Module 5

Sensations - Are features of the environment, like the electromagnetic wavelengths of the light or changes in air pressure that create sound that we use to create am understanding of the world.

The brain takes the sensations that have been translated or traduced by the sensory system and combines it with previous experience to create a perception

Perception - The processing of stimuli to create a sensory understanding of the world around us

Perception is only partly based on the information coming in from the world. We also use memories about the way the world works to interpret these messages.

The 2 process that create our perceptual world are:

1. Bottom-up Processing - the neural processing that starts with the physical message or sensations. This is the early level analysis that prepares the information for use

2. Top - Down Processing - When we combine this incoming neural message with our understanding of the world to interpret information in such a way that it has value. Perceptions are created from these processed working together

the Principles of Gestalt

These laws outline some fundamental ways we see the world.

The principle of proximity states that objects that are close to one another will be grouped together.

The principle of similarity states that objects that are physicallu similar to one another will be grouped together

The principle of closure states that people tend to perceive whole objects even when part of that information is missing

The principle o good continuation states that is lines cross each other or are interrupted, people tend to still see continuously flowing lines

The principle of common fate states that objects that are moving together will be grouped together

• Using these principles, we are able to organize information in a predictable and meaningful way

Vision: From Light to Sight

• The Eye

20% of the cortex play a role in the interpretation of visual information

The visible spectrum is a very small range (400-700 nanometers)

• The iris gives your eyes colour but does not play a specific role

2 common vision problems are caused by the lens interacting incorrectly with the retina

• Nearsighted (myopia) - Have longer eyes, so the lens focuses the image before it reaches the retina; by the time light arrives at the photoreceptors, the image is no longer clear. So they can see objects more clearly when they are close but as objects move further away it becomes harder for them to see

• Farsighted (hyperopia) - Can see objects in the distance quite clearly, but as they move closer they are harder to see. This is because the eye is shorter and when the image arrives at the retina, it is not yet in focus and is derived as quite blurry

Parts of the eye

• Iris - The ring of pigmented muscle tissue surrounding the pupil. the iris is responsible for controlling the diameter and size of the pupil, thereby controlling the amount of light that reaches the retina

• Cornea - The transparent covering of the eye. It is made of 3 layers and performs about 80% of the focusing of the visual imagine

• Anterior Chamber - Liquid filled space between the cornea and iris. This fluid is routinely cleaned from the eye but blockage can result in built-up pressure on the eye and the development of glaucoma

• Lens - Flexible piece of tissue, located behind the pupil, that focuses light on the retina. The lens changes shape in order to bring objects into focus, through accommodation. The lens becomes thicker the closer the object is to you, and the thinner the further away it is

• Choroid - A highly vascularized portion of the eye that delivers nutrients to the photoreceptor cells of the retina

• Optic Nerve - Translates information from the retina and sends that information to the visual cortex

• Fovea - The portion of the retina directly behind the pupil. It contains a large concentration of cones no rod.

• Retina - The thin layer of tissue on the back of each eye that contains the photosensitive receptor cells, rods, and cones. Rods are more sensitive to low-light, motion information and cones are more sensitive to high-light, detailed information

• Sclera - The relatively tough, white portion of the eye. It is vascularized and surrounds the cornea

The light must pass through 5 layers of cells in your retina to arrive at the photoreceptors in the back of your eye where the light is transducer into cellular activity

The order of which light travels in the eye

• Cornea

• Pupil

• Lens

• Retina

The Retina

Diffuse Bipolar Cells - They receive signals from the rods and send their messages to the large ganglion

Midget Bipolar Cells - Receive signals from the cones and send their message to the small ganglion

Small Ganglion Cells - Revive information from the midget bipolar cells. P-cells make up about 70% of the ganglion cells in the retina and send signals to the brain about qualities of colour and detail

Large Ganglion Cells - Found in the periphery and receive their signals from the diffuse bipolar cells. They send information about motion and visual simuli in the periphery

• The receptive fields of the ganglion cells are often recognized in a centre surrounded fashion

The messages finally leave the eye and enter the brain via the optic nerve, made up of axons of both the M ad P cells.

The Visual Cortex

• Optic Chiasm - where axons from each eye are reorganized from more sophisticated processing

The lateral geniculate Nucleus - The 6 layer portion of the thalamus that processes and organizes visual information

The visual cortex is located in the occipital lobe.

