Topic 6: Occipital Lobes Flashcards
Anatomy of Occipital Lobes
- Occipital Lobe is the beginning of visual processing pathways
Medial Surface (certain clear landmarks)
- Parieto-occipital sulcus
- Calcarine Sulcus/Fissure: Contains much of the primary visual cortex & separates upper & lower visual fields
Ventral Surface
- Lingual gyrus: contains V2
- Fusiform gyrus: runs along the bottom of the brain but contains components of V4(colour)
Thick Stripes
In V2. They receive projections from complex cells in V1 involving movement i.e., they process movement.
V5 is involved in the dorsal stream, so it will take its input from the thick stripes in V2.
Contain neurons that are sensitive to the direction and speed of visual motion, as well as the spatial organization of visual features.
Thin Stripes
In V2. The thin stripes process colour information from blobs in V1.
V4 plays a role in processing colour, so it will take its input from the thin stripes in V2
Receive direct input from the colour-sensitive neurons in the blobs of V1. The thin stripes are specialized for processing colour information, and they contain neurons that are sensitive to specific colours, such as red, green, or blue. The thin stripes are also involved in processing the shape and texture of objects, as well as their colour.
Blobs
Represent columnar organization of the cells that play a role in processing colour. In V1, in cortical layers 2 and 3.
- Relays information to thin stripes in V2.
Interblobs
- are the regions of V1 that lie between the blobs.
- contain both simple and complex cells and are specialized for processing form and orientation information, such as the detection of edges, lines, and other features of visual stimuli.
- integrate and analyze the information processed by the blobs and are important for the perception of shape, contrast, and spatial frequency.
- believed to play a role in processing visual features such as orientation, spatial frequency, and motion.
In V1, the inter-blobs are regions of the primary visual cortex that lie between the blobs, which are clusters of cells that are sensitive to color. The inter-blobs contain neurons that are involved in processing visual information related to object recognition and perception, and they are believed to play a role in processing visual features such as orientation, spatial frequency, and motion.
The inter-blobs contain both simple and complex cells, which are specialized neurons that are tuned to respond to specific features of visual stimuli. Simple cells in the inter-blobs are typically sensitive to the orientation and spatial frequency of visual stimuli, and they respond to bars or edges of a specific size, shape, and orientation. These cells are believed to be involved in detecting and encoding basic features of visual stimuli, such as the orientation and contrast of lines and edges.
Complex cells in the inter-blobs are tuned to respond to more complex visual features, such as motion and directionality. These cells integrate input from multiple simple cells and are thought to be involved in processing more complex aspects of visual stimuli, such as the direction and speed of moving objects.
Pale Regions
In V2; they process static information from simple cells in V1 - play a role in building form and shape
Orientation Columns
Found in V1. The orientation columns are specialized groups of neurons that respond to particular orientations of visual stimuli, such as horizontal or vertical lines. The cells within each column are aligned perpendicular to the surface of the cortex and respond maximally to stimuli with a specific orientation, while being less responsive to stimuli with different orientations. Adjacent columns are tuned to different orientations, creating a continuous map of all possible orientations across the visual field.
ocular dominance columns
The ocular dominance columns are another type of neuronal organization found in V1, and are responsible for processing information from the two eyes separately. Each column is dominated by inputs from one eye or the other, and the two sets of columns are organized in an alternating pattern, such that there is a left-eye dominant column followed by a right-eye dominant column, and so on. This arrangement allows for binocular vision and depth perception.
Primary Visual Cortex (V1)
The three main aspects that are processed by the primary visual cortex (VI) are:
- Colour (by blob regions)
- Form, Static (by simple and complex cells in the inter-blobs)
- Dynamic Movement (by neurons in the dorsal stream, specifically in the middle temporal area (MT) or V5)
The processing of color in VI occurs primarily in the blob regions, which contain clusters of neurons that are specialized for color perception. The processing of form and static features, such as orientation and spatial frequency, occurs in the inter-blobs, which contain both simple and complex cells that are sensitive to these features. The processing of dynamic movement, such as motion and directionality, occurs in the dorsal stream, specifically in the MT or V5 region, which contains neurons that are specialized for processing visual motion.
