Sensation and Perception

Sensation

The process of detecting a physical energy (a stimulus) from the environment and converting it into neural signals

Reception

the stimulation of sensory receptor cells by energy (sound, light, heat, etc)

Sensory Receptors

specialized cells that detect stimulus information and transmit it to sensory (afferent) nerves and the brain

Transduction

• The process that converts energy, such as light or sound waves, into the form of neural messages.

  • In all the sense organs, it is the job of sensory receptors to convert incoming stimuli information into electrochemical signals—neural activity.

Transmission

delivering this neural information to the brain to be processed

Absolute Threshold

• Absolute Threshold – is the weakest amount of a stimulus that a person can reliably detect.

• The minimum stimulation needed to detect a stimulus 50% of the time.

• Will differ person to person

Stimuli you cannot consciously detect 50% of the time are subliminal

Signal Detection Theory

• a theory predicting how and when we detect the presence of a faint stimulus (signal) amid background stimulation (noise).  

• Assumes there is no single absolute threshold

  • Detection depends on a person’s psychological state:

  • experience

  • expectations

  • motivation

    • alertness

Difference Threshold

Minimum difference between two stimuli required for detection 50% of the time, also called just noticeable difference (JND).

Weber’s Law

• Two stimuli must differ by a constant minimum percentage (rather than a constant amount), to be perceived as different. 

  • Weber fraction: k = δI/I.

Sensory Adaptation

• diminished sensitivity as a consequence of constant stimulation

  • Ever forgotten you are wearing a watch?

  • Ever gotten used to a smell?

• Then why don’t things disappear from your vision? (walls, clock)

  • adaptive quality - awareness for protection!

Sensory Interaction

• the process by which our five senses work with and influence each other

  • Example: smell + texture + taste = flavor

• When one sense affects another sense

• The taste of strawberry interacts with its smell and its texture on the tongue to produce flavor

Phototransduction (Vision)

the conversion of light energy into neural impulses that the brain can understand

Cornea

• eye’s clear, protective outer layer covering the pupil and iris. 
  Light first enters the eye through the cornea.

Pupil

small adjustable opening in the center of the eye through which light enters.

Iris

• ring of muscle tissue that forms the colored portion of the eye around the pupil 

controls the size of the pupil opening by expanding and contracting over the pupil.

Lens

• transparent structure behind the pupil

• changes shape to help focus images on the retina.

How does the lens change shape?

To focus the rays, the lens changes its curvature and thickness in a process called accommodation.

Myopia

Nearsighted Vision

Hyperopia

Farsighted Vision

Retina

• light-sensitive inner surface of the eye

Contains sensory receptors (rods & cones) plus a layer of neurons that begin the processing of visual information

What happens in the retina

1. Light waves transduced into neural impulses by the rods and cones

2. 2. then passed to the bipolar cells and the ganglion cells.

Blind Spot

Point where the optic nerve leaves the eye because there are no receptor cells located there.

Fovea

• central focal point in the retina, around which the eye’s cones cluster.

area of greatest visual acuity (sharpness of focus)

Optic Nerve

The optic nerve carries the impulse to the thalamus in the middle of the brain and then on to the visual cortex of the occipital lobes.

Photoreceptors

Light-sensitive cells (neurons) in the retina that convert light energy into neural energy.

Rods

• Photoreceptors that are especially sensitive to dim light, but not color. (125 million/eye)

  • Detects black, white and grey, responsible for peripheral and twilight vision

Cones

• Photoreceptors that are especially sensitive to colors but not dim light. (7 million/eye)

  • Cones are responsible for our ability to “see” colors

Visual Cortex

• most visual information is sent here before moving to other visual areas for further analysis 

  • located in occipital lobe

  • is the part of cerebral cortex 

• In the visual cortex, the brain begins working by transforming neural impulses into visual sensations of color, form, boundary and movement.

This process is called parallel processing

Parallel Processing

the simultaneous processing of several aspects of a stimuli

Shape Detection

Specific combinations of temporal lobe activity occur as people look at shoes, faces, chairs and houses.

