Sensation and Perception

• Our bodies are constantly bombarded with information whether we're awake or asleep.

Sensation

• Sensation is the process of detecting environmental stimuli or stimuli arising from the body.
• Sensory systems have been developed through natural selection to provide information that increases survival.
• Differences in sensation occur between individuals but are usually subtle (e.g., needing glasses).

Perception

• Perception is interpreting sensory information.
• Individual differences in perception are more obvious.
• The same stimulation and sensation can result in different interpretations.
• Our sensory systems are particularly sensitive to change.
• Begins with the interaction between a physical stimulus and our biological sensory systems.
• Stimulus: Anything that can elicit a reaction from our sensory systems.
• Transduction: The translation of incoming sensory information into neural signals, which are then sent to the brain.

Perception

• The brain perceives sensory information (in the form of neural signals).
• Perception allows us to organize, recognize, and use sensory information.
• Attention is an important gateway to perception.
• Sensory adaptation: The tendency to pay less attention to steady sources of stimulation.
• Unfamiliar, changing, or high-intensity stimuli have high priority for attention.
• Selective attention: prioritize input to focus on a subset of available information and exclude the rest.
• We can’t process all stimuli, so selective attention is required.
• Bottom-up processing: The brain uses incoming signals to construct perceptions.
• Builds simple input into more complex perceptions.
• Top-down processing: Impose a structure on the incoming information.
• Uses memories, other cognitive processes, and knowledge to interpret sensory information.
• Bottom-up processing brings sensations of letter shapes to the brain.
• Top-down processing allows us to recognize individual words drawing on knowledge and experience.

Thresholds

• Gustav Fechner developed psychophysics to study the relationship between the physical qualities of stimuli and the subjective responses they produce.
• Absolute threshold: The smallest amount of stimulus that can be detected.
• Difference threshold: The smallest detectable difference between two stimuli.

Signal Detection

• Signal detection is the analysis of sensory and decision-making processes in the detection of faint uncertain stimuli.
• It's a two-step process. Step 1: actual intensity of the stimulus. Step 2: the observer's criteria for determining if the stimulus occurred.
• A person more concerned of identifying patrol cars may use lenient standards, slowing frequently, but would get few tickets.
• Another one might use stricter criteria: they would have fewer false alarms but risk missing real patrol cars, therefore maximizing misses.

Vision

• The sense that allows us to process reflected light.
• Approximately 50% of our cerebral cortex processes visual information.
• Human vision only involves a small part of the light spectrum.
• Gamma rays, x-rays, ultraviolet rays, infrared rays, microwaves, and radio waves lie outside of human vision.
• The visual stimulus is visible light, radiation from the electromagnetic spectrum, such as from the Sun, stars, or a lightbulb.

The Biology of Vision

• Begins in the eye.
• The cornea, the clear surface at the front of the eye, begins the process of directing and bending light.
• The pupil is an opening formed by the iris.
• The iris is a brightly colored circular muscle surrounding the pupil.
• The iris adjusts the opening of the pupil depending on the amount of light and signals from the autonomic nervous system.
• The lens is behind the pupil and bends light toward the retina.
• Muscles change the shape of the lens, which allows for accommodation to see objects near or far.
• The retina transduces light information within layers of visual processing cells (rods and cones) at the back of the eye.
• Fovea: An area of the retina that is specialized for highly detailed vision.
• It is responsible for central vision.
• The image of what we stare at is projected onto the fovea.
• Rod: A photoreceptor specialized to detect dim light.
• It is more common as we move from the fovea to the periphery of the retina for peripheral vision.
• Rods view dim light better than central vision.
• Rods don't provide color or sharp images.
• The human eye has about 90 million rods.
• Cone: A photoreceptor in the retina that processes color and fine detail.
• Cones function best under sharp bright light.
• The human eye contains between 4 and 5 million cones.

Visual Pathways

• Blind spot: Optic nerve exit with no rods or cones.
• We're usually unaware of our blind spots because perception fills in the missing details.
• Optic nerve: Nerve exiting the retina of the eye.
• It crosses at the optic chiasm, where axons closest to the nose cross to the other hemisphere and outside axons proceed to the same hemisphere.
• Partial crossing occurs where everything to the left of center in the visual field is processed by the right hemisphere, and everything to the right of center is processed by the left hemisphere.
• To see something requires the brain to interpret the information gathered by the eyes.

