Module 6 Sensation and Perception

Sensation

When sensory receptors detect a stimulus and send the information to the brain; a physical process

Perception

The way sensory information is organized, interpreted, and consciously experienced; a psychological process

Sensory receptors

Specialized neurons that respond to specific types of stimuli

Sensation vs. perception example

Sensation = detecting the smell of cinnamon; perception = "this smells like Grandma's baking"

Senses beyond the classic five

Balance (vestibular), body position and movement (proprioception and kinesthesia), pain (nociception), and temperature (thermoception)

Transduction

The conversion of sensory stimulus energy into action potentials (neural signals)

Absolute threshold

The minimum amount of stimulus energy needed to detect a stimulus 50% of the time

Examples of absolute threshold

Seeing a candle flame 30 miles away on a clear night; hearing a clock tick 20 feet away

Subliminal message

A stimulus below the absolute threshold that is processed without conscious awareness; has little effect on behavior outside the lab

Just noticeable difference (JND) / difference threshold

The smallest difference between two stimuli that a person can detect

Why the JND changes

It depends on the intensity of the original stimulus (a phone screen is noticeable in a dark theater but not in a bright arena)

Weber's law

The just noticeable difference is a constant fraction (proportion) of the original stimulus

Ernst Weber

Proposed Weber's law in the 1830s

Signal detection theory

Our ability to identify a stimulus (signal) when it is embedded in a distracting background (noise); depends on motivation and expectations

Examples of signal detection

Thinking you hear your phone ring in the shower; a mother waking to her baby's murmur; air traffic controllers spotting planes on radar

Four outcomes of signal detection (from lecture)

Hit (signal present, detected), miss (present, not detected), false alarm (absent, "detected"), correct rejection (absent, not detected)

Sensory adaptation

No longer perceiving a stimulus that stays constant over a long time

Sensory adaptation example

No longer noticing a flashing light outside your hotel window, even though your eyes still detect it

Amplitude (waves)

The height of a wave, from the center line to the top of the crest

Wavelength

The length of a wave from one peak to the next

Frequency (waves)

The number of waves that pass a point per second, measured in hertz (Hz); longer wavelength = lower frequency

Visible spectrum

The part of the electromagnetic spectrum humans can see, about 380–740 nanometers

Characteristics of light that affect vision

Wavelength (color/hue), amplitude (brightness), and purity/saturation (from lecture)

Light wavelength determines

Color (hue); long = red, medium = green, short = blue/violet

Light amplitude determines

Brightness or intensity; larger amplitude = brighter

ROYGBIV

Red, orange, yellow, green, blue, indigo, violet (longest to shortest wavelength)

Cornea

The clear outer covering of the eye; protects it and begins focusing light

Pupil

The opening that lets light into the eye; dilates in dim light and constricts in bright light

Iris

The colored part of the eye; a muscle that controls pupil size

Lens

A curved, clear structure that changes shape to focus light on the retina

Retina

The light-sensitive lining at the back of the eye that contains photoreceptors; where transduction happens

Fovea

A small pit in the center of the retina packed with cones; where vision is sharpest

Photoreceptors

Light-detecting cells in the retina (rods and cones)

Cones

Photoreceptors that work best in bright light and provide color vision and fine detail; concentrated in the fovea

Rods

Photoreceptors that work in dim light and detect peripheral vision and motion; no color

Night blindness

Difficulty seeing in dim light because rods don't work properly

Retinal ganglion cells

Cells that receive signals from rods and cones (through interneurons); their axons form the optic nerve

Optic nerve

Carries visual information from the retina to the brain

Blind spot

Where the optic nerve leaves the eye; it has no photoreceptors

Why we don't notice our blind spot

The two eyes' blind spots don't overlap, and the brain fills in the missing information

Optic chiasm

The X-shaped point where the optic nerves cross; the right visual field goes to the left hemisphere and the left visual field to the right hemisphere

Process of vision

Light passes through the cornea, pupil, and lens to the retina; rods and cones transduce it; signals go through ganglion cells and the optic nerve to the optic chiasm, thalamus, and occipital lobe

Primary visual cortex

In the occipital lobe; interprets incoming visual information

"What" pathway

Visual pathway involved in recognizing and identifying objects

"Where/how" pathway

Visual pathway involved in an object's location, movement, and how to interact with it

Hubel and Wiesel

Nobel Prize winners who found visual cortex cells that respond to lines of specific orientations

Trichromatic theory

Three types of cones (red, green, blue) combine to produce all colors (Young-Helmholtz)

What trichromatic theory explains

Color blindness (a missing or faulty cone type)

