The linguistics text I’m reading has a sentence with this fragment: 「動詞の表す動作・作用が[…]」。 Consulting dictionaries just made me more confused; what’s the contrast between the two in this context? “Action” vs. “effect”?
動詞 in Japanese can represent 3 different things, 動作、作用 and 存在. An example will be easier to understand.
歩く is categorized as 動作をあらわす動詞, because when you walk, you move your legs, in other words "movement" or "action".
かける is categorized as 作用を表す動詞, here 壁にかける is having an "effect" on the wall.
ある is categorized as 存在を表す動詞, here ある indicates "existence".
So back to your question, "動作" doesn't directly place any influence on other "things" whereas "作用" directly "effects" other things.