Proceedings of the 27th IEEE International Symposium
on Robot and Human Interactive Communication,
Nanjing, China, August 27-31, 2018

MoBT3.2

Designing LED Lights for Communicating Gaze with
Appearance-Constrained Robots
Sichao Song1 and Seiji Yamada2
Abstract— Functional robots are generally restricted in appearance, thus lacking ways to express their intent. In humanhuman interaction, gaze is an important cue for providing
information and regulating interaction. In this pilot study, weinvestigate how we can implement gaze behavior in functional
robots since gaze communication can allow humans to read arobot’s intent and adjust their behavior accordingly. We explore
design principles based on LED lights as we consider LEDs to
be easily installed in most robots while not introducing featuresthat are too human-like (to prevent users from having highexpectations). In the paper, we present a design interface thatallows designers to explore the parameter space of an LED
strip attached to a Roomba robot. We then summarize a setof design principles for optimally simulating light-based gazes.
Finally, our suggested design is evaluated by a large group ofparticipants, and their comments are discussed.

I. I NTRODUCTION
There is a trend for functional robots to be involved in oursociety. A real live example is the Roomba robot1 , a seriesof autonomous robotic vacuum cleaners that are becoming
increasingly popular nowadays. However, due to the natureof the tasks such robots perform, they are generally restricted
in appearance, making it hard for them to express their intent[1]. With regard to the Roomba robot, while it uses an LED
display and beep sounds to indicate some of its internal
states, e.g., cleaning or charging, its behavior can still be
mysterious to many users. Since more and more functional
robots are required to interact with, communicate to, and/or
cooperate with human users, it is essential for such robots
to explicitly express their intent [2].
In human-human interaction, people use multiple communication cues to express themselves. Among these cues, gazehas been suggested as important for providing information,
expressing intimacy, and regulating interaction [3]. Due toits effectiveness, many researchers have tried to employ
gaze as an interaction modality for social robots. Plenty of
research has been done to evaluate the functionality anddesign principles of gaze behavior for HRI [4], [5], [6].
Unfortunately, most of it focused on human-like robots or
virtual human agents. Because of an adaptation gap [7],it is suggested that applying human-like gaze (eyes) tofunctional robots will cause humans’ expectations of suchrobots to exceed the real capabilities of the robots and resultin a negative HRI experience. Therefore, the appropriateness1 Sichao Song is with The Graduate University for Advanced Studies(SOKENDAI), Tokyo, Japan sichaos@nii.ac.jp
2 Seiji Yamada is with the National Institute of Informatics and SOKENDAI, Tokyo, Japan sichaos@nii.ac.jp
1 https://en.wikipedia.org/wiki/Roomba.

978-1-5386-7980-7/18/$31.00 ©2018 IEEEof applying anthropomorphic eyes to functional robots isquestionable.
To address this question of how best to apply gaze toappearance-constrained robots, a handful of previous work[8], [2] investigated light-based methods. Particularly, Szafir
et al. [2] explored the design space regarding explicit robot
communication of flight intentions using LED lights. They
tested their four signal designs (blinker, thruster, beacon,and gaze) and found that three of them (blinker, thruster,and gaze) were effective. In particular, they reported that
their participants appreciated the greater precision offeredby the gaze design. Therefore, their work showed that it
can be potentially effective and precise to simulate gazecommunication with LED lights.
However, their work leads to several unsolved design
issues. Because they did not focus on gaze signals alone, thedesign principles regarding how “eyes” can be simulated by
LED lights were not discussed in detail. As they mentioned
in the paper, they designed the signals by using measurements of the human eye. However, due to the huge differencein shape and the many other features between human eyesand LEDs, the appropriateness of such an approach canbe questioned. A better method could be offering a designinterface to allow designers to freely explore a design space(different combinations of parameters). In addition, color,
as a key feature, can be better investigated. To be specific,
different colors can be used for different parts of the eye(pupil and sclera). This allows the pupil part to be madeprominent, which could lead to a better resolution regarding
directionality recognition.

Fig. 1.

Configuration of Roomba robot with LED lighting system

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Fig. 2.

