WJEC AS Psychology PY2 - Gibson and Walk (1960)

Definitions:

• perception: process of understanding and making sense of the information that reaches the senses
• depth perception: interpreting how far an object is spacially, is important for staying safe within our environments

Importance: G+W wanted to investigate depth perception. The nativists, empiricists and interactionists all have different beliefs as to how we become aware of our surroundings as we wouldn't survive very long without depth perception e.g. descending stairs

Previous Research:

• Nativists believe we are born with certain abilities such as being able to perceive depth; believe that these abilities may not function properly when we're born but maturation process determines development abilities, learning has no importance, eg when a child is born, the nervous system has necessary components but immature; the optic nerve is shorter than adult sized and narrower = no myelin sheath to ensure good transmission of information

• empiricists: we acquire abilities through experience, depth perception would be acquired in response to environmental demands ie after we become independently mobile
• interactionists believe that our abilities are due to using both innate and environmental factors; assume depth perception is down to development of the visual system (the myelin sheath around the optic nerve is thought to be fully developed by 4 months) and combined with experience (eg being exposed to various complex stimuli such as faces which give some indication of depth)
• expect depth perception to be apparent when infant is mobile (6 months in humans, earlier in prococial animals) if perception is innate, we would expect animals mobile from birth as an adaptive behaviour (improves survival rate) meaning less developed in humans who are born immobile

Aims:

1) G+W aimed to investigate if human infants could discriminate depth by the time they could move independently and if it was due to learning through experience or what a child is born with; if perception is innate = apparent when mobile

2) they also used a range of non-human animals to investigate whether depth perception (cliff avoidance behaviours) was evident from when animals were mobile

EXPERIMENT - lab experiment

APPARATUS: enabled G+W to control optical, auditory and tactile stimuli and protect pps

• name: Visual Cliff
• construction: consisted of large glass sheet supported 30cm above floor, on one side, sheet of patterned material place directly beneath glass; on other side, patterned material laid on floor

METHOD:

• participants were placed on the centre board that lay inbetween the shallow and deep sides
• participants were then encouraged to move across the shallow and deep sides
• observed whether they would refuse to crawl over the drop

PARTICIPANTS

Humans:

• 36 human infants aged 6 - 14 months who could crawl

Animals:

• chicks, lambs and kids, all mobile at 1 day old
• kittens who are mobile at 4 weeks old
• kittens that have been reared in the dark for 27 days (no perceptual experience before they became mobile)
• rats who were mobile at 4 weeks old
• rats who were reared in the dark; some also wore hoods so they could use whiskers rather than visual cues
• aquatic turtles were used as depth perception may be different to land based animals as their normal environment is partially underwater

Human infants results from experiment

• of 27 infants that moved, only 3 attempted to crawl onto the deep side; all happy to crawl onto shallow side

Conclusion: infants able to detect difference in depth as preferred the shallow side; doesn't prove the nativist's view (could have learnt this after birth)

• many infants crawled away from mother when called them from deep side; others cried as they couldn't get there without crossing the deep side

Conclusion: infants wanted to get to their mothers (even getting upset), but only a minority willing to defy eyes and cross the cliff

Animal infants results from experiment

• chicks, kids and lambs never hopped or stepped onto deep side, even at 1 day old, kid/lamb placed on deep side, froze in a defence posture: front legs rigid and hind legs limp

Conclusion: from moment they're are born, can detect depth, afraid of it; supports nativist's view that born with depth ability: at 1 day old, no way to learn depth perception ability

• rats content to explore both sides, had to feel glass with whiskers, when centre board placed higher, glass out of reach, rats only went to shallow side (95-100%)

Conclusion: species which use different way of perceiving depth/environment use visual cues when others removed; rats support empiricist's view as when size/shape cues available, they were learning; further supported by the dark-reared rats having no preference to which side they went to as hadn't learn from their environment about perception

• kittens at 4 weeks old preferred the shallow side, froze when placed on deep side; dark reared kittens crawled onto both sides equally

Conclusion: kitten's perceptual abilities dependent on visual cues, supports ability is innate but dark reared kittens not afraid of deep side as hadn't learnt depth cues (empiricist); dark reared kittens kept in normal conditions, after a week, cautious of deep side, indicating that they had learned depth perception

• turtles preferred shallow side: 76% crawled onto shallow side

Conclusion: suggests that aquatic turtles could detect depth however expected they would have gone to the deep side as similar to surface of water but preferred shallow side

STRENGTHS

• controlled environmental conditions meaning potential causes of depth perception could be examined in highly control environment w/o risk to pps
• extraneous variables controlled such as potential distractions, background noise, reflections from glass etc
• animals and humans were not suffering or experiencing any harm

WEAKNESSES

• sampling of human infants very small, not representative of infants between age ranges (6-14 months) selected from availablility at Cornell uni
• some babies more mobile than others, less consistent and reduces reliability
• age of pps (6-14 months) difficult to identify if depth perception is innate or not, infants already had visual experience of world before crawling, so could learn
• visual cliff apparatus: child never actually 'fell', therefore could have learnt there was no deep side, difficult to measure innate ability
• ethics: some infants distressed when couldn't reach mother: physical/psychological harm; babies had no right to withdraw

1. Schwartz et al (1973) SUPPORTS

• placed 5 - 9 month old infants on deep/shallow side, measured heart rate
• placed over drop, 5 month old: no increase in heart rate, 9 month old did

SUPPORTS: those in same age group in G+W's study who were mobile showed physical changes, those who weren't mobile couldn't; younger babies showed no difference in heart rate; suggests innate ability may not be present; however, those with no increased heart rate may have depth awareness but no fear response to gap: survival ability questionnable

2. Sorce (1985) DEVELOPS

• performed variation in visual cliff expt, mother had to maintain expression of fear or happiness on other side of 'cliff'
• when mother smiled = babies crossed cliff
• when mother expressed fear = babies more reluctant to cross

DEVELOPS: depth perception may be innate, still learn through environment/upbringing depth response; ability to judge present but reaction learnt

3. Bower et al (1970) DEVELOPS/CONTRADICTS

• infants of 6 days shown 2 objects
• large disc apparoach to within 20cm of them
• small disc approached to within 8cm of them
• both objects created retinal image of same size suggesting equal distances
• infants so upset by smaller closer disc, study stopped early

DEVELOPS: suggests depth perception may be innate but may occur earlier than G+W claim (before crawling); suggests in species which are not prococial, depth perception could occur

4. Bremner (1994) DEVELOPS

• concluded that ability to interpret dynamic visual info (moves) occurs earlier than static visual info about depth

possibly DEVELOPS as links to ability shown by Bower; therefore perhaps depth perception involves different processes that must be broken down further e.g vertical, horizontal, distance perception, or movement, static, object perception etc