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PSYC 375: CHAPTER 9


How Do We Sense, Perceive & See The World? {Exam 2 2/4}
  
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What are sensory receptors?
 
- specialized cells that transduce (convert) sensory energy into neural activity
What are the parts of the sensory systems:
 
- Light: where light energy is converted to chemical {producing action potentials}
- Auditory: air pressure that is converted to mechanical energy
- Somatosensory: mechanical energy
- Taste/Olfaction: chemical molecules {air, food}
What is a receptive Field?
 
- region of the visual world that stimulates a receptor cell/neuron
What is optic flow?
 
- a stream of visual stimuli that accompanies an observer's forward movement through space
What is auditory flow?
 
- changes in sound heard as a person moves past a sound source or vice versa
What do both the auditory and optic flow tell us?
 
- it tells us how fast we are going
- the direction in which we are going
- and whether or not the object is moving {or if its us}
What is receptor density?
 
- it is important in determining the sensitivity of a sensory system
- our sensory systems use different receptors to enhance sensitivity under different conditions
- differences in receptor density in human auditory-receptor organs may explain things like how musicians have the ability ot "pitch perfect"
What is the neural relay
 
- this is where all receptors connect to the cortex through 3-4 intervening neurons
- most have 3, auditory has 4.
- they allow sensory systems to interact
- located in the spinal cord, brainstem, or the neocortex
How do sensory signals encode the features of particular sensations?
 
- the presence of a stimulus can be encoded as an increase/decrease in a neuron's firing rate
- the amount of increase or decrease can encode the stimulus intensity
what are sensory signals coded as?
 
- as incoming sequences of action potentials to the CNS
How do action potentials code the different kinds of sensations? (ex. vision vs. touch)
 
- different sensations are processed in different cortical areas
- learn to distinguish senses through experience
- each system has a distinct wiring set up at all levels of the neural organization
What is syntesthesia?
 
- mixing of the senses
- Ex. when you can "feel" sounds
- Ex. like nails on a chalkboard
What is the Topographic Map?
 
- spatially organized neural representations of the external world.
- how most mammals represent the sensory field of each modality in the neo/cerebral cortex
What is sensation?
 
- the registration of physical stimuli from the environment by the sensory organs
What is perception?
 
- subjective interpretation of sensations by the brain
- how we interpret what we see
What is the retina?
 
- the light-sensitive surface -- backing of your eye
- it consists of neurons and photoreceptors
- it translates light into action potentials
How does the eye work?
 
- as light enters, it bends by the cornea, travels through the pupil, and bends again by the lens
What is the opening where the blood vessels enter in the eye
 
- the optic disk {aka. blind spot}
What are the 2 types of optical errors of refraction?
 
- it's when the lens doesn't bend as much as it's supposed to, and the light just ends up being focused before/after the retina
What is myopia?
 
- nearsightedness
- the inability to see things far away
- light is undershot and doesn't reach the retina
What is hyperopia
 
- farsightedness
- inability to focus on near objects
- light is overshot so it goes past the retina
- more common in old people, not as elastic as before.
What is the Fovea?
 
- the region at the center of the retina that specializes in fine detail
- this is also where cones are concentrated (color vision)
- there are no rods in this area
What is the blind spot?
 
- region of the retina (optic disk) where axons form into the optic nerve and leave the eye
- no photoreceptors
What are 2 conditions of the blind spot?
 
- Papilloedema: swelling of the disk caused by cranial pressure
- optic neuritis: inflamation of the optic nerve
The difference between rods & cones?
 
Rods
- more in numbers
- sensitive to light -- good for night vision
- black & white
Cones
- color vision
- specialize in fine detail and only located in the fovea
- red, green, blue
What happens when light hits the photoreceptors?
 
- it triggers a chemical reaction that leads to the change in membrane potential
- the change leads to a change in the release of neurotransmitters
What are the 4 types of retinal-neurons?
 
- bipolar cell: receives input from photoreceptors
- horizontal cell: links photoreceptors & bipolar cells
- amacrine cell: links bipolar cells & ganglion cells
- retinal ganglion cell: gives rise to the optic nerve
What are the 2 types of retinal ganglion cells?
 
- magnocellular cell (M cell)
- parvocellular cell (P cell)
What is the magnocellular cell?
 
- receives input mainly from rods
- sensitive to light and moving stimuli {not color though}
- found mainly throughout the eye, but not at the fovea
- bigger than P-cells
What are parvocellular cells?
 
- Receive input from cones
- sensitive to color differences and form
- found ONLY in the retina
- small-cells.
What is the Optic Chiasm?
 
- junction of the optic nerves from each eye
Explain the crossing over & visual pathways
 
- axons from the nasal retina cross over to the OPPOSITE side
- axons from the temporal retina remain on the same side.
- just before the optic nerves enter the brain, the optic nerves cross forming the optic chiasm.
What is the dorsal visual stream?
 
- pathway that originates in the striate cortex and projects to the PARIETAL lobe.
- the HOW pathway {how it moves in the environment}
what is the ventral visual stream?
 
- The pathway that originates in striate cortex and projects to the TEMPORAL lobe
- the WHAT pathway
How many layers does the striate cortex have>
 
six. {I to V}
what do each of the 6 layers of the LGN do?
 
- layer 2, 3, 5: receive fibers from the ipsilateral eye (eye on the same side)
- layer 1, 4, 6: receve fibers from the contralateral eye (eye on the opposite side)
- this lets us combine the information from the eyes
Which layers do P cells go to?
 
- layers 3-6 because they are responsive to color and fine detail
Which layers do M cells go to?
 
- layers 1-2 because it controls info processing about movement.
What is the tectopulvinar Pathway
 
M cells -> Superior colliculus -> pulvinar
What are the 2 major divisions of the pulvinar
 
- medial pulvinar: which sends connections to the parietal lobe
- lateral pulvinar: which sends connections to the temporal lobe.
what is the primary visual cortex?
 
- receives input from the LGN
what is the extrastriate cortex?
 
- the visual cortical areas outside the striate cortex
Explain the heterogeneity of V1
 
- blobs: region in striate cortex that contains color-sensitive neurons
- interblob: regions that separate blobs --> peception of form and motion
explain the heterogeneity of V2
 
- thick stripes: receive information from movement sensitive neurons
- thin stripes: receives information from color-sensitive neurons
- pale zone: receives information from form-sensitive neurons
explain the left and right visual lobe
 
region of the visual world that is seen by your eyes
- left visual lobe: right hemisphere
- right visual lobe: left hemisphere
What is the on-center cell?
 
- when light falls onto the central circle
What is the off-center cell?
 
- where the lights fall on the periphery of the central circle.
What is the luminance contrast
 
-the amount of light reflected by an object relative to its surroundings.
What is stimulus equivalence
 
recognizing that an object is the same across different viewing orientations
- so even if you're looking at it through tinted glasses, you can still tell that your mac is black.

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