V1 MT Hubel and Wiesel, 1968 Maunsell and V an Essen, 1983
Relating MT responses to visual discrimination 0% coherence 50% coherence 100% coherence
Newsome and Paré, 1988
Downing & Movshon, 1989
Record LIP, VIP 7a DP FEF V1 M T V4 MST V 2 FST PITd STP VP PITv CITd VOT CITv AITd AITv Visual input
Record LIP, VIP 7a DP FEF V1 M T V4 MST V 2 FST PITd STP VP PITv CITd VOT CITv AITd AITv Visual input
Visual stimulus Neuronal Behavioral response judgement
Pref target Receptive field Dots Aperture + recording in MT Null target Fixation 10 deg Point Fix Pt Dots Targets 1 sec
MT responses depend on motion coherence 200 100 150 100 Firing rate (impulses/trial) 50 Preferred direction 50 Null direction 0 0 0 25 50 75 100 0 10 20 30 40 50 100 50 75 40 30 50 20 25 10 0 0 0 25 50 75 100 0 10 20 30 40 Coherence (%) Britten, Shadlen, Newsome & Movshon, 1993
Behavioral performance from one session Proportion correct Coherence (%) Britten, Shadlen, Newsome & Movshon, 1992
Barlow, Levick and Y oon, 1971 Britten, Shadlen, Newsome & Movshon, 1992
MT cells are as sensitive as monkeys to visual motion 60 Proportion correct Number of cells 40 20 0 0.1 1 10 Threshold ratio (neuron/behavior) Coherence (%) Britten, Shadlen, Newsome & Movshon, 1992
MT cell firing does not require the observer to make a decision Neuronal threshold, fixation (%) 100 10 1 1 10 100 Neuronal threshold, choice (%) Britten, Shadlen, Newsome & Movshon, 1992
Visual stimulus Neurometric function Psychometric function Neuronal Behavioral response judgement
Visual stimulus Neurometric function Psychometric function Neuronal Behavioral response judgement ?
MT cell firing is correlated with behavioral choice 0% coherence Choose “preferred” Choose “anti” Britten, Newsome, Shadlen, Celebrini & Movshon, 1996
MT cell firing is correlated with behavioral choice 0% coherence Choose “preferred” Choose “anti” Britten, Newsome, Shadlen, Celebrini & Movshon, 1996
MT cell firing is correlated with behavioral choice Response of "antipreferred" neuron Response of "preferred" neuron
MT cell firing is correlated with behavioral choice "antipreferred" Choose Response of "antipreferred" neuron Choose "preferred" Response of "preferred" neuron
MT cell firing is correlated with behavioral choice "antipreferred" Choose Response of "antipreferred" neuron Choose "preferred" Response of "preferred" neuron Choice probability ~ 0.85 Response of "preferred" neuron
Correlation of activity to choice is not accidental Britten, Newsome, Shadlen, Celebrini & Movshon, 1996
Choice-related activity has a “forward” time course Mean normalized response 0.4 0.2 0.0 0 500 1000 1500 2000 Time (msec) Difference in normalized response 0.1 0.0 -0.1 0 500 1000 1500 2000 Time (msec) Britten, Newsome, Shadlen, Celebrini & Movshon, 1996
The most sensitive neurons are most correlated to choice Britten, Newsome, Shadlen, Celebrini & Movshon, 1996
a n = 17,200 0.01 Choice probability for depth discrimination in V2 0.3 0.005 Disparity (º) a 0 0 Fixation marker Stimulus Choice targets –0.005 –0.3 0 2 Time (s) Trial start Trial end –0.01 0 1,000 2,000 b b 2 Amplitude 1 Disparity (º) 0.3 c 0 Mean choice –0.3 probability 0.54 0 10 20 30 40 2,000 n = 57 cells Time (ms) 0.5 c 0 1,000 2,000 Added signal: –50% –25% 0% 25% 50% Time (ms) Probability 0.5 d Temporal integration time (ms) n = 76 0.5 60 0 –0.5 0 0.5 –0.5 0 0.5 –0.5 0 0.5 –0.5 0 0.5 –0.5 0 0.5 Disparity (º) 40 0 d R 1 Percentage of near choices 20 0.5 –0.5 0 0.4 0.6 0.8 –50 –25 0 25 50 Choice probability Added signal (%) Figure 2 | Psychophysical kernel and choice-related signal have different Figure 1 | Methods. a , Sketch of the sequence of events during one trial. time courses. a , Psychophysical kernel (averaged over 76 experiments; b , Example time series of the stimulus. c , Probability mass distributions of n 5 17,200 trials; two monkeys) as a function of disparity and time. Colour the stimuli for one experiment (probability as a function of disparity), with represents amplitude (in occurrences per frame). b , Normalized amplitude signal disparities of 2 0.3 u and 0.15 u . Each plot depicts one signal condition of the psychophysical kernels decreases over time. c , Averaged choice-related (negative percentages indicate near signal disparities). d , The monkey’s signal over time. Shaded grey areas in b and c , 6 1 standard error. d , The performance for this experiment (in percentage ‘near’ choices as a function correlation coefficient, R , over time between choice probability (for of percentage added signal). individual neurons) and the amplitude of the mean psychophysical kernel, plotted against a neuron’s mean choice probability. Colour represents temporal integration time (Supplementary Methods); bold symbols, significant R ( P , 0.05, by resampling); circles, data from monkey 1; squares, data from monkey 2.
