Optimum stimulus size for the human brain to respond to motion: a magnetoencephalographic study

To determine if there is an optimum spatial extent for the detection of moving objects in humans.

We investigated human brain responses to motion at various speeds (2.9-23.5 deg/s) and stimulus sizes (2.2 × 2.9 deg to 44.8 × 57.4 deg) using magnetoencephalography. The results were compared with those for the flickers with the same stimulus sizes and temporal frequencies.

For every size, response latency was inversely related to speed. Further, the latency was lowest at a stimulus size of 16.8 × 22.4 deg for every speed. Although response latency was inversely related to the temporal frequency of the flicker stimulation for all stimulus sizes, it was not affected by stimulus size as much as motion stimulus.

For visual motion detection, the most efficient stimulus size is around 16.8 × 22.4 deg.

The results suggest that spatial summation mechanism is important for the detection of visual motion but a loss of reference frame information affects the detection of larger motion stimuli, supporting the view that illusory self-motion (vection) is caused by poor reference frame information for motion detection.