acquisition. First, there are three types
of lexical signs: one-handed, two-handed symmetrical, and two-handed asymmetrical.
Natural variation in hand dominance in the population leads to varied input to children
learning sign. Children must learn that signs are not specified for the right or left hand
but for dominant and non-dominant. Second, we posit that children have at least four
imitation strategies available for imitating signs: anatomical (Activate the same muscles
as the sign model), which could lead learners to inappropriately use their non-dominant
hand; mirroring (Produce a mirror image of the modeled sign), which could lead learners
to produce lateral movement reversal errors or to use the non-dominant hand; visual
matching (Reproduce what you see from your perspective), which could lead learners
to produce inward–outward movement and palm orientation reversals; and reversing
(Reproduce what the sign model would see from his/her perspective). This last strategy
is the only one that always yields correct phonological forms in signed languages. To
test our hypotheses, we turn to evidence from typical and atypical hearing and deaf
children as well as from typical adults; the data come from studies of both sign acquisition
and gesture imitation. Specifically, we posit that all children initially use a visual matching
strategy but typical children switch to a mirroring strategy sometime in the second year
of life; typical adults tend to use a mirroring strategy in learning signs and imitating
gestures. By contrast, children and adults with autism spectrum disorder (ASD) appear
to use the visual matching strategy well into childhood or even adulthood. Finally, we
present evidence that sign language exposure changes how adults imitate gestures,
switching from a mirroring strategy to the correct reversal strategy. These four strategies
for imitation do not exist in speech and as such constitute a unique problem for research
in language acquisition.
Keywords: sign language, Autism Spectrum Disorders (ASD), imitation, language acquisition, visual perspective-
taking, American Sign Language (ASL)

Shield and Meier Learning an Embodied Visual Language
LEARNING AN EMBODIED VISUAL
LANGUAGE: FOUR IMITATION
STRATEGIES AVAILABLE TO SIGN
LEARNERS
Nearly 60 years of research into the signed languages of the Deaf
have unequivocally demonstrated that they are fully comparable
to spoken languages in a linguistic and biological sense, utilizing
similar brain tissue as spoken languages and organized on the
phonological, morphological, semantic, syntactic, and discourse
levels (e.g., Klima and Bellugi, 1979; Poizner et al., 1990;
Emmorey, 2002; Sandler and Lillo-Martin, 2006). They are
acquired naturally by children who are exposed to them and
achieve language milestones at similar ages as children acquiring
spoken languages (Newport and Meier, 1985), and exist as
naturally-occurring, autonomous linguistic systems throughout
the world wherever a Deaf community is found. Yet signed and
spoken languages are not the same. In recent years, many scholars
have investigated the role that modality—the channel through
which language is expressed and perceived—plays in linguistic
structure, highlighting the ways in which signed and spoken
languages may differ (Meier et al., 2002). In this paper we focus on
the visual-gestural modality of sign in order to identify a crucial
difference between the acquisition of sign and speech. We begin
with a discussion of the mental representation of lexical signs as
a way to frame the unique challenges entailed in sign acquisition.
How do we represent signs? We can represent them as they
are typically (but not invariably) viewed by an addressee; that is,
from a viewpoint opposite the signer. This is the representation
most often seen in videos or in linguistics papers, where photos or
line drawings show a frontal view, from waist to head, of a signer.
The sign BL ACK 1(Figure 1A) viewed from this perspective,
moves to the addressee’s left (assuming that the signer is right-
handed). Yet movement to the addressee’s left is not linguistically
significant; if the addressee happens to be seated in the passenger
seat beside the signing driver of a (left-hand drive) car, the
sign BL ACK moves to the addressee’s right. The addressee’s usual
perspective, opposite the signer, is familiar but is not the basis for
a linguistically correct description of the sign.
A better linguistic characterization is that the sign BLACK
moves to the signer’s right, but even this is not quite correct
because this description does not capture the way in which left-
handed people sign (or even the way in which a right-handed
person signs when using the left hand). A still better description
is this: in the sign BLACK the active hand moves laterally; the
direction of movement is away from the signer’s midline (and
away from the side of the signer that is ipsilateral to the active
hand). To take another example, the sign GIRL (Figure 1B) makes
contact on the signer’s cheek, specifically on the cheek that is
ipsilateral to the signer’s dominant hand. Years of linguistic
research have demonstrated that the best description of signs is
from the signer’s perspective, not the addressee’s. Thus, the way
in which we generally picture signs does not match the way in
which they should be linguistically represented.
1In this paper we refer to signs from American Sign Language (ASL). However, the
hypotheses advanced here apply to other sign languages. As is conventional in the
literature, words in SM ALL C APS indicate signs.
Which perspective to take when representing signs has been
an issue in attempts to design writing systems for signed
languages. In the development of SignWriting, Deaf users
instigated a shift from writing signs from the viewer’s perspective
to the writing of signs from the signer’s perspective (Hoffmann-
Dilloway, 2017). But, visual representations of signs from the
signer’s perspective are somewhat unfamiliar; native signers are
less accurate and slower to recognize signer-perspective videos
of signs than they are to recognize addressee-perspective videos
(Emmorey et al., 2009). Maxwell (1980) detected a similar
problem in how deaf children decoded drawings of signs in
relation to English words (Sign Print). She noted that English
print is represented from left to right, but the direction of
movement depicted in the drawings of some signs (such as the
Signing Exact English plural noun TH ING-S) was from right to
left. As a result, a 48-month-old deaf child misinterpreted the
signs as occurring in the reverse order (as S-THING). She also
sometimes turned her body so as to share the same orientation
as the figure depicted in the book, evidence of the difficulty posed
by the illustrations.
These difficulties in correctly representing signs are not just
a problem for linguists seeking to understand grammatical
descriptions of a signed language or for people interested in
representing signs in written form (or for children attempting to
read Signing Exact English). They are a fundamental challenge
to children and adults who are acquiring a signed language. We
posit that these difficulties present problems for acquisition that
are unlike the challenges of acquiring speech. The parts of the
body that are used to produce and perceive signed languages
(the hands, face, and visual system) obviously differ from those
used to produce and perceive spoken languages (the vocal
tract and auditory system). In this paper we specifically argue
that the asymmetric control of the articulators (the dominant
and non-dominant hands) that are used to produce signs, the
characteristics of the sign language grammar and lexicon, and
the multiple strategies available for the imitation of signs have
important consequences for language acquisition and processing.
We address each of these issues in turn, marshaling evidence
from development, second-language acquisition, and atypical
learners to support our observations.
Handedness and the Sign Lexicon
It is perhaps a trivial statement to note that signed languages
are produced with the hands, but a few observations about this
fact are in order. First, the articulators are paired; under normal
circumstances we have two hands. There is no obvious parallel in
spoken languages. There are two lips, but they are not involved
in the production of every phoneme. Furthermore, the lips are
paired vertically rather than horizontally; the same is true for
the top and bottom teeth. We would have to imagine a creature
with two mouths in a horizontal configuration, each of which
could articulate semi-independently from the other, to obtain an
adequate analog.
A second observation is that the hands are controlled semi-
independently and show different phonological properties. Signs
can be one-handed (as in GI RL,Figure 1B), two-handed and
symmetrical, in which both hands exhibit the same handshape
and movement (as in SC HOOL,Figure 1B), or two-handed
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Shield and Meier Learning an Embodied Visual Language
FIGURE 1 | The ASL signs B LACK (A) and the signs GI RL,SC HOOL ,and TURT LE (B). All photographs, copyright Aaron Shield and Richard P. Meier, are reproduced
here and in Table 1 with written permission of the model.
and asymmetrical, in which the hands can exhibit different
handshapes and in which the non-dominant hand can be static
whereas the dominant hand moves (as in TURTL E,Figure 1B).
