Topic 110 - Object viewing, visual acuity, visual field, visual pathway

Question 1

Words to include in visual field

Answer 1

• Monocualr visual field
  
  • Preys
  • Spatial vision (less accurate)
• Binocular visual field
  
  • Predators
  • Primates
• Measurement of visual field
  
  • Perimeter
  • Hemisphere
  • Center of the sphere
• Spatial vision

Question 2

Words to include in visual acuity

Answer 2

• Sharpness of vision
• Minimal visual angle
• Anatomical mosaic of retina
• Functional mosaic of retina
  
  • Antagonizing system of the receptive fileds
• Chromatic aberration
• Difraction

Question 3

Words to include in object viewing

Answer 3

• Eye movement
  
  • Gaze movement
  • Saccadic movement
    
    • Scanning the object
  • The third eye movement
    
    • Fixation of an object
    • Small translocation
• Pupil reflex
  
  • Ampleness of the pupil
  • Smooth muscles
  • Sphinter muscles
    
    • Constricting the pupil
    • Parasympathetic nerves
  • Dilator muscles
    
    • Dilating the pupil
    • Sympathetic nerves
  • Reflex mechanism
    
    • Diameter of pupil

Question 4

Words to include in visual pathway

Answer 4

• Decussation in the optic chiasm
• Axons of the retinal ganglion cells
• Lateral geniculate body
• Primary visual cortex
• Temporal part of visual field
• Nasal part of visual field
• Dorsal part of visual field
• Ventral part of visual field
• Visual cortex
• Retina
• N. opitcus
• Optic tract

​

• ​Visual reflexes
  
  • ​Pupil reflex
  • Accommodation
  • Convergence
• Pretectum
  
  • ​Pretectal area
  • Midbrain structure
  • Subcortical visual system
  • Pupillary light reflex
  • Optokinetic reflex
  • Temporary changes to the circadian rhythm
• Superior colliculus
  
  • ​Tracts from the visual cortex (innervates superior colliculus)
  • Integrator of saccadical eye movement
  • Localization
• Lateral geniculate nucleus (LGN)
  
  • Thalamus
  • Relay station
  • Mangocellular part
    
    • M-type ganglion cells of the retina
  • Parvocellular part
    
    • P-type ganglion cells of the retina
  • Afferents
    
    • Sensory cortex
    • Thalamus
    • Brainstem
  • Filter
    
    • ​Non-retinal afferents
  • Retinal stimuli
    
    • ​Higher cortical areas (ø)
• Optic radiation​
  
  • Occipital lobe
  • Visual cortex
• Primary visual cortex
  
  • ​(Brodman’s 17)
  • Occipital lobe (medial and caudal)
  • Ocular dominance
    
    • ​Striated cortex
  • Neuronal columns
  • Cylinders
• Circadian rhythm
  
  • Hypothalamus and pineal gland
    
    • ​Suprachiasmatic nucleus
• Vestibulocerebellum

Question 5

Visual field

Define visual field

Answer 5

• Visual field: Fy fixed gaze the animal sees only a part of the surrounding space
• The sized of visual field differes for each color

Question 6

Visual field

Types

Answer 6

• Monocular vision
  
  • ​Spatial vision is less accurate, but the animal senses almost all the surrounding space by the eyes without moving the head
  • Preys
• Binocular vision
  
  • ​Controls a limited part of space but the accuracy of spatial vision is very high
  • Predators

Question 7

Visual field

Measurement of visual field

Answer 7

• Perimeter is used (can also measure color vision)

1. A small light spot is projected to the inner surface of a hemisphere positioned in front of the head
2. The eye examined is in the center of the sphere
3. The person examined signals when he/she sees the light spot moved into the visual field
4. Using different colors in different experiment, the edges of the visual field can be examined

• Visal field is smallest for red, and largest for white
• Nasal visual field is smaller than temporal visual field

Question 8

Visual acuity

Define visual acuity

Answer 8

• Visual acuity: Sharpness of vision (visual acuity) is the smallest angle under which two neghboring object-point will be still sensed as two distinguishable points
  
  • Minimal visual angle

Question 9

Visual acuity

What is the sharpness of vision determined by?

Answer 9

By the anatomical and functional mosaic of the retina

• Functional mosaic of retina: the vision of object is modified by the antagonizing system of the receptive fields
  
  • ​Several cones react together in the receptive field
• Anatomical mosaic of retina: light beams coming from the two neighboring object-points do not hit cones next to each other in the fovea

Question 10

Spatial vision

Answer 10

• Spatial vision is provided by two fundamental processes
  
  1. Only binocular vision​
  2. Both monocular and binocular vision
• Nearly perfect spatial vision is assured by:
  
  • Light intensity
  • Color and black-and-white contrasts
  • Head movements
  • Movement of objects relative to each other

Question 11

Eye movement

Give the types of eye movement

Answer 11

1. Gaze movement
   
   • ​​The animal is able to see the object sharply within the visual field
   • Slow, wide range movement
2. Saccadic movement
   
   • Scanning the object​​
   • Fast movement
3. The thrid eye movement
   
   • ​​Occuring with fixation of an object
   • Fast, with small translocation (drift)

• In some species (dogs) the eyes can move in a large range
• In other species (cat) the eyes cannot move as much, so the neck muscles play a role in looking at the object of interest

Question 12

Pupil reflex

Answer 12

• The amount of light entering into the eyes is determined by the ampleness of the pupil, which is regulated by smooth muscles
• The muscle constricting the pupil (sphincter muscle) is innervated by parasympathetic nerves
  
  • ​Mydriasis
• The muscle dilating the pupil (dilator muslce) is regulated by sympathetic nerves
• The diameter of the pupil is controlled by several reflex mechanisms
  
  • Throwing light into one eye elicits the constriction of the pupil, and at the same time a similar reaction is seen in the other eye.

Question 13

Visual pathway

Answer 13

• After decussation in the optic chiasm the axon of the retinal ganglion cells project to the lateral geniculate body, from where the next fibers reach the primary visual cortex
• The primary visual area (Brodmann’s area 17) projects to further brain regions
• Retina:
  
  • The temporal visual field and nasal visual field project to the opposite sides of the retina
  • The dorsal and ventral parts of visual field are reversed in the same way
  • The same mapping occurs in the visual cortex and retina
• Optic nerve:
  
  • ​Fibers of n. opticus originating from the same quartes of retina run together
• Optic tract:
  
  • ​Formed by medial and lateral bundle
    
    • Lateral branch:
      
      • Towards lateral geniculate body
      • Perception of visual information
    • Medial branch:
      
      • Towards pretectum, superior colliculus
      • Visual reflexes (pupil reflex, accommodation, convergence)
• Pretectum:
  
  • ​Midbrain structure
  • Involved in mediating behavioral responses to acute changes in ambient light such as:
    
    • Pupillary light reflex
    • Optokinetic reflex
    • Temporal changest to the circadian rhythm
• Superiro colliculus:
  
  • ​Innervated by tracts from the visual cortex
  • Integrator of accadical eye movement
  • Main function: localization of an object
• Lateral Geniculate Nucleus (LGN)
  
  • Part of thalamus
  • Important relay station
  • Function: filter which, depending on the non-retinal afferents, does not let certain parts of the retinal stimuli pass to the higher cortical areas
  • Fibers of the LGN radiate to the primary visual cortex (Brodman’s area 17)
    
    • Location: medial and caudal regions of the occipital lobe
• Optic radiation:
  
  • ​In the medial part of the occipital lobe, the information is transmitted to the visual cortex via radiation