- 精华
- 4
- 积分
- 4512
- 经验
- 4512 点
- 威望
- 394 点
- 金钱
- 1358 ¥
- 魅力
- 742
|
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: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: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
8)一道题是下面哪一条会削弱:是关于fixational eye movements和动物对所处环境危险程度的敏感程度的……
Wikipedia:http://en.wikipedia.org/wiki/Microsaccade
(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. |
|