SlipSet1 Specs

Programmer: Grant

This is fairly simple, with only one factor (Trial Condition = Weird or Normal) that is established by random independent drawing as described below.

Basic Task: This is a Choice RT task with 4 possible stimuli and 2 possible button-push responses. On each trial, subjects see a fixation point for 500 msec. Then a square appears. The square is one of four colors (Red, Green, Blue, or Yellow -- selected randomly and independently on each trial). The square and the fixation point remain present until response. The subject’s task is to press a button depending on the color of the square. We are interested in both reaction time and errors.

When the subject responds, the square and the fixation point disappear and there is a blank screen shown for 2000 msec. If the subject made an error, the first portion of this time is filled with a windows error sound. Try to time it so that whether or not there was an error sound played, the time between the response and the fixation point for the next trial is still always 2000 msec.

Note: Be sure you are always clearing the response buffer before you present the fixation point, so that if subjects respond several times, it doesn’t count a zero RT on the next trial. Try hitting keys multiple times and make sure the program behaves appropriately (discarding all but the first hit!).

Task Mapping: Red, Green -> N key; Blue, Yellow -> M key.

Small twist: the squares are always either slightly to the left of fixation or slightly to the right. With probability p=.90, red and green are to the left, and blue and yellow are to the right. These are the Normal Trials. The other 10% of trials are Weird, in the sense that a red or green stimulus is to the right, or a blue or yellow stimulus is to the left.

Rough Sample Display:

How you should implement this:

On each trial execute this sequence:

1. randomly select the color independently and without constraint (25% chance of choosing each color).

2. select a random variable p’ from a uniform distribution in the range (0,1).

3. if color=red or green do begin:

if p’>0.9 Trial Condition = Weird and Location = Right;

Else Trial Condition = Normal and Location = Left.

End;

4. if color= blue or yellow do begin:

if p’>0.9 Trial Condition = Weird and Location = Left;

Else Trial Condition = Normal and Location = Right.

End;

Blocks and Trials

On first page collect subject ID# and the usual (there is no subject condition in this study). Also remind the experimenter of what colors are mapped onto what keys.

There should be 8 blocks each composed of 120 trials per block.

At the end of each block, put up a message saying “Rest Period – Click to Resume” and then continue when they mouse click take away that message and insert a 3 second pause before the first plus sign appears to give them time to put their fingers on the response keys. During the rest period show them their mean RT and number of errors for that block and each of the preceding blocks.

Instructions for subject:

Thank you for participating in our experiment. This experiment is composed of repeated “trials”, in which a stimulus is presented and you make a response. On every trial, a plus sign appears to mark the beginning of the trial. Please look directly at the plus sign.

Shortly after the plus sign appears, a colored square will appear. The colored square is what you will respond to. Your task is simply to press one button if the square is red or green; or the other button if the square is blue or yellow. The two buttons are labeled. That is your whole job here today!

Note that the square may be located left or right of the plus sign, but its position is irrelevant to your task! You should always respond based on color, not location. We are interested in your speed and accuracy. Try to respond as quickly and accurately as you can. The computer will beep at you every time you make an error.

We will have you do 10 blocks of trials, each lasting just a few minutes. During each block, please keep the index and middle fingers of your right hand rested on the response keys. Between blocks there will be a pause for you to rest, and the computer will tell you your average response time and number of responses. Thanks again for participating, and we hope you find this task fairly interesting.

File Structure

In the R-file save the

<subject_ID#, block number, trial number, color of the square (R,G,Y or B), position of the square (L or R), Trial Condition (“Weird” or “Common”); Response Time, Identity of Response>