target 50 and the pursuer 55 the integrated distance between the target and the pursuer is calculated continuously for each target modality and is displayed and updated constantly on the screen this distance is also recorded as a function of time which can be displayed as a line graph the computer program calculates the number of 34 touches 34 the test subject scores by bringing the pursuer to within a predetermined distance of the target for example to within 0 5 cm the computer system 20 also controls a tone generator 60 which presents the test subject 80 with auditory stimuli through a pair of headphones 70 the tone generator 60 creates target tones warbling in intensity at some modulation frequency f 3 and charging in relative intensity between the right and left earphones the position of the tone may be varied between imaginary points auditory space inside the test subject 39 s head as a function of the relative amplitude loudness of the tone in each earphone the frequency pitch of the tone also rises and falls in a controlled manner to indicate vertical position in the auditory space the test subject 80 uses a second input control device 40 such as a second joy stick or second trackball to track the position of the tone left right location in the auditory space as well as its pitch up down location by varying the pitch and relative left right amplitude of intermittent.