Dialog with Robots: Papers from the AAAI Fall Symposium (FS-10-05)

Active Learning for Generating Motion and Utterancesin Object Manipulation Dialogue Tasks ∗Komei Sugiura, Naoto Iwahashi, Hisashi Kawai and Satoshi Nakamura
National Institute of Information and Communications Technology,
3-5 Hikaridai, Seika, Soraku, Kyoto 619-0289, Japansystems, the whether-to-conﬁrm problem receives considerable attention in the context of error handling (Komatani and
Kawahara 2000, Bohus and Rudnicky 2005).
The problem of how to conﬁrm is the problem of paraphrasing user’s commands. The sentence “Bring me a cup”
is ambiguous when there are multiple cups, and askinga conﬁrmation question such as “Do you mean the bluecup?” can disambiguate the sentence. Moreover, when direct and/or indirect objects are omitted (object ellipsis) in theuser’s utterance, such as “Place the cup down (on the table),”it would be preferable to generate an appropriate description of the objects. The how-to-conﬁrm problem deals withthe mapping between language and physical/virtual objects,
and has been widely explored in Natural Language Generation (NLG) studies (e.g., Dale and Reiter 1995, Jordan
and Walker 2005, Funakoshi et al.2009) presents a model
for priming speech recognition using visual and contextual
information.
The robotics community has recently been paying greaterattention to the mapping between language and real-worldinformation, mainly focusing on motion (Kruger et al. 2007,
Sugita and Tani 2005, Inamura et al. 2004). (Ogata etal. 2007) presents an application of recurrent neural networks to the problem of handling many-to-many relationships between motion sequences and linguistic sequences.
In (Takano and Nakamura 2009), a linguistic model basedon the symbolization of motion patterns is proposed. Moreover, we have proposed a robot language acquisition framework “LCore” that integrates multimodal information suchas speech, motion, and visual information(Iwahashi 2007).
In this study, we extend LCore with a scheme of dialogue management method based upon an adaptive conﬁdence measure. called the integrated conﬁdence measure(ICM) function. The proposed method has three key features:

Abstract
In an object manipulation dialogue, a robot may misunderstand an ambiguous command from a user, such as “Placethe cup down (on the table), ” potentially resulting in an accident. Although making conﬁrmation questions before all motion execution will decrease the risk of this failure, the user
will ﬁnd it more convenient if conﬁrmation questions are notmade under trivial situations. This paper proposes a method
for estimating ambiguity in commands by introducing an active learning framework with Bayesian logistic regression tohuman-robot spoken dialogue. We conducted physical experiments in which a user and a manipulator-based robot communicated using spoken language to manipulate objects.

1

Introduction

For practical reasons, most dialogue management mechanisms adopted for service robots process verbal (user’s utterances) and nonverbal (e.g., vision, motion and context)
information separately. With these mechanisms, neither thesituation nor previous experiences are taken into accountwhen a robot processes an utterance, so there is a possibility that it will execute motions that the user had not imagined. In this study, we deﬁne “motion failure” as occurring
when a robot has executed an undesirable motion because ofa recognition error.
The goal of this study is to decrease the risk of motion failure. A simple solution to decrease the risk of motion failure
is to make conﬁrmation utterances before motion execution,such as “You said ‘Bring me the cup.’ Is this correct?” However, there are two main hurdles to generating conﬁrmationutterances: whether to conﬁrm and how to conﬁrm.
The problem of whether to conﬁrm is a decision-making
problem of whether a conﬁrmation utterance should be madeor not. Although making conﬁrmation utterances before all
motion executions would be simple and effective, this would
however seriously disrupt the dialogue. Speciﬁcally, the user
will ﬁnd it more convenient if conﬁrmation questions are notmade under trivial situations. In the ﬁeld of spoken dialogue

1. A user model corresponding to each modality is assumed
to be shared by the user and robot. This assumption enables us to introduce an active learning framework into
human-robot dialogue. The user model is explained in
Section 3.

∗ This research was partially supported by the Ministry of Education, Science, Sports and Culture, Grant-in-Aid for ScientiﬁcResearch (C), 20500186, 2008, and the National Institute of Informatics.
c 2010, Association for the Advancement of Artiﬁcial
Copyright Intelligence (www.aaai.org). All rights reserved.

2. Active learning is used for selecting the optimal utterances to generate, which effectively train the ICM function. The introduction of active learning is evaluated us-

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ing likelihood criteria in Section 5.
3. Bayesian logistic regression (BLR)(Genkin, Lewis, andMadigan 2007) is used for learning the ICM function thatenables us to estimate the probability that the user’s utterances will be successfully understood from multimodal
information.

