PSYCH-101 Ch3 Notes
Introduction to Sensation and Perception
This chapter provides an introduction to the concepts of sensation and perception within the field of psychology, taught by Dr. Thomas Brice for Psych 101 in Autumn 2025.
A pre-survey was administered to assess common sensory and perceptual experiences among students, covering topics like night vision, color blindness, nearsightedness, farsightedness, hearing deficits, tinnitus, olfactory sensitivity, taste sensitivity, motion sickness, and temperature sensitivity.
Pre-Survey Results Summary (examples from class data):
reported trouble seeing at night.
identified as color blind.
wore glasses for nearsightedness.
wore glasses for farsightedness.
used a hearing aid.
constantly experienced ringing in their ears.
were often the first to detect a new odor in a room.
could usually detect tiny amounts of seasoning in food.
often experienced motion sickness.
were often the first to notice a room temperature change.
How We Sense and Perceive the World
The Processes and Purposes of Sensation & Perception
Bottom-Up Processing:
Sensory receptors register information about the environment.
This information is then sent to the brain for processing.
It involves taking in raw sensory information and attempting to make sense of it.
Top-Down Processing:
Begins in the brain.
Pre-existing ideas, expectations, or knowledge influence how incoming sensory information is interpreted.
Both bottom-up and top-down processing occur continually and are used together to make sense of the world.
Purposes of Sensation & Perception: Primarily adaptation to aid survival (e.g., the placement of eyes in predators versus prey affects their visual perception and hunting/evasion strategies).
Caution: Our expectations and stereotypes can significantly influence our sensation and perception. For example, the ability to "find the toothbrush" in an ambiguous image can be influenced by what one expects to see.
Sensory Receptors and the Brain
Sensory Receptors:
All sensation originates with specialized cells called sensory receptors.
These cells detect stimulus information and transmit it to sensory nerves.
Sensory Neurons: Adhere to the all-or-nothing principle, meaning they either fire completely or not at all.
Intensity Communication: The intensity of a stimulus is communicated by the frequency of action potentials, as individual action potentials cannot vary in height or strength.
Specialized Receptors:
Photoreception: For sight.
Mechanoreception: For touch, hearing, and balance.
Chemoreception: For smell and taste.
Synaesthesia: A rare neurological condition where stimulation of one sensory or cognitive pathway leads to automatic, involuntary experiences in a second sensory or cognitive pathway. Examples include seeing music or tasting a color.
Thresholds
Absolute Threshold:
The minimum amount of stimulus energy that a person can detect.
This threshold varies from person to person.
It is defined as the point at which a subject correctly detects a stimulus of the time.
Difference Threshold (Just Noticeable Difference - JND):
The minimum difference between two stimuli required for an individual to detect them as separately distinct.
The difference threshold increases as a stimulus becomes stronger (e.g., initially, two pin pricks on the back are perceived as distinct, but as they get closer, there's a point where they are perceived as only one).
Subliminal Perception:
The detection of information below the level of conscious awareness.
The brain can respond to information presented outside of conscious awareness.
Overall, it tends to have a weak effect. An example discussed was a betting/card experiment where subliminal cues had a minor influence.
Perceiving Sensory Stimuli
Attention:
Selective Attention: The process of focusing on a particular aspect of an experience while ignoring others. It is shiftable.
Novel Stimuli: Attract attention due to their size, color, or movement. This is why "good spies" try to fade into the background.
Cocktail Party Effect: An example of selective attention where an individual can focus on one particular voice in a noisy environment but may still notice their name being mentioned in another conversation.
Inattentional Blindness:
Failing to detect even unexpected or novel events because attention is focused elsewhere.
This highlights the dangers of multi-tasking, such as distracted driving, which increases the risk of a crash by .
Examples include 'Counting Passes' and 'Follow the Kiss' demonstrations.
Perceptual Set:
A predisposition or readiness to perceive something in a particular way.
It acts as a psychological filter for processing information.
An example is seeing an "ace of spades" where the color might be unexpected.
When applied to people, perceptual sets can help explain actions influenced by positive or negative stereotyping.
Sensory Adaptation
The sensory system is sophisticated enough to adapt to changing situations.
Examples:
Entering a dark room: Initially, little is seen, but eyes adapt over time to discern details. Conversely, walking into bright sunshine causes squinting and temporary difficulty seeing.
Habituation to constant, unchanging stimuli: A ticking clock, a faint smell, or the sensation of clothing on the skin can become unnoticeable over time as the sensory system adapts.
The Visual System
The Visual Stimulus and the Eye
Light:
A form of electromagnetic energy that travels in waves.
Wavelengths: The distance between two peaks of a light wave. They determine the hue (color) perceived.
Amplitude: The height of the light wave, which determines the brightness (intensity) of a stimulus.