Battison (1978) discussed the constraints that hold on these
three classes of signs in ASL and other signed languages. In
the case of one-handed signs, the signer can choose either
hand to produce the sign, as signs are not typically specified
for left or right2. Signers typically employ their dominant
hand to produce such signs, though in certain circumstances
they may choose to use their non-dominant hand (such as
if the dominant hand is holding an object or is otherwise
unavailable). The same is true for two-handed asymmetrical
signs: the dominant hand acts upon the non-dominant hand,
but whether the dominant hand is right or left depends on the
individual.
Now let us imagine being a young child who is exposed
to a sign language. Handedness is consistently evident by 6
months of age (Butterworth and Hopkins, 1993) or even in
utero (MacNeilage, 2008), long before children produce their
first signs. Let us further imagine that this hypothetical child is
an emergent lefty. But all of the adults around him are right-
handed, and all he sees is right-dominant signing. This situation
must be frequent: it is commonly accepted that about 90% of the
general population is right-handed (Corballis, 1980, 1992), and
the deaf, signing population shows similar percentages of right-
dominance (Conrad, 1979; Bonvillian et al., 1982; Sharma, 2014;
Papadatou-Pastou and Sáfár, 2016). How does our imagined child
come to understand that he may in fact perform signs with
his left hand, when all he sees are examples of right-handed
2Notable exceptions in many signed languages are signs indicating cardinal
directions (EA ST is typically produced with a rightward direction and WE ST with a
leftward direction, in correspondence with the directions on a compass); the same
is true for the lexical signs RI GHT and L EFT. We thank one of the two reviewers for
this observation.
input? Does his strong motor preference for the left dictate his
signing, or does a desire to imitate the exact movements of the
adults around him motivate him? We cannot know, of course,
what the child is thinking, but we can observe whether the
child signs with his right or left hand. In this paper we describe
several competing imitation strategies that are available to sign
learners and hypothesize that different groups of signers may
opt for different strategies due to how they interpret the sign
imitation/learning task.
Recent work also suggests that handedness plays a role in
sign recognition: Watkins and Thompson (2017) found that
left- and right-handed adult signers reacted differently to signs
produced by left- and right-handed sign models. Left-handed
adult signers responded more quickly on a picture-sign matching
task when they viewed two-handed asymmetric signs produced
by a left-handed model than by a right-handed model, suggesting
that the articulatory and perceptual complexity of this sign type
is more easily recognized when there is congruency between
signer and addressee, perhaps because the addressee can more
easily recognize the sign through simulation of the sign through
their own motor system. However, Watkins and Thompson
also found that for all other sign types (i.e., one-handed signs
and two-handed symmetrical signs), both left- and right-handed
participants identified signs produced by right-handed models
more quickly, suggesting a familiarity effect, since both left-
and right-handed signers are exposed to more right-handed
signing than left-handed signing. Similarly, Sharma (2014) found
that left-handed signers made fewer errors than right-handed
signers when forced to produce signs with their non-dominant
hand, either because they have more practice viewing and
processing signs with non-matched handedness or due to weaker
handedness than right-handed signers. There is simply no analog
to this situation in speech: there is no anatomical component of
the vocal tract that varies in such a significant way in a subgroup
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Shield and Meier Learning an Embodied Visual Language
of the population and that could have such important effects on
both production and comprehension of language as does hand
preference in sign3.
Perspective-Taking
Like hand preference, the role of visual perspective-taking in
sign learning represents a unique challenge for sign learners.
Many scholars have noted the role that the three-dimensional
signing space plays in sign grammar: the physical space in
front of the signer is exploited for pronominal and anaphoric
reference, for verb agreement, and for the description of spatial
arrays (Bellugi et al., 1990). As far as we know, signed languages
universally depict such constructions from the perspective of
the signer. Courtin and Melot (1998: 85) point out that such
constructions require “a visual perspective change; the addressee
has to reorient the linguistic space according to the angle
existing between himself and the signer.” Particularly difficult
are descriptions of spatial arrays (that is, signed depictions of
spatial configurations or movements), as discussed by Emmorey
et al. (1998, 2000).Emmorey (2002) provides a schematic for how
such constructions are produced and understood. In Figure 2,
the arrow indicates the direction of movement of a referent,
which is represented by the X and is first located in the sign
space in front of the signer. The signer wishes to communicate
that the referent moved through space, first to the left, then
forward, and finally back to the right. The direction of movement
is only properly repeated if reversed by the addressee (as in
Figure 2A), whereas mirroring the movement (as in Figure 2B)
suggests an incorrect interpretation (right, forward, left). Bellugi
et al. (1990: 287) note the challenges that such structures pose
to learners: “The young deaf child is faced with the dual task
in sign language of spatial perception, memory, and spatial
transformations on the one hand, and processing grammatical
structure on the other, all in one and the same visual event.”
Unsurprisingly, linguistic structures in sign that crucially depend
on such mental transformations appear later in development
than might otherwise be expected (Lillo-Martin et al., 1985;
Newport and Meier, 1985), since “the young deaf child, unlike
his or her hearing counterpart, must acquire non-language spatial
capacities that serve as prerequisites to the linguistic use of space”
(Bellugi et al., 1990: 287).
Shield (2010) proposed that visual perspective-taking
and spatial transformations are necessary not only for
comprehending complex descriptions of spatial arrays but
also for acquiring the phonological form of individual lexical
signs. Lexical signs are acquired much earlier in development
than are complex spatial descriptions. Unlike the spatial
descriptions described by Emmorey (2002), lexical signs are
not (typically) specified for right or left, but for the dominant
and non-dominant hand. This difference in the use of space has
important consequences for the sign-learning child, who must
realize that the use of space in lexical signs is fixed and does not
3An imperfect analogy is perhaps the different vocal tract sizes and resulting
fundamental frequencies of male and female speakers (Peterson and Barney,
1952). Six-month-old hearing infants are able to recognize phonemes produced
by speakers despite great acoustic variation (talker normalization;Kuhl, 1979).
FIGURE 2 | A signed spatial mapping correctly reversed (A) and incorrectly
mirrored (B) (reproduced from Emmorey (2002: 415)). Used by permission. All
rights reserved.
make reference to space itself, whereas the descriptions of spatial
arrays discussed by Emmorey are linguistic devices for talking
about space.
Shield (2010) suggested that some signs engage perspective-
taking skills in more challenging ways than others, and that
certain types of learners would produce specific error types in the
process of learning and reproducing these signs, especially very
young typically-developing children as well as individuals with
autism spectrum disorder (ASD), who may have difficulties with
visual perspective-taking (Hamilton et al., 2009). With regard
to the sign types that may be challenging, Shield hypothesized
that lexical signs exhibiting lateral path movements (from the
ipsilateral side of the body to the contralateral side of the body
or vice versa) as well as inward–outward movements (movements
originating at a point distal from the signer’s body and moving
to a point more proximal to the signer’s body or vice versa)
require learners to engage perspective-taking skills in order to
form correct phonological representations of signs in ways that
other types of path movement (such as vertical movements in
an upward or downward direction) do not. Likewise, he argued
that inward–outward palm orientations, such as those found in
the ASL signs TU ESDAY and BATHROO M (Figure 3) could also
engage perspective-taking, because these palm orientation values
appear differently from the signer’s and viewer’s perspectives.
