I've been reading The Eye's Mind: Bridget Riley, Collected Writings 1965-2009 with great pleasure recently, in particular her essay "The Pleasures of Sight," from which I excerpt here:
. . . whatever the occasion might be, the pleasures of sight have one characteristic in common — they take you by surprise. They are sudden, swift and unexpected. If one tries to prolong them, recapture them or bring them about wilfully their purity and freshness is lost. They are essentially enigmatic and elusive. One can stare at a landscape, for example, which a moment ago seemed vibrant and find it inert and dull — so one cannot say that this lively quality of sight is simply ‘out there in nature’, or easily available to be commanded as wished. Nor is it a state of mind which, once acquired, can bend the most stubborn and unrewarding aspect of external reality to its own purposes. It is neither the one nor the other but a perfect balance between the two, between the inner and the outer. This balance is a sort of convergence which releases a particular alchemy, momentarily turning the commonplace into the ravishing.
Naturally, as a child one is more open to such experiences. When one gets older these tend to take place less often — that is they seldom appear any longer as pure revelations. But this does not mean that one has come to see things as they really are or any more truthfully. The damage is mostly done by the daily round with its heavy load of pressures and preoccupations which comes between, like a plate glass window, and through which one can certainly see but through which no vision can penetrate.
It seems to me that as an artist one’s work lies here. I realised partly through my own experience and partly through the great masters of Modern art that it was not the actual sea, the individual rocks or valleys in themselves which constituted the essence of vision but that they were agents of a greater reality, of the bridge which sight throws from our innermost heart to the furthest extension of that which surrounds us.
I discovered that I was painting in order to ‘make visible’. On one hand I had to make something which had this essential quality of precipitating itself as ‘surprise’ and, simultaneously, there was no way of knowing with what one was dealing until it existed; so that in order to see one had to paint and through that activity found what could be seen.