Does the taste of a particular candy bar suddenly whisk you back to an earlier time in your life? That's an evocation, the summoning, usually unconscious, of a memory or emotional state caused by a particular stimulus.
The word invocation is often used interchangeably with evocation, though in fact they have quite different meanings. An invocation is a deliberate — as opposed to accidental or unconscious — summoning of a God or other form of supernatural power for aid. Very different, you'll agree. Unless of course you're trying to invoke the God of candy bars.