Experimental Evaluation of Galvanic Skin Response and Blood Pressure Change Indices During Criminal Interrogation

This 1968 study by Kugelmass, Lieblich, Ben-Ishai, and Opatowski examined the comparative diagnostic utility of galvanic skin response (GSR) and blood pressure change indices as physiological deception indicators during actual criminal interrogations. The research directly addressed the persistent discrepancy between findings from controlled laboratory investigations and psychophysiological response patterns observed in real-world police interrogation settings, providing one of the earliest empirical field-based assessments of these two core polygraph channels.

The research measured both galvanic skin response and blood pressure change indices simultaneously during actual criminal interrogations in Israel, enabling a direct within-subject comparison of channel performance under genuine high-stakes forensic conditions rather than simulated laboratory paradigms.

Conducted by Hebrew University researchers, this study addressed the methodological gap between laboratory deception research and real police interrogations by evaluating GSR and blood pressure changes during actual criminal investigations. The research used simultaneous dual-channel recording to directly compare the diagnostic value of these physiological measures in naturalistic interrogation settings. This represented one of the earliest empirical attempts to validate laboratory findings in real-world forensic contexts. The study challenged prevailing practitioner beliefs that blood pressure was superior to GSR for deception detection. The work contributed to the foundational understanding of autonomic response patterns in actual criminal interrogation environments.

This research provided crucial empirical validation for physiological deception detection methods in real-world settings, informing both scientific understanding and practical polygraph examination protocols for criminal investigations.

Background & Context

By the late 1960s, polygraph science stood at an important crossroads. A growing body of laboratory psychophysiology research had begun to document the differential utility of various autonomic measures — particularly galvanic skin response (GSR) and relative blood pressure change — in detecting deception, yet a persistent and troubling gap existed between those controlled laboratory findings and what was actually observed during real police interrogations. This study directly addressed the discrepancy between laboratory investigations and real-life police interrogations, making it one of the earliest empirical attempts to bridge that methodological divide within the peer-reviewed literature.

The research emerged from Israel, where a team of psychophysiologists at Hebrew University brought a rigorous scientific perspective to questions that had largely been explored through practitioner observation alone. The paper was authored by Sol Kugelmass, Israel Lieblich, Akiva Ben-Ishai, and Abraham Opatowski, published in the Journal of Criminal Law and Criminology at page 632. Kugelmass and Lieblich had already been active in psychophysiological deception research during this period, including work on ethnic and physiological baseline differences in GSR activity — a related thread of inquiry that gave their team unusual methodological depth.

The 1960s were a formative decade for deception detection science. Contemporary research programs, such as that of Thackray and Orne (1968), were simultaneously comparing multiple physiological channels — breathing, blood pressure, GSR, skin potential, and finger volume — to determine which measures most reliably discriminated deception. Field examiners generally considered blood pressure and respiration to be the most useful indicators of deception and largely discounted the value of the galvanic skin response — a practitioner bias that empirical studies of this era set out to test and, in several cases, challenge.

Research Design & Methodology

The study evaluated galvanic skin response and blood pressure change indices during criminal interrogation, appearing in The Journal of Criminal Law, Criminology and Police Science, volume 59, pages 632–635, in 1968. The paper spans four pages, reflecting the concise reporting style common to high-impact empirical notes of the era, in which brevity was valued and methods were described with efficient precision rather than extended narrative.

The research was designed to assess the comparative diagnostic value of GSR and blood pressure change as physiological indices within the context of actual criminal interrogation — not a simulated or mock-crime laboratory paradigm. This represented a meaningful ecological step forward from prevailing analog designs of the time. Key design elements included:

• Real criminal interrogation setting — participants were actual suspects or subjects involved in police criminal investigations, not recruited volunteers performing scripted mock crimes
• Dual-channel physiological recording — simultaneous measurement of galvanic skin response and blood pressure change, allowing direct within-subject comparison
• Israeli research context — conducted through an academic-forensic collaboration, lending the study a scientific independence from the U.S. commercial polygraph industry
• Quantitative index comparison — the study employed standardized indices (response magnitudes, change scores) to evaluate the relative discriminating power of each channel
• Focus on ecological validity — the interrogation conditions were naturalistic rather than artificially constructed, which was the study's defining methodological contribution

The team's approach was psychophysiological in the tradition of applied autonomic research, using established electrodermal and cardiovascular recording techniques that were standard in academic psychophysiology laboratories of the period. This grounded the findings in a scientifically credible measurement framework even as the application context moved beyond the laboratory.

Results & Key Findings

The central finding of the study was that physiological response patterns observed in real criminal interrogations differed meaningfully from those predicted by prior laboratory research, highlighting that the laboratory-to-field translation was not straightforward and that channel-specific performance could shift depending on ecological conditions. Both GSR and blood pressure change indices were evaluated for their ability to serve as reliable deception indicators in live interrogation scenarios.

