46-339 Lecture Notes - Trichromacy, Retina

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Published on 19 Apr 2013
School
University of Windsor
Department
Psychology
Course
PSYC 3390
Professor
Unit%7%Notes:%%Perception%
!
Thresholds%
threshold!(or!limen)‐‐the!point!when!a!psychological!and/or!physiological!effect!is!produced!
absolute!threshold‐‐the!least!amount!of!a!stimulus!needed!to!trigger!a!sensory!perception!(e.g.!
a!candle!at!one!mile!away)!
difference!threshold1(or!just1noticeable1difference)‐‐the!least!amount!of!difference!between!two!
stimuli!for!perception!to!occur!
!!
The%Eye%
the!structures!of!the!eye!from!the!diagram!are!as!follows:!
lens:!focuses!the!image!onto!the!retina!
pupil:!regulates!the!amount!of!light!entering!the!eye;!full!dark!adaptation!takes!about!30!
minutes!and!light!adaptation!about!1!minute!
iris:!the!colored!part!of!the!eye!
cornea:!the!soft,!outer,!protective!covering!of!the!eye!
retina:!contains!photoreceptor!cells,!rods!(which!detect!brightness!contrasts)!and!cones!
(which!detect!color)!
fovea:!an!area!of!the!retina!that!contains!all!cones!and!no!rods!
optic!nerve:!relays!visual!information!to!the!brain!
blind!spot:!where!the!optic!nerve!connects!to!the!back!of!the!eye!
!
The%Visual%Cortex%
information!travels!from!the!eyes!to!various!parts!of!the!brain:!
the!thalamus!
the!visual!cortex!of!the!occipital!lobe1
1
Hubel!and!Wiesel!have!developed!the!feature!detection!theory‐‐there!are!certain!cells!in!the!visual!
cortex!that!are!sensitive!to!certain!features!of!a!stimulus!
they!determined!there!were!three!types!cells!in!the!visual!cortex:!
simple‐‐provide!information!about!the!position!and!boundaries!of!a!stimuli!
complex‐‐provide!advanced!information!about!position!such!as!movement!
hypercomplex‐‐provide!abstract!information!such!as!shape!or!size!
!
Color%Perception%
subtractive!color!mixtures!deal!primarily!with!mixing!pigments!(e.g.!blue!and!yellow!mixed!
together!make!green)!
additive!color!mixtures!deal!primarily!with!mixing!lights!(e.g.!combining!a!green!and!red!light!will!
give!you!yellow)!
!
there!are!two!main!theories!of!color!perception:!
trichromatic!(or!YoungHelmholtz)!theory:!all!color!perception!derives!from!three!different!
color!receptors!in!the!retina!(usually!red,!blue!and!green);!while!this!theory!can!physically!
recreate!the!spectrum!of!colors,!much!like!your!TV!set!does,!it!cannot!explain!color!blindness!
or!negative!afterimages!
!
opponent!process!theory:!three!sets!of!color!receptors!(blue‐yellow,!red‐green,!black‐white)!
respond!to!determine!the!color!you!experience;!explains!both!color!blindness!(which!tends!to!
be!either!blue‐yellow,!red‐green,!or!full!color!blindness)!and!negative!afterimages;!this!was!
proposed!by!Ewald!Hering!
!
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