Unit 1.2 -> Sensation and Perception

Sensation and Perception

Two-step process of making sense of the world; they go hand in hand

Sensation

How we detect physical energy from the environment and decode it into neural signals; involves receiving signals and relaying them to the brain

Perception

How we select, organize, and interpret our senses/neural signals to MAKE MEANING; how the brain makes sense of the neural messages

What are the two ways of processing stimuli?

Bottom-Up Processing and Top-Down Processing

Bottom-Up Processing

Starting with raw sensory input and the brain trying to understand and make sense of it

Bottom-Up Processing Example

Seeing a random, line-like thing on the ground and your brain processing it as a snake

Top-Down Processing

Experiences, expectations, and memories are already active and influence the interpretation of sensory information, leading you to see what you expect to see

Top-Down Processing Example

An experienced hiker expecting to see snakes, which leads them to interpret visual stimuli as a snake

What are the three steps in processing sensory information?

1. Reception (receive stimulation); 2. Transduction (transform stimulation into neural impulses); 3. Transmission (deliver neural information to brain)

Reception

The first step: Receiving sensory stimulation via sensory receptor cells

Transduction

The second step: Transforming cell stimulation into neural impulses that the brain can interpret

Transmission

The third step: Delivering neural information to the brain to be processed

Transduction for Sight

Light Waves transformed into neural impulses

Transduction for Hearing

Sound Waves transformed into neural impulses

Transduction for Touch

External contact transformed into neural impulses

Transduction for Taste

Food Molecules (Chemical) transformed into neural impulses

Transduction for Smell

Odorant Molecules (Chemical) transformed into neural impulses

Transduction for Vestibular Sense

Mechanical and Gravitational Forces transformed into neural impulses

Transduction for Kinesthesis

Body Movement transformed into neural impulses

Why are sensation and perception interdependent?

They balance and complement each other; without sensation, perception isn't possible, and without perception, sensations would remain "unknown" to us

Psychophysics

The study of the relationship between the physical characteristics of stimuli and their affect on psychological experience (the connection between sensory stimuli and mental processes)

Absolute Threshold

The minimum stimulus energy required to detect a stimulus 50% of the time (the lowest level we can detect)

Factors that influence Absolute Threshold

Motivation, expectation, acclimation, age, and overall health

How is Absolute Threshold tested?

By changing the stimuli; for example, a hearing test exposes ears to varying sound levels to see what can be detected

Signal Detection Theory

A theory predicting how and when we detect the presence of a FAINT STIMULUS amid background stimulation

What two factors does Signal Detection Theory depend on?

1. Strength of Signal (How strong/noticeable is it?) and 2. Psychological State (Expectations, experience, motivation, alertness)

Subliminal Sensation

Stimuli we cannot consciously detect because they are below the absolute threshold, but our senses can still detect them

Priming

The unconscious activation of certain associations from subliminal sensations, which predisposes one’s perception, memory, or response

Can subliminal sensory information persuade people?

We can be affected by subliminal sensory information, but not persuaded by it

Difference Threshold

The minimum DIFFERENCE between two stimuli required for detection 50% of the time

Difference Threshold's alternative name

"Just Noticeable Difference" (JND)

How do companies use the JND in marketing?

To conceal negative changes, highlight positive changes, and ensure brand recognition (e.g., focusing on improving areas that boost sales)

Weber's Law

To perceive a difference, the stimuli must differ by a constant minimum percentage (PROPORTION), not a constant AMOUNT

Example illustrating Weber's Law

The difference is more noticeable between a coffee with 1 and 2 sugars than between one with 8 and 9 sugars

Absolute Threshold vs. Difference Threshold

Absolute Threshold is the minimum level of stimulation detected; Difference Threshold is the minimum DIFFERENCE between two stimuli perceived

How are Absolute and Difference Thresholds measured?