Imitation
Like children acquiring speech, children learning sign must
imitate the linguistic symbols produced by the language models
around them4. However, unlike the learning of spoken words, we
hypothesize that there are multiple strategies for the imitation
of lexical signs, and that not all of these strategies will result
in a correctly-formed sign. The psychological literature has
distinguished two kinds of imitation strategies: anatomical
imitation and mirror imitation (Koski, 2003; Franz et al., 2007;
Press et al., 2009). In anatomical imitation the imitator activates
4We do not suggest that imitation is the only mechanism through which children
acquire linguistic symbols. We focus here on imitation as one essential component
of the language-learning process.
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Shield and Meier Learning an Embodied Visual Language
FIGURE 3 | The ASL signs T UESD AY (left) and BATHRO OM (right).
Photographs are reproduced with written permission of the model.
the same muscles as the model being imitated, such that, for
example, he raises his right arm to imitate the model’s raised right
arm, or his left arm to imitate the model’s raised left arm. In
mirror (or specular) imitation, the imitator performs the action
as if looking in a mirror (e.g., raising his left arm to mimic
the model’s lifted right arm). Pierpaoli et al. (2014) found that
adults tend to spontaneously engage a mirror imitation strategy
more often than an anatomical strategy unless given specific
instructions about which limb to use, suggesting that the mirror
strategy is a default imitation strategy for typical adults.
For sign-learning children, however, neither the anatomical
strategy nor the mirror strategy is correct, for two reasons. First,
the anatomical strategy is inappropriate for learners imitating a
model with different hand dominance: signs are not specified for
the right or left hand but for dominant and non-dominant. Thus
the anatomical strategy will fail when the signer and the learner
are discordant in hand dominance.
Second, though some signs can be mirrored without error
(e.g., signs exhibiting inward–outward movements and palm
orientations as in Figure 3 above), the mirroring of signs
containing lateral movements (as in the sign BLACK,Figure 1A)
will lead to movement reversal errors if signer and learner are
both right-handed or both left-handed. In this case, only a
reversing strategy will result in the production of the correct
form. We follow Emmorey (2002) in using the term “reversing”
since it implies that the imitator must perform a mental spatial
transformation of what he or she sees in order to produce the
correct form. To this strategy, we add the caveat that learners
must monitor the handedness of the signer and compare it
to their own; if hand dominance is discordant, learners may
correctly deploy the mirroring strategy.
In addition to these three strategies, yet another imitation
strategy is available to learners. Learners may reproduce what
they see from their own perspective. This is a visual matching
strategy because the child’s imitative movements match the
appearance of what she sees. Let us imagine a child who
has adopted this strategy and who is facing the signer. The
child sees a sign which originates at a point distal from the
signer and which moves toward the signer’s own body. The
child could interpret the signer’s movement in an absolute
sense. She could then reproduce the sign as beginning relatively
proximal to her own body and ending at a point distal from
her body. Similarly, she could imitate signs exhibiting outward-
facing palm orientations (as in BAT HRO OM,Figure 3) with her
palm facing inward toward her own body, thus reversing the
palm orientation parameter. Thus, the visual matching strategy
would lead to movement and palm orientation errors on signs
exhibiting inward–outward movements and palm orientations.
Note that this strategy yields predictions about inward–outward
movements and palm orientations, but not about hand selection.
To summarize, it appears that children learning sign have at
least four possibilities for imitating signs during acquisition:
1. Anatomical strategy: Activate the same muscles as the model,
regardless of the hand dominance of the signer.
2. Mirroring strategy: Produce a mirror image of what the signer
does.
3. Visual matching strategy: Reproduce the sign as it appears
from the learner’s perspective.
4. Reversing strategy: Perform a mental spatial transformation
on the observed sign and reproduce what the signer does after
checking for differences in hand dominance.
Table 1 summarizes each imitation strategy, the conditions under
which each strategy will fail, the types of lexical signs that could be
susceptible to error when employing each strategy, and the error
types that are predicted.
Which strategy or strategies do sign learners adopt, and how
would we know? We predict that the difficulties posed by the
interaction of sign type (one-handed, two-handed symmetrical,
and two-handed asymmetrical), natural variation in handedness,
and the four imitation strategies available to learners will lead
some sign learners to make specific types of errors, namely hand-
switches,lateral and inward–outward movement reversal errors,
and inward–outward palm orientation reversal errors, depending
on the type of strategy or strategies adopted. We first turn to
evidence from published studies on gesture imitation and sign
acquisition by typical and atypical hearing and deaf children,
as well as by typical adult learners. We then present two new
studies of gesture imitation by non-signers, sign learners, and
fluent signers to show how exposure to a sign language changes
how adults approach imitation. Throughout we demonstrate
that hearing and deaf, typical and atypical, children and adults
produce errors that reveal the specific difficulties presented by
learning a visual language.
STUDIES OF GESTURE IMITATION AND
SIGN ACQUISITION BY TYPICAL HEARING
AND DEAF CHILDREN
Children begin imitating the actions and gestures of the people
around them early in development, for example producing early
communicative pointing gestures and conventional gestures
such as the “wave bye-bye” gesture by 12 months (Bates,
1979; Carpenter et al., 1998). Studies of the ways that typical
infants imitate others suggest that they may shift from an
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Shield and Meier Learning an Embodied Visual Language
TABLE 1 | Four imitation strategies in sign learning and predicted error types.
Strategy Under what circumstances will this
strategy lead to errors in sign formation?
Predicted errors Example signs
Anatomical: Activate the
same muscles as the model
When imitating one-handed and two-handed
asymmetrical signs if handedness of signer and
learner is discordant
Hand switches on one-handed signs such as
BATH ROOM and two-handed asymmetrical
signs such as TO MATO
Sign: BATH ROOM (produced by a
left-handed signer)
Produced (by a right-handed signer)
as:
Mirroring: Produce a mirror
image of what the signer
does
When imitating signs exhibiting lateral
movements if handedness of signer and learner
is concordant; for one-handed signs if
handedness of signer and learner is concordant
Lateral movement reversals (on signs such as
BLA CK,SUM MER,B ECAU SE,FARM ,UGLY,DRY,
WE,C OMMI TTE E,CON GRES S,BOA RD,SEN ATE,
ATLA NTA,TO RONT O,and POL AND); hand
switches on one-handed signs such as
BATH ROOM
Sign: BLA CK
Produced as:
Sign: BATH ROOM
Produced (by a right-handed signer)
as:
(Continued)
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Shield and Meier Learning an Embodied Visual Language
TABLE 1 | Continued
Strategy Under what circumstances will this
strategy lead to errors in sign formation?
