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Lecture 7

Lecture 7 – PSYB51.docx

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University of Toronto Scarborough
Matthias Neimier

Lecture 7 – PSYB51 Attention and Scene Perception What is the horopter? > Entity of all the points and space, where for the two eyes there‘s zero disparity.  Selective attention is a cognitive brain mechanism that enables one to process relevant inputs, thoughts, or actions while ignoring others that are less important, irrelevant or distracting.  Arousal: a global state of the brain reflecting an overall level of responsiveness. > As your arousal increases, your attention decreases Why we need attention. • Bottlenecks: It is impossible to process everything at once. Lack of brain, lack of arms, ... • Sensory–cognitive–motor? Why can attention help us? Where does attention play a role? • Attention to vision
 Attention to audition / touch / smell • Attention across modalities • Attention to thoughts
 • Attention to motor tasks: ex. when you‘re doing something complex, it‘d change your motor complex Today: What effects does attention have? • How can we study attention? – Cues bias attention
 – Visual search: ex. looking for waldo 
 – Attention in time: watching a movie • The physiological correlates of attention: what changes in brain activity • Scene perception How can we measure attention? • Reaction times: a measure of the time from the onset of a stimulus to a response (ex. if you‘re waving a hand, how long does it take for him to see that) • Perceptual thresholds: change with attention. • Motor accuracy • Brain activity • Eye movements: can reflect overt shifts of attention. But careful; attention can shift without eye movements: covert attention. • Perceptual biases : somethings that are symmetrical are not perceived as being symmetrical or vice versa How can we study attention? – Cues bias attention • Posner‘s attentional cueing paradigm (Michael Posner was the first person to develop attentional tasks) • Natural biases
 • Feature-based cueing – Visual search: where‘s waldo 
 – Attention in time Simple probe detection experiment measures RT (or perceptual thresholds) • Posner: adding a cue • Cue: A stimulus that might indicate where (or what) a subsequent stimulus will be: valid vs. invalid vs. neutral. => Cueing effect > if it‘s on the left, in this case, it‘s valid because in the next step the target is there. But not on the right side, so that‘s invalid. Stimulus-driven cues: info conveyed through previous events at the same location. • Voluntary cues:(spatial)info conveyed through cognitions & memory, often based on language or other symbols-> usually an arrow pointing at a direction, but other symbols also, L, R, etc. What‘s the difference between stimulus-driven/ peripheral and voluntary/symbolic? • Partially independent neural structures.
 • Stimulus onset asynchrony(SOA): the time between the onset of one stimulus and the onset of another. – Different time courses of SOAs; slower effects for voluntary cues. – Inhibition of return (IOR) …and something in between stimulus-driven and voluntary  Overt shifts of attention: A shift of attention accompanied by corresponding movements of the eyes.  Covert shifts of attention: A shift of attention in the absence of corresponding movements of the eyes  Perceptual biases: Asymmetries in perception between the left and right side of a stimulus. – Vary with task, e.g. listening to speech. – When it comes to perception, we tend to focus more on the left visual field  Line bisection task Grating scales: – Which bar has more of the thinner/thicker stripes? > People prefer to choose the one that has thin stripes on the left  Grating scales: Electroencephalography: leftward bias associated w/ greater negativity over the right brain >380ms.  Space-based cueing of attention  Feature based cueing of attention: attention is guided based on non-spatial information about features. – Cued feature becomes more ―visible‖ throughout the visual field = outside the focus of attention.  Feature-based attention can be a disadvantage.  Zhang&Luck(2009):EEG response to occasionally flashed online). To probe the selectivity of the visual system for the attended dots outside the focus of attention  Zhang&Luck(2009): EEG response to occasionally flashed dots outside the focus of attention. of - feature-dependent modulation of the P1 suggest early influences feature-based attention on extrastriate areas. How can we study attention? – Visual search • Task and terms
 • Feature searches
 • Inefficient searches
 • (Feature-)conjunction searches • Models of visual search Bunch of bars. Is there one that is unique?  Looking for a target in a display containing distracting elements • Target: the goal of visual search • Distractor: any stimulus other than the target • Set Size: the number of items in a visual display (for eg. In one set there were more squares) 
 – Has no influence on search time for ―efficient searches‖, because it pops out 
 – Impacts search time for ―inefficient searches” : the time it takes you to find the object takes long  How much time
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