Unit 5: Sensation & Perception (Chapter 4) Flashcards
Colour
A psychological constructon of the brain. Not a property of an object.
Ex: Lemons “are” yellow.
Ex 2: Blue and black / white and gold dress.
Colour constancy
The brain’s ability to recognize colour of an object as being the same even under different lighting conditions. It adjusts its perception of color to hold it constant, accounting for changes in lighting conditions & other contextual factors (e.g., shadows)
Ex: Potted plant and tiles shadow illusion.
Sensation
Raw data; process by which sensory organs detect environmental stimuli & convert them (though transduction) into electrical signals for the nervous system.
Stimulus
Something that elicits a reaction from our sensory systems.
Ex:
- Light (vision)
- Sound waves (hearing)
- Mechanical pressure, vibration, temperature, pain (touch)
- Chemicals in food or drink (taste)
- Airborne chemicals (smell)
Transduction
Transformation of sensory stimulus energy into neural impulses. “Common language” used by all sensory systems (i.e. no category for just the eyes, or just the mouth, etc.).
Ex: Light entering your eyes is converted into neural impulses by specialized cells.
Perception
Creating a coherent narrative using data; brain’s interpretation of these electrical signals to create an internal representation of the world. Relies on both raw sensory data (bottom-up processing) and prior experience, knowledge, and expectations (top-down processing).
Ex: Brain processes incoming neural signals, allowing you to recognize the expression on your friend’s face
Psychophysics
Study of the relationship between the physical qualities of environmental stimuli (physics) and our mental experience of them (psyche).
Earliest of said studies tried to establish the limits of awareness.
Absolute threshold
Minimum amount of stimulus that can be detected at least 50% of the time (NOT THE LOWEST). Inversly related to sensitivity (lower absolute threshold = higher sensitivity, vice-versa).
Thresholds are not static! Sensory systems respond more to changes than steady states.
Signal detection theory
An approach to measuring thresholds that takes into account both the intensity of the stimulus and psychological biases for a more accurate assessment. Takes place under conditions of uncertainty.
Ex: When different radiologists check for tumours, one might detect more than the other.
Signal detection theory terms (in relation to radiologist example)
Tumor present: Responds yes (Hit); got it right
Tumor present: Responds no (Miss); didn’t see it
No tumour: Responds yes (Flase Alarm); incorrect diagnosis
No tumour: Responds no (Correct Rejection); confirmed there was none
Liberal bias
Low threshold for detecting signal (i.e. higher rate of hits, but also higher rate of false alarms).
Signal detection depends both on strength of signal and individual bias. To properly calculate sensitivity, one must include both signal present and absent trials, so compare hits to false alarms.
Conservative bias
High threshold for detecting a signal (i.e. lower rate of false alarms, but also lower rate of hits).
Signal detection depends both on strength of signal and individual bias. To properly calculate sensitivity, one must include both signal present and absent trials, so compare hits to false alarms.
Alive or not? study
A person’s answer will likely depend on how socially connected or lonely they feel. Lonelier people will require fewer human characteristics to detect an animate object due to social cravings (liberal bias). Takeaway: Unmet belongingness needs can shape social perception.
Just-noticeable difference/difference threshold
Smallest difference between two stimuli that can be detected at least 50% of the time (i.e. reliably). Will depend on the size of the stimuli being compared.
Weber’s law / Weber’s fraction
As stimuli get larger, differences must also become larger in order to be detectable (i.e. the likelyhood of percieving a stimulus change is proportional to the magnitude of the stimuli). Weber’s fraction = ΔI/I, where Δ = minimum change, I = magnitude of stimulus
Ex: Drinking a glass of clean water with sugar added into it vs pop with sugar added into it.
Weber’s Law Practice Problem:
While you are on vacation with your brother, he tells you about a psychological study he recently participated in. When he was holding a 50-gram weight, he couldn’t tell that extra weight had been added until the added weight was more than 5 grams. According to Weber’s Law, how much of your stuff can you add to his 25-kg suitcase without his noticing?
Weber’s fraction = ΔI/I, where Δ = minimum change, I = magnitude of stimulus.
Weber’s fraction = 5/50 = .1
25,000 g x .1 = 2,500 g = 2.5 kg
Adaptation
Stop noticing a stimulus that remains constant over time. This is useful, since it allow us to focus on changes in our environment.
- Sensory adaption occurs at the level of the sensory receptors
- Perceptual adaptation occurs in the perceptual centers of the brain.
We don’t stop seeinf things due to the tiny involuntary movements our eyes constantly make (microsaccades).
Vision
Processing of light reflected from objects.
Visible light
Type of electromagnetic radiation emitted by sun, artificial light sources, etc. that can be detected by the eye. Made of of particles that move in waves (photons).