Predicted errors Example signs
Visual matching:
Reproduce the sign as it
appears from the learner’s
perspective
When imitating signs exhibiting inward–outward
movements and palm orientations; when
imitating signs exhibiting lateral movements if
handedness of signer and learner is concordant
Inward–outward palm orientation reversals on
signs such as TU ESDAY and BAT HROO M;
inward–outward movement reversals on signs
such as WA NT; lateral movement reversals
Sign: BATH ROOM
Produced as:
Reversing: Reproduce
what the signer does after
performing a mental spatial
transformation and
checking for handedness5
Never None Sign: BATH ROOM
Produced as:
or, for left-handed signers:
initial visual matching strategy to a mirroring strategy in the
second year of life. Evidence for this hypothesis comes from
studies on infants’ ability to perform role reversal imitation
(Tomasello, 1999; Carpenter et al., 2005), that is, performing an
action toward another person in the same way that the action
5Note that a right-dominant signer can correctly imitate a left-handed model (or
a left-dominant signer, a right-handed model) using the mirroring strategy. Under
this scenario, a signer would monitor the hand dominance of the model and then
employ mirroring if handedness is discordant.
was performed on the child. Two kinds of role reversal imitation
have been identified: self-self role reversal, in which the child
performs an action on his own body in imitation of an action
that the adult performed on her own body (e.g., the infant pats
his own head after the adult pats her own head), and other-
other role reversal, in which the child performs an action on the
adult’s body in imitation of an action that the adult performed
on the child’s body (e.g., the infant pats the adult’s head after the
adult pats the infant’s head). Carpenter et al. (2005) found that
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Shield and Meier Learning an Embodied Visual Language
50% of their sample of typical 12-month-old infants and 90%
of their sample of typical 18-month-olds performed self-self role
reversals, suggesting that this ability develops and strengthens
during the second year. The ability to perform such reversals
could be key for the development of the reversing or mirroring
strategies of imitation, as children imitate not just what they see
but what others do. By the time typical children are preschool
age, they are able to imitate the actions of others with high fidelity
(Ohta, 1987), and no longer appear to engage the visual matching
strategy of imitation.
How does the child’s ability to imitate action contribute
to the acquisition of signs? Movement errors have frequently
been reported for young, typical deaf children acquiring sign
(Siedlecki and Bonvillian, 1993; Marentette and Mayberry, 2000;
Meier, 2006; Morgan et al., 2007). A problem in interpreting this
literature, which is largely based on the observation of naturalistic
data, is that it can be difficult to separate errors that arise due
to young children’s immature motor control from errors that
arise due to the perceptual challenges that are the subject of this
paper. Crucially, there are very few reports of the development of
palm orientation. Palm orientation is the parameter that could
shed the most light on the issues raised in this paper because
data on inward–outward palm orientations can tell us if children
have adopted a visual matching strategy (in which they are likely
to reverse inward–outward palm orientations) or have acquired
either a reversing or a mirroring strategy (both of which would
result in the correct imitation of palm orientation).
To address this question, Shield and Meier (2012) examined
659 tokens in the database of children’s early sign productions
of four typical deaf children between 9 and 17 months of age
(on which Cheek et al., 2001, had based a previous report).
This examination revealed 14 tokens (6 inward substitutions
and 8 outward substitutions) of reversed inward–outward palm
orientation in a database of 659 signs produced by typical deaf
children in the first year and a half of life. Thus, it appears
that very young typical deaf children do sometimes reverse the
palm orientation parameter in a way that appears consistent with
their use of the visual matching imitation strategy. However,
it is unclear if they do so systematically. We do not yet have
a systematic, longitudinal examination of children’s acquisition
of those sign types that are directly relevant to the hypotheses
presented above.
One feature of the way in which infants are socialized to
language may contribute to their reconciliation of the different
appearances that an individual sign has when viewed from
different perspectives. Infants are sometimes seated opposite
their parent—say, when they are in a high chair being fed.
But infants may also be seated on the parent’s lap; in this
instance their perspective on the world is closely aligned with
that of the parent. Several studies of child-directed signing by
Deaf caregivers have shed light on these interactions. Maestas y
Moores (1980) studied how American Deaf parents interacted
with their infants (n=7); the infants ranged in age from
less than a month to 16 months. She found that Deaf parents
commonly signed in front of the infant while the infant was
seated on the parent’s lap such that the viewpoint of parent and
infant were shared. Parents also commonly signed on the infants’
bodies, molded their hand configurations, and guided their hand
movements, thus providing kinesthetic as well as visual feedback
to their children. Similar results have been found for Deaf British
mothers who use British Sign Language (Woll et al., 1988).
In a later study, Holzrichter and Meier (2000) reported that
four Deaf mothers of deaf children between 8 and 12 months of
age displaced signs with a place of articulation on the face onto
their children’s bodies about 18% of the time (21 of 116 tokens);
these instances occurred when there was no eye contact between
parent and child during or before the articulation of the sign, such
as when the child was sitting on the mother’s lap facing away
from her. Pizer et al. (2011) describe an interesting example of
such an interaction between a Deaf mother and her 18-month-
old deaf child. The child was seated on her mother’s lap; the
mother labeled the colors of the blocks that were on the floor
in front of them. The mother produced the ASL signs GR EEN,
BLU E, and YELL OW in the neutral space in front of the two of
them. She then produced the sign ORAN GE on her child’s mouth
rather than on her own body, as normal signing would dictate.
Why did the mother do this in this instance? If she had articulated
the sign in contact with her own mouth, the sign would not have
been visible to the child (because the mother was behind her
daughter). When, in these instances, the mother signed G REE N,
BLU E, and YELL OW in front of the child and ORAN GE on the
child’s mouth, she enabled her child to witness these signs from
the signer’s own perspective, rather than from the more typical
addressee perspective.
STUDIES OF GESTURE IMITATION AND
SIGN ACQUISITION BY HEARING AND
DEAF CHILDREN WITH ASD
We also find indications of the challenges presented by learning
sign in studies of atypical learners. Children with ASD, both
hearing and deaf, show distinctive patterns in imitation.
Hearing Children With ASD
Though language impairment is not considered a core feature
of ASD (American Psychiatric Association, 2013), many
children with ASD exhibit abnormal language in both speech
and sign. A significant minority of children with ASD are
considered minimally-verbal (Tager-Flusberg and Kasari, 2013),
with expressive vocabularies under 50 words. Manual signs have
long been used as an alternative communication strategy for such
children, with varying degrees of success (Carr, 1979; Bonvillian
et al., 1981, for reviews). In general, minimally-verbal hearing
children with ASD are not exposed to, and do not learn, a
fully-fledged sign language such as ASL with its syntax and
morphology, but instead see a restricted set of lexical signs
that are used to communicate basic wants and needs, akin
to Baby Signs (Acredolo and Goodwyn, 2002). The published
reports on hearing children with ASD who are exposed to signs
are unfortunately not useful for the purpose of testing our
hypotheses, although Bonvillian et al. (2001) speculate that an
unexpectedly high preference for left-handed signing in their
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Shield and Meier Learning an Embodied Visual Language
subjects may be attributable to mirroring. We now turn to the
literature on gesture imitation by children with ASD.
Various studies have observed that hearing children with
ASD do more poorly in general on gesture imitation tasks than
typical children, and numerous hypotheses have been advanced
to account for these deficits. Edwards (2014) recently performed
a meta-analysis of 53 studies on imitation in ASD. She found that
individuals with ASD performed on average about 0.8 standard
deviations below non-ASD individuals on the imitation tasks
contained in the studies, despite important differences between
the individual studies depending on the nature of the task and the
characteristics of the subject samples. In the section that follows
we do not claim to account for all children with ASD, but rather
focus on a subset of studies that describe a unique pattern that
thus far has only been documented in the imitative behavior of
children with ASD.
At least four studies have shown that children with ASD,
unlike typical children, produce gesture imitations suggestive of
the visual matching imitation strategy. Ohta (1987) was the first
to report such errors (which he called “partial imitations”): three
of 16 children with ASD between the ages of 6;3 and 14;4 (mean
age 10;2) imitated a “wave” gesture (in which the experimenter’s
open palm was oriented toward the child) with their palms facing
inward toward themselves, consistent with the visual matching
imitation strategy. Crucially, no member of an age- and IQ-
matched control group or of a second control group of 189 typical
preschoolers ages 3–6 imitated the wave gesture in this way,
suggesting that this imitation strategy does not occur in typical
development beyond a very early age.
