The gaze heuristic is a heuristic

Heuristic

Heuristic refers to experience-based techniques for problem solving, learning, and discovery. Heuristic methods are used to speed up the process of finding a satisfactory solution, where an exhaustive search is impractical...

 employed by people when trying to catch a ball. Experimental studies

Experiment

An experiment is a methodical procedure carried out with the goal of verifying, falsifying, or establishing the validity of a hypothesis. Experiments vary greatly in their goal and scale, but always rely on repeatable procedure and logical analysis of the results...

 have shown that people do not act as though they were solving a system of differential equation

Differential equation

A differential equation is a mathematical equation for an unknown function of one or several variables that relates the values of the function itself and its derivatives of various orders...

s that describe the forces acting on the ball while it is in the air and then run to the place at which the ball is predicted to hit the ground. Instead they fixate the ball with their eyes and move so as to keep the angle of the gaze either constant or within a certain range. Moving in such a fashion assures that the ball will hit the catcher.