Tutorial: Input/Output Relation

This lesson starts out from the basic setup found in ttBasic0.mat.

The Relation between Stimulus and Response

It is often profitable to investigate the relation between a stimulus and the resulting response, e.g. the magnitude of a response related to the magnitude of the given stimulus. One example could be the amplitude of a muscle twitch (force) related to the amplitude of the electrical stimulus that caused it.

We'll discuss two different schemes for determining the magnitude of the stimulus:

• Stimulus strength is controlled by Mr. Kick.
• The actual stimulus strength is determined from the acquired signal.

In either case classification comes into play. Also Y-Analysis will be introduced in order to display the result online.

Note: When measuring 'high-frequency' signals peak-peak value, e.g. M- and H-responses or alike, the sample rate should be accordingly high (say 10 kHz) and no filtering should be applied. Classification based on measured signal and Y-Analysis will be based on the preprocessed signal!

Controlled Stimulus Strength

There are three ways to control stimulus strength from Mr. Kick:

• Event timer pulse duration.
• Digital output (four bit).
• Analog output.

We'll leave the digital and analog output for a later lesson and concentrate on the event timer pulse duration. For this to work the stimulator must stimulate for the full duration of the event timer pulse. The relation between the duration of the stimulation and the output, e.g. the H-reflex, could be investigated this way.

For this example we'll stick to the sampling of one analog input channel at a high rate. The settings below can be found in the ttIOrel0.mat.

Classification: Stimulation

In order to control stimuli we set (Sub) Classification mode to Stimulus Type. And we choose to let classification Act On Event Timing, which includes the pulse duration parameter.

The Nmb Classes should be set to 9 in order to implement the nine different pulse durations given below. Mr. Kick can pick the different stimulation classes at random.

Classification: Y-Analysis

When Classification is enabled the Display Y-Analysis panel will pop up. The analysis result displayed in this panel is specified in the Y-Analysis section of the Classification Set-Up:
We'll measure the H-reflex as the peak-peak amplitude of the Soleus EMG in the time interval from 32 to 52 ms after stimulation onset.

Event Timing

In the Event Timer Setup you may now roll the (Sub) Stim. Class control to view and change settings for individual classes: Let's assign the following durations to the nine classes: 0.2, 0.5, 0.8, 1.0, 1.2, 1.5, 2.0, 2.5 and 3.0 s. The Edit All feature offers you a better overview once you've become acquainted with its functionality.

Measured Stimulus Strength

In this example we'll measure the M-H-reflex relation. This is based on the assumption that the effective strength of the stimulation is proportional to the size of the M-response measured in the EMG.

The settings below can be found in the ttIOrel1.mat.

Classification: Measured response

Classification should be based on the size of the M-response, i.e. from an analysis of the acquired sweep. To do so set (Sub) Classification mode to Analysis of Sweep - a number of new parameters will now appear:

We'll measure the M-response as the peak-peak amplitude of the Soleus EMG in the time interval from 8 to 28 ms after stimulation onset.

Let's assume we've measured the maximum M-response to 6.5 mV and we want to investigate the full range from zero to Mmax. Xmin and Xmax reflects this. To achieve a 0.5 mV resolution in the M-response classification we'll need 13 classes. Mr. Kick uses two classes for "trash" - in case some sweeps should fall outside the defined range. Nmb Classes is set to 15.

Classification: Y-Analysis

Same as above.

Event Timing

As Classification mode is set to Analysis of Sweep only one class will be available. Set pulse duration (and other parameters) to fit the purpose.