Lecture 4 – Spatial Vision: From Spots to Stripes PDF

3 Lecture 4 – Spatial Vision: From Spots to Stripes Chapter 3 Spatial Click to edit MasterVision: From Spots to Stripes title style 2 3.1 Visual Acuity: Oh Say, Can You See? 3.2 Retinal Ganglion Cells and Str...

3 Lecture 4 – Spatial Vision: From Spots to Stripes Chapter 3 Spatial Click to edit MasterVision: From Spots to Stripes title style 2 3.1 Visual Acuity: Oh Say, Can You See? 3.2 Retinal Ganglion Cells and Stripes 3.3 The Lateral Geniculate Nucleus 3.4 The Striate Cortex 3.5 Receptive Fields in Striate Cortex 3.6 Columns and Hypercolumns 3.7 Selective Adaptation: The Psychologist’s Electrode 3.8 The Development of Vision © Oxford University Press Figure 3.1 Cortical visual pathways 3 ClickVisual 3.1 to editAcuity: MasterOh Say, title Can You See? style 4 What is the path of image processing from the eyeball to the brain? Eye (vertical path) o Photoreceptors o Bipolar cells o Retinal ganglion cells Lateral geniculate nucleus Striate cortex © Oxford University Press ClickVisual 3.2 to editAcuity: MasterOh Say, title Can You See? style 5 Acuity: The smallest spatial detail that can be resolved. © Oxford University Press ClickVisual 3.1 to editAcuity: MasterOh Say, title Can You See? style 6 The Snellen E test Herman Snellen invented this method for designating visual acuity in 1862. Notice that the strokes on the E form a small grating pattern. © Oxford University Press Figure 3.6 A Snellen E 7 ClickVisual 3.1 to editAcuity: MasterOh Say, title Can You See? style 8 There are several ways to measure visual acuity. Eye doctors use distance to characterize visual acuity, as in “20/20 vision.” o Your distance/Normal vision distance © Oxford University Press ClickVisual 3.1 to editAcuity: MasterOh title style Say, Can You See? 9 Acuity: Smallest visual angle of a cycle of grating that can be perceived. The smaller the visual angle at which you can identify a cycle of a grating, the better your vision. © Oxford University Press Figure 3.3 Visual angle 10 ClickVisual 3.1 to editAcuity: MasterOh Say, title Can You See? style 11 Types of Visual Acuity Minimum visible acuity: The smallest object that one can detect. Minimum resolvable acuity: The smallest angular separation between neighboring objects that one can resolve. Minimum recognizable acuity: The angular size of the smallest feature that one can recognize. Minimum discriminable acuity: The angular size of the smallest change in a feature we can discriminate. © Oxford University Press Table 3.1 Summary of the different forms of acuity and their limits 12 Type of acuity Measured Acuity (degree) Minimum visible Detection of a feature 0.00014 Minimum resolvable Resolution of two features 0.017 Minimum recognizable Identification of a feature 0.017 Minimum discriminable Discrimination of a change in a 0.00024 feature Click to edit Master title style 13 3.1 Visual Acuity: Oh Say, Can You See? Why does an oriented grating appear to be gray if you are far enough away? This striped pattern is a “sine wave grating.” The visual system “samples” the grating discretely. © Oxford University Press Figure 3.4 Grating patterns 14 Figure 3.5 Visual crowding 15 ClickVisual 3.1 to editAcuity: MasterOh Say, title Can You See? style 16 Spatial frequency: Cycles of a grating per unit of visual angle (in degrees). Another way to think of spatial frequency is as the number of times a pattern repeats per unit area. In Figure 3.6, (A) has a low spatial frequency, (B) has a medium spatial frequency, and (C) has a high spatial frequency. © Oxford University Press Figure 3.7 Different spatial frequencies 17 ClickVisual 3.1 to editAcuity: MasterOh Say, title Can You See? style 18 Visibility of a pattern as a function of spatial frequency and contrast: Figure 3.7 shows the contrast sensitivity function for a person with normal vision. Figure 3.8 shows a pictorial representation of the same data. © Oxford University Press Figure 3.8 The contrast sensitivity function and the window of visibility 19 Figure 3.9 Visualizing your CSF 20 ClickRetinal 3.2 to edit Ganglion Cells Master title and Stripes style 21 How do the center-surround receptive fields respond to sine wave patterns with different spatial frequencies? © Oxford University Press Figure 3.12 ON-center ganglion cell response to gratings 22 ClickRetinal 3.2 to edit Ganglion Cells Master title and Stripes style 23 Not only is the spatial frequency important, but so is the phase. Phase: The phase of a grating refers to its position within a receptive field. © Oxford University Press Figure 3.13 The response of a ganglion cell depends on phase (Part 1) 24 Figure 3.13 The response of a ganglion cell depends on phase (Part 2) 25 Figure 3.13 The response of a ganglion cell depends on phase (Part 3) 26 Figure 3.13 The response of a ganglion cell depends on phase (Part 4) 27 ClickThe 3.3 Lateral to edit Geniculate Master title styleNucleus 28 We have two lateral geniculate nuclei (LGNs). Axons of retinal ganglion cells synapse there. Ipsilateral: Referring to the same side of the body (or brain). Contralateral: Referring to the opposite side of the body (or brain). © Oxford University Press Figure 3.14 The lateral geniculate nucleus 29 Figure 3.15 Topographic mapping of two eyes into the brain 30 ClickThe 3.3 Lateral to edit Geniculate Master title styleNucleus 31 Types of cells in the LGN Magnocellular: Large cells, bottom two layers. Receive input from M ganglion cells. Respond best to large, fast-moving objects. Parvocellular: Smaller cells, top four layers. Receive input from P ganglion cells. Respond best to fine spatial details of stationary objects. Koniocellular: Very small cells in between the manocellular and parvocellular sections. We are still not entirely sure what these cells do. © Oxford University Press ClickThe 3.4 Striate to edit Cortex Master title style 32 Striate cortex: Also known as primary visual cortex, area 17, or V1. A major transformation of visual information takes place in striate cortex. Circular receptive fields found in retina and LGN are replaced with elongated “stripe” receptive fields in cortex. It has about 200 million cells! © Oxford University Press Figure 3.16 Striate cortex 33 Figure 3.17 The mapping of objects in space onto the visual cortex 34 Figure 3.18 Cortical mapping 35 ClickThe 3.4 Striate to edit Cortex Master title style 36 The topography of the human cortex Much of our early information about cortical layout came from animals and humans with cortical lesions. Now, we can map human cortex using MRI and fMRI— safe, noninvasive imaging techniques. o MRI reveals the structure of the brain. o fMRI reveals brain activity through blood oxygen level– dependent (BOLD) signals. © Oxford University Press ClickThe 3.4 Striate to edit Cortex Master title style 37 Two important features of striate cortex 1. Topographical mapping 2. Cortical magnification o Dramatic scaling of information from different parts of visual field o Proportionally much more cortex devoted to processing the fovea than to processing the periphery © Oxford University Press Figure 3.19 A cortically scaled letter chart 38 Visual acuity declines in an orderly fashion with eccentricity—distance from the fovea ClickReceptive 3.5 Fields to edit Master in style title Striate Cortex 39 Cells in striate cortex respond best to bars of light rather than to spots of light. Some cells prefer bars of light, some prefer bars of dark (simple cells). Some cells respond to both bars of light and dark (complex cells). © Oxford University Press ClickReceptive 3.5 Fields to edit Master in style title Striate Cortex 40 Orientation selectivity Tendency of neurons in striate cortex to respond most to bars of certain orientations. Response rate falls off with angular difference of bar from preferred orientation. © Oxford University Press Discovering how visual Click to edit Master title cortex style works © Oxford University Press Figure 3.20 Nobel men (Part 2) 42 ClickReceptive 3.5 Fields to edit Master in style title Striate Cortex 43 How are the circular receptive fields in the LGN transformed into the elongated receptive fields in striate cortex? Hubel and Wiesel: Very simple scheme to accomplish this transformation. oA cortical neuron that responds to oriented bars of light might receive input from several retinal ganglion cells. © Oxford University Press ClickReceptive 3.5 Fields to edit Master in style title Striate Cortex 44 o Ifyou string several retinal ganglion cells together, they can form an oriented bar. oA cell that is tuned to any orientation you want could be created in cortex by connecting it up with the appropriate retinal ganglion cells. © Oxford University Press Figure 3.21 How striate cortex cells get tuned 45 ClickReceptive 3.5 Fields to edit Master in style title Striate Cortex 46 Many cortical cells respond especially well to Moving lines Bars Edges Gratings o Striate cortex cells respond to gratings of a certain frequency and orientation. Certain motion directions © Oxford University Press ClickReceptive 3.5 Fields to edit Master in style title Striate Cortex 47 Since striate cortical cells respond to such specific stimulus characteristics, they function like a filter for the portion of the image that excites the cell. © Oxford University Press ClickReceptive 3.5 Fields to edit Master in style title Striate Cortex 48 Each LGN cell responds to one eye or the other, never to both. Each striate cortex cell can respond to input from both eyes. By the time information gets to primary visual cortex, inputs from both eyes have been combined. Cortical neurons tend to have a preferred eye, however. They tend to respond more vigorously to input from one eye or the other. © Oxford University Press Figure 3.22 Two flavors of simple cells (Part 1) 49 Figure 3.22 Two flavors of simple cells (Part 2) 50 Figure 3.23 Simple and complex cells 51 Figure 3.24 End-stopping 52 End stopping: Some cells