Gibson & Walk (1960) - Aims & Context
- Depth Perception: The ability to comprehend that some objects are more distant than others.
- Nativists take the "nature" side of the debate. They believe that we are born with the capacity to perceive depth, but these abilities may not be functioning when we are born.
- Empiricists take the "nurture" side of the debate. They believe that we learn depth perception through our experiences.
- Interactionists believe that depth perception is innate and learned. They take both sides of the debate.
- When we are born, our optic nerve is shorter, narrower and has no myelin sheath. The myelin sheath ensures good transmission of information through the nervous system.
- The aim of Gibson & Walk's study is:
- To investigate if the ability to perceive depth is learned through experience or if it is innate.
- Gibson & Walk reasoned that, if it is innate, it should be apparent by the time infants were able to locomote (about the age of 6 months).
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Gibson & Walk (1960) - Procedures
- Set up the visual cliff at Cornell University, USA.
- 36 infants, aged 6-14 months, with the ability to crawl.
- Animals were also used, including chicks, lambs and kids (mobile at 1 day old), kittens and rats (mobile at 4 weeks old), and pigs, dogs and turtles. Kittens who had been reared in the dark for 27 days were also tested.
- Control experients were conducted to eliminate extraneous variables.
- There were two possible depth cues:
- Size/Spacing: This cue was removed by increasing the pattern on the deep side, so the retinal image on both sides was identical.
- Motion Parallax: This cue was removed by placing the patterned material directly beneath the glass on both sides.
- Each child was placed on the centre board, and then observed to see if it would crawl to the deep side, or crawl to the shallow side.
- Adjustable Cliff: Kids and lambs were tested. The shallow surface could be lowered to see how the animal would react when it felt the depth of it's surroundings going down.
- Grey Surface: The pattern was replaced by a uniform grey surface. This tested whether the pattern was the reason that the participants could sense depth and distance.
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Gibson & Walk (1960) - Findings & Conclusions
- All 27 babies who moved off the centre board crawled to the shallow side at least once.
- Only 3 babies attempted to crawl to the deep side.
- Chicks, Kids & Lambs never crossed to the deep side, even at 1 day old.
- Rats depended on their whiskers to navigate. When their whiskers couldn't feel the glass, they shied away from the deep side more than 95% of the time.
- At 4 weeks old, the kittens showed a preference for the shallow side, and froze on the deep side. However, the dark-reared kittens crawled to the shallow and deep side equally.
- 76% of the turtles crawled to the shallow side.
- Rats and chicks still preferred the shallow side when using the motion parallax cue.
- Rats preferred the shallow side when using the size/spacing cue, but chicks had no preference.
- Dark-reared rats preferred the shallow side with the motion parallax cue, but had no preference with the size/spacing cue.
- Most human infants can disciminate depth as soon as they can crawl.
- They can't prove that human depth perception is innate, however it does support the nativist view; all animals showed discrimination of depth as soon as they were mobile.
- Motion parallax is an innate cue, whereas the size/spacing is a learned depth cue.
- "The survival of a species requires that its members develop discrimination of depth by the time they take up independent locomotion."
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Gibson & Walk (1960) - Evaluating The Methodology
- Method - Lab Experiment:
- Standardised procedures, so experiment can be repeated.
- Controlled environment, so extraneous variables can be controlled.
- Pei et al (2007) have shown that human infants can make use of crude patterns, but they can't detect and understand more subtle differences in texture, so advanced visual perception requires experience and learning.
- High internal validity as the researchers did measure what they claimed. Also, babies are less likely to respond to demand characteristics.
- High ecological validity, even though it was a lab setting, the way the cliff was designed mirrored the sort of depth experience that an infant could come across.
- Small sample.
- Babies could have a more stimulating upbringing as their parents were from the university, so the results can't really be generalised.
- Ethical Issues:
- Protection From Harm: Babies were distressed by the cliff and when they couldn't reach their mother.
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Gibson & Walk (1960) - Alternative Evidence
- Schwarts et al (1973) - Contradicts:
- Used babies aged 5-9 months.
- Placed them on the shallow and deep sides, then measured their heart rate.
- The heart rate of the 5 month olds didn't increase, which shows that they can't detect the drop.
- Bower et al (1970) - Develops:
- Showed a group of infants 2 objects; a large disc that came within 20cm of them, and a small disc that came within 8cm of them.
- Infants were upset by the smaller, closer disc.
- This shows that they do have depth perception.
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