P C : B I

Basic Issues in Perception
Sensation vs. Perception
● Sensation:
− Early processing
− Physiological (neuronal)
● Perception:
− Later processing
− Psychological (interpretive)
Bottom-up and top-down processing
● Bottom-up processes (aka: data-driven)
− Based on information from the stimulus
● Top-down processes (aka: conceptually-driven)
− Based on knowledge, expectations, context
Perception: Constructed or Directly Experienced?
Constructive View
− Emphasizes the role of top-down processing in
arriving at a percept
Direct View
− Emphasizes the role of bottom-up processing in
arriving at a percept
The Basic Tasks of Visual Perception
● Pre-attentive Processing
− Before attention is directed at a stimulus array
− Organization of an incoming stimulus array into
discrete elements
● Post-attentive Processing
− After attention is directed at a stimulus array
− Identification of these elements for further processing
and categorization
 Perceptual Organizational Processes
» Grouping and Region Segmentation
● Grouping Principles
− Similarity
− Proximity
− Good Continuation
− Closure
Common Fate
− Element Connectedness
Common Region
Palmer and Beck (2007)
 Repetition discrimination task: “is repeated element a
circle or a square”
 RT was measured
 Stimuli
 Results
 Within was faster than between
» Figure-Ground
● Tendency to segment a visual scene as a figure
superimposed on a background
Figures relative to ground:
− Are bigger
− Contain more symmetrical features
− Are meaningful
− Are surrounded by other elements in the visual scene
− Are lower in the visual field
− Display convexity
» Global Precedence
● Aspects of the environment that are processed first
and automatically
− The whole or the parts?
Navon (1977)
 Presented big letters made up of small objects
 Different stimulus types:
 Big letter made up of small letters
♦ Consistent
♦ Conflicting
 Big letter made up of neutral stimuli
♦ Control Condition
 Subjects were given either
 “Local-directed” instructions: identify small object
 “Global-directed” instructions: identify large object
 RT to identify directed letter was measured
 RT to detect directed letter compared to neutral
 If local is a primitive
 Global directed condition
♦ Consistent
 No difference in RT
♦ Conflicting
 Slower RT
 Local directed condition
♦ Consistent
 No difference in RT
♦ Conflicting
 No difference in RT
 If global is a primitive
 Global directed condition
♦ Consistent
 No difference in RT
♦ Conflicting
 No difference in RT
 Local directed condition
♦ Consistent
 No difference in RT
♦ Conflicting
 Slower RT
Local is a primitive
Global is a primitive
 Global directed condition
 Consistent
♦ No difference in RT
♦ No difference in RT
 Conflicting
♦ Slower RT
♦ No difference in RT
 Local directed condition
 Consistent
♦ No difference in RT
♦ No difference in RT
 Conflicting
♦ No difference in RT
♦ Slower RT
Overall, global letters were reported more quickly (a
main effect)
Big letters not affected by identity of small letters (same
as neutral), but small letters were affected by identity of
big letter (Interaction)
Global Precedence Effect–global perceived before local
Is global precedence universal?
Ebbinghaus illusion
Davidoff, Fonteneau, and Fagot (2008)
 Tested Himba and UK participants
 Stimuli
Comparison stimuli
 Task
 Indicate which comparison stimulus “is most like the
 Global Precedence
♦ Choose left stimulus
 Local Precedence
♦ Choose right stimulus
 Results
 UK participants: global precedence (86% chose left)
 Himba participants: local precedence (77% chose right)
Multisensory Interaction and Integration
 Strong synesthesia (rare)
− Input to one sensory modality produces a perceptual
experience in that modality and another one
− Tend to be:
◘ Unidirectional
◘ Consistent
● Is strong synesthesia the result of early (sensory) or late
(perceptual) processing?
