PSY 315 Visual Perception
Contralateral Processing
Opposite side. For the left side of the brain that wants right visual field information, the right visual field information from the RIGHT eye will cross CONTRALATERAL to the left side of the brain. For the right side of the brain that wants left visual field information, the left visual field information from the LEFT eye will cross CONTRALATERAL to the right side of the brain. It will cross the optic chiasm.
Lateral Geniculate Nucleus (LGN)
Our input from the retina is mapped and organized in a specific way, and is continued into the LGN. There is retinotopic mapping and organization. It is a highly organized system of processing your sensory world. When an individual looks at a cup and saucer, different parts the cup and saucer will go into different parts of the retina. Each part of the retina is in charge of a different part due to the organization. This organization is maintained when going from the retina to the LGN, and still maintained when going from the LGN to the primary visual cortex (V1).
Apperceptive Agnosia
Patient DF. Able to draw objects from their memory (ie. being asked to draw an apple and a book). But cannot recognize what they drew.
Apperceptive Agnosia
Patient DF. Able to reach for objects with an appropriate grasp. But they cannot estimate size, orientation, or copy drawings.
Apperceptive Agnosia
Patient DF. Cannot recognize objects. Faced carbon monoxide poisoning and had damage in the occipital lobe. Their vision is all in lines and dots. They can detect orientation. They can interact with things, but they don't know what they are interacting with and what that object is.
Akinetopsia
Patient GL. Inability to see motion. This is due to damage in V5 which is mainly associated with motion. When she is staring at something, objects that are supposedly moving will either vanish or appear frozen. The next second they may have moved right infront of her. Example: Standing infront of a moving train. It is modality specific. She can still sense motion through her other senses, she just cannot see motion.
Magnocellular Cells
Receives information about periphery, light intensity, and motion. The neurons are receiving information / input only from rods, which are important for the perception of motion. They are only found in 2 layers. There is organization and mapping of cells.
Parvocellular Cells
Receives information from the cones about visual acuity and colour. They are found in 4 layers.
Extrastriate Body Area (EBA)
Responds to all things body parts (not faces, but our body parts). Specializes in responding to body parts. Found that the extrastriate body area (EBA) became very active when looking at body-like parts (ie. an arm, a stick figure). However, in non-body images such as a distorted stick figure or a face, there was no activity and no response in the extrastriate body area (EBA).
Ipsilateral Processing
Same side. For the left side of brain that wants right visual field information, the RIGHT visual field in the LEFT eye will STAY ipsilateral on the same side. For the right side of the brain that wants left visual field information, the LEFT visual field in the RIGHT eye will STAY ipsilateral on the same side.
Optic Radiation
The "fanning out" or "radiating" of axons from LGN connecting into the occpital lobe for primary visual cortex processing (V1). Axons are coming from the lateral geniculate nucleus (LGN) and then sent to occipital lobe.
Dorsal Stream
The "how" pathway. Deals with how you interact with what you are looking at. How you interact with your environment visually. Example: If I wanted to grab a water bottle vs a glasses case, we don't have to consciously see how to grasp an item or how far we need to reach. Parietal lobe.
Ventral Stream
The "what" pathway. Identifies and recognizes objects. Leads to your conscious perception of what you are looking at. Example: this stream is what lets you know you are looking at a water bottle. Temporal lobe.
Dorsal and Ventral Stream
The 2 streams (dorsal and ventral) receive very specific visual information from the occipital lobe that is used for a specific function.
Convergence of Receptive Fields
The 4 LGN cells then send their receptive fields to combine to form the receptive field of one single V1 cell. All the LGN cells converge their information and create a larger receptive field. All the information and all the receptive fields from the ganglion cells and the LGN cells are in the single V1 cell. There is a larger receptive field as you move further downstream.
Optic Nerve
The LEFT side of the brain only wants the RIGHT visual field information from BOTH eyes. The RIGHT side of the brain only wants the LEFT visual field information from BOTH eyes. This causes ipsilateral and contralateral processing.
Brain Allocation for Fovea Input
The amount of area allocated is due to the DENSITY of receptors and the IMPORTANCE of those receptors.
Primary Visual Cortex (V1) / Striate Cortex
The area where the LGN synapse (connects) to the occipital lobe. There are 3 cortical areas.
Primary Cortex
The first area that receives visual information from the lateral geniculate nucleus (LGN). It is the most primitive processing and the most upstream.
Damage
The further downstream that you have damage, the more precise damage you will have of executive visual functions because more visual processing will have already occurred.
