Lateral Inhibition and Receptive Fields

What is neural processing?

The interaction of electrical signals of many neurons

What is lateral inhibition?

The capacity of an excited neuron to reduce the activity of its neighbors

What did the experiment with the eye of limulus (horseshoe crab) help scientists understand?

Lateral inhibition - shining light at only one ommatidia (photoreceptor) produced a large response that shrank as neighboring receptors were stimulated

What are horizontal cells?

Cells in the eye that make inhibitory contact onto local bipolar cells- don't have axons or action potentials

What illusion does the Hermann Grid produce?

Seeing grey spots at intersections of white lines

What causes the illusion seen in Mach Bands?

Lateral inhibition - receptors responding to dark areas have the smallest output (and vice verse for bright areas), resulting in different amounts of inhibition at borders (differential inhibition) and the illusion of a brighter/darker line

What is the benefit of the Mach Band illusion on our vision?

It boosts our depth perception and creates better visual contrast between objects' contours

What illusion do Mach Bands produce?

Higher contrast at borders of light & dark areas

What illusion does Simultaneous Contrast produce?

Perceiving the same color area as brighter or darker depending on the brightness of an adjacent area

What cells' signal produces the effects seen in the Hermann Grid?

Bipolar cells - they send inhibitory signals to neighbor cells which causes the perception of gray where corridors connect

In Mach Bands, does the higher or lower intensity area have the dark band?

The lower intensity area

True or False: a colored area will appear lighter when surrounded by a light area.

False: it will appear darker

What causes the effect seen in Simultaneous Contrast?

Lateral inhibition of central, similarly colored areas by surrounding photoreceptors responding to lighter/darker areas results in misperception of the central areas as being darker/lighter themselves, respectively

What illusion cannot be explained by lateral inhibition?

White's Illusion

What is White's Illusion?

Perception of similarly colored rectangles within white/black bands as being darker/ lighter, respectively

Why would lateral inhibition not produce the effect observed in White's Illusion?

Lateral inhibition would create an opposite effect, because there is greater inhibition from lighter bands on grey rectangles and vice versa with black bands inhibiting grey rectangles less (which should make an effect like the one seen in simultaneous contrast)

What produces the effect seen in White's Illusion?

Belongingness

What is belongingness (IN VISION)?

Change in appearance of an area depending on where it is perceived to belong

Where does the effect of belongingness likely occur?

In the cortex (rather than the bipolar cells of the retina where lateral inhibition occurs)

What physiological mechanism produces belongingness?

The physiological mechanism is unknown

What is a receptive field (IN VISION)?

The region on the retina in which stimuli will activate a neuron in the optic nerve

What is a receptive field (IN GENERAL)?

An area of receptors that affects the firing rate of a given neuron in a circuit

How would you research a receptive field in vision?

Monitoring single cell responses after presenting an area of the retina with a stimulus (using light to stimulate and an electrode to measure)

What is center-surround antagonism?

(Assuming an excitatory center, inhibitory surround receptive field)

Center of the receptive field (excitatory portion) turns up firing rate; Surrounding area of the receptive field (inhibitory portion) turns it down.

[NOTE: effect will be flipped if the center is inhibitory and the surrounding area is excitatory]

What will create the highest response from a center-surround receptive field?

Stimulation of ONLY the excitatory portion

What will create the lowest response from a center-surround receptive field?

Stimulation of ONLY the inhibitory portion

What will create an intermediate response from a center-surround receptive field?

Stimulation of both the inhibitory and excitatory portions

Where do signals from the retina travel to via the optic nerve?

1) Lateral Geniculate Cortex (LGN), then to the 2) primary visual receiving area in the occipital lobe, then 3) through two pathways to the temporal and parietal lobes before reaching 4) the frontal lobe

What are the names of the primary visual receiving area in the occipital lobe?

1) The striate cortex or 2) Area V1

Where is the Lateral Geniculate Nucleus (LGN) in the brain?

In the thalamus (relay center)

Where does visual information from the left side of your visual fields go to?

The left side of your occipital lobe

Where does visual information from the left and right sides of your visual field cross to their respective sides?

The optic chiasm

What kind of receptive fields do Lateral Geniculate Nucleus (LGN) cells have?

Center-surround receptive fields

What is the major function of the Lateral Geniculate Nucleus (LGN)?

To regulate neural information from the retina to the visual cortex

Where are signals sent to the Lateral Geniculate Nucleus (LGN) originating from?

1) The retina, 2) the cortex, 3) the brain stem, and 4) the thalamus

How are signals in the Lateral Geniculate Nucleus (LGN) organized?

By 1) eye, 2) receptor type, and 3) type of environmental information

True or False: The pathway away from the retina shows neurons which fire to MORE complex stimuli.

True - as information is sent away from the retina, neurons fire for more complex or specific stimuli

What cells in the visual cortex are feature detectors?

1) Simple cortical cells, 2) Orientation tuning curve, 3) Complex cortical cells, and 4) End-stopped cortical cells

What is the orientation tuning curve?

A function relating the firing rate of a neuron to the orientation of the stimulus

What is the receptive field of ganglion cells (optic nerve fiber) like?

Center-surround; responds best to small spots but will also respond to other stimuli

What is the receptive field of simple cortical cells like?

Excitatory and inhibitory areas are arranged side by side; responds best to bars of particular orientations

What is the receptive field of complex cortical cells like?

Responds best to movement of a correctly oriented bar across the receptive field, usually responding better to specific directions of movement

What is the receptive field of end-stopped cortical cells like?

Responds to corners, angles, or bars of particular length moving in a particular direction