A Matter of Height: The Impact of a Robotic Object on Human Compliance
How a simple physical attribute influences social behavior
Role
UX Research (HRI Focus)
Lead Researcher
Methods / Tools
Foundational Research
Human-Subject Experimentation
Prototype-Driven Design
Behavioral UX Research
Qualitative Insight Extraction
Data-Driven Evaluation
Cliant / Framework
Thesis / Reichman University HCI MA Program
RoMan Conference, 2025
Background
Project Motivation
Interactions with robots often begin before the first word or gesture–sometimes before the robot does anything at all. Height, one of the simplest physical attributes, carries strong social meaning among humans. I wanted to understand whether that meaning extends to non-humanoid robotic objects, and whether height alone could influence something as concrete as compliance: a person’s willingness to do what the robot asks.
This project became my first published HRI study and a foundational moment in my research direction.
MORPHY
The Modular Robotic Platform
To isolate height as the only changing factor, we built a modular robotic service table that allowed us to change its height without altering its shape, functionality, or materials.
Two versions were used:
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Short robot – 95 cm
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Tall robot – 132 cm
Everything else — color, modules, tablet location, movement—remained identical.
This modularity ensured that any differences in behavior were driven solely by height.
Experiment Overview
Between-Participants Design
This experiment used a between-participants design with a single encounter.
Each participant interacted with either the Short robot or the Tall robot.
The interaction took place immediately after a cognitive task, when participants believed the study was “finished.” While waiting for their course credits, the robot entered with a tablet, requesting them to voluntarily complete a 300-question questionnaire.
The key measure:
How many questions did they choose to answer?
Method & Procedure
Participants, Setup and Procedure
Participants:
44 university students (22 per condition). Groups were matched by gender, Agreeableness, and NARS scores
Setup:
Participants sat in an armchair with a small table beside them. After finishing the Stroop task, the table was moved aside to allow the robot a direct path.
The robot’s movement was controlled via Wizard of Oz to ensure smooth, standardized behavior.
Procedure in simple steps:
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Participants arrived, consented, and completed pre-test questionnaires.
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They performed the Stroop task (~10 minutes).
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The researcher declared the experiment “over” and exited.
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The robot entered the room:
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Stopped 110 cm from the participant.
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Displayed the voluntary questionnaire on the tablet.
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Participants could:
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Pick up the tablet, or ignore it.
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After every 25 questions, they could continue or stop.
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Upon finishing, the robot exited.
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Participants completed RoSAS and a short interview.
Key Findings
Counterintuitive Outcomes
Compliance:
Nearly all participants picked up the tablet in both conditions.
But Short robot → higher compliance:
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Short robot mean: 132.9 questions
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Tall robot mean: 80.6 questions
The shorter robot led participants to voluntarily answer significantly more questions.
Perception (RoSAS):
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Discomfort was significantly lower in the Short robot condition.
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Warmth and competence showed no differences.
The key insight:
People felt more comfortable with the shorter robot, and this comfort was reflected in higher compliance.
What Participants Said
Shorter is Cuter
The interviews revealed three themes:
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Volunteering
Participants described their behavior as prosocial or curiosity-driven—
“I just wanted to help.”
“Why not try? It’s a robot with a tablet asking questions.” -
Functional interpretation
Participants saw the short robot as more useful and less awkward:
“It brings you things. It’s cool.”
The tall robot was sometimes perceived as too large or purposeless:
“It’s too tall and wide; I don’t see the use.” -
General perception
The Short robot was frequently described as: “cute”, “nice”, “alive”, “engaging”.
The Tall robot was more often described as: “weird”, “normal”, “scary”, “nervous”.
The emotional tone aligned with the quantitative results:
Positive affect → higher compliance.
Design & HRI Implications
Shorter is Cuter
The findings challenge assumptions drawn from human–human dynamics, where height often signals leadership, authority, or persuasiveness.
For non-humanoid robots, the pattern was reversed:
Shorter robots elicited higher compliance.
Implications:
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Height should not be treated as a direct analogue to human height effects.
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Designers should carefully test physical attributes, even those that seem intuitive.
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Shorter robots may encourage comfort, approachability, and voluntary cooperation.
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Perception (“cute”, “safe”, “pleasant”) can outweigh authority in influencing compliance.
This project underscores that robot morphology is part of the interface and can influence social behavior even without gestures, voice, or personality.
My Contribution
Concept to Implementation
I led the research from concept to publication, including:
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Experiment design and hypothesis development
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Robotic platform configuration (Short vs Tall modules)
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Room layout, movement script, and Wizard-of-Oz control logic
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Data collection, coding, and Bayesian analysis
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Thematic analysis of interviews
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Paper writing and conference presentation
This work became the foundation for my later exploration of multi-robot anchoring and height dynamics.
