Module 5

5.1 Sensation versus Perception

sensory receptors - specialized neurons that respond to specific types of stimuli

sensory info detected by sensory receptor → sensation

cause chemical changes in cells that relay messages in the form of action potentials to central nervous system

transduction - conversion from sensory stimulus energy to action potential

the senses

  • vision

  • hearing (audition)

  • smell (olfaction)

  • taste (gustation)

  • touch (somatosensation)

  • balance (the vestibular sense)

  • body position and movement (proprioception and kinesthesia)

  • pain (nociception)

  • temperature (thermoception)


absolute threshold - minimum amount of stimulus energy that must be present for the stimulus to be detected 50% of the time

  • how dim can a light be or soft a sound can be to still be detected half the time.

  • candle flame 30 miles away, clock tick 20 feet away


subliminal messages - messages presented below threshold for conscious awareness

people can process and respond to this OUTSIDE of awareness

different threshold/just noticeable difference - how much difference in stimuli is required to detect the difference between them (proposed by Ernst Weber - Weber’s Law)

  • changes depending on stimulus intensity


perception - the way sensory information is organized, interpreted, and consciously experienced

  • bottom-up processing and top-down processing

  • bottom-up processing - sensory information from a stimulus in an environment driven by a process

    • plates crashing and grabbing your attention

  • top-down processing - knowledge and expectancy driving a process

    • looking for the shade of yellow that matches your car keys


sensation - physical, perception - psychological

all perceptions are built from stimuli, but not all stimuli → perception


attention plays big role in determining what is sensed vs. perceived

inattentional blindness - the failure to notice something that is completely visible because the person was actively attending to something else


motivation also affects perception

  • signal detection theory - the ability to identify a stimulus when embedded in a distracting background


beliefs, values, prejudices, expectations, and life experiences can also affect perception

  • caused by differences in types of environmental features experienced on a regular basis by people in given cultural context

  • also affects ability to identify odor and rate pleasantness or intensity

  • personality can affect perception

    • thrill seeker children like intense sour flavors


5.2 Waves and Wavelengths

visual and auditory stimuli occur in waves

two physical characteristics of a wave are amplitude and wavelength

amplitude - distance from center line to the top point (crest) or bottom point (trough)

wavelength - length of a wave from one peak to the next

frequency - number of waves that pass a given point in a given time period (hertz - Hz)


visible spectrum is portion of electromagnetic spectrum that we can see

shortest → longest wavelength

gamma, x-ray, ultraviolet, visible, infrared, microwave, radio


other species can see different portions of electromagnetic spectrum

light wavelength associated with perception of color

red → longer wavelengths, green → intermediate, blue and violet → shorter wavelength

amplitude → associated with brightness or intensity of color


sound waves

frequency is related to sounds pitch

different species have different audible ranges that they can hear

loudness of a sound associated with amplitude, given in decibels (dB)

hearing damage → 80 dB to 130 dB


1/3 of all hearing loss due to noise exposure

louder sound → less exposure needed to cause hearing damage

15 minutes of earbuds with max volume → noise-induced hearing loss


timbre → a sounds purity (how different instruments can play same note but sound different)

  • affected by complex interplay of frequency, amplitude, and timing of sound waves


5.3 Vision


anatomy

light waves are transmitted across the cornea and enter eye thru pupil

cornea - transparent covering over the eye

  • barrier between inside/outside world

  • focuses light waves that enter the eye

pupil - small opening in the eye through where light passes

  • size of the pupil changes as light levels change OR emotional arousal

    • low light - pupil expands, high light levels - pupil constricts

  • pupil’s size controlled by muscles connected to the iris (colored portion)

lens - curved, transparent structure that serves to provide more focus

  • attached to muscles that change its shape to help focus light reflected from near or far objects

  • focuses light on to the fovea

fovea - small indentation in the back of the eye

  • part of the retina (light sensitive lining of the eye)

  • contains densely packed specialized photoreceptor cells (cones)

cones - specialized type of photoreceptors that detects light (high levels)

  • work best in bright light conditions

  • senstive to acute detail, provides tremendous spatial resolution

  • directly involved in our ability to perceive color

rods - specialized type of photoreceptor that detects light (low levels)

  • located throughout the rest of the retina

  • works best in low light conditions

  • vision in dimly lit environments, perception of movement on periphery of vision field


delay in transition from cone activity → rod activity

difficulty in transitioning from cone activity → rod activity = night blindness


rods and cones connected to retinal ganglion cells

axons from these cells converge and exit thru back of eye to form optic nerve

optic nerve - carries visual information from retina to the brain

blind spots - point in visual fied that we cannot see

  • blind spots in either eye do not overlap

optic chiasm - point where the optic nerve from each eye merges

  • x-shaped structure

  • info from right eye → left side brain, info from left eye → right side brain


parallel pathways where visual information might be processed

the what pathway - object recogntion

object identification


the where/how pathway

  • location in space

  • how one might interact with particular visual stimulus


color vision

trichromatic theory: all colors can be produced by combining red, green, and blue

applies to retina where color vision is controlled by three types of cones

  • opponent process theory

    • color is coded in opponent paris

    • black- white

    • yellow - blue

    • green - red


depth perception and cues

binocular cues

  • cue that relies on the use of both eyes

  • binocular disparity - slightly different view of the world that each eye receives

monocular cues

  • cue that relies on only one eye

  • linear perspective - when two parallel lines seem to converge

  • interposition - the partial overlap of objects


auditory transduction

  1. sound waves travel along the auditory canal and strike the tympanic membrrane, causing it to vibrate

