Kalsbeek100
Specs
Tasks
1. Letter -> Button choice reaction time
Stimuli = A, B, or C
Responses = n, m, , keys, respectively (adjacent keys on keyboard)
2. Responding vocally to verbal queries presented by
Overall Sequence of Events
1. Present Instruction #1. Do 3 blocks of practice, each consisting of 60 trials. On each trial, present one letter, which stays up until subject responds. Response-Stimulus Interval = 800 msec. Feedback = 500 msec windows error tone (making total response-stimulus interval = 1300); no sound for correct response. Pause between blocks saying “press any key to resume”.
2. Compute mean RT in Block 3 only. Denote that as X. We regard this as the subject’s maximum rate of performing the task.
3. Present Instruction #2. Give 2 more practice blocks but here the stimuli are paced by the computer and presented once every X msec. Stimuli stay up for 300 msec. The subject attempts to respond before the next stimulus is presented. No feedback during this period.
4. Present Instruction #3.
5. Now we present 6 more blocks of stimuli presented at a fixed pace, staying up for 300 msec with no feedback. But here the stimuli are presented at several different rates (1 stimulus per X msec; 1 stimulus per 2*X msec; 1 stimulus per 5*X msec) and sometimes the subject must also perform a verbal task. The conditions are designated as follows (the number 100, 50, or 20 refers to “percent of maximum rate”; S means single-task; D means dual-task). The number of stimuli is varied so as to keep the total time constant.
Cond
Stim Rate
Verbal
Task
Number of Stimuli
100S 1/X No 60
50S 1/(2X) No 30
20S 1/(5X) No 10
100D 1/X Yes 60
50D 1/(2X) Yes 30
20D 1/(5X) Yes 10
Randomize the order in which these 6 conditions are presented. The three verbal tasks are always given in the same order.
Instruction 1
Welcome to the experiment. We think you will find today’s experiment rather interesting. We are looking at people’s ability to perform two tasks at the same time. One task involves pressing buttons in response to letters; the other task involves speaking aloud about some topic.
In the first phase of this experiment, we would like you to practice performing a task in which you see letters and respond by pressing a button. On the screen in front of you a letter will appear. The letter will be an A, a B, or a C. If it is an A, you should press the key labeled A; if it is a B, you should press the key labeled B; if it is a C, you should press the key labeled C.
While you are performing the experiment, please keep the first three fingers of your dominant hand rested on these keys. Please try to respond as rapidly and accurately as possible. If you make a mistake, the computer will beep at you.
If you have any questions, please ask the experimenter. Otherwise, we can begin now. We will do three “blocks” of trials, each lasting just about a minute or so.
Instruction 2
In the next phase of this experiment, you will be perform the same task, but here there will be a new challenge here. In the first phase, the computer waited until after you responded to one letter before presenting the next letter. Now the computer is not going to wait for you. It will present the letters at a fast rate based on its own timekeeping. Your task is to keep up with this rate. Please try your best to respond accurately to each letter before the next letter appears. If you are a bit slow and cannot respond until after the next letter has appeared, you should still go ahead and make that response, but please try your best to not let that happen if you can help it.
We will do three more blocks of trials. Again, please keep your fingers rested on the response keys throughout each block.
Instruction 3
In the next phase of this experiment, we will be asking you to do the same letter task you have been doing. Sometimes the letters will appear fast, as in the previous blocks; sometimes they will appear more slowly. On some blocks, we will also ask you to perform another, more mentally demanding task at the same time. The computer will ask you to talk for thirty seconds about some topic (for example, the most recent movie you may have seen). The computer will play a voice message telling you what to talk about. The voice message will play before the letters start appearing. You don’t need to say anything elaborate or fancy in response to these questions; just try to talk for about 30 seconds on the topic.
When you have started talking about something and the letters appear, please try to keep talking and please try to respond to each letter before the next letter appears.
We will do six blocks of trials. The computer will tell you the pace at which the Again, please keep your fingers rested on the response keys throughout each block.
Verbal Tasks.
1. What town did you grow up in and what was it like?
2. Where did you go on the last vacation you took and what was it like?
3. Do you like living in San Diego -- and why?
Note on randomization. You just want to independently randomize the set
(100S, 50S, 20S, 100D, 50D, 20D)
Suppose you randomize it and you pick the order
(20D, 100S, 50S, 50D, 20S, 100D). In that case the final six blocks are like this:
1. 20D (“town”)
2. 100S
3. 50S
4. 50D (“vacation”)
5. 20S
6. 100D (“San Diego”)
So you just assign the verbal tasks in the fixed order to the conditions that have a D in them whatever they may be based on the randomization.
Data Storage
Create an R-file which contains the following:
1. For blocks 1 – 3 (initial practice), the stim presented, the response, the RT, whether it was correct or incorrect.
2. Save the value of X for that subject explicitly.
3. For the remaining blocks, which involve experimenter-paced stimuli, we cannot just save RTs and correctness information, since the subject may not respond until after the next stimulus. Better to save a complete undigested timeline of what events occurred and when in the format <Time since beginning of trial, event that occurred at that time> so part of the file might look like this.
…
14230 Present B
14250 Response=n
14340 Response=m
…
Naturally, millisecond clock should be zeroed out at the start of each block.