1995 Autorepeat 3.1 (tv)

Auto-repeat is the automatic repetition of a function by continuous pressing of a button. In three separate tests, the design and operation of this auto-repeat feature for various electronical devices was examined. Eleven subjects took part in the experiment. Each subject was given the same stratgies for optimizing the auto-repeat feature. Both performance variables (ie. task completion time, number of key strokes) and attitude variables (task difficulty, task effectiveness, task satisfaction) were employed. The results show that optimization of the auto-repeat feature in case of larger distances between origin and target is not only sensible but also desirable: three phases when varying repeat delay time, or two phases when varying repeat step size. 22:11 22:12 22:13 22:14 Initial value Button pressed Initial delay Repeat delays 0,0 0,1 0,2 0,3 0,4 0,5 seconds: Figure 1: The basic concepts of auto-repeat 2 A MODEL OF AUTO-REPEAT AND ASSOCIATED RESEARCH QUESTIONS 2.1 Parameters of auto-repeat Three of the most important parameters of the autorepeat function were studied: the repeat-step size (RSS), the repeat-delay time (RDT), and the number of distinct repeat phases. Initial-delay and repeat-delay time The initial delay time is the time span between the activation (ie. pressing) of e.g. a PLUS or MINUS button and the start of the auto-repeat function. Repeat delay time is defined as the time lag until a value is changed again by the system. Example Initial delay and repeat delay time do not necessarily have the same value, but in the preceding figure the value for both parameters is 0.2 seconds. Once the user has pressed say a dedicated button for clock setting, the displayed time repeatedly changes by a unit of one minute on the digital clock. This takes place after a constant delay of 0.2 seconds as long as the user keeps pressing this button. Repeat-step The repeat-step size is defined as the counting unit added to or subtracted from the current value of some counter, e.g. a clock. Example An increment of 10 used for setting a counter, ie. on a VCR. When the user presses and holds down a dedicated counter setting button, the counter value on the display changes by a unit of 10: initial value: 124 press PLUS: 125 keystroke step size is 1 hold PLUS: 135 auto-repeat step size is 10 hold PLUS: 145 auto-repeat step size is 10 2.2 Optimization model The simplest auto-repeat function has a constant repeat-step size (RSS), a constant repeat-delay time (RDT), and no acceleration phases. In the sequel, this is denoted as the 1-phase model, where RSS=1 and RDT=0.2 seconds, constantly. A phase-wise decrease in repeatdelay time In accordance with standard ergonomic recommendations also adopted by the FACE project, the following models were defined (note that a RDT of 0.08 represents the highest possible speed of the PC used in this experiment): Phase-wise increase of the repeatstep size For the purpose of this experiment, two different models dealing with the increase of the repeat-step size (numeral/time) are defined: 2 2-Phase Model (RSS=1): Phase 1 : RDT=0.20s Phase 2 (after 10 x Phase 1) : RDT=0.10s 3-Phase Model (RSS=1): Phase 1 : RDT=0.20s Phase 2 (after 10 x Phase 1) : RDT=0.10s Phase 3 (after 20 x Phase 2) : RDT=0.08s Figure 2: The speed indicator Phase 1 Phase 2 Phase 3 2-Phase Model (RDT=0.2s) Phase 1 : RSS= 1; 1m Phase 2 (after 10 x Phase 1) :RSS=10;10m 3-Phase Model (RDT=0.2s) Phase 1 : RSS=1; 1m Phase 2 (after 10 x Phase 1) : RSS=10;10m Phase 3 (after 10 x Phase 2) : RSS=100;1h 2 .3 Research Questions The following research questions have been tested: • Does a phase-wise decrease of the repeat-delay time lead to an improvement of the usability of the auto-repeat function? If so, with which kind of model (2-phase or 3-phase)? • Does a phase-wise increase of the repeat-step size lead to an improvement of the usability of the auto-repeat function? • Does an speed indicator providing feedback on the current repeat phase result in a better handling of a phase-wise reduction of RDT?