Response Time Measurement
The application rtm controls response time experiments. It may be
used to measure simple reaction time as well as choice reaction time
to various sorts of signals. Available signal types are:
Different types of warning signals are possible. One of them is a countdown
like the one used by Green, and von
Gierke (1983). Actually,
rtm may be used to run an experiment that is almost an exact
replication of the Green et al. (1983) or the Green and von Gierke
(1984) experiment, including exponentially distributed foreperiods.
- single and double optical signals varying in size, color, luminance,
duration, orientation, and in case of double signals in stimulus onset
- acoustic signals with variable frequency, loudness, and duration;
- simultaneous optic and acoustic signals with variable stimulus
- verbal signals of various colors for color Stroop experiments and
number strings for numeric Stroop experiments.
What Happens in a Trial
Many reaction time experiments follow the same procedural sequence. The
application rtm is designed such that it uses a basic sequential
pattern that is very general and may be adapted to many special cases by
setting certain parameters. The following list contains a description of
everything that happens within a single trial as it is run by rtm.
The above description is rather vague on the type of attention and response
signals, the response key patterns and the feedback type. These functions
are parametric and depend on the special configuration. The above scheme,
however, is the same for any experiment run by rtm. The program may be
adapted to special tasks by setting experimental parameters.
- Start. The trial starts with a waiting period of
- Preparation Message. After the initial wait a preparation
message defined by prepmsg may be put on the screen to tell the
subject that a new trial is
beginning right now.
- Wait for Start. Then we wait for the actual start signal. There
are two possible sources: (a) Automatic. In case the flag A is
set, the trial is started automatically after the preparation message
been shown for preptm ms. (b) Button Press. If the flag A is
not set, then we wait until the subject presses and releases one of the
available response buttons.
- Clear Screen. Clear the screen and wait another attwait ms.
- Attention Signal. Now the attention signal is presented. The
type of attention signal to be used is controlled by the value of
- Foreperiod. The actual time between attention signal offset and
response signal onset is stored in forewait. This time may be fixed or
random: (a) Fixed Foreperiod. In case the flag F is set, the
wait has a fixed duration of expectedwait ms. (b) Random
Foreperiod. In case the flag F is not set, the waiting period is the
sum of two intervals: the first interval is fixed to minwait ms and the
second interval is an approximately exponentially distributed random
variable with expectancy and variance equal to expectedwait ms. Since
the exponential distribution may generate infinite length intervals the
random period for the experiment is limited to maxwait ms. The actual
time interval between attention signal offset and signal start is stored in
- Check for Anticipation. At the end of the foreperiod wait we
check the response keys. If they do already satisfy the response criterion,
then we have an anticipation. In this case we do not present the signal but
immediately go to the response evaluation section with a warning string used
as a feedback message. The response pattern of such a trial will have the
response pattern set to EARLY. The response time will be 0.
- Set Signal. If no anticipation is found we finally start the
response signal. This automatically terminates the forewait and starts
the response time clock. Signal types are selected by the value of
- Wait for Response. Now we wait for a response. The wait is
limited to timeout ms.
- Feedback. There are two possible ways to stop the response wait:
(a) Response. If the response keys satisfy the response key mask, we
have an ordinary response. In this case the response time and key pattern
will be stored in rtime and response respectively. (b) Time
Out. If the subject misses the signal, we have a time out situation. In
this case we set the response pattern to MISS, the response time to 0,
and the feedback message to tmoutmsg.
- Feedback. The response pattern may be evaluated and the result
and response time may be used to give some feedback for the subject.
The evaluation and feedback type are controlled by evaluation.
- Finish. This starts the next trial.
Preparation and Attention Signal
The preparation message prepmsg may be used to tell the subject
that a new trial is starting. This either is automatic with a message
duration of preptm ms or may be
controlled by the subject, depending on how the flag A is set.
After the trial start there may be an attention signal. It starts
attwait ms after the subject has released the start key or after
intdsptime has passed if the procedure is automatic.
The attention signal type is
given by attention. This may be a visual countdown of a pair of
half disks moving in from the left and right edge of the screen until they
meet at its center, or it may be a sequence of acoustic beeps. The
number of attention signal steps is cdcount. On and off duration of
each single step is defined by cdontime and cdofftime. For
visual attention signals the size is cdsigradius, its final
screen position is cdsigxpos and cdsigypos, and its luminance
is cdlum. For acoustic signals the sound pitch is defined by
cdfrequency and the volume by cdvolume.