Bargary, Barnett, Mitchell, and Newell (2009)
 Stimuli
 McGurk Effect
♦ Simultaneous presentation of an auditory stimulus
(/b/) and a visual stimulus (/g/) leads to a blended
perception (/d/)
 Participants
 Graphemes-Color synesthetes
♦ For example: see purple when hear /b/ and see pink
when hear /d/
If synesthesia is due to:
 Sensory processing:
♦ Will see purple
 Synesthetic experience caused by sensation of a
 Perceptual processing
♦ Will see pink
 Synesthetic experience caused by blended
perception of a /d/
 Results
 Saw pink
 Strong synesthesia is the result of later (perceptual)
Weak Synesthesia (common)
− Linguistic cross-modal experiences (“cool” colors)
Martino and Marks (2001)
 Stimuli
 Tones presented with black or white square
 Task
 Classify tone as “high” or “low”
 Results
 Black square: low tones faster than high tones
 White square: high tones faster than low tones
 Weak synesthesia is the result of experience which leads
us to associate stimuli together
Comparing the Senses
» Vision and Audition
● Ventriloquist effect
− “Sound” perceived as coming from visual display
Schutz and Limbscomb (2007)
 Stimuli
 Musician playing a single note on a marimba with:
♦ Video
 Showing a long-note gesture
 Showing short-note gesture
♦ No video
 Task: estimate duration of notes
 Results
 No video: notes judged to be the same length
 Video: note with long-note gesture was judged to be
longer than note with short-note gesture
Vision and chemical senses
Morrot, Duchet, and Dubourdieu (2001)
 Stimuli
 White wine colored red
 Participants
 Wine experts
 Task
 Describe the smell of the wine
 Results
 Smell illusion: described smell with words used to
describe the smell of red wine (e.g., clove, cherry)
Vision and Touch
● Rubber hand illusion
Pavani, Spence, and Driver (2000)
 Methodology
 Held cubes vibrated on top and bottom
 Seen cubes lit up on top and bottom
 Light and vibration matched or mismatched
 Seen hands were aligned or misaligned with own hands
 Task: identify the source of vibration (top or bottom)
 RT was recorded
Cue-Position Mismatch
Cue-Position Match
Ehrsson, Rosen, Stockselius, Ragno, Kohler, and Lundborg
 Participants: upper-limb
 Rubber glove holding cube with LED on top and bottom
 Vibration to top or bottom of stump
 LED and vibration were simultaneous and consistent
 Results
 Participants felt vibration in phantom hand
♦ Resulted in feeling of ownership of the “hand”
» Audition and Touch
Hotting and Roder (2004)
 Participants: blind and sighted individuals
 Procedure
 Heard 1-4 tones
 Felt 1-4 vibrations to right index finger
 Task: Identify the number of vibrations
 Results
 As number of tones increased so did number of reported
vibrations (main effect)
 This effect was greater for sighted than blind participants
Enhanced tactile expertise or difference in multi-sensory
 Perception and Action
 Perception evolved to:
− maximize survival
− defend us from having to think
» Affordances
● Actions offered by an object
Ishak, Adolph, and Linn (2008)
 Apparatus
Candy at the end of a long flat stick
Task: Reach into aperture to retrieve candy
 Aperture size varied from trial to trial
 Possible Outcomes
 No attempt to retrieve candy
 Attempt to retrieve candy but got stuck (aperture too
 Retrieved candy
 Dependent variables
 Motor retention function
♦ % of trials on which an attempt was made, regardless
of success
 Affordance threshold
♦ Aperture size at which an attempt was made and
candy was retrieved 50% of the time
 Good aperture perception (knew when aperture was big
enough to retrieve candy):
 Motor decision function should be highest at aperture
threshold and drop precipitously below it
 Results
Motor decision function
Aperture Threshold
Enhanced visual analysis for items in close physical
Davoli and Abrams (2009)
 Task: visual search task (was target letter present in display
on a computer screen)
 Task Difficulty
♦ Difficult: many letters in display
♦ Easy: few letters in display
 Imagination
♦ Hands on sides of computer monitor
♦ Hands behind back
 RT to determine if target was present was measured
 Results
 RT increased as display size increased (main effect)
 RT increase was greater when imagining hands behind
back than when imagining hands on monitor (interaction)
Embodied perception
Proffitt, Bhalla, Gossweiler, Midgett (1995)
 Task: Estimate slant of two hills (both 5º)
 Before rigorous run
 After rigorous run (fatigue)
3 conditions
 Verbal
 Visual
 Haptic
Witt, Linkenauger, Backdash, Augustyn, Cook, and Proffit
 Participants did or did not suffer with minor, but chronic,
pain of back and/or lower extremities
 Task: estimate distance from various traffic cones
 Results
 Chronic pain sufferers judged distances to be longer
than those not suffering from chronic pain
 Visual perception evolved:
− to maximize survival (efficient “expenditure of energy”)
− to avoid having to think
Positive Complement
Witt, Linkenauger, Backdash, and Proffitt (2008)
 Participants putted into a practice putting hole
 Difficult: just over 7 feet
 Easy: just under 1½ feet
 Task: estimated size of hole
 Results
 Estimates of hole size were larger after easy than
difficult putts
 Another study found a negative correlation between
