Chapter 4 - Study Questions Flashcards
(10 cards)
1) How is the retina mapped on the striate cortex? What is the cortical magnification factor, and what function does it serve?
Points in the retinal image are represented spatially in the striate cortex. Spatial organization refers to the way stimuli at specific locations in the environment are represented by activity at specific locations in the nervous system.
Cortical magnification is this apportioning to the small fovea of a large area on the cortex, which means that more space is devoted to area of the retina near the fovea.
This extra cortical space allotted provides extra neural processing needed to accomplish tasks such as reading that requires high visual acuity.
*The fact that more space on the cortex translates to better detail vision rather than larger size is an example of the fact that what we perceive doesn’t exactly match the “picture” in the brain.
2) Describe the technique of brain imaging. How has it been used to determine the retinotopic map in humans? How do the results of the brain imaging experiment provide evidence for cortical magnification in the human cortex?
Brain imaging refers to a number of techniques that result in images that show which areas of the brain are active.
Retinotopic map is the electronic map of the retina on the cortex.
Using brain imaging to perform experiments to check where in the brain an stimulus activate, helped determine the retinotopic map in humans because the stimulus activated different areas of the brain.
Brain imaging experiment results provided evidence for cortical maginification in the human cortex because it showed how the stimulus in the fovea activated a larger area in the brain than the stimulus in the peripheral area. This showcases that visual acuity, such as seeing the details of a picture, takes more space in the cortex.
3) Describe location columns and orientation columns. What do we mean when we say that location columns and orientation are “combined”? What is hypercolumn?
The striate cortex is organized into location columns that are perpendicular to the surface of the cortex, so that all of the neurons within location column have their receptive fields at the same location on the retina.
The cortex is organized into orientation columns, with each column containing cells that respond best to a particular orientation.
One location column can have many orientation columns separated by 1mm from each other across the cortex.
A hypercolumn is a location column with all of its orientation columns. It receives information about all possible orientations that fall within a small area of the retina, and it is therefore well suited for processing information from a small area in the visual field.
4) How do feature detectors respond to a scene? Start by describing how a tree trunk is represented in the cortex and then expand your view to the whole forest scene.
The continuous tree trunk is represented by the firing of neurons in a number of separated columns in the cortex. Each of these location columns contains a complete set of orientation columns.
The continuous tree trunk is represented by the firing of neurons in a number of separated columns in the cortex.
Working together, these columns cover the entire visual field, an effect called tiling. The visual field is served by adjacent ( and often overlapping) location columns.
5) What does it mean to say that the cortical representation of a scene does not have to resemble the scene, but just has to contain information that represents the scene?
The cortical representation of a stimulus does not have to resemble the stimulus, it just has to contain information that represents the stimulus; The representation of the tree in the visual cortex is contained in the firings of neurons in separate cortical columns. At some point in the cortex, the information in these separated columns must be combined to create our perception of the tree.
1) How has ablation been used to demonstrate the existence of the ventral and dorsal processing streams? What is the function of these streams?
Ablation refers to the destruction or removal of tissue in the nervous system. When part of the temporal lobe of a Monkey was removed in an experiment, behavioural testing showed that it was difficult for monkeys to discriminate an object. This result indicates that the pathway that reaches the temporal lobe is responsible for determining an object’s identity.
The pathway leading from the striate cortex to the temporal lobe is called the ventral pathway or the what pathway.
In the same experiment, other monkeys had their parietal lobes removed, and they had difficulty solving a landmark problem ( locating an objet). This result indicates that the pathway that leads to the parietal lobe is responsible for determining an object’s location.
The pathway leading from the striate cortex to the parietal lobe is called the where or how pathway, also called the dorsal pathway.
The function of the ventral pathway is to help an individual recognize objects and the function of the dorsal pathway is to locate objects and also regulate actions in regards to those objects.
2) How has neuropsychology been used to show that one of the functions of the dorsal stream is to process information about coordinating vision and action? How do the results of a behavioural experiment support the idea of two primary streams in people without brain damage?
Neuropsychology is the study of the behavioural effects of brain damage in humans.
One of the basic principles of neuropsychology is that we can understand the effects of brain damage by determining double dissociations, which involve two people; In one person, damage to one area of the brain causes function A to be absent while function B is present; in the other person, damage to another area of the brain causes function B to be absent while function A is present.
Double dissociation enable us to conclude that recognizing objects and locating objects operate independently of each other.
The dorsal pathway is the how pathway, or the action pathway, because it determines how a person carries out an action.
Results from experiments with people without brain damage support the idea that perception and action are served by different mechanism.
3) What is the evidence that there are modules for faces, places, and bodies? What is the evidence that stimuli like faces, and places also activate a wide area of the cortex?
Brain imaging has been used to identify areas of the human brain that contains neurons that respond best to faces, while others respond best to scenes and human bodies.
Another evidence of an area specialized for the perception of faces is that damage to the temporal lobe – prosopagnosia – causes difficulty recognizing the faces of familiar people.
Other specialized areas in the temporal cortex have been identified:
The parahippocampal place area (PPA) is activated by pictures depicting indoor and outdoor scenes.
The other specialized area, the extrastriate body area (EBA), is activated by pictures of bodies and parts of bodies (but not by faces).
In brain imagines, objects such as faces may cause a large focus of activity in an area specialized for faces, such as the FFA, but they also cause additional activity that is distributed over a wide area of the cortex.
We can summarize what we know about organization in the visual system by noting that the visual system is organized both spatially and functionally. The spatial map is retinotopic, which means that points on the LGN or cortex correspond to specific points on the retina or in a scene.But spatial organization becomes weaker as we move to higher cortical areas, because in areas such as the IT cortex, neurons have very large receptive fields that extend over large areas of the retina and visual field. Most of the face neurons respond when the face is imaged on the fovea, which makes sense, because when we want to identify a face we usually look directly at it.
The visual system is organized functionally, with different streams for what and where/how and with specific cortical areas that are rich in neurons that respond to specific types of stimuli such as faces, places and bodies. It is no coincidence that the stimuli that have specific areas in the brain are the ones we see all the time ( faces and bodies) and that are important for helping us find our way through the environment ( place neurons).
5) Describe the possible role of experience-dependent plasticity in determining how neurons and brain areas respond to a) horizontal, vertical, and slanted lines; and b) Greebles.
There is evidence that the oblique effect occurs because there are more cortical neurons that respond to horizontal and vertical orientations, and it is no coincidence that horizontals and verticals occur more frequently in the environment than slanted orientations.
The participants trained in “ Greeble” recognition had become “ Greeble experts” and were able to rapidly identify many different Greebles by the names they had learned during the training.
Location of Dorsal Stream and Ventral Stream
