A mental disorder or mental illness is a psychological or behavioral pattern associated with distress or disability that occurs in an individual and is not a part of normal development or culture. The recognition and understanding of mental health conditions has changed over time and across cultures, and there are still variations in the definition, assessment, and classification of mental disorders, although standard guideline criteria are widely accepted.

Over a third of people in most countries report meeting criteria for the major categories at some point in their life. The causes are often explained in terms of a diathesis-stress model and biopsychosocial model. Services are based in psychiatric hospitals or in the community, and mental health professionals diagnose individuals by various methods, often relying on observation and questioning in interview.

Psychotherapy and psychiatric medication are two major treatment options as are social interventions, peer support and self-help. In some cases there may be involuntary detention and involuntary treatment where legislation allows. Stigma and discrimination add to the suffering associated with the disorders, and various social movements campaign for change.
Source: http://en.wikipedia.org/wiki/Mental_disorder

Object permanence is the understanding that objects continue to exist even when they cannot be seen, heard, or touched. Jean Piaget argued that object permanence is one of an infant’s most important accomplishments, as without this concept, objects would have no separate, permanent existence.

In Piaget’s Theory of cognitive development infants develop this understanding by the end of the “sensorimotor stage”, which lasts from birth to about 2 years of age. Piaget thought that an infant’s perception and understanding of the world depended on their motor development, which was required for the infant to link visual, tactile and motor representations of objects. According to this view, it is through touching and handling objects that infants develop object permanence.

Source:  http://en.wikipedia.org/wiki/Object_permanence

Reinforcement is a term in operant conditioning and behavior analysis for the delivery of a stimulus, (immediately or shortly) after a response, that results in an increase in the future rate or probability of that response . The response strength is assessed by measuring frequency, duration, latency, accuracy, and/or persistence of the response after reinforcement stops. Experimental behavior analysts measured the of rate of behaviors as a primary demonstration of learning and performance with non-humans. For example, rate is measured as the number of times a pigeon pecks a key in a 10 minute session,

A reinforcer is the stimulus, event, or situation whose presentation is dependent upon a response.

Punishment is the practice of imposing something unpleasant or aversive on a person or animal or property, usually in response to disobedience, defiance, or behavior deemed morally wrong by individual, governmental, or religious principles.
Source: http://en.wikipedia.org