Chapter 4- Sensation and Perception: Exam 2

Ungerleider and Mishkin presented monkeys with two tasks:

(1) an object discrimination problem and (2) a landmark discrimination problem.

Robert Dougherty and coworkers used brain imaging to demonstrate cortical magnification in the human visual cortex. The stimulus display viewed by the observer, who was in an fMRI scanner. The observer looked directly at the center of the screen so the dot at the center fell on the fovea. During the experiment, the stimulus light was presented in two places:

(1) near the center (red area), which illuminated a small area near the fovea; and (2) farther from the center (blue area), which illuminated an area in the peripheral retina. (Figure 4.4 page 76) - This activation illustrates cortical magnification because stimulation of the small area near the fovea activated a greater area on the cortex (red) than stimulation of the larger area in the periphery (blue).

Although there is good evidence that the ventral and dorsal pathways serve different functions, it is important to note that:

(1) the pathways are not totally separated but have connections between them and (2) signals flow not only "up" the pathway toward the parietal and temporal lobes but "back" as well.

This research on receptive fields showed that:

(1) the response properties of an individual neuron are determined by inputs from many other neurons and (2) neurons at higher levels of the visual system respond to more complex stimuli

Evidence supporting the idea that the dorsal stream is involved in how to direct action is provided by the discovery of neurons in the parietal cortex that respond:

(1) when a monkey looks at a object and (2) when it reaches toward the object - But the most dramatic evidence supporting the idea of a dorsal 'how' or 'action' stream comes from Neuropsychology- the study of the behavioral effects of brain damage in humans.

The cortical representation of a stimulus does not have to:

- 'resemble' the stimulus; it just has to contain information that 'represents' the stimulus

Milner and Goodale suggested that the ventral pathway should still be called the:

- 'what' pathway, as Ungerleider and Mishkin suggested, but that a better description of the dorsal pathway would be the 'How' Pathway, or the Action Pathway, because it determines 'how' a person carries out an 'action'.

What technique did Ungerleider and Mishkin use?

- Ablation (also called lesioning) to better understand the functional organization of the brain. - Ablation refers to the destruction or removal of tissue in the nervous system.

Demonstration: Cortical Magnification of Your Finger (pg. 76)

- An important thing to note about this demonstration is that even though the image of your finger on the fovea takes up about the same space on the cortex as the image of your hand on the peripheral retina, you don't perceive your finger as being as large as your hand. Instead, you see the 'details' of your finger far better than you can see the details on your hand. - That more space on the cortex translates into better detail vision rather than larger size is an example of the fact that what we perceive doesn't exactly match the "picture" in our brain.

Fusiform Face Area (FFA) function:

- Basic face processing

What causes improvement in recognizing faces over time?

- Biological maturation is clearly involved, as we saw when we described the connection between improvement of visual acuity and the development of rod and cone receptors. - On a longer time scale, there is evidence that some aspects of face recognition depend on the emergence of the fusiform face area (FFA), which is not fully developed until adolescence.

What has brain imaging been used to identify?

- Brain imaging has been used to identify areas of the human brain that contain neurons that respond best to faces.

"Neural Maps"

- But once the house, the tree, and the car have been transformed into electrical signals, the signals created by each object then become organized in the form of "neural maps", so that objects that create images near each other on the retina are represented by neural signals that are near each other in the cortex

What is the "backward" flow of information called and what does it provide?

- Called 'feedback' - Provides information from higher centers that can influence the signals flowing into the system. This feedback is one of the mechanisms behind top- down processing

How has the cortical magnification been determined in the human cortex?

- Cortical magnification has been determined in the human cortex using a technique called brain imaging, which makes it possible to create pictures of the brain's activity.

Milner and Goodale used the method of determining double dissociations to study D.F. A woman who suffered damage to her ventral pathway from carbon monoxide poisoning.

