"I still don't think we have played as well as in pre-season and you can look at that as a positive," Barker told the Friday edition of the Nottingham Evening Post.
"We are mid-table, have lost just the one game and are in the second round of the Carling Cup, yet I don't think we have clicked into top gear.
"Hopefully we can put three to four good performances together back-to-back and get some wins under our belt.
"We know that we are going to lose games but it was a blow to lose the Lincoln game in the way we did.
"But what matters now is how we react to that and hopefully we will see the right response at Wycombe."
The Stags need a positive result at Wycombe to stop their season turning into a bad start, when everything seemed positive just over a week ago.