Laboratory Studies: Factors Affecting Psychophysiological Detection

Background & Context

Ben-Shakhar and Furedy's 1990 chapter represents a comprehensive review of three decades of laboratory research on psychophysiological detection, primarily conducted by psychophysiologists and applied psychologists, with most studies utilizing the Guilty Knowledge Test (GKT). This work emerged during a critical period when polygraph science faced intense scrutiny regarding its scientific foundations and validity.

The authors noted that the GKT is the only standardized method for psychophysiological detection, and the only one which makes use of proper control questions, allowing for sound inferences from physiological responding patterns. The chapter highlighted a paradox that would shape the field for decades: most research in this area is based on the GKT, whereas most applications are based on the CQT.

This foundational review laid the groundwork for understanding what laboratory conditions can and cannot tell us about real-world polygraph validity, establishing critical benchmarks for evaluating detection accuracy and identifying the factors that moderate test performance.

Research Design & Methodology

Ben-Shakhar and Furedy (1990) reviewed and summarized 10 GKT laboratory experiments, analyzing data from 248 guilty examinees and 208 innocent examinees across these studies. The review employed a narrative synthesis approach, examining patterns of accuracy rates and identifying methodological variables that might account for between-study variability.

The authors critically examined several key experimental factors:

• Number of GKT questions: Studies varied from using single questions with multiple repetitions to protocols with up to ten separate questions
• Motivation to deceive: Some studies included monetary incentives while others used minimal motivational instructions
• Deceptive verbal responses: Studies varied whether participants had to give deceptive answers, remain silent, or repeat items
• Physiological measures: Electrodermal, cardiovascular, and respiratory measures were examined

The authors raised critical methodological questions about whether results from controlled experiments conducted in laboratory settings can be generalized to realistic criminal investigations, noting that typical laboratory experiments used mock crimes (e.g., stealing an envelope) with participants who faced no real consequences.

Results & Key Findings

Across the 10 laboratory experiments reviewed, 84% of 248 guilty examinees and 94% of 208 innocent examinees were correctly classified. This represented impressive accuracy rates under controlled conditions, particularly for protecting innocent examinees.

Key findings from the review included:

• The number of GKT questions used emerged as a natural candidate for accounting for between-study variability; studies using the largest number of questions (Bradley & Ainsworth, 1984 with nine; Bradley & Warfield, 1984 with ten) demonstrated the highest rates of correct classifications
• Ben-Shakhar and Furedy concluded that with a sufficiently large number of GKT questions the method could be used quite efficiently
• The authors characterized GKT detection as a "cognitive approach," emphasizing that it detects whether an individual knows something, rather than the individual's emotions, concerns, fears, conditioned responses, or deception
• This cognitive approach was supported by findings demonstrating that relevant information can be detected even under mild conditions where no motivational instructions are given and where no verbal response is required

Some studies concluded that deceptive answers to GKT questions are associated with increased detection accuracy, while other studies showed that this factor has no effect on detection accuracy, highlighting inconsistencies that required further investigation.

Discussion & Significance

The Ben-Shakhar and Furedy (1990) review fundamentally shaped how the scientific community understood laboratory-based polygraph research. There is now general consensus that the GKT relies on solid scientific principles and on proper control questions, with surveys showing that 77% of Society for Psychophysiological Research members and 72% of American Psychological Association members believe the GKT is based on scientifically sound psychological principles or theory.

The "cognitive approach" framework introduced by Ben-Shakhar and Furedy became influential in subsequent research. This approach emphasizes the individual's knowledge rather than emotions, the act of deception, or motivation to deceive, differing fundamentally from arousal-based theories. Supporting this framework, findings demonstrated that relevant information can be detected under conditions with no involvement of deceptive verbal responses and where no motivational instructions are presented.

The chapter's identification of question quantity as a critical variable influenced subsequent research design and practical recommendations. The principle that more questions yield better detection became a cornerstone of GKT/CIT application, though this created practical challenges for real-world implementation where sufficient salient crime details may not always be available.

Limitations & Considerations

As the authors themselves acknowledged, the reviewed studies were experimental studies conducted in laboratory conditions which do not resemble the realistic conditions of criminal investigation in which the GKT may be applied, with the experimental situation differing from the realistic one in several important aspects. Factors affecting perception and memory might be crucial for the efficiency of the GKT, yet the GKT studies, including those using mock-crime paradigms, used very simple scenarios.

Laboratory conditions do not begin to resemble the conditions of a real life investigation—there is no deception in the conventional sense, and there is no anxiety about the consequences of the exam. This external validity problem remains one of the most significant limitations when extrapolating from laboratory findings to field applications.

The authors acknowledged that the number of studies they analyzed was too small to allow for a statistical examination of the sources of between-studies variability, limiting their ability to conduct quantitative meta-analysis of moderating factors. This limitation was later addressed by Ben-Shakhar and Elaad's 2003 comprehensive meta-analysis.

Practical Applications

The chapter's findings have direct implications for GKT/CIT implementation in criminal investigations. The identification of question quantity as a critical success factor suggests that examiners should develop as many distinct GKT questions as possible from available crime details, aiming for protocols with at least 5-10 questions to maximize accuracy.

The cognitive approach framework supports practical recommendations that GKT administrators focus on ensuring crime-relevant information remains concealed from innocent suspects rather than on arousing anxiety or inducing deception. From a practical standpoint, the cognitive approach suggests that the CIT operator should guarantee that no relevant information has leaked to innocent suspects through rumors and mass media descriptions of the crime.

For consumers and examinees, this research provides reassurance that when properly administered with sufficient questions, the GKT demonstrates strong protective power for innocent individuals. The 94% accuracy rate for innocent examinees suggests that false positive outcomes can be minimized when tests are conducted according to scientific principles rather than practitioner intuition.