No attention signal is shown if cdcount is 0.
The foreperiod starts when the attention signal is switched off and is
finished when the signal starts. If the
flag F is set then the foreperiod is a fixed interval of
expectedwait ms. A random foreperiod has an initial fixed wait of
minwait ms and a following approximately exponentially distributed
random period with an expected duration of expectedwait ms.
However, the total foreperiod is limited to maxwait ms. The actual
duration of the foreperiod is stored in forewait for later use.
There are many different signal types available. The optic screen
signals are synchronized with the vertical screen refresh. Acoustic
signals are generated on the current audio device which my either be the
built in speaker or an Adlib compatible sound board, depending on the state of the
general parameter sounddevice.
The SIMPLEVISUAL signal type is a circular patch of radius sigradius on the
screen with its color defined by sigcolx, sigcoly, and siglum.
The DOUBLEVISUAL type contains 2 optic signals. The first one
is like SIMPLEVISUAL and the second one is a ring
around the first signal whose
radius is sig2radius and whose color is defined by sig2colx,
sig2coly, and sig2lum. The 2nd component's duration is
sig2duration and its stimulus onset asynchrony is soa.
LEFTVISUAL and RIGHTVISUAL are variants of SIMPLEVISUAL
showing arrows pointing to the respective direction.
Note, however, that the right arrow color
is defined by sig2colx, sig2coly, and
The types ONESTRING and TWOSTRINGS are string signals defined
by sigtext and sig2text. The presentation method is like the
one of SIMPLEVISUAL and DOUBLEVISUAL repsectively. Single
string signals my be rotated by setting sigrotation to the required
angle of rotation. They also may be displayed as mirror images by
setting sigmirror to 1. Character size is given by textsize.
and the character font is given by textfont. Note that the rotation
and mirror transformations are not possible with textfont set to
The SIMPLEAUDIO signal type is a simple acoustic beep with its frequency defined
by sigfrequency and its volume by sigvolume. Note that the
volume parameter is only valid for Adlib devices.
The BIMODAL type combines SIMPLEAUDIO and
SIMPLEVISUAL to get both a visual signal and an acoustic
signal with stimulus onset asynchrony defined by soa which my be
BIMODSTRING also is a bimodal signal. However, here the optic
signal is a string defined by sigtext.
Many variables of rtm are involved in controlling timing of the
procedural sequence in a single trial. Table rtmtm lists all
variables that control timing together with what happens during the
respective interval of time.
Insert Table rtmtm here.
Response, Evaluation and Feedback
The rtm program does not allow keyboard responses, only the mouse
or other response switches may be used for response input. The timing of
the keyboard simply is such that no valid response time measurement is
possible with keyboard response keys. Mouse response times also are
rather uncertain, however, the mouse is acceptable if it is not moved or
the mouse ball is removed such that no mouse movement signals are
generated. The parameter switch controlls which key actually may
be used for response and whether the response is a button push or a
If there is a Soundblaster compatible board installed then rtm also
supports voice key responses. These may be given via a microphone
connected to the Soundblaster's microphone input port.
The voice key works like a single response
button. Its threshold value is defined by voicekeythreshold which
is some value between 0 and 255. If the voice key is used then the
procedural control responses are expected from the keyboard.
The response evaluation is controlled by evaluation. The
RTIMEFEEDBACK evaluation shows feedbackmsg after each
successive trial. Invalid trials result in either earlymsg or
timeoumsg being shown instead of feedback. The message is
visible for feedbacktime ms.
The CHECKDSP evaluation type compares the subject's response, which
is stored in response with the current value of dspstate. If
these are identical then corrmsg is shown for feedback and
eval is set to 0. If dspstate and response
are not equal then falsemsg ist shown for feedback and eval is
set to 1.
Invalid trials are those where the "response" is given before the
signal starts and those where the response is not given within
timeout ms after signal onset, provided nogo is not set.
If the parameter minrtime is nonzero then trials with rtime
less than minrtime also are invalid.
Invalid trials result in an eval value of more that 1 and in a 0 response
time in rtime in case of early and timeout responses.
These trials are repeated later if the flag V is set.
Also note that the feedback messages may contain
parameter names enclosed between percent signs. These are then replaced
by the current parameter values.
