BARRAY

This stimulus consists of several parallel bars, each of which may appear at several positions within a grid. The diagram below shows the bar grid in the case of 3 bars and 4 positions. Possible positions are indicated by sets of X's.

  bar_n = 3
  pos_n = 4


              Bar 0          Bar 1          Bar 2
                                                      _
           XXXXXXXXXXX    XXXXXXXXXXX    XXXXXXXXXXX   |
Pos 3      XXXXXXXXXXX    XXXXXXXXXXX    XXXXXXXXXXX   | bar_w
           XXXXXXXXXXX    XXXXXXXXXXX    XXXXXXXXXXX  _|
                                                       
           XXXXXXXXXXX    XXXXXXXXXXX    XXXXXXXXXXX
Pos 2      XXXXXXXXXXX    XXXXXXXXXXX    XXXXXXXXXXX
           XXXXXXXXXXX    XXXXXXXXXXX    XXXXXXXXXXX

           XXXXXXXXXXX    XXXXXXXXXXX    XXXXXXXXXXX
Pos 1      XXXXXXXXXXX    XXXXXXXXXXX    XXXXXXXXXXX
           XXXXXXXXXXX    XXXXXXXXXXX    XXXXXXXXXXX  _
                                                      _| pos_gap
           XXXXXXXXXXX    XXXXXXXXXXX    XXXXXXXXXXX
Pos 0      XXXXXXXXXXX    XXXXXXXXXXX    XXXXXXXXXXX
           XXXXXXXXXXX    XXXXXXXXXXX    XXXXXXXXXXX

                                     |--|
                                    bar_gap

          |-----------------------------------------|
                             size


Other parameters:

st0        0.100     # start time (s) [start with 100ms of blank]
stn       40.000     # duration (s) [stimulus lasts for 40 seconds]
cx         0.0       # Center horizontal (deg) [placement on screen]
cy         0.0       # Center vertical (deg)
direction 45         # Orientation of the entire bar field (degr)
seed    1777         # Randomization seed
seq_type   0         # 0-each bar independent, 1-one bar overall
bar_n      3         # Number of bar segments
pos_n      4         # Number of bar positions
size       1.0       # Overall length of bar field (degr) [can use bar_l]
bar_w      0.1       # Bar width (degr)
bar_gap    0.0       # Separation between bar segments along bar (degr)
pos_gap    0.1       # Separation between positions orthog to bar (degr)
dt         1         # Number of video frames to hold bar (degr)
dt_off     0         # Gray frames between stimuli (degr)
bar_amp    1.0       # Brightness of bar [0..1] (black to white)
bgval      0.0       # background value [0..1] (black to white)

For sequence type 0 (seq_type), a bar is drawn at one (or none) of the positions for dt video frames (typically 10 ms) independently for each bar. So the stimulus will explore all possible patterns such as (where the bars are shown as a single line of X's):

        B1        B2        B3

P4   XXXXXXXX  
P3             XXXXXXXX            
P2                       XXXXXXXX
P1  


P4             
P3   XXXXXXXX  XXXXXXXX  XXXXXXXX            
P2                     
P1  


P4             
P3
P2   
P1   XXXXXXXX            XXXXXXXX              

Etc. For seq_type 1, only one bar is illuminated at a time, chosen randomly across the entire grid of bars, or no bar is shown at all.