Document Category: Penile Plethysmograph Evidence

This amicus brief urges courts to adopt a general presumption against admitting penile plethysmograph (PPG) evidence in sexually violent predator proceedings. It argues that PPG testing lacks scientific rigor and standardization, is vulnerable to manipulation, and depends on unsupported assumptions that physiological response reliably reflects subjective sexual arousal and predicts future criminal conduct. Because the procedure appears scientific, the brief warns that factfinders may give unreliable results undue weight, particularly in proceedings already marked by substantial stigma and prejudice.

The brief also argues that compelled PPG testing implicates fundamental rights to bodily and mental integrity and raises First Amendment concerns by treating private thoughts or physiological responses as evidence of future conduct. Given that SVP commitment may result in indefinite confinement, the brief contends that heightened due-process protections are required and analogizes PPG testing to polygraph evidence, urging a consistent, bright-line presumption of inadmissibility that would protect individual liberty and conserve judicial resources.