MECHANISMS OF

Perception

EXTEROCEPTIVE SENSORY SYSTEMS

1. Auditory

2. Somatosensory

3. Olfactory

4. Gustatory

5. Vision

Sensory Areas of Cortex

3 fundamentals

• Primary

• Secondary

• Association

PRIMARY SENSORY CORTEX

• System is the area of sensory cortex that receives most of its input directly from the thalamic relay nuclei of that system.

Primary Visual Cortex

Visual Association Area

RegionsModified from: http://www.bioon.com/book/biology/whole/image/1/1-8.tif.jpg

SECONDARY SENSORY CORTEX

• System comprises the areas of the sensory input from the primary sensory cortex of that system or from other areas of the secondary sensory cortex of the same system.

ASSOCIATION CORTEX

• Any area of cortex that receives input from more than one sensory system.

3 MAJOR PRINCIPLES OF THE INTERACTIONS

1. Hierarchical Organization

A system whose members can be assigned to specific levels or ranks in relation to one another.

• Association Cortex

• Secondary Sensory Cortex

• Primary Sensory Cortex

• Thalamic Relay Nuclei

• Receptors

NOTE:

• The hierarchical org. of sensory system is APPARENT from comparisons of the effects of damage to various levels:

• The higher the level the damage, the more specific and complex the deficit.

Example:

Destruction of a sensory system’s receptors produces a complete loss of ability to perceive in that sensory modality (blindness or deafness)

TWO GENERAL PHASES OF PERCEPTION

• Sensation – the process of detecting the presence of the stimuli.

• Perception- the higher-order process of integrating, recognizing, and interpreting complete patterns of perception

FUNCTIONAL SEGREGATION

• The functions is distinct that specialized different kinds analysis.

PARALLEL PROCESSING

• The different levels of a sensory hierarchy were connected in a SERIAL fashion.

• Information flows among the components over just one pathway.

• Research: Multiple pathways called PARALLEL SYSTEM

Until after 1960…..

• Sensory system are characterized by a division of labor : Multiple specialized areas, at multiple parallel pathways.

• Product of combined activity of different interconnected cortical regions.

SOMETHING TO THINK ABOUT

• What is top Down processing and Bottom up processing?

• How does this influence the case of depression?

INFOBIT

• iPods and other MP3 players can reach 120 decibels. At that level, you risk damage to your hearing after only 7 1/2 minutes. How do you know if the volume is too loud? It’s too loud if someone three feet away can hear your music, or if you need to remove

the ear piece to hear someone talking to you

The auditory system

• The Mechanism of HearingSound ( MOLECULAR VIBRATIONS) A,F, C---

( PERCEPTIONS) L, P, T,Pure tonesTheories ( Fourier analysis and fundamental

frequency)

• Hearing begins with sound waves—vibrations in air, water, or solid material. The number of sound waves that pass through a given point in one second is called the sound’s frequency.

• When your sensory system experiences the physical sensation of frequency, you also have the psychological experience of pitch. High-pitched sounds are high frequencies, and low-pitched sounds are low frequencies.

• Loudness of sound is a psychological experience that corresponds to the height of a sound wave, called amplitude. Amplitude is measured in decibels (dB).

• The greater the amplitude, the higher the decibels, and the louder the sound.

DIFFERENT WAVES OF FREQUENCY

• You experience this combination—or blending of frequencies—as timbre.

• Timbre is why you can recognize di erent fffriends’ voices over the telephone.

SOMETHING TO THINK ABOUT

• Why ear is a complex patterns of vibrations, how this affects what we hear/perceive?

• What happened if we combined sine waves together?

• What happen if we combine 100, 200 qnd 300 Hz?

OUTER EAR

• The outer ear is the part you see. It is the part of the ear that receives sound waves and sends them down a passageway called the auditory canal.

• At the end of the auditory canal is the eardrum, which is a thin, flexible membrane that vibrates in sequence with the sound waves.

MIDDLE EAR AND OUTER EAR

• The middle ear is an air-filled cavity that begins on the other side of the eardrum.

• As the eardrum vibrates, it sets in motion three tiny, interconnected bones (Occicles)—the hammer, anvil, and stirrup or malleus, incus and stapes

• When the eardrum vibrates from sound waves, these bones also vibrate against the cochlea, which is part of the inner ear.

• The cochlea (pronounced COKE-lee-ah) is a coiled, fluid-filled tube that is lined with special hair-like auditory receptor cells. When these hair cells are stimulated by sound wave vibration, they trigger the fi ring of sensory neurons that form the auditory nerve.

• Organ of corti ( basilar and tectorial membrane)

• The auditory nerve then transmits sound information to the brain.

