PsyBSc4: Neural Basis of Perception (2023) PDF

PsyBSc4: Allgemeine Psychologie I Neural Basis of Perception Session 2: 24.10.2023 Dr. Sandro Wiesmann 2 Reminder Some vocabulary excitatory = exzitatorisch (erregend) inhibitory = inhibitorisch (hemmend) instance = Beispiel, Exemplar retina = Netzhaut dilation = Erweiterung illumination = Beleuchtu...

PsyBSc4: Allgemeine Psychologie I Neural Basis of Perception Session 2: 24.10.2023 Dr. Sandro Wiesmann 2 Reminder Some vocabulary excitatory = exzitatorisch (erregend) inhibitory = inhibitorisch (hemmend) instance = Beispiel, Exemplar retina = Netzhaut dilation = Erweiterung illumination = Beleuchtung transduce = umwandeln transmit = übermitteln release = freisetzen wavelength = Wellenlänge converge = zusammenlaufen summation = Aufsummierung (visual) acuity = Sehschärfe distribution = Verteilung resolution = Auflösung baseline = Ausgangswert magnification = Vergrößerung elongated = länglich bar = Balken edge = Kante sparse = wenig, dünn besetzt reservation = Vorbehalte diminish = abnehmen sustained = anhaltend fatigue = erschöpfen surgery = Operation 3 Schedule Session Date Topic Goldstein Chapter 1 17.10.2023 Introduction to Cognitive Psychology 1 2 24.10.2023 Neural Basis of Perception 2 3 31.10.2023 Perception I 3 4 07.11.2023 Perception II 3 5 14.11.2023 Attention I 4 6 21.11.2023 Attention II 4 7 28.11.2023 Memory 5 8 05.12.2023 Knowledge 9 9 12.12.2023 Visual Imagery 10 10 19.12.2023 Language 11 11 09.01.2024 Problem Solving 12 12 16.01.2024 Reasoning and Decision Making 13 13 23.01.2024 TBA 14 30.01.2024 TBA 15 06.02.2024 Summary, exam preparation, questions 4 Today’s menu Part 1: Recap  Early pioneers of Cognitive Psychology  Behaviourism abandoning the mind  The Cognitive Revolution Part 2: Neural Basis of Perception  Neurons and neural signals In part based on Wolfe et al. (2021) Sensation & Perception, chapters 2 & 3  Anatomy and function of the eye  Visual processing in the brain 5 Part 1: Recap  Early pioneers of Cognitive Psychology  Behaviourism abandoning the mind  The Cognitive Revolution Four pioneers of cognitive psychology 7 Behaviourism: Abandoning study of the mind John Watson (1913): Proposal of behaviourism We can manipulate this (e.g., broccoli vs. ice cream) We cannot observe this! Stimulus We can objectively observe this (e.g., eating, smiling, disgust…) Response Mind “Black box” Focus on Stimulus  Response relationships (not interested in what happens “in between”) 8 The decline of behaviourism Edward C. Tolman (1938): The discovery of cognitive maps Phase I: Rat explores maze Phase II: Rat learns to turn right for food when placed at A Phase III: Rat is placed at C and turns left Mental representation Tolman’s conclusions:  More than just stimulus-response connection (behaviourism)  Rat must have developed a cognitive map of the maze’s layout The mind as an information processing system James (1890): Attention as “withdrawal from some things in order to deal effectively with others” Colin Cherry (1953): Dichotic listening experiment  Instruction: Focus on left ear, ignore right ear  Result: Heard right message, but were unaware of contents Donald Broadbent (1958): Filter model of attention  First flow diagram of the mind 10 Modern cognitive psychology  Behavioural approach: Measure relationship between stimuli and behaviour  Physiological approach: Measure relationship between stimuli and physiology  Infer cognitive processes afterwards 11  Can we interpret fMRI results causally? For those interested in fMRI: Functional Neuroimaging Can Support Causal Claims about Brain Function (Weber & Thompson-Schill, 2010) 12  TMS: Brain areas causally involved in tasks Transcranial Magnetic Stimulation Apple No clue!? binthistheperson TMS in action (1 minute) cannotdecipherthe 13 apple Questions? Part 2: Neural Basis of Perception  Neurons and neural signals  Anatomy and function of the eye  Visual processing in the brain Key questions  How does the mind create representations of the world?  Which brain areas are involved in vision (which areas would we have to “zap” with TMS)?  How can we draw conclusions about the brain from behavioural studies? 16 ET Neurons: Building blocks of the nervous system  Cells receiving and transmitting information in the nervous system longcable 17 Measuring activity of single neurons  Information is transmitted through the axon in the form of an electrical impulse (action potential)  Resting potential (–70 mV) becomes depolarized (+40 mV) and then returns to baseline Basis for EEG, MEG & TMS! 18 Neurons: Building blocks of the nervous system  Synapses: Gap between axon of one neuron and dendrites of another  Electrical signal is converted into biochemical signal: Release of neurotransmitters into the synapse  Neurotransmitters then bind to receptors of the postsynaptic neuron  Either excitatory or inhibitory effect on following neuron (triggering or inhibiting new action potentials) 19 Neurons: Building blocks of the nervous system  Neurons receive input from other neurons or the environment using specialized receptors Mechanoreceptor (touch) Photoreceptor (light)  Stimulus intensity is represented in firing rate: Dim light Bright light  Low intensity (e.g., dim light): Low firing rate  High intensity (e.g., bright light): High firing rate Each line symbolizes an action potential Time 20 Part 2: Neural Basis of Perception  Neurons and neural signals  Anatomy and function of the eye  Visual processing in the brain The Eye  “The mind is a system that creates representations of the world, so we can act within it to achieve our goals.”  