Seeing and Perceiving

Motion perception and sampling in space and time The next property of real objects that we want to be able to recover from images involves introducing a feature of your experience that we haven’t considered before: change over time. Besides having reflectance properties that are independent of the light falling on them and occupying positions in 3D space, objects also change the way they look over time. That is to say, objects can move . One of those objects that can move is you, which is another way that the images you receive on your retina change from moment to moment. We’d probably like to know something about the real movements that are happening out there in the world that give rise to the changing images that we measure with our eyes and our brain, so how do we interpret change over time in a way that allows us to make guesses about motion? To motivate this discussion, I want to start thinking about this problem by considering a simple model system that represents a basi...

Monocular cues for depth perception In our last post, we discussed how you can use the information from your two eyes to estimate the relative depth of objects in the visual field. Both vergence and binocular disparity provided cues to where objects were situated in depth relative some fixation point, allowing us to obtain some information about the 3D arrangement of objects in space. Clearly, two eyes are helpful in resolving the ambiguity that follows from projecting the light coming from a three-dimensional scene onto a two-dimensional surface. We said that this projection of light onto the retina made it much harder to make good guesses about depth from one image, and that using two images was a necessary step towards making it possible for you to recover this information from the retinal data. However, consider the picture below:   Figure 1 - A boid in some trees. Some things here look closer to you than others, but how do you tell that when you don't have bino...