• different parts of visual cortex used to identify different images

Feature Detection

• Nerve cells in the visual cortex respond to specific features, such as edges, angles, and movement. 

  • It is the reason we are able to detect the distinct features of Snoopy & his cooked turkey

Color

• The dragon is anything but red.

• The dragon rejects the long wavelengths of light that to us are red- so red is reflected of and we see it

• Also, light has no real color.

  • It is our mind that perceives the color.

Light Energy

• Humans detect visible light.

• Light travels as an electromagnetic wave.

  • Wavelengths:

    • Blue = short

    • Green= medium

    • Red = long

Physical Characteristics of Light

Light travels as an electromagnetic wave

Wavelength

what hue (or color) am I seeing?

Amplitude

how bright is the color I am seeing?

Young-Helmholtz Trichromatic (three-color) Theory

• the retina contains three different types of color receptors (cones)— (sensitive to red, green, or blue)

• when receptors fire, colors are mixed and we get combinations that make up the spectrum that we see in the world

Color Blindness

• Genetic disorder in which people are blind to green or red colors

• They lack functioning red or green sensitive cones

• These people have dichromatic (two-color) vision

• Supports Trichromatic Theory

Dichromatic Vision

People with dichromatic vision have two types of cone cells that work, but one type is not fully functional.

Protanopia

Blindness to Red

Deuteranopia

Blindness to green

Tritanopia

Blindness to blue

Monochromatic Vision

• People with monochromatic vision, also known as complete color blindness, can only see shades of gray, black, and white. 

  • This is a very rare type of color blindness.

Opponent Process Theory

• Further up in the optic nerve, neurons work in pairs to help process color vision signals.

• Red-Green = Xmas

• Blue-Yellow = Beach

• Black-White = Oreo

• We cannot see certain colors together in combination (red-green, blue-yellow, and white-black).  These are antagonist/ opponent colors.

After Images

• The ghostly birds are called afterimages. 

  • As you stare at the red bird, light-sensitive cells at the back of your eyes become less responsive to red light. This is a result of the Opponent Processing theory.

    • Color perception is controlled by the activity of two opponent systems; a blue-yellow mechanism and a red-green mechanism

    • there are some color combinations that we never see, such as reddish-green or yellowish-blue. 

Eg. When you shift your gaze to the birdcage, your visual system “subtracts” red light from the white light that’s being reflected from the white background. White light minus red light is blue-green light.

Prosopagnosia

• A neurological disorder characterized by the inability to recognize faces.

  • It is not related to memory loss, vision problems, or learning disabilities.

    • Often caused by damage to the fusiform gyrus, a region of the brain that plays a key role in facial perception

Blindsight

• A condition where individuals who have lost conscious vision due to damage in the visual cortex of the brain can still respond to visual stimuli.

  • Even though they cannot consciously "see" objects in their field of vision, they can detect their presence and movement without being aware of it.

    • It provides insights into how the brain processes visual information at an unconscious level.

Audition

the sense or act of hearing

Sound Waves

Sound waves are compressing and expanding air molecules → travels as a wave of air pressure.

Frequency

• What pitch am I hearing? (high tone or low tone) 

• determined by the wavelength of sound.

Volume (loudness)

• How loud is the sound I am hearing?

• determined by the amplitude

Outer Ear

Collects and sends sounds to the eardrum

Middle Ear

• Chamber between the eardrum and the cochlea.  

• Contains three tiny bones (hammer, anvil, stirrup) that concentrate the vibrations of the eardrum on the cochlea’s oval window.

Inner Ear

Innermost part of the ear, containing the cochlea, semicircular canals, and vestibular canals.

Cochlea

Coiled, bony, fluid-filled tube in the inner ear that transforms sound vibrations to auditory signals.

Sound Localization

• Because we have two ears, sounds that reach one ear faster than the other ear cause us to localize the sound.

• Time differences as small as 1/100,000 of a second can cause us to localize sound. 