Ventral / Dorsal Stream Processing
The grasp of the bar should be winder for the bar that looks bigger. However people were not tricked by the illusion even though the bars looked different, but people's fingers didn't change.
Visual Agnosia
The inability to recognize objects. Visual perception (they can see it) and general intellectual function is normal. Video example.
Optic Tract
The left optic tract is now carrying only RIGHT visual field information from BOTH eyes. The right optic tract is now carrying only LEFT visual field information from BOTH eyes.
Tertiary Cortices / Associate Cortices
The most downstream and complex. There is multimodal processing. They don't respond to simple aspects, it is multiple modalities together. There is a neuron that will process sound, vision, and smell.
Lateral Geniculate Nucleus (LGN)
The nucleus in the thalamus that only processes visual input. Input from the optic tract will be sent to different stations that are in charge of different specializations. ie. one station for colour, for motion, for orientation, etc. The LGN breaks everything down into smaller sections to process. Axons passing through the LGN will then go to the occipital lobe after.
Retinotopic Mapping
The retina is organized such that there is mapping that is maintained throughout visual processing. There are parts of the retina that are in charge of seeing certain parts of the visual world, and other parts of the retina see other parts of the visual world. This is all organized and mapped out.
Seizures
The seizure begins in one hemisphere, then crosses the corpus callosum into the other hemisphere. While it crosses the corpus callosum, the pathway gets burned in so seizures become more severe and more frequent.
Commissurotomy
The surgery that is performed to help with seizure disorder. They cut the entire corpus callosum down in the middle. That is the only way that allows the 2 hemispheres to communicate with each other so now the 2 hemispheres cannot coordinate and communicate.
Face Areas
There are 2 face areas in the temporal lobe that are dedicated to different ATTRIBUTES of a face. 1. Inferotemporal (IT) 2. Fusiform Face Area (FFA)
LGN Layers
There are 6 distinct layers in the LGN. The LGN will take in the information from the retina and process it in specific layers. The layers are different for each eye. Each eye has its specific layers that are in charge of processing different information. 3 layers (2, 3, 5) are ipsilateral (same). 3 layers (1, 4, 6) are contralateral (opposite).
Tertiary Cortices / Associate Cortices
There are cells that respond to multi-modalities. Example: Responding to the sound of a peanut, the smell of a peanut, the taste of a peanut (very specific). As you move downstream through the cortical areas, visual information is first being fractionated and taken apart, then are put back together with other modalities, experiences, and memories.
Convergence of Receptive Fields
There are different neighbouring ganglion cells that each see a different part of the visual world. These ganglion cells make up the optic nerve. There are receptive fields of many ganglion cells. The 16 ganglion cells then combine and converge to form the receptive field of 4 single LGN cells. Each different type of ganglion cell converges to a single LGN cell. There is a convergence of information. Each single LGN cell is the product of 4 ganglion cells, so it contains all of its receptive fields and just gets larger and converges its information. The LGN cell is an accumulation of the receptive fields of the ganglion cells.
Simple Cells
There is a very simple requirement in order for a neuron to fire. A simple will only respond in a couple of ways (baseline, rapidly, no response). There will be firing if light is oriented in a particular direction. 1. At baseline response, neurons will fire at a baseline rate. Even if they are not being stimulated, they won't stop and will still fire at the baseline rate. 2. If a light is being shown horizontally, it will cause a strong response and rapid firing rate. 3. If a light is being shown at a specific angle, there will be no response, it will inhibit the neuron.
Functional Modularity
There was very rapid firing of action potentials when there was a combination of a circle and a line, and also the combination of a square and a line. Whereas if it was just a line or just a circle, the action potential was not as high. This shows that there is a lot more specificity as you move more downstream out of the occipital lobe to the temporal lobe through into ventral stream.
Associative Agnosia
They can extract information about the general shape, and can sometimes make a close guess. They are seeing the whole picture a lot more than someone with apperceptive agnosia. They can draw objects and see them as a whole, they just can't name them. They can describe them.
Occipital Lobe
V1 processes motion, shape, and colour information. V5 is almost entirely dedicated to processing motion, so if there was damage to V5 they may not be able to detect motion.
Selective Adaptation
When a neuron adapts, our perception becomes less sensitive only to some orientations (that the neurons have adopted). Tested this by showing vertical black and white lines to find the difference threshold in order for a stimulus to be detected. Looking at the threshold contrast. People will stare at the stimulus for a long period of time so that the neuron adapts. They will then stare at it again after. Found that they will need more contrast in order to perceive the stimulus, because their perception is less sensitive now that they have adapted.
