In a document I found the following sentence:
listeners are more accurate at understanding speech spoken in their own accent…
Would it be an error to use "in" instead of "at"?
Actually in this case "at" sounds better than "in", but in general before verb is "at" always used?
Best Answer
Here are the first 25 COCA results for Adjective + in understanding (the number on the right is the number of hits for a sequence). In all of these the adjective preceding the prepositional phrase characterizes instrument which leads to understanding rather than characterizing some person's ability at understanding.
Now see the results for Adjective + at understanding. In all of these, the adjective characterizes a person's ability to understand.
It wouldn't be safe, however, to assume that this pattern holds for any given adjective + PP[pres.ppl] combination. When we search for skilled + (in/at) + V.pres.ppl we find 109 hits for skilled at V-ing and 173 hits for skilled in V-ing. Not much of a discrepancy as compared to the clear differentiation between in understanding and at understanding.