University of Waterloo PSYCH 207 - Chapter 3

What is the central problem of perception?

Explaining how we attach meaning to the sensory information we receive

distal stimulus

an object or event in the outside world

proximal stimulus

stimulus registered by sensory receptors

Percept

meaningful product of proximal stimulus, RECOGNITION (although your proximal stimulus thinks further away objects are smaller, percepts do not)

pattern recognition

The classification of a stimulus into a 'category'.

form perception

the organization of the visual field into objects (the figures) that stand out from their surroundings (the background).

Subjective contours

the perception of contours where none actually exist

- KEY perception requires the viewer's 'participation'

Gestalt psychologists rejected the claim that . . . ? What was their stance instead?

We recognize objects by identifying individual pieces

- Instead, they focused on understanding how we come to recognize objects as forms (form perception: "segregation of displays into objects and background"

What are the five major "Gestalt" principals of perceptual organization

1. Principal of Proximity (nearer things are related)

2. principal of similarity

3. principal of good continuation

4. principal of closure (finishing a 'suggestion')

5. principal of common fate (items that move together are related)

Law of Pragnanz

The most general Gestalt principle, which states that the simplest organization, requiring the least cognitive effort, will emerge as the figure.

bottom-up processing

analysis that begins with the sensory receptors and works up to the brain's integration of sensory information

top-down processing

information processing guided by higher-level mental processes, as when we construct perceptions drawing on our experience and expectations

templates

Part of bottom-up processing

When we receive a stimulus, we compare it to similar stimulus of the past to find out it's 'identity'

- KEY: Memory based

- Problem: Doesn't deal with the surface variation of stimuli

features

Part of bottom-up processing

Recognizing aspects of a stimulus to decipher the whole

- KEY: "CORTICAL FEATURE DETECTORS" Certain detectors appear to scan input patterns, looking for a particular feature. If that feature is present, the detectors fire rapidly!

Visual search task

Bottom-up processing

Looking for a particular letter in an array is easier when the surrounding letters have different features (behavioural demonstration of feature analysis)

pandemonium model

A model of letter perception based on a bottom-up hierarchy of feature detectors.

- levels of demons screaming loudly, softly if they detect their given feature

Problems with feature analysis

One stimulus can't be broken down into a finite amount of features

Prototype matching

Bottom-up processing

Matching a stimulus to an idealized representation of some class of objects/events to recognize it

- takes into account not only a stimulus' features, but also the RELATIONSHIP between them

- Demonstrated by the fact that people are likely to call a face 'old' if they have recently seen another 'similar' face with displaced features

Context effects

One of the problems with the concept of bottom-up processing (it needs to somehow incorporate context and expectations)

- People recognize microwaves situated in a kitchen more quickly than on their own

- Both accuracy and length of time taken to 'identify' vary with context

Marr Believed . . .

Top down processing

Visual perception is the result of three different mental representations:

1. Primal Sketch (brightness and structure)

2. 2 1/2-D Sketch (surface texture and DEPTH)

3. 3D sketch (using visual context . . . the TOP DOWN component)

change blindness

failing to notice changes in the surrounding environment

KEY: things that don't impact the 'meaning' of the situation are not relevant (perception is driven by expectation about meaning)

word superiority effect

The idea that letters are easier to identify when they are part of a word than when they are seen in isolation or in a string of letters that do not form a word.

Missing letter effect

Skilled readers skip over predictable words and thus cannot track the letters in those words

KEY: Ability to identify is inhibited by familiarity

Connectionist Model of world perception

Each level of processing is assumed to form a representation of the information at a different level of abstraction, with 'features' considered less abstract than letters, letters less abstract than words

- Nodes fire at each level to inform the next

- This in part explains the missing letter effect: Without the word context, the node for the individual letter is less active, so perception of the letter takes longer

When you show someone 'pseudo words' (and real words) while in a PET scan . . .

The non-visual regions of the left side light up -> an area that they claim is involved in semantic processing (looking for meaning)

Constructivist approach to perception

Distal Stimulus -> Proximal Stimulus -> Percept (Bottom up & top down processing)

KEY: people are active selectors, integrators, and constructors of information

Direct Perception

a theory arguing that sensory perception is the direct result of info. from the surrounding environment; this is contrary to the theory of our inferences and beliefs affecting sensory experiences

Gibson's theory

information available to an organism exists not merely in the environment, but in an 'animal-environment ecosystem'

- KEY: The environment is defined by it's 'affordances' -> what it can do for the animal

- People say this theory is inadmissible because of how poorly 'affordances' are defined

Perceptual cycle (Neisser)

Schema is something people bring to situations that is either confirmed or rejected -> forcing change

KEY: Assumes an active perceiver

visual agnosia

the inability to recognize a visual stimulus despite the ability to see and describe it

apperceptive agnosia

a failure to understand the meaning of objects (KEY:) due to a deficit at the level of object perception

- Can only see contours and outlines

- KEY: associated with damage to the right hemisphere

Associatie Agnosia

Focus on every little detail when trying to recreate a drawing

-KEY: associated with bilateral damage

category specific agnosia

a neurological syndrome that is characterized by an inability to recognize objects that belong to a particular category thought the ability to recognize objects outside the category is undisturbed

- Research shows that both physical and semantic similarity impact this

Prosopagnosia

inability to recognize faces

- Associated with damage to the right hemisphere

- There is evidence of covert (unconscious) face recognition (KEY GSR discriminate

unilateral neglect

A syndrome in which people ignore objects located toward their left and the left sides of objects located anywhere; most often caused by damage to the right parietal lobe

Prosopagnosia is a type of . . .

associative agnosia