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Lecture 15 Experiment 3

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Measure Hysteresis Loop. Aspect Ratios: 0.5, 0.75, 1, 1.2, 1.5, 2 ... Measure Hysteresis Loop. Register if subject saw at least one perceptual switch during the trial ... – PowerPoint PPT presentation

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Title: Lecture 15 Experiment 3


1
Lecture 15Experiment 3
  • Martin Giese

2
Programming the Experiments
3
DrawPoints
High-level function that plays a movie with
dots DrawDots(f, A, t) plays sinusoidal tone
with frequency with frequency f
and amplitude A for t seconds Playsound(f, A, t,
An, fn, Bn) plays sinusoidal tone with band pass
background noise with mid frequency fn and band
width /-Bn
4
Reading In Key Presses
Simple example function
function key_demo()   initialization ret_
strg wait for a valid key
press while strcmp(ret_strg, 'a', 'l') 0,
disp('Enter String.) ret_strg
getchar end actions for admissible
letters a and l if strcmp(ret_strg, 'a') 1,
disp('A') elseif strcmp(ret_strg, 'l')
1, disp('L') end
5
Data Analysis
6
Data Analysis
  • Thresholds from probability data
  • 50 threshold
  • Cool (optional) fit logistic threshold function
  • Thresholds directly from adjustment methods /
    stair case
  • Statistics for comparing thresholds
  • t-test (pairwise comparisons) if enough items
    watch for (de)pendent measures !
  • non-parametric test for few items
  • ANOVA (next lecture)
  • Extremely cool (idea for final project)run 2AFC
    experiment and estimate d

7
Data Analysis
  • Correction of the a level
  • Problem test difference between 2 AFs
  • Given N threshold values for K values of the
    frequency ?? Akn and Akn
  • Possibilities
  • t-test (pairwise comparisons) ? K independent
    tests
  • Better ANOVA (next lecture !)
  • How can we combine the results from K independent
    tests?

8
Data Analysis
  • P(single test significant even though H0 true) lt
    a
  • P(single test non-significant if H0 true) gt 1-
    a
  • Tests independent
  • P(all K tests non-significant if H0 true) gt (1-
    a)K
  • P(at least one out of the K tests significant if
    H0 true) lt 1 - (1- a)K aeq

9
Data Analysis
Equivalent significance level for K independent
tests aeq 1 - (1- a)K ?? a 1 - (1-
aeq)1/K For large K a ? aeq/K (Bonferoni
correction)
Example K 4 aeq 5 a 1.27
10
Experiments
11
Measuring Percept Probability Dependent on Aspect
Ratio
  • Aspect Ratios 0.5, 0.75, 1, 1.2, 1.5, 2
  • 3 display cycles
  • Register if subject saw horizontal or vertical
    motion or the whole trial
  • Neglect trials with a perceptual switch
  • Calculate percept probabilities
  • 30 repetitions per condition
  • 3 subjects

12
Measure Switching Probability Dependent on Aspect
Ratio
  • Aspect Ratios 0.5, 0.75, 1, 1.2, 1.5, 2
  • 6 display cycles
  • Register if subject saw at least one perceptual
    switch during the trial
  • Calculate switching probabilities
  • 20 repetitions per condition
  • 3 subjects

13
Measure Hysteresis Loop
  • Aspect Ratios 0.5, 0.75, 1, 1.2, 1.5, 2
  • Ascending and descending series

ascending 0.5-0.75 0.5-0.75-1 0.5-0.75-1-1.2
0.5-0.75-1-1.2-1.5-2
descending 2-1.5 2-1.5-1.2 2-1.5-1.2-1
2-1.5-1.2-1-0.75-0.5
14
Measure Hysteresis Loop
  • Register if subject saw at least one perceptual
    switch during the trial
  • Plot P(horizontal was seen in ascending trials)
    and 1-P(vertical was seen in descending trials)
  • Quantify area of the loop
  • 20 repetitions per condition
  • 3 subjects

15
Quantify Visual Inertia
  • Prime quartet with motion that forms angles a
    and 90o- a with the sides of the quartet
  • Angles 0, 15, 30, 45, 60, 75, 90o
  • Vary aspect ratio of the quartet in a staircase
  • 5 reversals of change of the AR
  • titrate the influence of the priming stimulus
    against the change of the aspect ratio (AR) of
    the quartet

16
Quantify Visual Inertia
  • Use deviation from aspect ratio without priming
    as measure for priming effect
  • 1 repeat per subject
  • 3 subjects
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