A Model to Estimate the Optimal Layout for Assistive Communication Touchscreen Devices in Children With Dyskinetic Cerebral Palsy

Abstract

Excess involuntary movements and slowness of movement in children with dyskinetic cerebral palsy often result in the inability to properly interact with augmentative and alternative communication (AAC) devices. This significantly limits communication. It is, therefore, essential to know how to adjust the device layout in order to maximize each child's rate of communication. The aim of this paper was to develop a mathematical model to estimate the information rate in children with dyskinetic cerebral palsy and to determine the optimal AAC layout for a touchscreen tablet that results in enhanced speed of communication. The model predicts information rate based on button size, number, spacing between buttons, and the probability of making an error or missing target buttons. Estimation of the information rate confirmed our hypothesis of lower channel capacity in children with dyskinetic cerebral palsy compared with age-matched healthy children. Information rate increased when the AAC layout was customized based on the optimal parameters predicted by the model. In conclusion, this paper quantifies the effect of motor impairments on communication with assistive communication devices and shows that communication performance can be improved by optimally matching the parameters of the AAC touchscreen device to the abilities of the child.

Fig. 1.

Touchscreen grid conditions for task 1. The left panel represents three representative grid conditions with non-highlighting condition. The right panel represents three representative grid conditions with highlighting condition in which the correct target button was surrounded by a green border, thickness of 3 mm (in the figure the thickness was enlarged for display purposes only).

Fig. 2.

Representative touchscreen layouts for task 2. The layout on the left represents the Standard layout, 28 buttons, 2 cm size and spacing 1. The layout on the right represents the Optimal layout for CP3 non-highlighting condition, 6 buttons, 4.2 cm size and spacing 1.2.

Fig. 3.

Plot showing the predicted information rate over a seed of 833 different combinations of size, buttons and spacing (solid circles) for participants CP1 (on the top) and TD1 (in the bottom) for non-highlighting condition. The numbered grey solid circles from 1 to 8 represent IRp predicted by the model for the eight experimental conditions of task 1. The maximum value of predicted information rate over all possible parameters combinations represents the channel capacity (grey open circle) of the participant, in which we selected the optimal layout of parameters size, buttons and spacing. The parameters size, buttons and spacing were distributed over the seed such that the number of buttons increased from left to right with a consequent decrease of size and spacing to fit the square grid into the touchscreen. It can be seen that predicted information rate increased with an increase of b for TD1, while for CP1 the peak of predicted information rate corresponded to a parameters combination that did not maximize the number of buttons but resulted with larger buttons size.

Fig. 4.

Plot showing the means and standard errors of predicted channel capacity (CCp) for both groups and highlighting conditions (non-highlighting on the left and highlighting on the right). Grey bars: children with cerebral palsy; white bars: typically developing children. Asterisk mark (∗∗) indicates a statistical difference P < .01.

Fig. 5.

Difference on empirical information rate as a function of difference on empirical information rate for non-highlighting (left plot) and highlighting (right plot) conditions. The straight lines show the best fits by the least squares method. Each participant matched pair is represented by different color of unfilled circles.

Fig. 6.

Plot showing the means of Information Rate during task 2 considering each participant separately (the bars represent the standard deviations) for the layout (Optimal and Standard) and highlighting conditions. Grey bars: NotHighlighting condition, HL0; white bars: Highlighting condition, HL1. Asterisk mark (∗) indicates a statistical difference P < .05.