- D.F. performed poorly in the 'static orientation- matching task' but did well as soon as 'action' was involved. - Milner and Goodale interpreted D.F.'s behavior as showing that there's one mechanism for judging orientation and another for coordinating vision and action.

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.

Amygdala (A) function:

- Emotional reactions (face expressions and observer's emotional reactions) - Familiarity (familiar faces cause more activation in amygdala and other areas associated with emotions)

Frontal Lobe (FL) function:

- Evaluation of attractiveness

In addition to biological maturation, what else plays a role in perceptual development?

- Experience in perceiving the environment also plays a role in perceptual development. - One line of evidence supporting the role of experience is the research on 'experience- dependent plasticity'

The fact that experience with the environment can shape the nervous system is the basis of the:

- Expertise Hypothesis, which proposes that our proficiency in perceiving certain things can be explained by changes in the brain caused by long exposure, practice, or training.

What three areas fit our definition of module as an area specialized for processing information about a specific type of stimulus?

- FFA, PPA, and EBA.

What does faces activate?

- Faces activate FFA, which has been called a module for faces, and faces also activate other areas as well, which is evidence for distributed representation.

Are faces multidimensional?

- Faces are multidimensional- they cause many different reactions and there different reactions are associated with activity in many different places in the brain

Superior Temporal Sulcus (STS) function:

- Gaze direction - Mouth movements - General face movements

Spatial Organization Definition:

- How different locations in the environment and on the retina are represented by activity at specific locations in the visual cortex

Hubel and Wiesel:

- Hubel and Wiesel carried out a series of experiments in which they recorded from neurons they encountered as they lowered electrodes into the cortex. When they positioned an electrode perpendicular to the surface of a cat's cortex, they found that every neuron they encountered had its receptive field at about the same location on the retina. (Figure 4.6 on page 76)

Results from Hubel and Wiesel's experiment:

- Hubel and Wiesel concluded that the striate cortex is organized into Location Columns that are perpendicular to the surface of the cortex, so that all of the neurons within a location column have they receptive fields at the same location on the retina.

A location column with all of its orientation columns was called a:

- Hypercolumn by Hubel and Wiesel - A hypercolumn receives information about all possible orientations that fall within a small area of the retina; it is therefore well suited for processing information from a small area in the visual field.

magnetic resonance imaging (MRI) Definition:

- In the 1800s, a technique called magnetic resonance imaging (MRI) made is possible to create images of structures within the brain - Since then, MRI has become a standard technique for detecting tumors and other brain abnormalities.

Increases and decreases in fMRI results:

- Increases or decreases in brain activity associated with cognitive activity are indicated by colors, with specific colors indicating the amount of activation - Each small square represents a voxels, and the colors indicate whether brain activity increased or decreased in the each voxel. - Red and yellow indicate increases in brain activity; blue and green indicate decreases. (Figure 4.3 page 75)

The mind- body problem goes beyond asking how physiological responses 'correlate' with perception.

- It asks how physiological processes 'cause' our experience. - The mind- body problem is asking how the flow of sodium and potassium ions across membranes that creates nerve impulses becomes 'transformed' into the experience we have when we see a friend's face or when we experience the color of a red rose. - Just showing that a neuron fires to a face or the color red doesn't answer the question of how the firing 'creates' the experience of seeing a face or perceiving the color red.

When Bernita asks how hot and cold, colors, sounds, fragrances, and tastes can be explained by electrical impulses, she is asking about the:

- Mind- Body Problem. - physical processes like nerve impulses (the body part of the problem) become transformed into the richness of perceptual experience (the mind part of the problem)

The idea that there are pathways that serve different functions leads us to:

- Modularity, the idea that specific areas of the cortex are specialized to respond to specific types of stimuli. - Areas that are specialized to specific types of stimuli areas are called Modules for processing information about these stimuli. - For example, there is a great deal of evidence for an area that is rich in neurons that respond to faces.