Important Features of the Visual System

• Cornea bends light toward the retina.
• Pupil forms an opening in the iris.
• Lens focuses light onto the retina.
• Retina contains rods, cones, and other visual neurons in its layer of cells.
• Fovea (area of the retina) processes detailed vision.
• Thalamus acts as the target for most axons forming the optic tracts.
• Primary visual cortex receives visual input from the thalamus and performs initial analysis of input.

Colour Vision

• Trichromatic theory: Color vision is based on different types of cones for detection of short (blue), medium (green), and long (red) wavelengths.
• Supported by observations of the three primary colors of light.
• Can’t explain color afterimages (seeing color elsewhere after staring for a long time).
• Opponent process theory: We have a red-green and a blue-yellow color channel. Activation of one color in each pair inhibits the other color.
• Most people have 3 types of cones.
• Very rare individuals can have either one type of cone or none, seeing the world in black and white.
• People with two types of cones are color blind.

Gestalt Psychology

• We are born with a number of tendencies to organize incoming visual information.
• Organization principle: We analyze visual input by dividing a scene into figure and ground.
• We identify the main object in the scene.
• Proximity principle: Objects that are close together tend to be grouped together.
• Continuity principle: We assume points which form smooth lines when connected belong together.
• Closure principle: We "fill in the blanks" when we see an image of lines or gaps.
• Simplicity principle: We use the simplest solution to a perceptual problem.

Depth

• Depth perception: The ability to use the 2D image projected onto the retina to perceive 3D.
• Achieved using monocular and binocular cues.
• Monocular cue: Depth cue that requires the use of only one eye.
• Texture gradients and shading.
• Occlusion: Blocking of the images of distant objects by closer objects
• Illusions from the environment result from the use of monocular cues to judge depth.
• Binocular cue: Depth cue that requires the use of both eyes.
• Our most effective depth cue is retinal disparity: the difference between images projected onto each eye.
• Binocular cues provide information on the relative distance between two objects.
• As distance between objects increases, disparity increases.
• Can help predators when hunting prey camouflage.
• Retinal disparity allows them to spot tiny variations in depths of objects in the visual field.

Hearing

• Audition: sense of hearing.
• It allows us to identify objects and to communicate using language.
• Sound is the movement of an object that sends vibrations in the form of waves in varying amplitudes and wavelengths.

Parts of the Ear

• OUTER EAR
• Pinna: Collects and focuses sound. It helps us localize sounds as being above/below head.
• Auditory canal.
• Tympanic membrane: also known as the eardrum.
• MIDDLE EAR
• Oval window: Boundary between outer and middle ear.
• Tiny bones: Transfer sound energy from air of outer and middle ear to fluid inside inner ear.
• INNER EAR
• Cochlea: structure in the inner ear that contains auditory receptors.
• Has three chambers, separated by membranes.
• Two chambers are the vestibular canal and the tympanic canal.
• Cochlear duct lies between the vestibular and tympanic canals, separated by the basilar membrane.
• Basilar membrane: membrane in the cochlea where the Organ of Corti is located.
• Organ of Corti rests on top of the basilar membrane containing auditory receptors.
• Contains hair cells that transduce sound energy into neural signals.
• Auditory nerve: Nerve carrying sound information from the cochlea to the brain.
• One branch of the auditory nerve cell makes contact with hair cells.
• Medulla - Midbrain manages reflexive response to sound.
• The thalamus analyzes sound.
• Secondary Auditory Cortex responds to more complex stimuli

Pitch Perception

• High frequency tones produce maximum movement of the base basilar membrane.
• Low frequency tones produce maximum movement near apex of basilar membrane.

Loudness Perception

• Frequency of sound interacts with our perception of its loudness.
• We can hear with maximum sensitivity sounds between 80 Hz - 10,000 Hz.

Localization of Sound

• Pinna localize sounds in the vertical plane (below or above head).
• Compare the arrival time of sound at each ear and the intensity of sound localizes sound in the horizontal plane.

Auditory Groupings

• Sounds, like vision, are grouped together based on their similarities.
• Sounds that start and stop simultaneously are perceived from the same source.

Important Structures in Audition

• The pinna collects sound and identifies its location (above or below head).
• Tympanic membrane begins the process of transduction of sound waves to neural signals when movement occurs.
• Cochlea contains auditory receptors.
• The thalamus receives auditory input from the brainstem and connects to the primary auditory cortex.
• Primary auditory cortex receives and performs an initial analysis of auditory input from the thalamus.

Touch and Feeling

• Somatosensory stimuli arise from within the body or make contact with its surface.
• Provides the organism with little need to react.
• Provides feedback for movement, speech, and safety.

