Lateral Inhibition

What is lateral inhibition?

Lateral inhibition refers to neural circuits that inhibit from the sides, allowing for pattern vision.

What is the result of lateral inhibition in ganglion cells?

It leads to center-surround receptive field organization.

What perceptual illusions are explained by lateral inhibition?

The Hermann Grid and Mach Bands.

Describe the phenomenon of the Hermann Grid.

In a Hermann grid, gray dots appear at intersections due to lateral inhibition.

What happens to the gray dots in the Hermann Grid as the eyes move?

A gray dot disappears and new ones appear;

What activates the ganglion cells in the Hermann Grid?

Luminance information from the white lines and intersections.

Why is the center ganglion cell at the intersection less active?

It is laterally inhibited by 4 neighboring cells, leading to less brightness perception.

How do surrounding ganglion cells respond to lateral inhibition in the Hermann Grid?

They are more active and only laterally inhibited by 2 neighboring cells.

What is a key difference between peripheral and central vision in the context of the Hermann Grid?

Peripheral vision has larger receptive fields and perceives gray dots, while central vision has smaller receptive fields with no gray dot perception.

What are Mach Bands?

An illusion of faint dark/light edges at the borders of differently illuminated blocks.

How do actual luminance changes appear in Mach Bands?

They appear like 'steps' on a graph but are perceived as curvy with dramatized luminance at the edges.

What causes the Mach band illusion?

Edge enhancement caused by ganglion cells exaggerating brightness differences.

What is edge enhancement?

It occurs when ganglion cells enhance brightness differences to detect edges more clearly.

How does the receptive field contribute to Mach Bands?

Small receptive fields are laterally inhibited at different levels, leading to perceived darker and lighter edges.

Explain the role of bipolar cells in Mach Bands.

Neighboring bipolar cells inhibit each other, affecting the perception of edges.

What happens to a more activated photoreceptor in regard to neighbor inhibition?

It provides more inhibition to its neighbors, leading to varied activation levels.

Describe simultaneous contrast.

It is a phenomenon where perceived brightness or color is affected by surrounding light.

Give an example of simultaneous contrast.

A gray square appears lighter against a black background and darker against a white background.

How does lateral inhibition explain simultaneous contrast?

The white background provides strong inhibition, making the gray square appear darker.

What complication arises in explaining simultaneous contrast solely with lateral inhibition?

The entire gray square appears altered, not just its edges.

What might be involved in simultaneous contrast beyond lateral inhibition?

Processes at the brain’s higher sensory processing level.

What perception occurs with a dark edge in terms of receptive fields?

A receptive field with some inhibitory surround and no excitatory center is stimulated less.

What type of receptive field perceives a lighter edge?

A receptive field with more inhibitory surround and an excitatory center is stimulated more.

How can the perception of dark and light edges be mathematically represented?

Through the unequal inhibition by neighboring bipolar cells.

What kind of brightness perception occurs with unequal stimulation in ganglion cells?

The perception of gray dots in peripheral vision due to lateral inhibition.

How does stimulating the entire receptive field affect perceived brightness?

It leads to no perceived gray dots, as the excitation and inhibition balance out.

In the Hermann Grid, what determines the firing rate of ganglion cells?

The number of lateral inhibiting neighbors influencing the overall activity.

Differentiate between peripheral and central vision in terms of receptive field stimulation.

Peripheral vision involves larger receptive fields, while central vision has smaller receptive fields.

What visual effect does strong lateral inhibition have in Mach Bands?

It creates an exaggerated perception of edges between contrasting luminance.

Why would central vision not see gray dots in the Hermann Grid?

Because the entire receptive field is stimulated, leading to equal excitation and inhibition.

What is the relationship between surrounding brightness and perceived color in simultaneous contrast?

The perceived color or brightness of an object is altered based on the brightness of its surroundings.

What is the function of horizontal and amacrine cells in lateral inhibition?

They laterally inhibit ganglion cells to create contrast in perception.

What visual phenomena utilize the concept of lateral inhibition?

Hermann Grid, Mach Bands, and Simultaneous Contrast.