You can shift your focus from defense to offense.
Prerequisite: Base attack bonus +1.
Benefit: When you use the attack action or full attack action in melee, you can take a penalty of −4 to your Armor Class and add a +2 bonus on your melee attack roll. The bonus on attack rolls and penalty to Armor Class last until the beginning of your next turn.
Source: Expanded Psionics Handbook, page 51.