Haptic fMRI: A novel five DOF haptic interface for multi-axis motor neuroscience experiments

We present a novel electromagnetically actuated Haptic fMRI Interface with five degrees-of-freedom (DOF), HFI-5. The interface uses two three DOF devices connected with a gimbal in a closed kinematic chain to achieve three-axis translation and two-axis rotation. To highlight the device's design, we develop a taxonomy of similar devices and demonstrate why HFI-5's design excels. We use a cross-correlation based novel analysis method to demonstrate that HFI-5 is transparent by showing that it does not affect unconstrained subject motions. This is due to its low friction (<; 0.31 N) and lightweight design. Next, we show that HFI-5 can accurately track positions, velocities, and accelerations, in part due to a 7.5 kHz servo loop. Finally, we demonstrate that HFI-5 is fMRI-compatible and does not interfere with fMRI scans even while applying large torques with its electromagnetic motors.