The US Department of Justice stumbles on visual perception

Thomas D Albright

doi:10.1073/pnas.2102702118

Abstract

A large and highly valuable category of forensic evidence consists of patterned impressions created during the perpetration of a crime. These crime scene artifacts, such as fingerprints or tire tracks, offer visual sensory information that is assessed by trained human observers and compared to sensory experiences elicited by model patterns that would have been produced under a hypothesized set of conditions. By means of this “forensic feature comparison,” the observer makes a judgment about whether the evidence and the model are sufficiently similar to support common origin. In light of documented failures of this approach, significant concerns have been raised about its scientific validity. In response to these concerns, the US Department of Justice has made assertions about how forensic examiners perform feature comparison tasks that are not consistent with modern scientific understanding of the processes of sensation and perception. Clarification of these processes highlights new ways of thinking about and improving the accuracy of forensic feature comparison and underscores the vital role of science in achieving justice.

Highlights

In response to these concerns, the US Department of Justice has made assertions about how forensic examiners perform feature comparison tasks that are not consistent with modern scientific understanding of the processes of sensation and perception
In cases where stimulus differences manifest along complex combinations of such dimensions, where there is no simple scale that captures the physical differences between stimuli, the stimulus properties are termed “nominal.” The DOJ maintains that the nominal properties of forensic patterns cannot be measured as scalar quantities by a human observer: “Measurement, does not apply to ‘nominal’ properties—features of a phenomenon, body, or substance that have no magnitude” [5]
Discrimination of Forensic Patterns by Biological Senses Building on this basic understanding of sensory measurement, we can illustrate the process by which forensic examiners make decisions when confronted with feature comparison tasks

Summary

Introduction

In response to these concerns, the US Department of Justice has made assertions about how forensic examiners perform feature comparison tasks that are not consistent with modern scientific understanding of the processes of sensation and perception. Motivated by the naivete of this claim, and in light of the DOJ’s structural authority, I briefly review here the established scientific understanding of the processes that underlie sensation and perception and give rise to brain-based measurements of sensory stimuli and judgments about their similarity.

Objectives

Results

Conclusion