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Questions and Answers
What do primates need to identify to successfully forage for food?
What do primates need to identify to successfully forage for food?
Shapes and 3D objects
The brain uses error signals and predictions to determine visual input.
The brain uses error signals and predictions to determine visual input.
True
What is the role of the V1 area in the visual system?
What is the role of the V1 area in the visual system?
Contour integration for object perception
What happens when there's a lesion in V1?
What happens when there's a lesion in V1?
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What does V4 specifically respond to?
What does V4 specifically respond to?
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The LOC demonstrates ______ invariance.
The LOC demonstrates ______ invariance.
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Match the following types of agnosia with their descriptions:
Match the following types of agnosia with their descriptions:
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What is prosopagnosia?
What is prosopagnosia?
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What perception arises from the presentation of stationary images?
What perception arises from the presentation of stationary images?
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Which area is key for motion perception?
Which area is key for motion perception?
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What happens if the MT and MST areas are lesioned bilaterally?
What happens if the MT and MST areas are lesioned bilaterally?
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Mammals with front eyes rely on ______ for depth perception.
Mammals with front eyes rely on ______ for depth perception.
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What is the role of binocular disparity in depth perception?
What is the role of binocular disparity in depth perception?
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What is Akinetopsia?
What is Akinetopsia?
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Which area is involved in the global integration of visual information?
Which area is involved in the global integration of visual information?
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What role do error signals play in the visual system?
What role do error signals play in the visual system?
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Lesions in V1 can lead to a condition known as blindsight.
Lesions in V1 can lead to a condition known as blindsight.
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What is the primary function of V2 in the visual processing system?
What is the primary function of V2 in the visual processing system?
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Long range horizontal connections in V1 are ______ and connect co-oriented cells.
Long range horizontal connections in V1 are ______ and connect co-oriented cells.
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Match the brain areas with their functions:
Match the brain areas with their functions:
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What is the main function of the lateral occipital complex (LOC)?
What is the main function of the lateral occipital complex (LOC)?
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V4 neurons demonstrate position invariance when responding to visual stimuli.
V4 neurons demonstrate position invariance when responding to visual stimuli.
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What does form-cue invariance allow the LOC to do?
What does form-cue invariance allow the LOC to do?
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A lesion in the back of the temporal lobe can lead to __________ agnosia.
A lesion in the back of the temporal lobe can lead to __________ agnosia.
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Match the type of agnosia with its characteristics.
Match the type of agnosia with its characteristics.
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What is the primary function of the fusiform gyrus?
What is the primary function of the fusiform gyrus?
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People with prosopagnosia can identify individual facial features but not the whole face.
People with prosopagnosia can identify individual facial features but not the whole face.
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What does 'apparent motion' refer to?
What does 'apparent motion' refer to?
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The area responsible for motion perception is called the ___ area.
The area responsible for motion perception is called the ___ area.
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Match the types of motion with their descriptions:
Match the types of motion with their descriptions:
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Which type of motion is characterized by an action like throwing a ball?
Which type of motion is characterized by an action like throwing a ball?
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All V1 cells exhibit direction selectivity in their response.
All V1 cells exhibit direction selectivity in their response.
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What is the role of MT/V5 in the visual system?
What is the role of MT/V5 in the visual system?
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The process of integrating neurons being activated by a moving stimulus is called ___ of ESPS.
The process of integrating neurons being activated by a moving stimulus is called ___ of ESPS.
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What is the effect of damage to the MT and MST areas?
What is the effect of damage to the MT and MST areas?
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Study Notes
Primates and Visual Perception
- Primates require object recognition, motion and depth perception to navigate their environment, particularly for foraging.
- The brain utilises error signals and predictions, with feedback from higher cortical processing to V1, to determine visual input.
- V1 is sensitive to global organisation of a scene due to feedback from higher-order areas like V4, IT, and MT.
- Long-range horizontal connections in V1 connect co-oriented cells, creating a clear straight line representation.
- Lesions to these connections impair conscious vision, resulting in blindsight.
V2: Boundaries and Illusory Contours
- V2 neurons are responsible for figure-ground segregation and illusory contours, enabling the human visual system to complete objects.
- V2 helps fill in gaps and create edges/shapes, even when the complete visual information is missing.
V4: Integrating Local Cues into Global Shapes
- V4 neurons respond to particular curvatures of objects anywhere within their receptive field (RF).
- V4 is critical for encoding features about the true shape of objects.
- Lesions in V4 cause severe disruptions in object discrimination.