Absolute Threshold is measured in physical units (e.g., Degrees, Decibels, lumens); Difference Threshold is calculated by assessing one's response to two similar stimuli

Sensory Adaptation

Diminished sensitivity to a stimuli due to constant stimulation

Sensory Adaptation Example

Not being aware of the socks on your feet because you're used to them

What is the survival advantage of Sensory Adaptation?

It saves attention for new stimuli, which is adaptive for survival; ignoring unthreatening/unchanging stimuli lets us focus on changing/new stimuli that might signal danger

How does Sensory Adaptation affect our perception of the world?

We perceive the world not as it is, but as it is useful for us to perceive it

Visible Light Spectra

The frequency of light humans can see, between (400 and 700nm).

Frequency (Wavelength)

The length of the wave that determines the hue (color) we see. (High frequency = blue, low frequency = red)

Amplitude

The height of the wave that determines the brightness of the color we see. (Higher amplitude = brighter colors)

Cornea

The clear, protective outer layer on the front of the eye; light enters here first. Pupil

Iris

The ring of muscle tissue that forms the colored portion of the eye; controls the dilation/size of the pupil.

Lens

The transparent structure behind the pupil that changes shape to focus light on the retina.

Accommodation

The process where the lens changes curvature and thickness to focus the image on the retina.

Nearsightedness (Myopia)

When the lens focuses the image in front of the retina, making distant objects blurry.

Farsightedness (Hyperopia)

When the lens focuses the image behind the retina, making close objects blurry.

Retina

The light-sensitive inner surface/back of the eyeball; contains rods and cones, and layers of neurons where visual processing begins.

Fovea

The central focal point in the retina; the area of greatest visual accuracy where cones cluster.

Blindspot (Optic Disk)

The point where the optic nerve leaves the eye; there are no rods or cones here, creating a gap in vision.

Optic Nerve

Comprised of the axons of the ganglion cells; carries neural impulses from the eye (via the thalamus) to the visual cortex.

Rods

Photoreceptors on the retina's outer periphery; detect black, white, and gray; sensitive in dim light; enable rough motion and black and white vision.

Cones

Photoreceptors concentrated near the center of the retina (fovea); function in daylight/well-lit conditions; detect fine detail and create color sensations.

Why are rods better than cones for vision in dim light?

Rods remain sensitive in dim light and many rods share a connection to a single bipolar cell, sending a combined, stronger message.

Why do cones provide better fine detail than rods?

Each cone has its own bipolar cell, allowing for a direct, non-combined transmission to the visual cortex.

Trichromatic Theory

The retina contains three types of color receptors (cones) that, when stimulated, can produce the perception of any color.

S-Cones

Type of cone sensitive to the color blue.

M-Cones

Type of cone sensitive to the color green.

L-Cones

Type of cone sensitive to the color red.

Opponent Process Theory

Color vision occurs because photoreceptors are paired together (red-green, blue-yellow, black-white); stimulating one color inhibits the other.

Monochromatic Colorblindness

The ability to see only one color because two of the three cone types do not function.

Dichromatic Colorblindness

The ability to see only two colors because one of the three cone types does not function.

How do the Trichromatic and Opponent Process Theories combine?

Cones respond to color stimuli (Trichromatic), and these cone responses are then processed by the opponent process pairing.

Fusiform Face Area

A specialized neural network in the temporal lobe that enables the recognition of faces.

Prospagnosia

An inability to recognize known or new faces due to a disorder (face blindness).

Feature Detectors

Nerve cells in the visual cortex that respond to specific visual features like shape, angle, depth, texture, and movement.

Parallel Processing

The brain's ability to process multiple aspects of a stimulus (motion, form, depth, color) simultaneously.

Dual Processing

Information is simultaneously processed on separate conscious and unconscious tracks; we are only aware of the final result, not the processing itself.

Blindsight

A condition where a person can respond to visual stimuli without consciously experiencing it, showing unconscious processing is still occurring.

What are the five steps of visual information processing (from scene to recognition)?

