Cognition, Sixth Edition, Robert J. Sternberg Chapter 2 Perception.

Cognition, Sixth Edition, Robert J. SternbergChapter 2

Perception


What you want to remember• Perception is more than photons

and pressure.

• Perception is divided from cognition/emotion but they are often intertwined.

• Perception follows laws and heuristics.


Sensation

• Sensation - the registration of physical stimuli– Hearing - anatomy and function of the

ear

– Vision - anatomy and function of the eye


Sensation

• What is the purpose of sensory processing?– To transform physical stimuli in the

environment into neural signals in the brain

– Example (Hearing): Sound waves are transformed into vibrations in the ear, and the strength of those vibrations are coded by sensory neurons


Some Questions of Interest

• How can we perceive an object like a chair as having a stable form, given that the image of the chair on our retina changes as we look at it from different directions?


Some Questions of Interest

• What are two fundamental approaches to explaining perception?

• What happens when people with normal visual sensations cannot perceive visual stimuli?


Perception Is…

• The process of recognizing, organizing, and interpreting information

• How do you recognize these items?


Basic Concepts (Gibson)

• Distal object– Grandma’s face

• Informational medium– Reflected light from Grandma’s face

• Proximal stimulation– Photon absorption in the rod and cone

cells of the retina

• Perceptual object – Grandma’s face


Perceptual Basics

• Sensory adaptation– Occurs when sensory receptors

change their sensitivity to the stimulus

– Constant stimulation leads to lower sensitivity

• Our senses respond to change

• Perceptual training


Perceptual Illusions

• Sometimes we cannot perceive what does exist

• Sometimes we perceive things that do not exist


Perceptual Illusions

• Sometimes we perceive what cannot be there

Cognition, Sixth Edition, Robert J. SternbergChapter 2http://www.vimm.it/cochlea/cochleapages/overview/history.htm


Figure 7.4 The basilar membrane of the human cochlea. High-frequency sounds produce their maximum displacement near the base. Low-frequency sounds produce their maximum displacement near the apex.

Figure 7.4


Corresponds to apex of cochlea

Corresponds to base of cochlea

Primary auditory cortex

Secondary auditory cortex

Auditory Cortex

• Tonotopic organization in superior temporal lobe


Audiograms for various species

Typical human range about 20 - 20 kHz


Our Visual System

• Light travels through the eye and focuses on the retina – Electromagnetic light

energy is converted into neural electrochemical impulses


Our Visual System

• Three main layers of neural tissue in retina– Ganglion cells

– Amacrine cells, horizontal cells, bipolar cells

– Photoreceptors• Rods and cones


Visual Pathways in the Brain

• What/where hypothesis– One path for identifying

• Temporal lobe lesions in monkeys

– Can indicate where but not what

– Another for spatially locating• Parietal lobe lesions in monkeys

– Can indicate what but not where


Theories of Perception• Bottom-up theories

– Parts are identified, put together, and then recognition occurs

• Top-down theories– People actively construct perceptions

using information based on expectations


Bottom-Up Processing Theories• Direct perception

• Template theories

• Feature-matching theories

• Recognition-by-components theory


Template Theories

• Basics of template theories– Multiple templates are held in memory

– To recognize the incoming stimuli, you compare to templates in memory until a match is found

See stimuli

Search memory for a match


Template Theories

• Weakness of theory– Problem of imperfect matches

– Cannot account for the flexibility of pattern recognition system

See stimuli No perfect match in memory

Search for match in memory


Feature-Matching Theories

• Recognize objects on the basis of a small number of characteristics (features)– Detect specific elements and assemble

them into more complex forms

– Brain cells that respond to specific features such as lines and angles are referred to as “feature detectors”


Pandemonium Model

• Four kinds of demons– Image demons– Feature demons– Cognitive demons– Decision demons


• Hubel & Wiesel (1979) – Simple cells detect bars or

edges of particular orientation in particular location

– Complex cells detect bars or edges of particular orientation, exact location abstracted

– Hypercomplex cells detect particular colors (simple and complex cells), bars, or edges of particular length or moving in a particular direction

Physiological Evidence for Features


• Biederman (1987)– Describes how 3D

images are identified

– Breaks objects down into geons

– Objects are identified by geons, relationship between them

Recognition-by-Components (RBC) Theory


Gibson’s Theory of Direct Perception (Ecological psych)

• The information in our sensory receptors is all we need to perceive anything– Do not need the aid of complex

thought processes to explain perception


Gibson’s Theory of Direct Perception (Ecological psych)

• Use texture gradients as cues for depth and distance– Allows us to perceive directly the relative

proximity or distance of objects


Top-Down Processing (Constructive Approach)

• Perception is not automatic from raw stimuli

• Processing is needed to build perception

• Top-down processing occurs quickly and involves making inferences, guessing from experience, and basing one perception on another


•Context effectsContext helps us to be able to recognize letters in many different styles.

Context helps us to be able to recognize letters in many different styles.Context helps us to be able to recognize letters in many different styles.

Evidence for Top-Down Processing


Configural-Superiority Effect

• Objects presented in context are easier to recognize than objects presented alone

• Task: Spot the different stimuli, press button


Configural-Superiority Effect

Measure reaction time

Target alone = 1884 Composite = 749

Target spotted faster in a context!

Target Composite


Which Approach Is Right?

