Just in time, via Arts and Letters Daily, comes this article by Oliver Sacks.

Whatever the mechanism, the fusing of discrete visual frames or snapshots is a prerequisite for continuity, for a flowing, mobile consciousness. Such a dynamic consciousness probably first arose in reptiles a quarter of a billion years ago. It seems probable that no such stream of consciousness exists in an amphibian, like a frog, which shows no active attention, and no visual following of events. The frog does not have a visual world or visual consciousness as we know it, only a purely automatic ability to recognize an insect-like object if this enters its visual field, and to dart out its tongue in response. It has been said that a frog's vision is, in effect, no more than a fly-catching mechanism.

And:

From such a relatively simple primary consciousness, we leap to human consciousness, with the advent of language and self-consciousness and an explicit sense of the past and the future. And it is this which gives a thematic and personal continuity to the consciousness of every individual. As I write I am sitting at a café on Seventh Avenue, watching the world go by. My attention and focus dart to and fro—a girl in a red dress goes by, a man walking a funny dog, the sun (at last!) emerging from the clouds. These are all events which catch my attention for a moment as they happen. Why, out of a thousand possible perceptions, are these the ones I seize upon? Reflections, memories, associations lie behind them. For consciousness is always active and selective—charged with feelings and meanings uniquely our own, informing our choices and interfusing our perceptions. So it is not just Seventh Avenue that I see, but my Seventh Avenue, marked by my own selfhood and identity

We add to our world our consciousness, and impose our modes of intuition on each stimulus. That's all (Kantian) idealism claims. Not that "it's all in our heads", not that the "ideal world" is primary and the real world a shadow (although I would claim that, if provoked, but it's not necessary right now); just that we cannot separate ourselves from what we observe, without losing all observation.

And you've got to respect a guy that seems able to get a giant squid on the cover of his book, despite their irrelevance to the subject matter.