Abstract:This document describes a methodology for the measurement of accuracy and precision of a remote eye tracker, the Tobii X2-30, under non-ideal condition (without the use of a chinrest). The test was performed with 10 people (without disabilities). The results are: 2.46 and 1.91 degrees for the accuracy and precision respectively, while the device datasheet describe values of 0.40 and 0.26 degrees (accuracy and precision respectively). As expected, values calculated are higher, but they are better descriptors of the device's performance in conditions of normal use, where user can move the head freely. The results will be used to establish targets' size on the screen while the eye-tracker is used by people with cerebral palsy.
Abstract-This paper analyzes the presence of positive and negative motor signs in people with cerebral palsy (CP). Positive motor signs are those that lead to involuntarily increased frequency or magnitude of muscle activity. Negative motor signs describe insufficient muscle activity or insufficient control of muscle activity. In this paper, a head-mounted alternative computer interface based on inertial technology was used to assess motor signs in seven users with CP. Task performance and control of posture was related to the impairment. There are no significant differences between users with CP and healthy control participants in the frequency domain of the head movement. Results suggest that this kind of motor disorders is not related to positive motor signs. Moreover, a control mode based on posture more than on movements is not optimum; an alternative control mode must be specially designed for users with poor postural control.
This paper presents an experiment to validate a head-mounted inertial interface for human-computer interaction (HCI) developed for people with cerebral palsy (CP). The method is based on Fitts's law, an empirical model of human motor performance for aimed movements. Head motion is recorded in a series of goal-crossing tasks and a regression model of the movement time (MT) is estimated for each user. Values of R 2 above 0.9 are indicators of a strong correlation of those motion patterns with the linear model proposed by Fitts. The analysis of MT confirmed that head movements of users without disability follow Fitts's law and showed that 3 users with CP (MACS IV and V) had the same behavior. There was a weaker correlation (R 2 =0.839) for one individual with cervical dystonia and ballistic movements and no correlation for two users with cervical hypotonia and dyskinetic CP. Results show the impact of ballistic movements and poor postural control in computer interaction. They also provide the foundation for new interaction techniques to develop a universal computer interface for motor impaired users.
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