What does perception depend upon? Describe the general path that stimulus energy takes through our brain, leading to conscious perception:-Objects in our environment emit or reflect energy that stimulates receptors on sensory neurons. This environmental energy is converted, or transduced, into action potentials via receptor signals in the brain. -We distinguish between 2 main types of stimulus energy:1. Form2. IntensityEx: Light, as we perceive it, is organized into waves, which can be tall or short dependingWavelength (frequency/form; interpreted as color) and wave height (amplitude/Intensity; interpreted as brightness); the same can be said for sound, whose frequency isInterpreted as pitch, and amplitude as loudness-Perception depends on multiple factors:- What types of receptors are stimulated? o Law of Specific Nerve Energies: proposed by Muller; states that the nature of perception is defined by the pathway over which sensory information is carried; the origin of the sensation is not important; rather, the differences in sensory quality (b/w hearing and touching, or b/w seeing and hearing, etc.) are caused bythe different nervous structures that these stimuli excite- How many/how much are the receptors stimulated?- In what pattern are they stimulated?- What neurons do those sensory neurons project to?-GENERAL ROUTE OF INFORMATION LEADING TO PERCEPTION:RECEPTORS ON SENSORY NEURONS > NERVE TO THE CENTRAL NERVOUS SYSTEM > THALAMUS >PRIMARY CORTEX > ASSOCIATION CORTEXV I S U A L R O U T ERETINAL PHOTORECEPTORS OPTIC NERVE LATERAL GENICULATE PRIMARY VISUAL SECONDARY VISUAL NUCLEUS CORTEX 1 (V1; CORTEX (V2-V8) STRIATE CORTEX)How does light enter the eye? Describe the path it takes through the cell layers of the retina:-When light hits the eye, photons of light enter through the pupil; these are focused by the cornea and lens to the retina at the back of the eye, where the image then becomes inverted-Photoreceptors on the retina are sensory neurons containing pigments that change form whenthey absorb photons (particles of light); this pigment alteration changes the firing activity; light energy is transduced into action potentials and neurotransmitter release-The success of the retina relies on its connections with other cells; light information is received by the cells on the very back of the eye and are then relayed to cells more rostral/anterior; connections across fewer cells=greater acuityHow 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?Rods:- Respond well to faint light- Overstimulated by bright light- Abundant in periphery- Necessary for black and white visionCones: - Need bright light to respond, but show more detailed info- Abundant in the center of the retina, especially in the fovea, which is a depression in theretina where light hits unimpeded by other cells- Essential for color vision; contain specialized photopigments -In the absence of light, photoreceptors spontaneously fire, yet absorbing light reduces the amount that they fire. -Photoreceptor cells have inhibitory synapses w/ bipolar cells-DECREASING inhibition by REDUCING the spontaneous firing rate of photoreceptors INCREASES the firing of the bipolar cell(s) with which the photoreceptor cells synapse -The bipolar cells have excitatory synapses w/ ganglion cells, and so they pass the message alongIN OTHER WORDS…when it’s dark, the inhibitory NT is released by the photoreceptor because there is no light present, therefore making it impossible for the postsynaptic cell to fire;however, in the presence of light, the inhibitory NT IS NOT released, enabling the postsynaptic cell to fire its own excitatory NTs to the ganglion cellsOn what is our perception of color based? What happens when the same photopigment is produced in 2 different types of cones?-Humans can perceive light whose wavelengths cycle between 400 nm to 700 nm per second-Color is not a property of light; it is the product of our perception based on the wavelength with which photons hit photoreceptors; individual colors are perceived based on the relative rates of response of 3 different cone subtypes that respond to certain ranges of wavelengths-Coding is based not only on what type of cone is responding, but also the frequency of the response relative to other cones-Color vision deficiency is when one has difficulty discriminating between different colors; this occurs when:- Genes do not code for the production of all 3 types of cones - The same photopigment is produced in 2 different types of cones-This serves as evidence that color is a result of biological changes that result in our perception, and is not a property of light itself ______________________________________________________________________________Describe the path of the optic nerve – what and where do fibers cross, and to what 2 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?-The axons of ganglion cells combine to form the optic nerve, which carries info from the eye tothe brain; portions of the optic nerve go to the superior colliculus where eye movement is controlled-A blind spot is created at the point of entry of the optic nerve on the retina and is insensitive tolight; humans don’t notice their blind spot because we have binocular (double-eyed) vision, andour brain will fill in gaps in a predictable environment -The optic nerves from each eye meet at the optic chiasm, defined as the crossing of the optic nerves from the 2 eyes at the base of the brain; Half of the axons from each eye cross to the opposite side of the brain, and the other half stay on the same side - Nasal side=contralateral- Temporal side=ipsilateral-This results in all information from the right side of each eye being processed by the left brain hemisphere and vice versa. What type of ganglion cells that project to the LGN are important for distinguishing detail andwhich are important for perceiving motion? How else do these cell types differ? -Once out of the optic nerve, information travels to the lateral geniculate nucleus of the thalamus, the primary relay center for visual information received from the retina of the eye; the LGN receives input from 3 types of ganglion cells via
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