COG-PSY-CHAP-3 (3) PDF - Visual Perception Concepts

Some Basic Concepts of Perception James Gibson (1966, 1979) provided a useful framework for studying perception. He introduced the concepts of distal (external) object, informational medium, proximal stimulation, and perceptual object. For example, you are seeing a car driving by: Distal Object: Th...

Some Basic Concepts of Perception James Gibson (1966, 1979) provided a useful framework for studying perception. He introduced the concepts of distal (external) object, informational medium, proximal stimulation, and perceptual object. For example, you are seeing a car driving by: Distal Object: This is the actual object in the real world. In this example, the distal object is the car that’s driving on the road. Informational Medium: This refers to the way information about the distal object is transmitted to your senses. For the car, the light reflecting off its surface and traveling through the air to your eyes is the informational medium. Proximal Stimulation: When the light waves from the car reach your eyes, they hit your retina (the back part of your eye that detects light). The cells in your retina absorb the light waves, and this is known as proximal stimulation. It’s the immediate physical interaction between the sensory receptors in your eyes and the light coming from the car. Perceptual Object: Finally, your brain processes the information from the proximal stimulation to create a mental image of the car. This mental image, or the car as you perceive it, is the perceptual object. It’s your brain’s interpretation of the car based on the information it receives. Works of our Visual System The precondition for vision is the existence of light. Light is electromagnetic radiation that can be described in terms of wavelength. Vision begins when light passes through the protective covering of the eye (Figure 3.7). o This covering, the cornea, is a clear dome that protects the eye. The light then passes through the pupil, the opening in the center of the iris. It continues through the crystalline lens and the vitreous humor. The vitreous humor is a gel-like substance that comprises the majority of the eye. Works of our Visual System Eventually, the light focuses on the retina where electromagnetic light energy is transduced—that is, converted—into neural electrochemical impulses (Blake, 2000). The retina is only about as thick as a single page in this book, it consists of three main layers of neuronal tissue o The first layer of neuronal tissue—closest to the front, outward-facing surface of the eye—is the layer of ganglion cells, whose axons constitute the optic nerve. Works of our Visual System o The first layer of neuronal tissue—closest to the front, outward-facing surface of the eye—is the layer of ganglion cells, whose axons constitute the optic nerve. o The second layer consists of three kinds of interneuron cells. Amacrine cells and horizontal cells make single lateral (i.e., horizontal) connections among adjacent areas of the retina in the middle layer of cells. Bipolar cells make dual connections forward and outward to the ganglion cells, as well as backward and inward to the third layer of retinal cells. o The third layer of the retina contains the photoreceptors, which convert light energy into electrochemical energy that is transmitted by neurons to the brain. There are two kinds of photoreceptors—rods and cones. Works of our Visual System Ø The rods are long and thin photoreceptors. They are more highly concentrated in the periphery of the retina than in the foveal region. The rods are responsible for night vision and are sensitive to light and dark stimuli. Ø The cones are short and thick photoreceptors and allow for the perception of color. They are more highly concentrated in the foveal region than in the periphery of the retina (Durgin, 2000). Ø Within the rods and cones are photopigments, chemical substances that react to light and transform physical electromagnetic energy into an electrochemical neural impulse that can be understood by the brain. Works of our Visual System When you see something, light enters your eyes and hits special cells called rods and cones in the retina, which is like the screen at the back of your eye. These cells turn the light into signals that get passed along through other cells until they reach the ganglion cells. The ganglion cells have long fibers that bundle together to form the optic nerve, which carries the signals from your eye to your brain. The optic nerves from both eyes meet at a point called the optic chiasma, located at the base of your brain. Here, the signals from the inner part of each eye (the side closer to your nose) cross over to the opposite side of the brain. The signals from the outer part of each eye (closer to your temples) stay on the same side. Interestingly, the lens in each eye flips the image upside down and backward before it hits the retina. So, the picture your brain receives is actually upside-down and reversed, but your brain automatically corrects it so you see things the right way up. APPROACHES