• The head acts as a “shadow” or partial sound

Place Theory

• Pitch (how high or low something is) is determined by location of vibration along the basilar membrane

• But this doesn’t explain low-pitch since we haven’t found specific positions for those on the bm

Frequency Theory

• Pitch is determined by frequency hair cells produce action potentials

• If the frequency of the sound is 100 waves per second then the neuron fires at 100 pulses per second

• But we can hear frequencies above 1000 waves per second but neurons can’t fire faster than 1000 pulses per second.

• Volley Principle

  • Pattern of sequential firing creates a combined high frequency signal

Conduction Hearing Loss

• Hearing loss caused by damage to the mechanical system that conducts sound waves to the cochlea.

  • Less common than sensorineural 

    • Surgery

Sensorineural Hearing Loss

• Hearing loss caused by damage to the cochlea’s receptor cells or to the auditory nerve, also called nerve deafness.

  • Hearing aid to amplify sound

  • Cochlear Implant

Coclear Implants

work by translating sounds into electrical signals that are transmitted to the cochlea and, via the auditory nerve, relayed to the brain.

Taste (Gustation)

• Chemical Sense 

• Four basic tastes: Sweet, Salty, Sour, Bitter

• Recently, receptors for a fifth taste have been discovered called “Umami” (savory)

  • from Japanese word meaning pleasant/savor

  • Recognizes glutamates and nucleotides

• And now.. oleogustus (“fatty”)

Papillae

• Those bumps on our tongue are called Papillae.

• Papillae help grip food while your teeth are chewing - and they contain your taste buds

Transduction of Taste

• taste buds shaped like miniature onions

• receptors for taste

• chemicals dissolved in saliva activate taste buds

• produce nerve impulses that reach areas of the brain’s parietal lobe

• brain transforms impulses into sensations of taste

Taste differs person to person

• Supertaster -  tongues more densely populated with fungiform papillae (taste buds), giving them a stronger ability to taste what others could not (25%)

• Medium taster - average # of taste buds (50%)

• Nontaster - a person who has a decreased ability to perceive taste, especially bitter or spicy flavors; have fewer taste buds than other people (25%)

Smell

• Another chemical sense!

• Odorants enter the nasal cavity to stimulate 5 million receptors to sense smell. 

• Unlike taste, there are many different forms of smell.

• NOT processed by the thalamus → olfactory bulb

Smell & Memories

• The brain region for smell (in red) is closely connected with the brain regions involved with memory (limbic system). 

  • That is why strong memories are made through the sense of smell.

Age, Gender, and Smell

• Ability to identify smell peaks during early adulthood, but steadily declines after that. 

• Women are better at detecting odors than men.

Pheromones

• Chemical signals released by animals (and potentially humans) that can influence the behavior or physiology of others of the same species.

  • Used by animals as a form of communication

• Can trigger immediate behavioral responses, such as attraction or alarm.

Pheromone Detection

Often detected through the vomeronasal organ (VNO), located in the nasal cavity. However, the presence and role of the VNO in humans is still debated.

Pheromone Pathway

Signals are sent from the VNO (or olfactory system) to the hypothalamus, influencing emotions, behaviors, and hormonal responses.

Touch

• skin is the largest sense organ

• There are receptors for pressure, temperature, and pain

• Touch appears to be important not just as a source of information, but as a way to bond with others

• Touch Localization

  • depends on the relative lengths of the pathways from the stimulated parts to the brain.

Pain

• tells the body that something has gone wrong.

• Usually results from damage to the skin and other tissues. 

  • A rare disease exists in which the afflicted person feels no pain.

Gate-Control Theory

Melzak and Wall (1965, 1983) proposed that our spinal cord contains neurological “gates” that either block pain or allow it to be sensed.

Kinesthetic Sense

• The sense of our body parts’ position and movement

• Keeps us informed about movement of body parts & their position in relation to each other.

• Muscle Movement, Posture, & Joints

  • Information comes from stretch receptors, the tendons, & the internal organs.

Vestibular Sense

• Hair cells in the inner ear bend in relation to the position & movement of the head 

  • Biological gyroscope located in the inner ear 

  • In the semi-circular canals and the vestibular sacs

  • Liquid moves when the head moves and signals the brain

• gives information that the brain uses to help us maintain our balance and to sense changes in our movement through space.

