Bit Mapped Image Displays
The application pics may be used to display bit mapped images, get
responses and measure response times. Currently pics can only display
PCX image files with 256 colors.
The program displays uncompressed PCX images with
256 colors. The images are expected to reside in a single directory named
imagedir. The image file names are given by image. The images
must not be larger than the available screen size is and only video modes
which support 256 colors (videomode higher than 21) are allowed.
The flag M activates a mask which is shown immediately after the image.
The mask is a random pattern of bright and dark dots. The mask size is
controlled by maskwidth and maskheight. The individual dot size is
controlled by maskcellwidth and maskcellheight. The mask is shown
for masktime ms and is created new for each image if the flag N is
active. The masking mechanism requires that the flag P is active.
There are two text strings available which may be shown simultanously with
the images. The strings are given by text and text2 and their
positions are textposx, textposy, text2posx, and
text2posy. Since the images use all of the available colors there may
be problems to find a text color for showing the text strings. pics
does its best to provide two text colors: black (0) and white (1). These are
defined in textcolor and text2color.
Note, however, that this restriction only holds for text which is seen
simultanously with the images. The message texts are not affected by it.
Each trial starts with a waiting period of intdsptime ms. This time is
needed to read the image file and put it into screen memory, although the
image still is invisible. If the flag A is set then there is an
attention signal of duration attduration and a waiting period of
stimwait after the signal is switched off. Then the image and the text
strings are switched on. The image is visible for dsptime ms.
If the trial message duration parameter dsptm is nonzero the message
dspmsg is shown immediately before or after the image display period.
If the flag P is on then the message is shown immediatley after the
image has been switched off and the message remains visible until there is a
response. Note that the exact value of dsptm is irrelevant in this
case and the response time rtime is measured from the start of the
If the flag P is off and dsptm is nonzero then the message is
shown before the image. In this case the start of the message dspmsg
finishes the initial pause intdsptime. If dsptm is negative then
the message remains visible until there is a response. If dsptm is
positive then it gives the duration of the message on screen. In any case
attwait gives the pause between the message disappears and the
attention signal or the image is switched on. Note that in the latter case
attwait has to be long enough to read and write the image.
Response and Feedback
The number of the response key is stored in response and the response
time is in rtime. If response is equal to dspstate then the
response is considered to be correct and eval is set accordingly. If
feedbacktime is positive then the respective feedback messages
corrmsg or falsemsg are shown for feedbacktime ms.
- attwait (int)
- Time to wait for the attention signal (or the image display,
if there is no attention signal) after the text of the trial message has
been switched off.
- attduration (int)
- Duration of the attention signal.
- centerx , centery (int)
- Screen position of image center.
- dspmsg (string)
- This string is displayed before or after the image is shown if
dsptm is non-zero. It is shown before the image if flag P is off
and after the image if it is on.
- dspstate (int)
- Response event number for a correct response.
- dsptm (int)
- Duration of dspmsg. If dsptm is negative then display
duration is on until a response switch is being pressed. A zero value of
dsptm suppresses the display of dspmsg.
- eval (int)
- Returns whether the response was correct (eval = 0) or not.
- feedbacktime (int)
- If positive then there is a feedback message shown after
the response. If the response event number is equal to dspstate then
corrmsg is shown, otherwise falsemsg is shown for
- flags (string)
- The application rtm uses the following flags:
- If A is set, then an acoustic attention signal ist presented
before the image becomes visible.
- Show count down while waiting in the intdsptime period.
- Activates the display of a mask immediately after the image.
- Recreates the mask pattern for each single image.
- If P is set then the trial message dspmsg is shown after
the image otherwise it is shown before the image. Note that this does not
affect the strings text and text2 which are always shown together
with the image.
- Acoustically notify wait key release.
- Take response time starting from wait key release event.
- image (string)
- The image file name.
- imagedir (string)
- The full access path for the directory where all the image
- maskcellheight , maskcellwidth (int)
- Size of individual dots in the mask.
These parameters are given in screen pixel counts.
- maskheight , maskwidth (int)
- Size of the mask. These parameters are given in
screen pixel counts.
- masktime (int)
- Duration of image mask.
- response (int)
- Response key pattern.
- rtime (int)
- Response time.
- sigwait (int)
- Waiting time between attention signal offset and target
- text , text2 (string)
- These strings are text messages that may be shown
simultanously with the image.
- textposx , textposy , text2posx , text2posy (int)
Horizontal and vertical center position for the two text signal messages.
- textcolor , text2color (int)
- For technical reasons the text strings text
and text2, which are shown simultanously with the image display, may
only be written in black (textcolor = 0) or white (textcolor = 1).
Stroop Interference in Picture Naming
The following example creates a Stroop-like interference experiment. The
subject sees an animal picture with some name written into the image. The
name may be an animal's name or some other word. Below the animal image
there is another word which always is an animal's name. The subject's task
is to repond with "yes" (left response key) whenever the word below the
picture gives the name of the animal shown in the picture.
Parameter file bstroop.x from directory \pxl\app\pics
The next example is a picture recognition test. Pictures are shown and the
subject has to classify them as "new" or "old". This task is
the second part of a learning experiment for testing the levels of
processing theory of memory.
Parameter file craik2.x from directory \pxl\app\pics
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