Hi there. I'll post what little I've discovered about learning ability so far. If anyone has different info, feel free to post it here.
Every time you add a first item to study, your learning ability drops. If you study the same item multiple times, it drops further. Studying different items in one study 'session' seems to increase the learning ability.
For example, if I study two smooth stones, my learning ability drops to 50%. If I study a chestnut with those two smooth stones, it increases back to 70%.
Learning ability seems to affect the points given from a curiosity. I haven't discovered whether or not it slows down the learning time.