“Seeing Black and White” Introduction Blawg

January 28, 2010

In the introduction to Alan Gilchrist’s “Seeing Black and White,” the author establishes that his book will take an objective look at how we see the lights and darks of the world around us.  The foundational concepts upon which Gilchrist bases his theories lie primarily with light, the objects themselves, and, finally, our eyes.  Gilchrist asserts that what we see is based on established, ordered reality that is uniform for all who see it, and certain properties of objects and light hold true regardless of the perceptions of the observer.  This differs from behavioral theorists, who assert that what we see is entirely based on our eyes and mental perceptions of reality.   The book hits the ground running, defining some important concepts that help the reader understand what it is the author is proposing.

Gilchrist starts by looking at scientific properties of objects and the light they reflect.  Some essential terms include distal stimulus, proximal stimulus, and percept.  Distal stimulus refers to the object in the environment, completely disregarding the observer.  It could be a chair, or a fence, or a tree, but it is just that object, before the observer comes along and projects their observational standpoint on the object.  These objects are illuminated by a certain amount of light, called illuminance, and reflect a certain amount of light, called reflectance.  These are quantifiable properties — illuminance is an absolute value of light, expressed in such measurements as candles per square meter, and reflectance is a percentage based on how much of the illuminance an object reflects.  A black object, for instance, reflects 3% of the light hitting it, while a white object reflects 90% of the light.

Proximal stimulus, on the other hand, refers to the point when the reflected light from the object makes contact with the actual retinal cells in our eyes.  The intensity of light measured at each point on the retina, called luminance, can take into effect the illuminance and reflectance properties of the distal stimulus.  Now, once the light has made contact with us, we move to how our mind decodes this information.  This is the percept, and it is where things become subjective.  The example Gilchrist uses is that of the moon:  while the reflected light is close to black, we perceive it as white.

One more concept Gilchrist puts forth is the difference between two terms, lightness and brightness.  For many people, these are synonymous; however, the author distinguishes between the two.  He says that lightness is the perceived reflectance of an object.  If we perceive an object as black, with low reflectance, it has low lightness.  Brightness, on the other hand, is perceived luminance, or how intense the light appears to be when it hits our eye.  As you may recall, luminance is a combination of how much light an object actually reflects and how much light is cast on it.  This distinction is subtle, but necessary to understand for this book.

Gilchrist also goes a bit into the term contrast.  Firstly he defines it as another word for luminance ratio, that is, the perceived difference in luminance between two objects of surfaces.  However, he also says contrast can be an illusion – for instance, a black surface in light may appear to be a different tone of gray as a white surface in shadow.  Yet, when taking into account the difference of reflectance and illuminance, they are actually the same tone.  It is only because of the contrast of surrounding black or white squares, combined with the shadow which is cast on the white square, that the two appear different.  For an example of this, see this link:  http://upload.wikimedia.org/wikipedia/commons/thumb/6/60/Grey_square_optical_illusion.PNG/360px-Grey_square_optical_illusion.PNG

A little while back in this class we defined tone as the neutrality of a color, or how gray it is.  After considering what Mr. Gilchrist had to say about contrast, I now think that tone is not a solid attribute of an object, but rather a perception based on other nearby objects.  Though an object may appear to have a lighter tone of red than another, it may just be caused by the “higher of two luminances at an edge” (Gilchrist, 2006); thus, even if two red vases with the same tone were next to each other and one were in shadow, the contrast can affect how we see the tone of them.  Tone is more subjective than I previously thought.

After having read the introduction to “Seeing Black and White,” I feel as if I have a stronger, if not completely clear, idea of how we see lights and darks in our reality.  The writing was clean, but the heady and scientific nature of the content made comprehension for me a bit difficult at times.  It was only after re-reading certain sections and coming up with my own words for the definitions that I grasped more of what Mr. Gilchrist had to say.  I like how he broke down the distal stimulus, or object, the proximal stimulus, or contact with our eye, and percept down into separate ideas, rather than one all-encompassing process of seeing.  If I have time, I may delve further in to the book.


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