Cognitive Psychology Final Exam Week 3
Give some examples, based on the "perceptual puzzle" demonstration and computer vision, to show that determining what is out there requires going beyond the pattern of light and dark on the receptors.
- The stimulus on the receptors is ambiguous. The perceptual system is not concerned with the object's image on the retina, but determines the object that created the image. This is the inverse projection problem, because it involves starting with the retinal image and extending rays out from the eye. - Objects can be hidden or blurred. People easily understand that the part of an object that is covered continues to exist, and they are able to use their knowledge of the environment to determine what is likely to be present. This is the same with objects that are not in sharp focus. - Objects look different from different viewpoints. The ability to recognize an object seen from different viewpoints is called viewpoint invariance.
Describe three reasons why it is difficult to design a perceiving machine
1) They lack viewpoint invariance 2) They struggle to recognize blurred or hidden objects 3) They struggle to solve the inverse projection problem Computers struggle to make contextualized inferences, like people do.
Define a "prior probability" in Bayesian inference and explain how this relates to perception.
A prior probability is the probability that something may have contributed to a given symptom, or that an experience would happen at all. The brain uses this in top-down processing to make sense of indistinct objects based on the context, i.e. the likelihood of their identity
Which of these factors will likely affect which depth cues are used? Circle all that apply. A. The overall luminance of the scene B. Whether or not objects in the scene are moving C. How tired you are that day D. If you have an injured left eye E. If you have an injured right eye
B. Whether or not objects in the scene are moving D. If you have an injured left eye E. If you have an injured right eye
Describe Bayesian inference in terms of how it would explain the "coughing" example and the inverse projection problem.
Bayesian inference takes into account prior probability and likelihood. In the "coughing" example, the prior probability rules out lung disease as causing a cough because lung disease is so rare. The likelihood probability rules out heartburn as causing the cough because it is not related. These all lead to the conclusion that the cough is most likely due to a cold. This applies to the inverse projection problem. The priors we have say that books are rectangular. The likelihood that the book is rectangular is provided by additional evidence such as the book's retinal image, combined with the perception of the book's distance and angle at which you view the book. These all lead a person to the conclusion that the book is most likely rectangular.
What is bottom-up processing? Top-down processing? Describe how the following indicate that perception involves more than bottom-up processing: (a) multiple personalities of a blob (b) the finding-faces-in-a-landscape demonstration (c) hearing individual words in a sentence (d) experiencing pain
Bottom-up processing: the sequence of events from eye to brain Top-down processing: processing that originates in the brain, at the "top" of the perceptual system (a) Even though all the blobs in all of the pictures are identical, they are perceived as different objects depending on their orientation and the context within which they are seen. (b) Once you perceive a particular grouping of rocks as a face, it is often difficult not to perceive them this way - they have become permanently grouped together to create faces within the scene (c) Someone who understands Spanish perceives an unbroken string of sound as individual, meaningful words in a conversation. Because of their knowledge of the language, they are able to tell when one word ends and another begins (speech segmentation). (d) 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. Studies have shown that a significant proportion of patients with pathological pain get relief from taking a placebo.
The brain is changed, or "shaped," by its exposure to the environment so it can perceive the environment more efficiently. The mechanism through which the structure of the brain is changed by experience is called ___. A. the Gestalt principles B. Sprague-Dawley plasticity C. Experience-dependent plasticity D. Vasopressin-mediated behavior
C. Experience-dependent plasticity
Visual perception can be roughly divided into two streams. Name and describe the two streams, and describe one experiment showing that these streams are dissociable.
Dorsal, "where" stream, magno Ventral, "what" stream, parvo People with damage to dorsal pathway can recognize what an object is, but not where it is going or where it is. People with damage to the ventral pathway can tell where an object is going/is, but not what it is.
What does Crystal's run down the beach illustrate about perception? List at least three different characteristics of perception. Why does the importance of perception extend beyond identifying objects?
Her experience with the umbrella illustrates how perceptions can change based on added information (her view became better as she got closer) and how perception can involve a process similar to reasoning or problem solving (she figured out what the object was based partially on remembering having seen the umbrella the day before). Her guess that the coiled rope was continuous illustrates how perception can be based on a perceptual rule (when objects overlap, the one underneath usually continues behind the one on top). Her experience also shows that perception can involve a process; it is not automatic. It also illustrates that perception occurs in conjunction with action; it involves dynamic processes that accompany and support our actions
Describe one piece of evidence that shows that the brain's response to stimuli is shaped by experience
Kittens who were raised in an environment with only vertical lines reacted to a vertical rod, but did not react to a horizontal rod.
