*spere-

The core idea of the root (according to English sources) was:

ankle

German sources have the meaning for focused on motion and describe it as

twitching with the foot, unrest

In German, it shifted toward a sense of tracking (by foot) and then kept going toward the sense of perceiving.

English doesn’t have many relatives – spur, spoor, spurn.
They haven’t shifted their meaning as much, so they’re still somewhat close to ankle or to a broad sense of twitching.