PSY270 Lecture 9
Visual imagery: seeing in the absence of a visual stimulus
Experience of being able to visually remember seeing the Pacific Ocean, what’s in your kitchen, etc.
Mental imagery: ability to recreate the sensory world in the absence of physical stimuli, also occurs in senses other than vision.
ability to imagine tastes, smells, tactile experiences, melodies of familiar songs…
Imagery provides a way of thinking that adds another dimension to the verbal techniques usually associated with thinking.
Imagery is associated with everyday experiences.
Imagery in the History of Psychology
Early images about imagery
Wundt : proposed images were one of three basic elements of consciousness, along with sensations and feelings.
oBecause images accompany thought, studying images was a way of studying thinking.
Debate: imageless thought debate – Artistotle: “thought is impossible without an image”
Galton: imagery not required for thinking – observed people who had great difficulty forming visual
images still capable of thinking.
Behaviorists: images are invisible to everyone except the person experiencing them, therefore should not
waste time studying. This changed when cognition was reborn.
Imagery and the cognitive revolution
Cognitive psychologists developed ways to measure behaviour used to infer cognitive processes
Paivio: showed it was easier to remember concrete nouns than abstracts (truth/justice), which are hard to image.
oTechnique: Paired-associate learning
oHypothesis: conceptual peg hypothesis: concrete nouns create images that other words can “hang onto”.
Shepard & Metzler: inferred cognitive processes by using mental chronometry, which determined amount of time needed to
carry out various cognitive tasks.
oCoglab: mental shape rotation experiment
oTime took to decide that two views were same directly related to how different angles were between the two views.
oParticipants were mentally rotating one of the views to see if it matched the other.
oFirst study to apply quantitative methods to study imagery and suggest imagery and perception may share same
Imagery and perception: do they share the same mechanism?
this assumption is based on observation that although mental images differ from perception (not as vivid/long lasting),
imagery shares many properties with perception
Shepard & Metzler results: mental and perceptual images involve spatial representation of stimulus.
Kosslyn’s mental scanning experiments
participants create mental images and then scan them in their minds
participants memorize picture of object (boat) and focus on one part of the boast (anchor) then asked to look for another
part of boat (motor) and press “true” button when they found this part or “false” if they couldn’t find it.
Reasoned that if imagery (like perception) is spatial, then take longer for participants to find images located farther from
initial point of focus (since they are scanning)
oThis is what happened.
oLea: proposed that participants may have encountered interesting parts (cabin) or distracted
oKosslyn et al: repeated this experiment by using a map.
Pylyshyn: proposed idea imagery debate: whether imagery is based on spatial mechanisms (like
perception) or based on mechanisms related to language (propositional mechanisms)
PSY270 Lecture 9
The imagery debate: is imagery spatial or propositional?
Kosslyn: im agery involve s spatial representation – different p ar t s of im age c a n b e d e s c ri bed a s cor r e s p o n ding to spe c
loc a tio n s in spa c e
oDis a gre e d – Pylyshy n
Just b e c a us e we ex p eri enc e im agery a s spati al, d o e s n’t me a n that is the u n d erlying repre s e n
Spati al ex p eri enc e of mental i m age s is an epipheno menon – something that a c c ompanie s re al me c hanis
b u t not a c tually par t of the me c hanism.
Mental im age s in dic a te that something is h ap p ening in the m i nd, b u t d o n’t tell u s h o w it is h
Propos e d a propositional representation: relatio n ships c a n b e repre s e nted b y abst r a ct symb ols
(eq u atio n/statement).
Spati al repre s e ntation: involve s a spati al layo u t sh owin g a c a t an d table
oDepictive repre s e ntatio n s: like re alistic picture s that re s e mble an o bje c t
Pylyshyn: p ropos e d tacit knowledge explanation – p ar ticipants u n cons cio u sly u s e k n owledge ab o u t the world in maki
their ju d g ments.
oPar ti cipants sti m ulated the re s ult in Kossly n’s ex p eri ment – sti m ulate a s pe c ts that wo uld o c c ur b a s e
kn ow that u sually h ap p ens when they are lookin g at the re al s c e ne.
Finke & Pink er: four d ot display an d ar row p ointin g a s king if there wa s a dot
oLonger to re s pond for g re a ter distanc e s b etwe e n ar row an d d o t.
oPar ti cipants did n’t h ave much ti m e to memoriz e distanc e s, therefore unlikely u s e ta cit k n owledge.
