Cognition

Chapter 3: Perception

PerceptionExperiences resulting from stimulation of the senses

Sometimes an effortful process; sometimes automatic

Occurs in conjunction with action Involves dynamic processes that accompany and support our actions

THE NATURE OF PERCEPTION

THE NATURE OF PERCEPTION

Perceiving a Scene

Urban Challenge

THE NATURE OF PERCEPTION

THE NATURE OF PERCEPTION

Google Driverless Car

THE NATURE OF PERCEPTION

Computers have problems

Not anytime soon

WHY IS IT SO DIFFICULT TO DESIGN A PERCEIVING MACHINE?The stimulus on the receptors is ambiguous

Inverse Projection Problem: Many different objects in the environment can be causing a retinal image; seems to confuse machines

Objects can be hidden or blurredMachines have trouble perceiving these as a whole

Objects look different from different viewpointsMachines are lacking in viewpoint invariance

INFORMATION FOR HUMAN PERCEPTION

Bottom-up processingPerceptions influenced by the visual field itselfCan be referred to as “true object” perceptions – making sense from our sensations

Top-down processingThese perceptions are influenced by what the person expects or has experienced before

Our experiences memories, and expectations are what's important here

Another view…

Top-Down Processing Demo

Perceiving Objects

Olivia & Torralba (2007)

Perceiving Objects

Can you find 13 faces in this picture?

• Speech Segmentation• A listeners familiarity with a particular language will

alter his or her perception• Identical sound stimuli from two different languages

will still lead to different perceptions if one particular listener is familiar with a language that the other listener is not familiar (for example, one listener understands only English, while the other understands only Spanish)

Top-down Processing: Speech

EXPERIENCING PAIN: BOTTOM-UP

Direct Pathway ModelNociceptors (Pain Receptors)Simple, bare nerve endings that travel along the peripheral nervous system until they reach the spinal cordPain messages then are eventually sent to the brain

EXPERIENCING PAIN: TOP-DOWN

Wager, Scott, & Zubieta (2007)•After being injected in the jaw with a stinging saltwater solution, men were given a placebo pill•The men were told that this pill had pain-killing chemicals that would relieve their pain•The men immediately reported that they felt better•Placebo injections led to release of pain-killing opiates

Wiech et al. (2008)•Patients told what to expect requested fewer painkillers after surgery and were sent home 2.7 days earlier than control group

Likelihood PrincipleObjects are perceived based on what is most likely to have caused the patternNote that this means that what we learn about our environment becomes part of the problem solving we do when we encounter an objectUnconscious InferencePerceptions are result of unconscious assumptions about the environment

HELMHOLTZ’S THEORY OF UNCONSCIOUS INFERENCE

The display in (a) is usually interpreted as being (b) -- a blue rectangle in front of a red rectangle. It could, however, be (c) -- a blue rectangle and an appropriately positioned six-sided red figure.

Helmholtz’s Theory of Unconscious Inference

GESTALT PSYCHOLOGY

Based on the assumption that the whole is different than the sum of its parts•We impose order and structure on what we see•Our expectancies affect how we interpret sensory input

GESTALT PRINCIPLES OF PERCEPTUAL GROUPING

Proximity If figures are near each other we tend to group them togetherSimilarity If figures are similar to each other we tend to group them togetherGood Continuation (Continuity) We tend to perceive smooth, continuous patterns rather than discontinuous onesObjects that are overlapped by other objects are perceived as continuing behind the overlapping objectWhen a familiar figure is interrupted we imagine the rest of the figure (we finish the picture)Simplicity People tend to group features of a stimulus in a way that provides the simplest interpretation of the world Law of Pragnanz

GESTALT PRINCIPLES OF GROUPING

• Proximity.

Proximity

GESTALT PRINCIPLES OF GROUPING

• Similarity.

Similarity

GESTALT PRINCIPLES OF GROUPING

• Good Continuation

GESTALT PRINCIPLES OF GROUPING

Good Continuation

Of all the possible interpretations, we will select the one that yields the simplest or most stable form.

Simple, symmetrical forms are seen more easily. In compound letters, the larger figure dominates the smaller

ones.

LAW OF PRAGNANZ

People are more likely to see (b) and (c) not (d) or (e) in figure (a)

This is usually perceived as five circles, not as the nine shapes in (b).

Law of Pragnanz

Regularly occurring physical properties of our environment must be taken into account Oblique Effect•Regularities in the environment: There is a preponderance of verticals and horizontals•People are more sensitive to these orientations

TAKING REGULARITIES IN THE ENVIRONMENT INTO ACCOUNT

TAKING REGULARITIES IN THE ENVIRONMENT INTO ACCOUNT

Relative LuminanceThe amount of light an object reflects is relative to its surroundings

Most of our light comes from above so it makes sense that we apply this idea universally

LIGHT FROM ABOVE ASSUMPTION

Why does (a) look like indentations in the sand and (b) look like mounds of sand?

