Colorful Origins

ACCORDING TO “Illusory Color and the Brain,” by John S. Werner, Baingio Pinna and Lothar Spillmann, an object's color is made relatively stable by the brain despite environmental changes. I am partially color-blind and have observed that when looking at a particular object in natural light, the vividness of its color will be affected by my proximity to it. Furthermore, in my trade as an electrician, I have found that the use of a flashlight shined on color-coded wires at close range assists in their discernment.

TJ Downey New Bloomington, Ohio

WERNER, PINNA AND SPILLMANN REPLY: Changes in illumination can indeed influence color discrimination. A partially color-blind individual may find such discrimination more difficult to make, either because one type of his or her retina's cones (those cells that are responsible for absorbing light during the day) ceases to function or because photoreceptor pigments in the cones overlap in their absorption more than usual. Small differences in spectra might be easier to detect when they are under brighter lighting or when they take up a larger field of vision.

It is important to distinguish between the dis crimination and the appearance of colors (the latter being the main topic of our article). If one looks at a small white patch in a larger field of vision as its illumination from the sun varies throughout the day, the physical changes in its wavelength composition are striking. If all we could know about the patch's color were based on this observation, we might call it blue in the morning and yellow in the afternoon. The identification of objects by color would be considerably flawed if this were the case. Because of mechanisms in the eye and brain, most individuals can identify colors in the same way as one another when viewing a broad range of objects under a number of light variations, but this ability may fail when viewing an isolated part of a scene.

Egocentric Archival

IN “A DIGITAL LIFE,” Gordon Bell and Jim Gemmell describe Bell's self-experimentation with the possibility of individuals digitally archiving their entire existence. The authors appear to be substituting the minute recordings of experience for a true life. One has the feeling that at some time Bell will begin to record his reviewing of his record of his experiences, setting him in an endless loop terminating only when his registers overflow.

The activity of recording an experience separates an individual from the experience itself. And digital recordings, being what they are, can be edited and reorganized. That stupid choice, the thoughtless remark, the road traveled—they can all be changed so that the record is no more than a “cult of personality.”

This kind of archiving, it seems to me, is different from a life of contemplation or of meditative concentration, because these have enlightenment as a goal. Bell's approach isolates, which, I suppose, is what all compulsions do.

David Hopp Durham, N.C.

Extent Horizon

IN “BLACK HOLE BLOWBACK,” Wallace Tucker, Harvey Tananbaum and Andrew Fabian refer to the diameters of black holes in regard to the size of our solar system. My understanding of black holes was that they have infinitesimally small volumes and densities that therefore approach infinity. How could a black hole have a diameter that could be related to the size of our solar system?

Matthew Briggs Seattle

TUCKER, TANANBAUM AND FABIAN REPLY: Our wording was imprecise. We should have specified that we were describing the diameters of the event horizons of the black holes in question.

The event horizon defines the “point of no return” around a black hole: matter or radiation cannot escape a black hole's gravitational pull unless it is outside the radius of the event horizon. This radius, which increases with the mass of a black hole, appears in equations describing black holes' properties. The radius of the event horizon of a rapidly spinning black hole with a mass of a billionsuns, such as we described, is about equal to the distance between Saturn and the sun.

Ancestral Avidity?

MICHAEL SHERMER'S reference in “(Can't Get No) Satisfaction” [Skeptic] to studies showing that individuals would prefer a lower income and even less for others, rather than a higher income and even more for others, does not surprise me. Most subjects would not believe that prices would stay the same if everyone else earned much more than they do. Humans have learned through personal experience, and perhaps that of many generations of ancestors, that resources are limited and often scarce. Lower income for others may be part of most people's prerequisite for happiness: being alive.

Brett Porter Australia

SHERMER REPLIES: The findings from these studies are counterintuitive when we think in rational terms, but using a model of evolutionary economics helps us to see that our wants related to what makes us happy or unhappy tend to be relative to what other people have and are not based on some absolute measure. In the Paleolithic past, humans evolved in tiny communities of economic simplicity and relative equality. Happiness could not be found through wealth accumulation, because there was so little to accumulate as well as social pressure to redistribute what could be accrued. Our senses and perceptions evolved for short-term assessments, direct comparisons and relative social rankings.

ERRATA The illustration at the top of page 95 in “Illusory Color and the Brain,” by John S. Werner, Baingio Pinna and Lothar Spillmann, contains an error. The black inside the colored rings was accidentally printed over cyan and magenta, making it physically darker than the black of the surrounding area. The correct illustration appears on the opposite page.

On page 82 of “Diesels Come Clean,” by Steven Ashley, the box “Spark vs. Compression” incorrectly states that a diesel engine is more fuel-efficient than a gasoline engine because diesel fuel has a higher energy content. The diesel's superior efficiency derives mainly from its higher compression ratio and unthrottled air intake, among other factors.

“Back to the Future,” by David Biello [News Scan], refers to Brodmann's area as a specific region of the brain. Brodmann's area in fact refers to several regions of the cerebral cortex.