Gibson & Walk

• What was the background?

  • Height perception is a form of distance perception
  • When both eyes are open the brain receives and integrates info from both eyes to allow objects to be perceived in 3D
  • When observer moves the apparent relative motion of several stationary objects against a background gives hints about their relative distance
  • If info about direction and velocity of movement is known  motion parallax can provide absolute depth info
  • Yerkes - aquatic turtles have poorer depth-discrimination than land turtles
  • Other studies found depth perception is innate in rats
• What were the aims?

  1.  To investigate if the ability to perceive and avoid a drop is learned through experience or is it part of the child’s original blueprint and innate

  2.  To discover the point in development which infants can perceive depth and whether this varies in different animal species – specifically does it come before or after or at the same time as the ability to move around independently

  3. To test which two visual cues is more important in depth perception – the density of pattern in the environment (texture) or motion parallax
• What was the method?

  • Lab exp
  • Repeated measures
  • IV – whether babies were called by their mothers across the shallow side or deep side of the visual cliff
  • DV – whether or not the baby crawled across the visual cliff
  • Studies with animals:
  • Quasi exp
  • IV - species of animal
  • DV - preference for deep or shallow side
• What was the procedure?

  • All placed in centre board and mother called to them from shallow or deep end for 2 conditions
  • Conditions slightly changed for animals
  • Reflections removed by lighting up below
  • Texture density - texture on deep side seems finer than shallow because further away - increased size of squares so appear same size
  • Motion parallax - cue to depth / distance because shallow side squares appeared to move quicker across babies FOV when moving across glass - attached checkered material to both sides of glass

  
• What were the results for babies?

  • 27 infants crawled off board onto shallow side at least once
  • Only 3 crawled off cliff onto glass
  • Many infants crawled away from mother when she called from deep side and cried when they couldn‘t reach her without crossing chasm
  • Infants peered through glass on deep side and backed away
  • Some patted glass with hands but still refused to cross
• What were the results for rats?

  • Could feel glass with whiskers so had no preference for shallow side and moved normally when placed over the deep side
  • When centre board was raised so glass was out of reach of their whiskers they showed good visual depth perception with 95 - 100% descending on shallow side
  • When cliff used to see whether depth perception as innate in rats at 90 days old both light and dark reared showed same preference for shallow side - it is innate
• What were the results for kittens?

  • Demonstrated excellent depth perception
  • At 4 weeks almost chose shallow side of cliff
  • On the glass over the deep side they either froze or circled aimlessly backward until they reached the centre board
• What were the results for turtles?

  • Turtles showed the poorest performance with 76% of them crawling off the board to the shallow side
• What were the conclusions?

  • Babies can perceive depth when they can independently move (motion parallax)
  • A seeing animal can discriminate depth when its locomotion is adequate but infants should not be left close to an edge
  • Depth perception in chicks, goats and kittens develop quick, while rats and kittens use cues from whiskers to help depth perception
  • Aquatic turtles actually have good depth perception
  • Depth perception is innate in rats and maturational in kittens
• What was the sample?

  • 36 human babies aged 6-14 months all capable of independent locomotion
  • Had parent consent as mothers also took part
  • Infants of other animals including chicks, lambs, kids, kittens (including reared in darkness for 27 days), rats (dark reared and wearing hoods), pigs, dogs and aquatic turtles
  • Animals were self-selecting, advertised in the local vets4pets magazine and parents verbally gave consent to taking part whilst filling out a questionnaire on mental wellbeing