PSYC220 Chapter 5 Vision PDF

Chapter 5: Vision  Sensation and Perception Sensation= the biological process of transforming physical energy into neurological impulses Perception= interpretation or experience of sensory information We use sensation and perception to understand and intera...

Chapter 5: Vision  Sensation and Perception Sensation= the biological process of transforming physical energy into neurological impulses Perception= interpretation or experience of sensory information We use sensation and perception to understand and interact with the world around us  Learning Objectives 1. Know the properties of light waves 2. Describe the anatomy and physiology of the eye, including the process of lateral inhibition and the concept of concentric receptive fields 3. Trace the route of visual information from the retina to the cortex 4. Explain the main features of color vision 5. Describe different types of cues for perceiving depth  Learning Objectives 1. Know the properties of light waves 2. Describe the anatomy and physiology of the eye, including the process of lateral inhibition and the concept of concentric receptive fields 3. Trace the route of visual information from the retina to the cortex 4. Explain the main features of color vision 5. Describe different types of cues for perceiving depth Light Form of electromagnetic energy Visible light is between 380 and 760 nanometers Properties of the Stimulus Wavelength Color Amplitude Brightness Purity Saturation  Learning Objectives 1. Know the properties of light waves 2. Describe the anatomy and physiology of the eye, including the process of lateral inhibition and the concept of concentric receptive fields 3. Trace the route of visual information from the retina to the cortex 4. Explain the main features of color vision 5. Describe different types of cues for perceiving depth  Learning Objectives 1. Know the properties of light waves 2. Describe the anatomy and physiology of the eye, including the process of lateral inhibition and the concept of concentric receptive fields 3. Trace the route of visual information from the retina to the cortex 4. Explain the main features of color vision 5. Describe different types of cues for perceiving depth (contains the fovea) Retina Photoreceptors (rods & cones) Phototransduction= light waves into electrical signals Bipolar cells Receive info from photoreceptors and pass info to ganglion cells Ganglion cells Form optic nerve, send info to the brain Horizontal cells & amacrine cells Alter and refine signals Lateral inhibition Retina Photoreceptors Rods (scotopic vision) Cones (photopic vision) More abundant (~120 million) Less abundant (~6 million) Convergence onto bipolar cell 1 cone → 1 bipolar cell → 1 ganglion cell Night vision/dim light Day vision/bright light/color Located in periphery Located in and near fovea Photoreceptors Cones have a 1:1 convergence onto bipolar cells Multiple rods converge onto a single bipolar cell, multiple bipolar cells converge onto a single ganglion cell What might be the functional consequence of these convergence differences? Visual acuity is higher for cones than for rods Fovea Small depression in the retina of the eye where visual acuity is highest The center of the field of vision is focused in this region High concentration of cones, no rods Phototransduction At rest (in the dark) Cation channels are OPEN Na+ & Ca++ flow into cells → depolarization Continuous release of glutamate In this context, glutamate is INHIBITORY Net effect: inhibition of bipolar cells Phototransduction Rods and cones contain photopigments Chemicals that release energy when struck by light Rhodopsin When activated (in the light) Rhodopsin absorbs photon G-protein (transducin) is activated Activates second messangers (phosphodiesterase), which close cation channels Stops the release of glutamate Net effect: disinhibition (activation) of bipolar cells Horizontal Cells Photoreceptors provide input to both bipolar cells and horizontal cells Horizontal cells inhibit bipolar cells Lateral inhibition Lateral Inhibition Photo- Lateral inhibition: process where receptors interconnected neurons (horizontal cells) inhibit neighboring neurons (bipolar cells) Horizontal If one bipolar cell is activated, horizontal cells cells will inhibit the adjacent bipolar cells Bipolar cells Sharpens contrast to emphasize the borders strong excitation of objects weak inhibition Light strength of excitation high low Lateral Inhibition Horizontal cells 30 -55 10 10 10 5 +20 10 10 10 -5 Lateral Inhibition Practice Photoreceptors 8-15 are activated Which bipolar cell will have the highest activity level? Which bipolar cell will have the lowest activity level? Bipolar and Ganglion Cells Bipolar cells receive input from photoreceptors and horizontal cells Ganglion cells receive input from bipolar cells Concentric receptive fields Receptive field= an area in visual space to which a cell responds Concentric receptive field= 2 circles with different polarities Center and antagonistic surround ON center cells- increase activity when light shines in the center and decrease activity when light shines in the surround OFF center cells- decrease activity when light shines in the center and increase activity when light shines in the surround Practice Consider this bipolar cell where light is covering both the center and the surround. Would this cell exhibit its maximum level of