estimate hole size and golfing score
Varieties of consciousness
● Access consciousness
− What the cognitive system is actually doing
Phenomenal consciousness
− Knowledge of what our cognitive system is doing
Monitoring consciousness
− Ability to reflect on one’s cognitive processing
− General knowledge of self
Most cognitive processes occur outside of phenomenal
consciousness making self-report highly suspect
− Signal detection theory
◘ Perceptual experiences are the joint product of:
 Sensitivity of the particular sensory system
 Response bias (willingness to report the
Dissociations in consciousness
» Authorship Processing
● Set of processes that leads actions to be attributed
to the entities that caused them
 Illusion of conscious control
− Results from close proximity between relevant thought and
Wegner, Sparrow, and Winerman (2004)
 Methodology
 Confederate in back is giving
 Passive participant
 Looking in mirror
 Hears commands
 Does not hear commands
 Dependent variable
 “Rate degree to which you feel you are consciously
willing the arm movement”
 Results
 Higher rating when heard command than when did not
hear command
♦ Phenomenal consciousness in the absence of
access consciousness
Metcalfe and Greene (2007)
 Investigated metacognition of one’s sense of agency
 Participants played video game in which X’s and O’s moved
downward on the computer screen
 Task: use mouse to move cursor to touch the X’s, but avoid
the O’s
 Received 1 point for each X they touched
 At random times, game stopped and participants were
asked to rate the degree to which they had been in
control of the cursor (judgment of agency)
 Three independent variables:
 Speed at which X’s and O’s moved down the screen
♦ Fast
♦ Slow
 Fidelity of mouse cursor relationship (turbulence)
♦ No turbulence: perfect correlation between mouse
movement and cursor movement
♦ Turbulence: loose correspondence between mouse
movement and cursor movement
 How close the cursor had to be to the X to receive credit
for touching it
♦ Magic: within 10 pixels to receive credit
♦ No magic: must touch it to receive credit
 Two dependent variables:
 Hit rate: proportion of X’s that were touched
 Judgments of Agency (JoA) ratings: How in control was
 Predictions
 Hit rates should show similar patterns as JoA ratings if
performance is basis for JoA ratings
 They were responsible for the hit rates
 If similar patterns are not obtained, something other than
performance is the basis for the JoA ratings
♦ They were not responsible for the hit rates
 Results
 Speed
♦ Hit rates were greater in slow than fast, but JoA ratings
were the same
 Participants were metacognitively aware that their
performance was due to the speed with which the
X’s and O’s were falling
 Turbulence
♦ Hit rates were almost identical in turbulence and no
turbulence conditions, but JoA ratings were greater in
no turbulence than turbulence condition
 Participants were metacognitively aware that they
had little control over their performance in the
turbulence condition
 Magic
♦ Hit rates and JoA ratings were greater in the magic
than no magic conditions, but the difference was
greater for hit rates than JoA ratings
 Participants were metacognitively aware that they
had less control over their performance in the
magic condition
 Conclusion
 There is good metacognitive awareness of one’s sense
of agency
 Wegner et al. study is most likely the exception, rather
than the rule
● Access consciousness in the absence of phenomenal
● D.B. was completely blind in left visual field
− Unable to identify objects (no phenomenal
− Possessed knowledge of those objects, such as
location (access consciousness)
Weiskrantz (1986)
 Presented stimuli to left visual field
 D.B. reported that he did not see anything
 Forced-choice procedure to see what he “knew” about the
 Two alternative answers (I don’t know was not allowed)
 D.B. was asked to make a forced choice about some
aspect of the stimulus (where it was located)
♦ Performance was well above chance
Two distinct neurologic systems underlying vision
− What system
◘ Located primarily in visual cortex
◘ Relatively late in visual processing
◘ Responsible for identifying, recognizing, and
becoming aware of visual stimuli
− Where system
◘ Located primarily in subcortical structures
◘ Relatively early in visual processing
◘ Responsible for detection and localization
Systems are dissociated in blindsight
Subliminal Perception
 Can semantic (meaning-based) processing occur
outside of phenomenal consciousness
» Preconscious identification
Costello, Jiang, Baartman, McGlennen, and He (2009)
 Utilized semantic priming
 Processing of one stimulus (the prime):
♦ enhances the speed with which a related stimulus
(the target) is processed
♦ does not enhance the speed with which an
unrelated target is processed
 Binocular suppression paradigm
Visible and consciously perceived
Increased in
until visible
 Initially invisible target emerged from suppression sooner
when prime was related than when it was unrelated
The effects of subliminal primes
Questions of definition and method
Do subliminally presented stimuli influence behavior
− Depends
◘ What does “subliminal” mean?
