Fig. 1.

Conceptual neural model of express saccade generation based on trigger thresholds in the superior colliculus intermediate layers (SCi). A: spiking activity from a visual-motor SCi neuron during a regular (blue lines) and express (red lines) latency saccade. Each vertical line represents a single action potential. B: spikes expressed as a continuous spike density function. An express saccade is triggered when the combined previsual activity (dashed red line) visual response (solid red line) cross a neural threshold (dotted grey line) to trigger an express saccade (Edelman and Keller 1996; Dorris and Munoz 1998). When this combined response does not cross threshold, a regular latency saccade can be triggered at a later time by a separate and distinct motor response (blue line). FP, fixation point; T, target; EYE, eye position; VROL, visual response onset latency; SRT, saccadic reaction time.