Cold Pressor

The procedure window is shown in Figure 1 and provides a visual summary of the procedure:

• The top bar displays the operator instruction .
• The center label shows the responder classification (responder-label or non-responder-label), based on whether the participant completed the task within the specified time limit.
• The circular chart represents the temporal structure of the procedure:
  • The blue segment corresponds to the pain detection threshold (PDT), i.e., the time from immersion to first pain sensation.
  • The red segment corresponds to the pain tolerance threshold (PTT), i.e., the time until the participant withdraws from the stimulus.
  • Additional segments may represent remaining or contextual time relative to the configured time limit.
• The legend displays the measured values using the configured labels (pdt-label, ptt-label) along with their corresponding times.

Figure 1: Procedure window of the cold pressor procedure

This visualization reflects the internal state transitions of the procedure and provides an intuitive overview of the participant’s response over time.

Procedure definition

A cold pressor procedure can be defined with the <psychophysics-cold-pressor> element within the <procedures> element in the Experiment Definition File (*.expx):

<psychophysics-cold-pressor 
    id="T01" 
    experimental-setup-id="cpt"
    name="Cold Pressor Test (PDT, Operator Controlled)" 
    measurement="pdt" 
    completed-instruction="completed-instruction"
    completion-instruction="completion-instruction"
    non-responder-label="non-responder-label"
    pain-instruction="pain-instruction"
    pdt-label="pdt-label"
    pending-instruction="pending-instruction"
    ptt-label="ptt-label"
    ready-instruction="ready-instruction"
    responder-label="responder-label"
    control="operator"
    time-limit="60" 
    button="button-01" />            

The <psychophysics-threshold-estimation> procedure has these procedure specific attributes:

Measurement modes

The behavior of the cold pressor procedure depends on the measurement attribute, which determines which thresholds are recorded and how button presses are interpreted.

Pain detection threshold (PDT)

When configured with measurement="pdt", the procedure measures only the time to first pain sensation.

• 1st press: Marks immersion and starts timing
• 2nd press: Marks pain detection → PDT is recorded and the procedure completes

No tolerance measurement is performed.

Pain tolerance threshold (PTT)

When configured with measurement="ptt", the procedure measures only the time to withdrawal.

• 1st press: Marks immersion and starts timing
• 2nd press: Marks withdrawal → PTT is recorded and the procedure completes

PDT is not measured (recorded as 0).

Both pain detection (PDT) and tolerance thresholds (PTT)

When configured with measurement="both", the procedure measures both thresholds.

• 1st press: Marks immersion and starts timing
• 2nd press: Marks pain detection → PDT is recorded
• 3rd press: Marks withdrawal → PTT is recorded and the procedure completes

This mode captures both the onset of pain and the maximum tolerance duration.

Time limit behavior

For all modes, if the time-limit is exceeded before the final event is recorded:

• The procedure ends automatically
• The participant is marked as a non-responder
• Any missing thresholds remain unrecorded

Extending the procedure beyond the cold pressor

While the procedure is designed for the cold-pressor test, it follows a general pattern for measuring time-based thresholds during sustained tasks. By recording the timing of button presses, it captures the onset of a sensation or event (PDT) and the point at which the task is terminated (PTT).

This makes the procedure applicable to a wide range of endurance- and threshold-based paradigms, in which participants experience a stimulus or perform a task over time.

General principle

The procedure measures:

• Onset → time to first relevant experience or event (e.g., pain, fatigue, urge)
• Tolerance → time to termination or inability to continue

These two measures can be interpreted flexibly depending on the task.

Example applications

The same procedure structure can be used in other domains:

• Isometric muscle endurance: Measure time to fatigue and task failure during sustained contraction.
• Thermal stimulation (thermode-based): Measure detection and tolerance thresholds during controlled temperature exposure.
• Pressure pain (algometry): Measure onset and tolerance during sustained pressure application.
• Breath-hold tasks: Measure urge to breathe and total breath-hold duration.
• Cognitive or stress endurance: Measure the onset of fatigue and disengagement during prolonged tasks.

Adapting the procedure

The procedure can be adapted without code changes by:

• Updating instructions (ready, pending, pain, completion) to match the task
• Renaming labels (pdt-label, ptt-label) to reflect the measured quantities
• Configuring the measurement mode (pdt, ptt, or both)
• Adjusting the time limit to suit the task duration

This flexibility allows the same implementation to support multiple experimental paradigms while maintaining consistent timing and data collection.

Scripting

The following properties are available in calculated parameters as the result of a cold pressor procedure. These properties provide access to the measured thresholds, configuration, and outcome of the procedure.

Notes:

• PDT and PTT may be NaN depending on the selected measurement mode or if the participant did not reach the corresponding threshold.
• A participant is marked as a non-responder if the TimeLimit is exceeded before the final event is recorded.
• The result inherits common properties from Result, such as timing, identifiers, and instrument information, which are also available in scripting.