The parameter nogo is used to define no-go trials where there is a
signal but there should not be a response. The feedback message for
correct behavior in no-go trials is nogomsg.
The screen background colors are defined by bgcolx, bgcoly,
and bglum. All message are white and their luminance is
msglum. The color of the first signal is defined by
sigcolx, sigcoly, and sigcoly the color of the second
signal by sig2colx, sig2coly, and sig2coly.
Insert Figure rtmkeys here.
Stroop Response Keys
The parameter stroopkeys modifies the ONESTRING signal type. If
it is nonzero then there is a display of color patches or color names
(depending on the state of flag C) at the bottom of the screen as
shown in Figure rtmkeys.
The colors are defined by stroopkeycolors and the labels are defined by
stroopkeylabels. Patch size is cdsigradius
and patch array center position is cdsigxpos, cdsigypos. The
color patch/label sequence is randomized for each trial and the response key
numbers are set accordingly. This can be used to create a red, green, blue,
and yellow response key array whose sequence is set anew for each trial.
Note that this mechanism requires a switch response panel if more than the
number of available mouse buttons are to be used. A non-zero value of
stroopkeys activates the display. The value of stroopkeys gives
the number of color patches/names to be used. If there are less
patches/labels than possible then it is made sure that the correct response
key is included in the array and that its position is randomized. The
correct response key is identified by the current value of dspstate.
The actual sequence of the color patches/labels is stored in the string
- attention (int)
- Type of attention signal. These are available:
- VISUALCOUNT (0)
- A visual countdown signal. The count down consists
of two half disks, one left half and one right half that move in from the
screen's border to its center in cdcount steps. Both halfes meet at the
screen's center and form a circular disk there. The disk's radius is
cdsigradius. The signal's color is identical to the background color
defined by bgcolx and bgcoly. Its luminance is defined by
cdlum. The variable cdontime gives the duration of a single ON
period. The whole count down duration is given by
cdcount * cdontime. The number of counts must not exceed 8.
- AUDIOCOUNT (1)
- An acoustic count down of a series of cdcount
single beeps of frequency cdfrequency and volume cdvolume. Beep
duration is cdontime, pause between beeps is cdofftime.
- COOPSHEP (2)
- In this case the attention signal is the string
sig2text at position sig2xpos, sig2ypos. If cdcount is
non-negative then there also is an arrow rotated by cdcount 1/10 degree
at position sigxpos, sigypos.
- attwait (int)
- The time between the trial start signal
detection (either automatic or subject initiated, depending on the state of
flag A) and the start of the attention signal.
- bgcolx , bgcoly , bglum (float)
- These are the CIE xy-coordinates and luminance
of the screen background color.
- cdcount (int)
- Number of periods for a count down warning signal. No count
down is shown if cdcount is 0.
- cdfrequency (float)
- The frequency of an acoustic attention
signal given as a floating point number in Hertz.
- cdofftime , cdontime (int)
- Count down signal off and on period duration.
- cdlum (float)
- Optical count down attention signal luminance.
- cdsigradius (int)
- Radius of the count down signal dot.
- cdsigxpos , cdsigypos (int)
- Horizontal and vertical
position of the attention signal.
- cdvolume (float)
- The volume of an acoustic attention signal
(currently not used).
- textfont (string)
- Name of font which is used for writing the string signals.
- textsize (int)
- Size of characters for string signals.
- earlymsg (string)
- Warning message for anticipatory responses before the
- eval (int)
- Result of the response evaluation. See evaluation how it
works. The value 0 indicates a correct reponse, while nonzero values
generally indicate false or illegal responses.
- evaluation (int)
- Type of response evaluation and feedback to
provide for the subject. Currently available are:
- RTIMEFEEDBACK (0)
- This function simply shows the
string defined by feedbackmsg on any valid trial. The string may
contain parameter names enclosed in percent signes like
which are replaced by the current parameter values,
In case of an anticipation the
string earlymsg is displayed, and in case of a miss, the string
timeoutmsg is used. The message is visible for feedbacktime ms.
- CHECKDSP (1)
- This is similar to the RTIMEFEEDBACK
case. However, instead of a feedbackmsg there are two messages available
here, one for correct and one for false responses (corrmsg,
falsemsg). The corrmsg is used if the response pattern
response is identical to the current value of dspstate, otherwise
falsemsg is used. Thus dspstate may be used to define the correct
response for each display. If response is not equal to dspstate
then the parameter eval is set to 1 otherwise it is 0.
