Background: Victor Jara was born in 1932 in Lonquen, near Santiago, to two peasants, Manuel Jara and Amanda Martinez. His father was illiterate and encouraged his children to work from an early age to help the family survive, rather than attend school. By the age of 6, Jara was already working on the land. His father could not support the family on his earnings as a peasant at the Ruiz-Tagle estate, nor was he able to find stable work.
Context: After joining the choir at the University of Chile in Santiago, Jara was convinced by a choir-mate to pursue a career in theater. He subsequently joined the university's theater program and earned a scholarship for talent. He appeared in several of the university's plays, gravitating toward those with social themes, such as Russian playwright Maxim Gorky's The Lower Depths, a depiction of the hardships of lower-class life.  In 1957, he met Violeta Parra, a singer who had steered folk music in Chile away from the rote reproduction of rural materials toward modern song composition rooted in traditional forms, and who had established musical community centers called penas to incorporate folk music into the everyday life of modern Chileans. Jara absorbed these lessons and began singing with a group called Cuncumen, with whom he continued his explorations of Chile's traditional music. He was deeply influenced by the folk music of Chile and other Latin American countries, and by artists such as Parra, Atahualpa Yupanqui, and the poet Pablo Neruda.  In the 1960s, Jara started specializing in folk music and sang at Santiago's La Pena de Los Parra, owned by Angel Parra. Through these activities, he became involved in the Nueva Cancion movement of Latin American folk music. He released his first album, Canto a lo humano, in 1966, and by 1970, he had left his theater work in favor of a career in music. His songs were inspired by a combination of traditional folk music and left-wing political activism. From this period, some of his best-known songs are "Plegaria a un Labrador" ("Prayer to a Worker") and "Te Recuerdo Amanda" ("I Remember You Amanda").
Question: what did he sing with this group?. Whats the answer?
with whom he continued his explorations of Chile's traditional music.