Purity: Refers to the uniformity or mixture of wavelengths, determining the saturation or richness of the perceived color.
Structure of the Eye (operates like a camera):
Sclera: The white, outer protective part of the eye.
Iris: The colored part of the eye, which contains muscles that control the size of the pupil.
Pupil: The black opening at the center of the iris, through which light enters.
Cornea: A clear membrane at the front of the eye that refracts (bends) light.
Lens: A transparent, disk-like structure behind the pupil. Both the cornea and lens bend light to focus it precisely onto the retina at the rear of the eye. As people age (often in their s), the lens can lose flexibility, making it difficult to focus on close objects, leading to the need for reading glasses (presbyopia).
Retina: The light-sensitive surface at the back of the eye that records electromagnetic energy and converts it into neural impulses. It contains approximately million receptor cells.
Rods: Approximately million rod receptors in each eye. They function well in low-light conditions and are responsible for black and white vision. They are not found on the fovea.
Cones: Approximately million cone receptors in each eye. They are primarily responsible for color perception and function best in well-lit conditions. They are concentrated on the fovea and scattered outside of it.
Fovea: A tiny central point on the retina where vision is keenest. It contains only cones and is where inputs are directly focused.
Optic Nerve: Composed of the axons of ganglion cells, this nerve transmits visual information from the retina to the brain for processing.
Blind Spot: An area where the optic nerve leaves the eye. It contains no rods or cones, resulting in a small gap in the visual field.
Comparison of Rods and Cones:
Characteristic
Rods
Cones
Type of vision
Black and white
Color
Responses to light conditions
Dimly lit conditions
Well-lit conditions
Shape
Thin and long
Short and fat
Distribution
Not on fovea
On fovea and scattered outside fovea
Visual Processing in the Brain
The Visual Cortex: Located in the occipital lobe of the brain, it contains specialized neurons known as feature detectors that respond to specific features of a stimulus, such as shape, angle, or movement.
Parallel Processing: The brain's ability to process multiple levels of visual information (e.g., shape, color, density, motion) simultaneously within different neural pathways.
Binding: The process by which the brain integrates different pieces of information (like color, form, depth, and motion) that have been processed in separate neural pathways, creating a unified perception.
Color Vision:
Color perception begins in the retina.
Trichromatic Theory: Proposes that color perception is produced by three types of cone receptors, each sensitive to different wavelengths: green, red, and blue. In most forms of color blindness, the green cones malfunction, making it difficult to distinguish green from combinations of red and blue.
Opponent Process Theory: This theory was developed to explain the phenomenon of afterimages (e.g., staring at a red image then looking at a white surface causes a green afterimage). It suggests that there are opponent processes for red-green and blue-yellow color perception.
The brain actually uses both trichromatic and opponent process theories to achieve full color vision.
Perceiving Shape, Depth, Motion, and Consistency
This section focuses on how the visual cortex makes sense of the complex visual stimuli it receives.
Shape Perception:
Figure-Ground Relationship: The organization of the visual field into objects (figures) that stand out from their surroundings (ground). Sometimes this relationship can be ambiguous.
Gestalt Psychology: A school of thought emphasizing that people naturally organize their perceptions into meaningful patterns rather than individual elements.
Gestalt Principles for Shape Perception:
Closure: The tendency to perceive complete forms even when parts are missing, by filling in gaps to create a whole object.
Proximity: The tendency to group together objects that are physically close to each other.
Similarity: The tendency to group together objects that are similar in appearance (e.g., color, shape, texture).
Depth Perception:
Our retinal images are two-dimensional, yet we perceive the world in three dimensions.
Binocular Cues: Depth cues that depend on the use of both eyes. They rely on the slightly different images each eye receives.
Convergence: An indication of how close or far something is, based on the degree to which our eyes turn inward to focus on an object.
Monocular Cues: Depth cues available with only one eye. These include:
Familiar sizes and shapes.
Height in a field of view (objects higher up are seen as farther away).
Linear perspective (parallel lines appear to converge in the distance).
Overlap (an object obstructing part of another object is perceived as closer).
Shading and texture gradient.
Motion Perception:
Crucial for survival, both as a predator and as prey.
Specialized neurons within the visual system are dedicated to detecting motion.
Example: Experiencing induced movement when sitting in a parked car and the adjacent car moves, causing the perception that one's own car is moving, leading to hitting the brakes.
Perceptual Constancy:
The recognition that objects remain constant and unchanging, even though the sensory information they project to the retina changes.
Size Constancy: Objects maintain their perceived size regardless of their distance from the observer (e.g., hot air balloons in the sky are recognized as large, even when they appear small due to distance).
Shape Constancy: An object's perceived shape remains the same even when the observer's orientation or viewing angle changes.
