PERCEPTION

Nature and Nurture

• Constructivists (Nurture)– Perception is constructed through learning– Declines due to environmental influences

• E.g., disease, loud noise etc.

• Nativists (Nature)– Perception does not require interpretation– Declines are universal, due to aging

Learning Objectives

• How are perceptual abilities of infants assessed?

• What are infants’ visual capabilities?

• What sorts of things do infants prefer to look at?

Methods of Studying Infant Perception

• Habituation: Discrimination Learning– “Learning to be bored”

• Preferential looking– Duration of looking at one of a pair

• Evoked Potentials: recorded as child looks

Vision

• Present at birth– Detect changes in brightness– Visually track moving objects

• By 4 months can discriminate colors

• Visual acuity at about 8 inches

• Visual accommodation: 6 to 12 mo

• Color vision mature at 2 to 3 mo

• Prefer contour, contrast, and movement

• Prefer complex over simple patterns

• Researchers must devise special ways to assess infants’ perceptual abilities. Here, an experimenter and camera record how much time the infant looks at each stimulus. The visual preference test was pioneered by Robert Fantz in the early 1960s.

Vision

• Depth perception– Newborns appear to have size constancy– The visual cliff: Gibson & Walk (1960)

• A crawler (7 mo) will not cross the cliff• Can perceive the cliff by 2 months• Fear of drop-off requires crawling

• Infants as Intuitive Theorists: able to make sense of the world

• An infant on the edge of a visual cliff, being lured to cross the “deep” side.

Hearing and Speech

• Humans can hear well before birth (clip)• Newborns discriminate sounds that differ

in loudness, duration, direction, and pitch• Two- to 3-month olds distinguish

phonemes – Eimas (1985) “Ba & Pa” studies

• Newborns prefer female/mother’s voice• Lose sensitivity to sounds not needed for

home language

Taste and Smell• Newborns can distinguish between sweet,

bitter, and sour tastes– Show a clear preference for sweet– Facial expressions reflect taste

• Cry and turn away from unpleasant smells• Breast-fed babies recognize mother’s

smell• Mothers can identify their newborns by

smell

Touch, Temperature, and Pain

• Sense of touch (& motion) before birth– Useful for soothing a fussy baby

• At birth sensitivity to warm and cold• Clearly sensitive to painful stimuli• Do babies require anesthesia for

surgery?– More harm from stress of pain – Recommended for circumcisions

Integrating Sensory Information

• Senses interrelated within the first month• Cross-modal perception: previously seen

objects identified by touch alone• Nature: Very early perceptual abilities • Nurture: Sensory system requires

stimulation to develop normally– First 3-4 months=Critical/Sensitive period

• Infant cataracts result in blindness• Delayed understanding after cochlear implants

The Development of Attention

• From infancy on:– Attention span increases– More able to concentrate on a task– Attention becomes more selective– Able to ignore distractions– More systematic perceptual searches in

order to achieve goals & solve problems

ADHD

• ADHD and the brain• Testing

• ADHD and girls

• ADHD

The Adult

• Sensory and perceptual capacities decline– May begin in early adulthood– Noticeable in 40s; Typical by age 65– Gradual and minor in normal adults– Compensation gradually increases

• Sensory threshold: point at which the least amount of a stimulus can be detected– Increases with age

Sensory/Perceptual Problems

• Sensory thresholds rise with age• Vision • By age 70: 9/10 wear corrective lenses

– 1 in 4 will have cataracts– Pupil less responsive to light

• Dim lighting is problematic• Dark and glare adaptation difficult

• Presbyopia: Middle age glasses– Thickening lens = poor near vision

Other Visual Problems

• Retinal Changes: cells die, no longer function

• Age-Related Macular Degeneration– Loss of center visual field, blurry vision

• Loss of Peripheral Vision (Tunnel Vision)

• Retinitis Pigmentosa (RP)– Deterioration of light-sensitive cells

• Glaucoma: increased eye-fluid pressure– Damages optic nerve

Attention and Visual Search

• Selective attention declines– More easily distracted

from task– Attend to irrelevant cues

• Novel, complex tasks more difficult– Familiar and well-

practiced skills remain

Hearing/Speech in Older Adults

• Most have at least mild hearing loss• Presbycusis: loss of high-pitched sounds

– More common and earlier in men

• Some difficulty with speech perception– May be cognitive or sensory– Background noise a problem

• Novel and complex tasks problematic

Speech Perception

• Dependent on hearing abilities• Also cognitive processes

– Attention, memory

• Listening conditions important– Background noise problematic

• Novel and complex tasks problematic– Familiar conditions allow use of

contextual cues

Other Senses in Older Adults

• Over 70: Taste and smell thresholds increase– Many are not affected at all: Mostly men – Affected by disease and medications – Loss of enjoyment of food may cause

malnutrition in older adults

• Less sensitive to touch and temperature• Less sensitive to mild but not severe pain