- expectedwait (int)
- Expected value of the foreperiod waiting time. For random
waiting times this is automatically equal to the square root of the waiting
time variance. Note that the waiting time is only approximately exponential,
since a real exponential distribution would allow infinite waiting times.
The longest wait for our experiment is limited to
maxwait. The random waiting time generator draws samples until the time
drawn ist less than maxwait. If minwait is nonzero, then its value
is added to the random time output of the random number generator. If the
flag F is set, then expectedwait gives the fixed time between the
warning signal and the response signal onset in milliseconds.
- feedbackmsg (string)
- This is the string that makes up the feedback
message in case evaluation is set to RTIMEFEEDBACK. See
evaluation for a description how it works.
- flags (string)
- The application rtm uses the following flags:
- If A is set, then trials are started automatically after
each feedback period. The default is to wait until the subject starts the
trial by pressing a response switch.
- If this flag is set then the response key indicators activated by
stroopkeys for ONESTRING signal types are color patches with
colors defined by stroopkeycolors. If C is not set then the labels
in stroopkeylabels are used.
- The flag F controls whether a random waiting time is used or
there is a fixed time between attention signal and response signal onset. If
F is set, then there is a fixed foreperiod.
- Repeat all invalid trials if this flag is set. Trials are
repeated by inserting them into the remaining list of trials of the
current block at a random position.
- forewait (int)
- Actual foreperiod waiting time. This value is computed from
the actual warning signal offset to actual response signal onset. There may
be up to 20 msec difference between the theoretical random wait and the
actual wait given in forewait, because of the time required for
synchronization between the video display system and other timing events.
- frametime (float)
- The time between two successive retrace
signals of the video system. This variable is only for output purpose.
rtm contains a function that measures the video frame duration in
order to compute valid stimulus onset asynchronies. The value measured is
returned to the user by setting frametime.
- ifc (int)
- For coding the type of interference in the data file
trials. The program does not use ifc, but one may use it
as a trial parameter to make data analysis easier.
- maxwait , minwait (int)
- maxwait is the maximum foreperiod waiting time
and minwait is the minimum waiting time. The waiting time distribution
is random if the flag F is not set which is the default. The random
number generator draws an approximately exponentially distributed number w
which has expectancy and variance
expectedwait. Numbers are drawn until a value is found that is smaller
than maxwait. The final value for the waiting time is w +
- nogo (int)
- Should be set nonzero to create a nogo-trial. In this case the
subject is expected to not respond and thus creating a time out situation.
If nogo is set then this is accepted to be a correct "response" and
nogomsg is used as a feedback message.
- nogomsg (string)
- Feedback message for correct behavior in nogo trials.
- prepmsg (string)
- Message to tell the subject that a new trial
may be started.
- preptm (int)
- If a trial is not initiated by the subject, but is
automatically started as may be requested by setting the flag A, then
the preparation message prepmsg is visible for preptm ms.
- rasterdelay (float)
- The time between the start of a vertical retrace period
and actual stimulus onset on the screen. The time only depends on a signal's
position on the screen. The default for rtm is to set
rasterdelay to the delay between start of retrace and a line at the
center of the screen. On an IBM VGA in 350-line mode this is about 6
milliseconds. The value of rasterdelay is used for computing correct
stimulus onset asynchronies between visual and acoustic signals.
- response (int)
- This is the response pattern that we get from
the response keys. In case there are multiple response keys available,
response may be used to control the feedback message. The response
pattern is also used to identify anticipations and misses and is evaluated
by the response evaluation procedure. response is the actual response
pattern while eval is the result of the response pattern avaluation.
- rtime (int)
- Response time. This is the actual time between
signal onset and response. If optic signals are used, then they always are
switched on at the start of vertical retrace periods. Thus response times
always are measured from the start of the video frame if the optic signal is
the main response signal. Acoustic signals are not bound to synchronization
and thus may start at arbitrary points in time.
- sigcolx , sigcoly , siglum , sig2colx , sig2coly , sig2lum (float)
- These are the CIE
xy-coordinates and luminance values of the signal colors. sigcolx and
sigcoly are for the first and standard optic response signal. If there
are two optic response signals, the sig2colx and sig2coly describe
the second signal's color.
- sigfrequency (float)
- The frequency of an acoustic response
signal in Hertz. Note that this is a float variable.
