Well first you have to set your models relationships, in your case , one to one relation , since the users table hold the person_id , that means a user belongs to a person . check the following example :

class Person extends Eloquent {  
    ...
    public function users(){

        return $this->hasOne('User');
    }
    ...
}

class User extends Eloquent {  
    ...
    public function persons(){
        return $this->belongsTo('Person');
    }
    ...
}

Now since we have our relation set in the two sides we can do something like this:

$user= User::first();

if ($user->persons->email === Input::get('email')) {
  //code here
}

//we can alse go with 
$person= Person::first();

if ($person->users->somefield=== Input::get('something')) {
  //code here
}

I hope this gunna help -_*

Thank you - is there a way to integrate this into the Auth::attempt() function?