babbling An infant’s repetition of certain syllables, such as ba-ba-ba, that begins when babies are between 6 and 9 months old.

balanced bilingual A person who is fluent in two languages, not favoring one over the other.

base rate neglect A common fallacy in which a person ignores the overall frequency of some behavior or characteristic (called the base rate) in making a decision. For example, a person might bet on a “lucky” lottery number without considering the odds that that number will be selected.

behavioral teratogens Agents and conditions that can harm the prenatal brain, impairing the future child’s intellectual and emotional functioning.

behaviorism A grand theory of human development that studies observable behavior. Behaviorism is also called learning theory because it describes the laws and processes by which behavior is learned.

Big Five The five basic clusters of personality traits that remain quite stable throughout adulthood: openness, conscientiousness, extroversion, agreeableness, and neuroticism.

bilingual schooling A strategy in which school subjects are taught in both the learner’s original language and the second (majority) language.

binocular vision The ability to focus the two eyes in a coordinated manner in order to see one image.

body image A person’s idea of how his or her body looks.

body mass index (BMI) The ratio of a person’s weight in kilograms divided by his or her height in meters squared.

Brazelton Neonatal Behavioral Assessment Scale (NBAS) A test often administered to newborns that measures responsiveness and records 46 behaviors, including 20 reflexes.

bulimia nervosa An eating disorder characterized by binge eating and subsequent purging, usually by induced vomiting and/or use of laxatives.

bully-victim Someone who attacks others and who is attacked as well. (Also called provocative victims because they do things that elicit bullying.)

bullying Repeated, systematic efforts to inflict harm through physical, verbal, or social attack on a weaker person.

bullying aggression Unprovoked, repeated physical or verbal attack, especially on victims who are unlikely to defend themselves.