laboratory experiments: conducted in a laboratory or a rigorously controlled environment, whereby the independent variable is manipulated, whilst all other extraneous variables are strictly controlled.

language acquisition: the processes by which children acquire or develop human language.

Language Acquisition Device (LAD): an innate mechanism that aids language development, through recognising grammatical structure.

language development: the study of the acquisition of language, with emphasis on the development of four sub-systems of language ?phonology, semantics, pragmatics and tense and gender.

latency stage : Freud's fourth stage of psychosexual development whereby sexual preoccupations are repressed, children focus on interact with same sex peers.

latent content : term used in Freud's stages of psychosexual development, to signify the underlying or hidden content represented in dreams.

lateral thinking: an approach to problem solving whereby an individual looks at a problem from many different perspectives to seek to find the best solution.

lateralisation of function: refers to the distribution of functions across the two hemispheres of the brain. For instance, language ability is localised in the left hemisphere.

law of effect: a principle of learning put forward by Thorndike, which proposes that whenever a response is followed by a reward, it is strengthened and therefore more likely to be repeated.

Lazarus (1922-2002): a hugely influential psychologist who focused on the study of cognition, in particular appraisal of emotion and stress, and coping mechanisms in response to stress.

leadership: the ability of an individual or member of a group to influence other group members, in achieving group goals. A variety of characteristics have been proposed to contribute to a successful leader, including cognitive ability, charisma, and leadership motivation.

leading questions: are questions subtly communicate to the respondent to answer in a particularly way, which results in a biased answer or recall of an event. Commonly used to illustrate how memory recall can be altered after eyewitness testimony.

learned helplessness: non-responsiveness demonstrated when there is a perception of possessing a lack of control over a situation, after experience of non-contingent, unavoidable negative stimuli.

learning: a change in behavior, knowledge and skills, from interaction with the environment and experience.

least preferred co-worker theory (LPC): examines how a leader prioritises work tasks and relationships, by asking leaders to either favourably or unfavourably evaluate the person who they found difficult to work with. High LPC leader used more favourable terms to describe the LPC, and vice versa for the low LPC. High LPC leaders commonly have close and warm relationships, often prioritising a relationship before a task, whereas low LPC leaders often put the task first and will only consider relationships once work is acceptable.

lesioning: injury or destruction of brain tissue.

level of measurement:  the type of data collected; nominal, order, interval or ratio, which subsequently affects the inferential statistic used.

levels of processing theory: Craik and Lockhart's theory that the 'deeper' information is processed, the more likely it is to be retained in memory.

libido: in psychoanalysis, a term used to represent energy that comes from the id, typically energy driven towards achieving sexual pleasure.

life events: refer to events that require a significant adjustment in a person's life, for instance divorce, moving house etc. Quantified on the Holmes and Rahe "Social Readjustment Rating Scale" whereby respondents indicate the events (differing scores allocated according to greater adjustment required) that have been experienced over the previous twelve months.

light adaptation: the process by which the eye adjusts to increasing levels of light intensity, whereby the pupil shrinks and cones function to aid the adjustment.

Likert scalea type of response format used in surveys developed by Rensis Likert. Likert items have responses on a continuum and response categories such as "strongly agree," "agree," "disagree," and "strongly disagree."

limbic system: exists in mammals only. It is a series of subcortical structures which connect the cortex with other parts of the brain and which are important in regulating emotional and motivation behavior and memory. Structures within the limbic system include the thalamus, hypothalamus, amygdala and hippocampus.

localisation of function: the assumption that specific functions (e.g. movement control, language production) are associated with specific brain areas.

locus of control:  the extent to which people believe they have control over situations in their life. An internal locus of control refers to the belief that actions and consequences are under an individual control (e.g. through hard work), whereas an external locus of control refers to consequences occurring as a result of external circumstances.

logic: (from Classical Greek λόγος logos; meaning word, thought, idea, argument, account, reason, or principle) is the study of the principles and criteria of valid inference and demonstration.

logical empiricism: in philosophy of science, the assumption that it is possible to compare and evaluate theories in terms of how well they account for the evidence.

logotherapy: a theory of development and therapy developed by Frank, which proposes that finding a meaning for life is crucial for individual growth and happiness.

long-term memory (LTM): enduring memories that retain and preserve information for later retrieval over long periods. Long-term memory includes episodic memory (memory of the personal episodes), semantic memory (memory of knowledge); declarative memory (knowing 'that' and procedural memory(knowing 'how'.

longitudinal study: a research method that examine changes in the same group of participants through repeated testing over an extended period of time.