How are visual representations of the world created? First instance of a representation  We look at an object  Light reflected by object enters the eye  Image of the object is focussed onto our retina 22 The Eye Netzhaut  Retina: Light-sensitive membrane in the back of the eye transforming light into neural signals Cable  Optic nerve: Transmits visual information from the retina to the brain  Fovea: Area at the centre of the retina with the highest visual acuity resulation full  Periphery: Parts of the visual field away from the fovea 23 The Retina 24 The Retina  Photoreceptors transduce light into neural signal  Two types: Rods and cones  Neural signal is passed to ganglion cells  Ganglion cells transmit signal to the brain via the optic nerve (bundle of ganglion cell axons) 25 Photoactivation in rods and cones  Photoreceptors transduce light into neural signal  Carry a protein (opsin) that changes its shape when struck by a photon (light)  Biochemical processes cause changes in the neurotransmitters released to bipolar cells There are different opsins for rods (rhodopsin) and cones (three different opsins) 26 Differences between rods and cones Rods (Stäbchen):  Specialized for vision under low-light conditions (scotopic vision)  Do not process colour Cones (Zapfen):  Specialized for vision under well-lit conditions (photopic vision)  Three different types for light at different wavelengths (“red-green-blue”) 27 Differences between rods and cones  Multiple rods usually converge on one ganglion cell Rods Cones  Summation of several signals  Higher sensitivity (e.g., in the dark)  Lower acuity  Cones usually* connect to a single ganglion cell  No summation of signals  Lower sensitivity (stronger signal needed to activate ganglion cell)  Higher acuity *at least at the fovea! 28 Distribution of rods and cones on the retina Periphery Fovea Periphery Fovea: Area at the centre of the retina with the highest density of cones (at its centre no rods) and therefore the highest visual acuity Periphery: Parts of the visual field away from the fovea (fewer cones, primarily rods), lower visual acuity 29 How accurate is peripheral vision? We only see a small part of the visual field in colour and “full resolution”! A little demonstration… 30 How big is the fovea? Thumb at arm length: ~ 2° visual angle Fovea: 3–5° visual angle Fovea ~ two thumbs next to each other b Actually everything isblurrybut themind fixesthe worldaround 31  What do we “see” in the periphery? + 32  The periphery is “texture like” (Ruth Rosenholtz) + + 33 Distribution of rods and cones on the retina What is going on here? 34 Optic disc or blind spot  Optic disc: Point where optic nerve leaves the eye (towards the brain)  Also called “blind spot” because there are no rods and cones here! 35 Find your own blind spot!  Close left eye, fixate the F with right eye  Slowly move closer to/away from the screen (try distances around 20–25 cm)  When you find the right distance… a) The red dot should disappear, but not the blue dots! b) The red line will suddenly be complete! More … demos … online 36 Why don’t we usually notice the blind spot?  Blind spot is away from the fovea  Two eyes compensating for each other  Brain “fills in” missing information 37 What happens after the photoreceptors? Ganglion cells  Ganglion cells are the final layer of the retina (last step before the brain)  Information from several receptors converges at single ganglion cell (depending on receptive field size) Receptive field = circular area of the retina that a ganglion cell receives input from 39 Receptive field of ganglion cells  Usually “doughnut-shaped” receptive field  On-centre, off-surround cell  Flashing light at centre increases firing rate  Flashing light at surround decreases firing rate  Respond strongest to a bright spot in the dark  Off-centre, on-surround cell  Flashing light at centre decreases firing rate  Flashing light at surround increases firing rate  Respond strongest to a dark spot surrounded by light On-centre cell Off-centre cell – + – + – – + – + + 40 ON-center ganglion cells Baseline activity: “Normal” firing rate when cell is not stimulated 41 OFF-center ganglion cells 42 What if light is across the receptive field? Some first coding of size and location already at the level of the retina! 43 Questions? What happens after the eye? Part 2: Neural Basis of Perception  Neurons and neural signals  Anatomy and function of the eye  Visual processing in the brain Information flow from the eye to the brain  Lateral Geniculate Nucleus (LGN)  Striate cortex (primary visual cortex)  Higher-level visual areas There isn’t just one “vision area”! 