Gibson & Walk (Topic 3 Perceptual dev-visual cliff) Flashcards
Aim
To investigate how humans and animals perceive depth, when depth perception develops in human infants and other young animals & whether depth perception is innate.
Also investigated which one of 2 visual cues play decisive role in depth perception: fact that distance decreases size and spacing of pattern elements projected onto retina or motion parallax-causes pattern elements on shallow side to move more rapidly across field of vision.
Research method
Main study was lab experiment.
IV: whether infant was called by mother from cliff side or shallow side of apparatus.
DV: whether child would crawl to mother or not.
Experimental design
Repeated measures design
because infant was called from both cliff side and shallow side.
Other studies research method
Quasi experiments
Naturally occurring IV= animal species
DV= whether animal preferred shallow or deep side.
Sample
36 infants
ranged 6-14 months
Mothers also participated-consent given
Unspecified number of animal species also used e.g cats rats goats sheep turtles.
Visual cliff apparatus
Specifically designed to test depth perception, whilst avoiding danger of falling.
Consisted of a board laid across large sheet of glass supported above floor.
One side was sheet of patterned material placed directly under glass (shallow side)
One side same material placed on floor under glass (cliff side) gave illusion of a cliff.
Procedure
Each child was placed on centre of board, other stood at shallow side and cliff side successively, from each position called child towards them.
Child could choose to crawl off board and cross over glass on shallow/ cliff sides.
Similarly for animals they were placed on same apparatus and subsequent behaviour was observed.
Baby findings
27 infants crawled off board, all of whom crawled onto shallow side at least once.
3 out of 27 crawled off brink onto ‘cliff’ side
Children peeped through glass at cliff edge and backed away; some tested glass, patting it, but did not cross.
When mother stood at deep side, most common reaction baby crawled away or cried because could not reach mother without crossing deep side.
Animal findings
Comparable results to babies for different species placed on visual cliff.
Most animals froze ‘defence’ posture when placed on cliff side.
Turtles showed poorest performance- 76% crawled onto shallow side- researchers expected they would prefer deep side (resembles underwater) 24% turtles preferred deep side- implies aquatic turtles either have poor depth perception or living underwater means they do not have to fear falling.
Findings overall suggest depth perception develops once animals becomes mobile- suggests survival purposes in animals that become mobile in first 24 hours of life e.g Lambs.
Dark-reared kittens did not back off cliff side like light-reared kittens (normal), but showed same behaviour exhibited on shallow side.
Once exposed to light, dark-reared kittens were tested daily. After a week showed preference for shallow side.
At age of 90 days both light & dark reared rats showed same preference for shallow side- supports idea depth perception is innate.
Conclusions
Most children displayed ability to perceive depth by time they could crawl, but not always aware of danger cliff edge presented.
Inability to perceive danger of cliffside was exemplified by 3 children who crossed glass to deep side.
Both nature & nurture appear to influence development of depth perception.
Survival of species requires they achieve development of depth perception before take up independent movement; e.g 1 day for chicks and goats, 3-4 weeks in rats and cats and 6-10 months in humans.
Methodological issues- Weaknesses
Weakness= It is possible verbal cues from mothers could vary when calling child- evokes extraneous variables.
Weakness= Inferring affects validity; perceptual processes involved inferring made from senses and behaviour= make assumptions about thoughts of ps ( not valid ) especially when no verbal communication supports assumptions.
Babies could already crawl meaning may have learnt aspected of depth perception before 6 months from behaviours that do not require locomotion (e.g looking & reaching) Leaves question: is depth perception innate or does it develop through experience?
Weakness= external validity limited- researchers acknowledged nature & nurture but non-human animal research does show depth perception is innate- but can we apply this to humans? limits external validity.
Methodological issues- Strengths
Strength= high reliability
Lab experiment- standardised procedures easily replicable. E.g apparatus was precisely set up and the same for each ps; each child had mother present, animal experiments also very controlled.
Strength= other research into perceptual dev also use reliable methods to measure behavioural responses like heart rate tracking devices. Kittens in Blakemore & Cooper exposed to highly controlled environments- casual conclusions can be inferred.
Ethical issues
Subjecting young babies ( some only 6 months ) to lab test involving crossing an area perceived as frightening causes psychological distress.
When mothers stood at cliff side calling for child some babies cried, showing distress in situation where felt unable to reach them.
Use of animals- selective rearing was used (e.g raising an animal in abnormal environments like darkness) can cause distress in animals, especially once exposed to normal environments which may never be able to effectively function in.
Effects can be irreversible like in Blakemore & Cooper’s study by visual deprivation- yet reported no distress from cats used.
Study complied with ethical guidelines for animal research, can also be argued harm to animals was outweighed by usefulness of research.
Usefulness
Is seen as useful.
Learning when children’s perception of depth and height develops differences from and changes in normal pattern of perceptual dev can be tracked.
Findings may allow parents and professionals to identify those with perceptional abnormalities.
This info can lead to practical applications like treatments to help perceptual problems e.g glasses.
Research useful by creating timeline for visual perception to track ‘normal’ development in newborns and infants. Help identify abnormalities in perception or vision.
Child may need intervention e.g hearing devices or braille to be taught.
Usefulness limited by…
Lack of validity.
Could not control for all factors e.g mothers facial expressions, tone of voice, bodily cues differ depending on encouragement from shallow or cliff side.
Mothers confidence levels may also have influenced whether they crossed cliff or shallow.
Creates additional extraneous variables influencing findings.
Nature / nurture
Research suggests development will occur at reasonably fixed age- innate for evolutionary reasons and supports nature.
Role of nurture should not be ignored particularly humans.
Environmental interactions and use of play strategies and toys essential for normal perceptual development to occur.
Human have innate reflexes which help sensory system. Psychologists agree perception is result of both nature and nurture. Some suggest depth perception and colour perception can’t develop without right environmental stimulation even though sensory capability may be present. (Sugita 2004)
Gibson & Walk supports nature explanation of depth perception due to ps being so young, presuming mainly biological, however we are aware depth perception changes quickly after birth (implies environmental influences (nurture)
Nativist & Constructivist theories of perception- nativist supports nature explaining why infants have perceptual abilities at young age.
Constructivist theory emphasises importance of experiences and memories- how they influence perception.
Interaction between nature & nurture= perception present at birth but experiences such as play strategies lead to further development of perception.
Reductionism vs holism
Reductionist= attributes perceptual development to innate factors ultimately genetic, reducing complex development of depth perception to single biological factor explanation uninfluenced by other factors, reinforced by attempts to extrapolate from animals to humans that mechanism is similar in both.
Holistic approach takes into account wide influences on perceptual dev e.g social factors, babies were able to ignore depth cues when responding to mothers facial expressions, if mother adopted ‘happy’ expression baby would cross to deep side but not when presented ‘fearful’ (James Source et al 1985)
Complex processes like perceptual development can best be explained by range of both non biological and biological factors.
psych as a science
Used lab conditions- objective & standardised, reduced potential bias and extraneous variables by getting rid of light reflection to improve validity.
Materials and instructions during visual cliff task were standardised- appear easily replicable.
