My answer attempts to solve the root cause of the problem you describe in your question: players are rolling for skill checks that might not even be appropriate there. Perception is only a mild issue, and often not even an issue at all, but by instructing your players (who are all first-time table top players) to pick the skills from their character sheets and roll them, you might be paving the way to bigger problems as their actions become more complex to adjucate. 

The style of play I am about to describe is one of the methods you can play the game, and mix fiction with mechanics. This is only **one** ethos of many you can follow to play the game, and it has really worked well for me in my campaigns.

Turn it around
=
Players shouldn't state the skill they want to use for a given situation, they should state their intentions. As the Game Master, **you** know how that intended action can be adjucated, and you will request the player to make a Perception / Diplomacy / Bluff / Whatever skill check.

Instead of the player saying
> I want to roll a Perception Check to look around the room.
>
> I want to roll a Diplomacy Check to tell the guard to calm down.
>
> I want to roll a Stealth Check to sneak past the sentry with these clothes I found.

You should teach them to describe their intentions and approaches
> I look around the room. What do I see?
>
> I want to unsheathe my sword and tell the guard to calm down.
>
> I want to use the clothes I found to sneak past the sentry.

Upon which you might (or not!) request the player to roll for a check. Remember that it is up to you to determine if a result should be randomly determined. If an action as described is simply impossible, or extremely hard, don't make them roll! Rolls without a true purpose only bog down on the pace of the game.
> You see a mural that depicts the battle of your ancestors. [You roll Perception Check behind screen, succeeds] You also see a key lodged between two bricks in the wall.
>
> You pull out your sword and tell off the guard. Roll for an Intimidate Check.
>
> You put on the clothes you found in an attempt to blend in with the crowd. Roll a Disguise Check.

Players are focused on what they are good at
=
Note how in the last two examples, you asked the player to roll a different skill than what I described in the very first example block. Players often look at their character sheets, find a skill that is highly trained and try to use that over something else. They might try to use Acrobatics instead of Climb, or Intimidate instead of Bluff. Make it a rule of thumb that they are not allowed to ask for skill checks. Only let them state intentions or ask you questions about the in-game world. And you can (or not!) ask them for a skill check.

The [Angry DM has a very good article on adjucating actions](http://angrydm.com/2013/04/adjudicate-actions-like-a-boss/). It has helped me with a situation like this.

A parting thought
=
The main reason to keep the crunching with the GM and the fiction with the players for me was that, in the end, it's going to be the GM's call. By avoiding to create 'rules lawyers' and keeping them focused on describing their intentions and approach rather than zoom in on one of their skills I think I have made the games I ran more fluid and fun. However, [this policy is a mixed bag](http://rpg.stackexchange.com/a/60599/10682), and you'd be wise to find out for yourself if this policy works for your group. It may not directly answer your specific question about the Perception roll, but it could solve the root problem in the long term.