PSYCH 201 Chapter 3

percentile

A point on a ranking scale of 0 to 100. The 50th percentile is the midpoint; half of the people in the population being studied rank higher and half rank lower.

co-sleeping

A custom in which parents and their children (usually infants) sleep together in the same room.

bed-sharing

When two or more people sleep in the same bed.

head-sparing

A biological mechanism that protects the brain when malnutrition disrupts body growth. The brain is the last part of the body to be damaged by malnutrition.

neuron

One of billions of nerve cells in the central nervous system, especially in the brain.

axon

A fiber that extends from a neuron and transmits electrochemical impulses from that neuron to the dendrites of other neurons.

dendrite

A fiber that extends from a neuron and receives electrochemical impulses transmitted from other neurons via their axons.

synapse

The intersection between the axon of one neuron and the dendrites of other neurons.

neurotransmitter

A brain chemical that carries information from the axon of a sending neuron to the dendrites of a receiving neuron.

myelin

The fatty substance coating axons that speeds the transmission of nerve impulses from neuron to neuron. 

cortex

The outer layers of the brain in humans and other mammals. Most thinking, feeling, and sensing involves the cortex.

prefrontal cortex

The area of the cortex at the very front of the brain that specializes in anticipation, planning, and impulse control.

limbic system

The parts of the brain that interact to produce emotions, including the amygdala, the hypothalamus, and the hippocampus. Many other parts of the brain also are involved with emotions.

amygdala

A tiny brain structure that registers emotions, particularly fear and anxiety.

hippocampus

A brain structure that is a central processor of memory, especially memory for locations.

hypothalamus

A brain area that responds to the amygdala and the hippocampus to produce hormones that activate other parts of the brain and body.

cortisol

The primary stress hormone; fluctuations in the body’s cortisol level affect human emotions.

pituitary

A gland in the brain that responds to a signal from the hypothalamus by producing many hormones, including those that regulate growth and that control other glands, among them the adrenal and sex glands.

transient exuberance

The great but temporary increase in the number of dendrites that develop in an infant’s brain during the first two years of life.

sensation

The response of a sensory organ (eyes, ears, skin, tongue, nose) when it detects a stimulus. 

perception

When the brain is conscious of a sensation or idea. Perception sometimes combines several senses and ideas: You might suddenly perceive that your mother is angry because of her face and voice and your past experience of her anger. 

binocular vision

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

motor skill

The learned abilities to move some part of the body, in actions ranging from a large leap to a flicker of the eyelid. (The word motor here refers to movement of muscles.)

gross motor skill

Physical abilities involving large body movements, such as walking and jumping. (The word gross here means “big.”)

fine motor skills

Physical abilities involving small body movements, especially of the hands and fingers, such as drawing and picking up a coin. (The word fine here means “small.”)

gaze-following

When someone looks at another person’s eyes to see where they are looking, and then looks at the same thing. This requires impressive perspective and social motivation — and infants do it. 

joint attention

When two or more people look at, listen to, or think about the same thing. This is considered a crucial aspect of cognition, beginning in infancy. 

implicit memory

Memory that is not verbal, often unconscious. Many motor and emotional memories are implicit.

explicit memory

Memory that can be recalled in the conscious mind; usually factual memories that are expressed with words.

sensorimotor intelligence

Piaget’s term for the way infants think — by using their senses and motor skills — during the first period of cognitive development.

circular reaction

The idea that knowledge builds like a circle, not a straight line, in that each new experience cycles back to build on what is known. 

object permanence

The realization that objects (including people) still exist when they can no longer be seen, touched, or heard.

little scientist

Piaget’s term for toddlers’ insatiable curiosity and active experimentation as they engage in various actions to understand their world.

babbling

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

holophrase

A single word that is used to express a complete, meaningful thought.

naming explosion

A sudden increase in an infant’s vocabulary, especially in the number of nouns, that begins at about 18 months of age.

grammar

All of the methods — word order, verb forms, and so on — that languages use to communicate meaning, apart from the words themselves.

stunting

The failure of children to grow to a normal height for their age due to severe and chronic malnutrition.

wasting

The tendency for children to be severely underweight for their age as a result of malnutrition.

immunization

A process that stimulates the body’s immune system by causing production of antibodies to defend against attack by a particular contagious disease. Creation of antibodies may be accomplished either naturally (by having the disease), by injection, by drops that are swallowed, or by a nasal spray.

herd immunity

The level of immunity necessary in a population (the herd) in order to stop transmission of infectious diseases. The rate is usually above 90 percent, and even higher for very infectious diseases. 

sudden infant death syndrome (SIDS)

A situation in which a seemingly healthy infant, usually between 2 and 6 months old, suddenly stops breathing and dies unexpectedly while asleep.