Expressive Gestures for NAO Robot Communication

Expressive Gestures for NAO

Quoc Anh Le- Catherine Pelachaud
CNRS, LTCI, Telecom-ParisTech, France

NAO TechDay, 13/06/2012, Paris

Motivation

 Importance of expressive
gestures [Li et al, 2009]
• Communicating messages
• Expressing affective states

 Relation between gesture and
speech [Kendon, 2004]
• Two aspects of the same
process of utterance
• Complement and supplement

 Believability and life-likeness
• Robot should communicate in
a human-like way (emotion,
persionality, etc) [Fong, 2003]

page 1 NAO TechDay 2012 Le Quoc Anh & Catherine Pelachaud

Objectives

 Generate communicative gestures for Nao robot
• Integrated within an existing platform for virtual agent
• Nonverbal behaviors described symbolically
• Synchronization (gestures and speech)
• Expressivity of gestures

 GVLEX project (Gesture & Voice for Expressive Reading)
• Robot tells a story expressively.
• Partners : LIMSI (linguistic aspects), Aldebaran (robotics),
Acapela (speech synthesis), Telecom ParisTech
(expressive gestures)

State of the art

 Several initiatives recently:
• Salem et Kopp (2012): robot ASIMO, the virtual
framework MAX, gesture description with MURML.

• Aaron Holroyd et Charles Rich (2011): robot Melvin,
motion scripts with BML, simple gestures, feedback to
synchronize gestures and speech

• Ng-Thow-Hing et al. (2010): robot ASIMO, gestures
selection, synchronization between gestures and speech.

• Nozawa et al. (2006): motion scripts with MPML-HP,
robot HOAP-1

 Our system: Focus on expressivity and synchronization of
gestures with speech using a common platform (SAIBA
compliant [Kopp, 2006]) for Greta and for Nao


Our methodology

 Gesture describes with a symbolic language (BML)

 Gestural expressivity (amplitude, fluidity, power,
repetition, speed, stiffness,…)

 Elaboration of gestures from a storytelling video corpus
(Martin et al., 2009)

 Execution of the animation by translating into joint values


Problem and Solution

 Using a common framework to control both virtual and
physical agents raises several problems:
• Different degrees of freedom
• Limit of movement space and speed
 Solution:
• Use the same representation language
- same algorithm for selecting and planning gestures
- different algorithm for creating the animation
• Elaborate one gesture repository for the robot and
another one for the Greta agent
• Gesture movement space and velocity specification


Steps

1. Build a library of gestures from a corpus of storytelling video: the gesture
shapes should not be identical (between the human, virtual agent, robot)
but they have to convey the same meaning.
GRETA
System

2. Use the GRETA system to generate gestures for Nao
• Following the SAIBA framework
- Two representation languages: FML (Function Markup Language) and BML (Behavior
Markup Language)

- Three separated modules: plan communicative intents, select and plan gestures, and
realize gestures
Behavior
BML
Intent Behavior Realizer
Text Planning FML Planning

BML Behavior
Realizer


Global diagram

Nao Lexicon Greta Lexicon

LEXICONs

Gesture Synchronisation
Selection with AI speech

Planification of Modification of
gesture gesture
expressivity
duration KEYFRAMES
FML BML


Nao Lexicon

Gesture annotations [Martin et al., 2009]
Gesture Lexicon

Gesture velocity specification
(Minimal duration,Fitt’s Law)
Position …
000 001 002 010
(fromto)
…
000 0 0.15:0.18388 0.25:0.28679 0.166:0.2270

…
001 0.15:0.18388 0 0.19:0.19552 0.147:0.2754

…
002 0.25:0.28679 0.19:0.19552 0 1.621;0.3501
Gesture space specification …
010 0.166:0.2270 0.147:0.2754 1.621;0.3501 0

…
… … … … …


Gesture Specification
 Gesture->Phases->Hands (wrist position, palm orientation, hand shape,...)
[Kendon, 2004]
 Only stroke phases are specified. Other phases will be generated automatically
by the system
1. <gesture id="greeting" category="ICONIC" min_time="1.0“ hand="RIGHT">
2. <phase type="STROKE-START" twohand="ASSYMMETRIC“ >
3. <hand side="RIGHT">
4. <vertical_location>YUpperPeriphery</vertical_location>
5. <horizontal_location>XPeriphery</horizontal_location>
6. <location_distance>ZNear</location_distance>
7. <hand_shape>OPEN</handshape>
8. <palm_orientation>AWAY</palm_orientation>
9. </hand>
10. </phase>
11. <phase type="STROKE-END" twohand="ASSYMMETRIC">
12. <hand side="RIGHT">
13. <vertical_location>YUpperPeriphery</vertical_location>
14. <horizontal_location>XExtremePeriphery</horizontal_location>
15. <location_distance>ZNear</location_distance>
16. <hand_shape>OPEN</handshape>
17. <palm_orientation>AWAY</palm_orientation>
18. </hand>
19.</phase>
20.</gesture> An example for a greeting gesture


