PSYC100 Sensation pt 1
Welcome to PSYC100
Course Introduction: PSYC100 aims to make psychological concepts understandable, encouraging active learning by testing what you remember (retrieval practice).
Activity: Students are challenged to describe how information travels through neurons without using notes, then check their accuracy.
Engagement Tools: Students are encouraged to prepare for class participation using Poll Everywhere (www.pollev.com/punchyocean).
Today's Topics
The focus for the day includes:
Discussion of epigenetics
Comparison between sensation and perception
Review of brain processing
Explanation of how processing functions as a two-way street
Exploration of how we interpret visual information.
Epigenetics
Definition: Epigenetics is the study of how external factors can turn genes "on" or "off" without changing the actual DNA sequence. It shows that both your genetics (nature) and your environment (nurture) work together, not separately, to shape who you are.
Example: If you're stressed for a long time, it might turn on (or turn off) certain genes that affect your mood or health, even if those genes were inherited from your parents.
Sensation and Perception Discussions
Sensory Experiences: Discussions centered around popular phenomena such as:
The Yanny vs. Laurel audio controversy, where different people hear different words from the same sound file.
The viral internet image of a dress (often referred to as "The Dress") and how individuals perceive its colors (e.g., blue and black vs. white and gold) differently.
Reality and Perception
The class explores the idea that people often believe their shared sensory experiences reflect an objective reality.
Key question: Do our senses provide an objective representation of reality, or is it more of a personal interpretation?
Process of Visual Information
Think about seeing a red apple:
Physical Stimulus:
Light waves reflected from the red apple enter your eye. These waves first pass through the clear outer layer (cornea) and then through the dark opening (pupil).
The eye's lens focuses these light waves onto the back of your eye (retina).
Sensation:
Special light-detecting cells in your retina, called rods (for low light and peripheral vision) and cones (for color vision and detail), sense these incoming light waves.
Transduction:
Rods and cones convert the light waves into electrical signals. These signals are then processed by other cells (ganglion cells) which create impulses (action potentials) that travel along the optic nerve to your brain.
Perception:
The electrical signals from each visual field (e.g., what you see to your left) are sent to specific visual areas in the brain, mainly the visual cortex.
The brain processes information by splitting it: signals from the left side of your vision go to the right side of your brain, and signals from the right side of your vision go to the left side of your brain. This is where you actually "see" and understand that it's a red apple.
Case Study: Prosopagnosia
Definition: Prosopagnosia, also known as face blindness, is a brain disorder where a person struggles to recognize faces, even familiar ones like family members, while their other visual abilities (like seeing objects or navigating) remain normal.
Discussion Prompts:
Consider the role of sensory receptors during varying light conditions for individuals with prosopagnosia.
Information from the eyes is processed in the brain's occipital lobe (the back part of your brain).
In prosopagnosia, the perceptual part related to facial recognition is disrupted (they can see a face, but not recognize it as a specific person), while skills like knowing where objects are in space still work.
Processing of Information
The concept that information processing is a “two-way street” means your brain uses both incoming sensory data and your past experiences to understand the world:
Bottom-up Processing: This starts with analyzing the raw physical details from your senses and building up a complete picture. It's like assembling a puzzle piece by piece without knowing what the final image is.
Example: Reading an unfamiliar word by first seeing each letter (sensory input) and then combining them to sound out the word.
Top-down Processing: This relies on your prior knowledge, expectations, and experiences to interpret sensory information. It's like having a general idea of the puzzle's picture and using that to guess where pieces go.
Example: Being able to read a sentence even if some letters are missing, because your brain uses context and your knowledge of words to fill in the gaps (e.g., "I lve pzza").
Environmental Cues in Perception
Binocular Depth Cues: Cues that require both eyes to perceive depth (how far away something is).
Binocular Disparity: The slight difference in the images seen by your two eyes. Your brain uses this difference to calculate how far away an object is.
Example: Hold your finger close to your face and alternate closing each eye. Your finger appears to jump because each eye sees it from a slightly different angle.
