A Stanford University research study that came out in August 2009:
People who are regularly bombarded with several streams of electronic information do not pay attention, control their memory or switch from one job to another as well as those who prefer to complete one task at a time.
Related to this, see Nicholas Carr’s July/August 2008 Atlantic article Is Google Making Us Stupid? and my 2011 Modern Reformation article “Coming of Age in the Facebook Age” (subscription required). This matter is also discussed in Thriving at College.