Chapter 4: Sensation and Perceptions

Sensation

Registration of simulation (light, sound, pressure, odor, taste) of the physical world

Perception

Organization, interpretation of a sensation

Perception is influenced by whether one primarily relies on external sensory information or internal prior expectation

Transduction

Process of converting one form of energy into another for that your brain can use. Receive → transform → deliver

Bottom Up Processing

Data driven; information flowing from the sensory receptors to the brain

Top Down Processing

Goal driven; information processing guided by our experience and expectations (schemas, perceptual sets)

Ex. the arrangements of letters don’t matter besides the first and last letters be in the right place

Role of Attention

Attention is an interaction of sensation and perception that is affected by internal and external factors

Selective Attention

Focusing conscious awareness on a particular stimulus

ex. focusing on a task in a noisy classroom

Cocktail-party effect

Tuning in on a conversation while filtering out others nearby or the ability to respond to your name if called to attention; an example of selective attention

Selective Inattention

Inattentional blindness: failure to see visible objects when attention is directive elsewhere

Change Blindness: failure to notice changes in the environment

Absolute threshold

Minimum stimulation needed to detect a particular stimulus 50% of the time

Measures sensitivity in sensory processing and perception.

Difference threshold

Just noticeable difference; minimum difference a person can detect between any two stimuli half the time; threshold increase with stimulus size(ex. harder to tell the difference between loud and louder music)

Weber’s law

For an average person to perceive a difference, two stimuli must be different by a constant minimum percentage (not a constant amount)

_{Sensory adaptation}

The diminishing responsiveness of our sensory systems to prolonged stimulation (neurons fire less frequently)

Deviations of Typical Sensation

There are four: synesthesia, phantom limb, rubber hand illusion, prosopagnosia

Synesthesia

An experienced of sensation in which one system of sensation is experienced through another

Phantom limb

The feeling that an amputated limb is still present, often manifested as a tingling or occasionally, painful sensation in the area of the missing limb

Rubber Hand Illusion

A visual tactile illusion that makes a participant feel like a rubber band is part of their body

Prosopangnosia

Face blindness that impairs the ability to recognize familiar faces, often due to brain damage.

Accommodation

Process by which the lens changes shape to maintain a clear image on the retina

When the process of accommodation is altered, nearsightedness or farsightedness might occur

Retina

Photo-sensitive tissue lining the back of the eyeball

Captures light energy for transduction

Myopia

Nearsightedness, light is focused in front of the retina causing faraway objects to be blurry

Hyperopia

Farsightedness, light is focused beyond the retina causing close objects to be blurry

3 characteristics of light energy

Wavelength, amplitude and purity

Wavelength

Distance from one peak to the other determines it hue(color)

Amplitude

Height of the wave determines brightness

Purity

Richness of color (saturation)

Pathway to Brain

Retinal receptor cells of the rods and cones process information to the bipolar cells then ganglion cells to the optic nerve. From the optic nerve, it is sent to the thalamus then the visual cortex in the occipital lobe where it is seen

Cones

Sensitive to detail and color; function in daylight and well lit rooms/concentrated in the fovea/less numerous than rods

Rods

Sensitive to low light/concentrated at the outer edges of the retina

Actived in low light environments

Handles peripheral vision

Rods and Cones

Both play a role in light-dark adaptation. Initially blackness is seen because our cones cease functioning in low intensity light

Thrichromatic Theory (1850)

Blue - short wavelengths

Green - medium wavelengths

Red - long wavelengths

Wavelengths are combined into other colors to create a visible spectrum, 1st level of processing

Wavelengths are combined into other colors to create a visible spectrum, 1st level of processing

Color Vision Deficiency

Involves damage or irregularities to one or more cones or ganglion cells (red/green, blue/yellow)

Includes dichromatism (only 2 functioning cones) or monochromatism (only 1 functioning cone)

Opponent Process Theory (1878)

Pairs of cones types work in opposition

Blue - yellow

Red -green

Black - white

Supported by afterimages. When one cone receptor tries out the other is activated, 2nd level of processing

Perceptual Constancy

Tendency to see familiar object as having standard shape, size, color, or location regardless of changes in the angle of perspective, distance, or lighting

Color

Compares wavelengths from objects and its background, relative to the objects surrounding it or what we are most used to

ex. snow is white throughout the day

Size and Shape

Perception of an object as having a fixed size or shape, despite the change in the size of the visual angle that accompanies changes in distance

Priming

Activating, often unconsciously, associations in our mind; exposure to a stimulus influences a perosn’s response to a subsequent stimulus; example of top down processing

Perceptual set

A concept that describes how individuals expectations, beliefs and experiences influence how they perceive and interpret sensory information

Pre existing schemas(or patterns of thought) organize and interpret unfamiliar information and influence our perception

Context effects

A given stimulus may trigger different Perceptions because of the immediate context or cultural forces

Phi Phenomenon

Illusion of movement when adjacent lights blink on and off

Stroboscopic Movement

When the brain perceives a rapid series of images as continuous movement

Gestalt Principles

Humans are naturally capable of perceiving objects as organized forms and patterns; the whole is greater than the sum of its parts

Closure

The principle of making a whole or completed object by filling in the gaps

Figure and ground

The principle in which the figure is the object and the ground is the surroundings

