Personality has a significant influence with a person's thoughts, actions, motivations, emotions and interpersonal relations. It is a generalised term to describe the many different characteristics, or traits people have that make up what is a person's personality. Peterson (1997) defines personality as, "psychological characteristics of an individual that are general, enduring, distinctive, integrated and functional". (Peterson, 1997, p.440).
One of the most influential trait theorists has been Hans Eysenck. Ryckman (1993) cites Eysenck's definition of personality as "a more or less stable and enduring organisation of a person's character. Temperament, intellect and physique, which determines his unique adjustment to the environment". (Ryckman, 1993, p.278). His theory of personality has gained global acceptance and is regarded as one of the major systems by which human personality is assessed. Eysenck believed that the basis of personality involves genetics, physiology and environment. Shackleton (1984) explains this association as follows, "Individuals inherit a particular type of nervous system that predisposes them in one direction or another, the final 'shape' of the personality being determined by the interaction between the person's biological predisposition and the environmental conditions encountered.
In the case of extraversion-introversion, the position of an individual rests in the first instance on the balance between excitation and inhibition processes within the central nervous system". (Shackleton, 1984, p.50).
Pervin (1975) defines traits as, "observed statistical relationships among pieces of behaviour." (Pervin, 1975, p.51). There are an enormous number of traits to personality, but Eysenck categorised them into three basic dimensions. Introversion - extraversion (the degree to which a person is withdrawn or open), neuroticism (the extent to which people control their feelings) and, psychoticism (the degree to which one is insensitive or detached). "Eysenck's factor theory of personality, which assumes three basic dimensions, extraversion - introversion, neuroticism and psychoticism". (Reber, 1995, p.274).