Bioinspired figure-ground discrimination via visual motion smoothing
Fig 8
Effect of simulated octopaminergic modulation on the lobula network.
(A) Two classes of stimuli. The dark bar (0 luminance; 8.9° width) moved rightward at a speed of 33°/sec over a background square grating with a Michelson contrast of 33% (the luminance was periodically set as 0.25 and 0.5; 17.8° spatial wavelength). The grating was either stationary (the ‘bar’ stimulus) or moving with the same velocity as the bar (the ‘bar+bg’ stimulus). The visual field was 70° × 180°. (B) Stimulus-evoked membrane potentials with (red curves) and without (black curves) octopaminergic modulation in the six lobula modules with the names indicated beside each row. Only the responses of the centrally located unit in each module were displayed. Octopaminergic modulation was realized by changing the half-activation voltage θ of the activation function of the Ir and Il modules from −40 mV to −28 mV. Dashed lines indicate the resting membrane potentials. (C) F-measure obtained under the corresponding stimulus condition. The F-measure with (red curves) and without (black curves) octopaminergic modulation was evaluated at the output stage of the Ir module during the continuous presentation of 300 input frames. For all simulations, the synaptic weights of the projections from the EMD array to the postsynaptic lobula modules were set as αEMD→lo = 100.