TO PERCEPTION Bottom-Up theories describe approaches where perception starts with the stimuli whose appearance you take in through your eye. Top-Down theories, according to this perception is driven by high-level cognitive processes, existing knowledge, and the prior expectations that influence perception (Clark, 2003). BOTTOM-UP THEORIES The four main bottom-up theories of form and pattern perception are; direct perception template theories feature theories recognition-by-components theory. BOTTOM-UP THEORIES Direct Perception: This theory suggests that we perceive the world directly, without needing to process or interpret what we see. Our sensory organs (like our eyes) take in information from the environment, and our brain instantly understands it. There’s no need for extra thinking or interpretation. Template Theories: According to this theory, we recognize objects by matching what we see with stored “templates” in our mind. Imagine you have a mental image of what a letter "A" looks like. When you see a letter, you compare it to this template. If it matches, you recognize it as an "A." If it doesn’t match, you keep comparing until you find the right match. Feature Theories: Instead of looking for a complete template, feature theories suggest that we recognize patterns by breaking them down into their basic features. For example, when you see a letter "A," you might notice the two slanted lines and the horizontal line. Your brain puts these features together to recognize the letter.(Pandemonium Model) Recognition-by-Components Theory: This theory expands on feature theories by suggesting that we recognize objects by breaking them down into simple 3D shapes, called "geons." For example, a coffee mug might be broken down into a cylinder (the body) and a curved shape (the handle). By identifying these basic shapes, our brain can recognize the entire object. TOP-DOWN THEORIES In constructive perception, the perceiver builds (constructs) a cognitive understanding (perception) of a stimulus. The concepts of the perceiver and his or her cognitive processes influence what he or she sees. This viewpoint also is known as intelligent perception because it states that higher- order thinking plays an important role in perception. It also emphasizes the role of learning in perception (Fahle, 2003). According to constructivists, we quickly form and test various hypotheses regarding percepts. The percepts are based on three things: o what we sense (the sensory data), o what we know (knowledge stored in memory), and o what we can infer (using high-level cognitive processes) TOP-DOWN THEORIES One reason for favoring the constructive approach is that bottom-up (data- driven) theories of perception do not fully explain context effects. Context effects are the influences of the surrounding environment on perception. Configural-superiority effect (Bar, 2004; Pomerantz, 1981), by which objects presented in certain configurations are easier to recognize than the objects presented in isolation, even if the objects in the configurations are more complex than those in isolation. Object-superiority effect, in which a target line that forms a part of a drawing of a 3- D object is identified more accurately than a target that forms a part of a disconnected 2-D pattern Word-superiority effect indicates that when people are presented with strings of letters, it is easier for them to identify a single letter if the string makes sense and forms a word instead of being just a nonsense sequel of letters. TOP-DOWN THEORIES Example of Context Effects Imagine you're looking at a puzzle piece on its own. It might be hard to figure out where it fits or what it represents. However, when you see the puzzle piece within the context of the whole puzzle, it becomes much easier to identify its position and what it represents. This is because the surrounding pieces (the context) help your brain make sense of the single piece. Configural-Superiority Effect Suppose you have a set of simple shapes, like lines or squares. If these shapes are arranged in a specific configuration (like a familiar pattern or shape), it becomes easier for you to recognize and make sense of the individual parts TOP-DOWN THEORIES Object-Superiority Effect Similarly, if you're looking at a drawing of a 3D object, like a cube, and you're asked to identify a specific line within that drawing, you’ll likely do it more accurately than if you were looking at a random, disconnected 2D pattern. Word-Superiority Effect Finally, imagine you’re shown a string of letters, like "WORD," and asked to pick out a specific letter, say "O." You'll find it easier to identify the "O" in a meaningful word like "WORD" than in a string of random letters like "RWOD." VIEWER- CENTERED VS. OBJECT-CENTERED One position, Viewer-centered representation, is that the individual stores the way the object looks to him or her. In the viewer-centered approach, perception depends on the viewpoint of the observer. The way you perceive an object changes depending on your angle, distance, and orientation relative to that object. Example: If you