Tutorial: Delayed Trig

This example will take external trig one step further. We'll use a digital trigger and start out from the settings found in ttExTrg0.mat.

For the purpose of illustration we'll use the H-reflex elicited during walking. A very simple foot switch can be used to synchronize data acquisition and stimulation to the step cycle.

We want to stimulate at a number of different points during the step cycle - preferable at random. To achieve this we'll define a number of different delays from acknowledgement of the incoming trigger to data acquisition and stimulation is applied. Event timers are made for this.

Common Settings

The only difference from the external digital trig setup is in the use of classification and event timers. Settings regarding -

• Acquisition
• Analog Input
• Trigger (External Digital)
• Analog Output (Off)

will therefore be the same. They shall not be discussed further here.

Random Delays

The foot switch generates a pulse when heel contact is detected. This incoming trigger is fed to all event timers through PFI line #1 (or any PFI line #0-#5, ref. Trigger settings).

Event timer #0 controls data acquisition, and can be used to delay acquisition. If we continue to use the output from this timer to trig the electrical stimulator both data acquisition and stimulation will be delayed and still synchronized.

Settings derived below are available from ttDelay0.mat.

Classification

We can define a number, say 8, different delays for event timer #0 if we let clasification act on event timing:
In the Classification SetUp set Sub (or Main) Classification to Stimulus Type, and set the Nmb Classes to 8. We set Stimulus Select to Random to let Mr. Kick choose delays at random - this may be changed during data acquisition. In the Act On control check only the Event Timing item.

Event Timing

Eight different classes are now available in the Event Timer SetUp. Assuming a step cycle lasts approx. 1 sec, we'll set 8 different delays 125 ms apart: 0, 125, 250, 375, 500, 625, 750 and 875 ms.