Simple Cells
The orientation of a line will trigger cells to fire.
Complex Cells
These respond to a particular orientation of line that is MOVING
Connections of Visual Cortex
- V1 receives information from the thalamus, in particular, the LGN
- After V2: you have outputs that go out into the ventral, dorsal, and STS streams
Dorsal Stream
The “Where” stream
- Visual guidance of movements
Ventral Stream
The “what stream”
- lines building up to create form
- object perception
superior temporal sulcus (STS) Stream
The superior temporal sulcus (STS) stream is a neural pathway in the brain that processes social and biological information, such as facial expressions, eye gaze, body language, and speech intonation.
- This stream begins in the posterior part of the temporal lobe and extends into the parietal lobe. It is sometimes called the “what” pathway or the ventral stream for social perception.
- thought to play a key role in social cognition and understanding the intentions and emotions of others.
- Movement perception (i.e., identifying if a biological system is doing movement)
- A neural pathway in the brain that is involved in processing complex visual information, particularly social cues and biological motion.
Double Dissociation: “Where” and “What” pathways - the Monkey-Object Task
We see evidence of double dissociation for these “what” and “where” streams;
Where task - Dorsal stream (on the left side of the image): the monkey indicates which tray has the food by using a cylinder. You place the cylinder on the side of the tray where the food is.
- Dorsal damage = difficulty understanding that the location of the cylinder to the tray is marking where the food is; marking where the food is in relation to the cylinder is not something they are able to do.
- Ventral damage = they can do this task
What task - Ventral stream (on the right side of the image): Monkeys find the food based on recognizing the form, they recognize the object and are able to tell where the food is.
- Ventral damage: they cannot distinguish between the sides of the tray, and they cannot identify based on object recognition
- Dorsal damage = they can do this task
Double Dissociation
A double dissociation occurs when two groups of individuals show opposite patterns of performance on two different tasks, indicating that the tasks rely on different neural mechanisms.
For example, imagine that researchers are interested in whether the ability to recognize faces and the ability to recognize objects rely on separate neural systems. To test this, they might study two groups of individuals: one group with impaired face recognition abilities but intact object recognition abilities, and another group with impaired object recognition abilities but intact face recognition abilities. If this pattern of results is consistently observed across different groups of individuals, it would suggest that face recognition and object recognition rely on different neural systems.
A double dissociation is a powerful tool because it provides strong evidence that two cognitive processes or functions are mediated by separate neural systems.
Responsiveness of Cells in Striate & Extra Striate Cortex
Looking at single-cell recording (in image)
- V1 Simple cells are responding to lines in a particular orientation and width.
- V2 We begin to see responsive to some greater complexities
- We begin to see the complexity of what the cells respond to increase as we move through the visual pathway
- PIT = posterior inferior temporal lobe
- AIT = anterior inferior temporal lobe; a single cell will respond to the detail of a hand; there is a lot of information feeding into the cells in this region to allow it to get to this level of complexity
Colour Vision
- Primary job of V4, but distributed throughout occipital cortex
- Plays a role in detection of motion, depth, and position
- Adding colour to illusions will help with object recognition
- Important role in the ventral stream (what is the object)
- Important for the dorsal stream (colour helping to tell where an object is)
Where do we see vidual functions take place beyond the occipital lobe?
- vision-related areas in the brain make up 55% of the total cortex surface area
- Vision is not unitary, not a serial system, it is in parallel and moving back and forth
- Multiple visual regions in temporal, parietal, and frontal lobes (integration of information)
“Vision is not unitary,” it means that visual perception is not a single, unified process, but rather a complex set of processes that involve multiple neural systems and brain regions. Different aspects of visual perception, such as color, motion, depth, and object recognition, are mediated by different neural systems and may involve different regions of the brain.
