Lecture3:Chapter5-Perception..Dr.Anna

Use with Atkinson & Hilgard’s Introduction to Psychology 15th edition

Nolen-Hoeksema, Fredrickson, Loftus, Wagenaar

ISBN 9781844807284 © 2009 Cengage Learning

Chapter 5

Perception




What is the Use of Perception?

• Processing & using incoming sensory information

– Humans require models of the environment to base

perceptions, decisions and behaviour on

– To create & maintain models, they need to acquire raw

sensory information & organize this into a coherent

structure

• Five functions of perception

– Need to decide which information to process, where

object of interest is, recognise what object of interest is,

abstract the critical features of the object and keep

appearance of the object constant




Attention

• Selective attention

– Refers to the process by which we attend to certain

stimuli and ignore others

– Eye movements – studies of visual attention monitor

people’s eye fixation patterns which attend to features

most likely to distinguish scene for other similar scenes

• Auditory attention

– Also use selective attention in audition, e.g. by focusing

on the direction the sound is coming from and features of

the speaker’s voice, e.g. pitch and intonation




Attention

• Attention, perception, and memory

– We are consciously unaware of, and remember little

about unattended stimuli

• Costs & benefits of selectively attending to stimuli

– One cost of selective attention is that observers are

often oblivious to other, potentially important, stimuli in

the environment

– That people are able to switch attention between sets

of information can be beneficial e.g. in medicine for the

treatment of cataracts




Localization

• To localize objects, need to first separate them and then

organise them into groups

• Separation of objects

– Figure and ground – in stimulus with two or more distinct

regions, usually see part as figure (contains objects of

interest) and rest as ground (or background)




Localization

• ...Separation of objects

– Grouping of objects - according to several determinants

– proximity to each other, similarity, good continuation or

closure. These serve to create most stable and simple

forms possible within a given pattern

• Perceiving distance

– To know where object is, we use depth cues

• Binocular cues – brain uses information from eyes to infer depth

• Monocular cues – for distant objects we use environmental

information e.g. perspective, interposition, relative size & height,

shading & shadows and motion




Localization

• Perceiving motion

– To move around environment effectively need to

know direction of moving objects either using

stroboscopic motion (illusion of motion) or real motion




Recognition

• Recognising object requires that the features of

an object are correctly bound together

• Global-to-local processing

– To know what object is, use the context (the scene) to

make inferences – global processing (what the scene

is) followed by local processing (using knowledge

about scene to identify object)




Recognition

• The binding problem: pre-attentive & attentive

processes

– Feature integration theory – information about primitive

features of an object acquired via pre-attentive

processes, and then integrated in subsequent attentive

processing stage (using attention to “glue” features

together)

– Problems with the feature integration theory because

research has found too many “primitives” to be

realistic. Dynamic control theory proposed – system

rearranges itself for different tasks




Recognition

• Determining what an object is

– Shape plays critical role in determining what object is

– Visual processing – early stages use information on

the retina to create description, later stages use

comparison with visual memory to select best match

– Feature detectors in the cortex – three types of cell

• Simple cells – respond when eye exposed to line stimulus at

particular orientation and position within receptive field

• Complex cells – also respond to bar or edge in particular

orientation but do not need specific position

• Hypercomplex cells – require stimulus to be in a particular

orientation and of particular length




Recognition

• ...Determining what an object is

– Relations among features – to describe a shape also

need to specify how features combine/relate

• Later stages of recognition: network models

– Simple networks – knowledge of features associated

and not associated with shapes contained in network of

connections (connectionist model) for comparison

– Networks with feedback – easier to perceive letter as

part of word than alone because the word is an

additional source of activation for letter – therefore have

top-down feedback connections which aid recognition




Recognition

• Recognising natural objects & top-down processing

– Features of natural objects

• More complex than lines – similar to simple geometric forms, e.g.

