Sept 25 Chapter 6 vision part 2 copy.pdf

PSYC/BIOL 2217 01 How We See: Vision and the Brain part 2 c. 6. 09-25-2024 Monday Sept 30th: No Class Wed October 2nd: 1st Midterm...

PSYC/BIOL 2217 01 How We See: Vision and the Brain part 2 c. 6. 09-25-2024 Monday Sept 30th: No Class Wed October 2nd: 1st Midterm Covers material from class lectures up to todays + Assignment 1 material (Moodle test similar to Assignment #1 - bring tablet or laptop) 3 Themes explored in this Class: V1 Cortical organization Colour vision Visual Experience is required to make sense of the world  Last class learned that our visual spectral sensitivity can be diminished via adaptation Can also be improved via attention and arousal? Gratings have three properties: 1. Spatial frequency 2. Contrast 3. Orientation Sensation and Perception are not Static, but are Dynamic Processes Imagine you are waking down a street at night, and you’re alone. You see a sudden movement off to your side accompanied by the sound of a sharp ‘crack’, what happens to all your senses, and perceptions? You orient towards the sound-movement Your pupils dilate, letting in more light and allowing a boost in visual perception This follows sympathetic nervous system arousal, flooding your body and brain with adrenaline and noradrenaline, at a slightly slower time scale your hypothalamic-pituitary-adrenal axis tells the adrenals to release more adrenaline and cortisol Other neurochemicals are also released (noradrenaline, dopamine and acetylcholine and these changes all help boost sensory experience, memory and motor response pathways Flash Bulb Memory 3 Noradrenaline, a neurotransmitter responsible for arousal in the brain, plays a vital role in our early sensory perceptions of the world. Adrenaline: Sympathetic nervous system activation, increased HR, BP, body tone Noradrenaline: In CNS involved in arousal Apart of the reticular activating system (RAS) RAS Operation of our senses can be tuned and modulated by arousal and stress. Used 3 drug treatment groups: Clonidine blocks noradrenaline release in CNS Reboxetine increases synaptic NE Placebo. 4 Noradrenaline Modulates Visual Perception and Late Visually Evoked Activity. Gelbard-Sagiv H, Magidov E, Sharon H, Hendler T, Nir Y. Curr Biol. 2018 Jul 23;28(14):2239-2249  Visual Masking: Stimulus sequence of one example trial in Experiment 2. A Gabor was presented in the centre of the screen. After a mask and an inter-stimulus interval of 200 ms each, participants were asked to adjust a bar to match the orientation of the previously presented Gabor. Lets say you want to present a visual stimulus for only 200 msec (1/5th of a sec). Turns out you can’t just flash a scene - word ‘radio’ for 200 msec - need to mask it. This is because of a phenomena called PERSISTENCE OF VISION. Visual stimulation of receptors and neurons continues for approx. 250 msec after the word ‘radio’ is flashed. Thus, in actuality we see the word ‘radio’ for a total of 450 msec - unless you mask it by presenting another image after ‘radio’ for at least 250 msec. 5  Gabor Pattern Matching: Used in visual and attentional research. Excite the primary visual cortex with an orientation stimulus of a particular spatial frequency. Subject instructed to match orientation. Testing visual attention and acuity - 6 Noradrenaline Modulates Visual Perception and Late Visually Evoked Activity. Gelbard-Sagiv H. et al., (2018). Curr Biol. Psychophysics EEG & Imaging Take-home: increasing NE in CNS has the effect of: Increasing perception and sensory discrimination. Increasing occipital EEG response. Increasing occipital metabolic activity. 7 Retinotopic mapping and cortical magnification and representation in V1 (striate cortex) Large area of V1 (and higher areas) devoted to Retinotopic Mapping of projections from retina to LGN to fovea, BUT, area not visual cortex (V1 & V2…others not devoted to size but to so much). detail: spatial resolution, colour, movement, texture, etc. Means that damage to an area in V1 will cause loss of sight in the corresponding area of visual field. 