# 空间频率

## 1. 视角 (visual angle)

1 degree ( $${}^\circ$$) = 60 minutes
1 minute ( $$'$$) = 60 second

## 2. 空间频率 (spatial frequency)

spatial frequency refers to the level of detail present in a stimulus per degree of visual angle.

### 2.1 空间频率的度量

spatial frequency is expressed by the number of cycles of alternating dark and light bars per degree of visual angle.

1个周期 (a cycle)，就是一次完整的明暗条纹的重复。我们说一个格栅的空间频率是 (1 cycle/degree)，就是说在视网膜中，一个单位视角内，这个格栅的明暗条纹重复1次，周期数为1。

A visual grating is composed of a regular series of light and dark bars.

I = Intensity on y axis; P = Location on x axis

### 2.3 对比灵敏度函数 (contrast sensitivity function /CSF)

We use a contrast detection experiment wherein one determines the minimum contrast required to detect sine wave gratings of various spatial frequency.

### 2.4 多空间频率通道 (multiple spatial frequency channels)

CSF is an envelope of sensitivity over several underlying mechanisms, each corresponding to neurons with differing preferred spatial frequencies (i.e., with different sizes of receptive field (感受野); larger = lower spatial frequency preference)

sensitivity is primarily determined by whatever channel (or set of neurons) is most sensitive to the stimulus

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