• Retinoptopic organization - Where the spatial organization of the retinal image is maintained through the visual pathway

• feature Detectors - Specialized cells in the VC that respond most actively to specific stimuli

Simple cells respond to small stationary bars of light oriented at specific angles

Complex cells respond most vigorously to vertical lines in motion

• Ventral Stream - Visual information is identified

• Dorsal Stream - Carries visual information to the parietal lobe

Colour Vision

• Colour is the perception of wavelength

  • Long (670nm) = Red perception

  • Medium (530nm) = Green Perception

  • Short (450 nm) = Blue Perception

The Trichromatic Theory - Proposes that colour I identified by comparing the activation of different cones in the retina

Opponent Process of Colour Vision

• that the human visual system interprets information about colour by processing signals from photoreceptor cells in an antagonistic manner

Perceiving Depth

Two kinds of depth

• Monocular Depth Cues - those that require only 1 eye

The first cue is occlusion, occurs when one image partially blocks the view of a second object. The partially hidden object is seen as further away than the whole object.

The second depth cue is relative height, objects closer to the horizon will appear further away, and the greater the distance between the object and the horizon, the closer object with appear.

Relative Size also relies on our understanding of the world

Perspective convergence is a common cue used in landscapes, as parallel lives move away from us into the distance, they seem to converge or come closer together

Familiar Size when we judge distances based in our knowledge of the objects size

Atmospheric Perspective occurs when more distant objects appear hast and often have a slight blue tint

• Binocular Depth Cues - those that require both eyes

Retinal disparity (due to your eyes being in slightly different locations on your head, each retina has a slightly different image of the world) is useful because as images become further away, they have a smaller degree of disparity on the retinas.

Hearing and Sound

what our brains interpret as sound us actually many small vibrating air molecules. They collide with other molecules, and the pressure travels across distance.

The frequency of sound is determined by the rate of vibrations. People can hear frequencies between 20 and 20 000 hertz (Hz).

The second dimension of sound is intensity of the wave, which is what we perceive as loudness.

When Sounds Enters the Ear

• Sound enters through the Pinna - it is shaped in such a way it helps filter the sound into the ear canal

• Tympanic Membrane - the eardrum, transfers energy to the three smallest bones in the body

• Ossicles - the smallest bones in the body (middle of the ear)

  • Consists of the malleus, Incus, and the Stapes

• Cochlea - Where sound is transferred into the neural language of the brain

• Basilar Membrane - A flexible piece of tissue found in the cochlea

• Transduction - Occurs when the vibrations against the oval window cause fluid inside the cochlea to move

Qualities of sounds, or cues can be represented with a 2 dimensional canvas

• Cue 1

  • Occlusion, the cells closest to the oval window to excite, while lower-frequency sounds excite the cells deeper in the cochlea. The brain uses the location of neural firing to understand sounds, this is call the Place Theory

• Cue 2

  • Frequency Theory - that the brain also uses information related to the date of cells firing. The more rapidly cells fire the higher the perception of pitch

Auditory Cortex

Located primarily in the temporal lobe.

Different components of sound are organized and analyzed in the medial geniculate nucleus if the thalamus.

The auditory system maintains a tonotopic organization from the basilar membrane to the auditory cortex

Sound Localization

The most important pieces of information sound can provide is the location of objects in space.

• Cues requiring comparisons between information from both ears are known as binaural cues

The two kinds of binaural cues for sound localization

• Intranural Time Differences - comparisons made between the arrival time of a sound in each ear.

• Intranural Level Differences - Intensity difference of the sound between the ears

Music and Speech Perception

• Music

Music can be used to tell a story and fundamentally influence mood. It has also been shown to have deep-rooted physiological effects on the brain and the rest of the body.

- Involuntary musical imagery is the experience of an inability to dislodge a song and prevent it from repeating itself in ones head

• Speech

Language and speech seems to be a uniquely human ability.

The production of speech has 3 basic parts

1. Respiration from the lungs

2. The vocal cords

3. The Vocal Tract

Correct and fluent speech requires a tremendous amount of coordination between these systems. In a typical conversation we produce about 10-15 sounds per second.

The McGurk effect demonstrates the role the visual system plays in speech perception

The Chemical Senses

Perception of smell and taste begin with activation of chemoreceptors. These are the only senses that require you to ingest the physical stimuli in order to analyze the incoming information

• Smell

The only sense that does not first go through the thalamus. Smell even plays a part in picking the people we like female preferences for the smell of particular types of men changes as their chances of becoming pregnant increases.

