Background/context
Height perception = a form of distance perception with both eyes, so the brain receives information from both visual fields so we can see in 3D
Depth cues let us perceive height, relative size, linear, perspective and texture gradient
If info about direction and velocity of movement is known, motion parallax provides depth information
Infants are more prone to fall, because their visual co-ordination hasn't fully developed
Aim
To investigate how humans and animals perceive height distance and to consider the stage they develop the ability to perceive height distance
Method
Humans
Lab experiment, repeated measures
Iv= whether infant was called by mother from cliff side or shallow side (of the visual cliff apparatus)
Dv= whether the child crawled to it's mother or not
Animals
Quasi-experiment
Iv= species, rat/chick/lamb/kitten
Dv= whether they preferred shallow or deep side of the visual apparatus
Procedure
Sample
36 infants, 6-14 months
Young animals
Design
Lab experiment, using a visual cliff to test height distance perception safely
It was a board laid across a sheet of glass, 1 foot above the floor and on one side, a patterned material was placed under the glass (shallow side) and the other side of the glass, the same board was on the floor (cliff side) = illusion of depth
Human trial
Each kid placed in the middle of the board, individually tested
Mothers were there to motivate the babies to move, they called from both sides and the child's behaviour was recorded
Animal trial
Animals from cornell behaviour farm, there was also dark reared kittens (reared in darkness for 27 days)
Controls
Number of changes to set up to check for bias, e.g. lighting, pattern and height distance
Separation of visual cues
Researcher included a variation with 2 materials placed under each side
Motion parallax = looking out a side and then front car window
Relative size = smaller it looks, further away it is
To remove cues, placed patterns at the same level
To remove object cue size they used a large pattern on low side of cliff = constant density
Results
Human trials
All 27 infants went to the shallow side, only 3 went to the deep side, many crawled away from mother
Some cried because they thought it would be dangerous to reach their mum on the deep side
Dependent on their vision to determine movement, even if they felt the glass, they'd refuse to change it or cross over it
Several would've fallen off if there had been no glass
Animal trials
Depth perception emerged once an animal became mobile = adaptive purpose = helping them avoid falls in the wild
Dark reared kittens equally likely to move to cliff as shallow and didn't freeze when on the cliff side
After a rock in light, they behaved the same as the other kittens = suggests light is needed for visual maturation
Control trials
Variations found no hidden bias
When researchers placed plain grey surfaces down instead, rats still had no preference, same when patterns were both against and under the glass
Separation of visual cues
Day-old chicks and rats in both conditions = preference for shallow side
Motion parallax = innate visual cue that develops through maturation
Conclusion
Nature + nurture influence development of depth perception
Binocular cues like motion parallax are innate
monocular cues like size constancy are learned
Humans and animals develop some depth perception by the time they're mobile
Evaluation
Stressed babies so some psychological harm, ethical issues with using animals, and subtle cues from mothers could've biased the findings and lowered the validity