· Phys measures currently used: Electrodermal Conductivity (skin conductance), Cardiovascular activity (bp and heart rate), Brain Electrical Activity (EEG, fMRI, PET)

· Historical Perspectives on I/E: Jung (where your psychic energy is directed), Eysenck (used factor analysis; indentified facets and sub-facets: high E’s: talkative, outgoing, sometimes impulsive, easily bored, hates routine — low E’s: quiet, withdrawn, prefer being alone, like routines and familiarity)

· Stability of I/E – very high (corr = ~ .72) – with two exceptions: higher when measured during childhood and > 30 years old, less consistent in adolescence and middle adulthood

· Eysenck’s Bio Theory of I/E: diff in functioning of ascending reticular activating system or ARAS; it was first proposed that introverts have a higher level of ARAS at rest, but the revised theory proposed that introverts are just more reactive to mdoer levels of stimulations with no significant difference during resting state; transmarginal inhibition is the mechanism by which a threshold of stimulation has been reached and stimulus decreases arousal – organism shuts down; Lemon drop test