Comparing imagery and perception
Siz e in the visual fi eld
oKosslyn: relatio n ship b etwe e n viewing distanc e an d ability to p erc eive d etails also occ ur for mental
Par ti cipants – im agine elep h ant an d rab bi t to g ether // rab bit an d fly
Asked q u e s tio n s about rab bit an d to d o a “mental walk ta sk” (i magine they were walking tow
mental im age of an ani m al, e s ti m ate h ow far away)
Answered q u e s tio n s about rab bi t more rapidly when it wa s clos e r / filled more of the visual fi
Par ti cipants h ad to mo v e clos er for small ani m als than large ani m als
Evidenc e: ide a that im age s are spati al just like p erc e ptio n
Intera c tio n s of im agery an d p erc e ptio n
oIf i m agery affe c ts p erc e ption (or vic e v ers a ) then b o th h ave a c c e s s to the s a me me c hanisms
oPerky: d emonst r ation of intera c tio n b /w p erc e ptio n an d im agery
Par ti cipants to “proje c t” visual i m age s of com m o n o bje c ts o nto a s c re e n an d d e s c ribe the s e
Perky wa s b a ck p rojecting a v ery dim i m age of this o bje c t onto the s cre e n
•Asked to cre a te im age of b anana, projec ted i m age of b anana.
Par ti cipants’ d e s c riptio n s of im age matched im age s Perky wa s proje ctin g.
Non e of his p ar ticipants notic e d there wa s an a c tual picture o n the s cre e n – mi staken a c tual
mental im age.
oFarah: replic a ted Perky’s re s ult s
Par ti cipants im agine eit her H o r T o n s cre e n, pre s s b u t t o n that c a us e s two sq u are s to fla s h o
an o ther.
One of the sq u are s h ad target, an d p ar ticipant indic a te whether let t er in first sq u are or s e c o n
Target let t er d ete c ted more a c c urately when im agining s a me lett er.
Perc e ptio n an d i m agery share me c hanisms.
Is there a way to resolve the imagery debate?
And erso n: c a n’t rule out pro p o sitio n al ex planatio n
Farah: difficult to rule out Pylyshy n’s ta cit kn owledge ex planation
oPossible influenc e d b y p a s t ex p erienc e s
oWe sh o uld inv e s ti gate h ow b rain re s ponds to visual im agery inste a d of b ehaviou ral ex p eri ments.
PSY270 Lecture 9
Imagery and the brain
Imagery neurons in the brain
Kreiman et al: study patients who had electrodes implanted in various areas of medial temporal lobe in ord
source of sever epileptic seizures (uncontrollable by medication)
oImagery neurons: respond both to perceiving an object and to imagining it (baseball but not face)
measured brain activity through PET of fMRI
oparticipants create visual images/ or not (baseline)
osubtract difference to see which areas were activated by imagery.
LeBihan et al: demonstrated both perception and imagery activate visual cor tex.
oActivity in the striate cor tex increased when person observed presentation of actual visual stimuli (m
“perception) and when people was imagining the stimulus (imagery).
oGreater response in visual cortex from imagery questions.
Ganis et al: de monstrated overlap between brain areas activated by perceiving an object and those activat
men tal image of t he object.
ofMRI to measure activation under 2 conditions – perception and imagery
perception: observed drawing an objet (eg tree)
imagery: told to imagine a picture they had studied before
oactivation in frontal lobe for perception and imagery
shows not much difference between activation caused by perception and imagery.
Some difference near back of brain – greater for perception because lovaction of visual recei
Amedi et al: showed overlap and found when par ticipates were creating images using visual imagery, som
with nonvisual areas (hearing/touch) deactivated.
oVisual men tal images more fragile than real perception, deactivation helps limit irrelevant activity fr
Overlap supports idea that imagery and perception share some mechanisms.
Transcranial magnetic stimulation (TMS)
Pylyshyn: brain activity in response to imagery may indicate that something is happening, bu t m ay have no
causing imagery epiphenomenon.
oKosslyn et al: did experiment using TMS technique.
Presented TMS to visual area of brain while carrying out perception / imagery task
•Perception: viewed display briefly and make judgement
•Imagery: actually looked at it
•Measured reaction time
•Stimulation caused slower response for both perception and imagery
Brain activation occurs in response to imagery is not epiphenomenon and brain activity in th
cortex plays a causal role in both perception and imagery.