Presentation on theme: "Seeing Things 2 Visual Processing in the Brain How Your Brain Works - Week 4 Dr. Jan Schnupp HowYourBrainWorks.net."— Presentation transcript:
Seeing Things 2 Visual Processing in the Brain How Your Brain Works - Week 4 Dr. Jan Schnupp HowYourBrainWorks.net
Visually Guided Behaviour To catch a prey, your sensory system has to “represent” the target to be caught in a manner that can “instruct” the appropriate motor commands. In reptiles and amphibia, this representation most likely resides in the optic lobe, also called the optic tectum, or (in mammals) superior colliculus.
Motor Maps in the Superior Colliculus Microstimulation studies have shown that the SC contains a “motor map”, which is in register with the retinotopic sensory map Retinotopic Map Motor Map
There is more to vision than visual reflexes Often we have to balance the desire to catch one object with the need to dodge another, or choose which from a variety of objects is most worth pursuing. Which objects need catching, and which need dodging, may change over time. This creates a need for quite abstract representations of objects within a flexible, rapidly adaptable system. Is that what sensory cortex is for?
Primary and “Extrastriate” Visual Cortex
Decoding Brain Activity Miawake et al. Neuron 2008 Observed activity of ca 1500 voxels of (3mm) 3. Reconstructed the image shown from recorded activity
Simple Cell Receptive Fields
Cortical Layers 1: “tufts” of apical dendrites receive cortico-cortical connections. 2/3: gets input from layer 4. Many simple cells. Outputs to other parts of cortex. 4: gets most input from LGN. Many LGN- like, non-oriented cells. Output to layers 2/3. 5/6: inputs from layers 2/3. Output to subcortical targets
Cortical Columns as “Computational Modules” Surface Supra- granula r Granul ar Infra- Granul ar White matter From Thalamus Subcortical Targets I II/III IV V VI
Representing Shape and Position Within an “Orientation Map” Pseudocolour “orientation tuning” map of ferret primary visual cortex (revealed with intrinsic optical imaging).
Binocular Fusion Try “shooting a hole” into your hand by rolling up a piece of paper into a tube, holding it in front of one eye, and holding your free hand flat in front of the other eye, as shown here. Your brain will try, as best it can, to paint a single scene out of the disparate images seen by each eye.
Stereopsis (Stereo vision for depth)
Cytochrome Oxidase Blobs
What would the world look like to a stripe reared kitten?
Three-eyed Frogs means that if you want to predict the PSTH of
Amblyopia Inputs from each eye are thought to “compete” for cortical territory during early development. If one eye is “weaker” (e.g. due to an optical defect), it may fail to get properly connected to the visual cortex. This in principle essentially healthy eye can then become functionally blind. To prevent amblyopia, children at risk sometimes have their stronger eye temporarily deprived of input.
Meltzoff & Moore 1977 means that if you want to predict the PSTH of Neonates are said to be able to mimic facial or hand gestures after 14 to 21 days. Wilderbeast run with the herd after just a few hours. Experience dependent maturation of the visual system may need to be rapid.
Face Cells means that if you want to predict the PSTH of Infero-temporal cortex contains neurons that appear to be selective for visual objects, such as faces or hands. Damage to these areas can lead to “visual agnosia”, and inability to recognize objects by sight even though there is no blindness.
Newsome’s Moving Random Dots
Neurometric Curves Hatched Bars: responses to movement in preferred direction Filled black bars: responses to movement in null direction Open (white) circles: psychometric function (animal’s choices) Filled (black) circles: neurometric function (neuron’s “choice”) From Newsome, Britten, Movshon (1989) Nature 341:52