  • Essential for balance, coordination, & equilibrium

Basics of Perception

• We do not actually experience the world directly, but instead we experience it through a series of “filters” we call senses. 

• The brain senses the world indirectly because the sense organs convert stimulation into the language of the nervous system: neural messages

Bottom Up Processing

Analysis of the stimulus begins with the sense receptors and works up to the level of the brain and mind.

• Starting with the sensory input, the brain attempts to understand/make sense.

• process this way when we have no prior knowledge → start @ bottom with individual pieces of data and work our way up to a theory or conclusion 

• relies more on sensation than perception
  Example: You’re on a hike and see a long, slim, slithering creature on the ground… you process… ah!

Top Down Processing

Information processing is guided by higher-level mental processes as we construct perceptions, drawing on our experience and expectations.

• Guided by experience and higher-level processes, we see what we expect to see.

• process this way when have prior knowledge → start at top & work way down as process specific details based on expectations/experiences 

• relies on perception over sensation

• An experienced hiker, you expect to see snakes on your hike so windy stick, lizards, etc. all seem like snakes.

Selective Attention

concentration on certain stimuli in the environment and not on others, enabling important stimuli to be distinguished from peripheral or incidental ones

failure of attention to particular physical or emotional stimuli

Cocktail Party Effect

• Our ability to attend to only one voice among many.

Inattentional Blindness

refers to the inability to see an object or a person in our midst.

failing to see visible objects when our attention or focus is directed elsewhere

Change Blindness

• refers to failing to notice changes in the environment

• failing to notice changes in the visual environment

Schemas and Perception

• Schema a collection of basic knowledge about a concept or entity that serves as a guide to perception, interpretation, imagination, or problem solving.

•  could be a mental model that provides a frame for interpreting information

  • What do you think of when you hear “dorm room”?

Perceptual Sets

• a tendency to perceive things in a certain way to a specific situation or stimulus based on their expectations, experiences, beliefs, and context

  • Listeners “hear” diabolical messages in rock music because they are prepared to “discover” certain messages, and therefore they do.

• Influenced by experience, context, motivation, and emotion

Context Effects

• top down influence on perception as we are influenced by experiences, ideas and emotions

• In which picture does the center dot look larger?  

  • Perception of size depends on context.

Parapsychology

The study of paranormal phenomena, including ESP and psychokinesis (the ability of the mind to move objects).

ESP

• The controversial claim that awareness can occur apart from sensory input. Includes: 

  • telepathy: mind to mind communication

  • clairvoyance: seeing remote events

    • precognition: seeing the future

Gestalt Psychology

• a school of thought interested in how people naturally organize their perceptions according to certain patterns. 

  • main principle: the whole is different from the sum of its parts -- computer screen image (sum) pixels (parts)

We see the world as we want instead of what it is.

Figure Ground

the organization of the visual field into objects (the figures) that stand out from their surroundings (the ground)

Grouping

• After distinguishing the figure from the ground, our perception needs to organize the figure into a meaningful form using grouping rules

  • Proximity, similarity, closure(+continuity & connectedness)

Closure

we fill in the spaces and see disconnected or incomplete figures  as complete figures

Proximity

see objects close together as a unit

Similarity

See Image

Continuity

• we perceive smooth, continuous patterns rather than discontinuous ones.

  • objects either in a straight line or smooth curve are more easily seen as a unit (together) 

Connectedness

The Principle of Common Region states that objects that are within the same region are perceptually grouped together. 

Perputual Constancy

• Our tendency to perceive objects as stable and unchanging despite changing sensory information

  • Color constancy

  • Lightness constancy

  • Size constancy

    • Shape constancy

Depth Perception

• he ability to perceive objects three-dimensionally (binocular and monocular cues)

  • Allows us to turn 2-D images into 3-D perceptions 

  • Depth perception enables us to judge distances.

Binocular Cues

depth cues that depend on the combination of both eyes (the two eyes work together)

Monocular Cues

depth cues that depend on one eye