Hypercolumns
When ocular dominance is maintained throughout. There are separate columns that either specialize in input for the left eye or input for the right eye. And specifically within each of the 2 columns, there are HYPERCOLUMNS, which are specific columns that are in charge of a very specific visual input at different orientations. Example: There is a hypercolumn in both the left eye and in the right eye that is dedicated to looking at straight lines. It isn't until later downstream that these columns begin to combine together.
Capgras Syndrome
When someone can look at a face and know it is a familiar face and say it looks JUST LIKE their mother and looks identical, but says THEY ARE NOT their mother.
Parallel Processing
When there is different processing occurring at the same time. The information coming into your eye is being processed in different paths. Each pathway processing has a different function and goal. 1. Geniculostriate processing 2. Tectopulvinar Processing 3. Retino-hypothalamic Processing
Developmental Window
Where the brain is being exposed to specific stimuli in the environment during specific windows of time when the brain is still developing. When you are exposed to these stimuli when your brain is still making all these connections.
Hyper-Complex Cell
Will fire if there is light at a specific angle that is moving in a particular direction, and is STOPPED at a particular point.
Parallel Processing
You are completely unaware of tectopulvinar processing and retino-hypothalamic processing. We are only consciously aware of geniculostriate processing.
Brain Allocation for Fovea Input
Your brain will allocate area for processing depending on how important that area of processing is, and NOT because of the size of that area. Example: Your lips, tongue, and fingers are densely populated with many somatic sensory receptors. So even though it is a small part of the body, it is important and hence has a large area of the cortex dedicated to processing that input.
Selective Adaptation
if there is a stimulus that is rapidly firing and it keeps going, eventually the neuron will tire out and it will decrease its firing rate (still responds but less vigorously). There will be less firing if the stimulus keeps going.
Parallel Pathways
1. Geniculostriate System 2. Tectopulvinar System 3. Retino-hypothalamic System
3 Cortical Areas
1. Primary cortex 2. Secondary cortices 3. Tertiary / Associate Cortices
Associative Agnosia
Damage in the temporal lobes. They can "recognize" objects at the perceptual level. They are able to see the whole picture, they can pick things out or copy objects, but they cannot name them.
Prosopagnosia
Face Blindness. You can identify attributes of a face, but they cannot recognize familiar faces. There isn't one face that will look more familiar than another. This is due to damage in the temporal lobe in the "face areas" such as in the FFA.
Ventral / Dorsal Stream Processing
Idea of illusion at depth when grasping bars. Shows that all visual areas are organized into 2 pathways, and are treated differently in the brain. 1. Ventral pathway was fooled by the illusion. 2. Dorsal pathway was not fooled and instead guided the hand to help you interact with the bars.
Functional Modularity
In the temporal lobe, you have neurons that become geared to very complex and specific stimuli. Because it is now more downstream, there are very specific requirements in order for a neuron to fire.
Ventral Stream Injuries
Injuries to "what" pathway. 1. Agnosia 2. Visual agnosia
Agnosia
Not knowing, having no knowledge. There is something missing in your ability to process a specific stream.
Blind Sight
They cannot identify or describe the object but can detect motion. He can see individual functions. There is a disconnection between actually being visually aware, and responding to that visual information.
Process of Visual Processing
1. Both eyes have both visual fields. 2. The optic nerve carries both left and right visual field for both eyes into the brain. Both visual fields from one eye. 3. Crosses the optic chiasm where axons will cross ipsilateral or contralateral. 4. Optic tract. One visual field from both eyes. 5. Lateral Geniculate Nucleus (LGN). 6. Optic radiation. 7. Occipital lobe.
Parallel Processing
1. Geniculostriate processing is the pathway that leads to conscious visual perception and visual recognition. 2. Tectopulvinar processing is the pathway for reflex processing. It comes from the eyes, goes through the superior colliculi in the tectum, and into the pulvinar nucleus in the thalamus. 3. Retino-hypothalamic processing is the master-clock that is in charge of controlling rhythmic behavour.
Types of Visual Processing at Optic Chiasm
1. Ipsilateral Processing (Same Side) 2. Contralateral Processing (Opposite Side)
Segregation of Visual Cortex
1. LGN -> V1 There is the separation of colour, form, and movement. 2. V1 -> V2 Specialization of visual function continues. 3. Parietal lobe (dorsal stream). Involves V3 and V5. V3: Looking at form / shape. V5: Detecting motion. (Most of V5 is dedicated to processing motion already). 4. Temporal lobe (dorsal stream). Involves V3 and V4. V3: Looking at dynamic form. V4: Looking at colour and form. (Most of V4 is dedicated to processing colour and form. The temporal lobe doesn't care about motion, but looks at the specific attributes.