see a car from the front, side, or back, the image you perceive is different each time. Your brain adjusts your perception based on your viewpoint and recognizes it as a car regardless of the angle. VIEWER- CENTERED VS. OBJECT-CENTERED The second position, Object-centered representation, is that the individual stores a representation of the object, independent of its appearance to the viewer. In the object-centered approach, perception is based on the object’s intrinsic properties rather than the viewer’s perspective. The object is recognized as having a consistent shape and structure, regardless of the viewer’s position. Example: A chair is recognized as a chair because your brain understands its essential structure—four legs, a seat, and a back—regardless of how you’re looking at it. A third orientation in representation is landmark-centered. In landmark-centered representation, information is characterized by its relation to a well-known or prominent item. Example: If you're trying to find your way through a city, you might use a landmark like a tall tower or a famous monument to guide you. You recognize other buildings or streets based on how close or far they are from this landmark. The Perception of Groups—Gestalt Laws The Gestalt psychologists proposed a number of laws of perceptual organization that indicate how elements in the environment are organized, or grouped together. o Figure-ground. When perceiving a visual field, some objects (figures) seem prominent, and other aspects of the field recede into the background (ground). o Proximity. When we perceive an assortment of objects, we tend to see objects that are close to each other as forming a group. o Similarity. We tend to group objects on the basis of their similarity. o Continuity. We tend to perceive smoothly continuous forms rather than disrupted or discontinuous ones. o Closure. We tend to perceptually close up, or complete, objects that are not, in fact, complete. o Symmetry. We tend to perceive objects as forming mirror images about their center. o Meaningfulness or Familiarity According to the law of familiarity, things that form patterns that are familiar or meaningful are likely to be grouped together. Two Different Pattern Recognition Systems The first system specializes in recognition of parts of objects and in assembling those parts into distinctive wholes (feature analysis system). This system specializes in breaking down objects into their smaller parts or features. It analyzes the individual components of an object (like lines, shapes, or colors) and then assembles these parts into a coherent whole. Example: When you see the letter "A," the feature analysis system breaks it down into two slanted lines and a horizontal line in the middle. It then assembles these parts to recognize the letter "A.“ The second system (configurational system) specializes in recognizing larger configurations. It is not well equipped to analyze parts of objects or the construction of the objects. This system is responsible for recognizing larger, overall configurations or patterns. It doesn't focus on the small parts or details of an object but instead identifies the object based on its overall shape or structure. Example: When you recognize a friend’s face, you don’t usually focus on each individual feature (like the eyes, nose, or mouth) separately. Instead, you recognize the face as a whole because of its overall configuration. The Neuroscience of Recognizing Faces and Patterns There is evidence that emotion increases activation within the fusiform gyrus when people are processing faces. Researchers do not all agree that the fusiform gyrus is specialized for face perception, in contrast to other forms of perception. Another point of view is that this area is that of greatest activation in face perception, but that other areas also show activation, but at lower levels. Another theory concerning the role of the fusiform gyrus is called the expert-individuation hypothesis. According to this theory, the fusiform gyrus is activated when one examines items with which one has visual expertise. Perceptual Constancies Perceptual constancy occurs when our perception of an object remains the same even when our proximal sensation of the distal object changes (Gillam, 2000). Here we consider two of the main constancies: size and shape constancies. o Size constancy is the perception that an object maintains the same size despite changes in the size of the proximal stimulus. Example: If you see a car driving away from you, the image of the car on your retina gets smaller as it moves further away. Despite this, you still perceive the car as being the same size, thanks to size constancy. o Shape constancy is the perception that an object maintains the same shape despite changes in the shape of the proximal stimulus. Example: When you look at a door as it opens, the shape of the door on your retina changes from a rectangle to a trapezoid. However, you still perceive the door as a rectangle, demonstrating shape constancy. DEPTH PERCEPTION Depth is the distance from a surface, usually using your own body as a reference surface when speaking in terms of depth perception. This use of depth information extends beyond the range of your body’s reach. Depth perception is the ability to perceive the world in three dimensions (3D) and to judge the distance of objects from us. It is crucial for navigating our environment, allowing us to understand how far away things are and how they relate to each other spatially. 