Frame Parameters
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The five stimulus parameters known as "frame" parameters can be used
to specify the spatial and temporal limits and resolution of the
stimulus. They define a frame within which the stimulus is defined.
The frame parameters are not required, and are ignored, when the
stimulus is used with a model, because the model file specifies these
values with its own set of parameters (specifically, *xn*, *yn*, *tn*,
*sscale* and *tscale*).  However, when a stimulus is to be manipulated
independently of a model, for example when making a movie of a
stimulus for viewing, then these frame parameters are required.

The frame parameters are as follows

* **stim_frame_xn** - width of frame in which to place stimulus (pix)
* **stim_frame_yn** - height of frame in which to place stimulus (pix)
* **stim_frame_tn** - duration of frame in which to place stimulus (pix)
* **stim_frame_sscale** - degrees/pixel
* **stim_frame_tscale** - sec/pixel