Body Position

• Vestibular system: System in the inner ear that provides information about body position and movement.
• When one is sick, the proximity of these structures can become congested, which makes us feel dizzy.
• Provides information about the position of the head.
• Contains hair cells that are bent back and forth in the fluid when the head moves.
• Movement of hair cells produces signals in the auditory nerve.
• Axons form connections in the medulla and the cerebellum (balance and motor coordination).
• Vestibular information travels from the medulla -> thalamus -> Primary Somatosensory.
• Cortex of the parietal lobe -> Primary Motor Cortex of the frontal lobe.

Touch

• Touch confirms our visual exploration of objects.
• Touch can be a form of social communication in infants.
• Our skin is embedded with specialized neurons.
• Different receptors respond to different features of touch stimulus.
• Receptors are also in blood vessels, joints, and internal organs.
• Touch information travels from the skin to the spinal cord.
• That goes to the thalamus, which transmits information to the Primary Somatosensory Cortex in the parietal lobe.
• Humans are more sensory sensitive in the hands and mouth.
• There are no touch receptors or pain receptors in the brain.

Pain

• Free nerve endings respond to pain and are triggered by stimuli with tissue damage.
• Some respond to mechanical damage, while others respond to temperature or chemicals.
• Pain fibers form synapses with cells in the spinal cord to send pain messages to the thalamus.
• This is a direct route for pain to be received quickly in the brain.
• Pain information is sent from the thalamus to the anterior cingulate cortex to manage the emotional components of pain.
• Stress is an example of a high order cognitive state that influences pain.
• The placebo effect can occur where people think they experience pain reduction even though they were exposed to a ineffective substance

Tastes and Smells

• Olfaction: the sense of smell.
• Begins with molecules in the air.
• Provides information at a distance (like vision and audition).
• Gustation: the sense of taste.
• Begins with molecules dissolved in saliva.
• Involves information from contact with body (like somatosenses).
• These senses can provide warning of dangers and contributes to our emotional and social experiences.

Olfaction

• Taken in through nostrils and circulated within nasal cavities while interacting with olfactory receptors.
• Olfactory receptors regularly die and are replaced by new cells.
• Olfactory nerve: Nerve carrying olfactory information from the olfactory receptors to the olfactory bulbs.
• Olfactory bulb: One of two structures below the frontal lobes that receive input from the olfactory receptors.
• Olfactory pathways do not directly contact the thalamus.
• Fibers from the Olfactory Bulb go to the Olfactory Cortex and Amygdala (controls emotion).

Gustation

• The purpose is to protect us from eating spoiled or poisonous food
• Taste receptors are located on tongue and other parts of the mouth.
• They are sensitive to all types of taste and are distributed across the tongue.
• Papillae: Bumps on the tongue that contains taste buds.
• Taste bud: A structure found in papillae that contains taste receptors.
• Has a limited life and can be replaced.
• Tongue sends info to medulla, thalamus, somatosensory cortex, and orbitofrontal cortex.

Perception and Cognition

• Three perceptual themes for olfaction and gustation
• First is we easily identify a number of complex stimuli combining many types of molecules
• The second is we can detect small differences among similar smells and tastes.
• Third, our experiences shapes our perception of olfactory/gustatory stimulus.

Vision Development

• Human infants can see what we see but with less detail.
• They may need more contrast.
• As we age, accommodation of the lens becomes slowing
• Older adults respond more slowly to changes in brightness.
• Muscles of iris lose their elasticity.
• Pupils remain smaller.
• The lens of the eye yellows, which affects perception of color.

Audition Development

• Human fetus can hear sounds.
• Newborns can recognize their mother's voice.
• Hearing loss is a result of aging.
• Occurs first at high frequencies
• Perfect pitch
• One can name a musical tone that is heard.
• Areas of the left hemisphere is larger in musicians with perfect pitch.
• Can be trained to have perfect pitch.

Somatosenses Development

• No other sensory modality is as dramatically affected by culture and experience as sense of pain.
• Hook-swinging ritual: A male volunteer is hung by steel hooks embedded into the skin and muscles of his back.
• Women who have participated in prepared childbirth classes generally report less pain than women who are uninformed.
• Compared to non-athletes, athletes in contact sports tolerate labels of pain before identifying a stimulus as painful.
• Patients who are allowed to self-administer morphine for pain require less medication than patients who receive injections from the hospital staff.

Olfaction and Gustation Development

• As we age, our number of taste buds decreases.
• Our sense of smell also decreases as we age.
• Females are generally more sensitive to smell than males.
• Disturbances in chemical senses are correlated with a number of psychological disorders
• Smell and PTSD: specific smells can bring back bad experiences or memories.