object permanence: an understanding that objects that continue to exist, despite being hidden from sight or awareness. An important cognitive concept that, according to Piaget, does not develop until infants are eight months old or more.

objectivity: conducting an investigation and collecting data without the process being influenced by personal interpretation or bias.

observation: used to describe a situation where an observer records behaviour demonstrated by a participant. An observation does not involve manipulation of an independent variable, but simply allows the observation of relationships between variables as they occur. Observation includes a variety of differing types of observation including naturalistic observation, participant and non-participant observation.

observational learning: a process of socialisation that takes place as a result of an individual observing and imitating the behaviour of another person who serves as a model, as opposed to through direct experience. See modelling.

observational learning: a process of socialisation that takes place as a result of an individual observing and imitating the behaviour of another person who serves as a model, as opposed to through direct experience. See modelling.

observer bias: the tendency for observers to record data that may be biased as a result of personal expectations (e.g. awareness of the hypothesis) or motives, rather than recording what actually happens.

obsessions: irrational thoughts and images that are normally unfounded, but over which a person may appear to have little control over, and which may ultimately affect the normal functioning of a person.

obsessive-compulsive disorder:  an disorder characterised by obsessions (uncontrollable, persistent and irrational thoughts or wishes) and compulsions(repetitive ritualistic acts).

occipital lobe: the rearmost region of the each cerebral hemisphere, located behind the parietal lobe and above the temporal lobes. Crucial for the processing of visual information.

occupational psychology: branch of psychology that focuses on human beings in the workplace, including job satisfaction, leadership, selection and recruitment of staff and the effect of different working conditions upon performance.

Oedipal conflict: in Freud's theory of development, the major conflict associated with the phallic stage which challenges the developing ego; class="d-title" named after the Greek story of Oedipus, who unknowingly killed his father and married his mother.

Oedipus complex: a term devised by Freud, to describe the intense sexual love that a young boy develops toward his mother, which is followed by jealousy and rivalry with his father to seek the attention and affection of the mother. The son subsequently demonstrates castration anxiety, fearing that his father might castrate him for his incestuous feelings towards his mother, and so represses his feelings and identifies with his father.

offender profiling: a technique used based on an examination of the crime scene, including how the crime was committed, and a consideration of previous offender profiles, to build and predict a detailed description (including socio-demographiccharacteristics) of a criminal offender.

one-tailed hypothesis: see directional hypothesis.

ontogeny: the evolution (i.e. the origin and development) of an individual organism, from conception to death.

open-ended questions: questions that do not contain fixed, pre-determined responses, that allow a respondent to answer relatively freely.

operant conditioning: a form of learning that is determined by consequences that either reinforce or punish particular behaviours, that can increase or decrease the probability of the behaviour.

operation: the act of something being carried out.

Operation Headstart: an enrichment intervention programme used in the US in the 1960s for preschool children, aimed at changing the effects of social disadvantage.

operational definition: a definition of a variable or condition on the basis of the exact operation or procedure that determines its existence and makes it usable. Variables can be identified by factors that are manipulated or measured.

opportunity sample: sampling technique not based on random selection orprobability; the researcher selects those who are convenient to him or her as respondents.

oppositional defiant disorder: a disruptive pattern of behavior of children and adolescents that is characterised by defiant, disobedient, and hostile behaviours directed toward adults in positions of authority.

optic nerve: a group of fibres, comprised of the axons of ganglion cells, that leave the eyeball, carrying information from the eye towards the brain.

optimal mismatch theory: based on Piagets theory of intellectual development, aims to accelerate learning by 'mismatching' a child's current level of competence with a set of problems slightly more complex than this level. If there is a correct, optimal?difference between what they can do, and what is being asked of them, children then experience a cognitive conflict and seek to find solutions through their own actions.

oral stage: the first stage in Freud's theory of development, from birth to about 15 months, when the primary source of gratification is stimulation of the mouth and lips.

order effects: differences in participants performance that occurs as a result of participants experiencing different conditions in a specific order. Subsequently, learning and practice effects can arise (whereby participants adapt and improve on later measurements) or fatigue effects (resulting in a decline in performance on later measures).

ordinal data: data that can be rank-ordered, but intervals between ranks are not necessarily equal.

ordinate: when plotting data on a graph, the ordinate refers to information on the vertical or y axis of the graph. The dependent variable is plotted on this axis.

organ of corti: a receptive organ in the inner ear, whereby sound waves are changed into nerve impulses.

organic disorder: a disorder with a known physiological cause. For instance, schizophrenia has been linked to enlarged brain ventricles and excessivedopamine.

Origin of Species: the book in which Darwin proposed his theory of evolution in 1859.

outcome study: a technique for exploring how successful a therapeuticintervention has been. For instance, an experimental group who has been given a drug may be compared to a control group that received a placebo.

out-group: individuals who are not members of, and are not accepted by the in-group.

overcompensation: a Freudian defence mechanism, whereby an individual attempts to offset weakness in an area of their lives by focusing on another aspect of it.