GIBSON & WALK OVERVIEW

AIMS

aimed to investigate if the ability to percieve depth is learned thorough experience or whether it is part of a childs 'original endownment' they needed to test human and non human animals to test the argument to see if cliff avoidance behaviours were evident from the time young animals were mobile

CONTEXT

• NATIVISTS; believe were are born with capacity to percieve depth,appears as you mature
• EMPIRICISTS; assume depth perception is acquired in response to environmental demands
• INTERACTIONISTS; believe both, they see nature: at birth we have depth perception but it isnt matured or developed until we are 4 months old. and nurture: exposed to complex stimuli such as faces, we learn too interpret 2D depth cues including shadowing

if depth perception is innate we would expect it to be apparent by the time a young animal is mobile, need it to survive - adaptive.

• Apparatus;
  • visual cliff table enables researcher to control optical, auditory and tactile stimuli and also protect participants
  • patterns underneath the glass gave visual clues - deep or shallow
  • participant was placed on centre board and encouraged to move to shallow or deep side
• Participants;
  • 36 human infants from the age of 6-14 months - all able too crawl
  • non human animals: chicks, lambs, kids, kittens, rats, pigs, dogs, turtles
• Testing depth cues;
  • size spacing of the pattern - squares appeared larger and more widely spaced on shallow side, sometimes the pattern on the deep side was increased so looked the same
  • motion parallax - pattern elements on shallow side move more rapidly accross the fielf of vision when animal alters it position or head. so pattern placed directly beneath glass on both sides but pattern size was bigger so it appeared closer

• Humans - 27/36 moved off centre board
  • all crawled onto centre board, only 3 attempted deep side
  • if mom called them they either went onto shallow or cried because couldnt get across
  • infants would tap glass with hand, but didnt cross
• Non human animals -
  • chicks kids lambs didnt move onto deep side, if put on deep side they froze in defence
  • kittens preffered shallow side and froze when placed on deep side, dark reared kittens went equally onto both
  • hooded rats searched both sides because they could feel glass with whiskers
  • unhooded rats went on both, but if centre board was placed higher they went shallow
  • turtles performed worse than other animals 24% crawles onto shallow
• Depth cues -
  • size/spacing depth que only; (both patterns placed under glass) unhooged rats preffered side with larger pattern 'shallow side' chicks showed no preference
  • motion parralax depth cue onle - rats preffered shallow side as did the chicks
  • dark reared rats preferref shallow side when using only motion parallax

• Most human infants can discriminate depth  as soon as they can crawl, some of them backed onto the cliff side accidently, which suggests infants shouldnt be left on a cliff edge
• Evidence cant prove that human depth perception is innate, but it does support the nativist view. this is further supported by the studies of non human animals - all findings fit with life history and ecological niche with the animals studied - all showed discrination of depth by the time they were mobile - goat and chick discriminated at 1 day old, cat and rats did at the age of 4 weeks. the poor performance from the turtles  suggested they have poorer depth discrimination - their natural habitat has less danger of falling off cliffs - adaptive
• The preference shown by rats for the shallow side when only size shape cues were available could be explained in terms of learning- older at time of testing than the chicks - so learned depth cues because dark reared rats showed no peference
• Research with rate suggests that motion parallax is an innate cue whereas 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 independant locomotion, whether it be at 1 day (chick and goat) 4 weeks (rat and cat) or 6-14 months (human infant) that such a vital capacity doesnt depend on possibly fatal accidents of learning  in the lives of individuals is consistent with evolutionary theory

DESIGN: -lab experiment

ETHICS: -infants demonstarted distress when couldnt get to mother, Dwkins (1990) notes that morally questionable research using non human animals might be acceptable if the goal is the alleviation of human suffering, but may not be acceptable if goal is the satisfaction or interlectual curiosity

VALIDITY: -one validity issue is whther the research with infants is actually capable of assessign whether depth perception is innate or learned. - age of the infants
-more recent experiments has tested younger kids - found older kids were more wary
-(Adolph and Berger 2006)claimed infants learned glass was safe and they didnt fall

SAMPLE: -limited to infants available to researchers
- humans are socially dependant, most animals were not socially dependant on their mother for survival and nurturing

Schwartz et al (1973)- placed infants on either side of the table and measured heat rates - between 5-9 months. 5 months didnt show change in heart rate whereas 9 months did

Sorce et al (1985)- conducted same research but when mother showed expression on happiness- infants crossed onto deep side, when they expressed fear infants were reluctant to cross

Witherington et al (2005)- found infants with strongest aversion too cliffs were older and had the most experience of walking and crawling, so infant is learning to associate the physical experience with visual experience

STRENGTHS

• small sample
• safe table - easy to measure
• tested range of creatures
• easily replicable

WEAKNESSES

• small sample
• old infants - had time to learn depth perception
• ethical issues- caused distress