SENSATION AND PERCEPTION
Sensation
Definition: Sensation is the process that detects stimuli from our bodies and our environment.
Perception
Definition: Perception is the process that organizes those sensations into meaningful information.
Absolute Threshold
Definition: Absolute Threshold is the minimum amount of stimulation that can be detected by the senses.
Examples of Absolute Threshold:
Vision: A candle flame at 30 miles away on a clear night.
Hearing: A watch ticking 20 feet away.
Taste: 1 teaspoon of sugar dissolved in 2 gallons of water.
Smell: A single drop of perfume in a three-room house.
Touch: A bee's wing falling from a distance of 1 centimeter onto the cheek.
Just Noticeable Difference (JND)
Definition: Just Noticeable Difference (JND) is the smallest increase or decrease in a physical stimulus required to produce a change in sensation that a person is able to detect 50% of the time.
Weber's Law: States that the JND is based on a percentage or proportion of stimulus change rather than a fixed amount of change.
For example:
A weight must increase or decrease by 1/50th or 2% for JND.
A 2 lbs difference is needed for a 100 lbs weight.
A tone must be 0.33% higher or lower for JND.
The Eye Structure and Function
Components of the Eye:
Cornea:
Tough, transparent, protective layer covering the front of the eye.
Bends light rays inward through the pupil.
Pupil:
Small dark opening in the center of the iris.
Iris:
Colored part of the eye.
Dilates and contracts the pupil to regulate the amount of light entering the eye.
Lens:
Transparent, disk-shaped structure behind the iris and pupil.
Focuses items on the retina.
Retina:
Contains visual sensory receptors.
Blind Spot:
Area of the retina where optic nerves exit; lacks photoreceptor cells.
Retinal arteries and veins:
Supply the retina with blood.
Effects of Pupil Size:
The size of the pupil affects strain on the eyes.
Dark surfaces versus light surfaces: Dark on light is less strenuous than light on dark; there are fewer changes in pupil size.
Large pupils are typically more attractive (common in cartoon characters or puppies).
Pupil dilation occurs in response to arousal from attractive or adverse stimuli.
Vision
Color Blindness:
There are three kinds of photo-pigments in the cones of the eye: red, blue, and green.
If a person is color blind, they lack one or more of these pigments.
Most common color blindness affects the ability to discriminate between red and green; blue cones function correctly, but red and green cones have the same pigment, typically resembling green.
Yellow-blue color blindness is less common.
Monochromacy (black and white vision) is the least common.
Rods and Cones:
Photoreceptors: Approximately 120 million rods and 6 million cones in each eye.
Rods: Responsible for night vision and peripheral vision.
Cones: Responsible for day vision and color vision.
Positioning: Color-sensitive cones are predominantly central in the retina, while color-blind rods are more concentrated in the periphery.
Visual Phenomena:
Phi Phenomenon:
Discovered by Wertheimer (1912), it is where the brain processes distinct sensations (movements of two static lines) to produce apparent motion.
Overall, the apparent motion is greater than the sum of its parts.
Beta Movement:
Related phenomenon facilitating the perception of motion in films and animations.
Perceptional Organization
Identifying Figures and Backgrounds:
Perceptional organization allows individuals to identify figures, objects, and events that stand out against the background.
Example: Following one conversation in a noisy party environment.
Principles of Perceptional Organization:
Figure/Ground Principle:
1) Figure is perceived as having form, while ground appears form-less.
2) A contour line divides a figure from the background, belonging to the figure, not the ground.
3) The figure appears to be located in the foreground, with the ground behind it.
Similarity:
Objects with similar characteristics are grouped together, perceived as units.
Proximity:
Objects that are close together are perceived as belonging together.
Continuity:
Figures or objects are perceived as belonging together if they form a continuous pattern.
Closure:
Figures with gaps are perceived as complete, leading to the understanding of whole figures from incomplete data.
Visual Tricks:
Linear Perspective: Optical illusion demonstrating that objects appear larger when positioned higher up in a visual field.
Hearing
Sound as a Stimulus:
Sound is created by compressing and expanding air molecules, which form sound waves.
Decoding Sound Waves:
Sound waves strike the ear drum, causing it to vibrate.
Tiny bones in the middle ear (ossicles) pick up the vibrations and transmit them to the cochlea, a coiled, fluid-filled tube in the inner ear.
Ripples in the fluid of the cochlea bend the hair cells lining the surface, triggering impulses in nerve cells.
These nerve cells transmit the signal to the auditory cortex for processing.
Touch
The sense of touch is comprised of four distinct skin senses:
Pressure
Warmth
Cold
Pain
Variations of these four sensations comprise other skin sensations.
Example: Cold dry metal feels wet if it stimulates adjacent cold and pressure sensors. Pain serves as the body's signal that “something has gone wrong.”
Taste (Gustation)
The Sense of Taste:
The primary tastes detected include:
Sweet
Sour
Salty
Bitter
Umami
Taste Buds:
Structures in many of the tongue's papillae composed of 60-100 receptor cells specialized for taste detection.
Papillae: Small bumps on the tongue containing the taste buds.
Key Terms
Absolute Threshold
Definition: Minimum stimulation needed for detection by the senses.
Examples of Absolute Threshold:
Vision: A candle flame at 30 miles away on a clear night.
Hearing: A watch ticking 20 feet away.
Taste: 1 teaspoon of sugar dissolved in 2 gallons of water.
Smell: A single drop of perfume in a three-room house.
Touch: A bee's wing falling from a distance of 1 centimeter onto the cheek.
Color Blindness – Rods and Cones
Definition: A condition where an individual lacks one or more of the color-detecting photo-pigments in their cones.
Types of Color Blindness:
Most common affects red and green discrimination.
Yellow-blue Color Blindness: Less commonly affects color vision.
Monochromacy: The rarest form, resulting in black and white vision.
Ground and Field, Figure and Form
Definition: Concepts in perceptual organization referring to how we distinguish an object (figure) from its background (ground).
Example: Identifying a person in a crowded place involves perceiving them as the figure against the ground of the crowd.
Just Noticeable Difference (JND)
Definition: The smallest change in stimulus intensity that can be detected 50% of the time.
Weber's Law: JND is based on the proportion of the original stimulus rather than a fixed amount.
Example: A weight must increase by 2% for it to be noticed.
Linear Perspective
Definition: An optical illusion where parallel lines appear to converge as they recede into the distance.
Example: Roads or rail tracks seem to come together at a distance, giving depth to a two-dimensional image.
Perception
Definition: The process of organizing and interpreting sensory information to give it meaning.
Perceptual Organization
Principles: How we organize information to perceive patterns and objects.
Figure/Ground Principle: Differentiating between the object and its background.
Similarity: Grouping similar items together.
Proximity: Objects that are close are perceived as related.
Continuity: Perception of continuous patterns.
Closure: Filling in gaps to perceive complete figures.
Phi Phenomenon and Beta Movement
Phi Phenomenon: The perception of motion when distinct images are presented in quick succession.
Beta Movement: The perception of moving objects in films through the rapid display of images.
Sensation
Definition: The initial process of detecting stimuli from the environment and body.