Fitts Law in People With Cerebral Palsy

The software used in this study was "Fitts' Reciprocal Aiming Task v.1.0 (Horizontal)" developed by Okazaki, in the public domain and available on the Internet, which was performed on a Toshiba notebook®, model Satellite A60-S1561 System Unit, with the use of an external optical mouse, Fortrek® OM-302.

This instrument can be used to verify motor control through analysis of the speed and accuracy of movement, which can be determined through the log-linear relation between movement time and task difficulty using a mathematical equation, and analyzed by Fitts' law, which describes the relation between movement accuracy and speed, associated with target size and distance11. Thus, the task used in this study was composed of targets of different sizes, being that the smaller targets require more time to execute due to the necessity of increased accuracy and, if the distance between targets reduces, the speed of movement becomes greater and the accuracy decreases.

In relation to target size (W) and distance between targets (D), the equation log2 (2D/W) results in an index of difficulty (ID), where the higher the ID, the more difficult the task, a fact that necessitates greater movement time.

To evaluate the speed and accuracy, two different indices of difficulty were used in this study (ID2 and ID4). The difficulty level was increased by changing the width and distance between the bars. In addition, ID4 was used in two different ways (ID4a and ID4b), for which the distance between the bars and the width were different, but the ID was maintained.

3 Procedure and design The experiment was composed of three trials at each of the two IDs: 2 and 4 (ID 4 had two kinds of measurement - ID4a and ID4b), and the participants performed the tasks individually in a room, with only the evaluator present, seated on a chair (or their own wheelchair), which was adjusted in height according to the needs of the individual. A footrest was available, when necessary. The computer was placed on a table, and each participant was given instructions and presented with the task, in which the individual, after hearing an alarm from the computer, was required to click with an external mouse cursor on two parallel bars which were arranged vertically, intermittently, with the greatest speed and accuracy possible, for a period of 10 seconds, followed by a second alarm which indicated the end of the attempt.

Directly following the attempt, the total movement time was registered, by dividing the seconds obtained in each attempt by the number of "clicks" on targets. If more than two clicks were wrong, the individual repeated the task.

Procedure and design The experiment was composed of three trials at each of the two IDs: 2 and 4 (ID 4 had two kinds of measurement - ID4a and ID4b), and the participants performed the tasks individually in a room, with only the evaluator present, seated on a chair (or their own wheelchair), which was adjusted in height according to the needs of the individual. A footrest was available, when necessary. The computer was placed on a table, and each participant was given instructions and presented with the task, in which the individual, after hearing an alarm from the computer, was required to click with an external mouse cursor on two parallel bars which were arranged vertically, intermittently, with the greatest speed and accuracy possible, for a period of 10 seconds, followed by a second alarm which indicated the end of the attempt.

Directly following the attempt, the total movement time was registered, by dividing the seconds obtained in each attempt by the number of "clicks" on targets. If more than two clicks were wrong, the individual repeated the task.

Inclusion criteria

• medical diagnosis of CP;
• levels I to IV according to the GMFCS;
• levels I to III according to MACS.

Exclusion criteria

• presence of surgery or a chemical neuromuscular blockade in the upper limbs within six months prior to participation in the study;
• lack of comprehension of the experimental instructions.