8 Retinotopic mapping means that the image projected onto your retina is preserved both in the LGN and V1 & V2 of the visual cortex. Retinotopic mapping, cortical magnification, Columnar representation in V1 (striate cortex) 9 Retinotopic mapping, cortical magnification, Columnar representation & Ocular Dominance in V1 (striate cortex) 2-Deoxyglucose labeled with tritium or carbon-14 has been a popular ligand for laboratory research in animal models, where distribution is assessed by tissue-slicing followed by autoradiography, 10 fMRI Imaging of flickering light with one eye closed (right eye in blue, left eye in red) Lying in FMRI scanner with left Bottom-line take home - eye open (blue) looking at flickering light - see blue area of There are many organizational V1 light-up, then close left and open right (red) - see red area principles in V1: light-up Retinotopic projections and organization Orientation columns Ocular dominance Essa Yacoub et al. PNAS 2008;105:30:10607-10612 11 ©2008 by National Academy of Sciences Remember Blakemore and Cooper? CP Critical Period, or perhaps more accurate to say sensitive period. the vast majority of experiential effects on development Figure 2 have been found to occur during sensitive periods. Molecular Psychiatry (2017) 22, 1085-1095; doi:10.1038/mp.2017.61 12  Also called lazy eye Amblyopia Amblyopia, or cortical blindness, is a term that refers to a variety of visual disorders when there is no problem with the eye (the optics and retina are fine), but one eye has better vision than the other. Amblyopia can be caused by strabismus (wandering eye) if it is not corrected in infancy. What appears to happen is that during development, if the signals from one eye are weak or out of register with input from the other eye, then the brain develops in a way that ignores the signals from the weak or misdirected eye. It's best to address amblyopia well before the age of 5 because the connections between the eyes and brain are still developing. Treatment past this age is possible but less effective because these connections have formed. Approximately 50% of children between 7 to 17 years old respond well to treatment. 13 Assignment 2 deals with this idea of a sensitive or critical period in early development Ocular Dominance Columns represent Hebbian Plasticity Synchronous activation of the cortical neuron results in the release of an activity-dependent retrograde signal (peptide growth factors) that influences the growth and maintenance of presynaptic branches and nerve terminals. Strong co-activation of pre- and postsynaptic cells causes synapse strengthening whereas uncorrelated or lack of firing causes synapse weakening. One evidence that Hebb’s postulate is relevant to ocular dominance is that eye patching during the critical period can result in the elimination of inputs from the covered eye onto V1.  When cortical columnar organization goes wrong! Artist example of a visual migraine (scintillating scotoma or “fortification spectra,”), as may be caused by cortical spreading depression. 15 ? 16  Figure 6.9 Distribution of Cones and Rods Humans have 120 million rods and 6 million cones At fovea equivalent to about a 30 megapixel camera (most new smart phones at least 50 MPs) but remember that more than 40% of human neocortex is also devoted to visual processing - 30 billion neurons and trillions of synapses The distribution of cones and rods over the human retina. The figure illustrates the number of cones and rods per square millimetre as a function of distance from the centre of the fovea. (Based on Lindsay and Norman, 1977). Copyright © 2021, 2018, 2014 Pearson Education, Inc. All Rights Reserved  Subjects wearing VR googles watching a video - in the experiment the peripheral display was gradually desaturated of colour - but colour remained where subject was looking by tracking pupil movement Brain fills in colour info! Michael A. Cohen et al. PNAS doi:10.1073/pnas.1922294117 18 ©2020 by National Academy of Sciences  Our brains fills in missing information: Perception, like language is always incomplete; we fill in what’s missing - Make stories out of the world Conclusion: Just like with our blind spot, our brains ‘fills-in’ much of our perceptual experience of colour. Other examples will follow as the class progresses. Change blindness Inattention blindness Blinking, Visual refresh rate (persistence of vision or flicker fusion) Need stability in our perception of the world/reality. Otherwise psychosis would result - Not knowing what is real. Called PERCEPTUAL CONSTANCY: Stability in perception brought about by both bottom-up wiring in the retina and top-down cortical processing based on experience and learning. 