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 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

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 OnscreenOffscreen

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

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

Direct drawing on the buffer versus using Sprites plunge sprite

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