Laboratory observation -  An observational research method in which information about subjects is collected in a laboratory setting.

Language -  A system of symbols and rules used for meaningful communication.

Latent content -  The hidden meaning of a dream.

Lateralization -  The difference in specialization between the two hemispheres of the brain.

Law of effect -  A law proposed by Edward Thorndike stating that any behavior that has good consequences will tend to be repeated, and any behavior that has bad consequences will tend to be avoided.

Learned helplessness -  A tendency to give up passively in the face of unavoidable stressors.

Learning -  A change in behavior or knowledge that results from experience.

Learning model -  The idea that psychological disorders result from the reinforcement of abnormal behavior.

Learning model of addiction -  The idea that addiction is a way of coping with stress.

Lens -  Part of the eye behind the pupil and iris. It can adjust its shape to focus light from objects that are near or far away.

Leptin -  A hormone secreted by fat cells.

Lesioning studies -  An invasive method of studying the brain in which a specific, small area of the brain is destroyed.

Lie scales -  Statistics used to provide information about the likelihood that a subject is lying in a test.

Light -  A kind of electromagnetic radiation emitted by the sun, stars, fire, and lightbulbs.

Light adaptation -  The process by which receptor cells become less sensitive to light.

Light intensity -  The amount of light emitted or reflected by an object.

Limbic system -  A part of the forebrain involved in emotional experience and memory.

Linguistic relativity hypothesis -  A theory proposed by Benjamin Lee Whorf that claims that language determines the way people think.

Link method -  The process of associating items with one another in order to remember them.

Lithium -  A drug prescribed for treating bipolar disorders.

Lobotomy -  A surgical procedure that severs nerve tracts in the frontal lobe, formerly used to treat certain psychological disorders but now rarely performed.

Locus of control -  People’s perception of whether or not they have control over circumstances in their lives.

Long-term memory -  A memory system that stores an unlimited amount of information permanently.

Long-term potentiation -  A lasting change at synapses that occurs when long-term memories form.

Lowball technique -  The act of making an attractive proposition and revealing its downsides only after a person has agreed to it.

Lucid dreams -  Dreams in which people are aware that they are dreaming.