visual stimulus generation icn, ucl session 5, 18 jan 2007 matlab for cognitive neuroscience
TRANSCRIPT
Visual stimulus generation
ICN, UCL
Session 5, 18 Jan 2007
MATLAB for Cognitive Neuroscience
Outline
• Display parameters
• Stimulus parameters
• Cogent 2000– Photographs and pictures– Text
• Cogent Graphics– Photographs and pictures– Text– Costume graphics
Display parameters
Reminder from previous session
thanks to Christian Ruff
config_display(screenMode, screenRes, black ,white, fontName, fontSize, number_of_buffers);
screenMode = 0; % 0 for small window, 1 for full screen, 2 for second screen if attachedscreenRes = 2; % 800 x 600 resolutionwhite = [1 1 1]; % foreground colour (optional)black = [0 0 0]; % background colour (optional)fontName = 'Helvetica'; % font parameters (optional)fontSize = 20; number_of_buffers = 5; % how many offscreen buffers to create
COORDINATE SYSTEM in cogent
Stimulus parameters
• Location• Size• Visibility• Number• Duration
The same parameters could be applied to TEXT stimuli as well
Let’s see a couple of examples
Limitations of Cogent 2000
• loadpict( filename, buff, x, y, w, h )
• preparestring( text, buff, x, y )
• t = drawpict(imageBufferNumber)• Gives control over location, timing, size and
number• Not flexible for: drawing shapes, generating noise,
changing contrast
Solution: use Cogent Graphics
Let’s see an example
Drawing screens in cogent graphics
Onscreen Offscreen
start_cogent
config_display(screenMode, screenRes, black ,white, fontName, fontSize, number_of_buffers);
Onscreen
Offscreen
Ons
cree
n
cgflip(0,0,0); cgflip(0,0,0);
cgtext(word,wordX,wordY);
plunge
t1 = cgflip;
Off
scre
en
plunge
Direct drawing on the buffer versus using Sprites
plunge
plunge
plunge
plunge
plunge
sprite
why Sprites?• Complicated graphics
(do once, use many times)
• Multiple items to be place in different locations
• Animations