Welcome back. Let's resume our journey that began in the outside world of light and color, then continued through the retinas of our eyes, and on to the brain where sensations become the visual signals needed for perception of that outside world.
In his interesting book on the "Theories of Visual Perception," Ian Gordon describes three levels of theoretical development in any science: 1) Great theories, such as Newton's theory of gravity, or Einstein's theory of relativity. Scientific theories evolve and mature through relentless experimental challenges. Great theories are sufficiently refined to withstand foreseeable new experimental attacks. We can count on great theories; the physicist Richard Feynman once called Newton's theory of gravity "the most powerful equation of all time." 2) Good theories lack the stature of great theories because predictions from good theories are not always reliable. 3) The remaining ideas in scientific fields like visual perception might be called Working theories -- "coherent sets of ideas that have prompted high quality scientific research."
Referring to his own book about visual perception, Ian Gordon flatly states, "There are no great theories in this book." He mentions the work of David Marr and the Young-Helmholtz theory of color perception as candidates to become good theories someday (more on that later). He concludes, "Given that there is no general agreement among vision researchers on what needs to be explained about perception -- conscious experience, neurophysiological mechanism, and so on -- it is not surprising that theories of visual perception have so far lacked the rigor and power of the great scientific theories. We should not be depressed by this fact. The brain is the most complex system in the know universe. It may never be fully understood." I personally think that is a bit harsh but I am not the expert.
As we move from the notion of a "raw" Primal Sketch of the outside world to the so-called "full" Primal Sketch and beyond, expect to experience substantially more uncertainty as well as complexity. We seem to be in the midst of an animated refinement of working theories for visual perception. We will encounter a much steeper terrain in this blog, made so by the inherent experimental challenges and also by what seems to be a substantial increase in the scope and complexity of the actual cognitive processes involved in visual perception.
Forgive an admittedly simplistic analogy but the situation reminds me of how a group of people approaches a jigsaw puzzle. They begin by dumping all of the pieces onto a suitable table. Then they prepare the pieces for building the puzzle by flipping them so the pieces all face up. The puzzle builders must do this in order to SEE all the pieces. They next organize the pieces in the best manner to build the puzzle, maybe according to dominant colors, distinctive patterns, etc. A few of the pieces have special significance -- those with straight edges and particularly the coveted four "corner pieces." That stage seems to be relatively straightforward and rule based. Perhaps it resembles the first steps in visual perception, from the eyes through the "raw" Primal Sketch.
With all the puzzle pieces prepared and the special pieces identified, the builders are finally prepared to assemble the pieces into a mosaic that represents the SCENE portrayed on the puzzle box. This is the much more difficult and complex task and, by analogy, so is our journey ahead.
I think it is only prudent to remember the strengths as well as the limits in our understanding of visual perception. Just how mature is the science in this field? As the old saying goes, “This is not rocket science.” We can only wish it were, because rocket science is simple by comparison to visual perception.
If you are young and curious about neuroscience, Ian Gordon’s somber grading of visual perception theory should give you great hope. In a world where so many important scientific mysteries have been solved, visual perception remains an exciting new frontier!