PSB2000 Test 3 Study Guide Vision 1 What does perception depend on Describe the general path that stimulus energy takes through our brain leading to conscious perception How does light enter the eye Describe the path it takes through the cell layers of the retina and the path of signal transduction How are rods and cones similar and different On what point of the retina are cones most densely packed With which types of cells do photoreceptors synapse Do they excite or inhibit those cells review slide 17 of the notes On what is our perception of color based Perception Sensory experiences are the result of brain activity responding to stimuli in the environment receptors in the brain convert environmental energy into action potentials We have sensory experiences because the environmental energy is Transduced converted from the environment into something our brain is able to process We perceive 2 types of stimulus energy Form and Intensity EX Light is organized into waves and waves can be tall or short we interpret the wavelengths as color frequency and wave height amplitude as brightness Perception also depends on What type of receptors are stimulated How many how much they re stimulated What pattern theyre stimulated What sensory neurons they project to General Route of Info leading to perception When Light hits the eye Receptors on sensory neurons retinal photoreceptors Nerve to the CNS Optic Nerve Thalamus Lateral geniculate nucleus Primary Cortex striate cortex V1 Association Cortex 2ndary visual cortex Photons of light enter through the Pupil which is then focused by Cornia and Lens to the Retina at the back of the eye where the position becomes inverted Pupil cornea lens retina Photoreceptors on the Retina Connections in Retina Sensory Neurons that contain pigments change form when they absorb light particles which in turn changes the firing activity of the receptor cells Light is transduced into action potential and neurotransmitter release The retina contains 2 types of photoreceptors Rods and Cones Rods Respond well to dim light overstimulated by bright light abundant in periphery how we know something is there using our peripheral vision necessary to see black and white Cones Need bright light to respond but provide detailed information Abundant in center of retina especially in Fovea depression in retina where light hits unimpeded by other cells essential for color vision because cones contain specialized photopigments Light info received by the cells on the very back of the eye and then relayed to cells more rostral anterior Photoreceptors Horizontal Cells Bipolar Cells Amacrine Cells Ganglion Cells Connections across fewer cells gives us better acuity sharpness definition Photoreceptors Bipolar Cells Ganglion Cells Transduction of light energy in the Retina Shows the pathway of light In the absence of light photoreceptor cells fire spontaneously Absorbing light reduces how much they fire Photoreceptor Cells have inhibitory synapses with bipolar cells Decreasing inhibition of photoreceptor cells by reducing the spontaneous firing rate increases the firing rate of bipolar cells The Bipolar cells have excitatory synapses with ganglion cells thus passing along the message Color Vision Energy of light is organized into wavelengths and we perceive those cycles btwn 400 700 nm per second Color isn t a property of light itself rather its our perception based on the wavelength with which photons hit photoreceptors Our perception of individual colors is based on the rates of responding of the 3 different subtypes of cones Red Blue Green Cones that respond to certain ranges of wavelengths Color Vision Deficiency Color Vs Brightness Coding is based on not only what type of cone is responding but also the frequency of response relative to other cones we may see something as Red more than it is yellow because of the rate of response from the Red cone as compared to the Green cone Is difficulty discriminating between colors Occurs when genes don t code for all 3 types of cones or same photopigment is produced in 2 different types of cones Instead of producing Green the Green cone would produce Red thus altering our perception of the color Serves as further evidence that color is result of biological changes that result in our perception and not a property of light itself light contains no actual colors its how we perceive the light that the colors are seen Describe the path of the optic nerve what and where do fibers cross and to what two areas do they project The axons of what type of cells make up the optic nerve and what is the result of the optic nerve passing through the retina What type of ganglion cells that project to the lateral geniculate thalamus are important for distinguishing detail and which are more important for perceiving motion How else do these cell types differ What is V1 necessary for What is it not necessary for Vision 2 The Optic Nerve Axons of ganglion cells combine to form the optic nerve which carries info from eye to brain Where these axons accumulate and leave the eye as the optic nerve interrupts the layer of receptor cells in the retina creating a blind spot we don t usually notice this blindspot because our brain will fill in gaps in a predictable environment because we have double eyed vision best way to think of blindspot is a blindspot while driving The Optic Chiasm and direction of Projections The optic nerves from each eye meet at the Optic Chiasm of the axons from each eye cross to the opposite side of the brain while the other remain on same side Nasal side contralateral Temporal side Ipsilateral This results in all info from the right side of the eye the actual right side of one eye not your right eye itself being processed by the left brain hemisphere and the info from the left side of your eye again same principal as above being processed by the right hemisphere Lateral Geniculate Nucleus of the Thalamus Receives input from 3 types of ganglion cells via Optic Nerve Parvocellular Magnocellular and Koniocellular Parvocellular small receptive fields good at discerning detail color and telling you what youre looking at Magnocellular large receptive fields good at discerning motion depth and answering where something was coming at you from Koniocellular diverse group with multiple functions Necessary for conscious perception of visual info Indiv who are blind due to eye damage Tony Sparano are able to engage in visual imagery Indiv who are blind
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