2

Task Environment

Object Manipulation Dialogue Task
Figure 3 shows the task environment used in this study. A
user sits in front of a robot and commands the robot by
speech to manipulate objects on the table located between
the robot and the user. The robot is also able to commandthe user by speech to manipulate the objects. The objects
used in the experiments are shown in Figure 2.
We assume that linguistic knowledge (e.g., phoneme sequence and, word sequence) and non-linguistic knowledge(e.g., motion and, visual information) are learned by using LCore(Iwahashi 2007). This knowledge is not given by
the designer, but is learned through interaction with users.
Knowledge representation in LCore is explained in Section
3 in detail. The main functions given by the designer are
object extraction and calculation of visual features.
The task has three phases:

Figure 1: An example of object manipulation dialogue
tasks.

1. Robot command phase (learning phase (a))
The robot commands the user to manipulate objects. The
ICM function is trained using the proposed method.

The visual features and positions of objects were extracted from image streams obtained from the stereo vision
camera. The extraction and tracking of objects are done
based on their color. The visual features have six dimensions: three for color (L*a*b* color space) and three forshapes. The shape features, object area farea , squareness
fsq , and width-height ratio fwhr are deﬁned as farea = whand fsq = Nobj /wh, where h, w and Nobj denotes the object’s height, width, and number of pixels, respectively. For
motion learning/recognition, the trajectories of objects’ centers of gravity are used.

Figure 2: Objects used in Figure 3: Robotic platform
experiments.
used in the experiments.

2. User command phase (learning phase (b))
The user commands the robot to manipulate objects. The
ICM function is trained with initialization based on the
results of the robot command phase.
3. Motion execution phase
The user commands the robot to manipulate objects, however the ICM function is not updated. Motion and conﬁrmation utterances are generated by the method proposedin (Sugiura et al. 2009).

3

Figure 1 shows an example of the user command phase.
The ﬁgure depicts a camera image in which the robot is told
to place Object 1 (Barbabright) on Object 2 (red box). The
solid line shows the trajectory intended by the user. The
relative trajectory between the trajector (moved object) andthe reference object is modeled with a hidden Markov model(HMM)(Sugiura and Iwahashi 2007). The reference object
can be the trajectory itself or a landmark characterizing the
trajectory of the trajector. In the case shown in Figure 1, thetrajector, reference object, and reference point are Object 1,
Object 2, and Object 2’s center of gravity, respectively.

The LCore Framework

LCore Overview
The LCore(Iwahashi 2007) selects the optimal action basedon an integrated user model trained by multimodal information when a user’s utterance is input. A user model corresponding to each modality (speech, vision, etc.) is called
a belief module. The user model integrating the ﬁve belief
modules – (1) speech, (2) motion, (3) vision, (4) motionobject relationship, and (5) behavioral context– is called theshared belief Ψ.

Utterance Understanding in LCore

Robotic Platform

An utterance s is interpreted as a conceptual structure z =(WT ,WL ,WM ), where WT , WL , and WM represent the phrases
describing the trajector, landmark, and motion, respectively.
For motion concepts that do not require a landmark object,z = (WT ,WM ). For example, the user’s utterance, “Place-on
Barbabright red box,” is interpreted as follows:
WT : [ Barbabright ], WL : [ red , box ], WM : [ place-on ]Figure 3 shows the robot used in this study. The robot
consists of a manipulator with seven degrees of freedom (DOFs), a four-DOF multiﬁngered grasper, a microphone/speaker, a stereo vision camera, 3D time-of-ﬂight
camera (SR-4000), and a gaze-expression unit. Teaching
signals can be provided by hitting a touch sensor on thegrasper.

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The LCore does not deal with function words such as prepositions and articles, i.e. the user is not supposed to use words
such as “on” and “the.”Suppose that an utterance s is given under a scene O. O
represents the visual features and positions of all objects inthe scene. The set of possible actions A under O is deﬁned
as follows: j
A = {(it , ir ,CV ) | it = 1, ..., ON , ir = 1, ..., RN , j = 1, ...,VN } {ak | k = 1, 2, ..., |A|},(1)
where it denotes the index of a trajector, ir denotes the index
of a reference object, ON denotes the number of objects in
O, RN denotes the number of possible reference objects for j
the verb CV , and VN denotes the total number of CV in thelexicon.
Each belief module is deﬁned as follows: First, the belief
module of speech, BS , is represented as the log probabilityof s conditioned by z. Here, word/phrase orders is learned byusing bigrams/trigrams. Next, the belief module of motion,
BM , is deﬁned as the log likelihood of a probabilistic model
given the maximum likelihood trajectory Ŷk for ak . The belief module of vision, BI , is represented as the log likelihood
i
of WT given Object i’s visual features xI , where Object i iseither the trajector it or the landmark ir . Similar to BI , the belief module of motion-object relationship, BR , is represented
as the log likelihood of a probabilistic model given the visualfeatures of Objects it and ir . The belief module of behavioral
context, BH (i, qi ), represents the adequateness of Object i
i ii
as the referent under the context qi = (q1 , q2 ), where q1
i
and q2 stand for truth values representing the statements“Object i is being grasped” and “Object i was manipulated
most recently”, respectively. The details of the deﬁnitions ofabove modules are presented in (Iwahashi 2007).