Behind the Scenes
Shorter is Cuter
Moments from the design and preparation:
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Early cardboard mockups used to validate ergonomics
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Height assembly tests (Short → Tall)
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Laying out the room and marking robot approach paths
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Wizard-of-Oz rehearsals to ensure consistent behavior
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Preparing the tablet request screen
Publication & Resources
Shorter is Cuter
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Paper: “A Matter of Height: The Impact of a Robotic Object on Human Compliance”
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Conference: IEEE RO-MAN
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PDF: [Upload link on your site]
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RISE Presentation Slides: [Optional link]
Closing Reflection
Shorter is Cuter
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This study taught me how subtle physical cues in robots shape human behavior—sometimes in ways that contradict our assumptions. It showed me the importance of designing and testing robotic characteristics with care, and it set the trajectory for my continuing work on how people interpret robotic presence in everyday environments.
Proxemics
Influence on proxemics behavior in Human-Robot Interaction (HRI)
In this part, I explored how physical proximity influences interactions and behaviors in Human-Robot Interaction (HRI), similar to human interactions. Understanding this "dance" when a robot meets a person is crucial, leading to both expected and surprising findings. Influential factors include:
Human Characteristics:
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Personality: Extraverts are more tolerant of close proximity.
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Age: Children maintain more distance than adults.
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Previous Experience: Familiarity affects comfort levels.
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Approaching Direction: Robot-approaching direction is influenced by gender preference.
Robot Characteristics:
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Voice: Synthesized voices are less favored, and male tones tend to be preferred.
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Form: Machine-like robots are favored over human-like ones.
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Speed: Movements should be slower than human walking speed.
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Height: Taller robots may be seen as more competent, but this effect varies.
In conclusion, putting it into actionable guidelines for proxemics:
The optimal robot design involves a height between 1.2 to 1.5 meters, a slower movement speed, and a non-human form. Proxemics guidelines include a learning algorithm to recognize people, a robot “head” for directional and communicative gestures without staring, and a human-like voice if used.
The Spatial Dimension
Context & Goal
Problem Statement
Robots today come in all shapes. From humanoids to delivery carts, cleaning bots, and mobile furniture. Unlike humans, whose physical attributes are fixed, robots can be intentionally designed to be taller, shorter, wider, or more subtle.
Previous research suggested mixed outcomes:
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Some studies found taller robots appear more authoritative.
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Others found people feel safer or more comfortable around short robots.
Yet these studies rarely examined non-humanoid robots.
Goal:
To test whether a simple height change would influence people’s voluntary compliance with a robot’s request, even when the robot is highly utilitarian and machine-like.
Signifiers
Establish Communication Baselines
Signifiers can be divided into Motion-inherent cues, Non-Verbal explicit cues, and signaling methods. In comparison to the world of autonomous vehicles, signs and cues slightly shift when we talk about delivery robots. For instance, while cars move at certain speeds, a delivery robot usually strolls slower than our walking pace. In this case, I will not pretend to present which signal is the most correct but highlight where and what signals are needed, dividing them into spatial and conceptual signals. The exact type of these signals, though, is something we'll need to explore further.
Motion-inherent cues
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Speed
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Distance
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Deceleration/ Acceleration
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Braking
Non-Verbal explicit cues
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Eye contact
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Head nodes
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Gesture
Signaling methods
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Headlights
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Signaling/ hazard lights
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Horn
Learning the industry
User Interviews
What I Learned from the Current Human-Human Delivery Interaction
To understand what makes a good delivery experience, I turned to interviews with people aged 20-65, who regularly receive deliveries (by human currier) living in both high-rise buildings and private homes, in cities and less central areas.
These interviews covered everything from their expectations and experiences meeting delivery personnel to issues of trust, courier behavior, and concerns about privacy and safety. Paradoxically, the insights gathered hinted that robot delivery services might offer a more considerate and human-like service experience.
HRI design considerations:
Interviews Insights
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Opportunity for personalization of the service (proxemics - “The Dance”).
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Cultural based interaction design.
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Establish familiarity to enhance attachment in the human-robot interaction (giving a robot a name - “Hi Siri”).
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Prolonging the interaction. Provide a feeling that the robot is "thinking of me."
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Establish standardizations for eHMI communication protocol
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Service design is crucial.
What makes for a good experience for me is a good communication and coordination of the hand-off time, much before the courier arrives.
It's gotten to the point where I'm already exchanging a few words with him here and there because he knows me and tells me “so we meet again...", by now I know him by his name.
When I got here I had a cultural shock because in Argentina the courier doesn't go up to your apartment, you meet the courier downstairs, that's the norm.