1.6 Sensation

Sensation

• sensation - process of detecting physical energy (stimuli) from the environment and converting it into neural signals

Thresholds: Limits of Sensation

• transduction - process by which the brain converts outside stimuli into a sensation

• absolute threshold - minimum amount of stimulation needed to detect stimulus at least 50% of the time

• difference threshold (just noticeable difference - jnd) - smallest change in stimulation needed to detect change at least 50% of the time

• weber’s law - difference threshold is proportional (not by constant amount) to the intensity of the original stimulus

  • ex) easier to notice small change in weight if you’re lifting a light object than a heavy one

  • it’s not absolute units that matter, but its the percentage up or down

• subliminal threshold - stimulus at a level at which participant is not aware of stimulus presented

Other Key Concepts

• signal detection theory - how we detect a faint stimulus in presence of background noise

  • depends on factors like expectations, motivation, alertness

• sensory adaptation - our senses become less sensitive to a constant stimulus over time

  • ex) getting used to smell of your own perfume

• habituation - decrease in response to repeated stimulus due to conscious or unconscious learning

  • ex) not noticing ticking of a clock after a while

• synesthesia - one sense is experienced through another

  • seeing colors when they listen to music

  • taste flavors when reading

Visual Sensory System

Structure of the Eye

• cornea - clear, uncurved front of eye; bends light to begin focusing it

• iris - colored part of eye, a muscle that controls size of pupil

• pupil - opening in iris that lets light into eye

  • dilates in dim light

  • constricts in bright light

• lens - transparent, flexible structure that further focuses light onto retina

  • accommodation - changes shape to focus on objects at different distances

• retina - light-sensitive inner surface of eye, containing photo-receptor cells

  • fovea - central point of retina, where vision is sharpest and most cones are located

  • optic disc (blind spot) - where optic nerve leaves the eye, creating area with no photo-receptors

• visual/optic nerve - nerve that carries visual information from the retina to the brain

Photo-receptors: Rods and Cones

• rods - detect black, white, and gray; responsible for peripheral and night vision

• cones - detect color (red, green, blue); responsible for sharp, detailed vision and require bright light

How We See

1. light enters eye through cornea and pupil

2. lens focuses light onto retina

3. rods and cones in retina convert light into electrical signals

4. these signals are sent through bipolar cells to ganglion cells

5. ganglion cells form optic nerve, which carries signals to brain for processing

Vision: Color and Perception

Color Vision: How We Perceive Colors

• hue - dimension of color we experience; determined by wavelength of light

  • short wavelength → bluish colors

  • long wavelengths → reddish colors

• intensity - brightness of color; determined by amplitude (height) of light wave

  • high amplitude → bright colors

  • low amplitude → dull colors

Vision Types

• nearsightedness (myopia) - difficulty seeing distant objects clearly

  • eyeball is too long, causing light to focus in front of retina

• farsightedness (hyperopia) - difficulty seeing close objects clearly

  • eyeball is too short, causing light to focus behind retina

• achromatism - only able to see black, white, and gray

  • lack of retinal cones

• dichromatism - lead individual to be confused between certain colors

  • most common → red-green color blindness

• monochromatism - individual cannot see different colors

  • lack of/malfunction of cone cells

  • see everything in different shades of one color

• trichromatism - individual can see all three colors (normal)

The Brain’s Role in Vision

• feature detectors - specialized neurons in visual cortex that respond to specific aspects of a visual scene (edges, angles, movement, faces)

• parallel processing - brain processes different aspects of a visual scene simultaneously (color, depth, movement, etc.)

Damage to Occipital Lobe

• prosopagnosia (face blindness) - lose ability to recognize faces

  • damage to occipital and temporal lobe

  • can describe facial features, but cannot identify

• blindsight - appear to be blind in part of visual field, as they cannot consciously see or respond to visual stimuli in an area

  • damage to primary visual cortex in occipital lobe

  • can still respond to certain visual stimuli without conscious awareness (navigate around obstacles or identify location of light source)

Theories of Color Vision

• trichromatic theory (helmholtz) - retina has three types of cones sensitive to red, green, and blue light; these cones work together to produce our perception of all colors

• color deficiency - genetic condition where one or more types of cones are missing or impaired, causing difficulty distinguishing certain colors

• opponent-process theory (hering) - we have three pairs of opponent color receptors (red-green, blue-yellow, black-white); when one color in a pair is stimulated, the other is inhibited

  • explains afterimages

• color constancy - ability to perceive object’s color as relatively constant even under varying lighting conditions

Auditory Sensory System

Sound Properties

• wavelength

  • distance between two identical parts of a wave

• frequency (pitch)

  • number of waves that pass in given point per second

  • determined by wavelength of sound wave

  • measured in hertz (Hz)

  • long wavelength → low frequency (low-pitched sound)

  • short wavelength → high frequency (high-pitches sound)

• amplitude (loudness)

  • strength of sound wave

  • determined by amplitude (height) of sound wave

  • measured in decibels (dB)