Other studies have replicated this striking finding. Smith
(1998) found that hearing children with ASD made significantly
more 180-degree reversal errors (e.g., palm toward the viewer
rather than away from him) than age-matched language-
impaired and typically developing children when imitating ASL
handshapes and bimanual gestures. Whiten and Brown (1998:
270–271) also found that hearing children with ASD made
similar gesture imitation errors, highlighting
responses in which the imitating subject creates an action which
to him will look similar to what he saw when he watched the
demonstrator, instead of what the demonstrator would see. He
fails to translate appropriately, or “invert” the action to his own
perspective as actor. An example is “peekaboo,” performed by the
demonstrator with palms toward her own face, and sometimes
inaccurately imitated such that the palms are oriented away from
the imitator’s face (i.e., the actor sees the backs of the hands both
when the demonstrator performs the act, and when he himself
attempts it) (emphasis ours).
Adding to these findings, Hobson and Lee (1999) provide a
crucial link between the reversal errors in gesture imitation and
the role reversal skills described by Tomasello (1999). They found
that adolescents with ASD were significantly less likely to imitate
a self-oriented action (wiping their own brow with a toy frog
after an adult did so) than were age- and language-matched
intellectually-disabled children: only five of 16 children with ASD
performed the self-oriented action while 14 of 16 of the control
children did so. This finding suggests that it is indeed this early
development of role reversal skills that enables typical children
to transcend the visual matching strategy. That visual matching
strategy has now surfaced in multiple studies of how children
with ASD imitate gestures.
Deaf Children With ASD
More recently, Shield and colleagues have published a number of
studies describing the acquisition of ASL by deaf children with
ASD who have Deaf parents (Shield and Meier, 2012; Shield,
2014; Shield et al., 2015, 2016, 2017a,b; Bhat et al., 2016). The
first report (Shield and Meier, 2012) described the formational
errors produced by five native-signing children with ASD (four
deaf children and one hearing child of Deaf adults) ranging in
age from 4;6 to 7;5. These children were compared to a control
group of 12 typical native-signing deaf children between the
ages of 3;7 and 6;9. The data came from spontaneous signing
produced under naturalistic conditions and from a fingerspelling
task (in which children were asked to spell English written words
with their hands). Despite lifelong exposure to ASL, three of the
children with ASD (ages 5;8, 6;6, and 7;5) reversed the palm
orientation of 72 of 179 (40.2%) fingerspelled letters such that
the children’s palm faced toward their own body rather than
outward. None of the 12 typical deaf children produced any
such palm orientation reversals. These reversals are consistent
with the visual matching strategy of imitation and are nearly
identical to the errors produced by hearing, non-signing children
with ASD in the previously-discussed studies of gesture imitation
(Ohta, 1987; Smith, 1998; Whiten and Brown, 1998). The three
children with ASD who made such errors had lower parent-
reported language scores (M=36.67, SD =13.61, range 26–52)
on the Language Proficiency Profile-2 (LPP-2; Bebko et al., 2003)
than those children who did not make such errors, including the
12 typical deaf children (M=90.25, SD =17.07, range 59–112)
or the child with ASD who did not make any palm reversals
(=90). This difference was significant [t(14) =5.23, p<0.001],
suggesting that children with lower receptive and expressive
language skills may be more prone to making such errors.
If the palm orientation reversals exhibited by native-signing
children with ASD are the result of the visual matching imitation
strategy, then how do such children perform on gesture imitation
tasks? Two studies have shown that even deaf children who are
exposed natively to a sign language nonetheless show difficulties
with gesture imitation. In his unpublished dissertation, Shield
(2010) asked 12 typical deaf children and 17 deaf children
with ASD to imitate nonsense signs similar to ASL signs. He
divided up the target stimuli into test items (hypothesized to
require a reversing strategy in order to be imitated correctly,
i.e., with lateral path movements) and control items (which do
not require a reversing strategy in order to be imitated correctly,
i.e., with up–down path movements). The children with ASD
made significantly more imitation errors than typical controls
overall, as well as significantly more errors on test items than
control items, suggesting that gestures that require a reversing
imitation strategy can be particularly difficult for such learners.
The children with ASD also had significantly lower language
scores on the LPP-2 (M=66.25, SD =31.49) than the typical
children (M=90.25, SD =17.07), again indicating a relationship
between these errors and overall language abilities. Children with
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Shield and Meier Learning an Embodied Visual Language
ASD made significantly more errors on inward–outward palm
orientations than on any of the other item types or parameters,
which may be a sign of the visual matching imitation strategy.
Thus, the observation of these palm orientation reversals in
gesture imitation by deaf, signing children provides a link
between the reversed signs observed by Shield and Meier (2012)
in spontaneous and elicited production of ASL and the reversed
gestures observed in hearing children with ASD by Ohta (1987),
Smith (1998) and Whiten and Brown (1998). All of the errors
indicate that some children with ASD use a visual matching
strategy in imitation far beyond the age that typical children stop
doing so.
Shield (2010) also examined whether right-handed children
switched hands during the task as a way of avoiding the reversing
strategy when imitating the right-handed investigator (thereby
using the mirroring strategy instead). Both typical and ASD
children switched hands significantly more often on test items
than control items, suggesting that both groups preferred to avoid
the reversing strategy for gestures that were more difficult to
imitate. Moreover, younger children switched hands more often
than older children, which implies that exposure to and practice
with imitation of gestures renders these processes easier over
time.
More recently, Shield et al. (2017b) examined the ability of 14
deaf children with ASD between 5 and 14 years old (M=9.5)
and 16 age- and IQ-matched typical deaf children to imitate
a series of 24 one-handed gestures exhibiting inward–outward
movements and palm orientations and up–down movements and
palm orientations. They found that children with ASD made
significantly more palm orientation errors than typical children
(though movement direction errors were largely absent in both
groups). Both groups were also inconsistent in the hand that
they used to imitate the gestures, possibly to avoid the reversing
strategy: on average children with ASD switched hands in 5.67 of
24 trials (23.6%), while typical children switched hands in 3.26 of
24 trials (13.6%). However, note that 10 of 16 typical deaf children
and 7 of 14 deaf children with ASD were consistent in using
the same hand to imitate all of the trials; these children never
switched hands.
Taken together, these studies lead us to think that the
imitation of certain types of signs and gestures is particularly
difficult for hearing and deaf children with ASD. The inward–
outward palm orientation reversal errors identified in studies
of gesture imitation by hearing and deaf children with ASD
(Ohta, 1987; Smith, 1998; Whiten and Brown, 1998; Shield,
2010; Shield et al., 2017b) and in the sign language of
some hearing and deaf children with ASD (Shield and Meier,
2012) suggest that some children with ASD employ the visual
matching strategy in gesture imitation, and that this approach
to imitation can then influence how children produce signs
on their own. Typical children do not appear to employ this
strategy once they have mastered role reversal during the very
earliest stages of language development. Both typical children
and children with ASD switch hands when imitating gestures
hypothesized to require the reversing strategy in order to be
imitated correctly, thus resorting to the less-difficult mirroring
strategy.
STUDIES OF GESTURE IMITATION AND
SIGN ACQUISITION BY TYPICAL ADULTS
In this section, we add to the evidence from studies of children,
by reviewing several studies of how typical adults learn signs and
imitate gestures. We ask if adults who are learning a sign language
exhibit patterns like those described for children, and we ask how
adults who have no exposure to sign imitate gestures.
