It is often characterized as 3 levels but if you read his book the algorithmic level is split into traversal and representation (which is highly useful as a way to think about algorithms in general) As four levels it also corresponds to Aristotle’s 4 whys: final, formal, efficient, and material.
https://en.wikipedia.org/wiki/David_Marr_(neuroscientist)#Levels_of_analysis
It is often characterized as 3 levels but if you read his book the algorithmic level is split into traversal and representation (which is highly useful as a way to think about algorithms in general) As four levels it also corresponds to Aristotle’s 4 whys: final, formal, efficient, and material.