Detect Thoughts Actions

[BlackRose]

Detect Thoughts states a few uses of using it's actions. In the first paragraph it says that when you cast the spell, and then as an action in subsequent turns, you can focus on the mind of a creature you can see within 30 feet. It then goes on to say that as an action you can switch targets or probe deeper. Does this mean it requires an action to simply maintain surface thoughts on a creature, or is the action only required if you want to target a new creature or else to probe further on the current target?

[ShadowSandbag]

Maintaining surface level thoughts is free, probing deeper or switch targets is an action.

[greenstone]

It requires an Action to do everything.

The Action could be to read the surface thoughts of a creature, to attempt to read deeper thoughts of the creature you read last turn, or to scan for minds within range.