Visual stimulus Neurometric function Psychometric function Neuronal Behavioral response judgement Choice probability
Albright, 1984
Stimulate LIP, VIP 7a DP FEF V1 M T V4 MST V 2 FST PITd STP VP PITv CITd VOT CITv AITd AITv Visual input
Receptive field Pref target Dots Aperture Null target + microstimulation in MT Fixation 10 deg Point Fix Pt Dots Elect Stim Targets 1 sec
Proportion of choices of the preferred direction Coherence (%) Salzman, Murasugi, Britten and Newsome, 1992
Number of cases Equivalent visual coherence Salzman, Murasugi, Britten and Newsome, 1992
Visual stimulus Neurometric function Psychometric function Neuronal Behavioral response judgement Choice probability Microstimulation
Decoding MT neurons for visual motion discrimination up X 1 up X 2 up X Pooled MT Signal 3 up 〈 X 〉 ● ● ● up X N Decision up > down 〈 X 〉 〈 X 〉 down X 1 down X 2 down X Pooled MT Signal 3 down 〈 X 〉 ● ● ● Britten, Newsome, Shadlen, Celebrini & Movshon, 1996 down Shadlen, Britten, Newsome & Movshon, 1996 X N Cohen & Newsome, 2009
Decoding MT neurons for visual motion discrimination up X 1 up X 2 up X Pooled MT Signal 3 up 〈 X 〉 ● ● ● up X N Decision up > down 〈 X 〉 〈 X 〉 down X 1 down X 2 down X Pooled MT Signal 3 down 〈 X 〉 ● ● ● Shadlen, Britten, Newsome & Movshon, 1996 down X Cohen & Newsome, 2009 N
Decoding MT neurons for visual motion discrimination Interneuronal correlation 0.5 0.0 up X 1 up X 2 0 90 180 up X Pooled MT Signal Difference in preferred direction (deg) 3 up 〈 X 〉 ● Zohary, Shadlen & Newsome, 1994 ● ● up X N Decision up > down 〈 X 〉 〈 X 〉 down X 1 down X 2 down X Pooled MT Signal 3 down 〈 X 〉 ● ● ● Shadlen, Britten, Newsome & Movshon, 1996 down X Cohen & Newsome, 2009 N
Where is sensory activity converted into decision and actions? Frontal eye field (FEF) Lateral intra-parietal area (LIP) V2d 7a 7b V4 V1 V2v MT/MST
LIP receives projections from MT and projects to areas that are known to contribute to the generation of saccadic eye movements
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A ● ● Target 1 Target 2 ✙ FP B + recording in LIP Fixate 350 msec ✙ ● ● Targets appear 500 msec Target 1 Target 2 ✙ ● ● Random dot motion 2 sec ✙ ● ● Delay 500-1000 msec ✙ ● ● Saccade task_panels_vert_noMF.isl Shadlen and Newsome, 2001
N=106 motion onset saccade 50 50 45 45 51.2% 25.6% 40 40 Mean response (sp/s) 12.8% 6.4% 0% 35 35 30 30 25 25 20 20 15 15 10 10 �-0.5 0 0.5 1 �-0.5 0 0.5 Time (s) Mike Shadlen
Responses in a reaction-time version of the direction discrimination task Mike Shadlen
Bounded accumulation of evidence MT – sensory evidence LIP – decision formation Motion energy “step” Accumulation of evidence “ramp” High motion strength High motion strength Spikes/s Spikes/s Low motion strength Threshold Low motion strength Time Time Stimulus on Stimulus off Stimulus on Stimulus off ~1 sec ~1 sec Mike Shadlen
Diffusion to bound model Criterion to answer “Right” Accumulated evidence for Rightward Momentary evidence and e .g., against Leftward ∆ Spike rate: µ = kC MT Right – MT Left Criterion to answer “Left” C is motion strength (coherence) Palmer et al (2005) Shadlen et al (2006)
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