Mapping stiffness perception in the brain with an fMRI-compatible particle-jamming haptic interface

Abstract

We demonstrate reliable neural responses to changes in haptic stiffness perception using a functional magnetic resonance imaging (fMRI) compatible particle-jamming haptic interface. Our haptic interface consists of a silicone tactile surface whose stiffness we can control by modulating air-pressure in a sub-surface pouch of coarsely ground particles. The particles jam together as the pressure decreases, which stiffens the surface. During fMRI acquisition, subjects performed a constant probing task, which involved continuous contact between the index fingertip and the interface and rhythmic increases and decreases in fingertip force (1.6 Hz) to probe stiffness. Without notifying subjects, we randomly switched the interface's stiffness (switch time, 300-500 ms) from soft (200 N/m) to hard (1400 N/m). Our experiment design's constant motor activity and cutaneous tactile sensation helped disassociate neural activation for both from stiffness perception, which helped localized it to a narrow region in somatosensory cortex near the supra-marginal gyrus. Testing different models of neural activation, we found that assuming indepedent stiffness-change responses at both soft-hard and hard-soft transitions provides the best explanation for observed fMRI measurements (three subjects; nine four-minute scan runs each). Furthermore, we found that neural activation related to stiffness-change and absolute stiffness can be localized to adjacent but disparate anatomical locations. We also show that classical finger-tapping experiments activate a swath of cortex and are not suitable for localizing stiffness perception. Our results demonstrate that decorrelating motor and sensory neural activation is essential for characterizing somatosensory cortex, and establish particle-jamming haptics as an attractive low-cost method for fMRI experiments.

Haptics-mediated approaches for enhancing sustained attention: framework and challenges

“…Various approaches have been proposed to attempt the elimination of motor artifacts in fMRI measurements. These approaches include avoiding electromagnetic actuation for haptic interfaces [154,155], placing actuators outside the scanner room [156], and using simple devices [157]. Such approaches usually lead haptic interfaces to be suitable only for a limited set of motor tasks.…”

Perceptibility of programmable softness displays using magnetorheological elastomers

“…The most common approaches utilize hydraulic and pneumatic mechanisms, which use fluid or gas to deform the geometry of soft chambers and generate contact forces (Park and Wood 2013). For instance, jamming approaches control the stiffness of silicone cells, where small coffee particles dispersed in a cell respond to regulated air pressure (Menon et al 2014;Stanley, Gwilliam, and Okamura 2013). While most hydraulic and pneumatic actuation techniques require extra instrumentation, such as an air compressor or fluid pump, other self-actuation devices utilize attraction forces between two electrodes, where a micro-chamber filled with air or fluid is deformed by internal pressure generated by electrostatic force (Leroy, Hinchet, and Shea 2020;Song et al 2019).…”

MRI-VisAct: a Bowden-cable-driven MRI-compatible series viscoelastic actuator

“…Finally, Discussion and Conclusion section provides an overall evaluation of the proposed approaches. (Newton et al 2008) No actuation Non-magnetic -Ankle, knee and hip 6-axis load cell torque measurements (Mehta et al 2009) No actuation -Optical encoder Pedaling speed measurements (Sergi et al 2011) No actuation -Optical encoders Post rehabilitation efficacy prediction (Menon et al 2014) Particle-jamming via --Mechanical modulation pneumatic actuation of device stiffness (Khanicheh et al 2008) ERF actuation Aluminum Optical encoders Mechanical modulation strain gage of device damping (Hara et al 2009) Electrostatic motors Non-magnetic Synchronous drive 2-Dof motion & force force sensor rendering joystick (Hollnagel et al 2011) Pneumatic actuation Resistive Optical encoder, Analysis of strain gauges foil potentiometer stepping patterns Hydraulic actuation Fiber optic Shielded optical Analysis of force sensors encoders reaching movements (Yu et al 2008) Pneumatic The first category belongs to devices with no actuation (Hidler et al 2006;Newton et al 2008;Mehta et al 2009). The purpose of these devices is to measure the interaction forces or movement patterns of patients during, just before, or just after the MRI process.…”

“…The second category of devices are the ones that are capable of passive modulation of their impedance through unconventional techniques, such as particle jamming (Khanicheh et al 2008) or electro-rheological fluidics (ERF) (Menon et al 2014). Even though these devices are capable of stiffness and/or damping modulation, their adaptation for rehabilitation stays limited as these devices are also incapable of providing active assistance to patients.…”