i 

i 

 j

it  ir   j
+γ4 log P(xI , xI |CV )
+γ5 BH (it , qit  ) + BH (ir , qir  ) ,4

Active Learning of the Integrated
Conﬁdence Measure Function

The schematic of the proposed method is illustrated in Figure 4. Each function in the ﬁgure is explained below.

Modeling Conﬁdence for Utterance Understanding
The proposed method quantiﬁes ambiguities in a user’s utterances. In this subsection, we ﬁrst explain the ambiguity
criterion used in this study.
Given a context q, a scene O, and an utterance s, the optimal action âk is obtained by maximizing the shared belief
function.
(3)âk = argmax Ψ(s, ak , O, q)
ak ∈A

We deﬁne the margin function d for the action ak ∈ A as thedifference in the Ψ values between ak and the action maximizing Ψ, a j ( j = k) :d(s, ak , O, q) = Ψ(s, ak , O, q) − max Ψ(s, a j , O, q)
(4)
j=k

Let al be an action that gives the second maximum Ψ value.
When the margin for the optimal action âk is almost zero, theshared belief values of âk and al is nearly equal; this meansthat the utterance s is a likely expression for both âk and al .
In contrast, a large margin means that s is an unambiguous
expression for âk . Therefore, the margin function can beused as a measure of the utterance’s ambiguity.
Now we deﬁne the integrated conﬁdence measure (ICM)
function by using a sigmoid function, as follows:1,(5)f (d; w) =1 + exp−(w1 d+w0 )where d is the value of the margin function for an action,
and w = (w0 , w1 ) is the parameter vector. The ICM function
is used for modeling the probability of success.
We now consider the problem of estimating the parameters w of the ICM function based on logistic regression. The
ith training sample is given as a pair consisting of the margin
di and teaching signal ui . Thus, the training set TN contains
N samples:(6)
TN = {(di , ui )|i = 1, ..., N},
where ui is 0 (failure) or 1 (success).
BLR(Genkin, Lewis, and Madigan 2007) is used for obtaining the MAP estimate of w. A univariate Gaussian priorwith mean mi and variance τi (i = 0, 1) on each parameter

The shared belief function Ψ is deﬁned as the weighted
sum of each belief module:
Ψ(s, ak , O, qit  ) =
γ1 log P(s|z)P(z; G)
[BS ]
max
z


it 
ir 
+γ2 log P(xI |WT ) + log P(xI |WL ) [BI ]+γ3 log P(Ŷk |x p t , x p r ,CV )Figure 4: Schematic of the proposed method.

[BM ]
[BR ]
[BH ]
(2)

i 
xpr

denotes the position of Object i, and γ =where(γ1 , ..., γ5 ) denotes the weights of the belief modules. The
MCE learning(Katagiri, Juang, and Lee 1998) is used forthe learning of γ.
Inappropriate speech recognition results are re-ranked
lower by using Ψ. There are several methods for re-ranking
an utterance hypothesis (e.g. (Lemon and Konstas 2009)). In
contrast, information on physical properties such as visionand motion is used in Ψ, since object manipulation requires
physical interaction.

