AX-CPT Task

 

BACKGROUND

AS RELATED TO DMC FRAMEWORK

DESCRIPTION OF AXCPT TASK SCRIPTS AVAILABLE FOR DISTRIBUTION

RELEVANT BEHAVIORAL MEASURES TO COMPUTE

 


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AX-CPT BACKGROUND
The AX-CPT task is frequently used as a cognitive control task to examine context processing and goal maintenance.  Because it is somewhat simple to perform, it has frequently been used in clinical and developmental populations.  The most common variant uses LETTER stimuli; however, other variants have also been commonly used (such as the Dot-Probe or DPX).   The key variable in the task is the CONTEXTUAL CUE, which interacts with target response biases produced by frequency manipulations involving target trials, and three nontarget trial types. Following the A-cue context, there is a high expectancy that the trial will require an AX target response.   In turn, this target expectancy produces interference when it is not valid, as occurs on AY nontarget trials (where Y refers to any non-X probe).  In contrast, activation and maintenance of the B-cue context (which can be any non-A letter), is critical to overcome the target response bias generated by the X-probe letter on BX nontarget trials.  Finally, BY nontarget trials provide as an internal baseline measure of general performance ability.  


 

AX-CPT as related to dmc framework

In the DMC framework, the primary assumption is that PROACTIVE control will be associated with a strong contextual cue-based expectancy, particularly when the A-cue is presented.    Prior research has shown that these cue-based expectancies can be enhanced through STRATEGY TRAINING procedures (Paxton et al, 2006; Braver et al, 2009; Edwards et al, 2010).  These procedures emphasize the differential expectancies associated with each cue-type and encourage the engagement of response preparation processes during the CUE-PROBE DELAY INTERVAL.

 

 

However, even without strategy training, proactive control biases are typically found in healthy young adults.   In order to minimize such biases in the BASELINE condition, we are using a new variant that includes NO-GO trials.  The addition of no-go trials reduces the predictive validity of the contextual cue, since the no-go status of the trial can only be detected at probe onset.   Our recent findings confirm that younger adults exhibit reduced proactive control in the no-go baseline condition, but that strategy training can reverse this pattern (even in the no-go variant; Gonthier et al, under review). 

 

In the DMC framework, a REACTIVE control strategy in the AX-CPT involves utilization of probe identification and conflict to facilitate context retrieval and selection of the appropriate response.  To enhance reactive control, we have developed another variant in which that includes LOCATION-COLOR PROBE-CUEING.   In this variant, probe stimuli on low conflict trial types (AX, BY) are presented in one spatial location and border color, while high-conflict trial types (AY, BX, no-go) are presented in a distinct spatial location and border color.   The key logic behind this manipulation is that location-color cueing does not uniquely identify the probe stimulus or response, but it does indicate the high vs. low conflict status of the trial. Thus, it should facilitate conflict-triggered contextual retrieval; but since the cueing manipulation occurs at probe onset rather than at the time of cue, it should encourage a reactive rather than proactive task strategy.  

 


DESCRIPTION OF AX-CPT TASK SCRIPTS AVAILABLE FOR DISTRIBUTION

Below is relevant information regarding the available task-variants and conditions, in terms of the relevant procedures and parameters.  Click here for background information about the task and associated measures.   Click here for more information about DMC-specific task variants and measures.

 

BEHAVIORAL TASK SCRIPTS

fMRI TASK SCRIPT 

 

 

 

 

 

Gonthier et al, 2016 tasks
If you are interested in using the condition variants implemented in Gonthier et al (in press 2016), please see that paper for details on all methods information. Eprime task scripts and raw data are available on OSF here.

 

Behavioral AXCPT task
This version includes baseline, proactive, and reactive conditions of the AX-CPT, coded for Eprime.  This version uses letters as stimuli, and manual responding made through a button-box. Click here if you would like access to these task scripts (and associated stimulus lists).

 

Behavioral AXCPT Baseline
This condition implements the letter AX-CPT with no-go stimuli included.  There are 4 different standard (go) trial types: AX, AY, BX, and BY.   The proportions of trial types are set to ensure equal frequencies of A-cue and B-cue trials.   The relative proportions of these trials match that used in Richmond et al (2015):  40% AX, 10% AY, 10% BX, 40% BY.   No-go stimuli occur with low frequency (16.7%) are indicated by digit (1-9) rather than letter probes (and equally follow A-cue and B-cue contexts).  Participants are instructed to withhold responding on these trials.    Presentation time of cues and probes is 500 msec.   Probes are accompanied by a white rectangular border, presented 250 msec prior to probe onset.  The cue-probe delay interval is 4 seconds, placing demand on goal (context) maintenance processes.  The full condition includes 216 trials (72 AX, 18 AY, 18 BX, 72 BY, 18 A-nogo, 18 B-nogo). 

