up: [[Sensation and Perception]] # Vision sensation and perception ![[Pasted image 20221003101904.png]] Why do images like this make us laugh? It's because our visual system, like other sensory systems, uses past knowledge to make perceptions about the objective sensory stimuli that signal to our brain. ![[Pasted image 20221003104435.png]] Put your finger in the middle of these shapes and you can see the shapes are the same color. ### Reception Light comes in through the pupil of the eye and travels through the layers of the retina to reach the receptor cells. ![[Pasted image 20221003102344.png]] The two types of receptor cells it reaches are rod cells and cone cells. ![[Pasted image 20221003102320.png]] #### What is the difference between rod and cone photoreceptors? Rods are very sensitive to light and therefore are great for seeing in dim light but have low acuity. Cones, however, come in many different varieties all of which are sensitive to different wavelengths (color) of light and have high acuity. #### What is the distribution in rods and cones across the eye? The center of the eye near the fovea has much more cones where as the periphery has more rods. This is why you can't distinguish between colors or shape very well on the sides of your eyes. #### What does opsin and rhodopsin activation do in rod and cones? Both rods and cones have discs which have opsin proteins activated by specific wavelengths of light that cause the release of G-proteins that have second order effects. Rods have more rhodopsin than cones which are especially useful in dim light. This reminds me of [[Neuropharmacology#^81cc80||metabotropic receptors.]] #### Transduction #### How is light transduction unique to other sensory pathways? Light transduction occurs when light stimulates a photopigment molecule opsin n in rods or cones that causes a second order cascading effect resulting in Na+ channels closing and causing hyperpolarization which reduces the release of neurotransmitters to bipolar cells rather than increasing it. ![[Pasted image 20221003105520.png]] These bipolar cells react to reducing neurotransmitter by increasing transmitter release to ganglion cells that then stimulate more action potentials which go to thalamus (see: [[Sensory informational flow]]). #### Why is adaptation critical for vision? [[Sensation and Perception#What is adaptation|Adaptation]] is critical for vision because it allows us to process differing light intensities. It may take a few minutes before you eyes adapt to a new light environment, but it does. #### How is the fovea different in receptor density compared to other places in the eye? Light passing through the fovea doesn't have to travel through a bunch of layers to reach the receptor molecules in the back of the brain. #### What is lateral inhibition? Your excited neurons capacity to inhibit the activity of neighbors. Our visual system uses this process to make the edges between dark and light vision more acute which evolutionary makes sense as the [[The brain has evolved to prioritize novel information]] which is what allows us to see the edges between objects. The most excited cells are the ones that win the battle of lateral inhibition. ![[Pasted image 20221003105021.png]] ##### How does lateral inhibition shape perception of motion? By stimulating cells responsive to one direction of motion, you tire them out and make yourself more apt to see motion from the other direction creating an illusion of movement. #### What factors determine how responsive cortex cells are to light? They respond to location of light, intensity of light, as well as the orientation of light. ![[Pasted image 20221005103244.png]] ### Transmission Like most other sensory pathways, action potentials caused from light coming to your left or right eye are transmitted to opposite sides of the brain when they reach the optic chiasm. However, it's a bit more nuanced than this because light coming in to our eyes on the right visual field go to the left side of the brain and light coming into our eyes from the left visual field go to the right side of the brain. The transmission process goes from eyes, to thalamus, to primary visual cortex. ![[Pasted image 20221003105851.png]] ### Analysis Analysis is the process of analyzing both orientation and movement of the visual stimuli in the primary visual cortex to perceive visual stimuli. #### How do complex cells in visual cortex respond to light differently than simple cells? Complex cells in the retina are sensitive to orientation as well as *movement* because they receive input from rows of ganglion cells rather than just orientation like simple cells. This is because the convergence of retinal ganglion cells creates complex receptive fields that make differing orientations and motions better for causing action potentials. ![[Pasted image 20221005104107.png]] #### What is ocular dominance? Cortical neurons have a specific and predictable preference for left or right eye activation. This monkey study was done to show that the brains cortical neurons switch from left to right eye dominance intermittently. ![[Pasted image 20221005104837.png]] This same thing can be done to show differences in cortical neurons preference for orientation. ![[Pasted image 20221005105159.png]] #### How is the visual cortex organized? It's organized in columns with each column preferring analysis of light in the same orientation. Neurons in adjacent columns have a similar but slightly different orientation preferences and also shift between left and right eye reception because of ocular dominance. ![[Pasted image 20221005105737.png]] #### How do we determine the shape of objects? We simultaneously combine spatial frequency and contrast. High frequency waves show fine details where as low frequencies show the gradual shift between light and dark. ![[Pasted image 20221007101717.png]] #### Color ###### What are the three components of color? - Hue - Brightness - Saturation As with other senses, color perception is shaped by context and previous experience. Our visual system can subtract away color from an entire image because of the background making us see different colors. ![[Pasted image 20221007102313.png]] In this image ###### What is the trichromatic theory of color vision? There are three kinds of cones and each respond to a different color of wavelength by causing more action potentials being released. Precise hue discrimination depends on the relative level of frequencies between the three cone classes. ![[Pasted image 20221007103154.png]] **Notice that none peak in the red.** We see red when the larger wavelength cones are activated while the others aren't. ##### How does staring at one color effect your vision? You will see more of the color on the opposite wavelength once looking away your opsin for that color get's used up. ##### How does red color vision blindness occur genetically? The gene for long wavelength opsin occurs in X chromosomes meaning a deficit causes phenotype change in males (they only have one X chromosome) but not females. People with this gene deficit have difficulty seeing red. This is why it makes no sense to paint fire engines red as a significant part of the population won't be able to see it well. Instead they should be colored bright yellow. ### Integration Integration is your brains process of understanding if a visual stimulus is from a person, object, or something else. #### What is the dorsal stream responsible for in vision? It integrates vision for the where and how of movement. It also includes mirror neurons that show action potentials when someone else does something. ##### What is the responsibility of the ventral stream in visual perception? It is responsible for naming and identifying objects and resides at the base of the occipital lobe to the temporal lobe. ![[Pasted image 20221017103626.png]] ##### How does the brain perceive faces? The left and right sides of faces are processed in different hemispheres of the brain inside of the ventral stream that goes from the base of the [[Areas and Functions of the Brain#Occipital Lobe|Occipital lobe]] to the [[Areas and Functions of the Brain#Temporal Lobe|Temporal lobe]]. Related: ___ # Resources