Examine this easier sentence: We see the world around us BY these basic processes. <-- Here, the word "by" indicates the means one uses to accomplish something. To turn this sentence into a noun phrase using a relative clause, we do the following: 1.) take the part after the preposition "by" and move it to the front: => THESE BASIC PROCESSES we see the world around us by 2.) add the relative pronoun "which" between the two of them: => these basic processes WHICH we see the world around us by 3.) move the preposition "by" before "which": => these basic processes BY WHICH we see the world around us This is what is happening in the fragment of your sentence. I hope this helps. :) "These basic processes by which we see the world around us" can also be expressed as "these basic process that/which we use to see the world around us". Notice how I had to insert "use to" between "we" and "see" though. This is done to retain the "by means of" relationship expressed by "by" in the original sentence.

"By + which" in this context is a preposition + relative pronoun which introduces a relative clause. That combination means basically "of how." It is saying that our processes influence how we see the world. I hope that helps!