Little is known about toilet training in pre-modern societies. Ancient Rome has been credited with the earliest known children's toilet. However, there is no evidence of what training techniques they may have employed.: 4  Later, during the European Middle Ages, according to one source "Recommended cures for 'pyssying the bedde'...included consumption of ground hedgehog or powdered goat claw and having dried rooster combs sprinkled on the bed."Cultural beliefs and practices related to toilet training in recent times have varied. For example, beginning in the late 18th century parenting transitioned from the use of leaves or linens (or nothing) for the covering of a child's genitals, to the use of cloth diapers (or nappies), which needed to be washed by hand. This was followed by the advent of mechanical washing machines, and then to the popularisation of disposable diapers in the mid 20th century, each of which decreased the burden on parental time and resources needed to care for children who were not toilet trained, and changed expectations about the timeliness of training.: 3 : 216  This trend did not manifest equally in all parts of the world. Those living in poorer countries usually train as early as possible, as access to amenities such as disposable diapers may still pose a significant burden. Poorer families in developed countries also tend to train earlier than their more affluent peers.: 43 Much of the 20th-century conceptualization of toilet training was dominated by psychoanalysis, with its emphasis on the unconscious, and warnings about potential psychological impacts in later life of toilet training experiences. For example, anthropologist Geoffrey Gorer attributed much of contemporary Japanese society in the 1940s to their method of toilet training, writing that "early and severe toilet training is the most important single influence in the formation of the adult Japanese character.": 50–1 : 201  Some German child-rearing theorists of the 1970s tied Nazism and the Holocaust to authoritarian, sadistic personalities produced by punitive toilet training.Into the 20th century this was largely abandoned in favor of behaviouralism, with an emphasis on the ways in which rewards and reinforcements increase the frequency of certain behaviors, and cognitive psychology, with an emphasis on meaning, cognitive ability, and personal values. Writers such as psychologist and pediatrician Arnold Gesell, along with pediatrician Benjamin Spock were influential in re-framing the issue of toilet training as one of biology and child readiness.