MODELING ONE-HANDED THUMB TOUCH PERFORMANCE FOR MOBILE DEVICES: Extending Fitts’ Law by Incorporating Grip Span and Hand Anthropometry

Open Access
Sung, Kiseok
Graduate Program:
Industrial Engineering
Doctor of Philosophy
Document Type:
Date of Defense:
June 13, 2017
Committee Members:
  • Andris Freivalds, Dissertation Advisor
  • Andris Freivalds, Committee Chair
  • Ling Rothrock, Committee Member
  • Conrad S Tucker, Committee Member
  • Frank Edward Ritter, Outside Member
  • Human Performance Modeling
  • Fitts' Law
  • User Experience
  • Human Computer Interaction
  • Human Factors
This dissertation aimed to develop a thumb performance model that addresses grip span for one-handed interaction on mobile devices. Toward that end, it achieved several objectives. First, it identified the limitations on thumb performance caused by increasing grip span during one-handed mobile phone interactions. Second, it identified the difference between the index finger and thumb touch motion in terms of Fitts’ law. Third, it investigated the effect of grip span on one-handed thumb touch interaction. Fourth, it developed and validated a new predictive model for one-handed thumb touch performance based on the Fitts’ law model by incorporating grip span and hand anthropometry. This dissertation consisted of two experiments. In Experiment I, the effect of grip type was examined through comparison of the cradled index finger and one-handed thumb interaction. In Experiment II, the effect of grip span size on performance was analyzed for one-handed thumb interaction. Using the collected data, a predictive regression model of one-handed thumb touch performance was developed based on Fitts’ law. A hold-out method of cross-validation (R2 = 47.8%) was conducted to validate the model. Finally, a case study illustrating the application of the model was investigated using a fictional scenario based on the persona method. The case study showed an example of the model application as it suggested the modification of user interface for a mobile rhythm game. This dissertation is significant in three ways. First, it raises the issue of grip span and its effect on one-handed thumb touch interaction from a different point of view related to thumb length’s limitation. Second, the raised issue was investigated and proven to exist through the experiments. Third, based on Fitts’ law, a new model was developed to help improve the usability issue of large smartphones. Finally, based on this research, it is expected that new large-screen mobile devices will need to have a more suitable user interface in the near future to provide a better user experience.