Abstract: Fitts’ law is an effective model to predict human performance in the field of human-computer interaction (HCI)．Its effectiveness has been confirmed in many situations,and it is the theoretical basis to study the human performance in HCI．However,due to the different muscle controlling mechanisms of eyes and limbs,Fitts’ law cannot be applied to the pointing task in gaze-based interactions．Recently,Zhang etc proposed a new index of difficulty (ID_eye) that can effectively model the human performance in dwell-based eye pointing．However,their model dose not specifically take account of the differences of the two kinds of saccades (i.e．centripetal and centrifugal saccades) involved in eye pointing．This paper aimed to investigate the different performance under the different conditions of the two typical saccadic eye movements:saccades toward the primary position (centripetal) and away from the primary position (centrifugal)．Carrying out an experiment,we confirmed that there is significant difference in moving time between these two eye movements,and that the IDeye model can still accurately model the performance even in the situation of pure centripetal or centrifugal saccades．This work is necessary to complete the study of modeling dwell-based eye pointing,and it further confirms the suitability and effectiveness of the IDeye model for gaze-based interactions.

Key words: Gaze-based interaction,Fitts’ law,Human performance,Centripetal saccade,Centrifugal saccade