The Impact of Encumbrance on Mobile Interactions

Abstract

Abstract. This paper investigates the effects of encumbrance (holding different types of objects while using mobile devices) to understand the interaction difficulties that it causes. An experiment was conducted where participants performed a target acquisition task on a touchscreen mobile phone while carrying different types of bags and boxes. Mobility was also evaluated since people carry items from one place to another. Motion capture hardware was used to track hand and arm postures to examine how holding the different types of objects caused excessive movement and instability therefore resulting in performance to decline. The results showed encumbrance and mobility caused target accuracy to decrease although input while holding the box under the non-dominant arm was more accurate and exerted quicker targeting times than holding no objects. Encumbrance affected the dominant hand more than the non-dominant hand as targeting error significantly increased and caused greater hand instability. The issues caused by encumbrance suggest the topic requires more attention from researchers and users would benefit greatly if better interaction techniques and applications are developed to counteract the problems.

Comparing evaluation methods for encumbrance and walking on interaction with touchscreen mobile devices

“…Ng et al [21] conducted an observational study across three different types of locations in a major city to identify the objects that users frequently held during interaction. The observations showed that users carried different types of handheld bags the most often (46% of 878 objects).…”

“…Hyman et al [10] reported that users walked slower and were more unaware to nearby events when using mobile phones. Users could be further affected if they also had to carry bulky objects during interaction, as shown by [21,22].…”

“…Mizobuchi et al [18] recorded a low average walking speed of 1.77 km/h when examining different button dimensions to identify the optimal size for text entry via stylus input. The encumbrance and mobile targeting experiment by Ng et al [21] reported a mean PWS of 2.3 km/h during input (unencumbered) which resulted in a mean target accuracy of 42%. When users were carrying a broad box under the non-dominant arm, PWS decreased to 1.6 km/h (a difference of 41% compared to normal walking speed) which caused a mean target accuracy of 37%.…”

“…Users may struggle to input accurately or in an effective manner when their hands are physically hampered by holding objects at the same time which can cause interaction to become frustrating and prone to errors. As a result, it is important to assess the impact of encumbrance, especially when the user is also on the move, a situation already known to cause interaction problems [21,22]. A greater understanding of the issues caused by encumbrance while walking would mean better interaction techniques and more efficient interfaces can be developed to assist the user in these physically awkward and mentally demanding situations.…”

“…There are many possible objects that a user may carry during interaction and many ways in which the objects may be carried. Ng et al [21] conducted an observational study to assess the typical objects that users carried when using mobile devices in the public and reported that different types of bags and boxes were the most common objects that users held. In the user study presented in this paper, we used a similar approach and selected a typical shopping bag and a packaging box as the encumbrance objects.…”