Final answer:
Charles Spearman contributed to psychometric testing with his theory of a general intelligence factor, known as 'g', which proposed a single underlying factor affecting all cognitive abilities.
Step-by-step explanation:
Spearman's Contribution to Psychometric Testing
British psychologist Charles Spearman made a significant contribution to the field of psychometric testing by introducing the concept of a general intelligence factor, known as g. Spearman's theory posited that intelligence consists of a single, overarching factor that influences performance on all cognitive tasks. This concept was revolutionary in that it suggested a universal aspect of intelligence that could be measured and compared among individuals. He emphasized the commonalities across different intellectual abilities, rather than focusing on the unique aspects of each ability. Spearman's work laid the groundwork for later intelligence tests and remains influential in contemporary psychometric testing and the understanding of intelligence.