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5

wi is used.
−w2i

1
exp
P(wi |τi ) = N (mi , τi ) = √
2τi
2πτi

Experimental Setup(7)

To evaluate the proposed method, we conducted two kinds ofexperiments: (1) active learning of the ICM function, and (2)evaluation of the proposed method. The objective of Experiment (1) is to investigate the number of samples necessary
for convergence of the learning. Experiment (2) was aimed
at evaluating the effectiveness of using the result of Experiment (1) as the prior distribution. Although the effectivenessis unclear since the assumption that the user and robot share
the ICM function is not always true, we will clarify the advantages of the proposed method.
In Experiment (1), the robot commanded the user byspeech to manipulate objects based on the proposed method.
This ﬂow which starts from the robot’s utterance and ends
with the user’s manipulation is called an episode. The maximum number of episodes was set to 30. The prior distribution of the parameter wi was deﬁned as a univariate Gaussian
distribution. The parameters of the prior, or hyperparameters, were set as (m0 , m1 , τ0 , τ1 ) = (0, 1, 100, 100). The hyperparameters (m0 , m1 ) were set as (m0 , m1 ) = (0, 1) so as
to make the initial ICM function be the standard logistic sigmoid function. The maximum length of (WT ,WL ,WM ) were
set to (3,3,1), respectively.
In Experiment (2), we obtained the training and test data
as follows. First, the subject was instructed to command
the robot in the same environment as Experiment (1). This
enabled us to obtain 60 pairs of camera image and speech,
which we labeled with the indices of {motion, trajector,
landmark}. Half of the data was used as a training set andthe other half was used as a test set.
We compared the case in which the parameter estimatedin Experiment (1) was used as the prior distribution witha case involving a “standard” prior distribution without parameter tuning. The parameters of the standard prior wereset as (m0 , m1 , τ0 , τ1 ) = (0, 1, 100, 100). To evaluate thesemethods, we compared test-set likelihood, where ten different combinations of a training and test set were used. Similar
to Experiment (1), we use the word “episode” to represent
the ﬂow that begins from the user’s utterance and ends withthe robot’s manipulation.
In Experiment (2), the number of motion failures was also
compared. We compared the average number of motion failures occurring from the ﬁrst to the ic th episodes, where ic
represents the episode in which a convergence condition regarding log likelihood L was met. The convergence condition is set as L < −20, based on the results of the experiment in (Sugiura et al. 2009). Although we continued theactual experiment after the convergence condition was met,
the learning should be terminated here for efﬁciency.
The lexicon used in the experiments contained 23 words(8 nouns, 8 adjectives, and 7 verbs). The user taught thenames or properties of objects in Japanese1 by showing theobjects to the robot. Unsupervised learning was used for
obtaining the phoneme sequences of the words(Iwahashi2007). Those words had been grounded to the physical prop-

Utterance Selection as Active Learning
The utterance candidate generator (see Figure 4) generates
all possible linguistic expressions for each action ak andcalculate their margin. The set of margin is input to thescoring function based on Expected Log Loss Reduction(ELLR)(Roy and McCallum 2001) and Bayesian logistic regression (BLR)(Genkin, Lewis, and Madigan 2007). Next,
the optimal margin linked with an utterance is selected andthe utterance is output as a speech command to the user.
The true/false judgment module recognizes the motion performed by the user, and judges the result as 0(false) or1(true). The result is input to the training set and used by
the scoring function.
Basically, a training sample for learning the ICM function
is obtained when a robot has executed a motion. Note that
we assume that belief modules and Ψ are shared by the user
and the robot to introduce active learning. Based on thisassumption, we can train the ICM function by using training
data obtained when the robot commands the user by speech
to manipulate an object.
The proposed method selects the utterance that is mosteffective for learning the function based on Expected Log
Loss Reduction (ELLR)(Roy and McCallum 2001). Among
many criteria, uncertainty sampling(Lewis and Gale 1994)
is the most basic method in active learning, however it selects a sample with the most entropic prediction. In contrast,
ELLR asks for labels on examples that, once incorporated
into training, will result in the lowest expected error on thetest set(Roy and McCallum 2001).
Now, let fˆN (d) denote the ICM function trained by thedata set TN . The log loss L(TN ) is deﬁned as follows:
L(TN ) =N ∑ fˆN (di ) log fˆN (di ) + (1 − fˆN (di )) log(1 − fˆN (di ))i=1

In this case, L(TN ) can be regarded as the sum of entropy.
Let V = {v j | j = 1, ..., |V |} denote the utterance candidates in the scene O, and e j denote the margin linked with
v j . Here, V means the possible combinations of a word sequence that consists of learned words. We make V a ﬁnite set
by limiting the length of a sequence. The proposed method
selects the utterance that minimizes the Expected Log Loss
E(TN , e j ). E(TN , e j ) is deﬁned as follows:
N+1
N+1
) + (1 − fˆN (e j ))L(T−),
E(TN , e j ) = fˆN (e j )L(T+N+1

Experiments

N+1

T+
 TN ∪ (e j , 1), T− TN ∪ (e j , 0)(8)Thus, Equation (8) takes into account the effect of a not-yetobtained sample. In ELLR, fˆN+1 (e j ) is trained in advanceof obtaining the (N + 1)th sample. On the other hand, uncertainty sampling(Lewis and Gale 1994) does not take into
account the effect of selecting the (N + 1)th sample.