Screenshot of design interface

II. P ILOT S TUDY
Our study is aimed at exploring the design space regarding
simulating gaze by using LED lights. We installed an LED
lighting system (NeoPixel LED strip) on an iRobot Create
2 robot, which is a Roomba robot. Figure 1 shows the front
side of the robot and the configuration of its LED lighting. To
be specific, we used one meter of a NeoPixel LED strip (60pixels). The LED strip was controlled by an Arduino Uno
R3 board, and both the strip and the board were powered by
a 5-V, 3-A portable powerbank. The same board was also
used to control the movements of the robot.
In this pilot study, we particularly examined parametersettings for simulating a gaze signal. We first developed aninterface that allows designers to freely investigate different
gaze designs. On the basis of the data and comments fromvolunteer designers, we summarized a set of (abstract) designprinciples that can be employed as a reference for both
HRI and CHI researchers. In addition, we further hired alarge sample of participants via an online survey platform
to evaluate our gaze design. The participants’ answers to
open-ended questions provided valuable insights on how ourdesigned gaze signal be perceived and interpreted by humans.
III. D ESIGN I NTERFACE
We developed a design interface by using Processing. As
shown in Figure 2, the interface allows designers to explore a
set of parameters regarding gaze simulation. Specifically, theassociated parameters include color of pupil, width2 of pupil,color of sclera, width of sclera, and interocular distance.
2 Number of LED pixels.

978-1-5386-7980-7/18/$31.00 ©2018 IEEE

The image in the upper left shows the front side of theRoomba robot with LED lighting. It provides an intuitive
idea of what the robot looks like and can, explicitly or
implicitly, help designers keep a correct mental model of therobot while setting parameters. The right hand side panel
allows interactions between designers and the interface. Designers can freely try out different combinations of parametervalues by setting the corresponding parameters. Particularly,
the interface provides a candidate set of basic colors3 inthe lower right side for the designers to select. The designinterface can be connected to our Roomba robot equippedwith an LED lighting system. By clicking on the “Confirm”
button, the interface sends the current parameter values to the
Roomba (to the Arduino Uno board attached to it), whichthen displays the corresponding gaze signal. Designers caniterate over and optimize their gaze designs. If they finallydecide on a set of parameters, they can click on the “Save &End” button to quit the design interface. The final parametervalues will be saved to a local file, allowing for later analysis.
A. Design Principles
We organized a design session in which we invited six
designers (one female) to join an experiment. At the beginning of the session, we showed a demo video as atutorial regarding how to use the design interface. Later, theparticipants were assigned to individual design trials without
any time restriction. At the end of the trials, they were asked
to provide comments and opinions in a free manner. Below,
3 http://www.creativecolorschemes.com/resources/free-colorschemes/basic-color-scheme.shtml.

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we summarize a set of design principles based on the findings
from this design session.
I The pupil part should be clearly identifiable. To ensure
this, it is suggested that the width of the pupil be morethan 1 LED pixel. In addition, the color of the pupil
should contrast highly with the color of the sclera.
II The brightness of the sclera part should be much lower
than the pupil part to look natural4 . This also helps thepupil to stand out.
III The width of sclera should be sufficiently long so thatthe directionality of gaze, e.g., left, normal, and right,
can be well recognized.
IV The interocular distance should be sufficiently long sothat the two eyes can be well distinguished.
Particularly, principle II provides partial evidence of theinappropriateness of using measurements of the human eye
in gaze signal design because the sclera of a human eye
is, in general, much brighter than the pupil. The descriptionof “look natural” means something different, depending on
the design space to be referred to. If the task is to design
an anthropomorphic eye, it could be preferable to imitate ahuman eye. However, with regard to designing a gaze signal
with LED lights, different design principles should be reliedon.
IV. E VALUATIONOn the basis of the findings from the design session, we
decided on an example of a gaze signal that well followed
the five principles. Specifically, we set the color of the pupil
to bright green and the color of the sclera to dim gray. We
set the width of the pupil to 2 LED pixels and the width of
the sclera to 3 LED pixels. In addition, we set the interoculardistance to 4 LED pixels.
We prepared two demo videos in which the Roomba
robot was displaying a “scan” behavior (gazing from left toright regularly in two cycles). In one demo (a screenshot
is shown in Figure 3), the robot was the only object inthe video. There was nothing in front of it while it wasscanning. However, in the other demo (a screenshot is shownin Figure 4), three objects were put in front of the robot.
The goal of the evaluation was to find out how people
would perceive and interpret our designed gaze signal thatuses LED lights. Due to the mechanic embodiment of theRoomba robot and neutral shape of the LED strip, wehypothesized that people’s perception of the robot would bethat it is hardly anthropomorphic. As a result, it would be
hard for them to interpret the light expressions as gaze signals
in general. However, we hypothesized that when reference
objects, or additional cues, are provided (the three objects inthe second demo), people would then understand the gazesignals and attribute more agency to the robot. This actually
meets a key design goal; gaze design should not introduce tomuch anthropomorphism as it otherwise could cause human’s
expectations of a robot to exceed its real capabilities.
4 The meaning of “look natural” does not suggest that it looks more similar
to human eyes. We prefer to interpret this as a lower brightness of the sclera
part making people more easily perceive LED lights as a gaze signal.

978-1-5386-7980-7/18/$31.00 ©2018 IEEE

Fig. 3.