activity? ON Basal level? Decreased level? What about this one? Light is mostly on the center and partially on the surround. Will it exhibit its maximum level of activity? Basal level? ON Decreased level? Concentric Receptive Fields Sharpens contrast to emphasize the borders of objects If these are ON center cells, which cells have the greatest level of activity? Ganglion Cells Midget Neurons Parasol Neurons Cell Bodies Small Large Receptive Fields Small Large Retinal Location In and near fovea Throughout the retina Color Sensitive? Yes No Respond to Detailed Shape Movement and broad outlines of shape Input from Cones Rods  Learning Objectives 1. Know the properties of light waves 2. Describe the anatomy and physiology of the eye, including the process of lateral inhibition and the concept of concentric receptive fields 3. Trace the route of visual information from the retina to the cortex 4. Explain the main features of color vision 5. Describe different types of cues for perceiving depth  Learning Objectives 1. Know the properties of light waves 2. Describe the anatomy and physiology of the eye, including the process of lateral inhibition and the concept of concentric receptive fields 3. Trace the route of visual information from the retina to the cortex 4. Explain the main features of color vision 5. Describe different types of cues for perceiving depth Route of Visual Information After being transduced, where does information go? Cells in the retina Optic disk Optic chiasm Lateral geniculate nucleus Primary visual cortex Further processing in other cortical areas Optic Disk Optic nerve & blood vessels exit the eye Lack of photoreceptors= blind spot Optic Chiasm Half of the axons from each eye cross over to the other side of the brain After the optic chiasm, the nerves are referred to as the optic tract Practice What happens if there is damage to the visual pathway? Different visual problems will occur depending on where the damage is. The black bars (labeled A-D) indicate where damage may occur. Describe what you would NOT be able to see for each location of the lesion (which areas of the visual field would you be blind to?). The visual field is reversed by the lens Lateral Geniculate Nucleus (LGN) In the thalamus Midget retinal ganglion neurons → parvocellular neurons in the LGN Visual details, color Parasol retinal ganglion neurons → magnocellular neurons in the LGN Movement, outlines of shapes, contrast between light and dark After the LGN, the nerves are referred to as the optic radiation Primary Visual Cortex (V1) In the occipital lobe Layer IV receives input from the LGN Projects to many regions, including the frontal cortex Frontal cortex projects back to V1 to modify experience Conscious visual experience Primary Visual Cortex (V1) Simple Cells Complex Cells End-stopped cells Location V1 V1 and V2 V1 and V2 Size of receptive field Small Medium Large Shape of receptive field Bar or edge shaped, with Bar or edge shaped, but Same as complex, but fixed excitatory and responding equally with a strong inhibitory inhibitory zones throughout a large zone at one end receptive field Simple cells Complex cells Ocular Dominance Eye inputs remain separate in the LGN and at the input layer IV of V1 Alternating bands/columns of ocular dominance across the cortical surface Ocular dominance= a neuron’s preference for one eye over another Orientation Columns Cells have a preferred orientation Cells with the same orientation preference are organized into columns Preference for neighboring columns are not random Orientation selectivity changes only slightly as you move from column to column; specific and consistent order Further Processing in Other Areas Secondary visual cortex (V2) Receives information from V1, processes further, and sends to other areas 2 major pathways Ventral stream: ”what pathway” Important for identifying objects Damage causes deficits in the identification of shapes/orientations of objects, naming objects, Path Retina LGN Visual cortex recognition, etc. “what” Midget Parvo-cellular Ventral Dorsal stream: “where pathway” ganglion LGN neurons (temporal) Important for visually guided movement neurons pathway Damage causes deficits in the integration of “where” Parasol Magno-cellular Dorsal vision with movements ganglion LGN neurons (parietal) neurons pathway MT and MST MT (V5)= middle temporal lobe Neurons respond selectively when something moves at a particular speed in a particular direction Detect absolute speed, acceleration, and deceleration Respond to photographs that imply movement MST = medial superior temporal cortex More complex stimuli Expansion, contraction, and rotation of a scene Occurs when you move your head forward and backward and when you tilt your head MT and MST Allow you to distinguish between eye movements and object movements Neurons respond when an object moves relative to its background No response if both the object and background move in the same direction at the same speed Damage → motion blindness (akinetopsia) Inability to determine direction, speed, or whether an object is moving Saccades= voluntary eye movement Brief decrease in the activity of the visual cortex during quick eye movements Temporary motion blindess Fusiform Gyrus/Fusiform Face Area Facial recognition Detailed visual recognition/expertise? Fusiform Gyrus/Fusiform Face Area Newborns are “wired” to pay more attention to faces than to other