Proximity

Principle that items close together group more easily than items far apart

Similarity

The principle that items more alike group more easily than times that are different

Binocular Cues

Comparing images with 2 eyes: retinal disparity and convergence

Retinal Disparity (difference)

Retinas receive different images. When images are compared your brain can judge how close an object is

Greater retinal disparity(difference between images), closer the object

Convergence (turning your eyes inward to look at close objects)

Cue caused by the way our eyes muscles turn our eyes inward

The closer an object, the more inward our eyes need to turn in order to focus

Monocular Cues

Clues that can be used for depth perception that involves using only one eye: relative clarity, relative size, texture gradient, linear perspective, interpostion

Relative Clarity

Objects that appear sharp, clear and detailed are seen as closer than more hazy objects

Relative Size

When objects are the same size the object that looks the largest will be judged as being the closest to the observer

Texture Gradient

The gradual change in the visual texture of an object or surface as it recedes in depth from the observer

Linear Perspective

Angled Parallel lines

Interposition

If one object partially blocks another it is seen as closer

Sensory Interaction

The process by which our senses work with and influence each other. Smell and taste are two senses that commonly interact with each other as well as sight and sound

Auditory Transduction

• Outer ear [pinna] funnels sound waves to the eardrum.

• The middle ear transmits the eardrum vibrations through a “piston” made of the ossicles (3 small bones -hammer, anvil and stirrup) 

• The incoming vibrations cause oval window to vibrate, moving the fluid that fills the cochlea (snail-shaped tube containing nerve cells). This motion causes ripples in the basilar membrane 

• The movement of hair cells [stereocilia/ specialized auditory receptor neurons]  triggers impulses in the adjacent nerve fibers which form the auditory nerve that connects via the thalamus to the temporal lobe & auditory cortex.

Cochlea

A fluid filled tube containing cell that transduces sound vibrations into neural impulses; divided along its length by the basilar membrane

Place Theory (space theory)

High Pitches - brain determines a sound’s pitch (higher or lower) by recognizing the place on the basilar membrane in the cochlea that is generating the neural signal

Pros: Explains how we hear high pitched sounds

Cons: Neural networks are not so localized for low pitched sounds

Frequency Code (temporal code)

Low Pitches - frequency of a sound wave matches the firing rate of the auditory nerve

Pro: explains how we hear low pitched sounds

Volley Theory

Extends the frequency theory to higher frequencies by proposing that groups of neurons fire in an alternating pattern. The volley pattern helps to encode frequencies higher than the firing rate of an individual neuron

Pros: accounts for mid-range frequencies

Cons: does not work well for very high frequencies where place Theory becomes more dominant

Sensorineural hearing loss

Nerve deafness; damage to cochlea; most common form of hearing loss

Can be treated with an cochlear implant

Cochlear implant

A device for converting sounds into electrical signals and stimulating the auditory nerve through electrodes threaded into the cochlea (bypasses the damaged inner ear)

Conduction/conductive hearing loss

Damage to hammer, anvil, or stirrup(middle ear) caused by ear infection or cold that causes more fluid to build up

Medicine or surgery can often help

Auditory Disparity

Slight differences in the sound signal that reaches each ear, allowing the brain to pinpoint the location of a sound source by interpreting the differences. Key mechanism behind how we can localize sound

Types of Auditory Disparity

Difference in timing (arrival time)

Difference in intensity (loudness)

Sound Localization

The ability to identify the position and changes in position of sound sources based on differences in time and intensity

Vestibular System

Provides the sense of balance and the information about body position

Semicircular canals and vestibular sacs in the ear, used with visual feedback to maintain balance

Kinesthesis

System for sensing the movement of individual body parts in relation to gravity (walking, laying down)

Being able to move in a coordinated way without looking at the various parts of the body as it moves

Four Basic Skin Senses

pressure, warmth, cold and pain. Our skin has sensory receptors for all 4

Sense of Hot is the activation of warm and cold receptors

Nociceptors

Sensory nerve receptors in our skin, muscles and organs that detect pain (noxious signal) and transmit signals to the spinal cord and brain

Gate Control Theory of Pain

Pain is reduced when you activate a non painful sensation such as shaking

Fast nerve fibers carry non painful sensory information. To block pain you can activate fast nerve fibers through shaking or rubbing an area and block the pain signal at the neurological gate.  

Sensitive to taste

Depends on the number of taste receptors on the tongue

Receptors cells release neurotransmitters when certain chemical in foods detected. Some receptors respond to different tasting molecules

Taste buds

We have 1000s of taste buds. On each bud there are 50-100 receptor cells that sense food molecules. Reproduce every week or 2

6 types of taste

Sweet, Umami, Bitter, Sour, Salt and Oleogustus (oily/fatty taste)

Spicy taste is just a combination of hot and pain sensation

Supertasters

Have a better sensitivity to bitter tasting foods

Flavor

Smell+texture+taste

Sensory interaction

Senses relying on one another

Olfaction

Molecules are carried in the air to olfactory receptor cells in the nasal cavity. Groups of ORNs send their axons (messages) to brain’s olfactory bulb to the temporal lobe (primary smell cortex) and parts of the limbic system. BYPASSES THE THALAMUS

Pheromones

Biochemical odorants emitted that can affect behavior or physiology