- sigmirror (int)
- Indicates that a single text string signal should be shown
as its mirror image. This requires textfont to be a vector font.
- signal (int)
- Type of response signal. The signal duration is defined by
dsptime. The following signal types are available:
- SIMPLEVISUAL (0)
- A circular patch of radius sigradius on the
screen with its color defined by sigcolx, sigcoly, and siglum.
- SIMPLEAUDIO (1)
- A simple audible beep with its frequency defined by
sigfrequency and its volume by sigvolume.
- BIMODAL (2)
- This combines SIMPLEAUDIO and
SIMPLEVISUAL to get a visual signal that is accompanied by an audible
signal. The stimulus onset asynchrony between both signals is given by the
variable soa. Signal parameters are taken from the simple signal
specifications. soa is the time by which the acoustic signal lags
behind the optic. Negative values of soa mean that the acoustic signal
comes first and the optic signal second.
- DOUBLEVISUAL (3)
- This is a signal that may be used to analyze
metacontrast effects on reaction times. The main signal is
a circular patch of radius sigradius on the
screen with its color defined by sigcolx, sigcoly, and
siglum. The masking signal is a ring around the first signal whose
radius is sig2radius and whose color is defined by sig2colx,
sig2coly, and sig2lum. The masking signal's duration is
sig2duration and its stimulus onset asynchrony is soa. Note that
video synchronization makes it necessary to only use approximate multiples
of frametime for visual signals and stimulus onset asynchronies in the
double visual signal task.
- ONESTRING (4)
- This is a single visual signal like the one of
SIMPLEVISUAL but made up of the text string sigtext.
- TWOSTRINGS (5)
- This is a double visual signal where both
signals are verbal material. The first signal is sigtext and the second
signal is sig2text. Both are presented as if they were double visual
signals of the case DOUBLEVISUAL, thus all parameters of these apply.
- LEFTVISUAL (6)
- This is a visual signal whose only
difference from SIMPLEVISUAL is that it forms a left pointing filled
arrow. The arrow color is defined by sigcolx, sigcoly,
- RIGHTVISUAL (7)
- Similar to LEFTVISUAL. The right arrow color
is defined by sig2colx, sig2coly,
- BIMODSTRING (8)
- This is a bimodal signal of the string in
sigtext and a simple audio signal.
- sigradius , sig2radius (int)
- Optic response signal patch
radius. The optical signal is a circular patch at the screen's center.
sigradius is the signal patch's radius in 1/10 mm. The second optical
signal also is a circular patch, it is put on the screen before the first
optical signal, thus if they are at the same position, it appears to be a
ring around the first signal.
- sigrotation (int)
- If nonzero the single text string signals are rotated by
sigrotation 1/10 degrees counterclockwise. This requires textfont
to be a vector font.
- sigtext , sig2text (string)
- The strings that make up the
first and second signal in case the signal type is a single or double string.
- sigtime , sig2time (int)
- The response signals' duration. If any of the signal
duration variables is 0, then the respective signal is response terminated.
- sigvolume (float)
- The volume of an acoustic response signal,
given as a floating point number. Requires a sound board to be present.
- sigxpos , sigypos , sig2xpos , sig2ypos (int)
Horizontal and vertical center position for optic signals.
- soa (int)
- Stimulus onset asynchrony between the two
components of two component signals.
- stroopkeycolors (int)
- The color patches which are shown with non-zero
stroopkeys values get their colors from the stdcolors array of
color coordinates. The parameter stroopkeycolors contains the indices
of the colors in stdcolors which are to be used for the color patches.
Simply redefine stdcolors for getting any arbitrary color assignement
for the color key patches. Note that the number of entries in
stroopkeycolors must be exactly 4.
- stroopkeylabels (string)
- This array of strings contains the labels of the
response key positions which are shown if stroopkeys is nonzero. Note
that the number of entries in stroopkeylabels must be exactly 4.
- stroopkeys (int)
- This parameter modifies the ONESTRING signal type. If
it is nonzero then there is a display of color patches or color names
(depending on the state of flag C) shown at the bottom of the screen.
The value of stroopkeys gives the number of color patches/names to be
- stroopkeysequence (string)
- If this parameter is defined to be a trial
argument then the actual sequence of Stroop response key patches/colors is
stored in this string as a sequence of response event numbers.
- switch (int)
- Defines the type of response that is expected.
