'Two researchers from Hokkaido University have empirically verified that the mere presence of a cell phone or smartphone can adversely affect our cognitive performance. The phenomenon was particularly marked among individuals who infrequently use such devices.
While it was well known that the use of cell phones or smartphones (hereafter, mobile phones) could cause oversights and delays in judgment, how the presence of such devices affects cognitive functioning was not well studied.
As a part of their research, Associate Professor Jun-ichiro Kawahara of Hokkaido University’s Graduate School of Letters and Motohiro Ito of Chukyo University (a special research student at Hokkaido University’ Graduate School of Letters) measured the effect of mobile phones on the ability to pay attention of 40 undergraduate students.'
You can read more here.