Comprehensive Guide to the Psychology of Testimony and Criminal Investigation and Memory

Concept and Scientific Significance of the Psychology of Testimony

A testimony is defined as a narrative of memory that a witness provides regarding events they have previously observed. Consequently, the Psychology of Testimony is often referred to in academic literature as the Memory of Witnesses, a term notably utilized by Manzanero in 2010. This field represents one of the most direct applications of experimental psychology, appearing consistently in textbooks focusing on experimental methods, human memory, and applied psychology. Its central objective is to determine whether an individual's account corresponds to the truth and to evaluate its credibility, a premise deeply ingrained in human society.

In the context of police and judicial investigations, the primary goal is to gather data from victims and witnesses to clarify the facts of a crime and establish authorship. Research by Hans and Vidmar in 1986 indicates that approximately $85\%$ of global criminal cases are based on testamentary evidence. The success of interviews and interrogations depends on the skill of the interviewer, the interviewee's cooperation, the time elapsed since the event, and the specific methodology of the interview.

Core Areas: Exactness and Credibility

The Psychology of Testimony is divided into two primary, interconnected dimensions: exactness and credibility.

Exactness refers to studies concerning attentional, perceptual, and memory factors that influence the accuracy of declarations and identifications. Key areas of focus include procedures for obtaining statements such as free recall, recognition, cognitive interviews, and memory aids. It also examines identification procedures like photograph arrays, line-ups, and composite sketches. Individual differences related to age, sex, involvement, and anxiety are analyzed, alongside the influence of perceptual processes on the interpretation of sounds, conversations, shapes, speed, and colors. This area also explores false memories, suggestibility, and the effect of attentional conditions during encoding, such as the "weapon effect" or the distinctiveness of details. Retention and recovery factors, including multiple recoveries and the effect of leading questions, are also critical components.

Credibility involves discriminating the origin of the information provided by witnesses to determine if it is based on real perception or if it is suggested, imagined, or false. This is approached through cognitive, social, and clinical psychology. Additionally, modern research has integrated findings from neuroscience, linguistics, and communication studies to better understand the nature of deception and the psychological indicators of lying.

Historical Evolution of the Discipline

The roots of the psychology of testimony are as old as the law itself, though its formal scientific development began in the late 19th century. Notable milestones include Karl Marbe, a disciple of Wundt, who in 1892 became the first expert witness recorded to testify on reaction times in a train accident case. Schrenk-Notzingen followed in 1896, informing a homicide case about the effects of pre-trial publicity. In the United States, Catell (1893) was the first to research the accuracy of witness statements, while in Europe, Hans Gross published "Kriminalpsychologie" in 1897, focusing heavily on testimony.

At the turn of the 20th century, Alfred Binet (1897) highlighted the lack of memory accuracy and the effects of suggestion on visual memory, publishing "La suggestibilité" in 1900. Hugo Münsterberg (1908) argued for legal reform based on scientific experimentation in his manual "On the Witness Stand." William Stern (1910, 1939) founded the first specialized journal in the field, analyzing errors of commission and omission in children's testimonies. Cesare Lombroso (1905) authored the first study on testimony and the judicial process. In Spain, Francisco Santamaría published the experimental work "Psicología del Testigo."

A significant growth period in the early 20th century saw the first expert testimony on a minor's credibility in a sexual assault case in 1921. However, the field faced a crisis between the late 1930s and the 1970s due to the rise of behaviorism and the disruption of World War II. During this interval, research focused almost exclusively on person identification. The discipline was revitalized in the 1970s and 1980s by cognitive psychology and the information-processing paradigm. This era saw the creation of academic committees and the frequent use of expert witnesses to advise judges on cognitive processes and identification evidence. Hermann Ebbinghaus remains the historical pioneer of experimental memory study, while modern research seeks to integrate laboratory rigor with ecological validity.

Factors Influencing Credibility and Perception

Credibility is the perception of a testimony's accuracy held by the witness or others. Researchers Mira and Diges identify common errors in judging credibility, such as the belief that observable non-verbal behaviors or physiological cues always coexist with lying, or that humans can easily develop a capacity to detect deception with minimal error.

Sobral identifies several factors that mistakenly elevate a witness's credibility in the eyes of a jury: apparent confidence, high social or economic prestige, formal clothing, physical attractiveness, extroversion, a relaxed attitude, and consistent eye contact. Furthermore, jurors often underestimate how environmental factors like lighting or exposure time affect observation accuracy. There is often a "prejudice of guilt" simply because an individual is being judged. Other factors identified by Martín include the attitudes of judicial operators (prosecutors, lawyers, judges), the judge's instructions, the race of the individuals involved, the order in which witnesses are called (prosecution vs. defense), and media influence. Historically, children have been viewed with skepticism by courts, frequently categorized as imprecise due to limited memory or highly sugestionable and easily manipulated.

Memory Systems and the Cognitive Process

Memory is categorized as either short-term or long-term. Short-term memory (or working memory) refers to the temporary maintenance of information. Long-term memory is subdivided into: 1. Declarative memory, which includes semantic memory (general knowledge and language) and episodic memory (personal experiences and autobiography). 2. Procedural memory, which involves skills and routines like riding a bicycle. The cognitive process consists of three distinct stages.

Encoding is the first stage, where information is not stored as perceived but is filtered, interpreted, and integrated into existing structures. This process is circumstantial and specific, heavily influenced by contextual information. The second stage is Storage and Retention, where the passage of time is a critical element. This stage may involve recoding, which refers to cognitive operations occurring after the original encoding that can alter the memory trace. The final stage is Retrieval (Recovery). For successful recovery, the cognitive system must be predisposed to retrieve, and appropriate recovery cues must be present to locate the stored information. Retrieval success depends on whether the memory task is deliberate or unintentional.

The Witness Figure and Forensic Psychology

In legal terms, a witness is a procedural figure who testifies before a tribunal on facts relevant to a case's resolution. Witnesses may be ocular (eyewitnesses) or non-presential. They are legally required to provide clear, precise answers and explain the basis of their assertions. Forensic psychology serves as an experimental science that supports the judiciary by providing principles, techniques, and instruments for a more objective assessment of human behavior. The forensic psychologist acts as an expert advisor, providing a clinical diagnosis of the mental state of individuals involved in a case. Their conclusions are formalized in a pericial report, a written document that the expert may be required to ratify verbally in court. This role is regulated in Spain by the Law of Civil Procedure (articles 335 to 352) and the Law of Criminal Procedure (articles 456 to 485).

Specialized Areas of Action and Line-up Protocols

Psychology of testimony is applied in criminological research to study personality traits based on Eysenck's models, socialization scales, sensation seeking, and cognitive problem-solving skills. Another critical application is the conduct of police line-ups (ruedas de reconocimiento). According to the Law of Criminal Procedure (LECrim), these must adhere to strict technical requirements: 1. They must be conducted in the presence of the suspect's lawyer. 2. The line-up must consist of at least five individuals with physical characteristics similar to the suspect. 3. The positioning of individuals must be random, and the suspect's lawyer should ideally choose the placement. 4. A second identification round must be performed with the order of individuals changed. 5. Security measures must ensure the witness does not see the suspect before the procedure and that witnesses cannot communicate with each other. 6. An individualized official record (acta) must be created immediately after the procedure, capturing the witness's statements in the presence of the defense lawyer. These protocols are supported by Article 520 of the LECrim.