# Pupillometry: how long needs the pupil to respond towards an cognitive stimuli?

I would like to know if somebody could give me some references on the latency of the pupil response after a cognitive stimulus.

I know that the light reflex is quite fast compared to cognitive stimulation, but I could not find more information than this. Does anyone know how long it takes the pupil to react toward a cognitive task? Or a good reference where I could read it on my own?