Your specialized training in shields allows you to avoid spell failure.
Prerequisite: Proficient in at least one type of shield.
While wielding a shield you are proficient with, you avoid the chance for spell failure. Additionally, using that shield does not prevent you from completing somatic spell components with the hand wielding the shield.
This feat does not work with tower shields.
Normal: Shields interfere with a spell-caster’s gestures, which can cause spells to fail if those spells have a somatic component.