# What does “non-linear processing” mean, exactly?

In the following sentence from "How does the brain solve visual object recognition?" by DiCarlo et al.:

In sum, our view is that the “output” of the ventral stream is reflexively expressed in neuronal firing rates across a short interval of time (~50 ms), is an “explicit” object representation (i.e., object identity is easily decodable), and the rapid production of this representation is consistent with a largely feedforward, non-linear processing of the visual input.

I'm familiar with "feed-forward" but not with the meaning of "non-linear processing" in a neuroscience context. What does "non-linear processing" mean, exactly?

• Do you know what non-linear functions and how they're different that linear functions? – Seanny123 Oct 22 '17 at 19:38
• @Seanny123 Probably not in the mathematical sense. I think of science from a physical standpoint rather than a mathematical one. – Viziionary Oct 22 '17 at 20:22
• Ok I read up on the difference between linear functions and non-linear functions in math (Yeah, I know, I should know that already), but I'm not exactly clear on how this translates to neural patterns. – Viziionary Oct 22 '17 at 21:25
• It's not really the neural patterns that are non-linear, as much as the function being computed by the neurons that are non-linear. Basically, there's a non-linear mapping between the input (visual stimuli) and the output (object). It's really just a way of saying "complicated" in this context. – Seanny123 Oct 22 '17 at 22:10

The idea of linear/non-linear in neuroscience is the same as in mathematics. A process $f(x)$ is linear if $f(\alpha x) = \alpha f(x)$ and $f(x+y) = f(x)+f(y)$ for all $x$, $y$, and $\alpha$.