英語(yǔ)聽(tīng)力文摘459 殘留的光線

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Afterglow

Here’s an experiment you can try: look at something bright relative to its surroundings, such as a lamp or a sunny window, for ten seconds without blinking. Then shut your eyes and cover them over with your hands.

You will find that the lamp or window still seem to be hovering in front of you, quite visible at first and only gradually fading away. Yet your eyes are closed and your hands are blocking them completely — so where is the light coming from?

The answer is that the afterglow light you see isn’t really light at all. It’s the result of residual activity of the nerve cells on the back of your eye, called the retina. In sensory psychology this effect is called a “positive afterimage.”

You can think of it as something like the vibration of a string after it has been struck. The player’s finger is taken away, and yet the sound continues, because the energy she or he put into the string takes a little while to dissipate.

It’s a similar situation with your eyes. In order to respond usefully to such a relatively faint signal as light, the cells in the retina need to be very sensitive. Over-stimulate them and some will continue responding for a couple of seconds after the stimulus is removed.

Of course, the only thing we ever “see,” really, is the activation of our retinal cells — that’s what our brains interpret as light from the outside world. So for as long as it takes for them to calm down, you will continue to see a faint glow of light — even though nothing is there.

你可以嘗試這樣的試驗(yàn)：不眨眼盯著看相對(duì)周圍而言光亮的東西十秒鐘，比如，一盞燈或?yàn)M陽(yáng)光的窗戶;接著閉上眼睛且雙手蒙住。

你會(huì)發(fā)現(xiàn)那盞燈或窗戶依舊浮現(xiàn)在眼前，最開(kāi)始清晰得很，又慢慢消失?？墒牵悴皇情]眼了嗎?況且雙手不是嚴(yán)實(shí)地蒙住了嗎?那么，光線從何而來(lái)?

答案是殘留的余光根本不是真正的光芒。其實(shí)這是視網(wǎng)膜(眼后的神經(jīng)細(xì)胞)的痕跡作用。感官心理學(xué)將這種現(xiàn)象稱作“正后像”。

你可以將“正后像”視為撥動(dòng)后琴弦的振動(dòng)。彈琴者手指離開(kāi)了琴，而琴音依舊。因?yàn)榍傧疑系哪芰啃枰c(diǎn)時(shí)間消退。

視覺(jué)的情況也類似，視網(wǎng)膜細(xì)胞的感光十分敏感以便及時(shí)感知像光線般微弱的信號(hào)。受到過(guò)度刺激的視網(wǎng)膜細(xì)胞，部分在刺激后持續(xù)反應(yīng)。

當(dāng)然，唯一我們“看到”的是視網(wǎng)膜細(xì)胞的激活也就是大腦解讀的：外界的光線。所以，只要刺激后需要時(shí)間平復(fù)，你就能持續(xù)看到微弱的燈光，雖然，實(shí)際上并不存在。