47 Stop 1: Lateral Geniculate Nucleus  Organization of brain areas involved in visual perception follows topographical mapping  Receptive fields very similar to those of ganglion cells from which they receive input What’s it good for then?  Feedback connections from higher brain areas to LGN Stop 2: Striate cortex (primary visual cortex)  Topographical mapping as LGN, but more than 100 times as many cells as LGN!  Cortical magnification: Much larger representation of the fovea compared to the periphery 49 Receptive fields in striate cortex (Hubel & Wiesel)  Tested whether receptive fields in striate cortex are similar to ganglion/LGN cells  Found that striate cortex cells did not respond to dots of light/shadow much! 50 Receptive fields in striate cortex  More elongated receptive fields than ganglion/LGN cells from which they receive input  Respond stronger to bars, lines and edges compared to spots of light  Orientation tuning: Respond best to certain orientations of lines/edges Cell responds strongest to its preferred orientation Cell does not respond to nonpreferred orientations 51 Simple and complex cells in striate cortex  Simple cells: Neurons with clearly defined excitatory and inhibitory receptive field regions  Edge detectors: Respond strongest to edges (light on one side and darkness on other side of receptive field)  Stripe detectors: Respond strongest to stripes of certain width surrounded by darkness  Both tuned to specific orientation 52 Simple and complex cells in striate cortex  Complex cells: Receptive field not clearly divided into excitatory and inhibitory regions  Also tuned to specific orientation and stripe width  However, will fire if stripe is anywhere within receptive field 53 End-stopped cells in striate cortex  Some cells prefer bars of light of certain lengths  When length is increased beyond size of the receptive field, response rate is decreased 54 Increasingly complex signals in striate cortex By combining signals from previous processing steps, the brain creates increasingly complex representations that can code for orientation, width, length, position, etc. 55 My perception is more than stripes and edges, what happens next? From low-level to higher-level areas 57 Localization of function…  Specialized brain areas for different stimuli  Category-selective cortex (Nancy Kanwisher):  Fusiform face area (FFA) for faces  Parahippocampal place area (PPA) for places  Extrastriate body area (EBA) for bodies/body parts Higher-level visual areas are increasingly specialized for certain stimuli/functions! 58 Localization of function… Gross et al. (1972) Responses of neurons in higher-level areas are therefore also increasingly selective for complex stimuli (not just bars….) Is there a “Jennifer Anniston cell” (Quiroga et al., 2005)? 59 …but also distributed processing Complex concepts (e.g., face identity) are not represented by single cells (specificity coding) but rather by the firing pattern of many cells (population coding) or a few cells (sparse coding). 60 …but also distributed processing Example: Face perception Functions are rarely processed in just one brain area! 61 Distributed processing and feature binding  Feature binding: Combining features that are processed in separate brain areas  We are usually not aware of this!  Not just for vision (distributed processing in memory, language, decision making, etc.) 62 Localizing cognitive functions in the brain Executive functions, higher-level cognition (decision making, problem solving…) Somatosensory cortex (touch, temperature, pain) Visual cortex (Seeing)  Most cognitive functions are located in the cerebral cortex (outside layer of the brain)  Cerebral cortex can be divided into four lobes:  Temporal TOPF-Lappen  Occipital  Parietal  Frontal Auditory cortex (Hearing) 63 Questions? A few words about animal studies… 65  A few words about animal studies…  A lot of our knowledge about the workings of the brain comes from animal studies  On the one hand, there are (obviously!) ethical reservations regarding animal research  On the other hand, these studies have advanced our understanding of the brain tremendously “ Most of the physiological research reported up to this point in the chapter was done using cats, monkeys, or other animals as subjects. Does the human visual system also include neurons selective for orientation, line width, direction of motion, and so on? The difficult thing about answering this question is that we can’t normally poke electrodes into a human’s brain (which is why Hubel, Wiesel, and their peers had to use cats and monkeys) […]. – Wolfe et al. (2021). Sensation & Perception, p. 81.  Decide for yourself: Do you think animal research is justifiable? What research is “important enough” to justify animal suffering? What criteria make up this importance? 66 Alternatives to animal studies  Modern neuroimaging methods are mostly safe and non-invasive for humans!  