Wavelength (Vision)
Distance betweem successive peaks. Decoded as colour. Inversly related to frequency.
Frequency (Vision)
Number of cycles per second. Inversly related to wavelength.
Amplitude (Vision)
Height of the wave. Decoded as brightness.
Cornea
Transparent tissue covering front of eye, focuses light.
Fun fact: 50% of the cerebral cortex is devoted to vision. 11% is devoted to touch, etc.
Iris
Opaque, colourful muscle encircling the pupil. Can increase or decrease size of pupil, determining how much light enters (by contracting, expanding).
Pupil
Hole in the iris where light enters the eye.
Lens
Membrane at front of the eye that focuses incoming light on the retina. The image on the retina is upside down, but our brains can interpret this.
Remeber as a camera lens that focuses in on something, able to adjust brightness on iPhone.
Accomodation
Adjustments of the lens’s thickness by specialized muscles in order to change the degree to which it bends light. Lens becomes elastic with age, less accommodation.
Retina
Surface in the back of the eye containing receptor cells specialized for transducing light (photoreceptors).
Rod
Photoreceptor cell that primarily supports nighttime vision.
Remember as “fishing in the dark”.
Cone
Photoreceptor cell that is responsible for high-resolution color vision.
Remember as COne, COlour.
Visual transduction
When light reaches the photoreceptors, light- sensitive molecules (photopigments) undergo chemical reactions generate electrical signals. Said signals are transmitted along the optic nerve.
Blind spot
Area in the middle of the visual field where there are no photoreceptors and no information can be received. Brain fills in blindspot.
Differences between rods and cones
1) Rods all have the same type of photopigment, but cones contain one of three varieties of photopigments. The mulltiple photopigments of the cones allows us to see colour.
2) Rods contain an extremely light-sensitive pigment called rhodopsin—allows us to see in the dark.
3) Differ in their quantity and distribution across the retina:
- Ratio of rods to cones is 20:1
- Cones concentrated in fovea (small pit in centre of retina). NO RODS IN FOVEA.
- Most rods are in central periphery (why peripheral vision is better in dim light/darkness).
4) Cones have more direct connections to neural cells; rods converge more.
5) Cones receive more cortical representation (allows more detail to go to the brain).
6) Cones have higher acuity (sharpness and specificity), whereas rods have higher sensitivity (ability to simply detect stimuli, ex: a flame, from far away!).
Rhodopsin
The rod photochemical that breaks down and becomes inactive when exposed to bright light (so as not to overstimulate us) and regenerates in the dark (takes about 25 mins, evolutionary perspective of sunset to darkness).
Ex: Turning a light on and off, and your eyes get used to the darkness/the light.
Colour vision
Objects differ in their capacity for absorbing or reflecting light, and thereby reflect different wavelengths to our eyes. Each cone has 1 of 3 distinct varieties of photopigment, which are sensitive to short (blue), medium (green) or long (red) wavelengths. At night, rods are most sensitive to blue-green wavelengths.
Trichromatic theory
The three types of cone cells work together to produce perception of colour.
Colour blindness
Some people only have two, not three, types of cone photochemicals (dichromocy) - most typically red or green. Linked to y-chromosome.
If you miss 2 of the 3 types of cone photochemicals, you can’t see any colour.
Optic nerve
A bundle of axons that converge from the retina and transmit action potentials to the brain.
Opponent-process theory
Our perceptual systems treat the visible spectrum as a circle, where the two ends meet (i.e. purple is an illusion). Plus, the informaton from the cones is seperated into 3 sets of opposing or oppenent channels in the ganglion layer. Thus, you cannot see “reddish-green” or “yellowish-blue” since they will cancel each other out. Afterimages occur when cones “tire out” (adapt) from looking at a certain colour, which decreases the cones ability to inhibit opposing colours in the ganglion cell (which is why you see the opposite colour when looking away).
Ex: Stare at green and black Canada flag.
Ganglion cells
Located in the retina. Receive input from cones (via bipolar cells). Organized in pairs that respond to opposing colours: red-green, blue-yellow, white-black.
Ex: Some ganglion cells are excited by red, inhibited green (R+/G-), and vice versa. Thus, when seeing an apple: R+/G- cells excited, R-/G+ inhibited, which tells the brain “there’s more red here than green”
Object identification (hierarchical due to increasing complexity)
1) Visual information travels along optic nerve to optic chiasm, where axons from each side of the retinas are diverted to corresponding side of the brain.
2) Thalamus (relay station) passes information on to primary visual cortex.
3) Image (from retina) reconstructed in primary visual cortex (also organized as a map) thanks to feature detectors.
4) Visual association cortex combines incoming sensory inputs with prior knowledge & expectations.
5) Additional processing in temporal lobe allows you to recognize specific objects, like faces.
