Psychology Dictionary -- D


Theory which states that memory fades and/or disappears over time if it is not used or accessed.

Declarative Memory

The part of long-term memory where factual information is stored, such as mathematical formulas, vocabulary, and life events.

Deductive Reasoning

Decision making process in which ideas are processed from the general to the specific.

Defenses (Defense Mechanisms)

Psychological forces which prevent undesirable or inappropriate impulses from entering consciousness (e.g., forgetting responsibilities that we really didn’t want to do, projecting anger onto a spouse as opposed to your boss).  Also called Defense Mechanisms, Defense System, or Ego Defenses.

Degrees of Freedom

The number of individual scores that can vary without changing the sample mean. Statistically written as ‘N-1’ where N represents the number of subjects.


False belief system (e.g., believing you are Napoleon, have magical powers, or the false belief that others are ‘out to get you.’).


Extensions of the cell body of a neuron responsible for receiving incoming neurotransmitters.

Dependent Variable

The variable in an experiment that is measured; the outcome of an experiment.

Descriptive Statistics

The branch of statistics that focuses on describing in numerical format what is happening now within a population. Descriptive statistics require that all subjects in the population (the entire class, all males in a school, all professors) be tested.

Developmental Psychology

The area of psychology focused on how children grow psychologically to become who they are as adults.

Deviation IQ Score

A standard score used for reporting IQ scores where the mean is set to 100 and standard deviation to 15

Difference Threshold

The smallest change in perception which is noticeable at least 50% of the time.


In behavioral theory, the learned ability to differentiate between two similar objects or situations.


Inability to recognize or be aware of who we are (person), what we are doing (situation), the time and date (time), or where we are in relation to our environment (place).  To be considered a problem, it must be consistent, result in difficulty functioning, and not due to forgetting or being lost.


The pushing out of older information in short term memory to make room for new information.

Dispositional Attribute

An attribute explained or interpreted as being caused by internal influences.


A separation from the self, with the most severe resulting in Dissociative Identity Disorder.  Most of us experience this in very mild forms such as when we are driving long distance and lose time or find ourselves day dreaming longer than we thought.


The phenomenon in memory that states we are better able to remember information if it is distinctive or different from other information.

Divergent Thinking

The ability to use previously gained information to debate or discuss issues which have no agreed upon definitive resolution.


A neurotransmitter associated with movement, attention and learning and the brain’s pleasure and reward system.

Dopamine Hypothesis

The theory that schizophrenia is caused by  an excess amount of dopamine in the brain.  Research has found that medication to reduce dopamine can reduce the positive symptoms of schizophrenia.

Double Blind Study

Research method in which both the subjects and the experimenter are unaware or ‘blind’ to the anticipated results.


An internal motivation to fulfill a need or reduce the negative aspects of an unpleasant situation.

Drug Therapy

The use of medication to treat a mental illness.