Chapter 5 - Study Questions Flashcards
(19 cards)
1) What are some of the problems that make object perception difficult for computers but not for humans?
a) The stimulus on the receptors is ambiguous
b) Objects can be hidden or blurred
c) Objects Look Different from Different viewpoints
2) What is structuralism, and why did the Gestalt psychologists propose an alternative to this way of explaining perception?
Structuralism was a School in psychology that focused on breaking down mental processes into the most basic components ( like atoms).
Structuralism distinguished between sensations – elementary processes that occur due to stimulation of the senses – and perceptions, more complex conscious experiences such as our awareness of objects.
The Gestalt psychologists rejected the idea that perceptions were formed by adding up sensations and also rejected past experience as playing a major role in perception.
Apparent movement can’t be explained by sensations, because there is nothing in the dark space between the flashing images. The whole is different than the sum of its parts, because the perceptual systemscreates the perception of movement where there actually is none. This idea that the whole is different than the sum of its parts became the battle cry of the Gestalt psychologists.
“ Wholes were in and sensations were out”
3) How did the Gestalt psychologists explain perceptual organization?
Gestalt psychologists proposed that perception depends on a number of organizing principles, which determine how elements in a scene become grouped together.
Principles:
- Principle of 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 part. The principle operates on surfaces as well: Objects that are partially covered by other objects are seen as continuing behind the covering object.
- Pragnanz ( roughly translated means “ good figure”), also called the principle of good figure or simplicity, is the central principle of Gestalt psychology: Every stimulus pattern is seen in such a way that the resulting structure is as simple as possible.
- Principle of similarity: Similar things appear to be grouped together. This law causes circles of the same color to be grouped together.
- Principle of proximity or nearness: Things that are near each other appear to be grouped together.
- Principle of common region: Elements that are within the same region of space appear to be grouped together.
- Principle of uniform connectedness, a connected region of the same visual properties, such as lightness, color, texture, or motion, is perceived as a single unit.
4) How did the Gestalt psychologists describe figure-ground segregation? What are some basic properties of figure ground?
The question of what causes perceptual segregation is often referred to as the problem of figure-ground segregation. When we see a separate object, it is usually seen as a figure that stands out from the ground. For example, you would probably see a book or papers on your desk as figure and the surface of your desk as ground.
Properties of Figure and Ground:
- The figure is more “ thinglike” and more memorable than the ground.
- The figure is seen as being infront of the ground.
- Near the borders it shares with the figure, the ground is seen as unformed material, without a specific shape and seems to extend behind the figure.
- The border separating the figure from the ground appears to belong to the figure.
5) What image-based properties of a stimulus tend to favor perceiving an area as “figure”? Be sure you understand Vecera’s experiment that showed that the lower region of a display tends to be perceived as figure, and why Peterson and Salvagio stated that to understand how segregation occurs we have to consider what is happening in the wider scene.
One image-based factor proposed by the Gestalt psychologists was that areas lower in the field of view are more likely to be perceived as figure.
In our normal experience, the “ figure” is much more likely to be below the horizon.
Another Gestalt proposal was that figures are more likely to be perceived on the convex side of borders ( borders that bulge out)
Segregation is determine not by just what is happening at a single border but by what is happening in the wider scene. This makes sense when we consider that perception generally occurs in scenes that extend over a wide area.
7) Describe Gibson and Peterson’s experiment that showed that meaning can play a role in figure-ground segregation.
The woman versus the black random figure with white background. When the person sees a woman, it is easier to differentiate figure from ground.
If you don’t recognize the object, it is hard to differentiate
8) What does the Bev Doolittle scene in Figure 5.32 demonstrate?
Once you have organized an image as something, it is difficult to not see it as this thing and as something else.
1) What is a “ scene”, and how is it different from an “ object”?
A scene is a view of a real-world environment that contains 1) background elements 2) multiple objects that are organized in a meaningful way relative to each other and the background.
Objects are compact and acted upon, whereas scenes are extended in space and are acted within.
Example: If we are walking down the street and mail a letter, we would be acting upon the mailbox ( an object) and acting within the street ( the scene).
2) What is the evidence that we can perceive the gist of a scene very rapidly? What information helps us identify the gist?
An example of your ability to rapidly perceive the gist of a scene is the way you can rapidly flip from one TV channel to another, yet still grasp the meaning of each picture as it flashes by – a car chase, quiz contestants, or an outdoor scene with mountains – even though you may be seeing each picture for a second or less and so may not be able to identify specific objects. When you do this you are perceiving the gist of the scene.
Observers use information called global image features, which can be perceived rapidly and are associated with specific types of scenes.
