Visual stimulus generation

1. Visual stimulus generation ICN, UCL Session 5, 18 Jan 2007 MATLAB for Cognitive Neuroscience

2. Outline • Display parameters • Stimulus parameters • Cogent 2000 • Photographs and pictures • Text • Cogent Graphics • Photographs and pictures • Text • Costume graphics

3. screenMode = 0; % 0 for small window, 1 for full screen, 2 for second screen if attached screenRes = 2; % 800 x 600 resolution white = [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 Display parameters Reminder from previous session config_display(screenMode, screenRes, black ,white, fontName, fontSize, number_of_buffers); thanks to Christian Ruff

4. COORDINATE SYSTEM in cogent

5. 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

6. 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

8. Let’s see an example

9. Drawing screens in cogent graphics Onscreen Offscreen

10. config_display(screenMode, screenRes, black ,white, fontName, fontSize, number_of_buffers); start_cogent Onscreen Offscreen

11. plunge plunge Onscreen Offscreen t1 = cgflip; cgflip(0,0,0); cgflip(0,0,0); cgtext(word,wordX,wordY);

12. plunge plunge plunge plunge Direct drawing on the buffer versus using Sprites plunge sprite

13. Complicated graphics (do once, use many times) Multiple items to be place in different locations Animations why Sprites?