Chapter 9 - Sensation and Perception

Question 1

What are the three key variables of sensory receptors?

Answer 1

1) Receptive fields - region of sensory space in which a stimulus modifies the activity of a receptor
2) Receptor density - sensory receptors are not evenly distributed across the body or its organs
3) Receptor sensitivity - different types of receptors are more sensitive to certain stimuli than others

Question 2

What’s the neuron discharge rate?

Answer 2

• The number of APs/second encoded by a stimulus or sometimes qualitative changes

Question 3

What’s the visible light spectrum?

Answer 3

• 400-700nm

Question 4

Which are more abundant, rods or cones?

Answer 4

• Rods outnumber cones
  -Cones more centralized at the fovea

Question 5

Why is our vision blurrier in dim lighting?

Answer 5

• Because we’re more reliant on our rods in low lighting, but our cones are respnsible for visual acuity

Question 7

Which nucleus in the thalamus is responsible for integrating visual inputs?

Answer 7

• The lateral geniculate nucleus (LGN)

Question 7

Which LGN layers are dedicated to P-cells and which layers are dedicated to M-cells?

Answer 7

• P-cells - layers 3-6
• M-cells - layers 1-2

Question 7

What are the general densities of the different types of cones?

Answer 7

• There are approximately equal numbers of red and green cones but fewer blue cones
• They’re a;; connected to retinal ganglion cells (RGCs)

Question 7

What are the two types of RGCs and which receptors do they correspond to?

Answer 7

• Magnocellular cells - magno- means large, and they receive inputs from rods
• Parvocellular cells - parvo- means small, and they receive input primarily from cones. Sensitive to colour and fine detail. Found mainly in fovea
• These two cells form the optic nerve and go to the thalamus

Question 8

Which side of the retina sends info across the optic chiasm (contralateral)?

Answer 8

• Info from the nasal retina sends info contralaterally while the temporal retina remains ipsilateral

Question 9

Where is the optic chiasm located in the brain?

Answer 9

• Underneath the hypothalamus

Question 10

What are the two major visual streams?

Answer 10

1) The geniculostriate system - used for conscious visual stimuli and contains all of the P-cells and some of the M-cells
2) The Tectopulviar system - more unconscious, better for orienting to visual stimuli and is evolutionarily older

Question 11

Dorsal vs. ventral streams?

Answer 11

• Dorsal - The “how” stream, vision for action, found up top
• Ventral - The “what” stream, vision for identification, found on the bottom

Question 12

Even though info from both eyes goes to both LGN’s but which layers receive which info?

Answer 12

• Info from the contralateral (nasal retina) side goes to layers 1, 4, and 6
• Info from the ipsilateral (temporal retina) side goes to layers 2, 3, and 5
• This way, M-cell and P-cell info are reaching both LGNs

Question 13

How is M-cell and P-cell info organized in the striate cortex (aka V1)?

Answer 13

• M-cells - layer 4 alpha
• P-cells - layer 4 beta
  *Makes sense because afferent info always goes to layer four

Question 14

What’s visual form agnosia?

Answer 14

• Individual is unable to recognize objects around them
• It’s a perceptual deficit (they’re still able to see)
• Also called blind sight
• Occurs if there’s injury/damage to the ventral pathway (“what” pathway)

Question 15

What’s optic ataxia?

Answer 15

• Deficit in the visual control of reaching and other movements
• Also a perceptual deficit
• Caused by injury/damage to the dorsal pathway