In addition to location and orientation columns, Hubel and Wiesel also described:

- Ocular Dominance Columns. - Most neurons respond better to one eye than to the other. This preferential response to one eye is called Ocular Dominance, and neurons with the same ocular dominance are organized into ocular dominance columns in the cortex. - This means that each neurons encountered along a perpendicular electrode track responds best to either the left eye or the right eye. There are two ocular dominance columns within each hypercolumn, one for the left eye and one for the right.

How is ablation performed on an animals brain?

- Once the animal's performance on a task has been measured, a particular area of the brain is ablated (removed or destroyed), either by surgery or by injecting a chemical that destroys tissue near the place where it is injected. - Ideally, one particular area is removed and the rest of the brain remains intact. - After ablation, the monkey is retested to determine how performance has been affected by the ablation.

When does one type of functional organization occur? Who was one of the first researchers to carry out evidence on this?

- One type of functional organization occurs when neurons that serve similar functions are connected together into "streams" or pathways. - Some of the first research on these pathways was carried out by Leslie Ungerleider and Mortimer Mishkin, who presented evidence for two streams serving different functions that transmit information from the striate cortex to other areas of the brain.

Additional evidence of an area specialized for the perception of faces is that damage to the temporal lobe causes:

- Prosopagnosia- difficulty recognizing the faces of familiar people. - Even very familiar faces are affected, so people with prosopagnosia may not be able to recognize close friends or family members- or even their own reflection in the mirror- although they can easily identify such people as soon as they hear them speak.

Representing spatial layout:

- Retinotopic map-> preserving the spatial layout of a stimulus - V1 (primary visual cortex) shows a retinotopic map

What pathways do some researchers refer to the dorsal stream as?

- Some researchers call the dorsal stream the 'where' pathway, and some call it the 'how' or 'action' pathway.

Two other specialized areas in the temporal cortex have been identified:

- The Parahippocampal Place Area (PPA) is activated by pictures depicting indoor and outdoor scenes (Figure 4.20a on page 84). Apparently what is important for this area is information about spatial layout, because increased activation occurs both to empty rooms and to rooms that are completely furnished. - The other specialized area, the Extrastriate Body Area (EBA), is activated by pictures of bodies and parts of bodies (but not by faces) (Figures 4.20b on page 84)

Cortical Magnification Definition: Cortical Magnification Factor Definition:

- The apportioning of a large area on the cortex to the small fovea is called Cortical Magnification. The size of this magnification is called the cortical magnification factor. (Figure 4.2 on page 74)

The extra cortical space allotted to letters and words:

- The extra cortical space allotted to letters and words at which the person is looking provides the extra neural processing needed to accomplish tasks such as reading that require high visual acuity.

What does the fMRI apparatus determine?

- The fMRI apparatus determines the relative activity of various areas of the brain by detecting changes in the magnetic response of the hemoglobin.

What is the goal of a brain ablation experiment?

- The goal of a brain ablation experiment is to determine the function of a particular area of the brain. - First, an animal's ability to carry out a specific task is determined by behavioral testing. Most ablation experiments have used monkeys because of the similarity of their visual system to that of humans and because monkeys can be trained in ways that enable researchers to determine perceptual capacities such as acuity, color vision, depth perception, and object perception.

What is the measurement of blood flow during an fMRI based on?

- The measurement of blood flow is based on the fact that hemoglobin, which carries oxygen in the blood, contains a ferrous (iron) molecule and therefore has magnetic properties. - If a magnetic field is presented to the brain, the hemoglobin molecules line up, like tiny magnets. Areas of the brain that are more active consume more oxygen, so the hemoglobin molecules lose some of the oxygen they are transporting, which makes them more magnetic and increases their response to the magnetic field.

Why is the need for organization important in the visual system?

- The need for organization is especially important in the visual system because of the tasks the visual system faces. - One task is to process information about various characteristics of objects, such as size, shape, orientation, color, movement, and location in space. Another task is to process information about different types of objects such as trees, faces, people, furniture, and animals.

