The program mvg shows one or two motion patterns and then waits for a
response. There also may be special inspection patterns while waiting for
the response. Possible applications involve paired comparisons of two motion
patterns, motion adjustment, and motion adaptation.
Adaptation and Inspection Pattern
The adaptation pattern is a sinusoidal grating which is computed as a convex
mixture of the colors a and b with coordinates ax, ay,
aL, bx, by,
bL where the weights of each component are sinusoidal functions of
spatial position: c(h) = w(h) * a + (1-w(h)) * b, where w(h) = 0.5 * (1 +
cos(2Pif h)). h is the position and f is the spatial frequency of the
sinusoid. The frequency is derived from cyclespm, the number of full
pattern cycles per meter and the size of the pattern area as defined by
width and height.
If the flag I is set then the pattern colors are changed when going
from the adaptation to the inspection phase. The spatial pattern remains
the same but colors (a,b) are replaced by (a_i,b_i) This feature may be
used to show an inspection pattern with less modulation than the motion
The motion direction is controlled by direction: 0 =
down/right/inwards, 1 = up/left/outwards. Motion speed is controlled by
pxlmps. This parameter gives the pxlm per second.
dsptime is the duration of the motion display and thus of the
adaptation phase. It is given in seconds.
Since adaptation experiments need rather long intertrial intervals there is
a countdown message between trials. The message string is countdown. If
it contains the character sequence "%d" then this sequence is
replaced each second
by the remaining number of seconds to wait.
Each adaptation period may start with a message telling the subject what to
do in the next trial. This may be used to tell the subject that she has to
change the eye for inspection. The message is shown for dsptm ms. The
message shown is changenote if the parameter change is ON and
dspmsg if change is OFF.
- ax , ay , aL , bx , by , bL (float)
- Color coordinates of those colors a and b
that make up the motion pattern.
- aix , aiy , aiL , bix , biy , biL (float)
- coordinates of the components a and
b during the inspection phase.
- fieldcolx , fieldcoly , fieldlum (float)
- Background field color.
- fieldheight , fieldwidth (int)
- Height and width of the background field.
- centerx , centery (int)
- Stimulus pattern center coordinates.
- change (int)
- Indicates that changenote should be shown before the trial
- changenote (string)
- This text is shown before the trial starts if
change is ON.
- clearfixmark (int)
- If this varaible is not 0 then the fixation
mark is cleared during the inspection phase.
- countdown (string)
- Count down message shown between trials.
- clearfixmark (int)
- Flag for not showing the fixation mark during inspection.
- csteps , csteps2 (int)
- Color steps per single sine wave in first and second
stimulus. Note that only around 250 color steps are available in total.
- cyclespm , cyclespm2 (int)
- Number of visible sine waves cycles per meter
whithin the stimulus fields.
- direction , direction2 (int)
- Motion direction of first and second stimulus
pattern. These are possible: MOVEUP (1), MOVEDOWN (0),
MOVERIGHT (0), MOVEOUT (1), MOVEIN (0).
- dspmsg (string)
- Message at start of the adaptation period.
- dsptime (int)
- Duration of the motion display given in seconds.
- dsptm (int)
- Duration of dspmsg. If dsptm is negative then
dspmsg is shown until a key is pressed.
- fixmarklum (int)
- Fixation mark luminance.
- fixmarksize (int)
- Size of fixation mark. No mark is shown if
fixmarksize is 0.
- fixmarkx , fixmarky (int)
- Position of fixation mark.
- flags (string)
- These flags are available:
- Give an acoustic cue at the start of the adaptation period.
- Show two moving patterns.
- Change the pattern colors (a,b) to (a_i,b_i) during the
- Immediately remove grating after inspection phase.
- Enable an acoustic cue at the start of the inspection phase in
those cases where change has the value 1.
- Use a circular background field instead of a rectangular one.
- Print speed table for debugging purpose.
- Recompute and repaint the motion pattern for each trial. Default
is to use only a single pattern for the whole block. This is necessary if
there are different spatial frequencies within a single block.
- Allow motion adjustment instead of constant motion display.
- height , width (int)
- Height and width of the stimulus field. For circular
stimulus fields width is the diameter of the circular area.
- intdsptime (int)
- Pause between consecutive trials, given in seconds. This
pause may be filled with a visual countdown message.
- lpp , lpp2 (int)
- Screen lines per sine wave period of the two stimuli. These
parameters are only used for the data protocol and are set at run time by
the program. They have no effect if set in the parameter file.
- pxlmps , pxlmps2 (int)
- Motion speed in pxlm per second for two stimuli.
- rtime (int)
- Duration between start of the inspection phase and the subject's
response. Should be duration of after effect.
- stripedir , stripedir2 (int)
- Orientation of the stripes in the two stimulus
patterns. These are possible: HSTRIPES (0) (horizontal), VSTRIPES
(1) (vertical), and CIRCULAR (2).
- stripeform , stripeform2 (int)
- Wave type of stripes: SINEPATTEN (0),
RECTPATTERN (1) (not used until know).
- timeunit (int)
- Number of milliseconds per unit of time for time between
trials (intdsptime), stimulation time (dsptime), and response
(after effect) time (rtime). This also is the count unit for the inter
trial count down process.
The following parameter file is an experiment with linear and radial motion
and a possible change of the observation condition between adaptation and
Parameter file bene.x from directory \pxl\app\mvg
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