Traditionally (at least to my memory) if you have a chance to spot a hidden object such as a secret door or a trap, the DM typically asks you to make a Wisdom (Perception) check. BUT, if you are actively searching for a hidden object,the DM typically asks you to make a Intelligence (Investigation) check.
I don't think that this distinction is made very clear on page 61 of the Basic Rules or page 7 of the Starter Set Rulebook. In fact the side bar implies that there is no difference between an active or passive search. This is despite the fact that the description of Investigation states; "You might deduce the location of a hidden object, ..."
Thoughts? Clarifications? 
You deduce the presence of a hidden object not because you "see" the hidden object like you would "see" the outline of a secret door, but because it logically follows that a secret door is in the north wall when you find the footprints that seem to walk right into the wall.
Wisdom (Perception) is for what you detect with your senses/insight
Intelligence (Investigation) is for what you reason must be so as the logical conclusion from the facts you find.
At least that's my take on first blush.
zgrose wrote:
There was some confusion on this during the playtest, but the playtest rules really spelled it out pretty well.
Basically, if a character is making a generalized search in an area looking around in hopes to find something, it would be a WIS check. If they decide to look for something in a specific place or specific way, it's an INT check.
So, for example, stopping and listening to see if you hear voices down an hallway would be WIS; looking for a map in the 3rd drawer of a cabinet would be INT.
More importantly do you have to spend an action to actively search for hidden creatures? If so there is probably a big problem with lightfoot rogues "hidden-attack-hide behind creature" every round attack sequence.