Sensation and Perception Flashcards
Sensation
The process of detecting external events by the sense organs
Transduction
Process in which physical or chemical stimulation is converted into a neural impulse that is relayed to the brain
Perception
Involves attending to, organizing, and interpreting stimuli that we sense
Absolute threshold
The minimum amount of energy or quantity of a stimulus required for it to be reliably detected at least 50% of the time it is presented
Difference Threshold
Smallest difference between two stimuli that a subject can detect
- “just noticeable difference” expressed as a Weber fraction
Weber’s Law
K = DL/S
K = Difference threshold/Standard
Signal Detection Theory
How we make decisions under conditions of uncertainty
- Thresholds can vary depending on the individual or context in which the decision is being made
Signal Detection Theory (Correct Responses)
- Hit: detecting the stimulus when it is present
- Correct Rejection: not detecting the stimulus when it is absent
Signal Detection Theory (Incorrect Responses)
- Miss: failing to detect the stimulus when it is present
- False Alarm: detecting the stimulus when it is absent
Subliminal Messaging
- Subliminal stimuli: presented to a person below their conscious threshold
- We detect subliminal stimuli without conscious awareness
- Activation in certain brain regions
- Effects are limited
- Will not make you do anything you would not normally do
Perceptual Organization
The process by which elements are organized to form perceptible objects
- Grouping and segregation
- Gestalt psychologists proposed several principles by which we achieve perceptual organization
Figure-ground principle
(Gestalt Principles of Perception)
Objects and figures in our environment tend to stand out against a background
Gestalt Principles
- Good Continuation
- Proximity
- Similarity
- Closure
Good Continuation
(Gestalt Principles)
Objects that are partially covered by other objects are seen as continuing behind those objects
Top-Down Processing
Occurs when prior knowledge and expectations guide what is perceived
Bottom-Up Processing
Is constructing a whole stimulus or concept from bits of raw sensory information
Selective Attention
Involves focusing on one particular event or task
Divided attention
Involves paying attention to several stimuli/tasks at once
- Self-proclaimed multi-taskers perform worse on cognitive tests
- Distracted driving
Inattentional blindness
A failure to notice clearly visible events or objects because attention is directed elsewhere
Amplitude
Height of the waves
Wavelength
Distance between waves
Sclera (Eye)
White outer layer of eye
Cornea (Eye)
Clear layer that covers the front of the eye
Pupil (Eye)
Regulates amount of light let into eye
Iris (Eye)
Round muscle that adjusts the size of the pupil
Lens (Eye)
Clear structure that focuses light onto back of eye
Myopia (Nearsightedness)
- Focus point falls short of the retina
- Lens and/or cornea bends light too much or eyeball too long
Hyperopia (Farsightedness)
- Ideal focus point falls beyond the retina
- Cornea/lens too rigid and fails to bend light enough or eyeball not long enough
Retina
- Cones concentrated on fovea to produce high-detail, colour vision at our point of visual focus
- Rods on outer regions of retina provide peripheral vision and are specialized for low light conditions
- Dark adaptation: the process by which rods and cones gain sensitivity to low light levels
Trichromatic theory
Colour vision is determined by three different cone types that are sensitive to short, medium, and long wavelength light
Trichromatic theory (PART 2)
The combined activity of all three cone types generates a unique signature associated with each perceived colour, even colours without a corresponding wavelength
Comparative Color Perception
Monochromatism vs Dichromatism vs trichromatism vs tetrachromatism
Opponent-Process Theory
We perceive colour in terms of opposite ends of the spectrum (red to green, yellow to blue, white to black)
- Ganglion cells provide three colour ‘channels’
- Certain colours are natural opposites
Opponent-Process Theory (PART 2)
- Opponent neurons found in the retina and lateral geniculate nucleus
- Allows for additional layer of organization and analysis
- Complementary with Trichromatic theory
Negative Afterimages
Opponent process theory supported by evidence from negative afterimages
Organization by opponent Neurons
- If vision was only based on thrichromatic theory, red-green colour deficient individuals should not see yellow
- Opponent cells respond to the ratio of certain cone responses to produce either an inhibitory or excitatory response
Why is Opponent Process Necessary?
