A one- and two-phased model of aimed movement with eye-hand incompatibility.

Aimed movement is ubiquitous and has been extensively investigated. However, little research exists when the hand movements are incompatible with eye movements such as when viewing through a mirror or when performing laparoscopic surgery. An experiment was designed to investigate how individuals perform under one-dimensional and two-dimensional inversion with direct viewing as a reference condition. Twenty-four right-handed university students participated in this experiment and completed all aimed movements with a full-factorial design of movement amplitude at three levels and index of difficulty at 10-levels in three visual conditions of direct, viewing through a mirror (1D inversion) and observing through a right-angled mirror (2D inversion). Learning is rather rapid with direct viewing and with 1D inversion. However, participants take a longer time to stabilize their performance in the 2D inversion condition. Fitts' law is robust under all visual conditions. The eye-hand incompatibility increases movement time with 2D inversion taking the longest movement time. Movement time (MT) was split into initiation time (IT), distance covering time (DCT) and acquisition time (AT) based on submovements. The distance covering part is the first submovement that is primarily ballistic and covers around 90% or more of total amplitude. Furthermore, AT allows the aimed movement to be split into two phases: ballistic and visual control. The results show that the transition from ballistic to visual control happens at lower Index of difficulty (ID) values as the level of incompatibility increases. Based on the experiment and prior research, it is appropriate to use the model MT = a + b ID + c√A as it can account for the two phases of ballistic and visual control.