Hollingworth (2005)ProcedureParticipants observed a scene for 20 secondsIdentical scenes “with target” or “without target” objectNext they are presented the target object alone (center of the screen)This is followed by a blank screenThey are asked to move a cursor on the blank screen to the place were it was in the original scene (with target group) or to a place they would expect to see the target (non-target group)

ResultsWith target group was accurate; so was without target group

SEMANTIC REGULARITIES

See next slide

Hollingworth (2005)

SEMANTIC REGULARITIES

JUMBLED SCENES

The same details are in both stimuli but people identify more objects when the overall scene makes sense

SEMANTIC REGULARITIES

Palmer (1975) Observers saw a

context scene flashed briefly, followed by a target picture.

Results showed that: Targets congruent

with the context were identified 80% of the time

Targets that were incongruent were only identified 40% of the time

Stimuli used in Palmer’s (1975) experiment. The scene at the left is presented first, and the observer is then asked to identify one of the objects on the right.

Neural activity behind every behavior; connections have been found between neural activity, the nature of the environment, and perception

Neurons are tuned to respond best to things occurring regularly in the environment

The Human Perceiving Machine Experience-Dependent Plasticity

The brain is changed by its exposure to the environment so it can perceive the environment more efficiently

This was witnessed in experiments on animals and on people

NEURONS AND KNOWLEDGE ABOUT THE ENVIRONMENT

See next slides

ProcedureKittens reared in an environment with just verticals or just horizontals

Experience-Dependent Plasticity

Blakemore & Cooper (1970)

Vertical-only environment

ResultsFound that rearing a kitten in certain environments led to changes in how their neurons respondedSpecific environment reshaped the kitten’s visual cortexIf reared in an environment with just verticals, the visual cortex would respond mainly to verticals if reared in an environment with just horizontals, the visual cortex would respond mainly to horizontals

Experience-Dependent Plasticity

Blakemore & Cooper (1970)

GREEBLES & FACES

Gauthier, Tarr, Anderson, Skudlarski, & Gore(1970)

ProcedurefMRI used to detect level of activity in an area of the temporal lobe called the fusiform face area (FFA)Participants asked to respond to either faces or Greeble objects Extensive “Greeble recognition training” over four days given to participants

“GREEBLE EXPERIMENT”

Gauthier et al. (1999)

Some of the Greeble family

ResultsGreeble novices have higher brain activity for faces than GreeblesGreeble experts responded about the same to Greebles as they did to facesInterpretationThis provides evidence that the FFA contains not just to faces but to other complex objects as well; the particular objects that the FFA responds to depends on experience with that particular object

“GREEBLE EXPERIMENT”

Gauthier et al. (1999)

Movement helps us to perceive objects in the environment more accurately

Moving reveals aspects of objects that are not apparent from a single viewpointExample: Distorted horse

Interaction of perception and action

MOVEMENT FACILITATES PERCEPTION

Ungerleider & Mishkin (1982)Monkey presented with two tasks:Object-discrimination problemPresented one object; later asked to identify from choiceLesions of temporal lobe make this difficult “What” pathway problemsLandmark-discrimination problemPicking food well closer to a cylinderLesions of parietal lobe make this difficult“Where” pathway problems

THE PHYSIOLOGY OF PERCEPTION AND ACTION:WHAT AND WHERE PATHWAYS

Neuropsychology Studying the behaviors of people with brain damage

Dissociations Situations where one function is present while another

function is absentSingle Dissociations

Can be studied in one person; single patient has some things impaired, other things not impaired

Examples: Broca’s Aphasics, Wernicke’s aphasics, Prosopagnosiacs

Double Dissociations Require two or more people to determine the effects of the

brain damage; two or more patients show opposite single impairments

Broca’s & Wernicke’s Aphasics considered together

PERCEPTION AND ACTION STREAMS

LIMITATIONS OF NEUROPSYCHOLOGY

At least for human processing, brain damage comes about from natural means (accident, etc.)Members of groups rarely have exactly the same damage (location or extent)

No record of processing or brain organization before the damage

Difficult to assess all possible types of functional impairment

Brain may actually reorganize following damage (called plasticity)

CREDITS

Some of the slides in this presentation prepared with the assistance of the following web sites: faculty.rio.edu/.../22803%20Cognitive%20Psychology/... www.smccd.edu/accounts/irigoyen/.../chapter3.ppt www.csupomona.edu/~nalvarado/PSY334%20PPTs/Chap2.ppt www.ba.metu.edu.tr/~cagli/.../ppt/solomon_cb09_ppt_02.ppt memoryandcognition.wikispaces.com/file/.../Ch2Pt2Localization.ppt

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