Figure 5.

Temporal encoding and decoding by the visual system. (A) A retinal mosaic (as in Figure 2) upon horizontal FeyeM scanning of a stationary object and a moving bar, both of which have the same color and luminance (the moving bar is indicated by a broken rectangle). The bar starts to move leftward around t₀ + 20 ms, at a velocity of 3 ’/s. The horizontal arrows mark the horizontal movement of the eye. The horizontal FeyeM amplitude (peak-to-peak) is 4′ and the frequency is 12.5 Hz. (B) FF responses of the horizontally oriented sRFs [red ellipses in (A)]. The sRF that scans the moving bar produces a FF response with higher inter-burst and intra-burst frequencies than its neighbors. (C) NPLL Decoding algorithm. PD, phase detector; X, phase detection, RCO, rate-controlled oscillator; ∼, local oscillations t_in, input time; t_OSC, oscillator time; R_out, PD’s output representing the phase difference between t_in, and t_OSC. Blue, temporal signals; red, intensity (rate) signal. (D). Implementation of phase comparison by gating. At each cycle, only those retinal spikes that arrive after the onset of the cortical feedback (blue squares) will “pass the gate.” Phase comparison is obtained by longer (shorter) delays yielding fewer (more) spikes due to decreased (increased) overlap between the inputs. Note the cycle-to-cycle temporal dynamics of both the retinal input and the periodic gating while processing the moving bar. Onset of the retinal signal is represented by t_in in (C) and onset of the gating signal by t_OSC in (C). (E) Output code of the proposed thalamocortical decoder. The stationary shape is represented by the temporal phase relationships among the outputs of the simple cells (first cycle). The velocity of the bar is represented by a change in the spike count (two instead of three spikes/cycle) of the simple cells [represented by R_out in (C)]. (Inset) Expansion of the second cycle in (B) to show inter-burst (I_r) and intra-beurst (I_b) intervals for stationary (black) and moving (magenta) bars.