Perceptual development

What is perceptual development

• How children start taking in, interpreting and understanding sensory input

• Eg visual perception and auditory perception

What are the measures and challenges of inferring perceptual abilities

• Measures:

• Head turning, sucking, eye tracking, heart rate

• Challenges measuring this:

• Attentional and motivational limitations

• Motor limitations

• Linguistic limitations

Foetal visual perception

• There has shown to be practical difficulties in studying foetus in utero

• Eyelids remain closed until week 26

• Eye movements at 18 weeks

• Foetus’ in utero can sense light shone on mothers abdomen, respond by moving and heart rate increase (Hepper, 1992)

• Can infer foetal capability from premature infants eg 31 weeks pre term can track a laterally moving target

Newborn visual perception

• Acuity is approx 30x worse than adults

• Focal length is fixed at 21cm

• Colour vision is not fully developed eg 8 week old can discriminate red-green but 4 week can’t

What is visual acuity like after birth

• (Courage and Adams, 1990)

• Newborn visual acuity is 30x worse than an adult

• 2months, 15x

• 4months, 8x

• 8months, 4x

What was Maurer, Lewis, Brent and levins study on visual acuity (1999)

• Participants were infants, 1 week- 9 month old

• Had congenital cataracts In one or both eyes

• Cataracts were removed then acuity was tested at 10 minutes, 1 hour, 1 week and 1 month after first visual input

• At 10 mins, all infants acuity was no different from a newborn, their visual acuity had not previously developed

• There was some improvement after an hour

• Over 1 month, acuity improved substantially

• Shows how visual experience is essential for development of visual acuity

Face perception of infants

• Faces have great significance

• Distinguish people from other objects

• Identify individuals therefore facilitating caregiver attachment

• Interprets others emotions

What was Maurer and Barreras study on face perception (1981)

• 1-2 month old infants

• Used a real face and scrambled faces

• 1 month old had no preference showing NO support for innate face preferences

• 2 month old preferred the ‘real face’, showed they have more than just a preference for complex symmetric forms

Can infants recognise different faces ?

• (Pascalis et al, 1995)

• Newborns (4 days old), can recognise their mothers face from an unfamiliar female face

• However not when scarves cover external features of their face

• This suggests newborns learn to recognise faces very rapidly

• Also suggests they use external rather than internal facial features

Are newborns insensitive to internal facial features ?

• (Slater et al 2000), facial attractiveness

• Two faces, ‘attractive and unattractive’

• Both faces had the same external features but different internal features

• Infant looking time for the ‘attractive face’ was 57.1% whereas only 42.9% for ‘unattractive’

• Suggests that newborns are sensitive to internal features

• Attractive faces are a better match to template

What is depth perception of infants

• The perception of 3D layout involving judging

• Distance to an object from oneself

• Distance between objects and 3D shapes

• This enables infants to plan actions eg hit and crawl

Gibson and Walk 1960 “visual cliff experiment”

• They put out a visual cliff

• Participants were 30 6month- 1 year old who can crawl

• 27 of them did not cross only 3 did

• Concluded that most infants can perceive depth by the time they can crawl

• Does raise question of , is depth perception innate or learnt and how accurately did the infants perceive depth

What information might infants use to judge depth?

• (Arterberry, Yonas and Bentsen 1989)

• Participants were 5 and 7 month olds

• Had 2 objects at same physical distance

• Used pictorial cues, the infant should reach for the lower object more often

• 5 months reached for the upper and lower equally

• Whereas the 7 month reached for lower 72% of the time

• They argued that use of pictorial cues (texture and outline) emerges between 5 and 7 months old

What is foetal auditory perception

• There is much auditory stimulation while in the womb eg loud external sounds and mothers speech

• Initially the foetus responds by moving and Increased heart rate but this expands as the foetus matures

• Foetal abilities are inferred from behaviour at birth

• Many studies show auditory perceptual development is influenced by auditory experience in the womb

Newborn auditory perception?

• At birth they prefer to listen to people

• Prefer speech to other sounds

• Respond most to tones 1-3KHz

• Prefer sounds with a range of tones eg speech

• Newborns will preferentially suck to hear voice recording

Speech perception of infants ?

• Evidence that the foetus can learn to recognise the mothers voice

• (DeCasper and Fifer, 1989) mothers read from the story book aloud during final stages of pregnancy

• On the first day preferential sucking to hear the same story read by either the mother or a female stranger

• Newborns preferred their mothers voice

• However all infants had 12 hours post natal exposure to their mother

DeCasper and Prescott 1984 speech perception test

• Similiar to DeCasper and Fifer

• 2 days old showed no preference however for father vs male stranger

• Despite hours of post natal experience with the father

Eimas et al 1971 speech perception test

• Suggested infants perception of speech is categorical

• Examined 1 and 4 months old ability to discriminate ‘ba’ from ‘pa’ to differ only in voice onset time

• Above a certain voice onset time, adults hear pa below this value but hear ba so do 1 and 4 month olds

• Infants habituated to ba (measured by sucking)

• Presented new sounds either a shorter voice onset time that adults hear as ba

• Or a longer voice onset time

• Infants dishabituated to a longer VOT showing that 1 and 4 month olds have categorical speech perception

• Also showed that infant phonetic boundaries are the same as adults

Werker et al 1981 speech perception

• Was studying whether infants are sensitive to the phonetic contrasts of all languages

• Examined 7 month old and adult sensitivity to a Hindi contrast

• Almost all 7 month olds detected change

• All native Hindi speaking adults detected change

• But at 10 months sensitivity to non native phonetic contrasts declines

• This was shown for several contrasts not found in English, eg Japanese (Kuhl, 1998)

• Declines to adult levels by around 12 months

Why do infants lose the ability to discriminate non native phonemes ?

• Possibly because auditory systems develop greater sensitivity to sounds of native language

• This allows accurate detection of same phoneme spoken by different people in different ways

• (Juscyzk et al 1994) compared preference for common vs uncommon phoneme sequence in English eg ‘chun vs ‘hush’

• 6 months old had equal preference

• 9 months old preferred listening to native language speech sounds

• This suggests innate speech predisposition, sensitivity to subtleties of native speech sounds which improve through experience