1 In this paper, the utterances are translated into English.

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Figure 7: Training samples. Yellow frames represent themost recently manipulated objects. Left: The input user
utterance was “Move-away Kermit,” and the correct output
was to move Object 86 away from Object 82. Right: The
input user utterance was “Place-on red box,” and the correct
output was to place Object 76 on Object 77.

[Situation: Object 1 was manipulated most recently]
R: Jump-over Pooh-doll Kermit.
U: (The user makes Object 3 jump over Object 2.)

Figure 5: Dialogue example in the learning phase. The correct action is to make Object 3 (Pooh-doll) jump over Object
2 (Kermit).

Figure 8: Left: The test-set log likelihood of (1) the proposed method and (2) a baseline. Right: Average number ofmotion failures.
Figure 6: Margin selected by Equation (8). The dotted line
shows an episode in which motion failure by the user occurred.

features of the extracted objects, context information (Object X was manipulated most recently, etc), and user utterances.
The left-hand ﬁgure of Figure 8 compares the averagetest-set log likelihood of (1) the proposed method and (2)the baseline which used a standard prior. The lines show theaverage log likelihood, where ten different combinations ofa training and test set were used. The ﬁgure clearly indicates that the proposed method outperformed the baseline in
the early episodes.
The right-hand ﬁgure of Figure 8 compares the average
number of motion failures occurring from the ﬁrst to the ic th
episodes. From the ﬁgure, we can see that the number of motion failure could be reduced by using the proposed method
if we terminated the learning at the ic th episode. The reduction in the number of motion failures supports the validity ofthe prior pre-trained by using active learning.

erties of objects and motions in the learning phase of thelexicon (Iwahashi 2007, Sugiura and Iwahashi 2007).

Results (1): Active Learning of the ICM Function
First, we address the qualitative results. Figure 5 shows anexample dialogue between the subject (U) and the robot (R).
In this case, the number of possible combinations of objects
and motion were 45, which means that 45 pairs of a word
sequence and margin are generated by the utterance candidate generator shown in Figure 4. Among the pairs, the margin d = 13.4 is selected based on Equation (8). Here, theutterance linked with the margin d = 13.4 was “Jump-overPooh-doll Kermit (Make the Pooh doll jump over Kermit.),”In Figure 6, the selected margin is plotted against an
episode that represents the number of robot utterances. In
the ﬁgure, the dotted line shows the episode in which motion failure by the user has occurred. From the ﬁgure, we
can see that the larger margin is selected at the (i∗ + 1)th
episode compared with the i∗ th episode, where i∗ represents
the episode in which such motion failure occurred. Thismeans that an utterance with less ambiguity is selected atthe (i∗ + 1)th episode.

Additional Result in Motion Execution Phase
In this subsection, we show an additional qualitative resultin the motion execution phase. The experiment conditions
are explained in detail in (Sugiura et al. 2009). Figure 9shows a dialogue example in which a user’s utterance is disambiguated by using grounded information.
In Figure 9, the ICM value of the optimal action â wassmall. Therefore, the robot ﬁrst asked whether “green box”
was the trajector. Here, the word “green” was used to describe the major difference between Object 2 (the green box)

Results (2): Evaluation of the Proposed Method
Figure 7 shows examples of camera images input for the proposed method. The inputs into the system were the visual

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[Situation: Object 2 was manipulated most recently]
U: Move-closer box Elmo.
R: Move-closer green box?
U: No.
R: Move-closer blue box?
U: Yes.
R: (The robot moves Object 3 closer to Object 1.)Figure 9: Dialogue example (2). Motion execution with a
conﬁrmation utterance. The correct action is to move Object
3 (the blue box) closer to Object 1 (Elmo).
and Object 3 (the blue box). In the second conﬁrmation utterance, the word “blue” was inserted into the phrase WT ,since this gave the maximum margin. In contrast, the landmark was not mentioned in either generated utterance since
no word insertion into WL had a signiﬁcant inﬂuence on the
ICM values.

6

Conclusion

Safe interaction with users is a critically important requirement for assistive robots supporting users in everyday
environments. In this paper, we proposed a methodthat decreases the risk of motion failure in the learning
phase. One of the contributions of this study is the introduction of active learning into a multimodal spoken
dialogue system. Some demo video clips can be foundat http://mastarpj.nict.go.jp/˜ksugiura/
video_gallery/video_gallery_en.html.

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