Perceiving Depth and Size - University of （感知深度和大小大学）.pdf

Chapter 7 Perceiving Depth and Size In this chapter we will describe how we perceive depth and sizes. As we mentioned before, the problem of finding depth from 2D retinal images is an under-determined problem. However, the human eye achieves this great ease in almost no time. The first question to ask is what information contained in this 2D image makes us perceive depth. This is called the cue approach. This approach focuses on identifying the elements of information in the 2D scene that is related to depth of the scene. According to cue theory, we make a connection between these cues and the actual depth by our accumulated knowledge from prior theories. So, these include several heuristics which may confuse us in pathological cases as we will see later in this chapter. The depth cues can be divided in three different categories. 1. Oculomotor: These are cues based on the ability to sense the position of our eyes and the tension in the eye muscles. 2. Monocular: Cues that work with one eye. 3. Binocular: Cues that depend on two frontal eyes. Figure 7.1: From left: Convergence of eyes when looking at nearby objects (1) and non-converged state when the eye looks far away (2), relative height cues (3) 97 98 CHAPTER 7. PERCEIVING DEPTH AND SIZE 7.1 Oculomotor Cues Oculomotor cues are due to convergence and accommodation. When looking at nearby objects our eyes move inwards. This is called convergence. and when looking at far away objects, our eyes move outward, as shown in Figure 7.1. This associated with accommodation. When the eyes move inward there is a tightening of the muscles that hold the lens to to get the eye to focus close by. When the eye moves outward, muscles relax. We can sense both of these which gives us an estimate about the depth of the object. You can experience