What is invariant information?

What is invariant information? How is invariance related to optic flow?

According to Goldstein (2014), invariant information is “…information that remains constant even when the observer is moving” (p. 155). Invariance is related to optic flow as the optic flow provides the necessary flow information which is present as the observer is moving through the environment (Goldstein, 2014, p. 155). Flow is there even if the scene appears differently due to variables such as position and speed.