# CNP SCAP

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## Contents

### Basic Task Description

The goal of this task is to probe behavior across different levels (loads) of a spatial working memory capacity task. There is evidence that spatial working memory is impaired in schizophrenia, and the deficit may be a core feature of the disease. From our previous schizophrenia twin studies we have evidence that the spatial working memory deficit (as assessed by a version of this task) may be heritable (Glahn et al, 2003). There is further evidence that performance on this task may differentiate between bipolar patients with and without a history of psychosis (Glahn, 2006).

The Cannon lab has a great deal of experience with this task, and it has been administered in a very wide variety of populations at a number of sites. We have administered it to adolescents with schizophrenia, prodromal subjects, aging Finnish twins with and without schizophrenia, chronic schizophrenia patients, bipolar patients, patients with neurofibromatosis-1, and healthy controls. The version that we have administered most frequently is the one used in the LA2K, a block design task with 4 memory loads (1,3,5 and 7 locations).

### 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_VCAP. This task differs in structure from the LA5C SCAP task design used in the scanner- that version varies delay in addition to load.

**Basic Task Info**
Loads: 1, 3, 5 or 7 dots

Trial layout:

1. Fixation for 1sec

2. Target array for 2 sec

3. Delay period for 3 sec

4. Probe array (single dot) 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**

During the spatial delayed response task (SDRT), participants were shown a target array of 1, 3, 5 or 7 yellow circles positioned pseudorandomly around a central fixation. After a fixed delay, subjects were shown a single green circle and were required to indicate whether or not that circle was in the same position as one of the target circles. A relatively long stimulus presentation of two seconds was used to allow subjects to fully encode the target array, minimizing a potential encoding on the basis of set size interaction. Likewise, decision or selection requirements were kept constant across set sizes to reduce possible effects of set size on response processes. Trial events included a one second fixation to orient attention, 2-sec target-array presentation, a 3-sec delay period, and a 3-sec fixed response interval during which the subject responded via keyboard presses. A central fixation was visible throughout each of the 48 trials (12 per memory set size). Before starting the scored trials, subjects underwent a supervised instruction and training period (4 trials).

Glahn, 2003

### 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:

- "Place your hand on the table with your fingers extended and resting comfortably on the LEFT and RIGHT keys.

- This is a short term memory test. You will be shown some yellow dots. After a few seconds, these dots will disappear and a green dot will appear. Your job is to say whether the green dot is in the same place as one of the yellow dots. Please respond as quickly as possible while giving the correct answer.

- Press the LEFT key if you think the green dot is in the SAME place as one of the yellow dots.

- Press the RIGHT key if you think the green dot is NOT in the same place as one of the yellow dots."

- Instruction slide 2:

- You will be shown either 1,3,5 or 7 yellow dots around a fixation cross.
- (gives a visual example of dot arrays for different loads.)

- Instruction slide 3:

- "If the green dot is in the same position as one of the yellow dots press the LEFT key. If the green dot is not in exactly the same position as one of the yellow dots, press the RIGHT key." (note that handedness of responses varies with group, such that each group responds "yes" with their dominant hand"

- (gives examples of correct and incorrect arrays)

- Practice Trials- 4 trials, one at each load, randomly selected

- ITI blank- 500ms
- ITI fixation- 500ms
- Target array- 2000ms
- Delay (fixation)- 3000ms
- Probe- infinite duration, until keypress advances to next slide
- Feedback slide- 1000ms

- Reminder Instructions slide:

- Now you will start the test, remember:

- Press LEFT key if you think the green dot is in the same location as one of the yellow dots.

- Press RIGHT key if you think the green dot is NOT in the same location as one of the yellow dots.

- Please ask the experimenter to start the TEST when you are ready.

**Testing Phase**

- ITI blank- 500ms
- ITI fixation- 500ms
- Target array- 2000ms
- Delay (fixation)- 3000ms
- Probe- infinite duration, until keypress

### Task Schematic

### Task Parameters Table

### Stimuli

### Dependent Variables

The primary variables of interest are mean correct at each load, mean reaction time at each load, and overall working memory capacity.

### 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 (SCAP_CAPACITY1, SCAP_CAPACITY3, SCAP_CAPACITY5, SCAP_CAPACITY7), 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 (SCAP_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 SCAP_AVE_CORR was previously incorrect; fixed by Stone in July 2012.

### Code/Algorithms

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).

