Figure 2.

The bump attractor model of the DRT. (A) The DRT includes fixation, cue, delay, and response periods of 1, 0.5, 2, and 0.7 s, respectively. The ×, black dots, and green dot, respectively, represent the fixation point, the 8 possible stimulus locations, and actual stimulus location (0°) in the simulations. Arrow indicates the saccade direction during the response period. (B) The recurrent excitatory-inhibitory network. (C) The f-I curve for young model excitatory neurons. (D) Ring connectivity among excitatory neurons. M_ji is the connectivity matrix element between excitatory neurons j and i, depending on the difference between their preferred directions (θ_j and θ_i, respectively). Each neuron is strongly connected to its nearest neighbors (red line), with the connection strength decaying with distance (yellow and green lines). The neuron with preferred direction 0° receives the strongest stimulus current, which follows a Gaussian distribution centered at 0°, generating a bump of activity during the delay period (persistent activity tuned to the stimulus location) when excitation and inhibition in the network are well-balanced. (E) Sample DRT model output (side and top views) when the 0° stimulus location is encoded correctly: excitatory neuron FR vs. simulation time with neurons labeled by their preferred direction.