Chapter 4: Spatial Questions Flashcards
What cortical brain structures does visual information pass through as it is processed?
Information first reaches the cortex in a region called striate cortex, so-called because it has a distinctive striped pattern under the microscope. Early vision processes are carried out here, then information is passed to extrastriate cortex, where the tasks of middle vision are carried out (for example, this is where illusory contours are processed). From here, information travels via two separate pathways, one that ends in the parietal lobe, and one that terminates in inferotemporal (IT; lower temporal lobe) cortex. It is in IT cortex that the end-stage processing of face and object recognition is carried out.
What are the receptive field characteristics of cells in IT cortex?
Many neurons in IT have been shown to respond most actively to particular objects or faces. The term “grandmother cell” was coined to describe these neurons, the implication being that a single cell might be ultimately responsible for deciding whether an image was of one’s grandmother’s face.
What methods are used to study the function of brain areas such as IT?
Some labs lesion (surgically remove) parts of the brains in nonhuman subjects to see what functions are impaired following the surgery. The results of such studies are often compared to deficits shown by human patients who have had homologous regions of their brains damaged by accident. Other labs use single-cell recording techniques to determine the responses of individual neurons to different types of stimuli (it was in these labs that grandmother cells were found). Recently, many resources have been poured into laboratories employing noninvasive techniques such as functional magnetic resonance imaging (fMRI), which can take snapshots of neural activity in human’s brains as they perform different tasks.
Why can’t we apply a simple rule like “homogeneous areas belong to the same object” in order to find an object’s contours?
Because humans sometimes perceive object contours even in areas of an image where there is no physical difference between the object and its background (see Figure 4.9).
Draw a figure that includes an illusory contour.
What is the guiding philosophy behind Gestalt psychology? How does it contrast with the earlier approach known as structuralism?
The structuralists believed that perception of a complex scene was simply the sum of the basic “atoms” of perception (color, orientation, etc.) in the scene. Gestalt psychologists reacted to this position, arguing that a perceptual whole was much more than the sum of its elemental parts.
What do the Gestalt grouping principles seek to describe?
The structuralists believed that perception of a complex scene was simply the sum of the basic “atoms” of perception (color, orientation, etc.) in the scene. Gestalt psychologists reacted to this position, arguing that a perceptual whole was much more than the sum of its elemental parts.
Why is it important to include the phrase “all else being equal” when stating the Gestalt grouping principles?
Because we can only be absolutely sure that a principle will adequately predict how elements will be grouped if no other principles can also be applied. For example, at right we see a display in which the proximity grouping principle would suggest that we organize the elements into four columns, while the similarity principle suggests we should perceive five rows. Only one principle can “win” (in this case, most people probably see rows rather than columns).
How is camouflage related to grouping principles?
To camouflage yourself, you have to make your features (that is, the visual elements that are visible to anyone who might observe you) group with the features present in your environment.
How are the Gestalt grouping principles related to texture segmentation?
A texture is really just a collection of many perceptual elements that are similar to each other and arranged fairly close together. Therefore, stating that areas of an image with different textures are segmented from each other (the definition of texture segmentation) is really the same thing as saying that areas of an image in which elements are similar to each other and/or close together group together.
What is the basic idea behind the “perception by committee” metaphor?
The visual world is a complicated place, and no one rule for interpreting the world can possibly do an adequate job. But once we introduce multiple rules, conflicts between interpretations will inevitably arise. Various parts of our visual system act like perceptual committees, considering which rules conflict and which agree in a given situation and eventually arriving at a single interpretation for the scene.
What are ambiguous figures, and how do they relate to the perception by committee metaphor?
What are some of the assumptions that perceptual committees make?
First, the committees must “know” something about physics; for example, understanding that opaque objects block light is a prerequisite for perceiving the illusory edges of the triangle in the Kanisza triangle. Second, the committees assume that we are not viewing a scene from an accidental viewpoint, which would mask the true structure of the objects in the scene.
What is figure–ground assignment?
The process of determining which areas of an image constitute a to-be-recognized object (the “figure”) and which areas form the background (the “ground”).
What is the notion of relatability and why is it important?
Relatability is the notion that line segments on either side of an occluding surface will look like they are part of a single object if they can be connected by a smooth curve that only bends once. This concept is important because it describes the constraints our brains use to fill in edge information that is missing from objects due to occlusion.
What do nonaccidental features tell us about a scene?
What evidence is there that the visual system starts with large objects and then divides them into smaller parts, rather than processing scenes the other way around?
What is the basic idea behind a structural description, and how do structural description theories improve on template theories?
Straightforwardly enough, a structural description describes the structure of an object in a more abstract way than a template. Different theories propose different sets of building blocks with which to create the descriptions, and most structural description theories also propose some way to describe how parts are related to each other. The advantage over templates is that a single structural description can potentially match a large number of slightly different shapes. For example, if an X is described as two oblique lines that cross near their centers, this description will match all the figures at left; however, each would require a different template in a naïve template theory.
