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Accurate Timing

Matlab Class 7 Hristiyan Kourtev & Xiaotao Su, Ph.D. Visual Psychophysicist & IT Group Leader Rutgers Center for Cognitive Science (RuCCS). Accurate Timing. GetSecs is a psychtoolbox function that provides highly accurate timing.

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Accurate Timing

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  1. Matlab Class 7Hristiyan Kourtev &Xiaotao Su, Ph.D.Visual Psychophysicist & IT Group LeaderRutgers Center for Cognitive Science (RuCCS)

  2. Accurate Timing • GetSecs is a psychtoolbox function that provides highly accurate timing. • It returns the number of seconds since the machine has started up • To test precision on your machine, type:GetSecsTick Command Window: a = GetSecs GetSecs – a GetSecs – a GetSecs – a GetSecs – a

  3. KbCheck • KbCheck is used to check if a key is being pressed and to find out what key is being pressed. • Returns three values • [key_press, secs, key_code]=KbCheck

  4. KbCheck • KbCheck is used to check if a key is being pressed and to find out what key is being pressed. • Returns three values • [key_press, secs, key_code]=KbCheck Vector representing all of the input keys. Elements in the vector are set to 1 if pressed or 0 if not Time that this test took place (This is from GetSecs function) 1 or 0 depending on if there was a key press

  5. Speed Test Game disp('NOW!'); timer = GetSecs; while 1 [key_is_down, secs, key_code] = KbCheck; if(key_is_down) break end end elapsed_time = secs - timer; disp(['Your time was ', num2str(elapsed_time)]); end %speed_test.m %tests your reaction time WaitSecs(1); disp('Ready?'); num_sec_to_start = rand*5+1; WaitSecs(num_sec_to_start); too_soon = 0; timer = GetSecs; while ((GetSecs-timer)<num_sec_to_start) ... && (~too_soon) [too_soon, secs, keyCode] = KbCheck; if(too_soon) break; end end if(too_soon) disp('you pressed the key too early'); else

  6. Task 1 • Make it so if someone presses a key too early, the program give a message and exits. (Tip:first remove WaitSecs • [key_press, secs, key_code]=KbCheck Vector representing all of the input keys. Elements in the vector are set to 1 if pressed or 0 if not Time that this test took place (This is from GetSecs function) 1 or 0 depending on if there was a key press

  7. Speed Test Game disp('NOW!'); timer = GetSecs; while 1 [key_is_down, secs, key_code] = KbCheck; if(key_is_down) break end end elapsed_time = secs - timer; disp(['Your time was ', num2str(elapsed_time)]); end %speed_test.m %tests your reaction time WaitSecs(1); disp('Ready?'); num_sec_to_start = rand*5+1; WaitSecs(num_sec_to_start); too_soon = 0; timer = GetSecs; while ((GetSecs-timer)<num_sec_to_start) ... && (~too_soon) [too_soon, secs, keyCode] = KbCheck; if(too_soon) break; end end if(too_soon) disp('you pressed the key too early'); else

  8. What key was pressed? • The third returned value is a vector representing all the keys with 1’s for pressed keys and zeros for keys that aren’t pressed • To find the value of the key, use: key_name = KbName(key_code); This will return a string corresponding to that key_code

  9. Simple program to find key mapping names % get_key_name.m %find out what the name of the key is WaitSecs(1); KbWait; [key_is_down, secs, key_code] = KbCheck; name = KbName(key_code); disp(name);

  10. KbName works the other way around as well As you have seen: • key_name = KbName(key_code); You can also do the following: • return_key = KbName(‘return’); • esc_key = KbName(‘esc’); • up_key = KbName(‘up’); And this will get you the index of the element in the key_code vector that corresponds to that key

  11. key_code vector when esc is pressed esc’s key code is 27 key_code vector: Values: Indexes So, key_code(27) is 1

  12. Exit on esc %exit_on_esc.m esc_key = KbName('esc'); i = 0; while 1 i = i+1 [key_is_down, secs, key_code] = KbCheck; if(key_code(esc_key)) break; end end disp('Good Bye');

  13. Moving Dot %moving_dot.m clear all; screen_setup; up_key = KbName('up'); down_key = KbName('down'); left_key = KbName('left'); right_key = KbName('right'); esc_key = KbName('esc'); shape = [20, 20, 100, 100]; color = [255, 0, 255]; tic whiletoc<10 Screen(window, ‘FillOval', … color, shape); flip; [key_is_down, secs, key_code] … = KbCheck; if(key_code(esc_key)) break end end clear screen;

  14. Task 2 • Draw a circle • Make it so the arrow keys will move the circle • Make sure the circle cannot go outside of the boundaries of the screen.

  15. Task 3 - color differentiation (part 1) • Take subject name • screen_setup • trial loop (start with 5)color = [rand*255, rand*255, rand*255] • put circles 1-4 on the screen • one of the four circles will be slightly off (start with +/-50), color from the others on one of the three color dimensions (randomly chose dimension); careful that your deviation doesn’t go >255 or <0 • The subject will click on the circle they feel is different • record data (whatever would be useful) • if the subject was right in the last loop, the amount the color is off is cut in half, otherwise, increase by half • save trial data to csv tip: make a function to determine if the cursor is in a shape function is_in = in_shape(vect, mouse_x, mouse_y)

  16. Task 3 - color differentiation (part 2) Further additions: • allow the subject to press 1 - 4 to select a circle (using KbCheck) • put numbers in the circles Hint: You need to use the following commands: Screen('TextFont', window, fontName*);Screen('TextSize', window, fontSize**); Screen('DrawText', window, textString, x, y, textColor);*fontName can be “Arial”, “Verdana” or other *fontSize can be any number. Start with around 20 and adjust as needed

  17. Deploying Matlab Programs on other machines • The Matlab Builder/Deploytool – ‘deploytool’ • The Matlab Component Runtime (MCR) • Creating a standalone version of a Matlab program (Windows) • Creating a standalone version of a Matlab program (OSX) • The .NET Builder and deploying to the web

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