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Lecture 8


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Matthias Niemeier

PSYB51 Lec 8 SAQ: under certain conditions we are very good at scene perception – how come? Why is it that sometimes we have great difficulties; when? And what explains the difference? - Global and local processing - Easy to recognize things in global perceptions o Ex scene perception  Seeing them one at a time  RSVPs  We can pick out complex scenes and remember them  Done with GLOBAL processing - Global processing: computer model doing something like that o Computer algorithm looking at certain aspects of a picture  spatial frequencies, contrasts, with some other features it was able to process  Openness of scene vs looking down a narrow canyon  Can quantify how open the scene is  Depth  how far can you see into the picture o Can arrange these scenes according to these two dimensions o Similar scenes were glued together - Emerged from simple algorithm of quantifying certain features that the problem was organizing scenes - Simple computer algorithms can extract these features - Global processing can be done fairly quickly - Spatial frequencies are different for human made scenes – more vertical and horizontal lines - Sometimes we have difficulties when specific things are different in a given scene – change blindness o Without paying attention to them, have trouble seeing the differences Attention contd - Selective attention: cognitive brain mechanism that enables one to process relevant inputs, thoughts or actions while ignoring others that are less important, irrelevant or distracting Attentional control and models of attention Models of attention – how attention is allocated to different networks Biased competition model – more about how neurons work Premotor theory of attention – eye movements, spatial shifts of attention go together most of the time Early vs late selection - Green boxes with arrows represent what the brain is doing - Sensory input at the first level which is then passed on to units of sensory and analysis - Executive functions has to do with planning and coming up with behaviour for the given input which leads to a response - Neglects the fact that arrows go the other way around - Red arrows show attention can play a role on either level of processing stream - Attention is a mechanism of early selection o Argument: retina gets so much information (sensory bottlenecks – too much info for us to process at one time) o Attention is like a plumber  pay attention to one sense and turn off the other - Early models cannot explain cues or facts that even things that are not attended to are processed at another level - Late selection models o Ex. study in which attentional blink paradigm was used  Need to look at two targets that come after one another  Unconscious  Can do this with words:  If you have a sentence starting with “today I am wearing a ---“ You predict the next word. When you hear dog you get confused  Some situations cause EEG things in the brain – n400  There is a high level of processing that you are not aware of - Best answer: there is multilevel filtering - Does not just matter on which level I t is happening at, the load at which it is being processed at is important too - Light phases are control conditions, dark grey are areas of motion while paying attention to a stimulus you are fixating on - Increased signal in a low load when there is motion - If perception task is complex, signal is much lower Spotlight model - There are 3 people standing on a stage, the person under the spotlight will be brighter and have greater luminance contrast - Attention works in a similar way; works like a spotlight and helps pick out things that are more important - Confined to a certain region of space and can move from one area to the next o Also called a search light model - Not only one person is in the spotlight, but when the spotlight is wider, all 3 will be in it o Explained by…. Zoom lens model - Attention expands from fixation and grows to fill whole region and also shrinks to include just cued location - Zooms in and out on area being paid attention to - Focusing on a small region – can pay attention to a certain thing - Attention resources stay the same – spreading over a big visual field – will not be a s effective Problems with these models: 1. If we have attention being like a spotlight or zoom lens then we should see that if the spotlight is on one person and shifts to the next person, we’d have a spotlight shifting continuously o This shows it should be paying attention to the space in between the two objects o Attention when resolved in time, decreases at the first location and builds up on the next location o 2 diff hills o More consistant of a spotlight being turned off in between o Like talking about 2 spotlights 2. Attention can split into more than one focus o Ex. fixating circle in the middle – like a placeholder  Task: to observe what happens at the top left corner  Have RSVPS and need to observe the one at the top left – press a button when you see an x at the top left circle  Can do this with another RSVP on the bottom right corner – press button when an x appears here  Focus of attention becomes larger  Has the shape of an oval  Problem: told to pay attention to corners and don’t pay attention to fixation point or other corners  Have 2 locations not in the same region that we have to pay attention to  Is still possible o Shows left and right sides both get activated o Black outlines: regions that cut across multi visual areas o Patch of the fovea gets activated by fixation point in the middle o ATT2 lh = top left, att2 rh = bottom right o Main activity is seen in the areas representing bottom right and top left whereas in the fovea have no activation  Directly shows we can split the spotlight into 2  Incongruent with spotlight models o Another problem: Ex. multiple object tracking  Can track multiple objects at the same time o Shows spotlight and zoom lens models have their limitations o Continue to use these models because they explain certain processes  Ex. the fact that light is a wave and - These models explain SOME things, but not all Biased-competition model - Desimone and Duncan - Orients itself more at physiological realities - Psychology models start with questions like : what should be there - Looks at what neurons are actually doing - Neurons starting from at least v4 have big receptive fields so typically a single neuron will be activated by multiple stimuli o Some of these stimuli may be ideal for that neuron or may not be o May become suppressed in activity o Many stimuli in receptive fields  Like many people trying to get through the same door  Makes everything inefficient - Competition – have this between different species of sensory input and is implemented in the visual fields - Have different neurons that overlap - Can resolve by -> strongest person gets through the door first o Ex. when visual stimuli coming in, preferred orientation is more salient o Like the bullies getting in the door first o Bottom up processes - Bias the competition in some way - Also bias coming from different directions - Yellow arrows coming from sensory input o Point of graph  there is a flow of visual input or sensory inputs o Get bottom up processes - Attentional control network o Blue arrows = top down influence o Can bias depending on top down influence o Like a bouncer letting others in and not other people o Letting certain stimuli in and not others - Bias competition illustrates how neural processes work in regulating bottom up and top down processing Premotor theory of attention - Has to do with eye movements and spatial shifts of attention go together in certain ways - Important component: Rizzolatti et al 1986 proposed o 1. Strict link between orienting of attention (covert attention) and programming explicit ocular movements (overt
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