Abstract: A system is disclosed for recognizing typing from typing transducers that provide the typist with only limited tactile feedback of key position. The system includes a typing decoder sensitive to the geometric pattern of a keystroke sequence as well as the distance between individual finger touches and nearby keys. The typing decoder hypothesizes plausible key sequences and compares their geometric pattern to the geometric pattern of corresponding finger touches. It may also hypothesize home row key locations for touches caused by hands resting on or near home row. The resulting pattern match metrics may be combined with character sequence transition probabilities from a spelling model. The typing decoder then chooses the hypothesis sequence with the best cumulative match metric and sends it as key codes or commands to a host computing device.

Abstract: A multi-touch system is disclosed that recognizes simultaneous touchdown of four fingers on, above, or below the home row of keys as a modifier chord and applies modifiers such as Shift, Ctrl, or Alt to subsequent touch activity until none of the chord fingertips remain touching. Touches by the thumb of the modifier chord hand that occur before any modifiable typing or clicking activity cause the modifier chord to be canceled and reinterpreted as hand resting. The Shift modifier may be released temporarily during thumb keypresses that are intermixed with typing of capitalized characters. Distributing the modifier chord touches across different zones or key rows selects multiple modifiers. In an alternative embodiment, different modifiers can be selected with different arrangements of the fingers relative to one another within the chord, irrespective of absolute hand alignment with the touch surface.