How do we perceive our environment?

• Complex stimuli are broken into individual features, relayed to the CNS, then reassembled as our perception

Sensation and Perception Terminology

• Stimulus: physical agent that interacts with a receptor

• Receptor: structure that transduces a physical stimulus

• Transduction: process of converting a physical stimulus into a neural signal (sensation)

• Sensations: neural representation of physical stimuli

• Perceptions: cognitive interpretations of sensations

Modes of Perception

• Bottom-up processing: our perceptions are the result of incoming sensations produced by physical stimuli

• Top-down processing: our perceptions are the result of experience, knowledge, bias, and contextual influences on incoming sensations

Vision: Receptors

Vision: Summary

• Stimulus: 400-700 nm electromagnetic radiation

• Receptors: rods & cones (know the difference)

• Transduction: Light activates sends action potential through optic nerve to the brain

• Pathway: ½ of eye crosses to form contralateral visual field perceptions in each occipital lobe

• CNS Areas: occipital lobe - feature detectors (simple/complex cells) reassemble perception

• Perception: Influenced by top-down “shortcuts”

Air pressure changes that unfold over time

Three dimensions for the stimulus

• Frequency of the sound – high versus a low sound

• Amplitude – loudness of a sound

• Complexity – how many frequencies are mixed together

6

Auditory stimulus

400 Hz

1500 Hz

Auditory: Receptors

• Outer ear Middle ear Inner ear = receptors

Auditory: Transduction

• The tectorial membrane “bounces” on the hair cells in rhythmic fashion to physically open ion channels and produce action potentials in the cochlear nerve

Auditory: Afferent Signals

• Receptors in the cochlea are “tuned” to send action potential only for certain frequencies from high (outermost) to low (innermost).

• More receptors/ afferent signals for 500-5,000 Hz

Auditory: Pathways

• Each auditory cortex receives input from both ears BUT primarily from the contralateral ear.

• Neural signal goes to the primary auditory cortex in the temporal lobe.

Auditory: Perception (Left Brain)

• There are specialized brain regions for complex sounds and language. (secondary auditory cortex = language & music)

Green = primary auditory cortex

Brown = language comprehension area

Gold = language production area

Auditory: Perception (Right Brain)

• The same areas of the right hemisphere appear to be specialized to detect all environmental sounds other than language.

Auditory: Summary

• Stimulus: 20-20,000 Hz sound waves

• Receptors: Hair cells in the cochlea

• Transduction: Physical opening of ion channels in the cochlea by the tectorial membrane

• Afferent Signals: unevenly distributed to allow most signals for range of human speech

• Pathway: contralateral to primary auditory cortex

• CNS Areas: Temporal lobe; Wernickes, Brocas, and right hemisphere specializations

• Perception: Complex processing of language in the left hemisphere and music in the right hemisphere.

The chemical senses . . .

• Taste and olfaction are grouped together as “chemical senses” because chemicals are the stimulus for both senses.

PHYSICAL STIMULUS:

• Taste (gustatory system) stimuli are dissolved chemicals (in solution or saliva)

• Smell (olfactory system) stimuli are typically chemicals suspended in the air

Olfactory Receptors

• Olfactory receptors are found in the back of the nasal cavity. (regenerate)

• Protected by mucous layer

• Olfactory receptors are modified neurons with cilia

Olfactory Transduction

• Olfactory receptors are similar to the neurotransmitter receptors (both stimuli are chemicals, right?)

• Odorants fit only in certain receptors like a lock & key

LOCK & KEY

Olfactory: Signals

• Chemicals bind to the receptor causing a reaction in the neuron to send a neural signal to the olfactory bulb

• Each odor has its own pattern of activity

LOCK & KEY

Olfactory: Pathways & CNS Areas

• What is your perception of odors?

• Olfactory bulb to:

• Amygdala – emotional value of stimuli

• Frontal Lobe – memories, moods

Olfactory Perception

• Projections to the limbic system and frontal lobe closely link smell with memories and emotions

• Evolutionary pressure to remember harmful stimuli – strong long-term memory mechanism

• Olfaction is a powerful component to flavor linked with gustation (taste).