Synchronization of gestures with speech

 The stroke phase coincides or precedes emphasized words of the
speech [McNeill, 1992]

 Gesture stroke phase timing specified by synch points


Synchronization of gestures with speech

 Algorithm
• Compute preparation phase
• Delete gesture if not enough time
• Add a hold phase to fit gesture planned duration
• Coarticulation between several gestures
- If enough time, retraction phase (ie go back to rest position)

Start end Start end

- Otherwise, go from end of stroke to preparation phase of next
gesture S-start S-end S-start S-end

Start
end

Gestural Expressivity vs. Affective States

 A set of gesture dimensions [Hartmann, 2005]
• Spatial Extent (SPC): Amplitude of gesture movement
• Temporal Extent (TMP): Speed of gesture movement
• Power (PWR): Acceleration of gesture movement
• Fluidity (FLD): Smoothness and Continuity
• Repetition (REP): Number of stroke phases in a gesture movement
• Stiffness (STF): Tension/Flexibility

 Example [Mancini, 2008]

Affective states SPC TMP FLD PWR
Sadness Low Low High Low
Happy High High High High
Angrily High High Low High


Spatial Extent (SPC)

A real number in the interval [-1 .. 1]
• Zero corresponds to a neutral behavior
• -1 corresponds to small and contracted movements
• 1 corresponds to wide and large movements

 Guarantee the unchangeability of the meaning
• Gesture (modifiable dimension, unmodifiable
dimension)
• Example: Negation (vertical position is fixed)


Temporal Extent (TMP)

• Slow if the value is negative
• Fast if the value is positive


Power (PWR)

• Movements more powerful correspond to higher
acceleration

 Affect hand shape (close to open)
• More relax/open if the value is negative
• Fist corresponds to 1

 Affect duration of stroke phase repetitions


Fluidity (FLD)

• Higher values allow smooth and continuous
execution of movements
• Lower values create discontinuity in the movements

 Not yet implemented for Nao


Repetition (REP)

 Number of stroke phase repeats in a gesture
movement

 Tendency to rhythmic repeats of specific
movements

 Each stroke coincides with a emphasized
word/words of the speech


Animation Computation & Execution

 Schedule and plan gestures phases
 Compute expressivity parameters
 Translate symbolic descriptions into joint values
 Execute animation
• Send timed key-positions to the robot using
available APIs
• Animation is obtained by interpolating between joint
values with robot built-in proprietary procedures.


Example
<bml> <lexicon> <bml>
<speech id="s1" start="0.0“ <speech id="s1" start="0.0“
<gesture id="hungry" category="BEAT" hand="BOTH">
vce=speaker=Antoine spd=180 vce=speaker=Antoine spd=180
Et le troisième dit en colère: vce=speaker=AntoineLoud <phase type="STROKE" twohand="SYMMETRIC"> Et le troisième dit tristement: vce=speaker=AntoineSad spd=90
spd=200 <tm id="tm1"/>J'ai très faim!
<hand side="RIGHT">
<tm id="tm1"/>J'ai très faim! </speech>
</speech> <vertical_location>YCenterCenter</vertical_location> <gesture id=“hungry" start="s1:tm1" end=“start+1.5" stroke="0.5“>
<gesture id=“hungry" start="s1:tm1" end=“start+1.5" <PWR.value>-1.0</PWR.value>
stroke="0.5“> <PWR.value>1.0</PWR.value> <horizontal_location>XCenter</horizontal_location> <SPC.value>-0.3</SPC.value>
<SPC.value>0.6</SPC.value> <location_distance>ZMiddle</location_distance> <TMP.value>-0.2</TMP.value>
<TMP.value>0.2</TMP.value> <FLD.value>0</FLD.value>
<FLD.value>0</FLD.value> <hand_shape>CLOSED</handshape> <STF.value>0</STF.value>
<STF.value>0</STF.value> <REP.value>0</REP.value>
<palm_orientation>INWARD</palm_orientation>
<REP.value>0</REP.value>
</gesture> </hand> </gesture>
</bml> </bml>
</phase>

</gesture>

</lexicon>

The same gesture prototype
Different expressivity Different expressivity
(i.e. Anger) (i.e. Sadness)


Video demo: Nao tells a story


Conclusion

 Conclusion
• A gesture model is designed, implemented for Nao while taking into
account physical constraints of the robot.
• Common platform for both virtual agent and robot
• Expressivity model

 Future work
• Create gestures with different emotional colour and personal style
• Validate the model through perceptive evaluations


Acknowledgment

 This work has been funded by the ANR GVLEX project
 It is supported from members of the laboratory TSI,
Telecom-ParisTech


Expressive Gestures for NAO Robot Communication

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