19 Rod- and cone-pigment absorption spectra 20 Rod- and cone-pigment absorption spectra  Cover one eye for 10 minutes (this allows for regeneration of photopigments in covered eye) - then look at image of the red and blue flower, switching back and forth closing one eye then the other. The blue should look lots brighter compared to the red in the dark adapted eye! Because rod cells are insensitive to long wavelengths, the use of red lights and red lens glasses has become a common practice for accelerating dark adaptation 22  Psychophysical demonstration of colour matching: By adjusting the strength of any 3 wavelengths you can match any reference colour (Any 3 can be used, as long as each can’t be matched by mixing the other two). James Clerk Maxwell (1831– 1879) and Hermann von Helmholtz provided psychophysical experimental evidence for what became known as the trichromatic theory of colour vision. Based on the finding that people with normal colour vision need at least three wavelengths to match any other wave- length, Maxwell reasoned that colour vision depends on three receptor mechanisms, each with different spectral sensitivities.  There is nothing objective about colours. Research has found that we all experience colours slightly differently, depending on gender, national origin, ethnicity, geographical location, and even what language we speak. If each us performed a colour matching experiment using 3 lights with fixed long, medium and short wavelengths and then adjusted their intensity in order to match a specific green light (reference light), the values we would choose would all slightly vary! Nevertheless we all agree on what ‘green’ is based on learning. Some languages use fewer or more words for colours. native English-speaking children, familiar with the rainbow of colours in the Crayola 64-pack, actually can tell “rust” from “brick” and “moss” from “sage” Journal of Experimental Psychology: General (Vol. 133, No. 4 Cis-women are more adept at distinguishing between subtle gradations in colour than cis-men. This sensitivity is most evident in the middle of the colour spectrum. In contrast men tend to be better at movement detection? Those with ASD also better at movement detection? 24 Trichromatic Theory - Physiological Evidence School bus yellow is found in the middle of the wavelengths that trigger our perception of red and green. This makes it almost impossible for us to miss a school bus—even when it’s in our peripheral vision. 25 Colour is a property of the light’s wavelength and/or physiological sensation/perception 26 Opponent-Process Theory of Colour Vision Theory based on phenomenological observations. Proposes that colour vision is the result of opponent physiological responses in the visual system between blue and yellow, red and green and black and white (Ewald Hering; 1834-1918). Hering observed that while yellowish-green, and bluish-red are possible, there can never be a bluish-yellow, or a reddish-green. Proposed that our colour vision is due to 4 primary chromatic colours arranged into 2 opponent pairs; yellow-blue and red-green. Herring notes that certain colours always seem to be opposite to A third pair, black and white added each other. We never talk about bluish-yellows but do see bluish- subsequently. greens or bluish-reds. 27 Suggests that visual system treats certain colours as opposites and therefore they can’t be combined! Opponent-Process Theory of Colour Vision Evidence for theory comes from: physiological recordings Can find neurons in LGN and occipital cortex that are excited by one complementary colour and inhibited by the other. Psychophysical experiments - After image complementarity People with colour vision deficiency. People who are colour-blind to red are also colour-blind to green, and that people who can’t see blue also can’t see yellow, 28 Physiological Evidence for Opponent- Process Theory Receptive fields of colour-sensitive retinal ganglion cells. When the centre portion of the receptive field is illuminated with the colour shown, the cell’s firing rate increases. When it is illuminated with the complementary colour, the firing rate decreases. 30 31 32 33 34  Colour Deficiency: Opponent-Process Theory of Colour Vision Deuteranomalia: ( Medium (Green) Cone pigment gene missing/mutated. Protanopia: Long (Red) Cone gene missing/mutated Tritanopia: Short (Blue) cone gene missing/mutated In humans 2 cone pigment genes (opsin genes) are present on X chromosome, thus approx. 