Sign Learning
Rosen (2004) studied 21 adult beginning learners of ASL
in a 15-week course and described the types of errors they
made in articulating signs. He predicted error types based on
perceptual and articulatory factors; here we discuss only the
former. He noted that perceptual errors would be rooted in
“the physical stance from which the learner views the input
source such as the teacher” and would occur “when signers
either mirror or make parallel their signs with those of the
teacher” (p. 38). Such perceptual errors could then lead to a
situation wherein “signers may reverse the handshape, location
of contacts, direction of movements, and the orientation of
palms within lexical signs as compared to their teacher” (p.
38). As he predicted, Rosen found that adult learners of sign
made location, movement, and palm orientation errors based
on what he called “mirrorization” and “parallelization.” In our
terminology, “mirrorization” errors reflect either the mirroring
or anatomical strategy and “parallelization” errors reflect the
visual matching strategy. Mirroring errors included reversals of
lateral movements; anatomical errors were evidenced by hand
switches from dominant to non-dominant. Visual matching
errors included palm orientation reversal errors such as the
ASL sign DO OR produced with palms facing inward rather than
outward. Thus, Rosen found that adult learners of sign struggled
with particular types of signs and utilized, in our terms, the
mirroring, anatomical, and visual matching strategies to produce
them. Unfortunately, he included no quantitative analyses so we
do not know how frequently the beginning learners made such
errors. Nonetheless, the documentation of these error types in
the literature is helpful insofar as it suggests that some signs are
more difficult to learn than others, and that typical adults employ
several of the imitation strategies we describe in this paper.
Gesture Imitation
We again look to studies of gesture imitation to verify if
the errors observed in sign production could be the result of
imitation processes. Shield (2010) asked 24 hearing, right-handed
undergraduate students who were naive to sign to imitate 48
manual gestures, half of which were extant ASL signs and half
of which were nonsense gestures created by modifying the ASL
signs. By hypothesis, half of the gestures required a reversing
strategy in order to be imitated correctly (i.e., lateral and
inward–outward path movements and inward–outward palm
orientations) and half did not (i.e., up–down path movements
and palm orientations).
The undergraduates made significantly more errors when
imitating ASL signs and nonsense gestures hypothesized to
require the reversing strategy in imitation (e.g., exhibiting a
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Shield and Meier Learning an Embodied Visual Language
lateral path movement) than on control items. Signs involving
a lateral movement were particularly vulnerable to error: 23
of 44 tokens (52.3%) of the sign BLACK (which moves from
the contralateral side of the forehead to the ipsilateral side; see
Table 1) contained a movement reversal error, while 16 of 44
tokens (36.4%) of the sign FLOW ER, which also entails a lateral
path movement across the face, contained a movement reversal
error. Two of the subjects imitated all gestures with their left
hand (despite being right-handed), thus employing the mirroring
strategy and avoiding the reversing strategy. Unlike children with
ASD, however, the undergraduates had no difficulty with inward–
outward movements or palm orientations and did not appear to
use the visual matching strategy.
Thus, this study suggests that typical adults tend to engage
a mirroring strategy when imitating novel gestures, which is
successful except in the case of lateral path movements when
handedness is shared between model and subject. In such cases,
typical adults made lateral movement reversal errors or switched
hands in order to mirror the gesture correctly.
DOES SIGN LANGUAGE EXPOSURE
CHANGE HOW LEARNERS IMITATE?
We have shown that the mirroring and visual matching strategies
both lead to specific kinds of imitation errors; furthermore it
appears that typical and atypical children as well as typical adults
produce errors consistent with these strategies in their signing
and gesture imitation. We now present two new studies to further
examine our hypotheses. We ask if sign language exposure can
change how learners imitate gestures. Specifically, we hypothesize
that sign language exposure could shift typical learners from a
mirroring strategy to a reversing strategy due to practice with
reversing.
Study 1: Mirroring and Signer Experience
Methods
To test the hypothesis that sign exposure may enable typical
adult learners to shift from a mirroring strategy to a reversing
strategy, we recruited non-signers, sign learners (intermediate
ASL students), and fluent signers for a study of gesture imitation.
Stimuli
We created 48 gesture stimuli based on four palm orientations
(up, down, in, out), six movements (inward toward the body,
outward from the body, up, down, ipsilateral→contralateral,
contralateral→ipsilateral), and two handshapes (the 1- and
5-handshapes); see Table 2. Each palm orientation type was
combined with each movement type to create 24 base gestures;
each of these gestures was then filmed twice, once with a 1-
handshape (with the index finger extended and all other fingers
retracted) and again with the 5-handshape (with all fingers
extended). Each videotaped stimulus lasted 1.5 s. None of the
gestures were extant ASL signs; thus, they were meaningless for
signers and non-signers alike.
We hypothesized that all subjects would be able to imitate
gestures with vertical and horizontal movements since these can
be imitated using the mirroring strategy. However, we predicted
that subjects with exposure to ASL would imitate gestures with
lateral movements more accurately than non-signers, since these
must be imitated using the reversing strategy. We did not predict
that any of the groups would have difficulty with the four palm
orientations, since these can also be imitated using a mirroring
strategy. In order to ensure that all participants would have the
opportunity to engage the reversing strategy, we verified the
handedness of each participant and then used either a right- or
left-handed version of the stimuli, such that every participant
imitated a model with concordant handedness. The left-handed
version of the stimuli was made by flipping the right-handed
stimuli horizontally; thus, the stimuli presented to left- and right-
handed participants were identical in every aspect, save for the
apparent handedness of the model.
Procedure
Participants stood in front of a 17′′ MacBook laptop computer,
which was placed approximately at eye level three feet away.
Participants were instructed to reproduce each gesture as
accurately as possible. Each participant viewed each of the 48
gesture stimuli in one of two pre-established random orders;
no stimuli were repeated. A 3-s pause followed each gesture
stimulus during which participants were asked to imitate the
gesture observed.
Participants
We recruited three groups of participants: (1) non-signing
undergraduate students at Boston University who had never had
any exposure to sign language (N=34; all right-dominant, 19
females), (2) sign learners, students who were then enrolled in
the fourth or fifth semester of an ASL course (N=25; 23 right-
dominant, 22 females), and (3) fluent signers, either professional
sign language interpreters or Deaf adults (N=18; all right-
dominant, 12 females)6.
Coding
Each trial was coded blindly by a Deaf native signer for movement
direction and palm orientation values so that the coder did not
know what the stimulus gesture had been. There were two values
per stimulus, a movement value and a palm orientation value. A
second coder, a fluent signer, then matched the coded trials to the
target movement and palm orientation values and re-coded each
trial as correct or incorrect. Any movement or palm orientation
value other than the target was considered an error. In order to
assess intercoder reliability, a third coder (also a fluent signer)
re-coded 20% of the trials. There were 10 disagreements out
of 288 re-coded trials; Cohen’s κwas 0.97 for palm orientation
(6 disagreements out of 288 trials) and 0.98 for movement (4
disagreements out of 288 trials), indicating very high levels of
agreement.
Statistical analysis
We fit a generalized linear mixed-effects model using error
frequency as the dependent variable. The independent variables
6Although we did not collect data on the ages of participants, it is worth noting
that the fluent signers were working adults or graduate students, while the other
two groups were undergraduate students.
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Shield and Meier Learning an Embodied Visual Language
TABLE 2 | Gesture stimulus types by palm orientation and direction of movement.
