The think that I find the most LSD-like, both in the visuals it generate and in principle is Google DeepDream. It works by using an image classifier in reverse

The think that I find the most LSD-like, both in the visuals it generate and in principle is Google DeepDream. It works by using an image classifier in reverse. So for example, you have a neural network that identifies bicycles, feed it an image, get the results, and feed them back to the image, boosting the bicycle-like characteristics of the image, repeat the process a number of times. In the end, you get something that looks like the original image, but made of bicycle parts. It is commonly done with faces, it can also be done on intermediate layers, amplifying more abstract details like geometric shapes. Originally intended as a way to reveal the inner workings of a neural network (for research, debugging, etc...), it has also been used by artists for really trippy visuals.