Portable operatively simple touch screen apparatus uses testing methods and systems that are free of age and language constraints include special signal processing techniques that provide a temporal resolution highly sensitive for probing cognitive function. The embodiments include or make use of one or more modules implemented at least partially in a set of instructions in software and configured to measure user reaction times to visual stimulus on a touch screen device having a capacitive sensor touch-sensitive surface and a detector of audio waves resulting from touch on the touch-sensitive surface. The modules employ recordation of acoustic vibrations resulting from a user's touching a target location on the touch screen surface spaced from a touched starting location on that surface, in one embodiment, to measure temporal response to a visual stimulus placed at the target location.