视觉系统~~~考古已确认

sweetyecho

人类的睡眠（高分区）

讲的是人类眼睛的眨眼之类的一种定义为M的行为可以使人们看清楚stationary objects.

好像叫（REM），意思是说睡觉时，眼睛仍在转动。

（老牛补充：我知道如果说到睡眠，REM是Rapid Eye Movement的缩写，RES是什么就不清楚了，但是和睡眠有关，应该八九不离十）

第一段：开头就提到一个假设。第一段先给了一个定义，解释了Microsaccade这个东西。大概是说什么眨眼之类的眼睛自己的运动，然后说researchers have been unsure about the function of Microsaccade，甚至曾经有的researcher have gone so far居然说这种眼睛自己的活动可能会因为blurring什么的对眼睛造成伤害。（后注：这种假设是错误的）。（这里有题，问文章提到这种对于Microsaccade功能的解释是为什么）接着第一段后面说了又有另外一种解释，说是这个M吧，可以让人们的眼睛看清楚静止的物体。

第二段：前半部分说了支持这种假设的证据，后半部分提出反对的意见，讲了一些眼球看物体的反应。还是拿青蛙作对比，说青蛙看不见静止的只看见活动的，但是人可以，因为人的眼睛有motion还是怎么的。说这种睡眠比较为深度睡眠更难醒，而且单从predator的角度来看，这种假设也难合理。

视觉方面的神经元的运作方式之类的。比如什么neuron会 generate more electro...（有着“电”的词根的某单词）with response to moving objects than to stationary objects（有题）。讲vision evolution之类的就是人们容易看到动的东西，visual system就退化了。然后还有一个类比是说人的眼睛很像青蛙的眼睛。就说青蛙就完全看不见静止的物体，但是对于移动的物体反应就会很快。但是人类的眼睛就因为有了这种Microsaccade，看静止的物体也没问题。

第三段：继续提一些反对这种假设的证据。说了一个实验，就说科学家找来一群人，让他们一直对着电脑频幕的一个central dot看，然后问他们对于电脑屏幕上的peripheral dot的视觉反应。接下来这段...我不是很明白他们之间的因果关系...反正大概意思是说，那些人看着看着，觉得那些peripheral dot在慢慢消失fading，而他们的Microsaccade也在逐渐变缓(sparser数量减少and slower)，然后又恢复normal when the peripheral reappear。

补充：首先提出一个概念Microsaccede，下简称m，中文是微动眼，指眼睛自然的细微运动。研究人员提出假设微动眼的作用可以使我们看得清静止的东西。在进化的过程中，视觉在看动态事物方面进化较快，之后讲了一些原因，有一个是因为动物可以见到猎物逃走。人的眼进化出微动眼帮助人不仅看到motion还能够看到静止事物。之后对比了人和青蛙。最后视觉神经是如何发生作用。神经一般是在看motion时才firing，而微动眼帮助人类即使在看静止的事物神经都可以keep firing。

主题：提出假设+推翻假设+实验结论

考题：

1）What is the theme of the passage?

选主要讨论一种假设

2）What is the function of the substance of Microsaccade?

基金主人选的是illustrate科学家对于Microsaccade功能不能达成共识。

3）视觉方面的神经元的运作方式之类的。比如什么neuron会 generate more electro...（有着“电”的词根的某单词）with response to moving objects than to stationary objects（有题）

4）infer题：从文中可以推出最后一段试验中的subject干什么呢？

基金主人选的是M帮助人看到什么东西来的。

（这题要对experiment的结果要求看仔细点，关系有点复杂。）记得其中2个选项是M开头，3个选项是visual neutron开头。

5）第二段有一个in additional，问作用

6） 推断视觉神经在青蛙的作用

备选对motion的反应比对静止事物强烈得多

7）主题题

8）一道题是下面哪一条会削弱？

是关于REM和动物对所处环境危险程度的敏感程度的……

(疑似)原文未缩减gitarrelieber

节选自Windows on the Mind (Scientific American Magazine @ August 2007)

And yet only recently have researchers come to appreciate the profound importance of such “fixational” eye movements. For five decades, a debate has raged about whether the largest of these involuntary movements, the so-called microsaccades, serve any purpose at all. Some scientists have opined that microsaccades might even impair eyesight by blurring it. But recent work has made the strongest case yet that the seminuscule ocular meanderings separate vision from blindness when a person looks out at a stationary world.

Indeed, animal nervous systems have evolved to detect changes in the environment, because spotting differences promotes survival. Motion in the visual field may indicate that a predator is approaching or that prey is escaping. Such changes prompt visual neurons to respond with electrochemical impulses. Unchanging objects do not generally pose a threat, so animal brains – and visual systems – did not evolve to notice them. Frogs are an extreme case. A fly sitting still on the wall is invisible to a frog, as are all static objects. But once the fly is aloft, the frog will immediately detect it and capture it with its tongue.

Frogs cannot see unmoving objects because, as Helmholtz hypothesized, an unchanging stimulus leads to neural adaptation, in which visual neurons adjust their output such that they gradually stop responding. Neural adaptation saves energy but also limits sensory perception. Human visual system does much better than a frog’s at detecting unmoving objects, because human eyes create their own motion. Fixational eye movements shift the entire visual scene across the retina, prodding visual neurons into action and counteracting neural adaptation. They thus prevent stationary objects from fading away.

The results of these experiments, published in 2000 and 2002, showed that microsaccades increased the rate of neural impulses generated by both LGN and visual cortex neurons by ushering stationary stimuli, such as the bar of light, in and out of a neuron’s receptive field, the region of visual space that activates it. This finding bolstered the case that microsaccades have an important role in preventing visual fading and maintaining a visible image. And assuming such a role for microsaccades, our neuronal studies of microsaccades also began to crack the visual system’s code for visibility. In our monkey studies we found that microsaccades were more closely associated with rapid bursts of spikes than single spikes from brain neurons, suggesting that bursts of spikes are a signal in the brain that something is visible.

In our experiments, we asked volunteers to perform a version of Troxler’s fading task. Our subjects were to fixate on a small spot while pressing or releasing a button to indicate whether they could see a static peripheral target. The target would vanish and then reappear as each subject naturally fixated more – and then less – at specific times during the course of the experiment. During the task, we measured each person’s fixational eye movements with a high-precision video system.

As we had predicted, the subjects’ microsaccades became sparser, smaller and slower just before the target vanished, indicating that a lack of microsaccades– leads to adaptation and fading. Also consistent with our hypothesis, microsaccades became more numerous, larger and faster right before the peripheral target reappeared. These results, published in 2006, demonstrated for the first time that microsaccades engender visibility when subjects try to fix their gaze on an image and that bigger and faster microsaccades work best for this purpose. And because the eyes are fixating – resting between the larger, voluntary saccades – in the vast majority of the time, microsaccades are critical for most visual perception.

serenazhang01

顶上来~~~~~~

sunnyevonne

many thanks for sharing...