Suppose you could not perceive movement. What would your perceptual world be like? An answer to this question can be gleaned from case reports of people who have experienced a brain lesion that selectively disrupted their ability to perceive visual movement. A particularly well-documented case is as follows:
The visual disorder complained of by the patient was a loss of movement vision in all three dimensions. She had difficulty, for example, in pouring tea or coffee into a cup because the fluid appeared to be frozen, like a glacier. In addition, she could not stop pouring at the right time since she was unable to perceive the movement in the cup (or a pot) when the fluid rose. Furthermore the patient complained of difficulties in following dialogue because she could not see the movements of the face and, especially, the mouth of the speaker. In a room where more than two other people were walking she felt very insecure and unwell, and usually left the room immediately, "because people were suddenly here or there but I have not seen them moving." The patient experienced the same problem but to an even more marked extent in crowded streets or places, which she therefore avoided as much as possible. She could not cross the street because of her inability to judge the speed of a car, but she could identify the car itself without difficulty. "When I'm looking at the car first, it seems far away. But then, when I want to cross the road, suddenly the car is very near." She gradually learned to "estimate" the distance of moving vehicles by means of sound becoming louder.
A brain scan revealed that the woman had a lesion of the cerebral cortex along the border of the occipital and temporal lobes. Psychophysical testing revealed that her perception of movement in senses other than vision was normal. Her only apparent deficit was an inability to perceive visual movement. Interestingly, the perception of illusory movement was also eliminated. Thus, unlike normal individuals, two lights blinking in succession did not produce the illusion of a single light moving back and forth (the phi phenomenon). Instead, she continued to see two separate lights.