  2. the vibration causes the 3 ossicles to move, this presses the stapes into the oval window of the cochlea

  3. the fluid inside the cochlea begins to move, stimulating the hair cells (sensory receptors for sound) which become activated

  4. the hair cells generate neural impulses that travel along the auditory nerve to the brain

  5. auditory information is sent to the inferior colliculus, then the medial geniculate nucleus of the thalamus and finally to the auditory cortex in the temporal lobe for processing


pitch perception

temporal theory

  • frequency is coded by the activity level of a sensory neuron

  • problem - the frequency of action potentials cannot account for the entire range that we are able to hear. There is a point at which a cell cannot fire any faster

place theory

  • different portions of the basilar membrane are sensitive to sounds of different frequencies

  • the base responds to high frequencies and the tip responds to low frequencies


sound localization and cues

  • monaural cues

    • one ear

    • each ear interacts with incoming sound waves differently

  • binaural cues

    • provide information on the location of sound along a horizontal axis

    • relies on difference vibration


hearing loss

  • deafness - the partial or complete inability to hear

  • congenital deafness - deafness from birth

  • conductive hearing loss - associated with a failure in the vibration of the eardrum and/or movement of the ossicles

  • can often be dealt with using hearing aids which amplify incoming sound waves to make vibration of the eardrum and movement of the ossicles more likely to occur

  • sensorineural hearing loss - failure to transmit neural signals from the cochlea to the brain

    • can be caused by meniere’s disease which results in degeneration of inner ear structures

    • most common from hearing loss


synesthesia

  • in a few select individuals, the brain circuits for two or more senses become joined in a phenomenon called synesthesia, where the stimulation of one sense (such as hearing sound) triggers and experience of another (such as seeing color)

  • synesthetes may hear music as colors or experienced numbers as tastes


taste (gustation)

research demonstrates that we have about 6 groupings of taste

  1. sweet

  2. salty

  3. sour

  4. bitter

  5. can possess taste of fatty content

  6. umami - associated with taste of monosodium glutamate

  • taste buds - groupings of taste receptor cells with hair-like extensions that protrude into the central pore of the taste bud



smell (olfaction)

  • olfactory receptor cells

  • contain small hair-like extensions into which serve as the site for odor molecules to interact with chemical receptors located on these extensions (located in a mucous membrane at the top of the nose)

  • transduction

    • odor molecules bind to receptors

    • chemical changes cause signals to be sent to the olfactory bulb (where the olfactory nerves begin)

    • information is sent to the limbic system and primary olfactory cortex


Taste/Smell/Memory

• Information from the taste buds (yellow arrow)

travels to an area between the frontal and temporal

lobes of the brain.

• This information registers near where the brain

receives input from our sense of smell, which

interacts with taste. 90% of our experience of food is

from smell

• The brain’s circuitry for smell (red area) also

connects with areas involved in memory storage,

which helps explain why a smell can trigger a

memory.


Touch

• There are many types of sensory receptors located in the skin, each attuned

to specific touch-related stimuli

• Meisnerr’s corpuscles – respond to pressure and lower-frequency vibrations

• Pacinian corpuscles – detect transient pressure and higher-frequency

vibrations

• Merkel’s disks – respond to light pressure

• Ruffini corpuscles - detect stretch


Thermoception and Nociception

• As well as receptors located in the skin, there are a number of free nerve

endings that have sensory functions.

• Thermoception – temperature perception.

• Nociception – sensory signal indicating potential harm and maybe pain.

• This type of sensory information travels up the spinal cord directly to the

brain, specifically the medulla, thalamus and the somatosensory cortex.


Pain Reception

• Pain perception is important because it motivates us to remove ourselves from the

cause of injury.

• Inflammatory pain – signals some type of tissue damage.

• Neuropathic pain – caused by damage to neurons of either the peripheral or central

nervous system.

• Congenital insensitivity to pain - a rare genetic disorder in which the individual is born

without the ability to feel pain.

Can detect differences in temperature and pressure but cannot experience pain.

Individuals are at greater risk of injury and infection and have shorter life

expectancies.


Vestibular Sense

Vestibular sense – contributes to our

ability to maintain balance and body

posture.

The major sensory organs of the

vestibular system are located next to

the cochlea in the inner ear.

These organs are fluid-filled and

contain hair cells which respond to

movement of the head and

gravitational forces.


Proprioception and Kinesthesia

• The vestibular system also collects information important for controlling

movement and reflexes that move parts of our bodies to compensate

for changes in body position

• Both proprioception and kinesthesia interact with information provided

by the vestibular system

• This information travels to the brain via the spinal column

• Information from the brain is then sent to the sensory organs of the

proprioceptive and kinesthetic systems


Gestalt Principles of Perception

• Gestalt psychology – field of psychology based on the idea that the whole is

different from the sum of its parts.

• The brain creates a perception that is more than simply the sum of available

sensory inputs.

• The brain does this in predictable ways which gestalt psychologists translated

into principles by which we organize sensory information


Figure-Ground Relationship

• The idea that we tend to segment our visual

world into figure and ground.

• Figure – the focus of the visual field.

• Ground – the background.

• Our perception can vary depending on what

we view as figure and what we view as

ground.


gestalt principle of proximity, similarity, continuity, closure