Gabor Gampang Week7-Thu

8/12/2019 Gabor Gampang Week7-Thu

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COGS 119

MATLAB for Experimental Research

Fall 2013 Week 7

Basic Vision Science with Psychtoolbox


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Gabor

! Simple cells in the primary visual cortex (V1) of theprimate brain can be modeled using Gabor filters, which

is a product of sine waveand a Gaussian.


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Gabor

! A gabor is characterized by several parameters:! Orientation (theta)! Spatial frequency (sf)! Width (sd)! Size


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Example gabors

theta = 90 theta = 45

sf = 5 sf = 10

sd = 0.2 sd = 0.2

size = 100; size = 100

theta = 90 theta = 45

sf = 10 sf = 10sd = 0.2 sd = 0.4

size = 100; size = 100


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Creating a gabor in Matlab

Gabor = Sinewave * Gaussian

Step 1: Create Sinewave

Step 2: Create Gaussian

Step 3: Multiply


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prep_gabor.m


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prep_gabor.m

sinewave andgrating

gaussian

multiply sinewave and gaussian

inputs


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Step-by-step

prep_gabor.m

sinewave andgrating

gaussian

multiply sinewave and gaussian

inputs


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Meshgrid

!" $ %&'( !) $ *%( +,-+. $ '/( 0.+!12- $ *%%(

33 45678 $ 0-!,9:1";.?-;@*6*60.+!12-A*BB(

33 10.9-!?;5B( .51! C))( ?C;9:.7B(

33 10.9-!?;7B( .51! C))(


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ramp33 :.0> $ ?C!;+,-+.D>1E*F%BD;5@5?B A !1=;+,-+.D>1E*F%BD;7@7?B(

33 10.9-!?;:.0>B( .51! !GH.:-( .51! C))(


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Sinewave (grating)

33 9:.+1=9 $ !1=;ID>1D!)D:.0>B(

33 10.9-!?;9:.+1=9B( .51! !GH.:-( .51! C))(


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Gaussian

33 9.H!! $ -5>; @;;5@5?B&JI A ;7@7?B&JIBE;ID!"JIBB(

33 10.9-!?;9.H!!B( .51! !GH.:-( .51! C))(


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Gabor

33 9.KC: $ 9.H!!&D9:.+1=9(

33 10.9-!?;9.KC:B( .51! C))(


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Orienting gabor

! Download gabor_sweep_orient.mfrom the classwebsite and run it.

!Now, lets look at the code closely to understand howthe gabor changes orientation.


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Displaying gabor in PTB

! Download disp_gabor.mfrom the class website andrun it.

!disp_gabor.mprepares a gabor (callingprep_gabor.m) and displays it in Psychtoolbox.

! Inputs:! sd, sf, theta (gabor parameters)! offx, offy (offset from the center of the screen)


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disp_gabor.m


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disp_gabor.m

Call prep_gabor.m

Make gabor texture

Draw gabor texture

inputs


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Experiment with gabors

! Lets display multiple gabors with various properties (sd,sf, theta) on various locations on the screen.

!Download gabor_experiment.mfrom the classwebsite and run it.

! Lets look at the code closely to understand how itdisplays gabors.


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gabor_experiment.m

Experiment has the following trial types:

! gabor with sd = 0.1, sf = 10, theta = 5;! gabor with sd = 0.1, sf = 10, theta = 355;! gabor with sd = 0.1, sf = 16, theta = 5;! gabor with sd = 0.1, sf = 16, theta = 355;


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gabor_experiment.m (trial set-up)

Open a file to write

Set-up the trials gaborparameters

!! #$%& '()


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rng

:=9;L!,H))


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gabor_experiment.m (open window

and set screen parameters)


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gabor_experiment.m (prepare and

display gabors) Call prep_gabor.m

Make a texture for

the gabor and then draw itas in disp_gabor.m

Get user response and rt

Write into a file


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Exercise

! Read Fine and Boynton chapter 5 and do the exercisesthere in Matlab.

! Submit project choices instructions via E-mail

Documents

Gabor Gampang Week7-Thu