4 Visual Cortex Flashcards
Q: What is the pathway of ganglion cell fibers from the retina?
A: Ganglion cell fibers leave the retina along the optic nerve.
Q: What is the optic chiasm?
A: The optic chiasm is the crossover point where some fibers of the optic nerve cross over to the opposite side of the brain.
Q: What happens to the optic nerve beyond the optic chiasm?
A: Beyond the optic chiasm, the optic nerve becomes the optic tract.
Q: How is information organized in the optic tract?
A: Information in the optic tract is separated by visual field rather than by eye.
Q: How is information from the right visual field represented in the brain?
A: Information from the right visual field is represented by the left hemisphere of the brain.
Q: What is the LGN?
A: The LGN (Lateral Geniculate Nucleus) is a bilateral structure that receives input from the optic tract.
Q: How does the LGN receive input from the eyes?
A: Each LGN receives input from both the left and right eyes but keeps the inputs separate.
Q: What receptive field organization do cells in the LGN have?
A: LGN cells have the same receptive field organization as retinal ganglion cells, exhibiting center-surround antagonism.
Q: What is the function of the receptive field organization in LGN cells?
A: The receptive field organization is ideal for detecting spots of light and edges but not the orientation of visual stimuli.
Q: Where is the primary visual cortex located in the brain?
A: The primary visual cortex is located at the back of the brain at the bottom.
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Q: What is retinotopic mapping in V1?
A: Retinotopic mapping in V1 means that objects close together in the visual scene are analyzed by neighboring parts of V1.
Q: What is cortical magnification in V1?
A: Cortical magnification in V1 refers to the distortion in the amount of cortex devoted to representing each part of the retinal field.
Q: How is the fovea represented in V1?
A: The fovea, though accounting for only 0.01% of the retina, is represented by a large area of cortex in V1, approximately 8-10%.
Q: What is the method used for studying receptive fields in V1?
A: Single-cell recording is used in V1, where a visual stimulus is presented to an animal, and an electrode is inserted into a V1 neuron to measure its electrical activity.
Q: What was the response observed in V1 cells during initial studies?
A: V1 cells exhibited baseline activity when no stimulus was presented, and researchers initially struggled to find a stimulus that excited them.
Q: What did Hubel and Wiesel discover about V1 cells’ response?
A: They found that V1 cells responded strongly when the edge of a slide moved across their receptive field, indicating that they respond to lines rather than spots.
Q: What is orientation selectivity in V1 cells?
A: Orientation selectivity refers to V1 cells’ preference for lines of a particular orientation.
Q: What are the three different types of cells in V1 with distinct receptive field organization?
A: The three types are simple, complex, and hypercomplex cells.
Q: What stimuli do simple cells respond to?
A: Simple cells respond to oriented lines and edges.
Q: What is the structure of the receptive field in simple cells?
A: The receptive field of simple cells has both excitatory and inhibitory regions, but they are elongated.
Q: Do simple cells have orientation selectivity?
A: Yes, simple cells exhibit orientation selectivity.
Q: What does it mean for a simple cell to be orientation tuned?
A: Orientation-tuned neurons respond best to their preferred orientation but also respond to similar orientations.
Q: What are the characteristics of complex cells?
A: Complex cells respond to oriented lines but do not have discrete on/off regions.
Q: What types of stimuli do complex cells respond best to?
A: Complex cells respond best to moving oriented lines and edges.
Q: What are hypercomplex cells also known as?
A: Hypercomplex cells are also known as end-stopped cells.
Q: What types of stimuli do hypercomplex cells respond to?
A: Hypercomplex cells respond to lines of a particular orientation, direction, and length.
Q: How do receptive fields change in complexity from simple to hypercomplex cells?
A: Receptive fields increase in complexity from simple to hypercomplex cells, with hypercomplex cells having more specific response characteristics.
Q: How many visual areas are there beyond V1?
A: There are over 30 visual areas beyond V1.
Q: How are visual areas beyond V1 interconnected?
A: All visual areas beyond V1 are interconnected, and there is no simple separation of function.
Q: What are some examples of specialized visual areas?
A: Examples include V4, which is specialized for color processing.
Q: What are the two processing streams in visual processing?
A: The “what” stream travels ventrally to the inferotemporal cortex, while the “where” stream travels dorsally to the posterior parietal cortex.
Q: What is the function of the “what” stream?
A: The “what” stream is important for recognizing and discriminating objects.
Q: What is the function of the “where” stream?
A: The “where” stream is important for determining where an object is located and how to act upon it.
Q: What is another name for the “where” stream?
A: The “where” stream is sometimes referred to as the “how” stream.
Q: Are the pathways of the processing streams totally separate?
A: No, there are many connections between the “what” and “where” streams, and signals flow both upwards and backwards between them.
Q: What evidence supports the distinction between the “what” and “where” streams?
A: Lesion studies in monkeys and neuropsychological studies in humans provide evidence for the functional distinction between the streams.
Q: What is visual form agnosia?
A: Visual form agnosia is a condition where damage to the ventral pathway results in an inability to identify objects despite knowing their features.
Q: What is optic ataxia?
A: Optic ataxia is a condition where damage to the dorsal pathway results in difficulties reaching to grasp objects, while object recognition and description remain intact.
Q: How do the deficits in visual form agnosia and optic ataxia differ?
A: Patients with visual form agnosia have deficits in object recognition despite intact reaching abilities, whereas patients with optic ataxia have deficits in reaching and grasping despite intact object recognition.
