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Page Revision: 2015/01/27 03:23

Cedrus XID element monitors button and line states on the Cedrus input devices that support the XID (eXperimental Interface Device) protocol. The supported XID devices include the RB Series and Lumina response pads, StimTracker marker and SV-1 voice key.

Table of Contents [Hide/Show] Actions aligned with epochs of the parent event Properties     Generic Properties Description Supported Cedrus devices (with links) Selection of the monitored button or line Triggering modes Button Names Triggered Snippet Practical Use     Implementing the "Press any button to continue" design pattern     Implementing the reaction time measurement with a single button     Recording times of multiple button presses within a single event Notes

Description ¶

The Cedrus XID element monitors a state of input device and collects accurate timing statistics of button presses, button releases and changes in the device's auxiliary input lines. The element uses an internal timer of Cedrus hardware (when available), which allows to record more accurate response times than when a standard keyboard is used. Multiple Cedrus XID element elements can be used to record from one or several input devices in parallel. The Cedrus XID element monitors button presses only within a scope of its parent event and return timing statistics relatively the onset of the parent event.

Supported Cedrus devices (with links) ¶

RB Series response pads

MRI compatible Lumina response unit

StimTracker marker unit

SV-1 voice key unit

Selection of the monitored button or line ¶

Cedrus XID element can monitor either one specific button or line, or all buttons and lines in the same time (when Any Button is selected in the Monitored Button property). In many experimental tasks, e.g.2AFC, there are two response buttons for a participant. Due to flexibility of the Cedrus XID element, for the 2ADC tasks you can use different design patterns:

1. Create two Cedrus XID elements, each monitoring one of the predefined response buttons or lines
2. Create one Cedrus XID element monitoring Any button and write code that checks what button is pressed. The name of the pressed button is returned by the Triggered Button property
   

Both patterns are eligible. The first pattern allows to automatically ignore presses of irrelevant buttons. The second pattern is more convenient for collecting a reaction time in trial, because you can get from a single proxy variable link to the Triggering Time property of Cedrus XID element.

Triggering modes ¶

The Cedrus XID element can detect any button state, not only presses. There are 5 'triggering' modes, in which the element can operate. You need to select the triggering mode in advance, according to your requirements:

• First Press Only
• First Release Only
• Multiple Presses
• Multiple Releases
• Holding Down
  

Depending on the working mode, the element becomes 'triggered' when a specific input pattern is detected. The First Press Only mode is the default choice for registering the fastest reaction time, because in this mode the element picks up the first button press ignoring the rest. Other modes are self-explanatory, save for the holding down mode, which detects continuous presses, commonly used in the game-like activities.

Button Names ¶

The Cedrus XID element uses simple button naming, based on the button index: "Button 1", "Button 2" and so on. The input lines are named similarly: "Line 1","Line 2" and so on. Be aware that you need to maintain capital letter in the names, while operating on them in C# code. You can easily find out the actual button name, using the design-time press detector on the Cedrus XID element. Open an editor for the Monitored Button property and move the mouse cursor over the picture with a web. Then, press the desired button and check its name in the top row:

Using the press detector to set the monitored button or find out the button name

Triggered Snippet ¶

The button element can invoke custom user code each time, when it becomes triggered (e.g. on a button press). To engage the triggering snippet, open it via the snippet panel and write your code there. Note that the triggered snippet is invoked only once, on the first press, when the First Press Only triggering mode is selected. The triggered snippet can be used for checking a name of the pressed button:

if (TriggeringButton=="LeftArrow")
    Positon.X=PositionX-1;
if (TriggeringButton=="Right")
    Positon.X=PositionX+1;

Practical Use ¶

Implementing the "Press any button to continue" design pattern ¶

1. Add the Cedrus XID element to the 'stop' event
2. Browse the Cedrus XID element properties in the property panel
3. Define a name of the Cedrus Port as it's set in your system, for example, 'COM1'
4. Select the baud rate according to the settings of your Cedrus device.
5. Leave Triggering Mode and Monitored Button with the default values, 'First Press Only' and 'Any Button'
6. Create a proxy variable linked to the Is Triggered property of the element
7. Go back to the parent event and add the conditional flow route leading to a successive event.
8. Write an expression for the conditional route as (IsTriggered==true), where the first part is a name of the proxy variable linked to the button element
   

Implementing the reaction time measurement with a single button ¶

1. Add the Cedrus XID element to the 'measurement' event, normally one where the stimulus is presented
2. Browse the Cedrus XID element properties in the property panel
3. Define a name of the Cedrus Port as it's set in your system, for example, 'COM1'
4. Select the baud rate according to the settings of your Cedrus device
5. Leave Triggering Mode with the default value, 'First Press Only'
6. Select Monitored Button
7. Create a proxy variable linked to the Is Triggered property of the element
8. Create a proxy variable linked to the Triggering Time property
9. Go back to the parent event and add the conditional flow route leading to a successive event, if you want to terminate the event on a button press.
10. Write an expression for the conditional route as (IsTriggered==true), where the first part is a name of the proxy variable linked to the Is Triggered property
11. After offset of the 'measurement' event, pick up the value of the Triggering Time proxy variable. For example, you can save it to the data report via the Reporter Element
    

Recording times of multiple button presses within a single event ¶

1. Add the button element to the 'measurement' event, normally one where the stimulus is presented
2. Browse the Cedrus XID element properties in the property panel
3. Define a name of the Cedrus Port as it's set in your system, for example, 'COM1'
4. Select the baud rate according to the settings of your Cedrus device
5. Set Triggering Mode to 'Multiple presses'
6. Select Monitored Button
7. Create a proxy variable linked to the Triggering Time property
8. Open the triggered snippet of the button element via the snippet panel
9. Add the following code to the snippet. The code adds a time of the current button press to a dedicated array list.
   

/// PressTime is a list declared in the header, e.g.
/// ArrayList PressTimes=new ArrayList();

PressTimes.Add(TriggeringTime);

Notes ¶

• If the monitored button is already pressed on the event onset, the element is not triggered by press immediately, it will happen only on the next press. Also, you can not rely on the Is Down property, which identifies a state of the monitored button only after a message from a Cedrus device is received within the parent event. The same logic is applied to monitored input lines.
• The Triggering Time, Is Triggered and Triggered Button properties are nullified on the onset of the parent event. However, you can read these values in other events after the offset of the parent event
• Is Down property can be used a button or line state flag, independently of the selected triggering mode