- Additional analysis of the ratio of cone responses allows for more fine color perception - unlike the mantis shrimp
- Pattern of opponent neuron responses reveals the wavelength of light that produced it
Horizontal cells (Enhancing Contrast)
Inhibitory interneurons (GABA releasing) that connect between photoreceptors
Optic Chiasm (Beyond the Retina)
crossover point for optic nerve at midpoint of the brain
Lateral geniculate nucleus (Beyond the Retina)
Region within thalamus that directs visual information throughout the brain
- Receives 90% of visual signals from optic nerve
Feature Detection Cells
(Primary Visual Cortex)
Neurons that respond selectively based on specific aspects of a stimulus (e.g., angles and edges) as well as to specific regions of the visual field
Ventral (‘what’) Stream
(Visual Pathways)
Extends from visual cortex to temporal lobe
- Responsible for object and face recognition
- Fusiform face area
- Pareidolia and prosopagnosia
Perceptual Constancy
The ability to perceive objects as having constant shape, size, and colour despite changes in perspective
Size Constancy
Size constancy relies on other depth cues to make perceptual corrections to the retinal image
- Size constancy illusions rely on contextual depth cues to achieve deception
Lightness Constancy
Maintaining perception under uneven illumination
Dorsal (‘where/how’) Stream
(Visual Pathways)
Extends from visual cortex to the parietal lobe
- Guides interaction with objects
- Responsible for depth and motion perception
Binocular Depth Cues
Distance cues that are based on the differing perspectives of both eyes
Convergence
Occurs when the eye muscles contract so that both eyes focus on a single object
Retinal Disparity
The difference in perspective provided by each eye
- Stereopsis: sense of depth
Strabismus
Eyes do not align properly when looking at objects
- The case of ‘Stereo Sue’
Binocular Depth in Animals
- Frontal vs Lateral eyes
- Eye placement depends on evolutionary demands of a species
Monocular Depth Cues
These are depth cues that we can perceive with only one eye
Accommodation
(Monocular Depth Cues)
Curving of lens to focus on nearby objects
Motion Parallax
(Monocular Depth Cues)
Used when surroundings are in motion
Pitch
Perceptual experience of sound wave frequencies
Loudness
Perceptual experience of amplitude
Sound Detection (Outer Ear)
- Pinna collects sounds
- Auditory canal amplifies frequencies between 1000 and 5000 Hz
Sound Detection (Middle Ear)
Vibrations of tympanic membrane get amplified by ossicles to convert wave in air to wave in fluid of inner ear
Inner Ear (Place Theory)
- Region along basilar membrane that gets stimulated also corresponds with frequency
- Base of basilar membrane 3-4 x narrower than apex and therefore about 100x stiffer
- Tonotopic map
Inner Ear (Frequency Theory)
- hair cells fire synchronously with rising pressure phase of a sound stimulus
- Refractory period limits frequency that individual nerve fibers can signal
- Volley principle
- Summed activity of groups of cells can provide more accurate representation of frequency
Cochlear Nucleus (Auditory Pathway)
Crossover of auditory signals to contralateral hemisphere
Medial Geniculate Nucleus
(Auditory Pathway)
Structure within thalamus responsible for routing of auditory information
Primary Auditory Cortex
Organized similar to the cochlea (tonotopic map)
Sound Localization
Process of identifying where sounds come from
- Achieved by:
- Interaural time differences
- Sound shadow
Determining Elevation
Folds of the pinna affect the intensities of frequencies differently depending on their elevation
Multimodal Integration
- Combining sensations from different modalities into single integrated perception
- Dependent on spatial and temporal association
- McGurk effect
Mechanoreceptors (Somatosensory System)
Detect pressure and touch
Nociceptors (Somatosensory System)
Detect heat and pain
Hearing through Touch
- Elephant foot stomping and low-frequency rumbles can be tactilely detected through seismic waves in the ground
- Waves travel through toenails to the ear via bone conduction
- Use low frequencies to Coordinate movements with other distant herds
Acuity (Touch Sensitivity)
Ability to discern points of pressure
- Two-point threshold test
- Sensitivity corresponds with areas of greater neural representation in somatosensory cortex
Tactile Acuity
Blind Braille readers
Haptics (Perceiving Objects)
Exploratory sense of touch
- Active vs passive touch
- Tactile agnosia
Sensory Integration
- Visual information influences perception of touch
- Rubber hand illusion
Proprioception
Our sense of bodily position
Kinesthesis
Our sense of bodily motion
Proprioception and Kinesthesis
Both work in conjunction with haptics to garasp and interact with objects
Neural Prosthetics
Feeling through machines
Nociception (Feeling Pain)
Sense of pain signaled by specialized nociceptors
- Fast fibres: register sharp, immediate pain
- Slow fibres: register chronic dull pain
Traditional Theory (Model of Pain)
Nociceptors are stimulated and send signals to the brain
- Very straightforward and purely physiological
Model of Pain
- Failure to account for
- Pain can be enhanced or suppressed by a person’s current mental state
- Phantom limb pain
- Placebo effect
Gate Control Theory
Explains our experience of pain as an interaction between nerves that transmit pain messages and those that inhibit these messages
Top Down Influences on Pain
- Pain perception has a subjective component
- Emotion and expectations influence our experience
Empathy and Pain
Having empathy for another person can result in a shared experience
Taste (Gustatory System)
- Receptors for taste (taste buds) located on small bumps (papillae) that cover the tongue
- Receptors detect sweet, salty, bitter, sour, and umami
- Projections go to thalamus > gustatory cortex
Taste Sensitivity
- Supertaster
- Non-taster
- Supertasters have more taste buds, increasing their sensitivity to bitter substances
Tuck (cats)
Lacks sweet receptors
Alice (parrots)
300 - 400 taste buds for sweet, sour, bitter, and salty
Catfish
Hunt through taste with > 100,000 taste buds located all over their body
Smell
(Olfactory System)
- Olfactory Epithelium: thin layer of cells that are lined by sensory receptors called cilia
- Cilia transmit transduced signal to olfactory bulb via the olfactory tract
Chemotopic Organization
- Olfactory bulb organized in clusters according to chemical type and structure
- Ability to understand smells depends on being able to retrieve reference points from memory
Macrosomatic (Olfactory System)
Strong sense of smell that is necessary for survival (Animals)
- Tuck: 45-80 million
Microsomatic (Olfactory System)
Weaker sense of smell that is not as crucial to survival (Humans)
- Dawson: 5 million
Olfactory System
Individual smell receptors equally sensitive, but differ in number across species
Top-Down Influences on Flavour Perception
Enjoyment and brain activity can be influenced by expectations of quality