Color Constancy: The perceived color of an object remains constant, even under different lighting conditions that might alter the wavelengths reflected from its surface.
Perception Demonstrations: The class used "Perception Goggle Volunteers" for activities like "Triangle Eye" (determining dominant eye) and using goggles for "High Five," "Sitting," and "Catching" to illustrate perceptual challenges.
The Auditory System
The Nature of Sound & How We Experience It
Sound Waves: Vibrations in the air that travel in waves, similar to light waves.
Wavelength: Determines the sound wave's frequency.
Pitch: The perceptual experience of the frequency of sound. High-frequency sound waves are perceived as high pitch, while low-frequency sound waves are perceived as low pitch.
Amplitude: The height of the sound wave, measured in decibels (). It represents the amount of pressure the sound wave produces and determines the loudness of the sound.
Structures and Functions of the Ear
Outer Ear:
Pinna: The visible part of the ear on the side of the head, which collects sounds and channels them into the ear.
External Auditory Canal: The passage leading from the pinna to the eardrum.
Middle Ear:
Channels and amplifies sound from the outside environment.
Contains the eardrum (tympanic membrane) and three tiny bones: the hammer (malleus), anvil (incus), and stirrup (stapes).
Sound travels through the air in the outer and middle ear until it hits the inner ear. The middle ear bones work to amplify the sound as it prepares to enter the fluid-filled inner ear.
Inner Ear:
Contains the oval window, cochlea, and basilar membrane.
This is where sound waves are converted into neural impulses.
This conversion is critical for hearing, and modern interventions like hearing aids amplify sound, while research explores regenerating hair cells or using electronic impulses to stimulate auditory nerves directly.
Theories of Hearing
Place Theory:
Suggests that different frequencies produce vibrations at particular places along the basilar membrane within the cochlea.
This theory explains the perception of high-frequency sounds better than low-frequency ones.
Frequency Theory:
Proposes that the perception of frequency depends on how often the auditory nerve fires.
However, a single neuron has a maximum firing rate of approximately per second.
The Volley Principle: To overcome this limitation for higher frequencies, clusters of neurons can send volleys of impulses in rapid succession, collectively signaling frequencies above per second.
Auditory Processing in the Brain
Most sounds originating from the left ear are primarily processed on the right side of the brain, and vice versa.
Auditory information is processed mainly in the temporal lobes of the brain.
Localizing Sound:
Similar to how our two eyes perceive slightly different visual information, our two ears hear slightly different aspects of a sound.
The brain processes and combines this sensory information, using variations in the timing and intensity of sounds reaching each ear, to accurately determine the sound's origin.
It is more difficult to localize a sound if it comes from directly in front of or above a person; turning one's head slightly can help in such situations.
Other Senses
The Skin Senses
The skin is our largest sensory system, containing various receptors for touch, temperature, and pain.
Touch:
The skin possesses an impressive variety of touch receptors.
The brain dedicates more cortical space to process touch signals from certain areas, such as the hands, compared to less sensitive areas like the legs.
Temperature:
Receptors for temperature allow the body to detect changes in environmental and internal temperature.
This is crucial for maintaining the body's optimal internal temperature ( or ).
Pain:
Acts as a vital warning system for the body, signaling potential damage or injury.
Pain receptors have a higher threshold for stimulation compared to touch and temperature receptors.
The perception of pain varies across individuals and can even change within an individual as they age.
The Chemical Senses
These senses involve processing chemicals from the environment.
Taste (Gustation):
The tongue contains approximately taste buds, though this number tends to decrease with age.
Beyond the traditional sweet, bitter, salty, and sour, the sense of taste also includes umami (savory).
Smell (Olfaction):
Unique among senses, olfactory information does not pass through the thalamus; it goes directly to the olfactory areas in the temporal lobes.
Smell has unusual and strong links to emotion and memory, often mediated through connections to the limbic system.
Research suggests an attraction to individuals who are genetically most different from ourselves, as potentially detected through smell (implying a biological advantage for offspring diversity), raising the question of whether "opposites attract" in this context.
The Kinesthetic and Vestibular Senses
Kinesthetic Sense:
Provides information about body movement, posture, and orientation in space.
Sensory receptors are embedded in muscle fibers and joints.
This sense allows for the smooth execution of movements and contributes to actions becoming automatic through repetition (muscle memory).
Vestibular Sense:
Provides crucial information about balance and movement (e.g., whether our head is tilted, accelerating, decelerating, or moving).
The sensory receptors responsible for detecting head motion are located within the semicircular canals of the inner ear.
Examples: Experiencing disorientation after spinning quickly, flipping, or spending a long day on amusement park rides.
Vision often works in combination with the kinesthetic and vestibular senses. For instance, the visual cues from a car next to you moving can trick your vestibular system into thinking your own car is in motion.