TD1 Specs
Overview
Subjects see objects and make 2-alternative choices. Sometimes they are rewarded. We keep track of their choices, and how long they take to choose. Each object represents a state that the subject is in. A markov model describes the states and their transitions. Subjects are randomly assigned to one of two conditions determining how long they have to make each choice (1 second or 4 seconds).
Markov Model
All subjects are navigating the same Markov model. They always make 300 choices. The model has 6 states. Each state is associated with a different picture of an object (e.g., fork, tree, etc.). In each state, the subject makes one of 2 responses (pressing the left Z key or the right . key). Subjects start in State 1. The state+choice determines (1) which state the subject goes into next, and (2) a reward, as follows:
State Response
1 2
1 2 6
2 3 6
3 4 6
4 5 6
5 6 6
6 1 6
Reward
State Response
1 2
1 -2 2
2 -2 2
3 -2 2
4 -2 2
5 +25 2
6 1 1
You will have six jpeg images of objects. These should be randomly assigned to the six states (separate randomization for each subject). The assignment of objects to states should be saved.
While the program is being tested, simply display the state “State 1”, etc.
Instructions
[expand to
3 screens]
In this experiment, you will play a
sort of “game”, giving you the opportunity to win a small amount of real money
(you will be paid at the end). You will
always make one of two responses -- pressing the left key or pressing the right
key. These keys have little stickers
labeled “L” and “R”. Before you respond,
you will see a line drawing of an object.
You can think of each picture as telling you what “location” you are
in. There are six locations, each
corresponding to a different picture (cat, balloon, apple, etc.)
Make whatever choice you want. When you make a response, the screen will
turn a bluish color, and you will get a positive or negative reward. The computer will tell you how much you won
(or lost). Then it will “move” you into
the next state.
[page
break.]
As mentioned above, you should think
of each picture as tell you where you are in an imaginary world. Where you are, and what response you make,
completely determines two things: (1) your reward (or loss) and (2) what state
you go into next. Luck or chance plays
no role in this game. What happens next
depends on where you are and what response you make.
The computer always displays your
total winnings in the bottom right-hand corner of the bluish screen. If at the end of the game you are below zero,
you won’t have to pay us any money. If
you are above zero, we will pay you whatever you have won.
[page
break]
Speed matters here. You will have 1 second [4 seconds] to
respond. [if it
is 1 second display this sentence: 1 second is not a lot of time, so this means
you have to respond based on your immediate hunch.] If you don’t respond within the allotted
time, the machine will warn you to respond more quickly. You will make 300
responses during the experiment.
Furthermore, the time between responses is fixed. Therefore, if you respond more quickly than
you need to, this will not give you a chance to earn more money, nor will it
mean that the experiment finishes up any sooner. Therefore, we suggest that you take
approximately the designated amount of time (1 second [4 seconds]) to respond.
Sequence
Subject sees picture (as determined by state). Accept only one of the two designated
responses. When
they respond, the screen should slightly change color, becoming bluish (with
the picture still present). [delete the visual
indication of winnings, because it is going to make the subject look away from
the center of the screen, and fail to clearly see the next picture. Also get rid of the casino sounds, because
they aren’t that compelling or fun after all.
Instead, please have Kitu make wave files in
which she says “You win two cents”, “You lose two cents”, “You win twenty-five
cents”, etc. The tapes should be less
than 3 seconds long.] Play the
appropriate wavefile. The Reward Screen
should remain present for 3 seconds.
At the bottom of the Reward Screen, you should show the subject their
total purse. Label that e.g., “Total winnings: $.47”
If the subject does not respond within the allocated time, go to a Warning Screen that says “Warning: You did not respond in the allotted time. Please respond more quickly in future.” This screen should stay up for 8 seconds (the delay will help deter the subject from being slow).
Before going to the next state,
insert a 500 second blank screen. The
new screen should of course not be bluish anymore.
When the subject *does* respond in time, you should still impose an artificial delay on the time the next trial begins. That is, if they are supposed to respond in 4 seconds, but they respond in 2.2 seconds, then you should add 1.8 seconds to the presentation time of the Reward Screen (making it 4.8 seconds long).
Storage of Data
Save:
1. one row per trial (1-300), with the following in each row:
a. trial#
b. state # they were in
c. object displayed
d. choice
e. reward
f. reaction time for choice
g. how long they were supposed to take (1000 or 4000)