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review for 2nd midterm .docx

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Matthias Niemeier

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Chapter 6: Space Perception and Binocular Vision 6 Muscles controlled by cranial nerves • Superior Rectus • Lateral Rectus • Medial Rectus • Inferior Rectus • Superior Oblique—goes thru the hook-like structure (trochlea) • Inferior Oblique 3 Cranial Nerves • #3-Occulomotor nerve: does most of the job; in the midbrain (works ipsilaterally) • #4-Trochlear nerve: innovates the superior oblique (works contralaterally) • #6-Abducens nerve: innovates the lateral rectus (works ipsilaterally) Frontal Eye fields & Parietal Cortex • Frontal eye fields and parietal cortex projects onto the Superior Colliculus • Eye movements are controlled by cerebral cortex • Superior Colliculus: structure in midbrain; initiates and guides eye movements Types of Eye Movements • Smooth Pursuit: movement of eyes of a moving object • Saccades: rapid movements of eyes to fixating points • Vergence: eye movement where two eyes move in opposite directions; convergence/divergence Functions of Eye Movements • Smooth Pursuit • To keep things stable in our fovea • Saccades • To move fovea to object of interest; move as quickly as possible to reduce travel time during which vision is blurred • Yarbus: scanpaths • False motion and retinal smear: the object looks like it’s moving, but really it’s our eyes that’s moving • We don’t notice this b/c of spatial constancy • Spatial constancy: tricky problem of discriminating in the retina if the object is moving or if the eyes are moving • Saccadic suppression: reduction of visual sensitivity that occurs when a saccadic eye movement is made; eliminates smear from retinal image motion during an eye movement • Compensation Theory--comparator: inhibits other parts of the visual system from interpreting the object as moving; solves problem of motion illusions Euclidian Geometry • Parallel lines remain parallel as they are extended in space—only in the real world; not in the retinal image • Objects become smaller as we move away because the image takes less space in our retina • Parallax: the 2 retinal images are not the same b/c the retinas are at slightly different places • Binocular Disparity: the differences b/w the images seen on both retinal images; the basis for stereoscopic vision Binocular depth cues provide: • Convergence—gives us an additional sense of depth • Stereopsis • Ability to see more of an object with both eyes than one eye Monocular cues • Occlusion: when one object in front blocks another but it’s a nonmetrical depth cue b/c it doesn’t tell us magnitude(distance) • Size and position cues • Relative size: the same object seems to be smaller when it’s further away • Texture gradient: items of the same size form smaller images when further away • Relative height: images further away seem to be higher • Familiar size: using previous knowledge to estimate size of an object • Relative: doesn’t tell exact distance • Absolute: tells us the exact distance • Aerial Perspective: when fainter objects seem to be further away • Linear Perspective: when parallel lines are not parallel in 2D world—they converge; only provides relative metrical depth info • Vanishing point: the point where the lines meet • Foreshortening: when an object appears to be shorter than it actually is • Anamorphosis: when special devices need to be used to actually view the image • Motion cues • Motion parallax: objects that are closer move faster and more than objects that are further away (need to move head); eyes are in different positions in the head at the same time; provides relative metrical info about how far away objects are • Accommodation and Convergence: depth; can tell us the exact distance to an object Binocular Vision and Stereopsis • Corresponding retinal points: when images points are corresponding to the retinal image in both eyes; same distance from the fovea—Zero binocular disparity • Horopter: place where zero binocular disparity is; depends on amount of convergence • Panum’s fusion area: area in front and behind the horopter • Diplopia: objects closer to or farther away from the horopter form images on non- corresponding points in the 2 eyes—double vision • Crossed disparity: when image is projected to the right side of the left eye and to the left side of the right eye • Uncrossed disparity: when image is projected to the right side of right eye and to the left side of left eye • Free fusion: technique of converging image without a stereoscope • Julesz’ random dot stereograms: evidence that disparity is enough for stereopsis • Correspondence Problem: figuring out which bit of the image in the left eye should be matched with which bit in the right eye • To solve this problem: • Blurring the image: only see the low spatial frequency images • Uniqueness constraint: an image is only seen once in each retinal image • Continuity constraint: except at edges of objects, neighbouring objects are similar in distance Chapter 7: Attention and Scene Perception • Selective Attention: the ability to focus attention on one thing that is more important, relevant than another thing • Why can attention help us?