function [loglik] = model_VFA_4states_v3(parameters, subj)
num_state = 4;
num_action = 2;
nd_alpha = parameters(1); % normally-distributed alpha
alpha = 1/(1+exp(-nd_alpha)); % alpha (transformed to be between zero and one)
nd_beta = parameters(2);
beta = exp(nd_beta);
% Initialize weights for linear function approximation
theta = zeros(num_state * num_action, 1);
% unpack data
actions = subj.actions + 1; % adding 1 such that actions are {1, 2}
outcome = subj.Outcome;
color = subj.Color;
orientation = subj.Orientation;
mouth_dir = subj.Mouth_dir;
% counter over all trials
ctr = 1;
% calculating numTrails
U = unique(subj.block());
numTrails = zeros(1, length(U));
for i = 1:length(U)
ind = find(subj.block() == U(i));
numTrails(i) = length(ind);
end
% to save probability of choice. Currently NaNs, will be filled below
p = nan(1, sum(numTrails));
for t1 = 1:length(numTrails)
% number of trials
T = numTrails(t1);
for t = 1:T
% determine state
state = subj.States4(ctr) + 1; % Ensure state is within bounds
action = actions(ctr);
% Ensure state is within bounds
if state > num_state || state < 1
error('State index out of bounds: %d', state);
end
% Feature vector
phi = zeros(num_state * num_action, 1);
phi((state - 1) * num_action + action) = 1;
% Q-value estimate for both actions
Q = zeros(1, num_action);
for a = 1:num_action
phi_a = zeros(num_state * num_action, 1);
phi_a((state - 1) * num_action + a) = 1;
Q(a) = theta' * phi_a;
end
% probability of action 1
p1 = 1 / (1 + exp(-beta * (Q(1) - Q(2))));
% probability of action 2
p2 = 1 - p1;
% read info for the current trial
a = actions(ctr); % action on this trial
o = outcome(ctr); % outcome on this trial
% store probability of the chosen action
if a == 1
p(ctr) = p1;
elseif a == 2
p(ctr) = p2;
end
% Value function approximation update using gradient descent
delta = o - Q(action); % prediction error
theta = theta + alpha * delta * phi;
ctr = ctr + 1;
end
end
% log-likelihood is defined as the sum of log-probability of choice data
% (given the parameters).
loglik = sum(log(p + eps));
% Note that eps is a very small number in Matlab (type eps in the command
% window to see how small it is), which does not have any effect in practice,
% but it overcomes the problem of underflow when p is very very small
% (effectively 0).
end
function [loglik] = model_VFA_4states_v3(parameters, subj)
num_state = 4; num_action = 2;
nd_alpha = parameters(1); % normally-distributed alpha alpha = 1/(1+exp(-nd_alpha)); % alpha (transformed to be between zero and one)
nd_beta = parameters(2); beta = exp(nd_beta);
% Initialize weights for linear function approximation theta = zeros(num_state * num_action, 1);
% unpack data actions = subj.actions + 1; % adding 1 such that actions are {1, 2} outcome = subj.Outcome; color = subj.Color; orientation = subj.Orientation; mouth_dir = subj.Mouth_dir;
% counter over all trials ctr = 1;
% calculating numTrails U = unique(subj.block()); numTrails = zeros(1, length(U)); for i = 1:length(U) ind = find(subj.block() == U(i)); numTrails(i) = length(ind); end
% to save probability of choice. Currently NaNs, will be filled below p = nan(1, sum(numTrails));
for t1 = 1:length(numTrails) % number of trials T = numTrails(t1);
end
% log-likelihood is defined as the sum of log-probability of choice data % (given the parameters). loglik = sum(log(p + eps)); % Note that eps is a very small number in Matlab (type eps in the command % window to see how small it is), which does not have any effect in practice, % but it overcomes the problem of underflow when p is very very small % (effectively 0). end