What does this 1-mm dimension for location columns mean?

- This 1-mm dimension for location columns means that one location column is large enough to contain orientation columns that cover all possible orientations. - Location columns can serve one location on the retina (all the neurons in the column have their receptive fields at about the same place on the retina) AND contains neurons that respond to all possible orientations.

You may think that all of these connections between electrical signals and perception provide a solution to the mind- body problem.

- This is not however, the case because as impressive as these connections are, they are all just 'correlations'- demonstrations of 'relationships' between neural firing and perception.

Retinotopic Map Definition:

- This organized spatial map means that two points that are close together on an object and on the retina will activate neurons that are close together in the brain

How to begin describing neural maps:

- To begin describing neural maps, let's describe how points in the retinal image are represented 'spatially' in the striate cortex (area V1). - We determine this by stimulating various places on the retina and noting where neurons fire in the cortex. (Figure 4.1 on page 74)

The 'what' and 'where' pathways are also called the:

- Ventral Pathway (what) and the Dorsal Pathway (where), because the lower part of the brain, where the temporal lobe is located, is the ventral part of the brain, and the upper part of the brain, where is parietal lobe is located, is the dorsal part of the brain.

What does the term 'ventral' refer to?

- Ventral is the opposite of dorsal; hence it refers to the lower part of the brain.

What are voxels?

- Voxels are not brain structures, but are simply small units of analysis created by the fMRI scanner. - One way to think about voxels is that they are like the small square pixels that make up digital photographs or the image on your computer screen, but because the brain is three- dimensional, voxels are small cubes rather than small squares.

How do you determine the retinotopic map on the brain?

- We determine the retinotopic map on the brain by measuring activity near the surface of the cortex.

What cortical magnification means when you look at a scene is that:

- What cortical magnification means when you look at a scene is that information about the part of the scene you are looking at takes up a larger space in your cortex than an area of equal size that is off to the side.

Can MRI's indicate neural activity?

- While this technique is excellent for revealing brain structures, it doesn't indicate neural activity

Can someone have no hippocampus and still recognize an object?

- Yes, you can still recognize objects with no hippocampus - the hippocampus is responsible for remembering

Nancy Kanwisher and coworkers used fMRI to determine:

- brain activity in the response to pictures of faces and other objects, such as household objects, houses, and hands. When they subtracted the response to the other objects from the response to the faces, Kanwisher found that activity remained in an area they called the Fusiform Face Area (FFA). - Kanwisher's results have shown that the FFA is specialized to respond to faces.

The beginning of the visual system- in the eye:

- describes how perception is affected by the eye's focusing system and by properties of the rod and cone receptors. (this is in ch. 2) - We saw how dark adaptation, the increase in sensitivity that occurs as we spend time in the dark, can be explained by a chemical process (pigment regeneration), and how visual sensitivity and detail vision can be explained by considering how the receptors are connected to other neurons (convergence)

How is the brain divided during an fMRI?

- for the purposes of measurement, the brain is divided into voxels, which are small cube- shaped areas of the brain about 2 or 3 mm on a side.

The ventral and dorsal streams are established by two different types of:

- ganglion cells in the retina, which transmit signals to different layers of the LGN. - the cortical ventral and dorsal streams can actually be traced back to the retina and LGN

Functional Magnetic Resonance Imaging (fMRI) Definition:

- has enabled researchers to determine how various types of cognition activate different areas of the brain - fMRI takes advantage of the fact that blood flow increases in areas of the brain that are activated.

Occipital Cortex function:

- initial processing

Where is the Fusiform Face Area (FFA) located?

- located in the fusiform gyrus on the underside of the brain directly below the IT cortex.

