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Basic Task Description

This task was designed by Ty Cannon and David Glahn as a verbal analogue to the SCAP (spatial capacity task). It has been run in a number of local samples, including Aftercare (first episode), ABBRC (adolescent psychosis), CAPPS (prodromal), and NF1 (neurofibromatosis).

This task manipulates verbal working memory load using arrays of letters. The loads (3, 5, 7, 9) are selected to be behaviorally analogous to the CNP_SCAP loads.

Task Procedure

This task manipulates working memory load. The loads were selected to be of parallel difficulty, in terms of performance, to the loads in the CNP_SCAP.

Basic Task Info Loads: 3, 5, 7 or 9 lowercase letters

Trial layout:
1. fixation for 1 second
2. target array (multiple uppercase letters) for 2 seconds
3. delay period (fixation) for 3 seconds
4. probe array (single lowercase letter) for 3 seconds.

First, subjects undergo an instruction and training period (4 trials), then the task begins and the subject performs 48 trials (12 trials per load, randomly selected).

Sample Text
We employed a modified Sternberg item recognition task (Sternberg, 1966 S. Sternberg, High-speed scanning in human memory, Science 153 (1966), pp. 652–654). A target set of 3, 5, 7, or 9 yellow uppercase consonants was displayed for 2 s, followed by a 3-s fixation. A green uppercase probe then appeared for 3 s, followed by 1 s of fixation before the next trial. Subjects indicated whether the probe matched the target set. The task included 12 trials per load, which were clustered by load into two-trial long blocks; presentation order of the blocks was counterbalanced, but remained the same for all subjects.
Karlsgodt, 2007

Task Structure Detail

  • Menu
  • A series of menus appear asking for subject ID, session number, and group number (1 = right handed, 2 = left handed).
  • Training Phase
  • Instruction slide 1:
This is a short term memory test. You will be shown some yellow uppercase letters. After a few seconds, these yellow letters will disappear and a lowercase green letter will appear. Your job is to say whether the green letter is the same as any one of the yellow letters. Don't worry about whether it is upper or lowercase, just whether the letters are the same. Please respond as quickly as possible while giving the correct answer.
Press the LEFT key if the green letter is the same as any one of the yellow letters.
Press the RIGHT key if you think the green letter is not the same as one of the yellow letters.
(note: hand requirements varied based on subject group)
  • Instruction slide 2:
You will be shown either 3, 5, 7, or 9 letters.
For example, you might see one of the following:
  • Instruction slide 3:
(shows correct and incorrect trial examples)
  • Practice Trials- 4 trials, one at each load, randomly selected
ITI blank- 1500ms
ITI fixation- 500ms
Target- 2000ms
Delay- 3000ms
Probe- 3000ms
  • Reminder Instructions slide:
You have just completed the Practice section. You will now begin the Test.
You will see sets of either 3, 5, 7, or 9 uppercase yellow letters. They will go away, and a few seconds later a lowercase green letter will appear. You will not receive feedback during the test.
Press the LEFT key if the green letter is the same as one of yellow letters.
Press the RIGHT key if the green letter is NOT the same as one of the yellow letters.
Please ask the experimenter to start the TEST when you are ready.
  • Testing Phase
  • ITI blank- 1500ms
  • ITI fixation- 500ms
  • Target- 2000ms
  • Delay- 3000ms
  • Probe 3000ms (advances with response)

Task Schematic

Vcap bigschematic.jpg

Task Parameters Table


Dependent Variables

Vcap variables.jpg
Vcap calc variables.jpg

Cleaning Rules

1. If any of the calculated variables are missing, that subject should be listed for exclusion.
2. If Trial Count is not =48, then that subject should be listed for exclusion.
3. If overall performance (average percent correct) is below 50% (chance, in this task), that subject should be listed for exclusion.
4. It is possible for a subject to have one or more capacities be a negative number (VCAP_CAPACITY3, VCAP_CAPACITY5, VCAP_CAPACITY7, VCAP_CAPACITY9), which usually results from too few true positives in a condition. However, no capacity should be greater than the associated load (i.e., no one can have >capacity=5 on load 5). And, if the average capacity is negative (VCAP_MAX_CAPAC), that subject should be listed for exclusion. However, it is highly unlikely, if not impossible, to achieve this without being already excluded in rule #2.
5. If average RT is greater than 6000ms that subject should be listed for exclusion.

It is worth considering dropping people who have a capacity lower than the lowest load (for instance on SCAP, a capacity of less than 1) but that is up to user discretion.

If you want to know if your group looks approximately like it should, in every sample run so far, accuracy decreases by load, and reaction time increases. This should be the first group level analysis, to quickly verify everything is correct. It would be highly unexpected to have a deviation from this pattern, even though the position along the y axis (overall accuracy or RT) may vary, especially in patient groups.

Note that the scoring code for VCAP_AVE_CORR was previously incorrect; fixed by Stone in July 2012.


Capacity is calculated according to the formula by Cowan: k=n*(H+CR−1), where k=capacity, n=load, H = hits (out of those responded to), CR= correct rejections (out of those responded to).

3*(vcap_corr_hit3 + (1 - vcap_corr_fa3) - 1)
5*(vcap_corr_hit5 + (1 - vcap_corr_fa5) - 1)
7*(vcap_corr_hit7 + (1 - vcap_corr_fa7) - 1)
9*(vcap_corr_hit9 + (1 - vcap_corr_fa9) - 1)

Capacity measurements may look unusual if there are an unusually high number of false alarms, which means that occasionally loads much higher than an individuals capacity can yield very low or negative numbers. Therefore, select the maximum capacity calculated out of all of the loads to represent that subject's k. (Karlsgodt, 2009, Schizophrenia Research). Furthermore, it is possible to perform functional imaging analyses by selecting the data from the load closest to that individual's capacity.

Data Distributions

Vcap all data tables.jpg

Vcap all useable tables.jpg

Vcap comp useable tables.jpg

Vcap comp useable outlier tables.jpg

Vcap percorr.jpg

Vcap rt.jpg

Vcap capac.jpg


Karlsgodt, 2009, Schizophrenia Research
Sanz, 2009, Psychiatry Research
Karlsgodt, 2008, Biological Psychiatry