Thanks to Nate's recent meme I see this entry from the 1911 Encyclopedia Brittanica which describes the Academy's descent into skepticism, from Socrates' former position "I know that I know nothing" to Arcesilaus taking the position that he did not even know that he knows nothing.
The article references the Stoics taking the position that certainty can come through "the Stoical theory of perception, the φαντασία καταληπτική, by which they expressed a conviction of certainty arising from impressions so strong as to amount to science," and then references Carneades (who Nikolsky says was probably the source for why Laertius erroneously thought the kinetic/katastematic distinction was significant to Epicurus)
take the Academy into "the doctrine of acatalepsia, which denied any necessary correspondence between perceptions and the objects perceived. He saved himself, however, from absolute scepticism by the doctrine of probability or verisimilitude, which may serve as a practical guide in life. Thus his criterion of imagination (φαντασία) is that it must be credible, irrefutable and attested by comparison with other impressions; it may be wrong, but for the person concerned it is valid. In ethics he was an avowed sceptic. During his official visit to Rome, he gave public lectures, in which he successively proved and disproved with equal ease the existence of justice."
This is a very useful quick but authoritative statement on these issues for which we frequently need reference - thanks Nate!