As Hubel and Wiesel lowered their electrodes along perpendicular tracks, they noted:

- not only that the neurons along this track had receptive fields with the same 'location' on the retina, but that these neurons all preferred stimuli with the same 'orientation' - Based on this result, Hubel and Wiesel concluded that the cortex is also organized into Orientation Columns, with each column containing cells that respond best to a particular orientation.

Distributed Representation:

- occurs when a stimulus causes neural activity in a number of different areas of the brain, so the activity is 'distributed' across the brain.

In our normal daily behavior, we aren't aware of two visual processing streams,

- one for 'what' and the other for 'how', because they work together seamlessly as we perceive objects and take actions toward them.

The discovery of two pathways in the cortex led some researchers to look back at the retina and the lateral geniculate nucleus (LGN). What were the two pathways?

- one for identifying objects (what) and one for locating objects (where)

What MTL structures are important for memory?

- parahippocampal cortex, the entorhinal cortex, and the hippocampus

In the ablation part of Ungerleider and Mishkin's experiment,

- part of the temporal lobe was removed in some monkeys. - After ablation, behavioral testing showed that the object discrimination problem was very difficult for these monkeys. This result indicates that the pathway that reaches the temporal lobes is responsible for determining an object's 'identity'. - Ungerleider and Mishkin there called the pathway leading from the striate cortex to the temporal love the What Pathway.

Hubel and Wiesel also showed that adjacent orientation columns have cells with slightly different:

- preferred orientations. - When they moved an electrode through the cortex obliquely (not perpendicular to the surface), so that the electrode cut across orientation columns, they found that the neurons' preferred orientations changed in an orderly fashion, so a column of cells that respond best to 90 degrees is right next to the column of cells that respond best to 85 degrees.

We can take this idea of widespread activity a step further by considering that the processes we have been describing not create perceptions, but they also:

- provide information that is stored in our memory so we can remember perceptual experiences later. - This link between perception and memory has been studied in a number of recent experiments that have measured responding in single neurons in the human Hippocampus, an area associated with forming and storing memories.

What does the term 'dorsal' refer to?

- refers to the back or the upper surface of an organism - Kind of like the dorsal fin of a shark or dolphin is the fin on the back that sticks out of water

What did David Milner and Melvyn Goodale suggest about the idea of ventral and dorsal streams?

- suggested that the dorsal stream does more than just indicate where an object is. Milner and Goodale propose that the dorsal stream is for taking action, such as picking up an object. Taking this action would involve knowing the location of the object, consistent with the idea of 'where', but it goes beyond 'where' to involve a physical interaction with the object. - According to this idea, the dorsal stream provides information about 'how' to direct action with regard to a stimulus.

What is the hippocampus crucial for?

- the formation of long- term memories

It is important to note that although there is good evidence that experience can influence the types of stimuli to which a neuron responds,

- the role of experience in establishing the FFA as a module for faces is controversial. Some researchers agree with Gauthier that experience is important for establishing the FFA as a module for faces; others argue that the FFA's role as a face area is based on built- in wiring that doesn't depend on experience.

Hubel and Wiesel also found that as they moved their electrode 1 millimeter across the cortex,

- their electrode passed through orientation columns that represented the entire range of orientations. - Interestingly enough, this 1-mm dimension is the size of one location column.

Other monkeys had their partial lobes removed during ablation of Ungerleider and Mishkin's experiment,

- they had difficulty solving the landmark discrimination problem. - This result indicates that the pathway that leads to the parietal lobe is responsible for determining an object's 'location'. - Ungerleider and Mishkin there called the pathway leading from the striate cortex to the parietal lobe the Where Pathway.

Each circle or ellipse in the scene represents an area that sends information to one location column. Working together, these columns cover the entire visual field, an effect called:

- tiling. - Just as the wall can be covered by adjacent tiles, the visual field is served by adjacent (and often overlapping) location columns - Think of the football field analogy for optic nerve fiber receptive fields on page 56. Each spectator was observing a small area of the field. In this example, the spectators were Tiling the football field.