Lateral cortical cortex (LOC)
- Helps to build our perceptions of objects
- Perceptual constancy for size, location, viewpoint, illumination
- Form-cue invariance: photos, real objects, line drawings
- Understanding that when the retinal images change it is a change in difference, so we change our cognition to understand the depth
- Understanding that a change in illumination does not change the object, just a lighting
- Understanding what an object regardless of the POV
The lateral occipital cortex (LOC) is a region of the brain located in the lateral or side portion of the occipital lobe, at the back of the brain. The LOC is involved in the processing of visual object recognition, particularly for complex objects such as faces and objects with multiple parts. It is also involved in the analysis of object shape, texture, and orientation, and in the integration of visual information across different viewpoints. The LOC is part of the ventral stream or “what” pathway, which is responsible for object recognition and identification. Damage to the LOC can result in deficits in object recognition and perception.
Lateral cortical cortex (LOC)
- Helps to build our perceptions of objects
- Perceptual constancy for size, location, viewpoint, illumination
- Form-cue invariance: photos, real objects, line drawings
- Understanding that when the retinal images change it is a change in difference, so we change our cognition to understand the depth
- Understanding that a change in illumination does not change the object, just a lighting
- Understanding what an object is regardless of our POV
What visual systems (V1, V2, V3, etc) contribute to the Dorsal and Ventral pathways?
Specifically, V1, also known as the primary visual cortex, is the first stage of visual processing in the brain and is responsible for basic features such as orientation and spatial frequency. V2 and V3 are responsible for processing more complex visual features such as color, texture, and motion. V5/MT is responsible for processing motion information.
V4 is specialized for color perception, while the inferior temporal cortex is responsible for object recognition, face recognition, and other complex visual processing tasks.
Five Categories for Vision
Visions for Action: using visuals to plan for action
- Parietal Visual Areas (Dorsal Stream - i.e., planning to reach out and grab something)
- Reaching
- Ducking
- Catching
Action for Vision: moving eyes to get the information we need
- eye scanning (recall, the right hemisphere is dominant for faces, so we focus on the left side of people’s faces so the information can get to the right hemisphere faster)
- eye movements and selective scanning
- Agnosic: eye movements are all over the place, and there is a low pattern of movements
Visual Recognition
- temporal lobes (involved in object recognition)
- object recognition
Visual Space
- parietal and temporal lobes
- spatial location
Visual Attention
- selective attention to specific visual input
- parietal lobes guide movements and temporal lobes help in object recognition
Allocentric
In the context of vision, allocentric refers to a type of spatial representation that is based on the relationship between objects or landmarks in the environment, rather than on the viewer’s own position or perspective.
Actions for Vision
Moving eyes to get the information we need
- eye scanning (recall, the right hemisphere is dominant for faces, so we focus on the left side of people’s faces so the information can get to the right hemisphere faster)
- eye movements and selective scanning
- Looking in the mirror, we focus more on the left side of our face and think we look different than what we look like in a photograph - because we are looking at a different side of your face
In the image:
- Agnosic: eye movements are all over the place, and there is a low pattern of movements (part C)
- In part B, we see more movement for the face
Visual Space
- using vision to help us determine our visual space, and this relies on both the ventral and dorsal streams
- parietal (where things are in space) and temporal lobes are associated with this
- spatial location: relies on two different spatial references
(allocentric, and egocentric)
Monocular Blindness
Monocular blindness, also known as unilateral blindness, is a condition in which individual experiences complete or near-complete vision loss in one eye. The other eye can see normally, and the individual can still perceive light and dark in the affected eye.
- often from damage to eye directly, or the nerve - blocking the eye form sending visual information
- cannot be explained by hemispheric damage (both eyes send information to each side individually)
Bitemporal Hemianopia
Results from lesion to medial region of optic chiasm;
- Hemianopia means complete loss of a visual field
- “Bi” means both temporal fields
- this is indicative of damage in a particular part of the brain; optic chiasm normally knocks out visual processing in these visual fields
- The left visual field falls onto the inner portion of the left eye, and the right visual field falls onto the inner portion of the right eye. The projections on those inner portions of the eye are crossing over at the optic chiasm. Only the inner portions (i.e., the nasal nervers) cross over.
