Changes of blood pressure and respiration during deception

Background & Context

The 1926 study by Carney Landis and L.E. Wiley represents a pivotal early investigation into the physiological basis of deception detection, conducted during the formative years of polygraph science. Published in the Journal of Comparative Psychology just five years after John Larson's development of the first modern polygraph in 1921, this research emerged at a time when the scientific community was actively debating whether cardiovascular and respiratory changes could reliably differentiate truth from deception.

What makes this study historically significant is that it challenged the prevailing optimism about blood pressure and respiration as deception indicators, reporting detection rates as low as 50% for mock crimes. This contrasted sharply with more enthusiastic contemporaneous claims and positioned Landis and Wiley as early scientific skeptics in the polygraph field. Carney Landis, a University of Minnesota graduate who had previously conducted groundbreaking work on emotional reactions and physiological responses, brought methodological rigor to this nascent area of research.

Research Design & Methodology

The researchers employed continuous measurement of relative blood pressure and respiration during deception tasks, using instrumentation similar to what field examiners were beginning to adopt. The study examined multiple stimulus types to assess how the nature of the deceptive material affected detection accuracy, including mock crime scenarios and neutral stimuli such as numbers and letters.

Key methodological elements included:

• Continuous physiological recording of blood pressure and respiration patterns throughout deception tasks
• Multiple stimulus conditions ranging from emotionally salient mock crimes to neutral alphanumeric items
• Comparison of detection rates across different types of deceptive material to examine the role of emotional salience
• Analysis focused specifically on cardiovascular and respiratory channels without electrodermal measurement

The research was designed to investigate whether detection accuracy varied based on the type or nature of the stimulus situation employed, a question that would prove foundational to understanding polygraph validity.

Results & Key Findings

The study reported detection rates of approximately 50% when mock crimes were employed, a finding that stood in stark contrast to the near-perfect accuracy claimed by some early polygraph advocates. More concerning still, detection rates ranged from 83% down to 40% with neutral stimuli such as numbers and letters.

Specific findings included:

• Mock crime detection: ~50% accuracy using blood pressure and respiration measures
• Neutral stimulus detection: 40-83% range depending on experimental conditions
• No consistent discriminative patterns in blood pressure changes that reliably indicated deception
• Performance barely exceeded chance levels in some conditions

Critically, despite employing continuous measurement of relative blood pressure—the same technique field polygraph operators were using—Landis and Wiley failed to find evidence for significant discrimination of deception. This negative finding proved influential in tempering early enthusiasm about the polygraph's capabilities and would be cited for decades as evidence of the technique's limitations.

Discussion & Significance

The Landis and Wiley study holds profound historical importance as one of the first rigorous scientific examinations to challenge the assumed validity of physiological deception detection. The study is referenced alongside Benussi's earlier work as evidence that subsequent researchers did not find the same degree of accuracy initially reported by polygraph pioneers. This established a pattern of scientific skepticism that would characterize academic research on polygraphy for nearly a century.

The findings suggested that the greater the degree of affect associated with the stimuli employed, the greater the obtained detection rate—an insight that foreshadowed modern understanding of the role of psychological salience in polygraph testing. However, even under optimal conditions with emotionally charged mock crimes, accuracy remained disappointingly low. The study's importance extended beyond its specific findings to influence the broader debate about whether physiological measures could ever serve as reliable indicators of deception in forensic settings.

Limitations & Considerations

Several methodological factors limited the study's conclusions. The research relied exclusively on blood pressure and respiration measurements, predating the widespread adoption of electrodermal (galvanic skin response) recording, which subsequent laboratory studies would show to be the single best index of deception. The lack of standardized questioning techniques—developed later with the Control Question Test—meant the study could not leverage psychological test construction advances that would improve polygraph performance.

Additionally, differences between studies in methods of stimulus presentation, analysis of data, and particular physiological measures used made valid comparisons virtually impossible. The study's laboratory conditions, while controlled, may not have captured the heightened arousal associated with real-world high-stakes deception. Finally, the continuous blood pressure measurement technique, while similar to field practice, may have been less sensitive than the intermittent peak measurement methods that would be developed later.

Practical Applications

For contemporary polygraph practice, the Landis and Wiley study serves as a historical reminder of the importance of multi-channel physiological recording and standardized test protocols. The finding that detection accuracy varied dramatically with stimulus type underscores why modern examiners must carefully construct psychologically relevant test questions. The study's negative results with blood pressure and respiration alone validate the field's subsequent adoption of electrodermal measurement as a critical third channel.

For consumers and policymakers, this early research demonstrates that scientific scrutiny of polygraph validity is not a recent phenomenon but has existed since the technique's inception. The study exemplifies why polygraph results must be interpreted cautiously and why no single physiological measure can serve as a definitive "lie detector." It remains a cautionary tale about the gap between the promise of physiological deception detection and the challenging reality of achieving reliable accuracy in practice.