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1、1,Neural Correlates of Visual Awareness,Sheng He University of Minnesota,2,3,Physical stimuli,Perceptual experience,Same stimuli,Different percepts,Different stimuli,Same percept,4,Physical stimuli,Perceptual experience,Localized neural activity,?,Areas in which activities change with stimuli are no
2、t good candidates of NCC.,different,same,5,Physical stimuli,Perceptual experience,Localized neural activity,same,different,?,moving,Areas in which activities change with perception are good candidates of NCC.,static,6,Physical stimuli,Perceptual experience,Localized neural activity,?,or,rivalry,Area
3、s in which activities change with perception are good candidates of NCC.,same,different,or,7,Part I: adaptation to invisible stimuli (with Don MacLeod) Part II: motion aftereffect (with Eric Cohen, Xiaoping Hu) Part III: binocular rivalry - parallel pathways to visual awareness (with Tom Carlson),8,
4、Physical stimuli,Perceptual experience,Localized neural activity,different,same,Can neurons in area X tell the difference?,Areas in which activities change with stimuli are not good candidates of NCC.,Part I: adaptation to invisible stimuli,9,Physical stimuli,Perceptual experience,Localized neural a
5、ctivity,V1?,can cause orientation-selective adaptation?,10,Spatial frequency (cycles/degree),Sensitivity,Resolution limit: 50cpd,Unresolvable,11,Orientation-Selective Adaptation,Adapt,Test,Same Orientation Hard to see! Need high contrast,Orthogonal Orientation Easy to see! Need low contrast,12,Tilt-
6、aftereffect,13,14,V1 is the first stage in the visual system where orientation information is extracted: orientation-selective adaptation is only possible at or after V1. If we find evidence for orientation- selective adaptation, then it implies that the orientation information has at least reached
7、V1.,15,Invisible vertical grating,Adapt,Test,Same Orientation Need higher contrast,Orthogonal Orientation Need lower contrast,Result,16,He and MacLeod,Nature 2001,17,18,Orientation-selective adaptation from an invisible spatial pattern: invisible to the observer but visible at V1. There is intra-cor
8、tical loss of spatial information. V1 activity is not sufficient for visual awareness.,19,Part I Summary Fine spatial patterns can be “visible” at V1 but invisible to the observer. V1 activity is not always correlated directly with visual awareness.,20,Caveats: 1. Maybe no single area will be “suffi
9、cient” for visual awareness. This approach may lead to the rejection of the whole brain as NCC. 2. Individual cortical area may not be the right unit to consider for the NCC. Different types of neurons exist in each area.,21,Physical stimuli,Perceptual experience,Localized neural activity,same,diffe
10、rent,?,moving,Areas in which activities change with perception are good candidates of NCC.,static,Part II: motion aftereffect,22,motion aftereffect demo,23,MT/V5 activity: motion - stationary,MT+,24,Physical stimuli,Perceptual Experience (after adaptation),Localized neural activity,MT?,Seeing Motion
11、 aftereffect,25,illusory motion,stationary,Adapt (moving),fixation,Perception,Test (stationary),Motion aftereffect:,26,27,He, Cohen, & Hu, Current Biology, 1998,28,Part II Summary MT activity is closely correlated with the perception of motion aftereffect. yet another exp from us (not reported here)
12、 showed that MT activity alone is not sufficient for the perception of motion.,29,Physical stimuli,Perceptual experience,Localized neural activity,Grating vs. Uniform field,Stationary vs. Stationary,Uniform field vs. Uniform field,Moving vs. Stationary,Summary of part I and II,30,Physical stimuli,Pe
13、rceptual experience,Localized neural activity,?,or,rivalry,Areas in which activities change with perception are good candidates of NCC.,Part III: parallel pathways to visual awareness,31,stereoscope,32,Binocular Rivalry,Percept: alternating views over time,Left eye,Right eye,Stimuli (e.g.):,time,33,
14、eye,LGN,V1,extrastriate,frontal,?,?,?,An simplistic view:,34,Not all dichoptic differences cause rivalry: OShea & Blake (1986). Dichoptic temporal frequency differences do not lead to binocular rivalry. Perception & Psychophysics, v39 (n1):59-63,35,Binocular Visual Beats,Integration of high temporal
15、 frequency luminance information between two eyes,Left Eye (28Hz),Right Eye (30Hz),Binocular percept (2Hz beat),36,Binocular rivalry: inter-ocular suppression Binocular beats: inter-ocular summation Can they be perceived simultaneously?,37,Stimulus,Left eye,Right eye,Differences in shape and color in the two eyes can potentially lead to binocular rivalry. Two eyes flickers with slight different temporal frequency can potentially lead to binocular beats.,38,Possible Percepts:,Beats:,Rivalry:,or,Or ?,39,Results,Observers perceive both rivalry