Some of the global image features proposed by Oliva and Torralba are:
Degree of naturalness Degree of openness Degree of roughness Degree of expansion Colour
3) What are regularities in the environment? Give examples of physical regularities and discuss how these regularities are related to the Gestalt laws of organization.
Characteristics of the environment which occur frequently are called regularities of the environment.
Physical regularities are regularly occurring physical properties of the environment. For example, there are more vertical and horizontal orientations in the environment than oblique (angles) orientations. This occurs in human-made environments (for example, buildings contain many horizontals and verticals) and also in natural environments (trees and plants are more likely to be vertical or horizontal than slanted)
Gestalt laws of organization groups similar features together to analyze perception. These physical regularities are an example of how similar features together can influence how we perceive a scene or object.
4) What are semantic regularities? How do semantic regularities affect our perception of objects within scenes? What is the relation between semantic regularities and the idea that perception involves inference?
In perception, semantics refers to the meaning of a scene.
Semantic regularities are the characteristics associated with the functions carried out in different types of scenes.
Growing up in modern society we have an idea of how certain scenes would be portrayed i.e a supermarket, a clothing store, a bank, a post office and we don’t have any trouble visualizing these scenes, sometimes even with great level of detail. If we know a certain object belongs to a scene, it is easier to infer an association between scene and object , meaning of a scene or meaning of an object. However, if an object doesn’t belong to a scene, we might have more difficult distinguishing the object and its meaning. For example, we can imagine a produce aisle as being part of the grocery store scene but we wouldn’t place a car as being part of the same scene.
People use their knowledge of physical and semantic regularities to infer what is present in a scene.
5) What did Helmholts have to say about inference and perception?
Helmholtz proposed a principle called the theory of unconscious inference, which states that some of our perceptions are the result of unconscious assumptions we make about the environment.
The theory of unconscious inference was proposed to account for our ability to create perceptions from stimulus information that can be seen in more than one way.
A corollary of the theory of unconscious inference is the likelihood principle, which states that we perceive object that is most likely to have cause the pattern of stimuli we have received.
6) What is Bayesian inference, and how is it related to Helmholtz’s ideas about inference?
Modern psychologists have quantified the idea of inferential perception by using a statistical technique called Bayesian inference, that takes probabilities into account. For example, let’s say we want to determine how likely it is that it will rain tomorrow. If we know it rained today, then this increases the chances that it will rain tomorrow, because if it rains one day it is more likely to rain the next day. Applying reasoning like this to perception, we can ask, for example, whether a given object in a kitchen is a lof of bread or a mailbox. Since it is more likely that a loaf of bread will be in a kitchen, the perceptual system concludes that bread is present.
1) Describe the Grill-Spector’s “Harrison Ford “experiment. What do the results indicate about the connection between brain activity and the ability to recognize faces?
1) Describe the Grill-Spector’s “Harrison Ford “experiment. What do the results indicate about the connection between brain activity and the ability to recognize faces?
Kalanit Grill-Spector and coworkers (2004) were interested in determining the relationship between the brain activation that occurs when looking at an object and a person’s ability to identify the object. The “object” they used were pictures of Harrison Ford’s face. They presented pictures to observers in a brain scanner while measuring the response of the fusiform face area (FFA) in the temporal lobe to each picture. On each trail, observers saw either a) a picture of Harrison Ford, b) a picture of another person’s face, or c) a random texture. Each of these stimuli was presented briefly (about 50ms), followed immediately by a random-pattern mask, which limited the visibility of each stimulus to just 50ms.
Results showed that neural activity that occurs as a person is looking at a stimulus is related to that person’s ability to identify the stimulus; a smaller response, with detecting the stimulus; and the absence of a response with missing the stimulus altogether. This is important because it shows that how the brain reacts to a stimulus as it is being presented determines our ability to identify the stimulus.
2) Describe Sheinberg and Logothesis’s binocular rivalry experiment in which they presented a picture of a butterfly to one eye and a sunburst to the other eye. What did the results indicate?
Binocular rivalry => If each eye receives totally different images, the brain can’t fuse the two images and a condition called binocular rivalry occurs, in which the observer perceives either the left-eye image or the right-eye image, but not both at the same time.
In this experiment, presenting different pictures to each eye cause the monkey to see the sunburst for part of the time and the butterfly for part of the time, but not both together.
As the monkey was reporting what it was perceiving, they simultaneously recorded the activity of a neuron in the inferotemporal (IT) cortex that had previously been shown to respond to the butterfly but not to the sunburst.
The result indicates that whenever the monkey perceived the sunburst, the neuron’s firing rate was low, but when the monkey’s perception shifted to the butterfly, firing increase.
3) Describe the Tong’s experiment in which he presented a picture of a house to one eye and a picture of a face to the other eye. What did the results indicate?