But we don’t always need neuroimaging or animal studies to learn something about the brain!  Selective Adaptation (“The psychologist’s electrode”):  Diminishing response of a sensory organ to a sustained/repeated stimulus  “Fatigues” cells selectively responding to that stimulus  Method to “knock out” groups of neurons for a short period of time without surgery 67 Demonstration: Tilt Aftereffect Look at the white bar at the centre of the image for 20 seconds 68 Demonstration: Tilt Aftereffect 69 Demonstration: Tilt Aftereffect 70 Explanation of the Tilt Aftereffect Adaptive stimulus (20°) Response to vertical pattern before adaptation Response to vertical pattern after adaptation Reduced response of cells around 20° Response of cell preferring vertical orientation is strongest, we “see vertical” Response of cell preferring -10° orientation is strongest, we perceive slight tilt away from adaptive stimulus 71 Interpretation of the Tilt Aftereffect  Perceptual illusion of tilt as a result of adapting to a pattern of a given orientation  Supports the idea that human neurons selectively respond to different orientations  Shows how we can study the brain without invasive methods and animal research! 72 Selective adaptation to motion: Motion Aftereffect Watch video at home and after 20 seconds see how your perception changes when you look at something else 73 Hermann Grid  Illusory “black dots” appear at intersections of white grid lines  Black dots disappear when fixated! 74 Hermann Grid: Ganglion cell explanation Periphery (parafoveal): - - + - + - - - -  Large receptive fields  Strong activation of surround (OFF) at intersections  perceived as dark  Less activation of surround (OFF) between intersections  perceived as light At fixation (foveal):  Smaller receptive fields  No difference in perception at/between intersections 75 The ganglion explanation has a problem…  Illusory “black dots” disappear when using wavy lines! 76 The ganglion explanation has a problem…  Ganglion cell explanation cannot account for this! - - - + - + - -  Illusion seems to depend on straight lines: Probably related to cells in striate cortex! -  Curvy lines do not change the activation of centre vs. surround - We can “localize” visual phenomena in the brain without using neuroimaging or animal studies! 77 Questions? Summary  Visual information enters our cognitive system through the eyes, where rods and cones transduce light intro neural signals and send it to the brain through the optic nerve.  There are significant differences between foveal and peripheral vision in our perception (acuity, colour, etc.) and the anatomy of the eye (distribution of rods and cones).  Cells along the visual processing hierarchy respond maximally to increasingly complex stimuli, and higher-level visual areas are increasingly specialized for certain tasks.  Most functions are processed across different brain areas making feature binding necessary.  Carefully designed behavioural and neuroimaging studies can (in some cases) replace animal studies. 79 What I want you to take away from this Although most of us experience vivid visual impressions in our daily life, we rarely appreciate the mere fact that we are able to have such experiences in the first place. To most of us, seeing an apple appears to be the logical consequence of looking at it. However, the processes that translate the light rays reflected by the apple onto our retinae into the semantic understanding of a red, round, crispy and sweet fruit are neither simple nor fully understood. I hope that this session could help you appreciate the complexity of the physiological basis of vision and also give you a basic understanding of the rapid but complex, multi-stage process that underlies (visual) perception. In the next sessions, we will build on this understanding and have it guide our discussions of attention, memory and other feats of the human mind. Sample exam question The fact that we usually have a harder time perceiving colour in the periphery is due to… a. the centre–surround organization of ganglion cells. b. the small number of cones in the periphery. c. the blind spot. d. differences between simple and complex cells. 81 Quiz question for the nerds… What is wrong here? Figure 2.4 Goldstein (2011) 82 Quiz question for the nerds… Updated version… 83 Suggested readings  Goldstein chapter 2  Wolfe et al. (2021). Sensation & Perception, chapters 2 & 3.  YouTube:  The brain explained in 2 minutes and in one minute (by John Cleese)  Hubel and Wiesel's classic experiment explained (6 minutes) and how they found out that cells in striate cortex respond to lines (1 minute)  Why is the right half of the visual field represented in the left brain hemisphere? (5 minutes)  Oliver Sacks: What happens to our perception, cognition and behaviour when certain parts of the brain don’t work as intended?  The Man Who Mistook His Wife for a Hat  An Anthropologist on Mars  Musicophilia: Tales of Music and the Brain 84 Any questions? Feel free to ask questions or give me feedback after the lecture! Enough neural stimulation for today, see you next week!