cylinders, cones, blocks and wedges. Particular set of such

forms is a geon

– The importance of context

• Bottom-up processes driven solely by the input (sensory data),

whereas top-down processes driven by person’s knowledge,

experience, attention and expectations

• When the context is appropriate (that is, it predicts the input

object), it facilitates perception; when the context is inappropriate,

it impairs perception




Recognition




Recognition

• Special processing of socially relevant stimuli:

face recognition

– Development of special face recognition processes

• Three sources of evidence – prosopagnosia – brain injury

where person able to recognise objects but not faces;

inversion effect – faces hard to recognise upside down but

not objects; and face and object recognition develop

differently in children

– Failure of recognition – happens routinely for people

with certain kinds of brain damage (agnosia)




Abstraction

• Exact to abstract

– Only need to know enough visual detail to carry out

whatever task is requiring you to perceive the object

• The advantages of abstraction: required storage

and processing speed

– More efficient to perceive and encode an abstraction

of an object than exact representation in memory

– Because abstraction uses less space, faster to work

with

– Information retained is the critical information needed




Perceptual Constancies

• The nature of constancy

– What we perceive is perception of what object is

actually like rather than perception based only on the

“objective” physical information acquired from

environment

• Color and brightness constancy

– Color constancy – ability of visual system to perceive

the reflectance characteristic (an inherent property of

the object) – no matter what the source wavelengths

(light source – sun/light bulb etc.)





• ...Color and brightness constancy

– Brightness constancy – perceived lightness of object

changes very little (if at all) even when intensity of

source changes significantly





• Size constancy

– An object’s perceived size remains relatively constant

no matter how far away it is

– Dependence on depth cues – perceived size of an

object increases with both the retinal size of the

object and the perceived distance of the object

(known as the size-distance invariance principle)

• Constancies in all sensory modalities

– Although visual constancies most salient, constancies

exist in all sensory modalities





• Illusions

– Perception differs systematically from physical

reality, often because visual system tries to

maintain constancy




Divisions of Labor in the Brain

• The neural basis of attention

– Three brain systems in attention

• One system functions to keep us alert while the other two

systems seem to mediate selective attention, the first

(posterior system) by orienting attention to the stimulus on

basis of location, shape or color, while the second (anterior

system) controls when and how these features will be used

for selection

– Neural processing on attended objects

• Regions of the brain that are relevant to attribute being

attended to (e.g. color) will show increased activity




Divisions of Labor in the Brain

• The visual cortex

– Visual cortex operates according to the principle of

division of labor – different regions specialised for

different perceptual functions

• Recognition versus localization systems

– Recognition depends on branch of visual system

which includes primary visual cortex and a region

near the bottom of the cerebral cortex, while

localization depends on branch of visual system

which includes primary visual cortex and a region of

the cortex near the top of the brain




Perceptual Development

• Nature and nurture

– Research seeks to assess contribution of nature and

nurture in perceptual development and identify

interactions

• Discrimination by infants

– Methods of studying infants

• Preferential looking method – infant’s tendency to look at

some objects more than at others

• Habituation method – allow infants to look at an object until

bored (habituated to it) and then present new object and

measure time looking at it





• ...Discrimination by infants

– Perceiving forms

• Visual acuity develops rapidly over the first six months, then

more slowly until reaches adult levels between 1-2 years

• Sensitivity to some shape features of objects appears very

early in life, e.g. three-day-old infant will direct eye

movements to edges when presented with triangle

– Perceiving depth

• Depth perception begins to appear at three months but not

fully established until about six months




Perceptual Development • ...Discrimination by infants

– ...Perceiving depth





• ...Discrimination by infants

– Perceiving constancies

• Also starts to develop in first few months of life, particularly

for shape and size constancy

• Controlled stimulation

– Absence of stimulation

• Animals raised in darkness suffered permanent visual

impairment suggesting that there is a critical period early in

life when lack of normal stimulation produces deficiency in

innate perceptual capacities





• ...Controlled stimulation

– Limited stimulation

• Animals receive stimuli in both eyes but only certain kinds –

leads to deficiency in stimuli they do not receive. Facts

indicate that certain kinds of stimulation essential for

development and maintenance of perceptual capacities

present at birth

– Active perception

• Learning plays major role for coordinating perceptions with

motor responses

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Lecture3:Chapter5-Perception..Dr.Anna