1*(scap_corr_hit1 + (1 - scap_corr_fa1) - 1)

3*(scap_corr_hit3 + (1 - scap_corr_fa3) - 1)

5*(scap_corr_hit5 + (1 - scap_corr_fa5) - 1)

7*(scap_corr_hit7 + (1 - scap_corr_fa7) - 1)

The code for generating the summary statistics viewed on this page was written in Stata, as follows:

//ALL SUBJECTS

//get breakdown of numbers in each group:

bysort status: summarize ptid

bysort la5ccontrol: summarize ptid

bysort gender: summarize ptid

//see how many complete cases there are.

count if scap_max_capac !=.

//exclusions

generate float scap_percent_corr= (scap1_correct_sum+ scap3_correct_sum+ scap5_correct_sum+ scap7_correct_sum)/48

count if scap_percent_corr <=.5

count if scap_trial_count < 48

count if scap_max_capac < 1

count if scap_average_corr > 6000 & scap_average_corr !=.

//create variable summing exclusion criteria

generate float useable_scap= 1 if scap_trial_count ==48 & scap_percent_corr>.5 & scap_max_capac>0 & scap_average_corr < 6000

count if useable_scap==1

//SUBJECTS WITH USEABLE DATA

bysort status: summarize ptid if useable_scap==1

bysort la5ccontrol: summarize ptid if useable_scap==1

bysort gender: summarize ptid if useable_scap==1

summarize age scap_percent_corr scap_average_corr scap_max_capac if useable_scap==1

bysort status: summarize scap_max_capac if useable_scap==1

bysort la5ccontrol: summarize scap_max_capac if useable_scap==1

bysort gender: summarize scap_max_capac if useable_scap==1

//COMPLETERS WITH USEABLE DATA

generate float comp_useable_scap= 1 if status==2 & scap_trial_count ==48 & scap_percent_corr>.5 & scap_max_capac>0 & scap_average_corr < 6000

count if comp_useable_scap==1

bysort status: summarize ptid if comp_useable_scap==1

bysort la5ccontrol: summarize ptid if comp_useable_scap==1

bysort gender: summarize ptid if comp_useable_scap==1

summarize age scap_percent_corr scap_average_corr scap_max_capac if comp_useable_scap==1

bysort status: summarize scap_max_capac if comp_useable_scap==1

bysort la5ccontrol: summarize scap_max_capac if comp_useable_scap==1

bysort gender: summarize scap_max_capac if comp_useable_scap==1

//OUTLIERS

sktest scap_max_capac scap_average_corr scap_percent_corr

histogram scap_average_corr if comp_useable_scap==1, title(Average Reaction Time) xtitle(Average Reaction Time) scheme(s2mono)

histogram scap_percent_corr if comp_useable_scap==1, title(Average Percent Correct) xtitle(Percent Correct (0-1 x 100)) scheme(s2mono)

histogram scap_max_capac if comp_useable_scap==1, title(Maximum Capacity) xtitle(Percent Correct (0-1 x 100)) scheme(s2mono)

grubbs scap_max_capac if comp_useable_scap==1, gen (grubb_scap_capac)

grubbs scap_average_corr if comp_useable_scap==1, gen(grubb_scap_rt)

grubbs scap_percent_corr if comp_useable_scap==1, gen(grubb_scap_percorr)

generate float comp_useable_nooutlier_scap=1 if comp_useable_scap==1 & grubb_scap_capac !=1 & grubb_scap_rt !=1 & grubb_scap_percorr !=1

count if comp_useable_nooutlier_scap==1

bysort status: summarize ptid if comp_useable_nooutlier_scap==1

bysort la5ccontrol: summarize ptid if comp_useable_nooutlier_scap==1

bysort gender: summarize ptid if comp_useable_nooutlier_scap==1

summarize age scap_percent_corr scap_average_corr scap_max_capac if comp_useable_nooutlier_scap==1

bysort status: summarize scap_max_capac if comp_useable_nooutlier_scap==1

bysort la5ccontrol: summarize scap_max_capac if comp_useable_nooutlier_scap==1

bysort gender: summarize scap_max_capac if comp_useable_nooutlier_scap==1

histogram scap_percent_corr if comp_useable_scap==1, frequency bfcolor(gs11) blcolor(black) normal normopts( clcolor(black) ) xtitle(Percent Correct (<61 = outlier))

histogram scap_average_corr if comp_useable_scap==1, frequency bfcolor(gs11) blcolor(black) normal normopts( clcolor(black) ) xtitle(Mean Response Time (>2000ms = outlier

histogram scap_max_capac if comp_useable_scap==1, frequency bfcolor(gs11) blcolor(black) normal normopts( clcolor(black) ) xtitle(Maximum Capacity)

### Data Distributions

### References

Cannon et al, 2005, Archives of General Psychiatry

Glahn et al, 2003, Biological Psychiatry

Glahn et al, 2002, Neuroimage

Glahn et al, 2006, Bipolar Disorders

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