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 Form 2 Intensity Ex Light as we perceive it is organized into waves which can be tall or short depending Wavelength frequency form interpreted as color and wave height amplitude Intensity interpreted as brightness the same can be said for sound whose frequency is Interpreted 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 by the different nervous structures that these stimuli excite How many how much are the receptors stimulated What neurons do those sensory neurons project to In what pattern are they stimulated GENERAL ROUTE OF INFORMATION LEADING TO PERCEPTION RECEPTORS ON SENSORY NEURONS NERVE TO THE CENTRAL NERVOUS SYSTEM THALAMUS PRIMARY CORTEX ASSOCIATION CORTEX V RETINAL PHOTORECEPTORS S I U A OPTIC NERVE LATERAL GENICULATE PRIMARY VISUAL SECONDARY VISUAL O U R E T L 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 when they 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 acuity 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 Rods Respond well to faint light Overstimulated by bright light Abundant in periphery Necessary for black and white vision Cones 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 the retina 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 along IN 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 cells On 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 to the 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 to light humans don t notice their blind spot because we have binocular double eyed vision and our 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 and which 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 the optic nerve 1 Parvocellular small receptive fields good at discerning color details answers the 2 Magnocellular large receptive fields good at discerning motion depth answers the question of what we re seeing question of where the thing is we are seeing diverse group w
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