Laura Beck 8 October 2012 Psychology 235 Lab Report 4 – Depth Perception Lab Description of Monocular Depth Cues Occlusion occurs when one object partially covers another, telling us that that object is in front. Relative Size refers to known objects of equal size, informing that the larger is closer. Texture Gradients show depth when equally spaced objects are seen to be closer together the further away they are, such as looking at carpet patterns. Relative Height refers to the phenomenon that objects in the upper visual field are smaller and appear farther away than those in the lower visual field which appear larger and nearer to the viewer. Familiar Size takes the information you know about the size of objects in your view and allows you to calculate the depth relative to that preexisting knowledge. Aerial Perspective (Atmospheric Perspective) deals with the density of air, dust, and water molecules which obscure the view of things that are further away in the distance, making them more hazy and blue. Linear Perspective is when we perceive depth as parallel lines converge in the distance. Monocular Cues in Action Davis Langer 6: The image is of the side of Old Main, and includes windows, ivy, and a glimpse of the roof. The most striking depth cue is the texture gradient, as the bricks each appear to be more closely packed the further up and to the left they are in the image. The bricks also play a role in relative size, since we know that they are mostly the same size, but as they appear more packed, they also appear smaller. In the same way the windows can inform relative size also, since the main window of the image is much larger than the corresponding segments of the other windows, making it appear to be closer. The windows and the lines of the bricks additionally add linear perspective, since while they don’t obviously converge in the image, they would converge if extended. Occlusion also plays a role with the bushes that are pictured, since they cover the building we assume they are in front. We also have inklings of relative height, since the roof is higher in the visual field (and smaller) it appears further away than the body of building. Finally familiar height helps ground our perspective of depth since we know (or think we know) the approximate size of a brick, scaling our perception of depth and the rest of the image. ErhartWilson3: The first cues that stand out are Atmospheric Perspective and Relative Height, since the upper visual field is more hazy, blue, and smaller than the lower visual field, reinforcing the idea that it is in the distance. The outline of the field is roughly parallel, so linear convergence also helps define the depth of the image, since the edges seem like they would converge. The texture gradient of the grass is more defined in the foreground, and almost undefined in the background, which also provides the signal that the foreground is indeed closer than the upper field. The leaves in the foreground and the cars along the side and back of the image provide a basis for familiar size, since we know how large they are, the image around them is scaled accordingly, which helps show how deep the picture is. The same objects in relation to the others of the same type inform relative size, since each car or leaf is about the same size, but the size varies throughout the image. Finally occlusion is also present since leaves block grass, trees block the street and houses, and cars block the street, showing the layers of depth. Crittenden3: The main depth cues in this image outside of Christiansen Hall of Music are linear perspective and relative size. The multiple parallel lines of the walkway and the sidewalk all appear to be converging as they extend, which we associate with distance. The parts of the walkway are also pivotal in using relative size as a cue, since we assume that the pillars are all identical and same with the horizontal supports, but as they move inward they are smaller, and therefore further away. In this way relative height also plays a role, since the smaller columns are also each increasingly higher in the visual field. The main textures which are present are the stone work for the building and the grass. While the two main sections of stonework aren’t continuous, in the inner section the stones are closer together than the outer section, which also says that it has more depth. The trashcan, the rise of the stairs, and the handicap door button all help provide the grounding of familiar size, so that the perception of depth is more accurate. Finally occlusion is also important as it helps develop the many layers of depth, such as that some pillars are nearer than others, the tree is further away than the pillars, and that the stairs are after the pillars. Depth Perception Eye Open Average Disparity Left -­‐0.6 Both -­‐0.38 To determine the disparity, we used the Howard-­‐Dolman apparatus, which has two mobile bars in front of a light background. I first did the test with my dominant eye, my left, then after with both eyes open. In both tests I found myself trying to use the width of the bars relative to each other to determine the depth. In both tests I consistently had a negative disparity, which only means that I routinely identified the bars as having equal depth when the comparator side was in front of the standard. With my left eye open my disparity was .6, while with both eyes open my disparity was .38. These values of disparity are different, but only by .28, which is less than the variability I had showed in each test, so I don’t know that it is actually significant. However the experience of trying to identify the depths felt easier with both eyes open, and correspondingly I think it also went faster. For this test it is important to use a static field without external cues because any external cues can give information about the depth. While finding an angle to view the test field, I experimented with various other fields of view for the device. I noticed that as soon as you could see the track above the rods or the base/sides of the box, the task was immediately easier, since you could use that as a reference. This tells me that depth perception is not meant to exist in a static field, rather that depth perception adapts to the surroundings, using the many cues to refine our perception. In each test case the horopter is moving to the object that we focus on, however with only one eye, we can’t determine whether both rods lie on the horopter in both eyes, which would present a unified image, and result in the perception that they are equidistant. This matters because this binocular depth is more reliable than only relying on external cues which may be misleading.