The task switcher on Sony Xperia devices is pretty minimal. Its basically just a screen of square thumbnails. There may not be a change to this until the next update to Sony Timescape UI. Good thing developers like "kuriboo" create awesome mods like the HTC Sense 4 task switcher for the Sony Xperia SP. The mod comes in the form of a flashable zip. Just flash in a custom recovery like Team Win Recovery Project or Clock Work Mod Recovery. Once installed, tapping the recent apps button will bring up the Sense 4 task switcher complete with full sized, horizontally scrolling 3d thumbnails of your recently opened apps. This mod is even compatible with the latest 4.3 update. Head to the link below for the download.
Via XDA