 

Behavioral AXCPT Proactive
This condition is identical in almost all respects to the Baseline condition.  The primary difference is that participants are given strategy training instructions and practice prior to performing the main task.   The strategy training instructions emphasize the expectancies associated with each contextual cue type.  Participants are instructed to encode the context cue in terms of these expectancies and then to use them to prepare their response during the cue-probe delay trial.  In a first practice phase, the strategy is implemented via overt rehearsal of context and expectancies and response preparation.  In a second practice phase, the task is performed with covert rehearsal.   The instructions and strategy training are similar to that implemented in prior papers (Braver et al, 2009; Gonthier et al, under review).   During the task phase, the only distinction is that in the inter-trial interval a reminder message is provided (“Remember to use the strategy”).

 

Behavioral AXCPT Reactive
This condition implements a location-color probe-cueing.  All task stimuli and proportions are identical to the Baseline condition.  The primary distinction that probe stimuli are presented in distinct locations and with distinct borders.  The AX and BY probes are presented in the upper half of the display, accompanied by a white border.  In contrast, AY, BX and no-go probes are presented in the lower half of the display and are accompanied by a red border. 

 

 

 

fMRI AXCPT task
This version includes baseline, proactive, and reactive conditions of the AX-CPT coded for Eprime.  It assumes manual responses coming in through a fiber-optic port. All conditions are implemented in a mixed block/event-related design. Within each scanning run, 3 task blocks alternate with 4 resting fixation blocks (30 sec duration); in each task block, the inter-trial interval randomly varies (across 3 step sizes).  Click here if you would like access to these task scripts.

 

fMRI AXCPT Baseline
The same conditions and trial type frequencies are used as the behavioral version.  Likewise the same trial timing parameters are used. The complete condition consists of 2 scanning runs, for a total of 144 trials, including 60 AX, 12 AY, 12 BX, 60 BY and 24 no-go.    

 

fMRI AXCPT Proactive
The same conditions and trial type frequencies are used as the behavioral and baseline version. Likewise the same trial timing parameters are used. Prior to the task, distinct instruction screens are presented. During the inter-trial interval a reminder message is provided (“Remember to use the strategy”). The complete condition consists of 2 scanning runs, for a total of 144 trials, including 60 AX, 12 AY, 12 BX, 60 BY and 24 no-go.   

 

fMRI AXCPT Reactive
The same conditions and trial type frequencies are used as the behavioral version.  Likewise the same trial timing parameters are used. The complete condition consists of 2 scanning runs, for a total of 144 trials, including 60 AX, 12 AY, 12 BX, 60 BY and 24 no-go. 


 

RELEVANT BEHAVIORAL MEASURES TO COMPUTE

In addition to standard behavioral measures of RT and accuracy (e.g., for each trial type), there are a number of measures that are specific to this task, which are described below.   Additionally, it can be useful to calculate the internal consistency (as split-half reliability, Cronbach’s alpha, or ICC) for various measures, particularly if you plan to use these to investigate individual differences.   If you would like to upload your data and have these measures computed, please click here.

A-cue bias. 
This computes the signal detection bias measure selectively for AX and AY trial types.  The A-cue bias measure indicates the general tendency to make a target response following an A-cue (which would lead to a high AX target hit rate, but also a high AY false alarm rate).  Positive values indicate a positive bias, and are predicted to increase in proactive conditions in the DMC framework. 

BX probe interference
This computes the magnitude of behavioral interference measured as BX-BY performance.  It is computed on both RT and accuracy. The DMC framework predicts a reduction in the accuracy interference effect in both Proactive and Reactive conditions relative to Baseline.   In contrast, the RT interference effect is predicted to selectively increase in the Reactive condition. 

D-prime context. 
This computes the signal detection dprime measure selectively for AX and BX trial types (i.e., AX hits vs. BX false alarms).  The d-prime context measure indicates the ability to discriminate target and nontargets based on the cue.   It is a measure frequently computed in the AX-CPT and so is included for comparison purposes, but there is not a strong prediction from the DMC framework.

Proactive behavioral index. 
This computes a normalized difference score of performance distinctions between AY and BX trial types (i.e., [AY-BX]/[AY+BX]).   It can be computed on both RT and accuracy measures as well as their sum.   This measure has often been computed in the AX-CPT (Braver et al, 2009).  The index measure is predicted to increase in the Proactive condition.   However, it is not clear yet whether there is a prediction to be made for the Reactive condition.