Exploring Squish
Understanding Dynamic Material Perception and Haptic Thresholds
M.S. Human Factors Engineering | Tufts University | Feburary 2026 | Read Full Thesis →
Imagine a World Where...
- Adaptive Interfaces Interfaces provide feedback with changes in compliance, rigidity, softness, and reformation
- Intelligent Prosthetics Prosthetics can change material properties to guide users through tactile feedback
- Dynamic Controls Buttons, switches, and controls dynamically adjust during use based on context
- Immersive VR Virtual objects push back with the right resistance and force to produce realistic and immersive experiences
What is Squish?
Squish is the dynamic sensory experience that emerges while interacting with an object's surface compliance and internal density.
Key Characteristics
- Requires cutaneous, proprioceptive, and kinesthetic inputs
- Defined mechanically through stiffness, elasticity, and viscosity
- Dynamic deformation introduces temporal cues
- Engages users in an iterative feedback loop
The Problem
We understand vibration, pressure, and texture. But squish—the dynamic sensation of material compliance—remains largely unmapped.
While human touch perception has been extensively studied through discrete sensory channels, the integrated, temporal experience of "squishiness" exists in a research gap between mechanical properties and human perception.
Why This Matters
What's Missing
We Know:
- → Force discrimination thresholds
- → Pressure sensitivity limits
- → Static stiffness perception
- → Vibrotactile frequency ranges
- → Surface texture discrimination
We Don't Know:
- → Just-noticeable difference for squish
- → How temporal dynamics affect perception
- → Individual variation in squish sensitivity
- → Physical/anatomical predictors of thresholds
- → How to design for dynamic compliance
The result: Haptic designers are building VR controllers, prosthetic interfaces, and adaptive systems without knowing if users can actually feel the differences they're engineering. This research closes that gap.
Research Goals
Investigate Perception
Study how the somatosensory system processes dynamic material compliance—mapping the relationship between mechanical properties and human perception.
Identify Bio-Mechanical Factors
Evaluate which physical and anatomical characteristics influence squish perception—from grip strength to finger length to fine motor skill.
Map Individual Variability
Explore how sensory identification, detection, and discrimination vary across individuals—understanding the range of human perceptual capability.
Driving Questions
At what increment of change is squish noticeable?
Establishing just-noticeable differences (JNDs) for dynamic material compliance
How consistent is squish perception across different individuals?
Quantifying inter-individual variability and identifying patterns
What physical factors affect how people feel squishiness?
Correlating anatomical, behavioral, and physical measures with perceptual thresholds
Methodology
Experimental Framework
Participants performed binary judgments using novel dynamic interfaces capable of incremental levels of simulated squish.
- → Method of Constant Stimuli framework
- → Two-alternative forced-choice (2AFC) paradigm
- → Response patterns modeled to estimate perceptual thresholds
- → Thresholds examined in relation to behavioral, physical, and anatomical measures
Dynamic Interfaces
- → Inflatable, pressure-controlled end-effector
- → Barometric sensor for simulated squish increment levels
- → Shape-memory polymer core compensated for vertical expansion
- → Reduced reliance on thickness as a sensory cue
Participant Protocol
- → IRB approved (Tufts University)
- → Hand placed through barrier to eliminate visual cues
- → 10 comparison rounds per condition
- → 7 conditions across +/- 30% pressure range
Key Findings
Squish is Perceptually Real—But Highly Individual
People can reliably discriminate between different levels of squish, but how they perceive these differences varies dramatically across individuals.
Threshold curves showed different shapes, slopes, and directional asymmetries—suggesting perception depends on individual sensory sensitivity, not just stimulus magnitude.
What Predicts Squish Sensitivity?
Strong negative correlations (r < -0.7) between perceptual thresholds and physical/behavioral factors
Fine Motor Skills
Higher fine motor task frequency and self-reported skill correlated with lower perceptual thresholds—more sensitive discrimination.
Regular dexterous activity may sharpen tactile resolution
Finger Length
Longer little and ring fingers correlated with improved tactile resolution—supporting links between hand anatomy and sensory acuity.
Anatomical structure influences perceptual capability
Physical Activity & Grip
Higher physical activity levels and greater grip strength correlated with increased sensitivity to squish changes.
General physical capability tracks with perceptual performance
The Response Bias Effect
Expected vs. Actual
When one interface matched the control exactly, participants still had to choose 'MORE' or 'LESS.' We expected random 50/50 responses.
Instead, noticeable directional bias emerged—judgments depended on how changes were experienced, not just stimulus magnitude.
Material Behavior Insights
Nonlinear Dynamics
- → Interfaces showed nonlinear force-displacement behavior
- → Hysteresis during compression and rebound
- → Greater hysteresis at lower inflation levels
Perceptual Impact
Mechanical nonlinearity and hysteresis may have influenced how changes in squish were perceived over time—suggesting the temporal dynamics of material behavior matter, not just static compliance.