• The chemical process of smell

Airborne molecules interact with receptor sites in the mouth and nose and are drawn into the upper nasal cavity. Olfactory receptors bind to the cilia of air cells embedded in the olfactory mucosa. This is where the odorant’s will come into contact with the olfactory receptor neurons.

*There are over 350 types of olfactory recptors

• Taste

Taste relies on the correlation between the molecular properties of a substance and the effect of that substance on the body.

5 basic tastes that we seem to use in conjunction with our sense of smell to evaluate food

1. Sweet

2. Salty

3. Sour

4. Bitter

5. Umami (savory)

The little bumps on our tongs are called papillae, there are 4 categories of these

1. Filiform - found over the entire surface of the tongue and give your tongue the fuzzy appearance

2. Fungiform - named because they look similar to mushrooms

3. Foliate - the little folds along the back of the tongue

4. Circumvallate - found on the back of the tongue that are shaped like little mounds

Each taste bud contains about 50-100 taste sensitive cells which protrude into a taste pore. Transduction occurs when chemicals bind to the receptor sites on the taste pore.

Sensations from both the smell and taste are combined in the orbitofrontal cortex (OFC)

Perception of flavour most likely occurs in the OFC

Skin and Body Senses

The physical message of touch is pressure. An object makes contact with the body receptor cells embedded in the skin respond, and then the message travels up the spinal cord to the somatosensory cortex of the parietal lobe.

Most information about texture comes from the response of 4 types of mechanoreceptors located on the skin

• The Merkel Receptor - fire continuously as long as the skin is making contact with an object, sending information about fine details (high concentration on the skin)

• The Meissner Corpuscle - Fires when the skin first encounters the stimulus and when it is removed.

Located close to the surface of the skin and respond to pressure that is applied and then removed.

• Ruffini Cylinder - associated with interpreting the stretching of the skin

• Pacinian Corpuscle - Feels vibration and texture

These are located deeper in the skin

The somatosensory cortex organizes information from the body

Somatotopic Organization - 2 adjacent points of contact on your skin map to 2 adjacent points of neural activity on the cortex.

Temperature

We sense temperature changes through both hot and cold thermoreceptors in the skin

Cold fibres respond by increasing their firing rate to cold objects, while warm fibres increasing firing to heat.

these receptors also fire in respond to chemical stimuli i.e. menthol = cooling effect or if you were to rub your eyes after touching a hot pepper

Pain

An adaptive response to tissue damage.

Nociceptors detect pain and send signals to our brains. It is very subjective to the person based on their expectation and enculturation.

Pain serves a purpose, of example when a limb is damaged we reduce the use of the limb because of the pain.

• Gate Control Theory of Pain

Pain is only adaptive if it helps keep the organism alive. This theory suggests that impulses that indicate painful stimuli can be blocked in the spinal cord by signals sent from the brain. There is 3 pathways that input can happen

1. Small Diameter Fibres (S - Fibres) - fire to damaging and painful stimuli

2. Transmission Cell (T - Cell) - Perception of pain in part depends on the excitation of this cell

3. Large Diameter Fibres (L - Fibres) - Send signals to the brain about stimulation that is not painful

• Subjective Nature of Pain

The experience of pain depends not only on the sensations from the world but also what we expect to experience.

• Life without pain

There are individuals in the population who are unable to experience pain.

Congenital Analgesia is a rare condition has 2 features

1. Inability to perceive pain

2. Inability to perceive temperature

This is resulting from a recessive allele on chromosome 2. This condition can be dangerous because it can result in unrecognized burns, injuries, and infection.

The Kinesthetics and Vestibular Senses

We have more than 5 basic senses, but many of them work so well that we typically take them for granted

• The Kinaesthetic Sense

  Provides us with a basic understanding of where our body is in space and how to move out bodies to accomplish specific tasks.There are cells that fire when specific body parts are oriented in specific posistions

• The Vestibular Sense

  Sensory cells located in the cochlea. 2 structures respond not just to movement but also to posture and acceleration. Semicircular canals sense changes in acceleration and rotation of the head

Methods of Investigating Sensation and Perception

Psychophysics attempt to evaluate the way the physical experiences of light, sound, and the chemicals in our nose are translated into psychological perceptions.

• Stimulus Detection

A technique rat attempts to answer the question “what is the minimum amount of stimulus required to generate a sensation”

• Difference Threshold

The smallest amount of particular stimulus required for a difference in a magnitude to be detected.