Palm orientation
Horizontal Vertical
MOVEMENT Out In Up Down
Vertical
Up
Down
Horizontal
In
Out
Lateral
Ipsi-Contra
Contra-Ipsi
Every gesture type above was shown to participants twice, once with a 1-handshape and once with a 5-handshape.
aExample of a stimulus with a 1-handshape (index finger extended).
bExample of a stimulus with a 5-handshape (all five fingers extended).
were experience (non-signer, sign learner, or fluent signer) and
gesture type (vertical, horizontal, or lateral movements; up–down
or in-out palm orientation). The mixed effects were necessary to
model the repeated measures design of the gesture type variable.
Results
Non-signers erred on 6.85% of the 48 gestures imitated
(M=6.56 errors, SD =4.62), sign learners erred on 2.63%
of gestures imitated (M=2.52 errors, SD =2.29), and
fluent signers erred on 1.39% of gestures imitated (M=1.33
errors, SD =1.88). Experience was a significant predictor
of performance, X2(2) =36.03, p<0.0001. Post-hoc Tukey
comparisons found that non-signers produced significantly more
errors than either sign learners (z=4.30, p<0.001) or fluent
signers, (z=5.59, p<0.001). The difference between the sign
learners and the fluent signers was not quite significant (z=2.08,
p=0.09).
Movement items
Non-signers produced a significantly higher error rate (24.3%;
M=3.88 errors, SD =3.41) than either sign learners (14.3%,
M=2.28 errors, SD =2.3) or fluent signers (6.3%, M=1.0
errors, SD =1.68) on lateral (ipsilateral-contralateral or vice
versa) movements [X2(2) =17.23, p<0.001], see Figure 4. Non-
signers also produced a significantly higher error rate (2.81%, M
=0.45 errors, SD =0.88) than either sign learners (0%) or fluent
signers (0%) on inward–outward movements [X2(2) =10.20,
p<0.01]. There were no group differences in error rates on up–
down movements; the non-signers produced two total errors on
this parameter, while the sign learners and fluent signers did not
produce any errors on this parameter.
Palm orientation items
Non-signers made more palm orientation errors than either sign
learners or fluent signers for both up–down [X2(2) =11.80,
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Shield and Meier Learning an Embodied Visual Language
FIGURE 4 | Error rate by movement type for non-signers, sign learners, and fluent signers. ***p<0.001.
p<0.01] and in-out [X2(2) =20.43, p<0.0001] palm orientation
types. Non-signers produced an error rate of 5.04% on up–down
palm orientations (M=1.2 errors, SD =1.1), compared to 0.83%
(M=0.2 errors, SD =0.1) for sign learners and 1.16% (M=0.28
errors, SD =0.57) for fluent signers. On in-out palm orientations,
non-signers produced an error rate of 4.04% (M=0.97 errors,
SD =1.58) compared to 0.17% (M=0.04 errors, SD =0.2) for
sign learners and 0.23% (M=0.06 errors, SD =0.24) for fluent
signers; see Figure 5.
Discussion
We predicted that subjects would make more imitation errors
on gestures involving lateral movements across the body than on
gestures involving vertical or horizontal movements due to a bias
toward a mirroring strategy rather than a reversing strategy. Our
prediction was borne out: lateral movements were significantly
more susceptible to error than other movement types. We
further predicted that imitation performance would interact with
exposure to sign language, with fluent signers making the fewest
number of errors, followed by sign learners, and finally by non-
signers (though note that we did not detect statistical differences
between the sign learners and the fluent signers). This prediction
was also borne out both for the movement and palm orientation
gesture types. In particular, non-signers produced a significantly
higher rate of reversals on lateral movement gestures (24%)
than sign learners (14%) or fluent signers (6%). Non-signers
also produced more errors on horizontal (in-out) movements
than either sign learners or fluent signers. Importantly, neither
signers nor non-signers made errors on the control condition of
imitating up–down (vertical) movements.
Non-signers also produced more errors on both kinds of palm
orientations than either sign learners or fluent signers. We did
not predict these error types; one plausible explanation for their
occurrence is that non-signers may have been paying particular
attention to the more perceptually salient movements and were
paying insufficient attention to palm orientation. Subjects with
sign exposure know to pay attention to both movement and palm
orientation, since both have linguistic value in sign.
Study 1 showed that certain types of gesture found in signed
languages are more difficult to imitate, especially for non-
signers who tend to employ the mirroring strategy, leading
to lateral movement errors. However, the reversing strategy
is only necessary when imitating lateral movements produced
by people with the same hand dominance, i.e., right-handers
imitating right-handers or left-handers imitating left-handers.
Would right-handed non-signers still make more errors on
lateral movements if they were imitating a left-handed model,
and thus could use a mirroring imitation strategy? In order to
test this specific hypothesis, we designed an additional study to
examine the role that handedness plays in perspective-taking.
Study 2: Mirroring and Discordant
Handedness
If the difficulty of the reversing strategy is truly at issue in
the imitation of lateral movement gestures, then right-handed
subjects should only have difficulty imitating other right-handers.
Thus, we predicted that right-handed subjects would not have
a problem imitating lateral gestures produced by a left-handed
model, since such movements can be imitated with a mirroring
strategy rather than a reversing strategy.
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Shield and Meier Learning an Embodied Visual Language
FIGURE 5 | Error rate by palm orientation type for non-signers, sign learners, and fluent signers. ***p<0.001.
FIGURE 6 | An example of how a gesture stimulus from Study 1 (left) was
flipped horizontally to appear as if produced by a left-handed gesture model in
Study 2 (right). Still images of gesture stimuli are reproduced here and in
Table 2 with written permission of the model.
Methods
To test the hypothesis that discordant handedness allows
imitators to avoid the reversing strategy on difficult lateral
movements, we modified the stimuli used in Study 1.
Stimuli
The 48 gesture stimuli used in Study 1 were flipped horizontally
such that it now appeared that the right-handed gesture model
was producing the gestures with her left hand; see Figure 6. We
predicted that right-handed non-signers would not make lateral
movement errors in this condition, since they should be able to
use mirroring to correctly imitate.
Subjects
For Study 2 we recruited 67 non-signing undergraduate students;
34 right-handed non-signers (19 women) were assigned at
random to the flipped condition, and 33 right-handed non-
signers (27 women) were assigned at random to the same non-
flipped condition as in Study 1.
Results
Results for Study 2 are shown in Figure 7. In the flipped
condition, participants made 10 errors on vertical movements
out of 544 trials (1.8%), while in the non-flipped condition,
participants made 2 errors on vertical movements out of 528
trials (0.4%). The difference between conditions for vertical
movements was marginally significant (Fisher’s Exact Test,
p=0.05). On horizontal movements, participants in the flipped
condition made 6 errors (1.1% of 544 trials); participants in
the non-flipped condition also made 6 errors on horizontal
movements (1.1% of 528 trials). There was no difference
between the two conditions for horizontal movements (Fisher’s
Exact Test, p=1.0, ns). On lateral movements, participants
in the flipped condition made just 5 errors (0.9% of 544
trials), but 109 errors in the non-flipped condition (20.6%
of 528 trials). A two-sample Cramer Von-Mises test found
that error rate on lateral movements was significantly lower
(p<0.001) in the flipped condition than in the non-flipped
condition.
No differences were detected between the error rates for palm
orientations. Participants produced errors on 1.64% of up–down
palm orientations in the non-flipped condition and 2.82% in the
flipped condition (Fisher’s Exact Test, ns), and 3.41% of in-out
palm orientations in the non-flipped condition and 1.47% in the
flipped condition (Fisher’s Exact Test, ns).
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Shield and Meier Learning an Embodied Visual Language
FIGURE 7 | Error rates on movement types in the flipped and non-flipped
conditions. Subjects were sign-naive undergraduates. ***p<0.001, *p=0.05.