prefer bars of light of a certain length. ClickColumns 3.6 and Hypercolumns to edit Master title style 53 Column: A vertical arrangement of neurons. Within each column, all neurons have the same orientation tuning. Hubel and Wiesel: Found systematic, progressive change in preferred orientation as they moved laterally along the cortex; all orientations were encountered within a distance of about 0.5 mm. © Oxford University Press Figure 3.25 Cortical Columns (Part 1) 54 Figure 3.25 Cortical Columns (Part 2) 55 Figure 3.25 Cortical Columns (Part 3) 56 ClickColumns 3.6 and Hypercolumns to edit Master title style 57 Not super important Hypercolumn: A 1-mm block of striate cortex containing “all the machinery necessary to look after everything the visual cortex is responsible for, in a certain small part of the visual world” (Hubel, 1982). Each hypercolumn contains cells responding to every possible orientation (0–180 degrees), with one set preferring input from the left eye and one set preferring input from the right eye. © Oxford University Press Figure 3.26 A model of a hypercolumn 58 ClickColumns 3.6 and Hypercolumns to edit Master title style 59 Each column has a particular orientation preference, which is indicated on the top of each column (and color-coded). Adjacent groups of columns have a particular ocular dominance—a preference for input from one eye or the other—as indicated at the bottom of the figure. Blobs are indicated as cubes embedded in the T hypercolumn. notsoimportant © Oxford University Press Figure 3.27 CO blobs 60 ClickSelective 3.7 Adaptation: to edit Master The Psychologist’s Electrode title style 61 Adaptation: A reduction in response caused by prior or continuing stimulation. An important method for deactivating groups of neurons without surgery. If presented with a stimulus for an extended period of time, the brain adapts to it and stops responding. This fact can be exploited to selectively “knock out” groups of neurons for a short period. © Oxford University Press Figure 3.28 ”The psychologist’s electrode” 62 ClickSelective 3.7 Adaptation: to edit Master The Psychologist’s Electrode title style 63 This demonstration will allow you to experience selective adaptation for yourself. © Oxford University Press Figure 3.29 Demonstrating selective adaptation: The Tilt Aftereffect 64 then theme alookatthily ClickSelective 3.7 Adaptation: to edit Master The Psychologist’s Electrode title style 65 Tilt aftereffect: The perceptual illusion of tilt, produced by adapting to a pattern of a given orientation. Supports the idea that the human visual system contains individual neurons selective for different orientations. © Oxford University Press ClickSelective 3.7 Adaptation: to edit Master The Psychologist’s Electrode title style 66 Selective adaptation for spatial frequency: Evidence that human visual system contains neurons selective for spatial frequency. © Oxford University Press Figure 3.30 A demonstration of adaptation to specific spatial frequency 67 ClickSelective 3.7 Adaptation: to edit Master The Psychologist’s Electrode title style 68 Adaptation experiments provide strong evidence that orientation and spatial frequency are coded separately by neurons in the human visual system. Cats and monkeys: Neurons in striate cortex, not in retina or LGN. Humans operate the same way as cats and monkeys with respect to selective adaptation. © Oxford University Press ClickSelective 3.7 Adaptation: to edit Master The Psychologist’s Electrode title style How can we test at what level of the visual system this adaptation occurs without recording neurons in the brain? cover 1 do adaptationtest eye Result incovered will be similarto eye that the uncovered eye of © Oxford University Press ClickSelective 3.7 Adaptation: to edit Master The Psychologist’s Electrode title style 70 Human vision is coded in spatial-frequency channels. Spatial-frequency channel: A pattern analyzer, implemented by an ensemble of cortical neurons, in which each set of neurons is tuned to a limited range of spatial frequencies. Why would the visual system use spatial-frequency filters to analyze images? © Oxford University Press Figure 3.33 Different spatial frequencies emphasize different information 71 ClickSelective 3.7 Adaptation: to edit Master The Psychologist’s Electrode title style 72 If it is hard to tell who the famous person is on the next slide, try squinting or defocusing the projector. © Oxford University Press Figure 3.34 Who is that masked man? 73 ClickThe 3.8 Development to edit Master titleofstyle Vision 74 How can you study the vision of infants who can’t yet speak? Infants prefer to look at more complex stimuli. use They The forced-choice preferential-looking paradigm Visual evoked potentials o VEPsare electrical signals from the brain that are evoked by visual stimuli. © Oxford University Press ClickThe 3.8 Development to edit Master titleofstyle Vision 75 Young children are not very sensitive to high spatial