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Frank A Proudlock, Zhanhan Tu, Parnika Sharma; The contribution of vision to balance during smartphone use. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):4769.
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© ARVO (1962-2015); The Authors (2016-present)
Smartphones are globally the most popular mobile device with over 1.75 billion users worldwide. Recent studies demonstrate that smartphone use leads to postural instability during standing and walking although the causes are unclear. We used computerised dynamic posturography (CDP) to explore the role of vision in balance during smartphone use also comparing the effects of attentional load and biomechanics.
Postural stability was measured using CDP in 20 healthy adults standing inside a static full field patterned visual surround at 0.5m. The degree of instability during reading and texting was compared to baseline values of normal vision (without phone) and no vision (eyes closed). To explore the effect of: (i) vision: a fixation target was viewed on the phone while being held compared to the same task with the phone fixed in near space; (ii) attentional load: passive reading was compared to counting 4 letter words in the text; (iii) biomechanics: the held phone was switched off and the surround attended to. Each task was performed with fixed base (FB) and under sway referenced (SR) conditions, which reduces somatosensory inputs.
Postural stability during reading and texting was equivalent to reducing the contribution of vision to balance by 81% and 73% during the FB task and 54% and 59% during SR conditions, respectively (comparison to baseline of normal vision, p<0.0001). Viewing a fixation target on the held phone led to a similar reduction in stability as during reading and texting (p<0.0001). In contrast, stability was significantly better for the same task with the phone fixed in near space (p<0.0001 for FB and SR tasks), similar to that of baseline normal vision. Changing attentional load (by comparing held phone tasks: fixation, passive reading, reading to identify 4 letter words and texting) did not significantly change stability (p>0.95 for FB and SR tasks). Also, different biomechanical loads caused by phone use did not significantly change stability (p>0.25).
Reading and texting leads to a significant reduction in postural stability. This is due to visual attention being paid to an object fixed to a body-centred rather than an earth-centred frame of reference. In comparison, attentional load and biomechanical factors do not significantly affect stability. These findings may help us in the prevention of accidents caused by smartphone use.
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