Motion After Effect

Background:

The visual system contains neurons that are sensitive to motion. Some of these motion sensitive neurons respond above baseline to motion in a particular direction and below baseline to motion in the opposite direction. Like many neurons, they adapt to prolonged exposure to their preferred stimulation. As they adapt, they respond less frequently to the stimulus.

So what should happen if you adapt a motion sensitive neuron by exposing it to its preferred motion for 30 seconds? It will respond less frequently. If you now stop the motion, the neuron should return to its baseline rate of neural activity. But because the neuron is temporarily adapted, it will respond below its normal baseline rate of activity. Remember that when the motion sensitive neuron responds below baseline, that normally indicates motion in the direction opposite to the preferred motion. Thus, if you adapt to motion in one direction and then stop the motion, you should perceive illusory motion in the opposite direction. This is the motion after effect.

The Activity:

In this activity, you will adapt to motion. Click on the "Start" button and stare at the center of the spiral while it rotates. When it stops rotating, notice the perceived direction of the illusory motion of the spiral.

You can change the rate of rotation of the spiral and adapt to the new motion. If you make the spiral rotate faster, what should you perceive when the spiral stops rotating?

Try adapting to the motion with only one eye (close or cover the other). Once the motion stops, close the eye that was open during adaptation and open the eye that was closed during adaption. Do you still get the motion after effect? What does that tell us about the locaton of the adapted neurons in the visual pathway?

Seconds per rotation: 0.05 (20 rotations per second) 1 (1 rotation per second)

Here is another example of the motion after effect.

Speed