The comparative analysis of the two physiological channels produced findings relevant to ongoing debates in the field at that time. Contemporaneous laboratory work by Thackray and Orne (1968), testing similar measures under controlled conditions, found that GSR and skin potential response consistently discriminated better than chance, with GSR and SPR significantly superior to finger volume, while blood pressure showed less consistent performance across stimulus conditions. The Kugelmass et al. findings, grounded in real interrogation data, provided a complementary and field-based perspective on how these channels performed outside of controlled settings.

Key findings and observations from the study include:

• GSR responsivity in actual criminal interrogation contexts proved informative, though its characteristics and reliability differed from what purely laboratory paradigms had predicted
• Blood pressure change indices demonstrated measurable responsiveness during live interrogation, aligning with the practitioner preference for cardiovascular measures but requiring careful interpretation
• The laboratory-to-field discrepancy was confirmed empirically — response magnitudes and patterns in real interrogations were not simply a replication of laboratory-analog results, underscoring the importance of ecological validity in psychophysiological deception research
• The study's findings contributed to a growing literature suggesting that no single physiological channel should be considered universally superior across all testing contexts
• The real-world criminal interrogation context introduced motivational and situational variables — heightened personal stakes, ambient stress, and genuine consequences — that were qualitatively different from laboratory conditions and influenced autonomic response profiles

Discussion & Significance

The significance of the Kugelmass et al. (1968) study lies less in any single numerical accuracy statistic and more in its foundational challenge to a dominant assumption of mid-century polygraph science: that laboratory findings could be straightforwardly generalized to real-world forensic settings. By taking psychophysiological measurement out of the controlled laboratory and into authentic criminal interrogation, the authors illuminated the limits of ecological extrapolation — a concern that would grow substantially in subsequent decades of polygraph validity debate.

The paper's publication in the Journal of Criminal Law, Criminology and Police Science — one of the most prestigious interdisciplinary journals in its field — ensured that its findings reached both legal scholars and forensic scientists simultaneously. This cross-disciplinary placement was itself significant: it placed psychophysiological evidence in direct dialogue with legal and investigative practice, contributing to the broader conversation about the admissibility and reliability of polygraph evidence. The study's citation in the U.S. Office of Technology Assessment's landmark review of polygraph validity further underscores its enduring influence on the foundational scientific record.

The Israeli academic team's contribution was also notable for its independence from the U.S. commercial polygraph industry. Research produced outside the American practitioner community brought a degree of scientific detachment to questions that were frequently entangled with professional and economic interests, and the Kugelmass group's work — spanning GSR, ethnic baseline differences, and now real interrogation performance — constituted one of the most sustained international research programs in psychophysiological deception detection of that era.

Limitations & Considerations

As with all pioneering field studies of this period, the Kugelmass et al. (1968) paper carries important methodological caveats that must be acknowledged:

• Small publication footprint — at four pages, the paper necessarily compresses its methodological description, limiting the reader's ability to fully evaluate sampling procedures, criterion verification, and statistical approaches
• Ground truth verification challenges — in real criminal interrogation settings, establishing a definitive, independent criterion of guilt or innocence against which physiological classifications can be validated is inherently more difficult than in laboratory mock-crime designs
• Sample characteristics — the specific number, demographic composition, and crime types associated with interrogation subjects are not detailed in available abstracts, making replication and generalization assessment difficult
• Historical instrumentation — 1960s-era physiological recording technology, while scientifically credible for its time, lacked the signal fidelity and artifact-rejection capabilities of modern digital polygraph systems
• Cultural and jurisdictional specificity — the Israeli interrogation context may differ in legally significant ways from American or European forensic settings, potentially limiting direct cross-jurisdictional generalizability

Despite these limitations, the study's ecological ambition was itself a methodological strength relative to the prevailing laboratory-only paradigm. The inherent messiness of real criminal interrogation was the point: understanding how GSR and blood pressure behaved under genuine forensic conditions required going beyond the artificial certainties of the laboratory.

Practical Applications

For practicing polygraph examiners, the Kugelmass et al. study offers an early empirical caution against over-relying on laboratory-derived response norms when interpreting charts collected in high-stakes, real-world interrogation contexts. The demonstrated discrepancy between laboratory and field response patterns suggests that examiners should be attentive to the ways in which genuine investigative stress, personal consequences, and situational complexity can alter the magnitude, latency, and patterning of both electrodermal and cardiovascular responses relative to what analog research predicts.

For consumers and legal professionals evaluating polygraph evidence, the study reinforces a core principle that remains relevant today: the ecological validity of the testing context matters enormously. A physiological measure that performs well under controlled laboratory conditions cannot be assumed to perform identically in the emotionally and legally charged environment of a genuine criminal investigation. This insight — articulated with empirical force more than five decades ago — continues to inform standards-setting discussions in professional polygraph bodies and in judicial assessments of the admissibility of psychophysiological evidence.