How would I create an AI that can't see behind it?

After the most recent roblox update, my AI have just been refusing to walk sometimes. The game will say that they are walking, but they won't walk.

So i'm gonna rework them, and I want them to not be able to see you unless you are infront of them. Kinda like how in dark souls you can sneak up on enemies.

I was thinking about using raycasting for this, but i'm unsure how I would go about this. Pathfinding isn't the issue, but detecting if the AI can see the player is what the problem is. Any ideas? Not looking for code, just some advice/help

tl;dr - ai that can't see behind them until attacked.

• Not gonna post code because i'm restarting from scratch