Hearing Loss

• Two types of hearing loss, conduction and sensorineural.

• Conduction hearing loss occurs when there are physical problems sending sound waves through the outer or middle ear. Sensorineural hearing loss involves nerve problems in the inner ear.

• Conduction hearing problems often involve a punctured eardrum or damage to any of the three bones in the middle ear.

• A common treatment for conduction hearing loss is hearing aids, which are tiny instruments worn just inside the outer ear. Hearing aids change sound waves into amplified vibrations and send them to the inner ear.

• Sensorineural hearing loss is a more common problem. It often occurs because hair cells in the cochlea are damaged either by disease, injury, or aging.

• The only means of restoring hearing in people su ering from nerve deafness is a ffcochlear implant, which is a miniature electronic device that is surgically placed into the cochlea.

• The implant changes sound waves into electrical signals and sends them to the auditory nerve, which transmits them to the brain.

• Young children born with hearing loss are the best candidates for this implant.

Why do some people hear voices that aren’t really there?

• Inner speech vs actual speech

Ear to Auditory Cortex

• The axons of each Auditory nerve synapse in the ipsilateral Cochlear nuclei------which leads to the superior olives on both sides of the brain stem at the same level.

• The axons of the olivary neurons project via the lateral lemniscus to the inferior colliculi----where they synapse on neurons that project to the medial geneculate nuclei of the thalamus.....which is projected to the primary auditory cortex.

• The complexity of the subcortical auditory pathways......make the analysis of the sound difficult------but there is one function of the subcortical auditory system -----the localization of sounds in space.

Subcortical Mechanisms of Sound Localization

• The localization of sounds in space is mediated by the lateral and medial superior olives but in different ways.

• When the sound originates to a person’s left, it reaches the left ear first-----louder left ear

Located in the temporal lobe, hidden view from lateral fissure.

TWO AREAS

Core region----surrounded by a band----called BELT----areas of secondary cortex----outside the belt is the PARABELT AREAS

Streams of Auditory Cortex

• Anterior auditory pathway---is more involved in identifying sounds (What)

• Posterior auditory pathway-----is more involved in locating sounds (Where)

The Olfactory System

• The stimuli for smell are airborne molecules.

Ex.

When you smell hot chocolate you

are sensing molecules that have left the hot chocolate and traveled through the air

to your nose.

• These molecules then enter your nasal passages and reach tiny receptor cells at the top of the nasal cavity.

• These receptor cells then transmit neural impulses containing smell information through the olfactory nerve to the brain. Once your brain has processed these neural signals, you experience the hot chocolate’s aroma

• The olfactory receptor cells are located in the upper part of the nose-----embedded in a layer of mucus-covered tissue---called Olfactory Mucosa

• Cribriform plate ( porous portion of the skull) where the axons passes through.

• Olfactory bulbs-where they synapse on neurons that project via the olfactory tracts to the brain.

Did you know that? Humans have about 10

million olfactory receptors while dogs have 200 million receptors.

Research indicates that women’s smell sensitivity is better than that of men.

• Brain scans taken while people are smelling objects find that smells trigger more brain activity in women than in men.

• Olfactory receptor proteins---located at the membranes of the dendrites of the olfactory receptor cells, where they can be stimulated by circulating airborne chemicals in the nasal passages

• Olfactory glomeruli----a cluster where the olfactory receptor axons terminate. It receives input from several thousand olfactory receptor cells, all with the same protein.

• Medial Temporal Lobes----includes the Amygdala and Piriform cortex

• Piriform cortex- considered to be primary olfactory cortex.

• Olfactory system- the only sensory system whose major sensory pathway reaches the cerebral cortex without first passing through the thalamus

• The two major pathways ----projects diffusely to the limbic system and to the medial dorsal nuclei of the thalamus to the orbitofrontal cortex-----the area of cortex on the inferior surface of the frontal lobes next to the orbits (eye sockets)

• Thalamic-orbitofrontal projection-mediate the conscious perception of odors,

Eardrum- A thin, flexible membrane that vibrates in sequence with sound waves

Cochlea- The coiled, fluid-filled tube in the inner ear that contains hair-like auditory receptors

Perception

“Perception refers to the interpretation of what we take in through our senses. In terms of optical illusions this means our eyes.”

Simply put, our brains are tricked into seeing something which may or may not be real.

http://www.keele.ac.uk/depts/aa/widening/uniworld/webclub/rs/optical.htm

Factors that Influence

Perception The Object of Perception:

some things in our environment tend to attract attention

Backgrounds and Surroundingsour surroundings at the moment of perception will affect our perceptions

The Perceiverwe each bring unique experiences and personal points of view to each situation