Nasal Hemianopia
Results from the lesion of the lateral region of the optic chiasm
- you will either have left or right nasal hemianopia, very rare to have both
Pemietry Tests
Perimetry tests are used to assess the visual field of a person. These tests measure the extent and quality of an individual’s peripheral vision, which is the part of the visual field outside of the center of gaze.
Optic Chiasm
The optic chiasm is a structure located at the base of the brain where the left and right optic nerves cross over. It is a crucial point in the visual pathway where information from the left and right visual fields is combined and transmitted to the brain for further processing.
The optic nerves carry visual information from the eyes to the brain, with each optic nerve transmitting information from the opposite visual field. At the optic chiasm, some of the nerve fibers cross over to the opposite side of the brain, while others remain on the same side. This results in the left half of the brain processing visual information from the right visual field and vice versa.
Homonymous Hemianopia
The complete loss of a portion of the visual field in both eyes (therefore suggests a cortical issue).
Results from the complete cut of the optic tract (beyond optic chiasm) or complete damage to LGN or V1 in one hemisphere
- in the image, it is a left homonymous hemianopia
Quadrantanopia
Results from lesion to the occipital lobe in one hemisphere
- If in the upper right visual field, the damage is below the calcarine fissure in the left hemisphere
- Does not lose a complete visual field, only a portion, and is consistent of between the eyes.
- Damage in the V1, because V1 can still receive information from the optic chiasm
Scotomas
Often goes unnoticed due to nystagmus;
A scotoma is an area of partial or complete loss of vision within the visual field. It can occur in one or both eyes and can be temporary or permanent.
Scotomas can have various causes, including ocular disorders such as glaucoma, cataracts, age-related macular degeneration, and neurological conditions such as migraine, multiple sclerosis, or brain tumors. Certain medications or toxins can also cause scotomas.
Scotomas can be classified into different types based on their location within the visual field. For example, a central scotoma occurs in the center of the visual field, while a peripheral scotoma occurs in the outer regions of the visual field.
B.K.: V1 Damage & Scotoma
- Right infarct (dead tissue) in the occipital lobe
- Experienced blindsight - perceive motion & location without perceiving content.
- Lost one-quarter of the fovea, poor vision in the upper left quadrant
- Slow facial recognition
- suffered a stroke in the left hemisphere brought on by migraines, and the damage is below the carriage fissure
- right VI
- The main source of blindness is in the central fovea, he cannot look at things straight on
Case V.K.: Parietal Damage
- Bilateral hemorrhages in occipitoparietal regions (dorsal stream)
- Disordered control of gaze (i.e., planning of eye movements), impaired visual attention (dorsal stream damage), & optic ataxia (deficit in visually guided hand movements)
- Can recognize & name objects but cannot accurately reach for objects
- Double dissociation with Case DF
Case DF - Occiptial Damage and Visual Agnosia
- Bilateral damage to LO region & tissue between the parietal & occipital lobes
- Visual form agnosia - inability to recognize line drawings of objects
- Can use visual information to guide movements but not to recognize objects
- carbon monoxide damage
- double dissociation with VK
- Damage to the ventral stream
Interpret
DF (ventral damage)
- issue with the form, cannot tell you whether the objects are the same or different (ventral task)
- can pick up objects at the correct points (dorsal task)
VK (dorsal damage)
Associative Agnosia
The person can form the percept (putting the object together), but they cannot link the percept to knowledge. The damage is later down the ventral stream, which is more in the anterior regions where they cannot link the image to memory.
E.g., in the image, the associative agnosia can copy the image but cannot tell you what it is. When saying “draw an anchor,” they can’t because of there is a lack of knowledge of the object.