1 in 12 males have colour blindness as opposed to 1 in 100 females. Caucasian male 8/100 Asian, African 3/100 https://www.colorblindnesstest.org/farnsworth-munsell-100-hue-test/35  Tetrachromatic humans: In humans, two cone cell pigment genes (opsin genes) are present on the X chromosome. A mutation in one of the genes means that cis-females with two X chromosomes could possess multiple cone cell pigments with slightly different spectral sensitivities. One study suggested that 15% of women might have a type of fourth cone whose sensitivity peak is between the standard red and green cones, giving, theoretically, a significant increase in colour differentiation. 36  Concetta Antico (artist) has 4th cone class of photoreceptor. Offering potential to resolve 99 million more colours than regular vision 37 Dual Process Theory: Human colour vision uses both trichromatic & opponent processing for colour vision. Two stages in colour perception: 1st, the receptors respond with different patterns to different wavelengths (trichromatic theory); then, later, neurons integrate the inhibitory and excitatory signals from the receptors (opponent-process theory). Trichromatic processing in the retina: 3 cones detecting different and overlapping parts of visible spectrum. Opponent Process Theory: Applies at all levels; in LGN and visual cortices. Opponent neurons found in many areas of the cortex, including V1; the inferotemporal cortex (IT), which is associated with form perception; and V4, which was originally proposed as the colour centre. Brain damage on colour perception has shown that when brain damage causes achromatopsia (colour blindness), it causes other effects as well, including prosopagnosia—the inability to recognize faces. 38 The task of determining the object responsible for a particular image on the retina is called the inverse projection problem, because it involves starting with the retinal image and extending rays out from the eye. The perceptual system is not concerned with determining an object's image on the retina. Stimulus on the Receptors is Ambiguous Trapezoid: Inverse Projection Problem: because we begin with a projection on the retina and have to work backwards to figure out what the object- scene is that makes that projection. perceptions are not just created by adding up sensations Objects can be hidden or blurred Look different from different viewpoints Viewpoint invariance. Need rules of thumb - Heuristics or Perceptual grouping - Gestalt short cuts to solve the problem, what’s out there in the world based on whats projected onto my retina. Artist Julian Beever  Structuralism: Wilhelm Wundt (1832-1920) borrowed from atomic structure in chemistry to propose that perception is based on elemental ‘sensations’ which together add-up to conscious perceptions. The whole is simply the sum of all the parts 42  Scha·den·freu·de /ˈSHädənˌfroidə/ Gestalt—a unified and coherent whole doppelgänger, Kindergarten Gestalt theory: Rejected Structuralism, theorized instead that ‘whole is not the same as the sum of the parts’ (Max Wertheimer, 1880-1943). Phenomena of apparent movement, can’t be explained by sensations. Gestalt psychologists believed that humans tend to perceive objects as 43 complete rather than focusing on the gaps that the object might contain. Gestalt perceptual principle of grouping and closure: 44 Brain can perceive a complex scene with only a little information, it fills in what’s missing. Kanizsa’s illusion also highlights special importance of corners. Dogs are susceptible to the Kanizsa’s triangle illusion. Train dogs to discriminate a triangle from other geometrical figures using a two-alternative conditioned discrimination task Gestalt Principles of Grouping 46 Semantic Consistency: Object recognition & priming in visual scenes, importance of context. Brain looks for relationships in sensory stimuli by looking for their interactions. Associates meaning to those interactions. Example 1: language and reading. “Ca y u rea t is?.” Stephen Palmer (1975): Presented a context scene such as the one on the left and then briefly flashed one of the target pictures on the right. When observers asked to identify the object in the target picture, they correctly identified an 47 object like the loaf of bread (which is appropriate to the kitchen scene) 80 percent of the time, Sesame Street: One of these but correctly identified the mailbox or the drum (two objects that don’t fit into the scene) only 40 things belongs with the other, percent of the time. one of these things is kinda the same!