frequencies. Visual system is still developing. o Cones and rods are still developing and taking final shape. o Retinal ganglion cells are still migrating and growing connections with the fovea. o Thefovea itself has not fully developed until about 4 years of age. © Oxford University Press Figure 3.36 Assessing vision in infants (Part 1) 76 Figure 3.36 Assessing vision in infants (Part 2) 77 Figure 3.36 Assessing vision in infants (Part 3) 78 ClickThe 3.8 Development to edit Master titleofstyle Vision 79 Story of Jane: Abnormal early visual experience resulting in possibly permanent consequences. Jane had a severe cataract in her left eye. aromaggotorolmmmo woman © Oxford University Press ClickThe 3.8 Development to edit Master titleofstyle Vision 80 Monocular vision from deprivation can cause massive changes in cortical physiology, resulting in devastating and permanent loss of spatial vision. Amblyopia: Reduced spatial vision in an otherwise healthy eye. Strabismus: A misalignment of the two eyes. Anisometropia: A condition in which the two eyes have different refractive errors. © Oxford University Press Click to edit Master title style 81 3.8 The Development of Vision Cataracts and strabismus can lead to serious problems, but early detection and care can prevent such problems! There appears to be a critical period of about 4–5 years early in life during which problems can be corrected. © Oxford University Press ClickThe 3.8 to edit Master titleofstyle Development Vision 82 If input from one eye is limited (due to cataract, amblyopia, or strabismus), then the neurons that were meant to process that eye may get reassigned to process the other eye instead. If corrected early enough, this process can be reversed. © Oxford University Press ClickThe 3.8 Development to edit Master titleofstyle Vision 83 Does the Duck’s Left Eye Know What the Right Eye Saw? Question: If a duckling imprinted on its mother with one eye, would it recognize her with the other eye? Hypothesis: Birds do not have a corpus callosum connecting the left and right hemispheres, so information obtained by the left eye might not be recognized when viewed with the right eye. © Oxford University Press ClickThe 3.8 Development to edit Master titleofstyle Vision 84 Does the Duck’s Left Eye Know What the Right Eye Saw? (cont’d) Test: One eye of each of 64 ducklings was blindfolded, and then they imprinted on a fake red or blue adult duck “mom”. Result: When the blindfolds were switched to the other eye, the ducklings no longer recognized their “mom”. Conclusion: Each side of the avian brain seems to have a separate memory. © Oxford University Press Visual Perception Notes created on January 16, 2025 at 1:06 PM by Minutes AI Double Stars and Minimum Resolvable Activity (00:00 - Double stars are two star systems that can be seen as more than one star. Minimum resolvable activity relates to the smallest angle on the retina where features Recognizable features are about details and spatial changes. Typical resolution is around 2 degrees on the retina. Spatial Frequency and Contrast Sine wave gradients are used to measure spatial acuity. High frequency stimuli can appear as gray due to indistinguishable black and Sensitivity to spatial frequency is affected by contrast. High contrast makes it easier to see. Both very high and very low spatial frequencies can be hard to detect. Visual Crowding Visual crowding affects the ability to discriminate objects in the periphery. Fixating on a center object limits the ability to identify objects nearby. Discriminability is high in the center but limited in the periphery. Cell Response and Spatial Frequency Certain cells are selective to specific spatial frequencies. Cells respond differently based on the frequency of stimuli. The phase of the gradient affects the response of cells. These notes were taken with Minutes AI (https://myminutes.ai)  Shifts in the gradient lead to different responses in the perceptive field. Connections in the Visual System Most connections from ganglion cells go to the lateral geniculate nucleus (LGN). LGN has layers corresponding to different types of ganglion cells. The organization of the LGN includes magnocellular and parvocellular layers. Conocellular layers contain more sparse neurons. Visual Field Processing (09:52 - 19:51) Left visual field goes to the right LGN, and right visual field goes to the left LGN. Nasal portion of the left eye goes to the right LGN. Lateral portion of the right eye goes to the same side. The LGN is a subcortical structure, part of the thalamus. Not all animals have the same visual field crossing. In some animals, the right path stays on the right side, and the left side stays on LGN and Visual Information In the LGN, the two eyes are still separate. Visual fields go to the contralateral eye, but information from each eye remains M ganglion cells connected to rods go to the magnocellular layer. Magnocellular layer is larger and responds best to moving