WPA leverages TKIP (Temporal Key Integrity Protocol) for data protection and 802.1X for authenticated key management. WPA key management supports two mutually exclusive management types: WPA and WPA-Pre-shared key (WPA-PSK). Using WPA key management, non-root access point/bridges and the authentication server authenticate to each other using an EAP authentication method, and the non-root access point/bridge and server generate a pairwise master key (PMK). Using WPA, the server generates the PMK dynamically and passes it to the root access point/bridge. Using WPA-PSK, however, you configure a pre-shared key on both the non-root access point/bridge and the root access point/bridge, and that pre-shared key is used as the PMK. Check the following document for a comparison:
http://www.cisco.com/en/US/products/hw/wireless/ps4570/prod_technical_reference09186a00801c5223.html