—it allows us to choose what’s more important Cueing as a Tool for Examining Attention • Simple Probe detection experiment: measures RT • Posner—adding a cue • When a cue is added that helps the person know where the stimulus is going to appear • Stimulus-driven/peripheral cues: info conveyed thru previous events at the same location • Symbolic/voluntary cues: info conveyed thru cognitions & memory (language or other symbols) • Stimulus Onset asynchrony (SOA): the time b/w the onset of one stimulus and the onset of another • Overt shifts of attention: attention where eye movements move correspondingly • Covert shifts of attention: attention where eyes do not move • Perceptual biases: asymmetries on a stimulus • Line-bisection task • Feature-based cueing: attention where non-spatial features are used to find a target Visual Search • Finding an object in a set of distracting elements • Feature search: when the target is defined by a single attribute; efficient search • Conjunction search: when the target is defined as having more than a single attribute; inefficient search • Spatial configuration search: more inefficient • Salience: the vividness of a target compared to the surrounding ones • Parallel: the processing of more than one stimulus at a time Is conjunction search serial? • Yes—Serial self-terminating search: items are examined one after the other until the target item is found • No—Limited capacity parallel process: difficult to look at all images at the same time Feature Integration Theory • 1-preattentive stage: looking at all the images in a set at same time before selective attention is deployed • 2-attentive stage: spatial attention binds together features for one item at a time--serial search • Guided search theory: when you know the basic features of an object, you look for that target based on this knowledge The Binding Problem • The challenge of tying together different attributes of visual stimuli to the appropriate object so that we perceive a unified object • Illusory conjunctions: when we mismatch certain features of a stimuli with others; happens when the image is shown for only a brief time The Attentional Blink • Rapid Serial Visual Presentaion (RSVP): when pieces of info are shown one after the other in a certain location; presented in a stream • Attentional blink: the difficulty of perceiving the second target when shown after the other (200-500 ms before) 3 Ways Responses of a Cell Could be changed by Attention • 1-Response enhancement: when a neuron gives a more enhanced response • 2-Sharper tuning: when a neuron gives a more precise response • 3-Altered tuning in space Change Blindness • Change Blindness: when we are unable to figure out the difference b/w two pictures; something more relevant to the scene is easier to notice than something irrelevant Spatial layout of a scene • Description of the structure of a scene • Scenes organized according to 2 dimensions • Similar meaning group together Chapter 8: Models of Attention • Early vs. Late selection • Early: the retina has so much info that it’s hard to process all at once (bottleneck); focus on one thing then another • Late: high level of processing but we are unaware of it • Spotlight model: attention is focused on a coherent region of space and can move from one point to the next • Zoom lens model: attention expands from fixation…it either grows to fill entire region or shrinks to include just cued location • Biased-competition model of attention • Competition of stimuli for limited processing capacity and control of behaviour • Competition is biased towards certain stimuli depending on • Bottom-up processes: salience • Top-down processes: instructions, spatial cues, feature cues • Premotor theory of attention • 1-there is a strong link b/w overt and covert shifts of attention • 2-attention is oriented to a given point when the oculomotor program for moving the eyes to this point is ready to be executed • 3-covert orienting of attention is achieved by inhibiting this execution of eye movement Problems with spotlight and zoom lens models • Attention shifts rather instantly • We should pay attention to the space b/w the two objects/persons, but we don’t • Attention is not based on a coherent region • We can focus attention on more than one object at the same time Support for the premotor theory of attention • Attention and eye movements are closely coupled • Performance differs as a function of whether you make an eye movement to that point or not (better at saccade) • Shifting attention and eye movements—largely overlapping frontoparietal networks Networks of attentional control • Attentional cuei
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