In his introduction to Art Since 1940 (p 15), Fineberg says this:
The implicit underlying subject matter of art is always the artist's encounter with reality — the alternately painful and exhilarating intersection of psychological forces, intellect, society, and events ... in literally giving form to these subjective perceptions, the artist arrives at what ... A N Whitehead called "symbolic truth". What makes the great artists ... so fundamentally important is that (1) they have a heightened sensitivity to what is new or undisclosed in the world, ... (3) they find a way to express [it] as form so that we can all begin to look at these realities before we have the words to describe them or the distance to analyze them.
Alfred North Whitehead discussed his concept of symbolic truth as one of several kinds of truth-relation (relationship between appearance and reality). He did not directly connect this with visual art but it would be hard to avoid inferring that connection, as Fineberg does. Here is what he said in his Adventures of Ideas, 1955, 247:
Section VII - there is a third type of truth-relation which is even vaguer and more indirect than the second type considered above. It may be termed the type of 'symbolic truth'. ...
The relation of Appearance to Reality, when there is symbolic truth, is that for certain sets of percipients the prehension of the Appearance leads to the prehension of the Reality, such that the subjective forms of the two prehensions are conformal. There is, however, no direct causal relation between the Appearance and the Reality; so that in no direct sense is the Appearance the cause of the Reality, or the Reality the cause of the Appearance. A set of adventitious circumstances has brought about this connection between those Appearances and those Realities as prehended in the experiences of those percipients. In their own natures the Appearances throw no light upon the Realities, nor do the Realities upon the Appearances, except in the experiences of a set of peculiarly conditioned percipients. Languages and their meanings are examples of this third type of truth ...
There is, then, the vague truth-relation via the community of subjective form, between the music [i.e. or visual art] and the resulting Appearance. There is also the truth-relation between the Appearance and the Reality—the Reality of National Life, or of Strife between nations, or of the Essence of God. This complex fusion of truth-relations, with their falsehoods intermixed, constitutes the indirect interpretative power of Art to express truth about the nature of things. ... the delicate inner truth of Art is mostly of this sort.
Notice that Whitehead's "symbolic truth" is the truth of allusion, not representation.