up: [[Sensation and Perception]] # Vision sensation and perception ![[Pasted image 20221003101904.png]] 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 ###### What path does light take to reach the photoreceptors at the back of the eye? Light comes in through the pupil of the eye and travels to the retina to reach the receptor cells. ![[Pasted image 20221003102344.png]] ###### What are the two types of receptor cells in the retina? 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. #### Transduction #### How does photoreceptor activation cause light transduction? Light transduction occurs when light stimulates G-coupled protein receptor opsin in cones and rhodopsin in rods that causes a second order cascading effect resulting in Na+ channels closing and leading to hyperpolarization which reduces the release of neurotransmitters to bipolar cells. These bipolar cells react to reducing neurotransmitter by sending [[Excitatory postsynaptic stimulus (EPSP)]]s to ganglion cells which send their action potentials to thalamus (see: [[Sensory informational flow]]). ![[Pasted image 20221003105520.png]] #### Why is adaptation critical for seeing different light intensities? Without [[Adaptation]] we wouldn't be able to process different light intensities. In the dark, we couldn't increase our sensitivity to light and in a light environment we couldn't decrease our sensitivity to light. #### What is lateral inhibition? [[Lateral inhibition]] is your excited neurons capacity to inhibit the activity of neighbors. ###### What does our visual system mostly use lateral inhibition for? 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 stimuluses in 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 three 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 ###### What determines if light coming to your eyes goes to the left or right side of your brain? Light coming in to our eyes through our 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. ![[Pasted image 20221003105851.png]] ###### What is the typical transmission pathway for visual information in the brain? The transmission process goes from eyes, to thalamus, to primary visual cortex. ### 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 cortical cells in visual cortex respond to light differently than simple cells? Where as simple cortical cells are sensitive only to orientation of light, complex cortical cells in the retina are sensitive to orientation *and* movement because they receive input from multiple rows of ganglion cells rather than just one. 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 and right or left eye dominance. Neurons in adjacent columns have a similar but slightly different orientation preference and a opposite eye 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]] Like in this image. ###### What is the trichromatic theory of color vision? There are three kinds of cones, small, medium and large wavelength. Each respond to their color wavelength by stimulating more action potentials. 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.** ###### How do we see the color 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? The cone cells for that color become fatigued and you will likely see more of the color opposite in wavelength for a bit once you look away. ##### 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 are the dorsal and ventral streams responsible for in vision? ![[Pasted image 20221019083209.png]] Dorsal stream integrates vision for motion and spatial relationships. It also includes mirror neurons that show action potentials when someone else does something. Ventral stream is responsible for the identification of objects and resides at the base of the occipital lobe to the temporal lobe. ##### How does the brain perceive faces on the right and left side of the brain? The left and right sides of faces are processed in different hemispheres of the brain inside of the ventral stream. Related: ___ # Resources