A theory of perception must explain two major phenomena: lack of correspondence and paradoxical correspondence. Please describe each of these concepts and give an example of each.
Lack of correspondence: distal and proximal stimuli don't match; what you are actually seeing and how you perceive it are not the same - ex: bowl of strawberries, visual illusions Paradoxical: the incomplete info in the distal stimulus doesn't hinder perception - ex: viewing objects from different angles, color/size constancy
Was the dress illusion an example of paradoxical correspondence or lack of correspondence?
Lack of correspondence; what the actual color is and how it was perceived did not match
What are regularities of the environment, and how do they influence perception? Distinguish between physical regularities and semantic regularities. What is a scene schema?
Regularities of the environment are characteristics of the environment that occur frequently. They can influence perception through the oblique effect and the light-from-above assumption. Physical regularities are regularly occurring physical properties of the environment. Semantic regularities are the characteristics associated with the functions carried out in different types of scenes. A scene schema is the knowledge of what a given scene typically contains.
How does the Gestalt approach differ from the other three? How do modern psychologists explain the relation between experience and the principles of organization?
The approaches of Helmholtz, regularities, and Bayes all use data about the environment, gathered through past experience in perceiving, to determine perception. This makes top-down processing a core concept. Gestalt psychologists emphasize built-in principles of organization. Modern psychologists believe that the believe that the principles of organization are likely caused by by past experience
What is the oblique effect? Describe how this effect could be caused by evolution and by experience.
The oblique effect is the concept that people can perceive horizontals and verticals more easily than other orientations. This could be caused by evolution because organisms whose neurons fired to important things in the environment would be more likely to survive than those that didn't have these neurons. This could be caused by experience through experience-dependent plasticity
How well can present-day computers recognize objects?
They are okay; they are not as good as humans because they struggle with viewpoint invariance, blurred or hidden objects, and the inverse projection problem.
Describe the Gestalt approach to perception, focusing on the principles of organization. How do these principles originate, according to Gestalt psychologists?
This approach proposed a number of laws of perceptual organization, where were based on how stimuli usually occur in the environment. The whole is different than the sum of its parts. The principles of perceptual organization are: - good continuation: points that, when connected, result in straight or smoothly curving lines are seen as belonging together, and the lines tend to be seen in such a way as to follow the smoothest path. Also, objects that are overlapped by other objects are perceived as continuing behind the overlapping object. - pragnanz: every stimulus pattern is seen in such a way that the resulting structure is as simple as possible - similarity: similar things appear to be grouped together These are intrinsic laws that are built into the perceptual system. Although a person's experience can influence perception, the role of experience is minor.
What is experience-dependent plasticity? Describe the kitten-rearing experiment and the Greeble experiment. What is behind the idea that neurons can reflect knowledge about properties of the environment?
This is the mechanism through which the structure of the brain is changed by experience. In the kitten-rearing experiment, kittens were raised in an environment with only vertical lines. They would respond to a vertical rod, but not a horizontal rod. The Greeble experiment showed that training individuals to become experts on an identification task showed increased activation of neurons in the FFA.
Describe Helmholtz's theory of unconscious inference. What is the likelihood principle?
This was the idea that perception depends on knowledge. Our perceptions are the result of unconscious assumptions, or inferences, that we make about the environment The likelihood principle states that we perceive the object that is most likely to have caused the pattern of stimuli we have received.
In class we showed the visual illusion that when a bowl of strawberries is illuminated in blue light, we still perceive the strawberries to be red, even though the distal stimulus in the picture has the strawberries being more of a gray color. Interestingly, if you alter the shapes of the objects in the bowl, your perception of the color changes. Why?
We no longer see the objects as strawberries and don't use top-down processing to know that they should be red. Now, they look brown.
What was an example from lecture or the textbook that countered direct perception (i.e. purely bottom-up) theories of perception?
We understand that objects interposed behind another object is a whole object, not a cut-out around the front object like it might look. Also, the ability to recognize the same blurry shape as different objects based on context.
People, but not computers, are very good at perceiving the ambiguous shapes as different objects, even though they look the same. Using evidence from lecture and the readings, provide an explanation
We use the contextual clues of the scene to determine the blur's most likely identity (top-down processing) via Bayesian inference