◘ What does “influence” mean?
Marcel (1983)
 Task: identify color of presented patch
 Patch preceded by a word (prime) that was:
♦ Neutral (table)
♦ Matched (blue)
Priming: RT for match should be faster than neutral
 Two types of trials
 Supraliminal
 Subliminal
♦ Pretest: words presented until chance performance
(50%) was reached
 Predictions
 If subliminal perception exists
♦ Priming in both
 If subliminal perception does not exist
♦ Only priming in supraliminal
 Priming occurred in both conditions, but it was larger in
supraliminal than subliminal
But was subliminal truly subliminal?
Cheesman and Merikle (1984)
 Subjective vs. objective thresholds
 3 conditions
 Subjective (pretest: 50% identification of color patch)
 Objective (pretest: 25% in forced choice selection of
color patch)
 Supraliminal
Awareness (Supraliminal)
Subjective Threshold
Subject says
“I don’t see it” BUT
can guess what it is
Objective Threshold
Subject says
“I don’t see it” AND
can’t guess what it is
 Objective threshold
♦ If subliminal perception exists
 Priming should be obtained in objective
threshold condition
♦ If subliminal perception does not exist
 Priming should not be obtained in objective
 Results
Amount of priming (ms)
Subliminal Objective Subliminal Subjective
What is meant by influence behavior?
 Cognitive psychologists find effects of subliminal
perception to be on the order of 1/20th of a second
increase in RT
 Social psychologists claim that subliminal perception
increases the activation of a concept, which is unlikely to
have any long range effects on behavior
− Consistent with this view, priming a concept relevant
to a current goal or motive can lead to subliminal
priming effects
 Karremans, Goelz, Johr, Neumann, Ecker, and Doerr (2009)
− Subliminally presented drink brand names influenced
preference for that brand, but only for those who were
 Bermeitinger, Goelz, Johr, Neumann, Ecker and Doerr
− Consumption of a particular brand of dextrose (sugar)
pills was influenced by subliminally presented logos, but
only for those who were tired
● Lowery, Hardin, Eisenberger, and Sinclair (2007 )
− Students primed with a word related to intelligence did
better on a midterm exam that occurred days later
 Top-down processing
Greenwald, Spangenberg, Pratkanis, and Eskenazi (1991)
 Participants took tests to assess their memory and selfesteem
 Given subliminal messages embedded in taped nature
sounds, classical music, or popular music
 Tapes were labeled as memory improvement or selfesteem improvement
 Label was unrelated to content of subliminal message
♦ Listened to tapes each day for one month
 After one month:
 Retested memory and self-esteem
 Asked if they felt their memory or self-esteem had
 Results
 No effect of subliminal message
♦ Memory or self-esteem did not improve
 Effect of tape label
♦ Those with memory improvement label felt their
memory had improved
♦ Those with self-esteem improvement label felt their
self-esteem had improved
Vokey and Reed (1988)
 Experimenter creatively listened to 23rd Psalm and
Jaberwocky played backwards
 “Found” 6 passages from each that were meaningful
 Participants were given both passages
 For one, they were asked to listen for the “experimenter
heard” passages
♦ Task: Identify the passages
 For the other they were not told anything
♦ Task: Identify any meaningful passages
 Results
 Experimenter heard passages were only identified if told
the passages in advance (i.e., expected to hear them)
● Most are skeptical of the effectiveness of subliminal
● Dijksterhuis, Aarts, and Smith (2005) suggest there are good
reasons to continue research
− There may be potential benefits (e.g., studies by social
− Understanding them and informing the public about how
they work would be one effective tool for preventing
misuse and abuse
− Abandonment would be an overreaction to fallacious and
preposterous claims made by shoddy researchers