Fig. 4.
objects

Screenshot of demo showing Roomba robot alone

Screenshot of demo showing Roomba robot together with three

We performed the evaluation by using online surveys. A
Japanese online crowdsourcing platform5 was employed torecruit participants. We hired 120 participants, 60 of them foreach condition (demo video). In a questionnaire, we asked
two open-ended questions: 1) What was the robot doing? 2)
Is it easy to understand the robot’s intent?
A. Results
The results confirmed our hypotheses. In general, participants who viewed the demo showing the robot alone found it
hard to understand the robot’s intent. Their perceptions andinterpretations regarding the robot’s behavior were highlybiased by the type of robot: cleaning robot. To be specific,
many participants described the robot as “searching for
garbage” or “cleaning (its current place).” Other participants
thought that the robot was charging or waiting for commands.
Such descriptions indicate that participants did not attributeagency to the robot. This suggests that, without hints regarding the functionality of the light expressions, it can bedifficult for people to perceive them as gaze signals.
However, participants who viewed the demo showing
objects in front of the robot found it easy to understandthe robot’s intent. This is not surprising since the provided
objects, as an additional cue, allowed them to dramaticallyreduce the number of potential scenarios for guessing. An
5 Fastask: https://www.fast-ask.com. The website is only available inJapanese.

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analysis on the participants’ descriptions of the robot’s
behavior clearly shows that they attributed a certain levelof agency to the robot. Specifically, many participants usedanthropomorphic descriptions such as “observing the objects” or “choosing among the objects.” Such descriptions
suggest that they interpreted the light expressions as gazesignals (scanning the objects). Importantly, almost none ofthe participants explicitly described the light expressions as
eye-like or gaze-like, suggesting that they did not attributetoo high a level of agency to the robot.
V. D ESIGN I MPLICATION
Besides the design principles we proposed, our findings
offer several important design implications that can be beneficial to HRI and CHI researchers:• Light-based gaze signals may not be explicit cues thatindicate directionality. However, when a reference (objects) is provided, people can easily learn or recognize
the functionality of the light expressions, similar togaze. To be general, such reference information does notnecessarily need to be an object. A robot’s motion, forinstance, that is coordinated to light expressions could
probably help people to recognize a gaze signal too.
• Light-based gaze signals should be designed by using
measurements of the human eye with caution. Somefeatures (parameter settings) that fit the design of anthropomorphic gaze may not be appropriate for lightbased gaze signals.
• Light-based gaze signals can be suitable for functional
robots as they will not introduce too much anthropomorphism, which biases people to have expectations thatexceed a robot’s real capabilities.

R EFERENCES[1] Bethel Cindy L. 2009. Robots without faces: non-verbal social humanrobot interaction. [dissertation/Ph.D.’s thesis]. University of South
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[2] Daniel Szafir, Bilge Mutlu, and Terry Fong. 2015. Communicating Directionality in Flying Robots. In Proceedings of theTenth Annual ACM/IEEE International Conference on HumanRobot Interaction. ACM, New York, NY, USA, 19–26. DOI:
http://dx.doi.org/10.1145/2696454.2696475[3] AJung Moon, Daniel M Troniak, Brian Gleeson, Matthew KXJ Pan,
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[4] Maria Staudte and Matthew Crocker. 2008. The utility of gaze inspoken human-robot interaction. In Proceedings of Workshop on
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[5] Markus Hring, Jessica Eichberg, and Elisabeth Andr. 2012. Studies ongrounding with gaze and pointing gestures in human-robot-interaction.
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[6] Gabriel Skantze, Anna Hjalmarsson, and Catharine Oertel. 2013.
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[7] Takanori Komatsu, R Kurosowa, and Seiji Yamada. 2010. How does
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[8] Kim Baraka, Ana Paiva, and Manuela Veloso. 2016. Expressive Lights
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VI. N EXT S TEPThe next step will be to evaluate the effect of light-based
gaze signals in real HRI contexts. Because gaze can beused to indicate a robot’s intent and direct people’s attention[3], it is important to examine whether light-based gazesignals possess such functionalities. We will consider several
evaluation methods to be applied for this purpose. Typicalhuman-robot cooperation contexts can be designed in whichtask performance can be improved if a human is able toread a robot’s intent (next move). Video-recorded data isneeded to analyze how humans behave when reacting to arobot’s gaze signals. Importantly, we will consider using awearable eye-tracker device (Tobii Pro Glasses 2) to trackpeople’s corresponding gaze behavior on-the-fly. This willallow us to easily identify the joint-attention behavior ofa person. In addition, future work could also involve gazeanimation design. Gaze animations may cause people toattribute more agency to a robot. In addition, other robot
shapes and arrangements of LEDs should be investigated.
ACKNOWLEDGMENT
This study was partially supported by JSPS KAKENHI“Cognitive Interaction Design” (No. 26118005).

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