  • high amplitude → loud sound

  • low amplitude → soft sound

The Ear: Structure and Function

• outer ear

  • pinna - visible part of ear, funnels sound waves into ear canal

  • ear canal - carries sound waves to eardrum

• middle ear

  • eardrum (tympanic membrane) - vibrates in response to sound waves

  • ossicles (hammer, anvil, stirrup) - tiny bones that amplify vibration and transmit them to inner ear

• inner ear

  • cochlea - snail-shaped, fluid-filled tube containing hair cells that convert vibrations into neural signals

    • hair cells - sensory receptor cells responsible for detecting sound vibrations and converting them into electrical signals for brain

    • basilar membrane - thin, vibrating tissue that supports hair cells

  • semicircular canals - not involved in hearing; responsible for balance and equilibrium

  • auditory nerve - carries neural signals from cochlea to brain

Theories of Hearing

• frequency theory - rate of nerve impulses traveling up auditory nerve matches the frequency of the sound, allowing us to perceive pitch

  • explains why we hear low-pitch sounds

  • 100HZ would cause auditory nerve to fire 100 times per second

• volley theory - groups of neurons work together to fire in a staggered manner, allowing them to collectively match frequency of higher-pitched sounds

  addresses limitations of frequency theory

• place theory - different pitches (frequencies) activate specific areas on cochlea

  • explains why we hear high-pitch sounds

• sound localization - we determine location of a sound based on slight timing and intensity differences between our two ears

Hearing Loss

• noise-induced hearing loss - damage to hair cells due to loud noises, often affecting high-frequency sounds first

• conduction deafness - hearing loss due to damage to middle ear (eardrum, ossicles), often treatable with hearing aids or surgery

  • prevents sound from traveling efficiently from outer ear to middle ear and inner ear

• sensorineural deafness (nerve deafness) - damage to hair cells or auditory nerve, usually permanent

  • decline in clarity of loudness and range of sounds

• cochlear implants - electronic devices that bypass damaged hair cells and directly stimulate auditory nerve, providing sense of sound

Touch & Pain Sensory System

• four basic sensations - pressure, warmth, cold, pain

• pain - vital warning sign something is wrong

  • congenital insensitivity to pain - rare condition where individuals cannot feel pain

• thermoreceptors - sensory receptors located in the skin and respond to temperature changes

  • When we encounter a hot stimuli, warm receptors are activated by an increase in temperature. These receptors send signals to the brain indicating warmth. When we encounter a cold stimuli, cold receptors in the skin are activated. However, when we encounter extreme heat, our warm and cold receptors become active. When both are simultaneously activated, the brain interprets this mixed signal as a sensation of hot.

Factors Influencing Pain Perception

• biological - activity in spinal cord, genetics (endorphin production), brain interpretation

• social-cultural - presence of others, empathy, cultural expectations

• psychological - attention to pain, past experiences, expectations of relief

Key Concepts & Theories

• gate control theory - pain signals can be blocked (“gated”) in spinal cord by competing signals from other senses or by brain signals

• phantom limb pain - sensation of pain in limb that has been amputated

  • likely caused by “cross-wiring” in brain’s somatosensory cortex where areas responsible for missing limb are taken over by nearby areas

Chemical Sensory System

Smelling (Olfaction)

• process - odor molecules enter nasal cavity, bind to olfactory receptors, and send signals to olfactory bulb in brain

  • unique, bc sense of smell is the only sense that does not pass through thalamus (relay station)

• olfactory bulb - located near limbic system (emotion) and hippocampus (memory), explaining why smells can trigger strong emotions and memories

• sensory interaction - taste and smell work together to create flavor

• pheromones - chemical signals released by individual that affect behavior or physiology of others

Tasting (Gustation)

• taste buds (papillae) - tiny bumps on tongue that contain taste receptors

  • When we eat, food molecules dissolve in saliva and then bind to receptor cells, which triggers a chemical reaction that causes taste receptor cells to release neurotransmitters. Neurotransmitters stimulate sensory neurons, which transmit electrical signals to brain. The signals go to the thalamus which are sent to various parts of the brain such as limbic system and gustatory cortex.

• six basic tastes

  • sweet (sugars and energy)

  • salty (amount of sodium in food)

  • sour (acidic substances and can tell us that food may have spoiled)

  • bitter (potentially toxic substances)

  • umami (savory - protein)

  • oleogustus (fats)

• chemical sense - taste receptors detect chemicals in food

• supertasters - individuals have a higher than average number of taste receptors

  • more intense taste

• medium tasters - individuals with average number of taste receptors, who have a more balanced sensitivity to different tastes

• non-tasters - individuals have fewer taste receptors, making them less sensitive to certain tastes

• taste and smell interact closely to create full sensation of flavor

  • taste buds detect basic taste

  • olfactory receptors identify aromas released from food

  • these inputs are processed by brain to produce different flavors that we experience

    • ex) skittles experiment

Body Position and Movement

• kinesthesis - sense of body position and movement of individual parts

  • allows you to know where your limbs are in space and how they are moving

• vestibular sense - sense of balance and head position, located in inner ear

  • When you move your head, fluid inside semicircular canals moves, causing hair cells in canals to bend, ultimately allowing you to maintain balance.

