PSYCH481 Lecture Notes - Optic Disc, Christoph Scheiner, Color Vision
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25 Nov 2012
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●One rock group accused of encouraging suicide by including command “do it”
recorded backward
●Begg, Needham, Bookbinder – examined this by playing backwards or
forwards message and tested whether people could recognize message played
backward and whether they agreed with message played in forward direction
found that hearing backward message helped you recognize same message
played backward again – but meaning was lost
●subliminal perception – perception of stimulus, as indicated by a change in
behaviour, at an intensity sufficient to produce a conscious sensation
person denies detecting stimulus yet stimulus has measurable effect on
behaviour
effects are subtle and special procedures required to demonstrate them
■Cheesman and Merikle – looked at effect of presenting word just
before students were asked idenity colour of brief flash of light
●if word and colour name were different then it took longer to identiy
colour – incongruent priming
■indicate that perception is complex process
●involves sense receptors and physiological process
●Merickle – some tapes contain messages that are too weak for human ear to
detect under any conditions and some when subjected to specrtographic
analysis (detects voiceprints) contained none at all
●Pratkanis – tapes for memory or self-esteem – participants didn't know which
was which and mixed them up
Vision
Light
●light consists of radiant energy similar to radio waves – oscillates as it is
transmitted from source
●wavelength – distance between adjacent waves of radiant energy; in vision,
most clearly associated with perceptual dimension of hue
●wavelegnth for visible light ranges from 380-760 nanometres (380 – violet, 760
– red)
●entire range of wavelength is called electromagnetic spectrum and part our
eyes can detect is visible spectrum
The Eye and Its Function
●cornea – transparent tissue covering front of eye; admits light
●sclera – tough white membrane that is outer layer of eye
●iris – pigmented muscle of eye that controls size of pupil – contains two bands
of muscle
brain controls these muscles and regulates size of pupil
●aqueous humour - space behin cornea is filled with (watery fluid)
constantly produced by tissue behin cornea that filters fluid from blood
nourishes cornea and other portions of eye in place of blood vessels – must
circulate
if produced too quickly or if passage that returns it to blood becomes
blocked, pressure within eye can increase and cause damage to vision
(glaucoma)
no blood vessels – transparency of cornea
●lens – transparent organ situated behin iris of eye; helps focus an image on
retina (inner surface of back of eye)
image is upside down and reversed from left to right
brain compensates for this alteration and interprets information
appropriately
contains no blood vessels – functionally dead tissue
shape is flexible – special set of muscles can alter shape so eye can obtain
images of nearby or distant objects
accommodation- change in shape of lens to adjust for distance
●length of eye normally matches bending of light rays produced by cornea and
lens so that image of visual scene is sharply focused on retina
for some people length of eye doesn not match bedning of light rays so
iamge is out of focus – need extra lens in front of eye
near sighted - eyes too long (front to back) so need concave lens to
correct focus
far sighted – eyes too short so need convex lens
as people age, lens becomes less flexible and becomes difficult to focus on
objects close to them – need convex lens
●retina – tissue at back of inside surface of eye that contains photoreceptors
and associated neurons (performs sensory functions of eye)
embedded in retina are over 130 million photoreceptors
photoreceptors – receptive cell for vision in retina (rod or cone);
specialized neurons transduce light into neural activity
■information from photoreceptors is transmitted to neurons that send
axons toward one point at back of eye (optic disc)
■optic disc – circular structure located at exit point from retina of axons
of ganglion cells that form optic nerve; all axons leave eye at this point
and join optic nerve which travels to brain
■no photoreceptors in form of optic disc so that portion of retina is blind
retina has three layers – light passes successively through ganglion cells
(front), bipolar cells (middle) and photoreceptor layer (back)
■cells located above photoreceptors are transparent
●Johannes Kepler – astronomer suggested that retina, not lens, contained
receptive tissue of eye
●Christopher Scheiner – 1625 proved that lens is only focusing device
●photoreceptors respond to light and pass info to bipolar cells by means of
transmitter substance
bipolar cells – neuron in retina that receives information form
photoreceptors and passes it on to ganglion cells, from which axons
proceed through optic nerves to brain
●bipolar cells transmit information to ganglion
ganglion cells – neuron in retina that receives informaiton from
photoreceptors by means of bipolar cells and form which axons proceed to
optiv nerves to brain
●photoreceptor – responds to light that reaches its immediate vicinity
●ganglion cells – responds to information from many different photoreceptors
●retina also contains neurons that interconnect both adjacent photoreceptors