stationary displays What might be the evolutionary benefit of this? Face configuration matters Prosopagnosia Impaired ability to recognize faces Occurs after damage to the fusiform gyrus of the inferior temporal cortex (or doesn’t form correctly) Prosopagnosia Impaired ability to recognize faces Occurs after damage to the fusiform gyrus of the inferior temporal cortex (or doesn’t form correctly) Can you identify these celebrities? Prosopagnosia Impaired ability to recognize faces Occurs after damage to the fusiform gyrus of the inferior temporal cortex (or doesn’t form correctly) Brad Pitt, Margot Robbie, Will Smith, Jennifer Lopez, Ryan Gosling and Beyonce Fusiform Gyrus/Fusiform Face Area Area near the fusiform gyrus also important for recognizing bodies and biological motion https://www.biomotionlab.ca/html5-bml-walker/  Learning Objectives 1. Know the properties of light waves 2. Describe the anatomy and physiology of the eye, including the process of lateral inhibition and the concept of concentric receptive fields 3. Trace the route of visual information from the retina to the cortex 4. Explain the main features of color vision 5. Describe different types of cues for perceiving depth  Learning Objectives 1. Know the properties of light waves 2. Describe the anatomy and physiology of the eye, including the process of lateral inhibition and the concept of concentric receptive fields 3. Trace the route of visual information from the retina to the cortex 4. Explain the main features of color vision 5. Describe different types of cues for perceiving depth Theories of Color Vision Visible light= ~380-760nm Shortest wavelengths perceived as violet, longer wavelengths as blue, green, etc. If receptors are designed for detecting light, how do they distinguish color? Trichromatic Theory Wavelength discrimination via ratio of activity across 3 types of cones Frequency of response in each cell relative to the frequency of other cells Trichromatic Theory Distribution of cones across the retina Way more red and green than blue Individual variations (esp. red and green) Not many in the periphery Evidence – color blindness (color vision deficiency) One type of cone fails to develop (or develops abnormally) Most common type of color blindness is red-green color deficiency Long and medium cones have the same photopigment instead of different Trichromatic Theory Can not explain negative color afterimages Trichromatic Theory Can not explain negative color afterimages Opponent Process Theory We perceive color in terms of opposites Continuum from red to green, another from yellow to blue, another from white to black After you stare at one color in one location long enough, you fatigue that response and swing to the opposite ↑ activity = blue ↑ activity = red ↓ activity = yellow ↓ activity = green Blue Yellow Red Green Opponent Process Theory How does this explain negative afterimages? Brain perceives green where there is decreased activity and red where there is increased activity ↑ activity = red ↓ activity = green Red Green Opponent Process Theory How does this explain negative afterimages? When the stimulus is removed, the fatigued neuron rebounds ↑ activity = red ↓ activity = green Red Green Opponent Process Theory How does this explain negative afterimages? The neurons that had been suppressing activity now increase their activity, which the brain interprets as red ↓ activity ↑ activity ↑ activity = red ↓ activity = green Red Green Opponent Process Theory How does this explain negative afterimages? The neurons that had been increasing their activity now decrease their activity, which the brain interprets as green ↓ activity ↑ activity ↑ activity = red ↓ activity = green Red Green ↑ activity ↓ activity Which Theory is Correct? Both OPPONENT PROCESS THEORY TRICHROMATIC THEORY Which Theory is Correct? Retinex Theory Trichromatic theory and opponent process theory can’t explain color consistency Recognizing colors despite changes in lighting Retinex = retina + cortex Other brain regions (like the PFC) alter functioning of visual cortex (V1/V2) Retinex Theory  Learning Objectives 1. Know the properties of light waves 2. Describe the anatomy and physiology of the eye, including the process of lateral inhibition and the concept of concentric receptive fields 3. Trace the route of visual information from the retina to the cortex 4. Explain the main features of color vision 5. Describe different types of cues for perceiving depth  Learning Objectives 1. Know the properties of light waves 2. Describe the anatomy and physiology of the eye, including the process of lateral inhibition and the concept of concentric receptive fields 3. Trace the route of visual information from the retina to the cortex 4. Explain the main features of color vision 5. Describe different types of cues for perceiving depth Depth Perception Two types of depth cues: Monocular depth cues Relative size Height in plane Interposition Linear perspective Binocular depth cues Retinal disparity- where the visual cue hits the retina in each eye  Learning Objectives 1. Know the properties of light waves 2. Describe the anatomy and physiology of the eye, including the process of lateral inhibition and the concept of concentric receptive fields 3. Trace the route of visual information from the retina to the cortex 4. Explain the main features of color vision 5. Describe different types of cues for perceiving depth