objects. Parvocellular cells are smaller and respond to details, less sensitive to quick changes. Primary Visual Cortex (V1) V1 is located in the occipital lobe and is responsible for significant visual processing. V1 in humans has about 200 million cells, compared to around 10 million in the These notes were taken with Minutes AI (https://myminutes.ai)  Layer 4 of V1 is the primary input layer, showing a strong band due to high input. Connections from the retina to the LGN and then to V1 maintain a topographic map of Cortical Representation Cortical magnification occurs where foveal areas have more cells dedicated to Peripheral areas have less dedicated processing space. Early information on visual processing came from studies of patients with cortical Modern fMRI allows for detailed mapping of visual responsiveness in the brain. Two key features of V1 are topographical mapping and cortical magnification. Visual Processing (19:51 - 29:51) Importance of spatial information Need for more information covering more space for acuity. Preference for bars of light or dark spots between light. Neuronal response to visual stimuli Complex cells respond to broader ranges of stimuli. Neurons respond selectively to orientations and edges. Experimental Findings Initial experiments with cats Early experiments did not yield responses. Discovery of response to edges of slides led to significant findings. Nobel Prize-winning discovery Testing various stimuli revealed strong responses to edges and bars. Receptive Fields These notes were taken with Minutes AI (https://myminutes.ai)  Transformation of receptive fields Circular receptive fields in LGN transform into different fields in V1. Neurons receive input from selective ganglion cells aligned together. Orientation selectivity Neurons respond most to specific orientations and less to others. Ocular Dominance Combining information from both eyes V1 is the first cortical area to combine inputs from both eyes. Presence of preferred eye in certain areas. Columnar Organization Structure of cortical columns Cells respond to similar orientations when recorded perpendicularly. Different orientations are represented in small areas of cortex. Mapping orientation selectivity Patterns of orientation selectivity are repeated across the cortex. Similar orientations may be constructed from overlapping cells. Loss in Hydro Column (29:52 - 39:47) Existence of loss related to color processing in hydro column. Found due to a particular set of chemicals. Related to kitty stain. Adaptation in Visual System Adaptation involves exposure to the same stimulus. These notes were taken with Minutes AI (https://myminutes.ai)  Neurons responding to the stimulus fatigue and reduce firing. Experiment predicts response to different orientations. Cells responsive to a specific orientation become less active after adaptation. Effect on perception of orientation after adaptation. After Effect After effect occurs after adaptation to a stimulus. Example: Staring at a 15-degree tilt leads to perceiving a straight line as tilted the Supports the idea of individual neurons selected for different orientations. Spatial Frequencies Adaptation experiments also apply to spatial frequencies. Different orientations and spatial selectivity are independent. Evidence of adaptation occurring at the cortical level (V1) rather than the retina. Evolution of Visual System Visual system evolved to process different spatial frequencies. Higher spatial frequencies useful for detail recognition. Lower spatial frequencies useful for general awareness (e.g., detecting Development of Vision Studying vision development in non-verbal subjects (e.g., infants). Methods involve observing what they look at. Infant Visual Preferences (39:47 - 47:57) Young infants prefer complex stimuli. These notes were taken with Minutes AI (https://myminutes.ai)  This suggests they can differentiate between various stimuli. Experiments often use a four-choice paradigm. Measure how much time infants spend looking at one side versus the other. Visual Processing in Infants EEG experiments show brain responses to visual stimuli. Young children are not sensitive to high spatial frequencies. Physical development of the eye affects clarity. The retina shape causes blurriness; nervous system development also plays a Effects of Visual Impairments Case example of a patient with a cataract in one eye. Disruptive input can lead to significant developmental changes. Early detection and correction are crucial. If addressed within the first four or five years, visual system can develop normally. Environmental Influences on Vision Experiments in animals show the impact of visual environment. Cats raised in environments with only vertical stripes become sensitive only to Duckling imprinting study highlights differences in visual processing. Ducklings blindfolded on one eye showed inability to recognize their mother when These notes were taken with Minutes AI (https://myminutes.ai)