Mini view in folder gone

I had jpeg photo files in my documents folder. Before when I single clicked on one of them a mini image of the file would pop up on the left side of the screen. I don't know what I did but now when I single click on one of those jpeg files I done get that mini picture of the file anymore. It maked it more difficult to know which picture is which without having to double click and opening the file into the full blown image. Does anyone have any suggestions or knows what I can do?