Please look at this sentence from "The God of small things" written by Arundhati Roy.
The news didn't perturb him as much as excite his curiosity.
Shouldn't it be excited his curiosity? I'm confused by the usage of excite in the sentence.
"Excite" is used here in keeping with "perturb" in a parallel structure. One way of understanding it is to see it as following an implied auxiliary did.
The news didn't perturb him as much as it did excite his curiosity.
Since the verb "excite" is part of the parallel structure under an auxiliary verb, it is not conjugated.
Edit: as FumbleFingers points out, it is not limited to this one possibility. The sentence could also be understood as:
The news didn't perturb him as much as (it) excited his curiosity.