Lateral Geniculate Nucleus (LGN) Cells
1. Magnocellular Cells 2. Parvocellular Cells
Other Specialized Areas
1. Parahippocampal Place Area (PPA) 2. Extrastriate Body Area (EBA)
Tectopulvinar Pathway
1. Superior colliculi in the tectum -> pulvinar in nucleus of thalamus -> other visual areas. Leads to reflex visual orientation. Information is received directly from optic chiasm. Doesn't require complex processing. You orient and process information faster. There is usually something unusual that happens in your periphery so it rapidly helps orient you. It is faster because you don't have to consciously recognize that it is different, it is automatic.
Blind Sight
2 separate pathways that observe different aspects of vision. 1. Eye -> LGN -> V1. The geniculatostriate pathway is consciously seeing things. 2. Tectopulvinar pathway. Goes directly to the brain stem and is more prominent in animals. Concerned with reflexing behaviour. So if there is damage in your visual cortex, you can still use the tectopulvinar pathway to guess the movement based on the reflexes.
Face Areas
A primate's face reveals a lot of information about: 1. Friend or faux 2. State of emotion 3. Threatening
Dorsal Stream
A visual guidance of movement. Your action. Involves V5, where 95% of its neurons are selective for motion. Many This is important for how you walk and move around your world, or knowing how far an object is so you don't hit it. V5 goes exclusively to the parietal lobe. The parietal lobe is the cortical area in charge of SPATIAL awareness.
Dorsal and Ventral Stream
After information is processed in the occipital lobe, it moves downstream as a stream of information. It will go to 2 different streams. Each stream receives specific information from the occipital lobe. 1. Dorsal Stream 2. Ventral Stream
Fusiform Face Area (FFA) Neurons
An experiment where each "greeble" that was presented had different characteristics. They found that humans were still able to learn to identify the greebles, even though they were all different. Each greeble was given a short biography so participants had to identify each greeble based on the characteristics being described. They found that before training, there was a much higher FFA response when seeing faces. However, after the experiment there was a significant increase in the FFA response activity when greebles were presented.
Temporal Lobe Processing
As you move downstream from occipital lobe into the temporal lobe, it gets even more complex. There is now the combining of the different columns and hypercolumns (ie. a specific column that responds to colour, shape, motion, etc.) There are columns that will only respond to specific stimuli. Each column is a different specific stimuli. Example: Only interested in primate faces, body parts, fruits.
Secondary Cortices
As you move downstream out of the occipital lobe, there are cells that will respond to specific stimuli (ie. body parts, shapes, faces, etc.). It is responding to all the upstream processing. The secondary cortex is gathering information and putting it all back together.
Convergence of Receptive Fields
As you move downstream, there is a convergence of information and the receptive fields get larger and larger. Your sensory information / receptive fields get larger and converge as you move further downstream. 16 ganglion cells -> 4 lateral geniculate neuron (LGN) cells -> 1 single primary visual cortex (V1) cell
Occipital Lobe
As you move more downstream from the different occipital areas from V1 to V5, there is more specialization. The different occipital areas process different aspects of visual information. As you move more downstream, there are more precise deficits that can occur if there is damage.
Primary Visual Cortex (V1 / Striate Cortex)
As you move more downstream, there is a difference in the complexity in order for a neuron to be fired / stimulated. Located in the LGN. 1. Simple Cells 2. Complex Cells 3. Hyper-complex Cells
Secondary Cortices
Begins to start processing the different aspects. Different areas specializing in processing colour, motion, orientation, etc. Includes V2-V5 processing.
Face Areas
By looking at single cell recordings that specialize in looking at primate faces, they found that the cell recordings were very active not just when monkeys looked at primate faces, but also when they looked at human faces. In contrast, when a monkey was shown a non-face (ie. a building). the neurons became less active than baseline and there was a low firing rate. This shows that there are face areas that are dedicated to the different ATTRIBUTES of the face.
Injured Visual pathway
Depending on where in the geniculostriate pathway you damaged, you may have different symptoms. If you damage your retina or optic nerve of one eye, there may be monocular blindness.
Visual Field
Each eye detects fro both visual fields. The left eye sees mainly the left visual field but also some of right visual field. The right eye sees mainly the right visual field but also some of the left visual field.
Fusiform Face Area (FFA) Neurons
Experiment shows that there is plasticity in the fusiform face area (FFA) for learning new faces. FFA neurons change their activity IN RESPONSE to the greebles, in the direction of how the FFA is active when looking at primate faces. So after the experiment, FFA neurons were able to identify greebles because of the plasticity in the FFA.
