Pineal gland—endocrine gland in brain that pro-
duces melatonin that helps regulate circadian
rhythms and is associated with seasonal affective
disorder.
Pituitary gland (sometimes called master gland)—
endocrine gland in brain that produces stimulat-
ing hormones which promote secretion by other
glands, including TSH (thyroid-stimulating hor-
mone); ACTH (adrenocorticotropic hormone),
which stimulates the adrenal glands; FSH, which
stimulates egg or sperm production; ADH (antid-
iuretic hormone), to help retain water in your
body; and HGH (human growth hormone).
Placebo—a physical or psychological treatment
given to the control group that resembles the
treatment given to the experimental group, but
contains no active ingredient.
Placebo effect—a response to the belief that the
independent variable will have an effect, rather
than to the actual effect of the independent vari-
able; can be a confounding variable.
Plasticity—modifiability of neural connections that
enables generation of new synapses which results
in storing and retrieval of memories or one part of
the brain taking over the function of another, etc.
Pleasure principle—Freud claims that the id part of
the personality seeks immediate gratification of its
wants and needs.
Pons—part of brainstem that includes portion of
reticular activating system or reticular formation
critical for arousal and wakefulness; sends infor-
mation to and from medulla, cerebellum and
cerebral cortex.
Population—all of the individuals in the group to
which the study applies.
Positive reinforcement—a rewarding consequence
that follows a voluntary behavior thereby
increasing the probability the behavior will be
repeated.
Positron emission tomography (PET)—shows
brain activity when radioactively-tagged glucose
rushes to active neurons and emits positrons.
Postconventional level—Kohlberg’s third and final
level of moral development, in which people
come to understand that moral rules include prin-
ciples that apply across all situations and societies.
Post-traumatic stress disorder (PTSD)—an anxi-
ety disorder in which the individual has feelings of
social withdrawal accompanied by atypically low
levels of emotion caused by prolonged exposure to
a stressor, such as a catastrophe; may experience
flashbacks and nightmares.
Power tests—difficulty level measured; untimed
tests which include easy to more difficult
questions, used to assess intelligence and other
capacities.
Preconscious—the level of consciousness that is
outside of awareness but contains feelings and
memories that can easily be brought to conscious
awareness.
Preconventional level—Kohlberg’s first level of
moral development, which bases moral behavior
on obedience and punishment, or acting in one’s
own best interests.
Predictive validity—the extent to which a test accu-
rately forecasts a specific future result.
Prefrontal lobotomy—a surgical procedure that
destroys the tracts connecting the frontal lobes to
lower centers of the brain, once believed to be an
effective treatment for schizophrenia.
Prejudice—unjustified attitudes we hold about
others; generally negative evaluation based on eth-
nicity, race, sex or some other criteria.
Prelinguistic speech—initial steps of cooing and
babbling, later accidental imitation, and finally
deliberate imitation as precursors to language
development.
Premack Principle—a high probability response
can serve as a reward for a low probability behavior,
thus increasing it.
Prenatal development—period of development
that begins with fertilization, or conception, and
ends with birth.
Preoperational stage—Piaget’s second stage of cog-
nitive development (2-7 yrs) during which the
child represents and manipulates objects with
symbols (language) and is egocentric.
Primacy Effect (Law of Primacy)—the tendency to
remember initial information; in the memoriza-
tion of a list of words, the primacy effect is
evidenced by better recall of the words early in
the list.
Primary emotions—joy, fear, anger, sadness, sur-
prise and disgust which are inborn.
Primary motives—internal mechanism directing
behavior dealing with sustaining processes biolog-
ically necessary for survival such as thirst, hunger,
and sex.
Primary reinforcers—important automatic and
unlearned (inborn) rewards like food and drink.330 ❯ Glossary