Two-bit quartering, extended report

Due to uncommon neurological diseases such as ALS and pure motor aphasia, some people loose the ability to write and to talk but keep the ability to read and to formulate. To create text one may try electronic switches and (passive) scanning, a reliable and simple but generally speaking also an extremely slow process of about ten characters per minute or less. Several scanning techniques are described, as well as two-bit quartering, a new technique for switch input developed by the author. Like Morse Code, once learned it is relatively fast. Also, it combines rather well with text prediction. Three variants were tested with two healthy test-subjects and a copy task of voiced poetry. Input rates were 16.5 characters per minute (cpm) with one switch and 26.9 cpm with two switches and after additional practice. Curve fitting was done to a simplified Michaelis-Menten equation v(t)=at/(t+c) or v(t)=a/(1+c/t) where v=input rate, a=asymptote of input rate, t=time and c=learning time. This leads to expected input rates of 19 and 35 cpm respectively and learning times of about 20 minutes. To compare different scanning-techniques without further experimentation frequency-weighted clicks and pauses per character were computed. Also, possibilities for more research are discussed