Gibson's Direct Theory of Perception

Gibson's Direct Theory of Perception

• Perception is based on what is directly visible.
• Perception relies on immediate surroundings.
• Prior experience/learning is unnecessary to fill perceptual gaps.
• Humans perceive the world from birth.
• Gibson's theory supports the nature side of the nature vs nurture debate.
• Gibson did not differentiate between sensation and perception.

Gibson & Walk (1960)

• A study demonstrated young infants' innate depth perception.
• Infants crawled on a raised glass top, visually creating a sudden drop.
• Babies could see that the ground beneath them had seemingly disappeared, even when the glass was safe to cross.
• Researchers predicted babies would halt at the 'edge' and not cross the glass, even with maternal encouragement.
• 92% of babies stopped at the 'edge' and did not cross the glass.
• This suggested humans are born with depth perception.

Motion Parallax

• Motion parallax happens when a person moves through space.
• This can happen on foot, or in vehicles, etc.
• Sensation that objects move towards a person while a destination remains stationary.
• Visual streaming is a continuous movement in one direction, known as optic flow.
• The retina is constantly stimulated by changing images, which signals motion to the brain.
• Motion parallax involves cues that the brain gets from optical flow.
• Objects closest in the visual field appear to move faster than distant objects.
• Objects at mid-range in the visual field move in the opposite direction to the person.
• Distant objects move in the same direction as the moving person.
• Gibson's theory applies to pilots, especially during landing, and was developed with pilots during WWII.
• Pilots use optical flow for data about:
• Distance between the plane and ground.
• Potential obstacles.
• Landing surface.
• Approach speed and deceleration.
• Runway outline.
• The patterns of light on the pilot's retina determine if it is safe to land.

Evaluation of Gibson’s Direct Theory

• The theory trains pilots effectively, demonstrating validity.
• Gibson & Walk's (1960) study supports innate perception, as babies cannot fake their responses.
• The theory does not explain visual illusions, where perception is inaccurate.
• Research with young babies has inherent issues like:
• They cannot explain their behavior.
• They can be unpredictable.
• Procedures like the Cliff Walk raise ethical concerns.

Limitations of Gibson’s Theory

• Cannot explain inaccurate perception from visual illusions.
• Lab experiments lack ecological validity, not reflecting real-world depth perception.
• Does not account for factors like expectation and culture.
• Is challenged by blind individuals who regain sight and must learn to navigate.

Gregory’s Constructivist Theory of Perception

• Perception is a product of learning and physical world experience.
• Past experiences and stored information help with understanding.
• Humans use senses to infer about the world, especially with limited information.
• Inferences help fill gaps and make sense of information.
• Perception requires active processing.

Gregory & Wallace (1963) Case Study

• Study involved a man (SB) blind since infancy who had his sight restored after 50 years.
• SB was tested 48 days post-sight restoration.
• Initial sight abilities included:
• Navigating a corridor.
• Enjoying moving objects.
• Understanding object sizes.
• Difficulties experienced by SB:
• Focusing only when asked.
• Crossing the road (despite ease when blind).
• Understanding depth and distance.
• Depth and distance perception improved with practice.
• Concludes perception may be more nurture than nature.

Inferences from Visual Cues

• SB supplemented non-visual cues with newly gained visual cues.
• Visual cues help with navigating and understanding the physical world.
• Visual illusions can give faulty information.
• Gregory discussed 'mistaken hypothesis', which explains brain errors in visual illusions.
• Gregory's theory is a 'top-down' theory, inferring predetermined ideas.

Evaluation of Gregory’s Constructivist Theory of Perception

• Supported by cross-cultural research showing effects from differing environments.
• It explains illusions by emphasizing depth and distance.
• The nurture argument does not account for babies' ability to utilize their senses.
• Gregory & Wallace’s study of SB cannot 'prove' that perception is all nurture as SB did not relearn every aspect of sight.

Describing Gregory’s Theory

• Perception is active, involving inferences from sensory data.
• Perception is constructed by sensations and stored knowledge through experience, interpreting sensory data with prior knowledge.
• Knowledge and expectations are from individual past experiences in their environments.
• Visual illusions show the constructivist theory

Criticisms and Evaluation of Gregory’s Theory

• Illusions reveal that expectations drive perception, as people use stored knowledge of a 3D world on 2D images.
• Research evidence shows that motivations and emotions affect perception.
• Cross-cultural studies reveal that experience influences perception.
• Direct perception theories challenge the theory above, but suggest that senses are detailed enough for one to interpret without prior inference.
• It cannot explain how newborns use sensory data to interpret their environment.
• It may be more applicable to 2D images and illusions, instead of real-world perception.