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CogPsych 3
Chapter 3: (Sensation and) Perception
| Question | Answer |
|---|---|
| What is perception? | Conscious experiences resulting from stimulation of the senses. |
| What is sensation? | Raw stimulus energy from the environment. |
| What is the nature of perception? | - Perceptions can change based on added information - Perception involves a process similar to reasoning or problem solving - Perception can be based on a perceptual rule; based on past experience - Perception occurs in conjunction with action |
| What is the inverse projection problem? | The task of determining the object responsible for the image on the retina. A particular image on the retina can be created by many different objects in the environment. |
| How are people able to easily understand that covered parts of an objects continue to exist? | They use their knowledge of the environment to determine what is likely to be present. |
| What is bottom-up processing? | Processing that starts when environmental energy stimulates the receptors. |
| What is top-down processing? | Processing that originates in the brain. e.g. knowledge of the environment. |
| What is speech segmentation? | People well versed in one language are able to tell when one word ends and the next one begins because of their knowledge of the language. |
| How is speech segmentation an example of top-down processing? | Listeners can receive identical sound stimuli but experience different perceptions means that each listener's experience with language or lack of it is influencing his or her perception. |
| What is the direct pathway model of pain? | Pain occurs when receptors in the skin called nociceptors are stimulated and send their signals in a direct pathway from the skin to the brain. |
| How has modern research proven the direct pathway model of pain wrong? | Pain can be influenced by what a person expects, how the person directs his or her attention, and the type of distracting stimuli that are present. |
| Describe Helmholtz's theory of unconscious inference. | Problem of ambiguous image on the retina solved by the likelihood principle, which occurs by a process called unconscious inference. Perception resembles problem solving process which happens rapidly and unconsciously, making perception seem “automatic”. |
| What is the likelihood principle? | Perceiving the object that is most likely to have caused the pattern of stimuli we have received. |
| What is unconscious inference? | Our perceptions are the result of unconscious assumptions or inferences that we make about the environment |
| What is the main principle of Gestalt psychologists? | The whole (of perception) is more than the sum of its parts (of sensation) . The whole precedes the parts. |
| What are the 6 Gestalt laws of perceptual organization? | - Law of Pragnanz (Simplicity) - Law of Similarity - Law of Good continuation - Law of Proximity - Law of Common fate - Law of Familiarity |
| What is the law of Praganz? | Every stimulus pattern seen so the resulting figure perceived as simple as possible |
| What is the law of similarity? | Similar things appear to be grouped together. |
| What is the law of good continuation? | - Points that, when connected, result in straight or smooth curving lines grouped together - Lines follow the smoothest path - Objects that are overlapped are perceived as continuing behind the overlapping object |
| What is the law of proximity? | Things that are near to each other are grouped together |
| What is the law of common fate? | Things moving in the same direction are grouped together |
| What is the law of familiarity? | Things are more likely to form groups if groups appear familiar or meaningful |
| What is the role of the Gestalt laws? | • Perceptual principles described as “intrinsic laws” that are built into the visual system • Consistent with Gestalt idea that although personal experience can influence perception, the role of experience is minor compared to perceptual principles |
| What is the modern view on perception? | Perception is influenced by our knowledge of regularities in the environment: characteristics of environment that occurs frequently. Our system is adapted to respond to the physical characteristics of our environment. |
| What are physical regularities? | Regularly occurring physical properties of environment |
| What are some examples of physical regularities? | • Oblique effect - individuals recognised vertical or horizontal lines faster than oblique lines due to more horizontal/vertical lines in natural environment (trees) • Light-from-above assumption and the Cornsweet illusion (the sun) |
| What are semantic regularities? | Characteristics associated with the functions carried out in different types of scenes. |
| What are some examples of semantic regularities? | - Scene schema - knowledge of what a scene typically contains |
| How did Palmer (1975) demonstrate semantic regularities? | She presented the scene of a kitchen, and then briefly flashed a few target pictures. She then asked observers to identify the object in the target picture. Nearly 80% chose the loaf of bread. |
| What is Bayesian inference? | Estimate of probability of an outcome is determined by two factors: 1) The prior, which is our initial belief about the probability of an outcome 2) The likelihood, which is the extent to which the available evidence is consistent with the outcome |
