Effect of a word prediction feature on user performance

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Abstract
This study examines the influence of a word prediction feature on several measures of user performance during text entry tasks. Fourteen subjects transcribed text with and without a word prediction feature for seven test sessions. Eight subjects were able-bodied and used mouthstick typing, while six subjects had high-level spinal cord injuries and used their usual method of keyboard access. Use of word prediction significantly decreased text generation rate for the spinal cord injured (SCI) subjects and only modestly enhanced it for the able-bodied (AB) subjects. While fewer selections were required with the word prediction system, each selection took significantly longer to make, which we attribute to the additional cognitive and perceptual processes associated with use of word prediction. Performance was further analyzed by deriving subjects' times for keypress and list search actions during word prediction use. All subjects had slower keypress times during word prediction use as compared to letters-only typing, and SCI subjects had much slower list search times than AB subjects. Under the conditions of this experiment, the cognitive cost of using word prediction largely overwhelmed the benefit provided by keystroke savings. SCI subjects appeared to incur higher cognitive costs than AB subjects, possibly due to their prior expertise in letters-only typing.