Apperceptive Agnosia
- An issue with Perceptual categorization
- Cannot form a percept of the whole; cannot connect the lines
- Can recognize local aspects earlier in the ventral stream
- Issues with LO (i.e., lateral occipital cortical area or V3)
- Damage is early in the ventral stream, in the posterior and inferior temporal region - we know this because they cannot form objects which is early in the processing stream
E.g., in the figure, we see them perceive parts of the images but not the entire image.
Fusiform Face Area (FFA)
A region of the brain located in the fusiform gyrus of the temporal lobe is involved in processing faces. It is a specialized area believed to recognize and differentiate faces from other objects in the visual field.
- configuration of faces (i.e., the eyes on top, then the nose, then the mouth, that’s the configuration it is looking for)
- In the posterior right hemisphere (right hemisphere dominance)
The FFA is part of a larger network of brain regions involved in face processing, including the occipital face area, the superior temporal sulcus, and the amygdala. These regions work together to extract and process visual features of faces, such as facial expressions, gaze direction, and emotional cues.
Inversion Effect
- Larger for faces than houses
- people take longer to determine whether a face is different when it is inverted than other objects
The inversion effect is a phenomenon in which the recognition of faces and other objects is significantly impaired when presented in an inverted or upside-down orientation compared to when presented in their normal upright orientation.
Research has shown that the inversion effect is particularly pronounced for faces, which are processed differently in the brain than other objects. When faces are presented in an inverted orientation, the brain has difficulty processing and integrating the different facial features, impairing facial recognition and identification.
In contrast, the inversion effect is less pronounced for other objects, which are typically processed more holistically and rely less on the integration of individual features.
Role of Experience in Recognition: X-ray Example
Looking at experts in visual information, in this example, we have novices, residents, junior radiologists, and senior radiologists.
If someone becomes an expert at something, is the visual information they are becoming very good at recognizing being recruited to the FFA?
- Senor is better at recognizing abnormalities in x rays - they are better at identifying abnormalities and can quickly recognize when something is wrong
- Novice and resident are better at recognizing normal x rays
Role of Experience in Recognition: Car and Bird Experts Example
Looking at fMRI (brain activation) in two types of experts;
- expert in cars
- expert in birds
Suggests that FFA can become involved in processing other configurations if it deems that other configurations are important for a long period of time. It is not limited to faces.
In this study, they showed people pictures and monitored their brain activity.
- control image: beer
- experimental images: face, car, bird (these are the comparison images, and we look at the activation in comparison to the control)
Both experts looking at a face: we see more FFA activation in comparison to the control for both
Both experts are looking at a car:
- car expert has activation in FFA
- bird expert has no activation in FFA
Both experts are looking at a bird:
- car expert has no activation in FFA
- bird expert has more activation in FFA
Greebles (configural creatures)
When ppl first see the Greebles, they have trouble differentiating between the families. Researchers wanted to examine how well participants could identify if two were the same using the Inversion method and if their FFA was activated, as the participants practiced with them other time.
With practice, both human faces and greeble faces, we see:
- ppl become better at identifying whether faces are the same or different whether they are upright or inverted (the inversion effect becomes smaller the more ppl practice)
- ppl are still better at the upright task than the inverted task
Difference between Greeble novices and Greeble experts
- initially, we see no activation in FFA regions (upon first exposure)
- in greeble experts, we see activation in FFA regions (i.e., FFA is being recruited to identify the Greebles)
Covert Face Recognition
Covert = not asking them to identify who the face is, or tell you who it is - they are only asked to read the name in the bubble
E.g., name reading task, some names in the bubbles match the face some don’t.
- ppl with intact FFA = can read the name in the bubble very quickly when the name matches the face; reaction time increases when the name does not match the face
- ppl with damaged FFA (prosopagnosia) = did the exact same as the intact FFA - they cannot tell you who the face is, but there is still a delay, suggesting implicit knowledge.
