Which prism orientation would cause a patient to feel as if the ground is sloping upwards?

The feeling of the ground sloping upwards is associated with the Base Down prism orientation. When a Base Down prism is placed in front of a patient, it effectively shifts the perceived visual field downward. This can create a perception where objects and the ground below appear higher than they actually are.

The mechanism behind this perception lies in how our visual system interprets the information received from our eyes. With Base Down prism, the image of the ground is displaced upwards, which leads the brain to believe that it is physically elevated compared to its true position. This phenomenon can be particularly noticeable in individuals with certain visual processing challenges or in those adjusting to new prism corrections.

In contrast, other prism orientations would produce different visual effects. For example, a Base Up prism would shift the visual field upwards, potentially causing the ground to seem lower than it is. Similarly, Base Out and Base In prisms manipulate the perceived horizontal plane rather than affecting vertical orientation. Thus, Base Down is correctly associated with the perception of an upward sloping ground.