Questions and Binary Responses

The program lop runs experiments where there are verbal questions and the subject has to give binary yes/no-responses. The questions may contain different parts which do not all change from one trial to the next. lop was developed to run incidental learning experiments. These experiments use an orienting task which usually implies a response to a question like "Does the following word fit into the sentence 'The boy's xxx is red'?" then there is a word like "coat" and the subject has to give a yes/no-response. After a list of about 30 questions there is a surprise recall or recognition test. In case of a recognition test a list of target and distractor words is presented and the subject has to decide whether a word is new or old.

Program Features


During each trial there is at least one word given by the parameter item. The display duration is dsptime. If dsptime is 0 then the item is shown until there is a response. With an osent asynchrony of soa ms the string question is shown on the screen. soa will usually be negative such that question comes before item. question my be empty or may contain more than one line of text. After the item has been shown the program waits for a response which is a binary yes/no response where the cursor left key corresponds to "yes" and the cursor right key corresponds to "no". There may be a response dependent feedback. If the response is equal to dspstate then the feedback is corrmsg otherwise it is falsemsg. The feedback message is shown for feedbacktime ms. There is a pause of intdsptime ms between trials.


In addition tho question and item there may be permanent messages on the screen. title is a title message on top of the screen which is visible throughout a whole block. The same holds for reskeynote at the bottom of the screen. Examples for title and reskeynote are
  title = "Please answer the following question:"
  reskeynote = "<- yes     no ->"
All PXL-programs start a block with blockstartmsg. However, lop has a special effect implemented here: If surprisetime is nonzero then the text of surprise is shown before blockstartmsg. surprise may be an array of strings which will be shown as a text paragraph on the screen. This mechanism is used to give instructions for the surprise recognition test after the orienting task has been finished. The message is visible surprisetime ms. If surprisetime is negative then surprise is shown until a key is pressed. Note that timing values in milliseconds are only valid up to 30 s (30000 ms). Longer times have to be controlled externally.

The screen display attributes of the respective messages are given by the following parameters: itemattr, questionattr, titleattr, reskeyattr, und msgattr. All messages are written as centered text. The screen rows are given by itemrow, questionrow, titlerow, reskeyrow, and feedbackrow.

Some Special Parameters

The program lop also can run display only trials without waiting for a response. In this case the parameter task must be 0. If task is nonzero then the program always waits for a response.

Usually there are different types of orienting tasks in an incidental learning experiment. The parameter questiontype may be used to code the type of task. This parameter is not used by lop but may be helpful for statistical data analysis.

The program counts the number of correct responses without intervening error. If the flag R is set then a block is stopped if this number is larger than corrlimit. The number of correct responses in a sequence since the last error is strored in corrcount and the trial number of the last error is stored in lasterror.

A possible visual orienting task is to watch for a color change of the target item. If itemchange is larger than 0 then item changes its attribute from itemattr to itemsecattr itemchange ms after the onset of item.

Program Parameters

corrmsg (string)
Feedback text for correct responses.

corrcount (int)
Number of correct responses since the last error within a block.

corrlimit (int)
If the flag R is set then a block is stopped if corrcount reaches corrlimit.

dspstate (int)
Defines correct responses. "yes" (cursor left key) corresponds to 1 and "no" (cursor right key) corresponds to 2. The response is compared to dspstate to figure out the feedback message.

dsptime (int)
Display duration of item.

evaluation (int)
Type of response evaluation. Currently only

falsemsg (string)
Feedback text for false responses.

feedbackrow (int)
Screen row where feedbackmsg is shown.

feedbacktime (int)
Duration of feedback.

flags (string)
If the flag R is set then a block is stopped when there are corrlimit correct responses in a sequence.

intdsptime (int)
Pause between trials.

item (string)
The target item.

itemattr (int)
Initial screen attribute of item.

itemchange (int)
Time asynchrony between item onset and color change of item happens.

itemrow (int)
The screen row where item is shown.

itemsecattr (int)
Second screen attribute of item.

lasterror (int)
The trial number of the last error within a block.

msgattr (int)
Screen attribute for session and feedback messages.

question (string)
Question string.

questionattr (int)
Screen attribute of question.

questionrow (int)
Screen row whe question is shown.

questiontype (int)
Code for the type of question. This parameter is not used by lop.

reskeyattr (int)
Screen attribute of reskeynote.

reskeynote (string)
This message is shown throughout the whole block.

reskeyrow (int)
Screen row where reskeynote is shown. Should be below questionrow and itemrow.

rsequence (string)
This string holds the sequence of responses within a block. For each response there is either a "1" or a "2" in rsequence.

rtime (int)
Response time measured from onset of item to response. Note that a response before the display time of item is finished does not terminate the display.

soa (int)
The time interval between onset of item and onset of question. If soa is negative then question is shown before item.

surprise (string)
If surprisetime is nonzero at the start of a block then this string or array of strings is shown at the start of a block.

surprisetime (int)
Display time of surprise. If surprisetime is negative then surprise is shown until a key is pressed.

task (int)
If task is 0 then no response is expected. If task is nonzero then lop waits for a response after item has been shown.

title (string)
Message text on top of the screen which is visible throughout the whole block.

titleattr (int)
Screen attribute of title.

titlerow (int)
Screen row where title is shown. Should be above questionrow and itemrow.

Example Experiments

Verification of Logical Statements

The first example is from Baddeley (1968). It requires verification of simple logical statements.

Parameter file ablog.x from directory \pxl\app\lop

Incidental Learning

The next example is an incidental learning experiment with different orienting tasks in the first and a recognition test in the second block.

Parameter file vti.x from directory \pxl\app\lop

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Author: Hans Irtel