How about this, when we think of a general concept a particular image pops into our mind because we use particulars to abstract into generalities. For instance, Hume, being an empiricist, argues that Ideas(i.e. abstractions) are us just thinking about a particular Impression.
However, it is not entirely true that when we envision an abstract object we tend to a particular Image. For instance, in mathematic, especially in proofs, we seldom appeal to particulars. But, In most cases it is true that we envision a particular in order to understand abstracts.
So, In essence it boils down to a person/philosopher's epistemological outlook. Empiricists tend to argue experiences are fundamental, and therefore abstractions being a derivative of it, are secondary. Rationalists, on the contrary, would argue, since rationality is the source of knowledge, abstraction, then, are fundamental .
References & Further Readings
. An Inquiry Concerning Human Understanding, by Hume
. Stanford Plato (Empiricism vs Rationalism, by numerous authors
. Critique of Pure Reason, by Kant