1. Scene 2. Retinal processing (rods/cones → bipolar cells → ganglion cells) 3. Feature detection 4. Parallel processing 5. Recognition

Why is the fovea crucial for detailed vision?

It is the central point in the retina with the highest concentration of cones, which function best in bright light to detect fine detail.

What is the function of the Iris and Pupil in controlling the light entering the eye?

The Iris (muscle) controls the size of the Pupil (opening) to regulate the amount of light that passes through to the lens and retina.

How does the process of Accommodation relate to Nearsightedness and Farsightedness?

Accommodation is the process of the lens focusing the image. In Nearsightedness, the lens focuses the image too soon (in front of the retina). In Farsightedness, it focuses the image too late (behind the retina).

Sound Waves

Vibrations of air molecules that travel through the air, characterized by compressions and rarefactions

Amplitude of Sound Waves

The height of the wave; determines the LOUDNESS (measured in decibels)

Frequency of Sound Waves

The length of the wave; determines the PITCH (how high or low the sound is, measured in Hertz)

Outer Ear Structures

Auditory Canal and Eardrum (Tympanic Membrane); function is to collect and focus sound waves on the middle ear

Middle Ear Structures

Three tiny bones: Hammer (Malleus), Anvil (Incus), and Stirrup (Stapes) (collectively Ossicles); they amplify and relay the eardrum's vibrations to the oval window

Inner Ear Structures

Innermost part of the ear; contains the Cochlea, Semicircular Canals, and Vestibular Sacs

Cochlea

A coiled, bony, fluid-filled tube in the inner ear; where sound energy is converted into neural impulses

Transduction in the Ear

Fluid movement in the cochlea causes the Hair Cells on the basilar membrane to bend, converting the physical movement into neural messages

Basilar Membrane

The membrane inside the cochlea that holds the Hair Cells (the auditory receptor cells)

Place Theory (Pitch Perception)

Theory that links the pitch heard with the place where the cochlea's membrane is stimulated (Best explains high pitches)

Frequency Theory (Pitch Perception)

Theory that the rate of nerve impulses traveling up the auditory nerve matches the frequency of the tone (Best explains low pitches)

Volley Principle

Neural cells can alternate firing in rapid succession, allowing for combined frequencies above 1000 waves/sec to be perceived (works with Frequency Theory)

Conductive Hearing Loss

Caused by damage to the mechanical system that conducts sound waves to the cochlea (Outer or Middle Ear damage); often treatable with surgery or hearing aids

Sensorineural Hearing Loss

Caused by damage to the cochlea's receptor hair cells or the auditory nerve (Inner Ear damage); often permanent, may be treated with a cochlear implant

How is loudness perceived?

The brain interprets loudness based on the number of hair cells activated by the sound wave

How do we locate sounds?

The brain detects the difference in arrival time and intensity of sound between the two ears (Sound reaches the closer ear first and louder)

Skin Senses

Includes receptors for Pressure, Warmth, Cold, and Pain; detected by specialized nerve endings in the skin

Pressure

The only skin sensation for which scientists have identified a specialized receptor

Pain

The body's alarm system that alerts you to potential injury; a product of both physical sensation and psychological interpretation

Pain Tolerance vs. Pain Sensitivity

Tolerance is the maximum pain a person can endure; Sensitivity is the minimum pain needed to register the sensation

Gate-Control Theory

Theory that the spinal cord contains a neurological "gate" that blocks pain signals (closed by large nerve fibers or brain messages like endorphins/distraction) or allows them to pass to the brain (opened by small nerve fibers)

Effective Pain Control Methods

Physical: Medication, acupuncture, electrical stimulation; Psychological: Placebos, distraction, hypnosis

Chemical Senses

The senses of Taste (Gustation) and Smell (Olfaction); both use sensory receptors that respond to molecules (chemicals)

Gustation (Taste)

The sense of taste; achieved by taste buds detecting dissolved molecules (tastants)

Five Basic Tastes

Sweet, Sour, Salty, Bitter, and Umami (Savory) Umami