Millisecond Forums

Clarifying Output Variable Names in Change Blindness Task

By skotturi01 - 1/30/2015

I have some data from the Change Blindness task (

I understand the task and what it's measuring but I cannot decode the variable names Inquisit in outputting nor can I find any documentation explaining the variables. 

For each trial I get the following column names:
values.prechange3_hits, values.prechange3_fas, expressions.prechange3_diff,
values.postchange3_hits, values.postchange3_fas, expressions.postchange3_diff

I understand the pre and post trials, "diff" is just "hits - fas". 
I cannot figure out what "hits" & "fas" are though. 
Hits looks like it could be the serial position of the item that was removed/replaced and fas is the subject response, correct of false. However Fas occasionally takes the value of 2 (almost always 0 or 1 otherwise). These aren't intuitive, abbreviations or acronyms though which makes me think it must be something else. 

Looking for an "AHA" moment :)

By Dave - 1/30/2015

If you open the script in Inquisit Lab (or any other text editor -- it's just a text file), you will find all of this documented throughout the comments included in the script. The detailed documentation for the data output starts at line 505.

A relevant excerpt:

/postchange_FAs:  sums up hits/False Alarms (FAs) for prechange and postchange recognition
/prechange3_diff:   difference in values.prechange_hits - values.prechange_FAs for array number = 3 (same for all array numbers)
/postchange3_diff: difference in values.postchange_hits - values.postchange_FAs for array number = 3 (same for all array numbers)

Hits and False Alarms are standard technical terms in Signal Detection Theory. See e.g.