Significance
New Perceptual Category
Establishes 'squish' as a perceptually discriminable tactile interaction, not merely a material property
Standardization Need
Demonstrates the need for standardized measurement to compare across individuals and systems
Design Considerations
Identifies learning effects, response bias, and directional asymmetries as critical design considerations rather than experimental noise
Multi-Factor Interaction
Squish perception is shaped by multiple interacting factors, including systematic response bias, rather than stimulus magnitude alone
Applications
Understanding squish enables the next generation of adaptive interfaces
This research provides the perceptual foundation needed to design systems where material properties communicate information, guide interaction, and respond dynamically to context.
Prosthetics & Rehabilitation
Prosthetic limbs that adapt material compliance in real-time—soft when grasping fragile objects, firm when gripping tools. Interfaces that communicate grip security through tactile feedback users can actually perceive.
Design challenge: Matching perceptual thresholds to the range of human sensitivity discovered in this research.
Teleoperation & Remote Manipulation
Robotic systems that transmit material compliance from remote environments—operators feel the stiffness of objects being manipulated hundreds of miles away. Critical for deep-sea operations, space exploration, and hazardous material handling where tactile feedback improves control and prevents damage.
Design challenge: Maintaining perceptual fidelity across the control loop while accounting for transmission delays and mechanical limitations.
Virtual & Augmented Reality
VR controllers and haptic gloves with programmable squish—virtual objects that feel soft, firm, or springy based on what they represent. Training simulations where material feedback matches real-world counterparts.
Design challenge: Creating immersive tactile experiences that operate within just-noticeable difference thresholds.
Medical Training & Simulation
Surgical simulators that replicate tissue compliance during palpation, catheter insertion, and laparoscopic procedures. Training platforms where learners develop tactile discrimination skills for identifying abnormal tissue, masses, or anatomical landmarks through simulated material feedback.
Design challenge: Replicating the full range of tissue compliance variations within perceptually realistic thresholds.
Automotive & Aviation
Controls that stiffen when approaching operational limits, or soften during automated modes. Steering wheels, throttles, and flight controls that communicate system state through dynamic compliance rather than visual displays.
Design challenge: Accounting for individual variability in pilots' and drivers' perceptual sensitivity.
Surgical Instruments & Medical Devices
Surgical instruments that provide tactile feedback about tissue compliance during minimally invasive procedures. Diagnostic tools where material response aids in detection and assessment of tissue abnormalities.
Design challenge: Translating mechanical compliance into perceptually meaningful haptic cues for surgeons.
Consumer Electronics
Smartphone screens and wearables with programmable tactile properties—buttons that feel different based on function, surfaces that adapt to application context, interfaces that communicate through touch.
Design challenge: Implementing perceptually discriminable squish levels within consumer device form factors.
Accessibility & Assistive Technology
Non-visual interfaces that encode information through material compliance patterns. Communication devices for individuals with sensory processing differences that leverage tactile channels.
Design challenge: Accounting for population-specific perceptual thresholds and individual differences.
Design Implications
Individual Calibration
Systems should adapt to individual perceptual thresholds, not assume universal sensitivity
Temporal Dynamics Matter
Material response over time influences perception—static compliance alone isn't enough
Directional Asymmetry
Increasing vs. decreasing squish may be perceived differently—design accordingly
Conclusion
Squish is a dynamic, perceptually meaningful material interaction
This research establishes the psychophysical foundation needed to design interfaces where material compliance communicates information humans can reliably perceive and act on.
What This Research Establishes
Perceptual Reality
Humans can reliably discriminate between different levels of dynamic material compliance under controlled conditions. Squish exists as a distinct perceptual phenomenon, measurable through psychophysical methods.
Individual Variability
Perceptual thresholds vary dramatically across individuals, with strong correlations to fine motor skills, anatomical features, and physical activity. One-size-fits-all haptic design ignores fundamental human differences in tactile sensitivity.
Perceptual Complexity
Response bias, directional asymmetries, and temporal dynamics all shape how squish is experienced. Perception depends on how changes unfold over time, not just final stimulus magnitude—introducing design considerations beyond simple threshold values.
Mechanical-Perceptual Coupling
The nonlinear, hysteretic behavior of dynamic materials influences perception in ways static compliance measurements miss. Material response over time matters as much as instantaneous stiffness.
What This Opens Up
For Designers
A validated framework for specifying perceptual requirements in haptic systems. Instead of guessing at compliance values, designers can work with empirically-derived thresholds and individual variability ranges.
For Researchers
A methodological foundation and experimental paradigm for investigating dynamic material perception. Opens questions about how squish scales across magnitudes, populations, and interaction contexts.
This is a foundation, not a complete model.
Dynamic materials introduce perceptual complexity that warrants further investigation—larger sample sizes, diverse populations, expanded stimulus ranges, and refined mechanical control systems.
But the core finding stands: squish is perceptually real, individually variable, and designable. The next generation of human-machine interfaces can be built on that.