Use It or Lose It
Experiment where a cat who has passed their development window, is placed in a vertical striped environment, vs cat in horizontal striped environment. Found that cats raised in a vertically oriented environment have a lot of cells that responded to vertical input, but no cells that responded to horizontal input. Because the cat was never exposed to horizontal lines, there were no cells that responded to horizontal stimulus. They were never aware of it, so they don't have any cells to understand the stimulus. Found that this can be applied to other sensory systems too.
Brain Allocation for Fovea Input
Fovea is the center of the field of vision that only contains cones. Because the center of field of vision is more important than the periphery, more of your cortex is allocated to process visual input in the fovea.
Fusiform Face Area (FFA) Neurons
Fusiform face areas (FFA) are hardwired to perceive faces, where if you meet new people you will acquire knowledge about their face. However, they found that the FFA neurons also showed plasticity.
Achromatopsia
He ended up changing his lifestyle completely and started eating things that were white / gray / black, he got a Dalmatian. He ended up being active at night since things tend to be black and gray.
Homonymous Hemianopia (HH)
If someone with homonymous hemianopia is asked to fixate on a specific point in the center of their field of vision (fovea), then they will only perceive one visual field. They can detect motion but cannot identify it due to the tectopulvinar pathway. They know that something is moving and can tell you which direction it is moving in, but they cannot say what is there. The tecto-pulvinar pathway is due to orienting reflexes, so it can detect motion. They are able to detect the motion and tell you the direction even if they cannot identify the object that is moving.
Split-Brain
In a normal brain, the left hemisphere is in charge of speaking. So after the commissurotomy, there will be a struggle between the 2 hemispheres.
Ocular Dominance
In the LGN, there are separate layers and columns of cells that are dedicated to each eye. There are layers of cells in charge of processing the left side of the brain's right visual field information coming from both eyes. There are separate layers and columns of cells that are in charge of processing the right side of the brain's left visual field information that is coming from both eyes. Occular dominance occurs in the LGN, and will go down to the occipital lobe. The separation of processing information of the eyes is important for depth perception.
Achromatopsia
Inability to see colour. There is damage in V4 (which is in charge of colour). Could only see everything in black and white. As a result, this completely destroyed his life because he couldn't watch coloured-TV, he thought human flesh looked dead because their skin was gray, he thought food was disgusting because it looked black.
Complex Cells
It is more complex, and just simply having a light at the right orientation isn't enough for firing to occur. More complex rule to cause a firing in the cell. There needs to be a light at a specific angle that is MOVING in a particular direction across the retina.
Retino-hypothalamic Pathway
Job is to note whether it is light or dark. Helps to keep our rhythmic behaviour on time. It receives information about how long the dates are and tells you the different seasions. This is important for animals in evolution because they have certain times where they mate. In charge of our daily, monthly, yearly rhythm. Helps keep the body clock in check.
Geniculostriate Pathway
Lateral geniculate nucleus (LGN) -> striate cortex (V1) -> other visual areas. Leads to your conscous perception of what you are seeing. Will take longer because you need to be conscious of it happening.
Use It or Lose It
Looking at what happens if the developmental window is over and you were never exposed to a stimulus. Found that if your brain was never exposed to it, it will either be unable to or not be very good at processing it.
Monocular Blindness
Loss of sight in one eye. Destruction in the retina or the optic nerve of one eye. Because it has not passed the optic chiasm yet so there is still left and right visual field information from both eyes. There may be damage in depth perception, especially in older age. However if the damage is past the optic chiasm, there will be much more complex deficits / damage.
Ventral Stream
Neurons are excited by complex visual stimuli (ie. faces, expressions, paintings). There is stimulus equivalence. You are able to see something as the same object even when looking at it at different conditions. Example: If you've never seen a truck from the top view, you will still recognize that it is a truck because you have stimulus equivalence.
Homonymous Hemianopia (HH)
Occurs after the optic-chiasm, so it results in the total loss of a visual field. Blindness to one entire side of visual field. You can have total damage of the optic tract, LGN, or primary visual cortex (V1). Since the axons have already passed the optic-chiasm, you will lose one visual field from both eyes.
Parahippocampal Place Area (PPA)
Only responds to environmental scenes (ie. buildings). Found that the parahippocampal place area (PPA) was very active when it say patterns that may be from your environment. They found that if other input that is not related to the environment is presented, or if it was a pixelated builiding, there would be no activity and no response in the parahippocampal place area (PPA).