2.1 Perception

• perception - how we organize, interpret, and make sense of these sensory signals through our five senses

  • sensation ≠ perception!!!

    • sensation = detecting a stimulus

    • perception = interpreting a stimulus

How We Process Sensory Information

• bottom-up processing - building perception from smallest sensory details and working up to a complete picture

  • ex) seeing individual dots and recognizing them as a picture

• top-down processing - using our existing knowledge, expectations, and context to interpret sensory information

  • ex) reading misspelled word but still understanding

Making Sense of Sensations

• visual capture - tendency for vision to dominate other senses

  • ex) movie sound seems to come from screen, not speakers

• gestalt psychology - the whole is greater than the sum of its parts; we organize sensory information into meaningful patterns and wholes

  • figure-ground - organizing the visual field into objects that stand out (figure) from their surroundings (ground)

  • proximity - we group nearby figures together

  • similarity - we group figures that are similar to each other

    • anomaly - when an object is different from the others, it becomes the focal point and stands out

  • continuity - we perceive smooth, continuous patterns rather than discontinuous ones

  • connectedness - we see uniform and linked objects as a single unit

  • closure - we fill in gaps to create complete, whole objects

  • symmetry - objects that are symmetrical to each other are perceived as one object

Depth Perception: Seeing in 3D

• depth perception - ability to judge distance and see objects in three dimensions, even though the images on our retinas are two-dimensional

• visual cliff experiment - showed that infants and young animals have innate depth perception

Types of Depth Cues

• monocular cues - cues that can be perceived with one eye alone

  • interposition (overlap) - closer objects block the view of objects farther away

  • shading and contour - helps us perceive the shape and form of an object

  • linear perspective - parallel lines appear to converge with distance

  • relative size - if two objects are similar in size, the one that appears smaller is perceived as father away

  • relative height - objects higher in the visual field are perceived as farther away

  • texture and gradient - objects with finer, less detailed texture are perceived as farther away

  • motion parallax - objects closer to you appear to move quickly while those that are farther away seem to move more slowly

• binocular cues - cues that require both eyes

  • convergence - eyes turn inward more to focus on closer objects

  • retinal disparity - brain compares slightly different images from each eye to calculate distance

    • the greater the disparity, the closer the object

Perception: Movement, Constancy, and Interpretation

• movement perception

  • apparent motion/movement - when we perceive motion even though nothing is actually moving

    • stroboscopic motion - illusion of movement created by a series of rapidly changing still images

      • ex) flip books or animated films

    • phi phenomenon - illusion of movement created by flashing lights in a sequence

      • ex) holiday lights

    • induced movement - when a stationary object appears to move because of the motion of surrounding objects

    • autokinetic effect - when a stationary point of light in a dark environment appears to move

• perceptual constancy - we perceive objects as stable and unchanging even as sensory input (light, angle, distance) changes

  • size constancy - we perceive an object’s size as constant even when its distance changes

    • illusions

      • muller-lyer illusion - two lines of same length appear different due to direction of arrows at their ends

      • ponzo illusion - two horizontal lines of same length appear different because of converging lines around them

      • ames room - a distorted room that makes people appear to shrink or grow as they move across it

  • color constancy - we perceive the color of an object to remain consistent, even if the lighting changes

  • shape constancy - tendency of brain to perceive an object’s shape as the same, even when it moves

  • lightness constancy - our ability to perceive the blackness, whiteness, and grayness of an object as consistent even under different lighting conditions, essentially this is the shading of an object

Perceptual Interpretation

• perceptual adaptation - ability to adjust to changed sensory input, such as inverted or distorted visual field

• perceptual sets - mental shortcut your brain uses to quickly interpret what you’re experiencing

• schemas - mental frameworks that organize our knowledge and influence how we interpret new information

• context effects - surrounding environment or situation can alter our perception of a stimulus

  • cultural context - culture can also shape how we perceive things

Factors Influencing Perception

• biological - sensory processing, innate visual abilities, critical periods for development

• psychological - attention, learned schemas, emotions, expectations

• socio-cultural - cultural norms and beliefs, physical contact

Human Factors and Perception

• human factors psychology - field that focuses on how people and machines interact

  • these psychologists use their understanding of perception and behavior to design user-friendly products and technology

• extrasensory perception (esp) - controversial claim that some people can perceive information without using the normal senses

  • telepathy - mind-to-mind communication

  • clairvoyance - perceiving remote events

  • precognition - predicting future events

  • psychokinesis - moving objects with the mind

• sensory deprivation - reducing sensory input to a minimum

  • can lead to altered states of consciousness and even hallucinations

• selective attention - ability to focus on specific sensory information while filtering out other stimuli

  • ex) listening to friend’s voice in a crowd

  • cocktail party effect - ability to focus on a single sound, like a conversation, while filtering out other distracting sounds

• inattentional blindness - when our attention is divided, we often experience inattentional blindness, which is the failure to notice stimuli in our visual field due to our attention being focused elsewhere

• change blindness - type of inattentional blindness where we fail to notice changes in environment