Olfactory: Summary • Stimulus: Chemicals in air from nostrils or mouth

• Receptors: Olfactory receptor neurons with lock & key shape binding

• Transduction: Binding actives sending signal

• Afferent Signals: Odors produce unique patterns

• Pathway: Olfactory bulb Amygdala & Frontal Lobe

• CNS Areas & Perceptions: Amygdala (emotional value), Frontal Lobe (memory association), Orbitofrontal cortex (flavor perception)

Gustatory: Receptors

• Taste buds are found on the surface of the tongue

Gustatory: Transduction

Chemicals dissolve in saliva

and enter the taste bud pits

Chemicals are interact

with receptors on the

taste receptor cells

Taste cells release

neurotransmitters

on afferent taste

neurons

Gustatory: Pathways

• 3 sensory nerve relay taste sensations to the brain

• Insular cortex = primary taste quality (between the temporal & parietal lobes)

Gustatory: CNS Areas

• Many secondary areas

Limbic system

& Frontal Lobe

Hypothalamus – hunger & satiety

Flavor Perception

• Flavor - the overall perception of an oral stimulant

• Includes taste, smell, texture, temperature, even color & appearance

% subjects correctly identify

flavored solutions

Black bars = normal

Gray bars = pinched nose

Gustatory: Summary

• Stimulus: Chemicals in saliva or solutions

• Receptors: Taste receptor cells in taste buds

• Transduction: Different for each taste category

• Afferent Pathway: 3 nerves from oral cavity to the NST of the brainstem

• CNS Areas & Perceptions: Insular cortex (primary taste categories), Amygdala (cravings and aversions), Frontal Lobe (memory association), Hypothalamus (hunger & satiety) Orbitofrontal cortex (flavor perception)

Touch: Somatosensory

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Many types of specialized receptors!

Somatosensory: Transduction

• Mechanoreceptors (Meisners, Merkel, Ruffini, Pacinian, and Hair cells): physical movement opens ion channels to depolarize the neuron and send action potentials to the brain

• Bare or Free Nerve endings: detect increases or decreases in temperature and chemicals released in response to tissue damage (like histamines) (pain detection)

• Pain following injury is often 2 sensations:

• Sharp immediate pain

• Dull throbbing secondary pain

• Speed difference due to myelin on axons!

Pain Perception

- unmyelinated neurons

- myelinated neurons

Immediate Sensation Delayed Sensation Overall Perception

Controlling Pain Sensations & Perceptions

• Pain perception can be modified!

• Reduction of the sensation through the :

Gate control theory

Natural Pain Management System

• Efferent signal

from the brain to

the spinal cord at

pain sensation

level.

Pain input

to brain

Brain output

to block pain

• Localized release of endorphins to block the sensation at a precise site

Somatosensory: Summary • Stimulus: mechanical, thermal, and chemical

• Receptors: Mechanoreceptors & Free nerve endings

• Transduction: Physical movement, change in temp, or chemicals released by tissue damage

• Afferent Pathway: Dorsal column pathway for touch, anterolateral pathway for temp and pain

• CNS Areas & Perceptions: Postcentral gyrus is the primary somatosensory cortex (touch organized by body part); anterior cingulate gyrus (pain)

• Gate control theory is natural pain management

Psychophysics

• Psychophysics is the study of the our perceptions (behavior) to physical stimuli

• The first field of experimental psychology!

• Two types of thresholds:

– Absolute: can you detect a stimulus or not?

– Difference: can you detect a change in a stimulus?

Signal Detection Theory

• The sensory system must deal with interference and noise to detect appropriate stimuli

False

alarm

Correct

decision

Correct

decision

Miss

Actual situation

NO sense Sense

Sensation

No

sensation

Person’s

Decision

Difference Thresholds

• Usually our perception of stimuli does not exactly match changes in the actual stimulus

• Weber’s law provided an equation to quantify (& predict) changes in perceptions based on changes in stimuli

• 1800s – 1st quantification of brain activity!