We assume that there is a panel of response switches available. If there is
only a single response switch, use it as if it were the left one of a double
switch. Double switch panels are handled as if they were the inner two of a
quadruple switch panel. Left and right positions refer to double switch
panels. The following values of switch are possible:
- LEFTRELEASE (0)
- The response is a release of the left button.
- RIGHTRELEASE (1)
- Release the right button.
- ANYRELEASE (2)
- Release any one of the buttons.
- LEFTPUSH (3)
- The response is by pressing the left button.
- RIGHTPUSH (4)
- Press the right button.
- ANYPUSH (5)
- Press any one of the buttons available.
- VOICEKEY (6)
- Voice key response to signal. Control inputs are
expected from the keyboard.
- timeout (int)
- Time out limit. If the subject does not respond within
timeout milliseconds, then the trial is stopped and a warning is
printed on the screen.
- timeoutmsg (string)
- Warning message if the subject has not
responded within timeout milliseconds after signal onset.
Simple Visual or Acoustic Signals
The simple experiments selected by SIMPLEVISUAL or SIMPLEAUDIO use
visual or acoustic signals. Signal intensity, size, and duration may be
controlled by experimental variables.
Here is a an example parameter file. It runs a simple reaction time
experiment where there are different signal luminance values. Each display
contains information about the signal luminance, the actual foreperiod
duration, the response time and the response pattern. Each signal luminance
is presented 20 times and the luminance values used are values between 10
and 50 cd/qm in steps of 10 cd/qm. The attention signal is a single
acoustic beep. There is only one block.
Parameter file erzv.x from directory \pxl\app\rtm
Two Choice Reaction Times and Donders C Response
Use LEFTVISUAL and RIGHTVISUAL to create a two coice reaction time
experiment. A Donders C type experiment may be created by a proper
combination of left/right signals and the appropriate response mechanism
selected by switch.
Parameter file rz2.x from directory \pxl\app\rtm
Metacontrast and Response Time
The double visual signal created by DOUBLEVISUAL may be used to run an
experiment similar to classical metacontrast experiments.
The first signal is a small patch, the second signal is a ring
around the first one. Stimulus onset asynchrony, signal colors and intensity
may be controlled by experimental variables. The subject's task is to
respond as soon as there is something visible. The signal parameters may be
adjusted such that the subject is not aware of the existence of the first
signal, but reports to respond to the second one. The response times,
however, show that the subject actually responds to the first signal.
Parameter file meta.x from directory \pxl\app\rtm
Facilitation and Time Order Judgements
The signal type BIMODAL uses two signals, one optical and the other
acoustical. The signals may have variable stimulus onset asynchronies and
arbitrary intensities and duration. This type of signal is used in time
order judgements, where the subject has to tell which of the two signals was
first, depending on the actual delay. This type of double signal has also
been used to test whether a redundant signal has any effect on the response
time to some other signal.
Parameter file colonius.x from directory \pxl\app\rtm
Stroop Interference in Color Naming
The signal type TWOSTRINGS may be used to create an experiment that
models the one described by Treisman and
Fearnley (1969). These authors used paper cards with two possibly
colored words printed on the cards. The subjects had to sort the cards
according to different criteria. The standard Stroop interference task
requires a colored word in the upper half of the card and a color name in
the lower half. The subject has to decide whether the color of the first
word is named by the second word. Our implementation presents one single
card on the screen for each trial. The subject has two response switches.
The first one has to be pressed if the top word's color is named by the
bottom word. The second switch has to be used if the bottom word does not
name the top word's color. We measure response time and report
correct/incorrect responses. Response feedback may include a
correct/incorrect message and the response time.
The following parameter file example defines a Stroop color name comparison
task. It uses macro preprocessing and range expansion to combine all colors
and words needed.
Parameter file stroop.x from directory \pxl\app\rtm
Polson's Mental Chronometry Tasks with Letter Comparisons
The TWOSTRINGS task may also be used to compare single letters and run
choice experiments in the sense of Polson's mental chronometry.
Parameter file samediff.x from directory \pxl\app\rtm
Stroop Interference in Counting Numbers
Setting the signal type to ONESTRING may be used to create a numeric
Stroop interference task. Here the cards
contain a sequence of characters and the subject's task is to count the
characters and respond with the correct number. sigtext contains the
sequence of characters. The feedback function CHECKDSP can be
used to create a corresponding feedback message.
Parameter file nstroop.x from directory \pxl\app\rtm
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