Attention, prediction and fMRI (cont.) Adaptation-fMRI

Class project: due Tues. April 29th April 29th: Just before start of “reading week” How long? The shorter the better! Max. 6 pages Format? Front-load the information 1st sentence: What Q are you asking? 2nd sentence: How are you going to ask it? 3rd sentence: Why should the reader care?

Class project: due Tues. April 29th Content? Show that you have explored to find out what is currently known, what is unknown Show that you have thought about what an interesting new direction to look would be Describe in broad terms an expt which would look in that direction State an explicit hypothesis Describe explicitly how the data will test that hypothesis Give elevator pitch?

Prediction and prediction errors http://www.scholarpedia.org/a rticle/Reward_signals

Predictive coding Subtract expectations from bottom-up input Helmholtz, Mumford, Rao & Ballard, Friston Jehee & Ballard (2009)

Top-down enhancement Kastner et al. (1999)

Attention within a receptive field: Moran & Desimone (1985) Figure from http://kybele.psych.cornell.edu/~edelman/Psych- 4320/week-2.html

Trying to pull apart attention and expectation Kok et al. 2012

Trying to pull apart attention and expectation: predictions Kok et al. 2012

Trying to pull apart attention and expectation: results Kok et al. 2012

Top-down feedback of information: Decoding the yellow of a gray banana Bannert & Bartels, 2013

Top-down feedback of information: Decoding the yellow of a gray banana Bannert & Bartels, 2013

Adaptation fMRI A bit like pattern-based analyses: Beyond “what lit up” Motivation very similar to that of pattern-based fMRI Just because two stimuli produce equally intense local avarge activations, that doesn’t mean that the brain can’t tell the two stimuli apart

Gaussian spatial smoothing to improve signal-to-noise Distinction between representations is lost: After smoothing, there’s no difference left Boynton Kriegeskorte Haxby Raizada /ra/ /la/ Gaussian spatial smoothing to improve signal-to-noise Stimulus A activation pattern Stimulus B Average activation same, but spatial patterns different Smoothed local average activation ends up the same

Key idea: neurons get tired Neurons have a preferred stimulus Repeated presentation of a neuron’s preferred stimulus habituates it (makes it tired) Activation goes down Presentation of something that the neuron counts as different allows it to recover again

Adaptation fMRI as a probe of neural difference-detection (Grill-Spector & Malach) Two stimuli: can neurons tell the difference? A voxel containing neurons that respond to all politicians, irrespective of party A voxel containing some specifically Democratic neurons, and other specifically Republican neurons. Rajeev Raizada - UW MRI talk, Oct. 2003

Responses to individual stimuli do not show whether neurons can tell the difference Different sets of neurons are active within the voxel, but overall fMRI responses are indistinguishable Rajeev Raizada - UW MRI talk, Oct. 2003

Neural adaptation to repeated stimuli does show the difference: What counts as repetition for neurons in a voxel Same neurons, adapting: It’s a politician again It’s a politician It’s a Republican Different, fresh neurons: It’s a Democrat Rajeev Raizada - UW MRI talk, Oct. 2003

Categorical perception: Not all differences make a difference as speech (Alvin Liberman & colleagues) Stimuli spread evenly along the /ba/-/da/ continuum Pure /ba/=1, pure /da/=10, perceptual boundary ~ 5 Presented as pairs, constant 3-step distance apart acoustically 1-4 and 7-10 do not cross boundary: perceived as same 3-6, 4-7 do cross boundary, perceived as different Rajeev Raizada - UW MRI talk, Oct. 2003

A brain area is processing the stimuli categorically, and therefore as speech, if activity parallels the subject’s same/diff curve Acoustic difference within each pair is constant (1-4, 4-7, 9-6 etc.) Phonetic difference depends on whether category boundary is crossed Raizada & Poldrack (2007) Rajeev Raizada - UW MRI talk, Oct. 2003

Release from adaptation Activation due to release from adaptation = Extra activation caused by stimulus change = (Response to the two different stimuli paired together) - (Response to same stimuli presented without the change) E.g. (1/4 + 4/1) - (1/1 + 4/4) To look for adaptation paralleling same/diff perception Make a contrast weighting each adaptation release value by the subject’s behavioural responses on that part of the same/different curve Rajeev Raizada - UW MRI talk, Oct. 2003

Parallel with infant studies Suppose we measure how long a baby looks at its mother’s face and its father’s face Suppose it looks for equal amounts of time at each parent Does that mean that the baby can’t tell Mom and Dad apart?

Infant habituation studies: overall design Johnson, M. H. (2001). Functional brain development in humans. Nature Reviews Neuroscience, 2(7), 475-483.

Infant habituation studies: time-course Turk-Browne, N. B., Scholl, B. J., & Chun, M. M. (2008). Babies and brains: habituation in infant cognition and functional neuroimaging. Frontiers in Human Neuroscience, 2.

Another adaptation-fMRI example: what counts as different? From Turk-Browne et al., (2008), adapted from Kourtzi & Kanwisher (2001)

Another adaptation-fMRI example: tuning, and what counts as different Malach, R. (2012). Targeting the functional properties of cortical neurons using fMR-adaptation. Neuroimage, 62(2), 1163-1169.