Random assignment -  A way of placing subjects into either an experimental or a control group such that subjects have an equal chance of being placed in either one group or the other.

Range -  The difference between the highest and lowest scores in a set of scores.

Rapid eye movement (REM) sleep -  A stage of deep sleep in which brain wave activity is similar to that in the waking state. It is also called paradoxical sleep.

REM rebound effect -  The tendency to spend more time in the REM stage of sleep after a period of REM sleep deprivation.

Rational-emotive therapy -  A type of cognitive-behavioral therapy, developed by Albert Ellis, that aims to identify catastrophic thinking and to change the irrational assumptions that underlie it.

Rationalization -  A defense mechanism that involves using incorrect but self-serving explanations to justify unacceptable behavior, thoughts, or feelings.

Ratio schedule -  A schedule in which reinforcement happens after a certain number of responses.

Reaction formation -  A defense mechanism that involves behaving in a way that is opposite to behavior, feelings, or thoughts that are considered unacceptable.

Reaction range -  The limits that heredity places on characteristics such as IQ.

Reaction time -  The amount of time a subject takes to respond to a stimulus.

Reality principle -  The awareness that gratification of impulses has to be delayed in order to accommodate the demands of the real world. It also acts as the operating principle of the ego.

Recall -  The process of remembering without any external cues.

Receptive language -  The ability to understand language.

Reciprocal determinism -  The process of interaction between a person’s characteristics and the environment. This interaction results in personality.

Reciprocity norm -  An implicit rule in many societies that tells people they should return favors or gifts given to them.

Recognition -  The process of identifying learned information by using external cues.

Reflex -  An innate response to a stimulus.

Regression -  A defense mechanism that involves reverting to a more immature state of psychological development.

Regression toward the mean -  The tendency for extreme states to move toward the average when assessed a second time.

Rehearsal -  The process of practicing material in order to remember it.

Reinforcement -  The delivery of a consequence that increases the likelihood that a response will occur.

Reinforcement schedule -  The pattern in which reinforcement is given over time.

Relearning -  A method for measuring forgetting and retention, which involves assessing the amount of time it takes to memorize information a second time.

Reliability -  The ability of a test to produce the same result when administered at different times to the same group of people.

Replicability -  The ability of research to repeatedly yield the same results when done by different researchers.

Representativeness heuristic -  A rule-of-thumb strategy that estimates the probability of an event based on how typical that event is.

Representative sample -  A sample that corresponds to the population from which it is drawn in terms of age, sex, and other qualities on the variables being studied.

Repression -  A defense mechanism that involves keeping unpleasant thoughts, memories, and feelings shut up in the unconscious.

Reproductive advantage -  The outcome of a characteristic that helps an organism mate successfully and thus pass on its genes to the next generation.

Resistance -  A client’s usually unconscious efforts to block the progress of treatment.

Response tendency -  A learned tendency to behave in a particular way.

Resting potential -  The slight negative charge inside an inactive neuron.

Resting state -  The period during which the inside of a neuron has a slightly higher concentration of negatively charged ions than the outside does. A neuron during this time is inactive.

Retention -  The proportion of learned information that is retained or remembered.

Reticular formation -  A structure that includes parts of the hindbrain and midbrain and that is involved in sleep, wakefulness, pain perception, breathing, and muscle reflexes.

Retina -  A thin layer of neural tissue in the back of the eye.

Retinal disparity -  The difference between the images picked up by the two eyes.

Retrieval -  The process of getting information out of memory.

Retrieval cues -  Stimuli that help to get information out of memory.

Retroactive interference -  Forgetting of old information because of newly learned information.

Retrograde amnesia -  An inability to remember events that occurred before a brain injury or traumatic event.

Reuptake -  The process by which neurotransmitter molecules return to presynaptic neurons.

Reversibility -  The ability to reverse actions mentally.

Reversible figure -  An ambiguous drawing that can be interpreted in more than one way.

Risky shift -  The tendency for a dominant, risky point of view in a group to be strengthened to an even riskier position after a group discussion.

Rods -  Photoreceptor cells in the retina that allow people to see in dim light.

Rorschach test -  A series of ten inkblots that subjects are asked to describe. Psychologists then use complex scoring systems to interpret the subjects’ responses.