What trichromatic theory doesn't explain

Afterimages and why we can't see a reddish-green

Opponent-process theory

Color is coded in opposing pairs (red-green, yellow-blue, black-white); a cell excited by one color is inhibited by its partner (Hering)

What opponent-process theory explains

Negative afterimages and why we don't see greenish-reds or yellowish-blues

Afterimage

A visual sensation that continues after the stimulus is removed

Negative afterimage

Seeing the opposite colors after staring at an image (e.g., staring at a green, yellow, and black flag and then seeing red, blue, and white)

How trichromatic and opponent-process theories fit together

Trichromatic theory works at the retina (cones); opponent-process theory works beyond the retina on the way to the brain

Color blindness

Inability to tell certain colors apart; red-green is the most common type, X-linked, and much more common in males

Depth perception

The ability to perceive spatial relationships in three dimensions

Binocular cues

Depth cues that require both eyes

Binocular disparity

The slightly different view each eye gets; a binocular depth cue (the basis of 3-D movies)

Monocular cues

Depth cues that need only one eye

Linear perspective

Monocular cue; parallel lines seem to converge in the distance

Interposition

Monocular cue; a closer object partially blocks a farther one

Relative size and closeness to the horizon

Monocular cues; smaller objects and objects closer to the horizon seem farther away

Stereoblindness

Inability to use binocular depth cues

Characteristics of sound that affect hearing

Frequency (pitch), amplitude (loudness), and timbre (quality)

Pitch

How high or low a sound seems; determined by frequency

Loudness

Determined by amplitude; measured in decibels (dB)

Human hearing range

About 20–20,000 Hz

Decibel (dB)

A logarithmic unit of sound intensity

Common decibel levels

Conversation is about 60 dB, rock concert about 120 dB; hearing damage from about 80–130 dB; pain threshold about 130 dB

Timbre

A sound's quality or purity, from the mix of frequencies, amplitudes, and timing (why a piano and guitar sound different playing the same note)

Pinna

The visible outer ear; funnels sound into the ear and helps locate sound

Auditory canal

Carries sound from the pinna to the eardrum

Tympanic membrane (eardrum)

Vibrates when sound waves hit it

Ossicles

Three tiny middle-ear bones that pass vibration along (malleus/hammer, incus/anvil, stapes/stirrup)

Oval window

Membrane of the cochlea that the stapes presses on

Cochlea

Fluid-filled, snail-shaped inner-ear structure containing the hair cells

Basilar membrane

Strip of tissue in the cochlea where hair cells are embedded

Hair cells

Auditory receptor cells in the cochlea that transduce vibrations into neural signals

Semicircular canals

Inner-ear structures involved in balance

Process of hearing

Sound waves travel through the pinna and auditory canal, vibrate the eardrum, move the ossicles, press the oval window, move cochlear fluid, and bend hair cells, which send signals to the brain

Path of auditory information to the brain

Auditory nerve, then inferior colliculus, then thalamus (medial geniculate nucleus), then auditory cortex in the temporal lobe

Temporal theory of pitch

Pitch is coded by how fast neurons fire; can't explain high frequencies

Place theory of pitch

Different parts of the basilar membrane respond to different frequencies (base = high, tip = low)

How the two pitch theories fit together

Both work up to about 4,000 Hz; above that, only place theory works

Monaural cues

Sound-location cues from one ear (pinna shape); help locate sounds above, below, in front, or behind

Binaural cues

Sound-location cues from comparing both ears; help locate sounds left or right

Interaural level difference

A sound is louder at the ear closer to it

Interaural timing difference

A sound reaches the closer ear slightly sooner

Conductive hearing loss

Hearing loss from problems with the eardrum or ossicles; helped by hearing aids

Sensorineural hearing loss

The most common hearing loss, from damage to the cochlea or auditory nerve (aging, noise); may be helped by a cochlear implant

Cochlear implant

Electronic device that directly stimulates the auditory nerve

Chemical senses

Taste and smell, whose receptors respond to molecules

Flavor

The combination of taste and smell

Gustation

The sense of taste

Basic tastes

Sweet, salty, sour, bitter, umami, and possibly fat

Umami

A savory taste associated with monosodium glutamate (MSG)

How we taste

Food molecules dissolve in saliva and bind to taste receptor cells in taste buds; signals go to the medulla, thalamus, limbic system, and gustatory cortex

Taste buds

Groups of taste receptor cells; regenerate every 10 days to 2 weeks

Olfaction

The sense of smell

How we smell

Odor molecules dissolve in mucus at the top of the nose and bind olfactory receptor cells; signals go to the olfactory bulb, limbic system, and olfactory cortex