Neuromorphic Spiking Ring Attractor for Proprioceptive Joint-State Estimation
Authors: Federica Ferrari, Flavia Davidhi, Bernard Maacaron, Alberto Motta, Luuk van Keeken, Elisa Donati, Giacomo Indiveri, Chiara De Luca, Chiara Bartolozzi
Organizations: Istituto Italiano di Tecnologia, Genoa, Italy · Department of Neurosurgery, University Hospital Zürich, Switzerland · Institute of Neuroinformatics, Univ. of Zurich and ETH Zurich, Switzerland · DIEEI, University of Catania Catania, Italy · IDLAB, University of Antwerp, and AI & Algorithms, imec, Leuven, Belgium · Digital Society Initiative, University of Zurich, Switzerland
Maintaining stable internal representations of continuous variables is fundamental for effective robotic control. Continuous attractor networks provide a biologically inspired mechanism for encoding such variables, yet neuromorphic realizations have rarely addressed proprioceptive estimation under resource constraints. This work introduces a spiking ring-attractor network representing a robot joint angle through self-sustaining population activity. Local excitation and broad inhibition support a stable activity bump, while velocity-modulated asymmetries drive its translation and boundary conditions confine motion within mechanical limits. The network reproduces smooth trajectory tracking and remains stable near joint limits, showing reduced drift and improved accuracy compared to unbounded models. Such compact hardware-compatible implementation preserves multi-second stability demonstrating a near-linear relationship between bump velocity and synaptic modulation.
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Fig. 1: Ring attractor architectures used in the simulation (with and without boundaries) and on DYNAP-SE. Top row: symmetric profiles across architectures, bottom row: asymmetric profiles. Connections are only shown for neuron on top. (a) The symmetric cosine-shaped profile in the original model. (b) The asymmetric sinusoidal profile in the original model. (c) Symmetric cosine-shaped profile with boundaries ( θ0 , θl ) and the middle out-of-bound angle θm∗ ; gray area indicates the out-of-bound region.(d) The asymmetric profile in the bounded model obtained modulating the original profile through a+ and a− . (e) DYNAP-SE symmetric profile, where number of connections increases with connection strength. (f) asymmetric profile in the DYNAP-SE implementation, where number of connections increase with the velocity intensity.
Fig. 2: Neural encoding and validation of angular trajectory tracking. (a) Tracking using instantaneous velocity input. Raster plot of spiking activity (black) and ground–truth joint angle (blue). Top: input velocity; left: initialization current; right: mean firing–rate profile within the highlighted region. (b) Tracking using target velocity commands only. Comparison between the unbounded (orange) and boundary–constrained (red) models for wide (solid) and limited (dashed) motion ranges. Incorporating boundary conditions reduces drift and improves alignment with ground truth.
Fig. 3: Ring–attractor stability and velocity modulation on the DYNAP-SE neuromorphic processor. (a) Experimental setup: a 1- s Gaussian input is encoded by a LIF neuron and sent to the DYNAP-SE ring attractor; velocity connections are updated from the host computer. (b) Bump drift over time. Box plots show peak-position error across 0.5-s windows after stimulus offset (0–0.5 to 4.5–5.0 s ), pooled across ring populations; lower values indicate higher stability. (c) Mean bump angular velocity vs. number of velocity connections with weighted linear fit ( wi=1/SEMi2 ). For each connection count, angular velocity was computed by unwrapping the bump trace and fitting a line over 2.5–9.0 s . (d) Spike raster during 12 s baseline ( v=0 ). (e) Spike raster during velocity modulation showing baseline (0-1 s ), translation(2–9 s ) and recovery (9–12 s ). (f) Spike raster during “acceleration” test with stepwise addition and removal of velocity connections.