Convergence: The inward turning angle of your eyes when you look at close-up objects. The more your eyes turn inward, the closer your brain perceives the object to be.
Example: If you look at something very close, your eyes will cross a bit; this muscle strain gives your brain info about its closeness.
Monocular Depth Cues: Cues that can be perceived with just one eye, including:
Occlusion (Interposition): When one object blocks part of another, the blocking object appears closer.
Example: If a tree is blocking part of a house, you know the tree is in front of the house.
Relative Size: If two objects are known to be the same actual size, the one that appears larger in your vision is perceived as closer.
Example: Two identical cars, one far away looks tiny, the one close up looks normal size.
Familiar Size: Your knowledge of an object's typical size influences how you perceive its distance.
Example: Because you know how big a standard STOP sign is, you can estimate its distance based on how large or small it appears.
Linear Perspective: Parallel lines appear to converge (come together) in the distance.
Example: Looking down a long, straight road, the edges of the road seem to meet far away on the horizon.
Texture Gradient: The texture of surfaces appears less detailed and smoother as they get further away.
Example: A field of flowers has clear, individual flowers up close, but appears as a smooth, blurry patch in the distance.
Position Relative to Horizon: Objects closer to the horizon line (if below it) appear further away, and objects higher in the visual field (if above the horizon) appear further away.
Example: In a landscape picture, a boat drawn near the bottom of the paper appears closer than another boat drawn higher up, near the horizon.
Additional cues include more complex spatial relationships, which accurately inform perception.
Psychological Concepts
Philosophical Roots of Perception:
Various psychological theories address how we perceive and organize visual information, including:
Structuralism: Focuses on breaking down mental processes into the most basic components, like trying to identify the individual sensations (e.g., color, shape, texture) that make up a visual experience.
Functionalism: Considers mental processes in terms of their practical purpose or function in adapting to the environment, asking why we perceive things the way we do (e.g., why do we recognize faces?).
Gestalt Psychology: Emphasizes the human tendency to perceive patterns and wholes, rather than just individual parts, often summarized by "the whole is greater than the sum of its parts." Exemplified through principles like:
Figure-Ground: Distinguishing a central object (figure) from its surrounding background (ground).
Example: Seeing a vase or two faces in the Rubin's vase optical illusion.
Proximity: Objects close to each other are perceived as related or belonging together.
Example: A group of dots arranged closely together is seen as a cluster, not separate dots.
Similarity: Similar objects (e.g., in color, shape, size) are grouped together in perception.
Example: In a crowd, you might group people wearing the same color shirt together.
Illusory Contours: The perception of edges or borders even when none physically exist in the stimulus.
Example: Seeing a white triangle in the middle of three Pac-Man shapes, even though no lines define it.
Closure: The inclination to complete incomplete figures to perceive a whole, familiar shape.
Example: Seeing a full circle even if part of its outline is missing.
Good Continuation: A preference for viewing smooth, continuous patterns rather than disjointed ones.
Example: Seeing an 'X' made of two continuous lines crossing, rather than two 'V' shapes touching at their points.
Sensory Information Processing
Sensory Thresholds:
Absolute Threshold: The minimum level of stimulus intensity needed to detect a stimulus 50% of the time, meaning if it's any weaker, you probably won't notice it.
Example: If you're in a completely quiet room, the softest sound you can hear half the time would be your absolute threshold for hearing.
Difference Threshold (Just Noticeable Difference - JND): The smallest detectable difference between two stimuli that you can notice 50% of the time.
Example: Adding one sugar cube to an already very sweet drink might not be noticed (below JND), but adding it to plain water would be very noticeable.
Sensory Adaptation: The process where your sensitivity to an unchanging stimulus decreases over time because your sensory receptors get used to it.
Example: When you first put on a watch, you feel it on your wrist, but after a while, you stop noticing it.
Habituation: A form of learning where an organism reduces its response to a repeated, harmless stimulus because it learns the stimulus doesn't require action.
Example: Initially, a new ticking clock in your room might keep you awake, but after a few nights, you no longer notice the sound.