How to Draw 'oval' for 50 ms for 5 times and 350 ms for 5 times "randomly"'. The total number of trials will be 10

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ANKIT MAURYA
ANKIT MAURYA 2022-1-25
回答： Chetan 2023-11-16
How to Draw 'Oval' for 50 ms for 5 times and 350 ms for 5 times "randomly"'. The total number of trials will be 10
Following code I have written, but i am not getting where I am making the mistake. Please do help me immediately regarding this. I would be grateful to you all. Thank You.
Code:
% Clear the workspace and the screen
Screen('Preference', 'SkipSyncTests', 1);
sca;
close all;
clear;
% Delay_time is a variable that will take up 10 random values among 0.05s and 0.35s
Delay_time = zeros(1,10);
Delay_time (1:5) = 0.05;
Delay_time (6:10) = 0.35;
Delay_time = Delay_time (randperm(10));
% Here we call some default settings for setting up Psychtoolbox
PsychDefaultSetup(2);
% Get the screen numbers
screens = Screen('Screens');
% Draw to the external screen if avaliable
screenNumber = max(screens);
% Define black and white
white = WhiteIndex(screenNumber);
black = BlackIndex(screenNumber);
% Open an on screen window
[window, windowRect] = PsychImaging('OpenWindow', screenNumber, black);
% Get the size of the on screen window
[screenXpixels, screenYpixels] = Screen('WindowSize', window);
% Get the centre coordinate of the window
[xCenter, yCenter] = RectCenter(windowRect);
% Make a base Rect of 200 by 250 pixels
baseRect = [0 0 200 250];
% For Ovals we set a miximum diameter up to which it is perfect for
maxDiameter = max(baseRect) * 1.01;
% Center the rectangle on the centre of the screen
centeredRect = CenterRectOnPointd(baseRect, xCenter, yCenter);
% Set the color of the rect to red
rectColor = [1 0 0];
for i_trial = 1:10
% Draw the rect to the screen
Screen('FillOval', window, rectColor, centeredRect, maxDiameter);
% Flip to the screen
Screen('Flip', window);
WaitSecs (Delay_time (i_trial));
end
% Clear the screen
sca;

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回答（1 个）

Chetan
Chetan 2023-11-16
Hi @ANKIT MAURYA
I understand you're working on a use case in MATLAB's Psychtoolbox, where you aim to display an oval on the screen for specified durations in a random order.
The issue seems to lie in how you're managing the screen updates and wait times. In Psychtoolbox, `Screen('Flip', window)` refreshes the screen, followed by `WaitSecs` to maintain the display for a certain duration.
You also need to clear the screen after each display. This can be achieved using `Screen('FillRect', window, black);` to fill the screen with the background color, followed by `Screen('Flip', window);` to update the screen.
Here's a revised portion of your code:
for i_trial = 1:10
Screen('FillOval', window, rectColor, centeredRect, maxDiameter);
Screen('Flip', window);
WaitSecs(Delay_time(i_trial));
Screen('FillRect', window, black);
Screen('Flip', window);
end
This should effectively clear the screen after each display.
I hope this helps!

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