f MRI and neural encoding models Voxel receptive

f. MRI and neural encoding models: Voxel receptive fields 1

Class project: the next steps I have now replied to all of your proposals (finally!), with suggestions for next steps. What is known about this topic? 1. Find a recent review article (e. g. using “review” term in Pub. Med, Trends in Cognitive Sciences, Current Opinion in Neurobiology) 2. Find papers that cite this review (Google Scholar). See what Qs they are looking at. 3. Try to identify an open question that hasn’t been looked at yet 2

Class project: the next steps Guiding principles: • Would the imaging provide information over and above what we can get from behaviour? • When people look the same from outside the head (behaviour), but are different inside (imaging) • Maybe imaging can catch early signs of a process which won’t manifest itself in behaviour till later? Look at representations and mechanisms, not just what lit up • Structure of representations, e. g. via neural similarity • Try to relate neural activation to behaviour 3

Voxel receptive field models: Jack Gallant et al. Identifying natural images from human brain activity. Kay KN, Naselaris T, Prenger RJ, Gallant JL. Nature. 2008 Mar 20; 452(7185): 352 -5. 4

Modeling a continuous space Standard decoding: Neural responses for Stim A Neural responses for Stim B Present some test-set neural data: Q: Was it elicited by A or by B? Problem: What if it is a new stimulus, C? 5

Interpolating between stimuli, using a model of the stimulus space Pattern-information analysis: from stimulus decoding to computational-model testing. Kriegeskorte N. Neuroimage. 2011 May 15; 56(2): 411 -21. 6

One way of making a model: voxel receptive fields What is a receptive field? From Kandel et al, Principles of Neural Science 7

What is a receptive field? (continued) Receptive field (RF) doesn’t just have a spatial position, it also has a preferred type of stimulus, e. g. orientation From Kandel et al, Principles of Neural Science 8

Receptive fields in early visual cortex: Different orientations and spatial scales “Gabor jet” or “Gabor pyramid” 9

A simple example: colour in the retina http: //en. wikipedia. org/wiki/Cone_cell 10

Colour channels in cortex, for neural decoding Brouwer, G. J. , & Heeger, D. J. (2009). Decoding and reconstructing color from responses in human visual cortex. The Journal of Neuroscience, 29(44), 13992 -14003. 11

A voxel receptive field model of visual cortex: Kay et al, Nature, 2008 12

A voxel receptive field model of visual cortex: Kay et al, Nature, 2008 13

A voxel receptive field model of visual cortex: Kay et al, Nature, 2008 14

A specific voxel’s receptive field 15

Videos! https: //www. youtube. com/watch? v=6 Fs. H 7 RK 1 S 2 E https: //www. youtube. com/watch? v=u 9 n. Mfa. Wqk VE 16