If a neutral density filter is placed over a patient's right eye, in which direction does the pendulum appear to move?

When a neutral density filter is placed over one eye, it reduces the amount of light entering that eye without altering the wavelengths of light. This affects the visual perception of motion, particularly in the context of the pendulum's movement.

In this scenario, with a neutral density filter over the patient's right eye, the brain receives less light signal from the right eye compared to the left eye. This discrepancy in visual input causes the perceived movement of the pendulum to appear biased towards the more illuminated eye, which is the left eye in this case.

As a result, the patient would perceive the pendulum as moving in the opposite direction of the eye that has been shaded by the filter. Hence, when the neutral density filter is placed on the right eye, the pendulum appears to move counterclockwise. This phenomenon is related to the brain's interpretation of motion when there is an imbalance in sensory information from both eyes, leading to a perceived shift in direction.