Chapter Three Flashcards
(36 cards)
What is neural processing?
The interaction of electrical signals in many neurons
What is lateral inhibition?
Lateral Inhibition
Lateral - sides of neighboring neurons
Inhibition - decrease of neural firing across the neighboring neurons in the retina
Note that convergence plays a role in lateral inhibition.
Focus - how inhibition occurs across the retina & affects perception
Action Potentials - Neural firing
Size of firing remains the same - always +40mv
Rate (speed) of neural firing - changes intensity or strength of the electrical signal
- neurons can inhibit (slow down) other neurons
- neurons can excite (speed up) other neurons, making electrical signals stronger
How does lateral inhibition affect lightness?
Lightness - being aware of different shades ranging from white to gray to black
3 Lightness Perception phenomena explained by lateral inhibition:
The Hermann Grid
Mach Bands
Simultaneous Contrast
Why do we see spots at the intersections of the Hermann Grid?
The Hermann Grid
-Seeing “ghostlike” gray spots in the white intersections
Why do we see those spots? - some neurons (bipolar cells) have inhibitory affects on neighboring neurons
- these neurons inhibit the NEURAL area in the center of the intersection
- lateral inhibition reduces light in center = produces grey spots
- Why do we see light-dark borders in Mach bands?
Mach Bands - perceiving light and dark between borders
Why do we see light-dark borders in Mach bands? - Bipolar cells receive lateral inhibition from neighboring bipolar cells in the borders (contour line) of the Mach Bands
- HIGH intensity side (BRIGHTER light band) - LESS inhibition
- LOW intensity side (DARKER light band) - MORE inhibition
Explain how lateral inhibition affects simultaneous contrast
Simultaneous Contrast
-An illusion of brightness or color due to the affect of surrounding area.
An area of the same light intensity can appear:
- DARKER when surrounded by a LIGHT AREA
- LIGHTER when surrounded by a DARK AREA
How lateral inhibition affects simultaneous contrast
- BRIGHT surrounding area sends LARGE amount of inhibition to neurons in center area
- perception = dark in center
DARK surrounding area sends SMALL amount of inhibition to neurons in center area
-perception = lighter in center
The Hermann Grid
-Seeing “ghostlike” gray spots in the white intersections
Mach Bands
- perceiving light and dark between borders
Simultaneous Contrast
-An illusion of brightness or color due to the affect of surrounding area.
What is White’s illusion and why can we not explain it based on lateral inhibition? What is belongingness?
White’s Illusion
-Seeing light and dark rectangles even through lateral inhibition would result in opposite effect
cannot explain lateral inhibition = if lateral inhibition, rectangle B should be darker in the white surrounding area - not the case
Because it is not lateral inhibition, the reason is
Belongingness - an area’s appearance is affected by where that is perceived in its surrounding
+ effect probably occurs in cortex rather than the retina
How do receptive fields in the retina affect the electrical signals of the optic nerve?
Optic Nerve - electrical signals go from retina to optic nerve
- made up of axons (nerve fibers) from the ganglion cells in the retina
- about one million nerve fibers in the optic nerve for humans
Receptive Fields
-Nerve fibers (axons):
+ receive light from converging electrical signals to the ganglion cells in the retina
+process light info from receptive fields in the retina
Convergence
multiple neurons converge or connect to single neurons, sending electrical signals [rods]
Describe the “football analogy” for receptive fields. (pp. 61)
• One way to think about receptive fields is to image a football field & a grandstand full of spectators, each with a pair of binoculars trained on one small area of the field
• Each spectator is monitoring what is happening in his or her own small area
• All of the spectators together are monitoring the entire field
• Since there are so many spectators, some of the areas they are observing will wholly or partially overlap
Each spectator = an optic nerve fiber
Football field = retina
Small areas viewed by each spectator = receptive fields
• Just as spectators each monitor a small area but collectively take in information about what is happening on the entire football field, each optic nerve fiber monitors a small area of retina, and all of them together take in information about everything that’s happening in the retina
• Perception doesn’t occur based just on responses of optic nerve fibers, but the optic nerve fibers do contain information about everything that’s happening on the retina
excitatory area
increased firing
inhibitory area
decrease firing
center-surround receptive fields
Center-surround receptive fields- processing patterns in neurons
-Center - middle area of receptive field
-Surround - outside the middle area
Electrical signals in center can fire differently than the surround receptive field
center-surround antagonism
center-surround antagonism
-Electrical signals change based on where light hits receptive field
HIGH electrical response = light his EXCITATORY area
LOW electrical response = light hits INHIBITORY area
INTERMEDIATE electrical response = light hits BOTH areas
Know the pathways of light entering the eye into parts of the brain (pp. 62-64)
Visual Pathway to the Brain
Retina –>
Optic Nerve –>
Optic Chiasm- electrical signals can criss-cross –>
Lateral Geniculate Nucleus (LGN) - thalamus (feedback) –>
Occipital lobe - cerebral cortex - consists of visual receiving area (area V1 striate cortex)
How does the receptive fields affect the neurons in the striate cortex (area V1 or the visual receiving area of the occipital lobe)?
How do orientations of a bar affect the neural firing in the visual cortex?
• Lateral Geniculate Nucleus
- Receives 90% of light info from optic nerve
- Other 10% → goes to the superior colliculus (controls eye movement)
- LGN → receives info from retina & striate cortex
⇒ Holds on visual info about receptive fields
• Striate Cortex (V1): visual info from receptive fields continues to be processed
• Striate cortex
- Receptive Fields
⇒ Not organized as center-surround like retina & LGN
- Neurons in striate cortex have side-by-side receptive fields called simple cortical cells
• Feature Detectors in Striate Cortex
- Simple cells → firing occurs based on non-moving stimulus presented in a specific direction through a side-by-side receptive field
- Complex cells → firing occurs based on moving stimulus in a specific direction where neurons produce electrical signals
- End-stopped cells → firing occurs based on certain moving corners, angles, and length of stimulus where neurons produce electrical signals
Know the three types of cells: simple cells, complex cells, and end-stopped cells. (pp. 64-66)
Simple cells - firing occurs based on NON-MOVING STIMULUS presented in a specific direction through a side-by-side receptive field
Complex cells - firing occurs based on MOVING stimulus in a specific direction where neurons produce electrical signals
End-stopped cells- firing occurs based on certain moving corners, angles, and length of stimulus where neurons produce electrical signals.
Simple cells
Simple cells - firing occurs based on NON-MOVING STIMULUS presented in a specific direction through a side-by-side receptive field
Complex cells
Complex cells - firing occurs based on MOVING stimulus in a specific direction where neurons produce electrical signals
End-stopped cells
End-stopped cells - firing occurs based on certain moving corners, angles, and length of stimulus where neurons produce electrical signals.
Review Table 3.1 about receptive fields in the optic nerve, lateral geniculate nucleus (LGN), and visual cortex (pp. 66)
? (pp. 66)
