A bridge circuit that is located between a peripheral device and a USB connection to a host. At least some illustrative embodiments are methods including: creating a video signal of an eye, the video signal comprising a stream of frames; and finding an indication of pupil position. The hub has slots configured to accept the plurality of strands lengthwise, and at least one projection that extends beyond an outer perimeter of the hub. Based on this light-intensity-distribution signal, it is possible to derive the spot centroid, with the offset in the spot centroid due to the crosstalk substantially eliminated, resulting in an improved accuracy of the spot centroid detection, as compared with conventional methods.