Experiment design
Research Methods
Fall 2010
Tamás Bőhm
Elements of experiment design
• Question
• Method
• Stimulus
• Control
• Interpretation
Question
• Functional specialization of the cortex
• Development of functions
(ontogenesis & phylogenesis)
• Operation of specific functions
Question
• Functional
specialization
of the cortex
Question
• Development of functions
Question
• Operation of specific functions
What determines
the brightness of a
surface?
Method
• Behavioral/psychophysics
• Electrophysiology
• Imaging
• Genetics
• …
Stimulus
Ishihara plates:
tests wavelength
sensitivity
(the tuning of
retinal red and
green cones)
Stimulus
Brightness of the
spots need to be
controlled
1. Constant
brightness
(isoluminance):
hard to achieve
2. Randomizing
light intensity
Stimulus
Stimulus
• Stereopsis (binocular
depth perception):
based on retinal
disparity
• Can break camouflage
Stimulus
Julesz Béla’s random dot stereograms (RDS)
Stimulus
Stimulus
http://ruccs.rutgers.edu/%7Eikovacs/SandP/rds/rds.html
Stimulus
At which level of visual
processing does
stereopsis happen?
Question:
functional specialization
Method: psychophysics,
electrophysiology
– 1950s: at very high level (after figure-ground
separation and form recognition)
• Monocular form cues & contours are essential
• Could not find neural substrates
– Julesz: it must be early in processing!
• No monocular cues on RDSs
• Could find the corresponding binocular depth cells
Stimulus
response of a
binocular depth cell
• Hubel and Wiesel 1962
• Barlow, Blakemore and Pettigrew 1967
• Bishop 1969
• Gian Poggio 1984: disparity selective
neurons in V1, V2, V3, V3a
Stimulus
Take home message: use ‘clean’ stimuli
Stimulus
Binocular
rivalry
Stimulus
At which level of visual
processing does this
happen?
Question:
functional specialization
Method: psychophysics
– 1980s: at low level
• Competition between the two eyes
• Reciprocal inhibition of monocular neurons
Stimuli
• Conventional rivalry inducing pair:
eye-of-origin and stimulus coherence
Stimuli
• Patchwork rivalry stimulus (Kovács et al
PNAS 1996): stimulus coherence only
Stimuli
Stimulus
At which level of visual
processing does this
happen?
Question:
functional specialization
Method: psychophysics
– 1980s: at low level
• Competition between the two eyes
• Reciprocal inhibition of monocular neurons
– Kovács et al.: later in processing
• Competition also between two coherent pictures
• After the input layer of V1
Stimulus
Logothetis
Stimulus
Take home message:
get rid of extraneous
factors in the stimuli