# Visual Stimulation

In this specification layer, we define visual stimuli. 

In the following XML morphology specification file, we define an input stimulus targetting cell population "0" (defined in the previous layer). Each visual stimulus is parametrized with different fields. Here we specify an alternative (bright / dark) expanding rings of light. This stimulus is defined using:

* **Field:** the size of the stimulus, assuming a square area. The value of the field specifies the size of one of its sides.
* **Frequency:** the bright / dark alternation frequency  (in Hz)
* **Blocked field**: the radius of a blocked round field, placed at the stimulus' center (relevant to some experimental settings in which the soma is not iluuminated)
* **x0, y0**: the location of the stimulus' center
* **Delay:** allowing the stimulus to initiate following some delay

```
<visual_stimulation xmlns = "RSME.simulation_parameters">

  <stimulation_description> Alternating expanding rings of light </stimulation_description>
 
  <stimulation type = 'alternating_expanding_circles'>
      <tgt_population> 0                </tgt_population>
      <synapse>        'light_synapse'  </synapse>
      <field>          315              </field> 
      <frequancy>      4                </frequancy> 
      <blocked_field>  0                </blocked_field> 
      <x0>             135              </x0>
      <y0>             125              </y0>
      <delay>          0                </delay>
  </stimulation>
    
</visual_stimulation>
```

There are many other stimuli available, including:

* Collapsing rings of light
* Gratings
* Moving / alternating bars
* Moving bars with background noise
* Moving bars with background dots

{% hint style="info" %}
Additional visual stimuli can be defined in the Stimuli\_visual\_pattern.py file
{% endhint %}


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