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Feature detectorsNeurons that fire to specific features of a stimulusPathway away from retina shows neurons that fire to more complex stimuli Cells that are feature detectors:Simple cortical cellComplex cortical cellEnd-stopped cortical cellSingle cell recording of neurons in the temporal lobeAn electrode is inserted in this area,and measure neural responses when stimuli are changed graduallyNeurons in this area respond to complex stimuli like those shown on the left.Selective adaptationSelective adaptation to size123456789101112123456789101112Figure 3.30 How neurons that respond best to narrow(N),medium(M),and wide(W)bars respond to the medium-bar grating on the right of Figure 3.28.(a-b):Response before adaptation.(c)Response after adaptation to the wide-bar grating at the top left.(d)Response after adaptation to the narrow-bar grating on the bottom left.After ImageAfter images:Red GreenGreen RedBlue YellowYellow BlueRGBYColor perceptionRGBYadaptationadaptationAfter imageAfter imageBinding problemTwo visual pathways(what&where/how systems)Image from Neuroscience,2nd Ed.(2000).Columnar organizationNeurons that respond to the same orientation are packed in the same columnImage courtesy of Dr.Paul Wellman and Neuroscience,2nd Ed.(2000).Distributed coding;then what do you need?Combining inputFeature integration theory by Treisman&GeladeAttention plays a central role in solving the binding problem.Attention helps organize information.Attention and Figure-ground segregationDepending on where you look at,the figure and the ground switch rapidly.Attention plays some role in determining the figure and the ground.Attention and 3D structureDepending on where to look at,you get different 3D structures.Damage to the parietal lobe creates binding errors.Copies of the black(A)and the white(B)vertical contour.Copies of the black(A)and the white(B)diagonal contour.Copies of the left sub-figure(A)The right subfigure(B)And the central sub-figure(C)Feature integration theoryAttention is the“glue”that combines the information from the what and where systems.What can you predict from this theory?If you cant attend,you cant combine information.Illusionary conjunctionDemonstrationI will show you a scene quickly.Report first the black numbers.Report what you see at each of the 4 locations.+Mask+Report first the black numbers.Report what you saw at each of the 4 locations.Illusionary conjunctionsWe tend to put different features from different objects together.Some brain damaged patients(parietal lobe)show illusionary conjunctions even when the patients were allowed to view the stimuli for 10 seconds.Visual search experimentsFeature searchThis is easy because you find the target by looking for a single feature.you dont need attentionConjunction searchFor this you need to combine two or more features(color and orientation)you need attentionLooking for the target Conjunction searchFor this you need to combine two or more features(color and orientation)you need attentionBecause you can attend an item one at a time,the difficulty in the conjunction search increases proportional to the number of items in the stimulus frame.This is not the case in the feature search.FindWhich is more difficult?FindWhich is more difficult?Feature binding and attention(Treisman,1988)Experiments:TaskGiven a stimulus frame containing visual items,subjects were asked to indicate whether or not a target item was present in the frame.Target:Target:Target:Target:Feature search vs.conjunction searchFeature searchThe target item has a unique feature.Conjunction searchYou need to combine features to find the target.You need attention.Because you can attend only one item at a time,the conjunction search becomes more difficult when more items are in the stimulus frame.Generality of the results:Feature searchConjunction searchExperiments:Measure accuracy and response times(conjunction cases vs.non-conjunction cases)Response time#of distractors1000 ms500msResponse time#of distractors1000 ms500msThe physiology of attentionHow do you combine features?Synchrony hypothesisWhen neurons in different parts of the cortex are firing to the same object,the pattern of firing is synchronized(they fire at the same time,and in the same manner).So when neurons are firing in synchrony,the corresponding features are bound together.Separate neurons respond to color(green,blue,white),contours(orientations),textures,so on.Synchrony hypothesis:When the features come from the same object(i.e.,the woman),these neurons fire at the same time in the same manner.When the neurons fire at the same time and in the same manner,we perceive“binding”of features.Attention is likely to increase synchronyAttentionSelecting informationEnhancing informationCombining information谢谢！
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