The motivational impairment effect in the communication of deception

Background & Context

The DePaulo and Kirkendol (1989) chapter represents a seminal contribution to deception research, challenging the intuitive assumption that high motivation improves deceptive performance. This work documented a counterintuitive "motivational impairment effect," showing that people who are more highly motivated to succeed with their lies are actually less successful at doing so whenever observers can see or hear their nonverbal behaviors, potentially due to deliberate attempts to control expressive behaviors which result in performances that appear overcontrolled and inhibited.

Published in J.C. Yuille's edited volume "Credibility Assessment," this chapter emerged during a pivotal period when deception researchers were moving beyond simple cataloging of behavioral cues to develop theoretical models explaining why lies fail. The Motivation Impairment Effect hypothesis posited that when deceivers try harder (are motivated), they end up with impaired nonverbal performance but also improved verbal performance, creating distinct patterns of detectability across communication channels.

The work built directly on earlier foundational studies by DePaulo and colleagues, including research on detecting the deceit of motivated liars and the effects of telling ingratiating lies to attractive targets, synthesizing these findings into a comprehensive theoretical framework with important implications for both basic deception science and applied credibility assessment.

Research Design & Methodology

The empirical foundation came from multiple experimental studies where subjects told ingratiating lies under conditions in which they thought that the ability to convey particular impressions was an important skill (high "competence-relevance"), and these lies were judged by observers who could see or hear varying combinations of nonverbal behaviors. The research program employed a multichannel design examining verbal transcripts, audio, visual, and audiovisual presentations.

Key methodological features included:

• Motivation manipulation: Researchers varied whether subjects believed successful impression management was an important, valued skill (high competence-relevance) versus a routine experimental task
• Channel isolation: Judges evaluated deception from isolated channels (verbal transcripts only, audio only, visual/silent video, or full audiovisual) to identify where impairment appeared
• Lie type variation: Studies examined both ingratiating lies (pretending to agree) and noningratiating lies (pretending to disagree) with targets varying in attractiveness and sex
• Individual difference measures: Variables such as confidence, experience at deceiving, and physical attractiveness were examined as potential moderators of the impairment effect

The core finding was replicated across multiple studies published in the Journal of Nonverbal Behavior in 1988, providing conceptual replications with different operationalizations of motivation and different participant samples.

Results & Key Findings

The motivational impairment effect was consistently demonstrated: People who were more highly motivated to get away with their lies were less successful at doing so whenever observers could see or hear any of their nonverbal cues, with subjects who told ingratiating lies under high competence-relevance conditions being less successful when judges could observe their nonverbal behaviors.

Specific empirical findings included:

• Channel-specific impairment: When senders talked to opposite-sex targets, their lies were most easily detected from channels that included nonverbal cues, and for ingratiating lies, detectability was greatest for channels that included visual nonverbal cues
• Gender differences: Under conditions of ingratiating lies and high competence relevance, women were more likely to show the motivational impairment effect than were men
• Attractiveness moderation: More attractive speakers were less susceptible to the motivational impairment effect than less attractive speakers, with more attractive speakers being less likely to show the impairment under high motivational conditions
• Target characteristics: Lies told by women were more readily detected than lies told by men, lies told to opposite-sex targets were more easily detected than lies to same-sex targets, and ingratiating lies were more successfully detected than noningratiating lies, particularly when told to attractive targets

Evidence suggested that the motivational impairment effect may occur when subjects are trying deliberately to control simultaneously all of their verbal and nonverbal behaviors, supporting a cognitive overload explanation for the phenomenon.

Discussion & Significance

This research fundamentally challenged the prevailing assumption that motivation aids deception. The findings suggested that heightened motivation triggers deliberate self-regulatory efforts that paradoxically undermine performance—a phenomenon analogous to "choking under pressure" in athletic performance. The impairment may be a consequence of the liars' deliberate attempts to control their expressive behaviors which result in performances that appear overcontrolled and inhibited.

The work had profound theoretical implications. By demonstrating that verbal and nonverbal channels respond differently to motivation—with verbal content potentially improving while nonverbal leakage increases—the research explained why multichannel observation is critical for deception detection. Both the motivational impairment effect and Interpersonal Deception Theory suggest that high levels of motivation actually improve performance in a written context, while impairing nonverbal performance.

For practitioners, the findings suggested that high-stakes lies (where liars are highly motivated) should actually be easier to detect from nonverbal channels than low-stakes lies, contradicting the common assumption that motivated liars are more dangerous. Highly motivated liars are likely to manage their verbal cues more effectively than nonverbal cues, leading to an increase in the leakage of nonverbal cues compared to less motivated liars.

Limitations & Considerations

The research was conducted entirely in laboratory settings with modest stakes compared to real-world interrogations or criminal investigations. While motivation was experimentally manipulated through competence-relevance framing, the actual consequences for deceptive failure remained minimal compared to forensic contexts.

The chapter synthesis drew heavily on studies involving college students telling relatively inconsequential lies about opinions or fake attitudes. Whether the motivational impairment effect generalizes to high-stakes lies involving criminal culpability, employment, or life-threatening situations remained an empirical question. Subsequent research has yielded mixed findings about whether the effect holds in truly consequential contexts.

Individual differences in deceptive skill, experience, and psychopathic traits may moderate the effect. The research identified physical attractiveness as one moderator, but many other variables such as confidence and experience at deceiving could also moderate the impairment effect, requiring further systematic investigation.

Practical Applications

For credibility assessment professionals, this research suggests focusing on nonverbal channels when interviewing highly motivated subjects. Interrogators should recognize that suspects with the most to lose may paradoxically display more detectable nonverbal leakage due to overcontrol, even while their verbal statements become more polished and rehearsed.

The findings also have implications for training. Detection accuracy may improve by teaching evaluators to recognize signs of behavioral overcontrol—stiffness, lack of spontaneity, inhibited gestures—as potential indicators of high-motivation deception rather than assuming motivated liars are inherently more difficult to detect. The multichannel methodology underscores the value of video recording interviews to capture both verbal content and nonverbal behavior for comprehensive analysis.