Fig. 4: Obstacle tracking and collision detection with LGMD-like spike response.
a Illustration showing the vision system of a locust with the Lobula giant movement detector (LGMD) neuron. b LGMD neuron performs a complex computation with θ and \(\theta {\rm{\mbox{'}}}\) to stimulate an escape response based on the size (l) and speed (v) of an object. Firing pattern of an LGMD neuron can be approximated by the expression \(f\left(t\right)={\rm{\theta }}{\rm{\mbox{'}}}{\rm{exp }}(-{\rm{\alpha }}{\rm{\theta }})\). A smaller l/v represents a higher threat and elicits a larger response. c Firing pattern of the neuron with SFA and PIR shown in Fig. 3a is plotted for a range (100–1000 pA) of Isyn amplitudes. A low value of Isyn of 100 pA resulted in discontinuation of spiking due to excess hyperpolarization by ICaK. Sustained spiking was observed with moderate (200–700 pA) Isyn values. Higher (800–1000 pA) Isyn resulted in halting of spikes because of excess depolarization of the membrane. These traits, along with PIR, help the artificial neuron mimic LGMD behavior closely. d Response (VM and raster plot) of the circuit for an Isyn pulse (100–250 ms time span) to mimic synaptic current into an LGMD neuron for a looming stimulus. Time to collision (tC) is set at 250 ms after which the synaptic current remains constant. e Instantaneous spike rate (top) and spike time (bottom) for Isyn inputs similar to (d) for a range of l/v values. Peak spike rate is achieved in each case prior to tC. f Peak ISI−1 and total number of spikes (and hence, energy) increase with decreasing l/v indicating that an input with higher threat triggers an enhanced response at the cost of higher energy consumption. g–i Similar data as in (d–f) for receding stimuli, and with 2× leakage conductance (gL).
