Despite the increasing popularity of social networking Web sites (SNWs), very little is known about the psychosocial variables that predict people's use of these Web sites. The present study used an extended model of the theory of planned behavior (TPB), including the additional variables of self-identity and belongingness, to predict high-level SNW use intentions and behavior in a sample of young people ages 17 to 24 years. Additional analyses examined the impact of self-identity and belongingness on young people's addictive tendencies toward SNWs. University students (N = 233) completed measures of the standard TPB constructs (attitude, subjective norm, and perceived behavioral control), the additional predictor variables (self-identity and belongingness), demographic variables (age, gender, and past behavior), and addictive tendencies. One week later, they reported their engagement in high-level SNW use during the previous week. Regression analyses partially supported the TPB: attitude and subjective norm significantly predicted intentions to engage in high-level SNW use with intention significantly predicting behavior. Self-identity, but not belongingness, significantly contributed to the prediction of intention and, unexpectedly, behavior. Past behavior also significantly predicted intention and behavior. Self-identity and belongingness significantly predicted addictive tendencies toward SNWs. Overall, the present study revealed that high-level SNW use is influenced by attitudinal, normative, and self-identity factors, findings that can be used to inform strategies that aim to modify young people's high levels of use or addictive tendencies for SNWs.

Set-shifting refers to a process of cognitive control which is shown through flexible behavioural adaptation to changes in task parameters or demands, such as the switching of an explicit rule (extra-dimensional rule shifting) or the reversal of a reinforcement-contingency (reversal-learning). Set-shifting deficits are widely documented in specific neuropsychological disorders, but seldom investigated in relation to normally-occurring individual differences. In a sample of healthy adults (N=78, 28% male), we demonstrate that Working Memory and trait Psychoticism have independent involvement in extra-dimensional rule shifting as measured using an analogue of the Wisconsin Card Sorting Test. Only Psychoticism, however, was involved in reversal-learning, as assessed using a recent modification of the Iowa Gambling Task. Individual differences in extra-dimensional rule shifting were explained in terms of rule abstraction speed, while individual differences in reversal-learning were explained in terms of response perseveration. These results clarify component processes in different forms of set-shifting, and highlight the role of individual differences, especially personality, in cognitive control.