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Lecture

PSY230H1 Lecture Notes - Stimulus Modality, Blauw-Wit Amsterdam, Afterimage


Department
Psychology
Course Code
PSY230H1
Professor
d

Page:
of 6
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 perceptionperception 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 cellsneuron 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 and
adjacent ganglion cells – indicates that some kinds of information processing are
performed in retina
retina – contains 2 types of photoreceptors: 125 million rods and 6 millions
cones
rodssensitive to light but cannot detect changes in hue; function in dim light
cones – responsible for acute daytime vision and for colour perception; function
when light is bright enough to see things clearly
fovea – small pit near centre of retina containing densley packed cones;
responsible for most acut and detailed vision; 1 mm in diameter
cones connected to one ganglion each
when we look at point in visual field, we move our eyes so that image of that
point falls directly on cone-packed fovea
rods – increase as move further from fovea; connected to many ganglion (up to
100 each)
ganglion receiving info from many rods is sensitive to very low levels of light
rods are responsible for sensitivity to dim light but visual information lacks
sharpness
Transduciton of Light by Photoreceptors
molecule responsible for transduction is derived from vitamin A, in absence of
light it is attached to protein and forms photopigment
photopigment – complex molecule found in photoreceptors; when struck by
light, splits apart and stimulates membrane of photoreceptor in which it
resides
photoreceptors of human eye contain 4 kinds of pigment (1 for rods, 3 for cones)
when photon strikes photopigment it splits apart into 2 molecules causing series
of chemical reactions that stimulate photoreceptor and causes it to send
message to bipolar cell and form synapse
bipolar cell sends message to ganglion cell – sends message to brain
intact pigment has characteristic colour (Rhodopsin, in rod, is pink) but are
bleached once split apart
Franz Boll – discovered this when he removed eye from animal, pointed it
toward light and found image on retina was still there but faded where light had
fallen – led investigators to suspect chemical reaction
after photopigment is split, energy from photoreceptor's metabolism cause 2
moelcules to recombine and is ready to be bleached again
photoreceptors – contain thousands of molecules of photopigment each; number
intact depends on rate which they are being split and put back together
Adaption to Light and Dark
dark adaption – process by which eye becomes capable of distinguishing dimly
illuminated objects after going from bright to dark area
when high levels of illumination strike retina, regeneration falls behin bleaching
so rods aren't sensitive to light (only small number of photopigment intact –
probability that photon will strike molecule is low)
eventually regeneration overcomes bleaching process
Eye Movements
Riggs, Ratliff, Cornsweet and Cornsweet – devised way to project stabilized