CPE Calibration 3 — Questions and Answers
Question 1: What standardized procedure do most polygraph examiners use to verify instrument accuracy before each examination?
- A biofeedback session with the subject
- A mechanical or electronic calibration check against a known signal source (Correct answer)
- A comparison of the current chart with charts from previous subjects
- A visual inspection of all sensor wires for physical damage
Correct answer: A mechanical or electronic calibration check against a known signal source
Calibration against a known signal source (mechanical or electronic reference) allows the examiner to confirm the instrument is measuring accurately before use.
Question 2: The term 'drift' in polygraph calibration refers to:
- Subject movement that displaces sensor placement
- A slow, gradual shift in the baseline tracing over time unrelated to stimuli (Correct answer)
- The lag between a stimulus and the recorded physiological response
- Chart paper advancing at an incorrect speed
Correct answer: A slow, gradual shift in the baseline tracing over time unrelated to stimuli
Drift is a slow, stimulus-independent shift in baseline that can be caused by temperature changes, electrode polarization, or amplifier instability.
Question 3: Why is it important to allow a warm-up period for analog polygraph instruments before calibration?
- To allow the subject's physiology to stabilize in the examination room
- To allow electronic components to reach thermal equilibrium for stable readings (Correct answer)
- To give the chart paper time to advance and align to the correct starting point
- To allow the cardio cuff to reach the correct inflation pressure
Correct answer: To allow electronic components to reach thermal equilibrium for stable readings
Electronic components, especially amplifiers, produce stable output only after reaching operational temperature, making a warm-up period essential for accurate calibration.
Question 4: An examiner sets pneumograph sensitivity too high during calibration. The most likely consequence is:
- Respiratory tracings that are clipped or go off-scale, obscuring fine details (Correct answer)
- An artificially reduced amplitude that makes responses hard to detect
- The cardio channel bleeding into the pneumograph channel
- Electrodermal responses appearing on the respiratory tracing
Correct answer: Respiratory tracings that are clipped or go off-scale, obscuring fine details
Excessive sensitivity causes large respiratory movements to exceed the recorder range, clipping peaks and troughs and destroying diagnostic detail.
Question 5: Which of the following best defines 'standardization' in the context of polygraph calibration?
- Using the same question set for every examinee regardless of the case
- Applying uniform procedures so results can be compared across examiners and instruments (Correct answer)
- Calibrating only one channel at a time to isolate variables
- Ensuring all examinees are tested at the same time of day
Correct answer: Applying uniform procedures so results can be compared across examiners and instruments
Standardization means using consistent, documented procedures across examiners and instruments so findings are reliable, comparable, and defensible.
Question 6: A cardio tracing during calibration shows a normal pulse wave but also a low-frequency oscillation superimposed on it. This secondary oscillation most likely represents:
- Artifact caused by the subject moving or talking
- Mayer waves or vasomotor rhythms in blood pressure (Correct answer)
- A 60 Hz electrical interference pattern
- Incorrect cuff placement over the ulnar artery
Correct answer: Mayer waves or vasomotor rhythms in blood pressure
Low-frequency oscillations (approx. 0.1 Hz) superimposed on the pulse wave are typically Mayer waves, reflecting vasomotor rhythms in sympathetic vascular tone.
Question 7: Before conducting a polygraph examination, the examiner should verify the chart paper speed is set to the standard of:
- 6 mm per second
- 15 mm per second (Correct answer)
- 25 mm per second
- 50 mm per second
Correct answer: 15 mm per second
The American Polygraph Association standard for chart paper speed is 6 mm/second for conventional analog instruments, though 25 mm/s is a common clinical standard — in US polygraph practice the APA standard of 6 mm/sec is used.
CPE Calibration 3
What standardized procedure do most polygraph examiners use to verify instrument accuracy before each examination?