The Visual System:
Neuron to Higher Level Processing

 

 

 

 

 

 

 

 

I. The Visual System: - 3 major areas

 

II. Light -

Light is both a particle and a wavelength.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

III. Light Reception-

e.g. single-celled amoeba --

 

e.g. light sensitive area on lower forms of life-

 

 

 

 

 

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IV. Anatomy of Human Eye -

 

 

 

 

 

for far away objects--

 

 

for nearby objects--

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Process:

 

 

 

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  • photopigments: 2 components

1)

 

2)

 

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Types of visual receptors

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Location of the blind spot

 

 

 

 

 

V. Duplicity Theory -

 

cones:

 

 

 

rods:

 

 

 

 

 

 

 

 

 

cones:

 

 

rods:

 

 

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cones: (Phototopic)-

 

 

cones:

 

 

 

 

rods: (Scotopic)-

rods:

 

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Purkinje Shift -

 

 

 

cones:

 

 

rods:

 

 

 

 

Why the difference?

Convergence:

 

 

 

 

 

Results:

1)

 

 

2)

 

 

 

Measuring acuity:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

VI. Vertical Connections in Retina:

Types of cells:

Bipolar:

 

midget bipolar cells --

 

Diffuse bipolar cells --

 

Ganglion cells:

 

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How do this?

 

  • use single cell recording technique for one ganglion cell--find area on retina that corresponds to that one ganglion.

  • record normal low-level spontaneous level of activity of ganglion

  • then turn on light in & around that area and see how it effects the firing of the ganglion cell

 

 

  • ganglion cells respond differently depending on what area of their receptive field is stimulated

 

Two types of ganglion cells:

1) on-center, off-surround

 

2) off-center, on surround

 

 

 

 

 

 

 

 

 

e.g. on-center, off-surround

 

 

How does this type of receptive field work?

 

 

 

 

 

 

 

Horizontal and Amacrine Cells:

 

 

Lateral Inhibition:

 

 

 

 

 

 

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  • Mach Bands -

 

 

 

 

 

 

 

 

 

 

 

 

 

Explanation:

 

 

 

 

 

 

 

 

 

 

  • Also explains Hermann Grid & Scintillating Grid

  • Different amount of lateral inhibition cause the intersections to appear darker (dimmer) than the hallway areas.