Chapter 3. Responses of Simple Cells in V1
3.1 Title slide
Demonstration 3.2
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Responses of Simple Cells in V1
Simulate an experiment to find the location and structure of the receptive field of a simple cell in V1.
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Each patch of color shows the location of a column of neurons with similar response properties. The columns aren't arranged in a grid, but in a kind of pinwheel pattern. [From Bosking et al., 1997]
What Determines the Responses of Simple Cells in V1?
A simple cell in V1 responds most strongly to a bar, or edge, of light with a particular orientation at a particular location on the retina—the location of the cell's receptive field. The small spots of light that most effectively stimulate retinal ganglion cells (RGCs) are quite poor in eliciting a response from simple cells, and this makes sense: the center–surround receptive fields of RGCs help tell the visual system where light is located, while the responses of simple cells to oriented edges begin to tell the visual system what objects are at those locations. We recognize objects largely by their shape, and the shape of an object is defined by the position and orientation of its edges.
The preferred orientation of the cell—that is, the orientation that tends to produce the strongest response—is determined by flashing bars with various orientations in the receptive field and measuring the response (spikes) evoked by each orientation. Such experiments produce results like those shown in Figure 1, where the orientation tuning curves represent the responses of two different simple cells (A and B) to bars with a full range of orientations.
What are the connections—from RGCs to cells in the lateral geniculate nucleus (LGN) to simple cells in V1—that make these response patterns possible? Multiple RGCs with aligned receptive fields connect one-to-one with multiple LGN cells that all connect to the same simple cell. Each LGN neuron has a circular, center–surround receptive field corresponding to the receptive field of the RGC to which it connects. The simple cell's receptive field is an elongated shape with an excitatory central area and inhibitory surrounding area, corresponding to the way in which the excitatory centers and inhibitory surrounds of the receptive fields of the RGCs and the LGN cells overlap.
As shown in Figure 2 (top) the simple cell responds strongly when the excitatory centers of the LGN cells' receptive fields are covered by a bar of light oriented at the same angle as the aligned receptive fields. Figure 2 (bottom) shows that if the bar is oriented at a different angle, it covers less of the excitatory centers and more of the inhibitory surrounds, resulting in a weaker response from the simple cell.
The preferred orientation of the cell—that is, the orientation that tends to produce the strongest response—is determined by flashing bars with various orientations in the receptive field and measuring the response (spikes) evoked by each orientation. Such experiments produce results like those shown in Figure 1, where the orientation tuning curves represent the responses of two different simple cells (A and B) to bars with a full range of orientations.
What are the connections—from RGCs to cells in the lateral geniculate nucleus (LGN) to simple cells in V1—that make these response patterns possible? Multiple RGCs with aligned receptive fields connect one-to-one with multiple LGN cells that all connect to the same simple cell. Each LGN neuron has a circular, center–surround receptive field corresponding to the receptive field of the RGC to which it connects. The simple cell's receptive field is an elongated shape with an excitatory central area and inhibitory surrounding area, corresponding to the way in which the excitatory centers and inhibitory surrounds of the receptive fields of the RGCs and the LGN cells overlap.
As shown in Figure 2 (top) the simple cell responds strongly when the excitatory centers of the LGN cells' receptive fields are covered by a bar of light oriented at the same angle as the aligned receptive fields. Figure 2 (bottom) shows that if the bar is oriented at a different angle, it covers less of the excitatory centers and more of the inhibitory surrounds, resulting in a weaker response from the simple cell.
3.2 Explain - dnd
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This area of the retina contains the receptive fields of Simple Cells A and B in the primary visual cortex (area V1). Each simple cell has a preferred orientation:
it responds most strongly to a stimulus that covers the entire excitatory center of its receptive field without covering any of the inhibitory surround.
Drag different stimuli across the retina and watch the cells' responses. Can you determine the preferred orientation of each cell and the location of its
receptive field? Click SHOW RECEPTIVE FIELD to check your conclusions.
3.3 Explain
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What Determines the Responses of Simple Cells in V1?
A simple cell in V1 responds most strongly to a bar, or edge, of light with a particular orientation at a particular location on the retina—the location of the cell's receptive field. The small spots of light that most effectively stimulate retinal ganglion cells (RGCs) are quite poor in eliciting a response from simple cells, and this makes sense: the center–surround receptive fields of RGCs help tell the visual system where light is located, while the responses of simple cells to oriented edges begin to tell the visual system what objects are at those locations. We recognize objects largely by their shape, and the shape of an object is defined by the position and orientation of its edges.
The preferred orientation of the cell—that is, the orientation that tends to produce the strongest response—is determined by flashing bars with various orientations in the receptive field and measuring the response (spikes) evoked by each orientation. Such experiments produce results like those shown in Figure 1, where the orientation tuning curves represent the responses of two different simple cells (A and B) to bars with a full range of orientations.
What are the connections—from RGCs to cells in the lateral geniculate nucleus (LGN) to simple cells in V1—that make these response patterns possible? Multiple RGCs with aligned receptive fields connect one-to-one with multiple LGN cells that all connect to the same simple cell. Each LGN neuron has a circular, center–surround receptive field corresponding to the receptive field of the RGC to which it connects. The simple cell's receptive field is an elongated shape with an excitatory central area and inhibitory surrounding area, corresponding to the way in which the excitatory centers and inhibitory surrounds of the receptive fields of the RGCs and the LGN cells overlap.
As shown in Figure 2 (top) the simple cell responds strongly when the excitatory centers of the LGN cells' receptive fields are covered by a bar of light oriented at the same angle as the aligned receptive fields. Figure 2 (bottom) shows that if the bar is oriented at a different angle, it covers less of the excitatory centers and more of the inhibitory surrounds, resulting in a weaker response from the simple cell.
The preferred orientation of the cell—that is, the orientation that tends to produce the strongest response—is determined by flashing bars with various orientations in the receptive field and measuring the response (spikes) evoked by each orientation. Such experiments produce results like those shown in Figure 1, where the orientation tuning curves represent the responses of two different simple cells (A and B) to bars with a full range of orientations.
What are the connections—from RGCs to cells in the lateral geniculate nucleus (LGN) to simple cells in V1—that make these response patterns possible? Multiple RGCs with aligned receptive fields connect one-to-one with multiple LGN cells that all connect to the same simple cell. Each LGN neuron has a circular, center–surround receptive field corresponding to the receptive field of the RGC to which it connects. The simple cell's receptive field is an elongated shape with an excitatory central area and inhibitory surrounding area, corresponding to the way in which the excitatory centers and inhibitory surrounds of the receptive fields of the RGCs and the LGN cells overlap.
As shown in Figure 2 (top) the simple cell responds strongly when the excitatory centers of the LGN cells' receptive fields are covered by a bar of light oriented at the same angle as the aligned receptive fields. Figure 2 (bottom) shows that if the bar is oriented at a different angle, it covers less of the excitatory centers and more of the inhibitory surrounds, resulting in a weaker response from the simple cell.
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