LOC: Complex Shape Representation
- LOC represents complex shapes and displays size invariance.
- fMRI studies reveal that LOC responds selectively to objects, both familiar and unfamiliar.
- LOC exhibits form-cue invariance, identifying objects based on their shape regardless of changes in appearance.
Visual Agnosia
- Visual agnosia is the inability to recognize visually presented objects.
- Apperceptive agnosia, caused by lesions near the occipital lobe, results in the inability to integrate visual features into a whole.
- Associative agnosia, caused by lesions in the frontal temporal lobe, impacts the ability to identify objects due to a lack of object knowledge.
- People with associative agnosia may be able to copy objects but not recognize them.
Prosopagnosia: Face Blindness
- Prosopagnosia, often associated with damage to the fusiform gyrus in the IT area, is the inability to recognise faces.
- Individuals with this condition can recognize individual facial components but struggle to integrate them into a complete percept.
Motion Perception: Real vs. Apparent Motion
- Apparent motion is a perception of motion arising from presenting stationary images or objects.
- Biologically important types of motion include smooth motion, optic flow, and complex biological motion.
Motion Processing Stream
- V1 can directly innervate V2, V4, or MT/V5.
- Many V1 cells exhibit direction selectivity.
- Motion perception mainly relies on the pathway: V1 -> MT/V5 -> MST -> PPC
- Summation of ESPS occurs when neurons activated by a moving stimulus converge simultaneously at the target cell.
MT/V5: Global Integration
- MT/V5 contains neurons with large receptive fields, sensitive to moving stimuli, and displaying motion adaption.
- MT/V5 is responsible for globally integrating objects and stimuli in the environment to interpret their collective meaning.
MST: Integrating Motion Information Across Larger Visual Fields
- MST, adjacent to MT/V5, also plays a crucial role in motion processing.
- MST integrates motion information across larger visual fields, allowing for the detection of complex patterns like expansion, contraction, and rotation.
- Lesions to MT/V5 and MST bilaterally severely impact everyday tasks involving motion, such as pouring tea.
Alternate Pathways for Motion Perception
- There are multiple pathways for perceiving motion, different from the typical LGN -> V1 -> MT pathway.
Depth Perception: Frontal vs. Side Eyes
- Front-eyed mammals rely on stereopsis, using overlapping retinal images from both eyes to estimate depth.
- Side-eyed animals have limited or no retinal image overlap, impacting depth perception but providing wider peripheral vision.
- Binocular disparity refers to the difference between the two retinal images due to the eyes' different positions in space.
- The horopter is an imaginary curve representing points in space where objects project images onto corresponding points on each retina.
- Objects on the horopter create no disparity, appearing at the same depth from the observer's viewpoint.
- Objects farther away from the horopter create binocular disparity, providing cues about depth.
- V1 neurons are sensitive to binocular disparity, displaying tuning to either near or far objects.
- V1, V2, V3, MT, and MST all exhibit high levels of disparity tuning.
Monocular Cues for Depth
- Monocular cues aid depth perception for each eye individually, crucial for individuals with visual impairments in one eye.
- Some monocular cues include: relative sizes, occlusion, cast shadows, shading, aerial perspective, linear perspective, texture perspective, motion parallax, and blurring.
- Monocular cues are necessary to calculate absolute distances, as disparity only provides relative information based on the horopter.
Akinetopsia: Loss of Motion Perception
- Akinetopsia is the impairment of motion perception.
- Bilaterally damaged MT/V5 is the most common cause of Akinetopsia.
- MT neurons are sensitive to motion and involved in visual information integration.
- MT receives input from V1, especially from direction-selective cells, but some input bypasses V1, via koniocellular LGN cells and pathways from the superior colliculus/pulvinar.
Higher Visual Functions: Perception of Objects, Motion, and Depth
- Primates require object recognition, motion, and depth perception for foraging and navigation.
- The brain uses error signals and predictions as feedback from higher cortical areas to the early visual areas (V1) to determine the visual input and guide responses.
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Gestalt Principles: V1 is sensitive to the global organization of a scene due to feedback from higher-order areas (V4, IT, or MT), modulating its responses.
- Long-range horizontal connections in V1 connect co-oriented cells, creating a clear straight line across V1.
- Lesions in this area impair conscious vision, resulting in blindsight.
V2: Borders, Figure-Ground Segregation, and Illusory Contours
- V2 neurons respond to partially occluded objects in natural scenes, enabling the completion of the objects.