| What is Bayesian inference based on? | It combined Helmholtz’s idea of unconscious inference and the concept of environmental regularities - restates Helmholtz’s idea of unconscious inference in terms of probability |
| What happens during Bayesian inference? | People start with a prior, then use additional evidence to update the prior and reach a conclusion. |
| How can Bayesian inference be applied to the inverse projection problem? | - Prior: environmental regularities (both physical and semantic) built up based on previous experience - Likelihood: additional bottom-up evidence such as retinal images based on changing viewing angle and distance |
| What are visual heuristics? | Rules of thumb, “best-guess predictions”. They: - Reflect experience or evolutionary forces - Do not always provide correct solution, but sufficiently correct most of the time - Fast, automatic and effortless |
| How are visual heuristics used? | •The mind uses visual heuristics to disambiguate the signal received from the retina • Visual heuristics constraint the number of 3- dimensional objects that could be projected into the 2-dimensional image |
| What are the 5 visual heuristics? | Collinearity, common region, uniform connectedness, occlusion and interposition. |
| What is collinearity heuristic? | Collinear points in 2-dimension are collinear in 3-dimension and edges that meet in 2- dimension also meet in 3-dimension |
| What is common region heuristic? | Elements that are within the same region of space are grouped together |
| What is uniform connectedness heuristic? | Things that are physically connected or have similar surface color/texture are perceived as a unit |
| What is occlusion heuristic? | When an object is partially covered by a smaller occluding object, the larger object is seen as continuing behind the smaller occluder |
| What is the interposition heuristic? | If object A covers part of object B, then object A must be closer than object B |
| What are the three main theories of object recognition? | - Template theories - Feature theories - Structural theories |
| Describe the template theory of object recognition. | Objects represented in memory as pictures, called templates • Input stimulus compared to all templates • Similarity between input shape and template computed by correlating brightness of input and preferred brightness for each point in template |
| What are the advantages of the template theory of object recognition? | - All other classes of theories must have templates at some level - Cells in visual cortex are responding like simple templates |
| What are the disadvantages of the template theory of object recognition? | - Inputs must be normalized (resized, rotated, repositioned) prior to matching - Does not address viewpoint invariance, inverse optics and partial occlusion problems - Difficult to generalize to new instances |
| Describe the feature theory of object recognition. | • Objects stored as features • Features of input image compared to feature list stored in memory • Object in memory matching most number of features recognized |
| What are the advantages of the feature theory of object recognition? | - No normalization required - Can overcome depth rotation by having different sets for different views of an object by using 3-dimension features - Allows easy generalization to new instances |
| What are the disadvantages of the feature theory of object recognition? | - Problems with recognizing different objects with similar features - No coding for relations between features |
| Describe the structural theory of object recognition. | • Objects stored in memory in terms of features and categorical relations between them • Features and relations extracted from image and compared to shape descriptions stored in memory |
| What are the advantages of the feature theory of object recognition? | - No normalization required - Generally used 3-dimensional “units” and a small number of description for each object to overcome depth rotation - Allows easy generalization to new instances - Predict recognition problems when features are scrambled |
| What are the disadvantages of the feature theory of object recognition? | - Unclear which features and relations are used in description - Unclear how visual system stores and analyzed features and relations |
| Describe Biederman's Recognition By Components (RBC) theory | - Objects represented as a set of geons (geometric icons) and their categorical relations to one another (e.g. relative size, position, orientation) - Geons are generalized cylinders that can be generally recognized from any perspective - 36 geons |
| What are the disadvantages of RBC theory? | • Difficulty with differentiating objects with same geons • For example, ‘Dogs’ and ‘Cats’: Large cylinder above 4 small cylinders and next to 2 small cylinders |
| What are the 6 problems of visual attention? | 1. the inverse projection problem 2. Ambiguity in surface features of objects 3. Object size and distance ambiguous in 2-dimensional representation 4. Viewpoint invariance 5. Occlusion 6. Illusory contours |
| Describe low-mid- and high level vision. | • Low-level vision: detects pixels, features, edges, etc • Mid-level vision: Grouping/segmentation, figure/ ground organisation (identifying a figure from the background) • High-level vision: Object & scene recognition |
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