1. A computer implemented method for changing an output of a computer system based on a determination of a person's cognitive load, the method comprising: (a) receiving, at a processor of a computer system from an interactive interface of the computer system, stroke data sensed by the interactive interface, the stroke data comprising data points, each having a time reference and a spatial reference, wherein the stroke data is representative of hand-based strokes produced by a person while performing a task on the computer system via the interactive interface; (b) identifying, by the processor, sets of data points in the stroke data that have adjacent spatial references for each time reference in time series order, each of the sets of data points representing an individual hand-based stroke; (c) determining, by the processor, that one or more of the sets of data points in the stroke data meets one or more predetermined stability criteria by having a variance that is less than a threshold and selecting, by the processor, the one or more of the sets of data points; (d) identifying, by the processor, one or more predetermined stroke features in the selected one or more of the sets of data points and determining, by the processor, a measure indicative of the person's cognitive load based on the one or more predetermined stroke features identified in the selected one or more of the sets of data points; and (e) automatically changing an output of the computer system, via the processor, based on the measure indicative of the person's cognitive load to alleviate or increase the person's cognitive load.