- Illusory edges are used to study the response of V2 neurons, demonstrating the brain's ability to fill in missing information to create edges and shapes.
V4: Integration of Local Cues into Global Shapes and Object-Based Representation
- V4 neurons respond to specific curvatures of objects presented anywhere in their receptive field, displaying position invariance within their receptive fields.
- V4 neurons encode features in a visual scene that provide information about the true shape of objects.
- Lesions in V4 result in severe disruptions of object discrimination.
Lateral Occipital Complex (LOC)
- The LOC represents complex shapes.
- fMRI studies demonstrate the LOC responds selectively to objects, both familiar and unfamiliar, exhibiting size invariance.
- The LOC shows greater responses to actual objects (familiar or not) compared to patterns without objects.
- The LOC demonstrates form-cue invariance, recognizing an object regardless of the type of visual cue used to represent it.
Visual Agnosia: The Inability to Recognize Objects
- Apperceptive Agnosia: Lesion towards the back of the temporal lobe near the occipital lobe (primitive visual processing areas, closer to V1). Individuals cannot integrate the visual features of objects into a complete whole.
- Associative Agnosia: Lesion towards the front of the temporal lobe (higher-cortical processing area). Individuals cannot identify the object using their knowledge of it. They may be able to copy it but cannot recognize it.
Prosopagnosia: Face Blindness
- Damage to the IT area, specifically the fusiform gyrus, responsible for face recognition.
- Individuals with prosopagnosia can identify individual objects that make up a face (nose, eyes) but cannot integrate them into a complete facial percept.
Motion Perception: Real vs. Apparent Motion
- Apparent Motion: Perception of motion arises from the presentation of stationary images or objects.
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Biologically important forms of motion:
- Smooth motion (throwing a ball)
- Optic flow (moving an object closer or further away)
- Complex biological motion (specific movements from animated objects, like people)
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Key area for motion perception: MT/V5
- V1 can directly innervate V2, V4, or MT/V5.
- V1 cells show direction selectivity in their response.
- Pathway: V1 > MT/V5 (middle temporal) > MST (medial superior temporal) > PPC (posterior parietal cortex)
- Summation of ESPS: Neuron activation from a stimulus moving in its preferred direction converges in the target cell at the same time, resulting in summation of ESPSs.
Depth Perception and the Horopter
- Depth perception relies heavily on binocular disparity, the difference in images seen by each eye due to their horizontal separation.
- Corresponding retinal points: When an object is on the horopter, its image falls on corresponding points on the retinas, resulting in no disparity and a single, clear perception of the object.
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Disparity and depth perception:
- Objects in front of or behind the horopter project to non-corresponding retinal points, creating binocular disparity that is interpreted as depth.
- Greater disparity signifies greater distance from the horopter.
- Objects in front of the horopter have crossed disparity, while objects behind it have uncrossed disparity.
- V1, V2, V3, MT, and MST have high levels of disparity tuning, with cells sensitive to near or far distances from the horopter.
Monocular Cues to Depth
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Relative size: Objects further away appear smaller.
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Occlusion: When one object partially hides another, the hidden object is perceived as further away.
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Cast shadows: Size and angle of shadows convey the distance between objects.
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Shading: Light and shadow on an object contribute to depth perception.
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Aerial perspective: Objects further away appear hazier due to atmospheric effects.
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Linear perspective: Parallel lines appear to converge in the distance.
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Texture perspective: Texture details appear less distinct further away.
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Motion parallax: Objects closer to the observer appear to move faster during motion.
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Blurring: Objects further away appear more blurred.
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Monocular cues provide information for each eye individually, essential for computing absolute distances since disparity is relative to the horopter.
- Important for animals with eyes on the sides of their heads.
- Motion parallax: Objects move at different speeds on the retia depending on their distance from the observer.
Akinetopsia
- Loss of motion perception.
- Often results from bilateral damage to area MT (V5).
- MT neurons are sensitive to motion and involved in the global integration of visual information.
- They receive input from V1, especially direction-selective cells in V1.
- MT also receives projections from the koniocellular LGN cells (geniculo-extrastriate pathway) and the superior colliculus/pulvinar (colliculo-cortical pathway).
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Description
Explore how primates perceive their environment through object recognition, motion, and depth perception. This quiz covers the roles of different brain areas, including V1 and V2, in processing visual information and highlights the significance of visual pathways in creating perception. Test your knowledge on the mechanisms that enable visual completion and awareness in primates.