1. Binocular Cues Binocular cues depend on the fact that we have two eyes, which are slightly apart. Because each eye views the world from a slightly different angle, the brain can compare these two images to determine depth. Retinal Disparity: This is the slight difference in the images seen by each eye. The brain combines these two images, and the degree of difference (or disparity) between them helps us perceive depth. The greater the disparity, the closer the object. Convergence: This cue comes from the way our eyes move inward (or converge) when focusing on a close object. The more our eyes converge, the closer the object appears to be. DEPTH PERCEPTION Monocular cues are depth cues that are available even when we use just one eye. These cues rely on visual information from the environment and can still provide a strong sense of depth. Relative Size: If two objects are known to be the same size, the one that appears smaller is perceived as being farther away. Interposition (Overlap): When one object overlaps another, the overlapping object is perceived as being closer. Linear Perspective: Parallel lines (like railroad tracks) appear to converge as they get further away. The more the lines converge, the greater the perceived distance. DEPTH PERCEPTION Texture Gradient: The texture of surfaces becomes denser and less detailed as they recede into the distance, providing a cue for depth. Shadow and Light: Shadows and lighting can give clues about the depth and shape of objects, with the brain interpreting light sources and shadow patterns to perceive 3D shapes. Relative Height: Objects that are higher in the visual field are generally perceived as being farther away than those that are lower. Motion Parallax: As you move, objects closer to you move faster across your field of view than those further away, helping you gauge their distance. The Neuroscience of Depth Perception The brain contains neurons that specialize in the perception of depth. These neurons are, as one might expect, referred to as binocular neurons. The neurons integrate incoming information from both eyes to form information about depth. The binocular neurons are found in the visual cortex (Parker, 2007). EXAMPLE OF MOTION PARALLAX DEPTH PERCEPTION Texture Gradient: The texture of surfaces becomes denser and less detailed as they recede into the distance, providing a cue for depth. Shadow and Light: Shadows and lighting can give clues about the depth and shape of objects, with the brain interpreting light sources and shadow patterns to perceive 3D shapes. Relative Height: Objects that are higher in the visual field are generally perceived as being farther away than those that are lower. Motion Parallax: As you move, objects closer to you move faster across your field of view than those further away, helping you gauge their distance. The Neuroscience of Depth Perception The brain contains neurons that specialize in the perception of depth. These neurons are, as one might expect, referred to as binocular neurons. The neurons integrate incoming information from both eyes to form information about depth. The binocular neurons are found in the visual cortex (Parker, 2007). DEFICITS IN PERCEPTION Understanding "How" Pathway Deficits Optic Ataxia: A condition caused by damage to the "how" pathway in the brain, particularly in the posterior parietal cortex. Example: Individuals with optic ataxia struggle to use their visual system to guide movements accurately. However, they can improve their aim if they delay their movements by a few seconds. Agnosia: A disorder where individuals have trouble perceiving sensory information due to damage, often at the border of the temporal and occipital lobes. Example: A person with visual agnosia can see colors and shapes but cannot recognize objects or faces. They might see a cup but be unable to identify it as a cup. DEFICITS IN PERCEPTION ANOMALIES IN COLOR PERCEPTION Rod Monochromacy (Achromacy): A rare condition where individuals have no color vision at all. Example: A person with achromacy sees the world entirely in shades of gray. Dichromacy: A condition where only two of the three color perception mechanisms work, leading to various types of color blindness. Red-Green Color Blindness: The most common form, where individuals have difficulty distinguishing between red and green. Protanopia: An extreme form of red-green color blindness where individuals cannot see red. Deuteranopia: Trouble seeing greens. Tritanopia: Difficulty distinguishing blues from greens, with yellows sometimes appearing as light shades of red. Example: Someone with protanopia might not be able to differentiate between a red apple and a green apple.