Observers in the Tong et al.’s (1998) experiment viewed the overlapping red house and green face through red-green glasses, so the house image was presented to the right eye and the face image to the left eye. Because of the binocular rivalry, the observers’ perception alternated back and forth between the face and the house. When the observers perceived the house, activity occurred in the parahippocampal place area (PPA) in the left and right hemispheres. When the observers perceived the face, activity occurred in the fusiform face area (FFA) in the left hemisphere.
These results show that even though the images on the retina remained the same throughout the experiment, activity in the brain changed depending on what the person was experiencing.
4) Describe how “decoders” have enabled researchers to use the brain’s response, measured using fMRI, to predict what orientation or what picture a person is looking at. Be sure to understand the difference between semantic encoding and structural encoding.
Thomas Naselaris and coworkers (2009) created a brain-reading device by developing two methods for analyzing the patterns of voxel activation recorded from visual areas of an observer’s brain. The first method, called structural encoding, is based on the relationship between voxel activation and structural characteristics of a scene, such as lines, contrasts. Shapes, textures.
The second method, called semantic encoding, is based on the relationship between voxel activation and the meaning or category of a scene.
The information provided by the structural decoder and by the semantic decoder provides a clue to what the subject is seeing. For example, the structural encoder might indicate that there are straight lines of various orientations on the left of the scene, that there are curved contours in some places and that there are few straight or curved contours in another area. The semantic decoder, which provides a different type of information, might indicate that the subject is looking at an outdoor scene.
Thus, the structural encoder alone does a good job of matching the structure of the target image, but a poor job of matching the meaning of the target image. Adding semantic encoder improves performance.
5) Why is it correct to say that faces are “special”? What do the face inversion experiments show? Do faces activate the brain mainly in one place or in many different places?
First, faces are pervasive in the environment. Unless you avoid people, faces are everywhere. But what makes them special is that they are important sources of information. Faces establish a person’s identity, which is important for social interactions and for security surveillance. Faces also provide information about a person’s mood, where the person is looking, and can elicit evaluative judgements in an observer (the person seems unfriendly, the person is attractive, and so on).
Faces are also special because, there are neurons that respond selectively to faces, and there are specialized places in the brain, such as the fusiform face area, that are rich in these neurons. Furthermore, when people are given a task that involves moving their eyes as rapidly as possible to look at a picture of either a face, an animal, or a vehicle, faces elicit the fastest eye movements.
One research finding that had been repeated many times is that inverting a picture of a face ( turning it upside down) makes it more difficult to identify the face or to tell if two inverted faces are the same or different. Similar effects occur for other objects, such as cards, but the effect is much smaller.
Finally, although the existence of areas of the brain that respond specifically to faces provides evidence for specialized modules in the brain, faces provide evidence for distributed processing as well. Initial processing of faces occurs in the occipital cortex, which sends signals to the fusiform gyrus, where visual information concerned with identification of the face is processed. Emotional aspects of the face, including facial expression and the observer’s emotional reaction to the face, are reflected in activation of the amygdala, which is located deep within the brain.
Evaluation of where a person is looking is linked to activity in the superior temporal sulcus; this area is also involved in perceiving movements of a person’s mouth as the person speaks and general movement of faces. Evaluation of a face’s attractiveness is linked to activity in the frontal area of the brain, and the pattern of activation across many different areas of the brain differs in familiar faces compared to unfamiliar faces, with familiar faces causing more activation in areas associated with emotions. Faces, it appears, are special both because of the role they play in our environment and because of the widespread activity they trigger in the brain.
6) What is the evidence that newborns and young infants can perceive faces? What is the evidence that perceiving the full complexity of faces does not occur until late adolescence or adulthood?
At birth, the contrast perceived between light and dark areas is so low that it is difficult to determine it is a face, but it is possible to see very high contrast areas. By 8 weeks, however, the infant’s ability to perceive the contrast between light and dark perception has improved so that the image looks clearly face like. By 3 to 4 months, infants can tell the difference between faces that look happy and those that show surprise, anger or are neutral and can also tell the difference between a cat and a dog.
Using preferential looking in which 2-day old infants were given a choice between their mother’s face and a stranger’s, Ian Bushnell, and coworkers 9 1989) found that newborns looked at the mother about 63 percent of the time.
One reason for this prolonged course of the development of face perception can be traced to physiology the fusiform face area (FFA) is small in an 8-year older child compared to the FFA in an adult. In contrast, the parahippocampal place area (PPA), is similar in the 8 year olde child and the adult.
It has been suggested that this slow development of the specialized area may be related to the maturation of the ability to recognize faces and their emotions, and especially the ability to perceive the overall configuration of facial features. Thus, the specialness of faces extends from birth, when newborns can react to some aspects of faces, to late adolescence, when the true complexity of our responses to faces finally emerges.
