Perception: Interpreting Our Sensory World
Sensation vs. Perception
Sensation: The process by which our sensory receptors and nervous system receive and represent stimulus energies from our environment.
It is a more passive process, like your brain receiving raw data from your eyes, ears, taste buds, skin, and nose.
Everything you see, hear, taste, touch, and smell are sensations.
Perception: The process of organizing and interpreting sensory information, enabling us to recognize meaningful objects and events.
It is your personal interpretation of those sensory impulses.
Often referred to as top-down processing because your brain interprets the raw sensory data based on prior knowledge, experiences, and expectations; once you perceive and interpret it, you sometimes react.
Perception is subjective; what one person perceives and likes, another might dislike, due to individual backgrounds and experiences.
Factors Influencing Perception: Perceptual Set
Perceptual Set: A mental predisposition to perceive one thing and not another; it is influenced by our experiences, backgrounds, and expectations.
Our unique life experiences lead us to like or dislike certain things.
Example 1 (Concert): Someone with prior concert experience might enjoy a show immediately, while another person without such experience might feel bored or unimpressed when expectations aren't met (e.g., expecting lights and singing but getting a different atmosphere).
Example 2 (Ambiguous Images):
Images like "Bigfoot" or the "Loch Ness Monster" are often perceived as such by individuals who have a perceptual set (background knowledge, stories, or expectations) related to them.
Foreign exchange students, lacking this specific cultural background or perceptual set, might describe the "Bigfoot" image simply as "a gorilla" or "something in a suit" because they don't have the prior knowledge to interpret it as Bigfoot.
Similarly, a highly distorted image of a recognizable celebrity (e.g., Batman's face) can be identified by those with a perceptual set (prior exposure to the image/character) but not by those who have never seen it.
Classroom Activity (Priming):
This activity demonstrates how a perceptual set can be created or 'primed.'
One group (Group A) was shown images of animals before viewing an ambiguous figure, leading them to perceive an animal in the ambiguous figure.
Another group (Group B) was shown images of faces before viewing the same ambiguous figure, causing them to perceive a face.
A similar demonstration involved an ambiguous image that could be seen as an old woman or a young woman. By first showing images that accentuated either the 'old woman' or 'young woman' features, students were primed to see one interpretation over the other.
Priming refers to the activation, often unconsciously, of certain associations, thus predisposing one's perception, memory, or response.
Significance: Our backgrounds, expectations, and assumptions are the reasons why we all experience and interpret things very differently.
Factors Influencing Perception: Context
Context: The background, environment, or surrounding circumstances in which something takes place; it significantly influences how we perceive it.
Example 1 (Height Comparison):
Basketball player Sun Ming Ming (who is feet inches tall) makes normal-height individuals (like Randy Gill, at feet inches) appear short by comparison.
However, if Randy Gill were compared to the average individual, he would be perceived as very tall.
The context (who you are comparing someone to) changes your perception of their height.
Example 2 (Facial Expression):
In a college study, an image of a man with a blank expression was cropped into two different scenes: an amusement park and a funeral.
When placed in the amusement park context, observers perceived the man as "having fun" or "excited."
When placed in the funeral context, the same blank expression was perceived as "sad."
This demonstrates that the context heavily sways our interpretation of emotions or situations.
Example 3 (Ambiguous Characters): A visual display of a character that could be interpreted as a letter 'B' or a number '13' changes its perception depending on its surrounding characters. For instance, if surrounded by letters "A C", it's perceived as 'B'. If surrounded by numbers "12 14", it's perceived as '13'. The context of the surrounding characters dictates the interpretation of the ambiguous one.
Perceptual Constancies
Perceptual Constancy: The tendency to perceive familiar objects as having constant lightness, color, shape, and size, even as illumination, retinal image, or distance changes.
Types of Perceptual Constancy:
Shape Constancy: We perceive the form of familiar objects as constant even while our retinal image of it changes.
Example: A door is a rectangle. When it opens, its image on our retina becomes a trapezoid. However, we still perceive it as a rectangular door, not suddenly a trapezoid.
Size Constancy: We perceive objects as having a constant size, even while our distance from them varies.
Example: As a student walks further away, they appear smaller on your retina. Yet, you still perceive them as "people-sized" and don't assume they have physically shrunk.
Color Constancy: We perceive familiar objects as having a consistent color, even if changing illumination alters the wavelengths reflected by the object.
Example: Red brick buildings in a city at night, under very dim light, might not reflect red wavelengths directly to your retina (since only rods, not cones, are active in dim light, and rods don't perceive color). However, because your brain knows bricks are red, you'll still perceive them as red, even if you're not actually seeing the red color.
Perceptual Plasticity (Adaptation)
Perceptual Plasticity (Perceptual Adaptation): The ability of the brain to adapt to a very distorted or unusual visual field.
The brain can actively compensate for changes in sensory input.
Example 1 (Cataracts): Individuals developing cataracts (spots on the lens of the eye) initially experience difficulty judging depth or distance due to distorted vision. However, over time, their brains adapt and learn to compensate for these visual distortions.
Example 2 (Stratton's Inverting Goggles):
Psychologist George M. Stratton invented special goggles that flipped the wearer's entire visual field upside down.
Volunteer research participants wore these goggles for extended periods to test visual adaptation.
Case Study (Suzanne LaFine): A British art student, Suzanne LaFine, wore these inverting goggles for a week.
Initially, she struggled significantly (e.g., reading, drawing).
Remarkably, within a few days, her brain began to adapt. She could eventually perform complex tasks like reading inverted letters, writing her name right-side up while seeing upside down, pouring coffee, and even riding a bike.
This demonstrates the brain's incredible ability to adapt to radically altered visual input, eventually making sense of an upside-down world by inverting the perception to match reality.
Development of Depth Perception
Depth Perception: The ability to see objects in three dimensions although the images that strike the retina are two-dimensional; allows us to judge distance.
Gibson and Walk's "Visual Cliff" Experiment (1960s):
Motivation: Researchers Eleanor Gibson and Richard Walk, while at the Grand Canyon with their young, crawling son, wondered when humans develop the ability to perceive depth and fear heights.
Hypothesis: Infants, once mobile, possess depth perception to avoid falls.
Methodology: They created a "visual cliff" – a table with a solid surface on one side and a clear glass surface extending over a patterned 'drop-off' on the other, covered by a tablecloth to create a visual illusion of a cliff.
A baby was placed on the shallow (solid) side, and the parent stood on the 'deep' glass side, coaxing the baby to crawl across.
Results & Conclusion: Most babies, once they could crawl, refused to crawl over the perceived "cliff" onto the glass, even when their parents called them. Many babies would reach the edge and try to put their leg down, finding only glass, demonstrating their accurate perception of depth. This indicated that depth perception largely develops by the time an infant learns to crawl.
Later Research on Earlier Development of Depth Perception:
More recent studies have investigated whether depth perception develops even earlier.
Methodology: Babies (around - months old) were placed in car seats with a glass barrier in front of them. An object was then thrown directly into their line of sight, appearing to fly towards them but stopping at the glass.
Results & Conclusion: Around months of age, most babies consistently turned their heads to avoid the incoming object, despite the glass barrier. This suggests that even at this young age, infants have developed some understanding of distance and will react defensively, indicating an earlier, nascent form of depth perception prior to crawling.