A system of testing a subject for impairment, comprising: a measurement apparatus configured to measure the subject's right eye positions and the subject's left eye positions; a display (106, 308) configured to present to the subject a display of a smoothly moving object repeatedly moving over a tracking path; a computer control system coupled with the measurement apparatus and the display, the computer control system including one or more processors, memory, and one or more programs stored in the memory, the one or more programs comprising instructions to: present on the display a smoothly moving object, repeatedly moving over a tracking path; while presenting the display to the subject, use the measurement apparatus to: measure the subject's right eye positions, wherein each right eye position is a display location indicating where the right eye of the subject was looking at a respective instant in time; and measure the subject's left eye positions, wherein each left eye position is a display location indicating where the left eye of the subject was looking at a respective instant in time; generate a disconjugacy metric based on a measure of variability of differences between the measured right eye positions and corresponding measured left eye positions measured while the object is moving; compare the disconjugacy metric with a predetermined baseline to determine whether the disconjugacy metric is indicative of a cognitive impairment; and generate a report based on the disconjugacy metric. a measurement apparatus configured to measure the subject's right eye positions and the subject's left eye positions; a display (106, 308) configured to present to the subject a display of a smoothly moving object repeatedly moving over a tracking path; a computer control system coupled with the measurement apparatus and the display, the computer control system including one or more processors, memory, and one or more programs stored in the memory, the one or more programs comprising instructions to: present on the display a smoothly moving object, repeatedly moving over a tracking path; while presenting the display to the subject, use the measurement apparatus to: measure the subject's right eye positions, wherein each right eye position is a display location indicating where the right eye of the subject was looking at a respective instant in time; and measure the subject's left eye positions, wherein each left eye position is a display location indicating where the left eye of the subject was looking at a respective instant in time; generate a disconjugacy metric based on a measure of variability of differences between the measured right eye positions and corresponding measured left eye positions measured while the object is moving; compare the disconjugacy metric with a predetermined baseline to determine whether the disconjugacy metric is indicative of a cognitive impairment; and generate a report based on the disconjugacy metric. present on the display a smoothly moving object, repeatedly moving over a tracking path; while presenting the display to the subject, use the measurement apparatus to: measure the subject's right eye positions, wherein each right eye position is a display location indicating where the right eye of the subject was looking at a respective instant in time; and measure the subject's left eye positions, wherein each left eye position is a display location indicating where the left eye of the subject was looking at a respective instant in time; measure the subject's right eye positions, wherein each right eye position is a display location indicating where the right eye of the subject was looking at a respective instant in time; and measure the subject's left eye positions, wherein each left eye position is a display location indicating where the left eye of the subject was looking at a respective instant in time; generate a disconjugacy metric based on a measure of variability of differences between the measured right eye positions and corresponding measured left eye positions measured while the object is moving; compare the disconjugacy metric with a predetermined baseline to determine whether the disconjugacy metric is indicative of a cognitive impairment; and generate a report based on the disconjugacy metric.