Discussion
Study 2 showed that handedness interacts with imitation in
specific and predictable ways. First, subjects in the non-flipped
condition exhibited a high error rate (20.6%) when imitating
lateral movements, replicating the results of Study 1 and
confirming that imitating these gestures is difficult. Second,
subjects in the flipped condition (who thus appeared to be
imitating a left-handed model) made significantly fewer errors
(0.9% error rate). We thus demonstrate that gestures exhibiting
lateral path movements can be successfully imitated by right-
handed subjects when the model being imitated performs the
movements with her left hand, thereby enabling a mirroring
strategy rather than a reversing strategy. Thus, we find strong
evidence that gesture imitation strategies are influenced by
handedness and that lateral movements are easier for non-
signers to imitate when handedness is discordant, in line with
our predictions. We find no difference in the flipped and non-
flipped conditions for palm orientation, in accordance with our
prediction that palm orientation would not be affected by the
handedness of the model.
The two new gesture imitation studies described here support
three hypotheses about the difficulties involved in learning a
sign language. First, sign language exposure changes how adults
approach imitation, shifting them from a mirroring strategy to
a more difficult reversing strategy. Second, lateral movements
across the body are more difficult to imitate than either horizontal
(inward–outward) or vertical (up–down) movements, since
they require a reversing strategy in order to be successfully
imitated, provided that the handedness of the imitator and the
model is concordant. Since left dominance is relatively rare,
concordant handedness is likely to be true of the large majority
of sign learning encounters. Third, we demonstrate the role that
handedness plays in the imitation of lateral movements, as right-
handed non-signers were significantly better at imitating lateral
movements when imitating an apparently left-handed model.
GENERAL DISCUSSION
We have described some of the ways in which language
acquisition in the visual-gestural modality poses unique
challenges for sign language learners. Our argument can be
summarized as follows:
1. Signed languages use space for several purposes. They
can use space to talk about space, as in the descriptions of
spatial arrays discussed by Emmorey (2002). They can use
space to mark grammatical relations, as in verb agreement
and anaphora. Finally, they can use space in a fixed way,
as in lexical signs. The sign-learning child must learn to
distinguish these different constructions and uses of space.
Spatial arrays and grammatical uses of spatial anaphora are
relatively advanced skills that appear later in development,
but the acquisition of lexical signs occurs early. Children
must figure out that lexical signs are not specified for right
and left (unlike the spatial layout depicted in Figure 2) but,
instead for the movements of the dominant and non-dominant
hands.
2. The sign lexicon is composed of different types of
signs. Some are one-handed and some are two-handed; two-
handed signs may be symmetrical (with both hands exhibiting
the same handshapes and movements) or asymmetrical (with
each hand exhibiting a different handshape and movement).
Signers vary in hand dominance, thus input to children is
varied in terms of how they see one-handed and two-handed
asymmetrical signs being produced. Children also view signs
from various perspectives, further complicating the input they
receive.
3. At least four imitation strategies are available for imitating
signs. One strategy is the anatomical imitation strategy, in
which subjects activate the same muscles as the model they
are imitating, resulting in the switching of the hands from
dominant to non-dominant when signer and model do not
share handedness. We find evidence that typical adults, as well
as typical and atypical children, sometimes use this strategy,
particularly when imitating difficult gestures. A second strategy is
the mirroring strategy, in which subjects produce a mirror image
of the gestures or signs they are imitating. We find evidence
that typical adults learning sign and imitating gestures tend
to use this strategy, and that this results in lateral movement
errors when handedness is shared. A third strategy is the visual
matching strategy, in which subjects imitate what they see from
their own perspective. This leads to reversals in inward–outward
palm orientations and inward–outward movements in gesture
imitation and sign production. We find evidence that typical
adults learning sign, very young typical children, and older
hearing and deaf children with ASD sometimes employ this
strategy. Finally, skilled signers employ a reversing strategy, in
which they perform a mental spatial transformation in order
to reproduce the model’s gesture. We find that fluent sign
language users and sign language learners are better at imitating
gestures using the reversing strategy than are non-signers, who
prefer the mirroring strategy. We thus find evidence that sign
language exposure changes the way that typical adults imitate
gestures.
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Shield and Meier Learning an Embodied Visual Language
CONCLUSION AND FUTURE DIRECTIONS
We argue that the visual-gestural modality presents challenges
to sign language learners unlike the challenges faced by learners
of spoken languages. Learners confront variation in input
due to differences in handedness in the population, with no
obvious analog in speech. One potential analog in speech is the
acoustic variation in phoneme production caused by differently-
sized vocal tracts, but it is unclear how comparable these two
phenomena are. Furthermore the visual-gestural modality allows
for multiple ways to interpret the imitation task, while the vocal-
auditory modality generally does not. An exception in speech
arises in the imitation of pronouns, such that an imitation of the
sentence “Mommy loves you” can retain the modeled pronoun or
can replace it with “me”, thereby preserving the reference of the
model sentence.
In the future we need further work on the acquisition of the
sign lexicon by typical deaf children. In particular we need better
documentation of their early sign development with regard to
the specific predictions made here, especially with respect to the
movement and palm orientation types discussed. It would also be
interesting to know if signs hypothesized to be difficult to imitate
are acquired relatively late in development. A systematic analysis
of the MacArthur-CDI database for ASL signs (Anderson and
Reilly, 2002; http://wordbank.stanford.edu) could shed light on
this problem.
The reports of reversed inward–outward palm orientations in
children with ASD, whether hearing children imitating gestures
or deaf children producing signs, are a robust indicator that some
children with ASD use the visual matching strategy in imitation.
However, we still do not have a clear understanding of which
children with ASD tend to use this strategy nor how frequently
the phenomenon occurs. It may just be a subset of children with
ASD who use this strategy rather than being a characteristic
strategy of all children with ASD; a crucial question to ask
is if those children who employ the visual matching strategy
also share a cognitive profile and if other related cognitive
characteristics can be identified.
Lastly, we need further work on the gesture development of
hearing children in the first 2 years of life. We need systematic
documentation of whether or not typical infants reverse the
direction of their palm when producing early gestures such as
the “wave bye-bye” gesture, when they produce the gesture in
its mature form, and what other cognitive milestones occur
contemporaneously. Such work on typical deaf and hearing
children will put us in a better position to understand the
development of sign and gestures in children with ASD. It will
also help clarify how children approach imitation and if emergent
imitation strategies can be more clearly linked to sign language
development.
ETHICS STATEMENT
All subjects gave written informed consent in accordance with
the Declaration of Helsinki. The protocol was approved by the
Institutional Review Board of Boston University.
AUTHOR CONTRIBUTIONS
AS designed and conducted the original studies reported in
this paper, contributed to the development and refining of the
hypotheses described in the paper, and was the primary author of
the paper. RM contributed to the development and refining of the
hypotheses described in the paper, the designing of the original
studies reported, and the writing of the paper.
FUNDING
This work was supported by grant 1F32-DC0011219 from
NIDCD and Research Enhancement Grant 14-04 from the
Autism Science Foundation to AS.
ACKNOWLEDGMENTS
We thank T. Sampson and A. Hough for coding data, A. Hough
for modeling gestures, F. Ramont for modeling ASL signs, A.
Marks for taking photos of ASL signs, N. Coffin, A. Hensley, and
H. Harrison for statistical consulting and analysis, B. Bucci and
the Deaf Studies Program at Boston University for recruitment
of ASL students, and H. Tager-Flusberg for research support.
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Conflict of Interest Statement: The authors declare that the research was
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