• Top-down or bottom-up– Perhaps a bit of both


Beginning of Gestalt psychology

• 1910 – Max Wertheimer on vacation noticed that distal objects seemed to move with the train; nearby objects went past. Why?

• Study of apparent motion – why stationary objects appear to move

34


Apparent motion

• Phi phenomenon – flashing a vertical light that is followed 50-60 msec later by a horizontal light produces the appearance of movement. The light appears to move from vertical to horizontal

• Movement only perceived if delay was 50 – 60 msec

• The perceptual experience had properties the individual components did not

• 1st Gestalt paper presented in 1912

35


Basic premise of Gestalt psychology

• Humans are not passive receivers of sensory information. Our perceptions are active, lively, and organized

• We actively organize perceptions into coherent wholes – today the process is referred to as top-down or conceptually driven processing

36


Scientific Method• Gestalt perspectives on scientific method reflect

their acceptance of field physics as a model for psychology.– They emphasized the physical

environment.– They used experience to guide analysis in

psychology.– They started research with

phenomenological investigation.– They accepted a broad range of methods

in psychology.


Mind and Brain• Gestalt perspectives on mind and brain reject

reductionistic and linear models of mind. – Köhler argued for models of mind based in natural

systems.– He used models of mind based in the brain.– He described models in terms of free dynamics.– Köhler advocated isomorphism (ex. psychophysical

isomorphism).• There is a structural correspondence between experience

and underlying brain processes.


Key terms in gestalt psychology: Geographical versus behavioral

environment• Geographical environment – the physical world

• Behavioral environment – our interpretation of the physical world

• Our interpretation or organization can produce a behavioral world that is very different from the physical world

• Illusions, dreaming, fantasies39


Gestalt’s View of Perception

• Basic tenet– “The whole is more than a sum of its

parts”

• Law of Prägnanz– Individuals organize their experience in

as simple, concise, symmetrical, and complete manner as possible


Perception is not just detection• Perception is not just about detecting

color or shape.• Perception is about organizing visual

information.• How do we organize visual

information?


Müller-Lyer-illusion Ponzo illusion


Or when do we fail to organize visual information?


Gestalt’s Principles of Visual Perception


• Closure



• Figure-ground– Organize perceptions by

distinguishing between a figure and a background

• Proximity– Elements tend to be grouped

together according to their nearness

• Similarity– Items similar in some respect tend

to be grouped together


The figure represents “some thing.”

The contours belong to the figure rather than to the ground.


Which one if the figure and which is the ground?

This is easy.

The figure tends to have solid and continuous surface.



ContinuityBased on smooth continuity,

which is preferred to abrupt changes of direction

ClosureItems are grouped together if

they tend to complete a figure

SymmetryPrefer to perceive objects as

mirror images

C

B

A

D


Rules for Linking Contours• Good continuation: group elements to

form smoothly continuing lines


The Relatability Principle


Meaning in the Edges• Non-accidental features provide clues

to object structure


Is the Whole Seen Before the Parts?

• Global superiority effect (Navon, 1977)


Complex listening: several concurrent sound sources

• Auditory scene analysis

• “cocktail-party effect”


Stream segregation


Continuity


Grouping by similarity


Tactile illusions

61


Depth Perception

• The ability to see the world in three dimensions and detect distance– Vision only has a two-dimensional view– We must interpret the information given to

perceive depth– We take flat images and create a three-

dimensional view– Optical illusions demonstrate that this

interpretation does not always have to be correct


• Texture gradients– Grain of item

• Relative size– Bigger is closer

• Interposition– Closer are in front of other objects

Monocular Depth Cues


Monocular Depth Cues

• Linear perspective– Parallel lines converge in distance

• Aerial perspective– Images seem blurry farther away

• Motion parallax– Objects get smaller at decreasing

speed in distance


Binocular Depth Cues

• Binocular convergence– Eyes turn inward as object moves

toward you; brain uses this information to judge distance

• Binocular disparity– Each eye views a slightly different

angle of an object; brain uses this to create a 3D image


Agnosias, Ataxias, & Cognition

• Demonstrate the modularity of cognition

• Help us to understand what brain locations are associated with different types of higher-level processing

• Provide us with a model of how normal processing must work


Deficits in Perception

• Disruption of the “what” pathway– Inability to recognize and identify objects or

people, despite having knowledge of the characteristics of the objects or people

• Disruption of the “how” pathway• Cannot use vision to guide movement• Unable to reach for items


Fusiform Gyrus in Temporal Lobe

• Implicated in pattern recognition

• Studies illustrate it is active in facial recognition

• However, also active if high expertise in any item (birds, cars) recognition– Expert individuation

hypothesis


• Prosopagnosia– Inability to recognize faces after brain

damage

– Ability to recognize objects is intact

• Associative agnosia– Difficulty with recognizing objects

– Can recognize faces

Evidence for Separate Systems


Psychophysics• the measurement of sensory

experiences

• Webers Law

Δφ = cφ φ = Stimuli• Fechners Law

Ψ = log φ Ψ = Sensation magnitude


Perception or Attention

• Movement patterns / reflexes

• What cannot be unseen / heard

• Pop-out effect

• Change blindness


What you want to remember• Perception is more than photons

and pressure.

• Perception is divided from cognition/emotion but they are often intertwined.

• Perception follows laws and heuristics.

Cognition, Sixth Edition, Robert J. Sternberg Chapter 2 Perception.

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