Feature detectors
Specialized neurons that respond to specific attributes of visual stimulus (ex: edges, angles, orientation).
Prosopagnosia
Inability to recognise faces. Those who suffer from this may only recognize incoherent shapes. Result of damage to the visual association cortex.
Ex: “The Man Who Mistook His Wife for a Hat”.
Ventral stream
Processes “what” information (from occipital to temporal lobe).
- Responsible for recognizing objects and faces.
- Damage here leads to visual agnosias where subject is not able to recognize object.
Dissociable from the “where” pathway.
Dorsal stream
Processes “where” information.
- Responsible for determining location and the perception of movement.
- Damage here may result in seeing movement as series of statistic “snapshots”.
- Stop-motion movies use apparent motion, aka the phi phenomenon (illusion where snapshot images appear to be fluid) to create stop-motion movies.
Dissociable from the “what” pathway.
Gestalt psychology
perspective that we perceive whole, organized patterns & objects through an unconcious mental process.
- Gestalt = German for “organized shape” or “whole form”.
- “The whole is different from the sum of its parts”. Ex: Illusiory contours (triangle image).
Gestalt principles
1) Proximity: We percieve features as grouped when they are close together.
2) Similarity: We group together things that look alike.
3) Closure: We fill in gaps to create continuous edges, allowing us to percieve an object as a whole.
4) Good continuation/Continuity: We tend to look for smooth, contininuous patterns in objects.
5) Synchrony: We group itemps together that move at the same time.
6) Connectedness: We group tegether objects that are connected.
Figure
Object of main focus.
Often not arbitrary, but guided by certain principles. Ex: Reversible figures (rabbit/duck, old lady/young woman).
Ground
Background.
Often not arbitrary, but guided by certain principles. Ex: Reversible ground figures (vase/2 faces).
Bottom-up processing
Raw and sensory data; body to brain.
Top-down processing
Prior knowledge, experience, and expectations; brain to body. A perceptual set, related to top down processing, is a predisposition that influences what we percieve based on recent experience or context.
Depth perception
Image projected on retina is 2-D. Brain uses various cues to translate this 2-D image into 3-D perception of real-world object. Uses both binocular and monocular cues.
Binocular cues
Depth information gathered from the separation between an individual’s two eyes; compares both views to construct 3-D views.
Binocular disparity
Cue for depth perception stemming from the slightly different (disparate) views that two eyes have of an object or scene (i.e. the magnitude of difference between the images projected on an individual’s two eyes).
- More disparate views for objects close by, more similar as object moves further away.
- This is used by the brain to gauge depth.
Ex: Staring at finger close to your face v.s. far away.
Monocular cues
Depth information that can be gathered using just one eye.
Motion parallax
Example of monocular cue
When you move your head, objects closer to you appear to move faster than objects farther away.
Ex: Closer objects whipping by and going in opposite directions.
Monocular cue examples (pt.2)
- Linear perspective: Parallel lines appear to converge in distance.
- Interposition: Nearby objects occlude more distant ones.
- Relative height: Objects further away appear closer to the horizon.
- Relative size: Objects further away appear smaller than nearby objects.
Size constancy
Objects further away project a smaller image on the retina (we can still see the object as a certain size, though). The brain accounts for variation in retinal images in terms of distance, and interprets it as a cue for depth. Can leverage knowledge of various depth cues to create optical illusions (ex: monster chaasing the other, moon seems bigger).
Sound
Waves of vibration in the form of mini collisions between adjacent molecules in a medium like air or liquids.
Amplitude (Sound)
Height of the wave, measured in decibels (dB). Determines percieved volume of the sound. Higher amplitude = louder, low amplitude = softer.
Frequency (Sound)
Number of cycles that occur per second, measured in Hertz (Hz). Inversly related to wavelength. Determines pitch (highness or lowness of the sound).
The human auditory stimulus
- On average, can hear range of frequencies from 20 to 20,000 Hz.
- Some individual variation & changes with age.
- Best attuned to frequencies corresponding to human
voice. - Other animals can hear sounds at infrasonic (e.g., elephants) and ultrasonic (e.g., bats) ranges of spectrum.
- Humans cannot hear infrasounds, but some evidence that infrasound increase physiological arousal (activation of the sympathetic nervous system) & symptoms like nausea and sleep disturbances.
Human ear
Divided into outer, middle and inner ear. Its components work together to amplify, colect an transducer vibrations into neural signals.
Pinna
Captures & funnels soundwaves through auditory canal towards the middle ear.
Middle ear
Contains the eardrum and the ossciles (the hammer, the anvil, and the stirrup).
Ossciles
Tiny bones located between two membranes (tympanic membrane / eardrum & oval window). Made up of the hammer, the anvil, and the stirrup.
– Amplify vibrations of incoming soundwaves.
– Help protect the inner ear from very loud noises.
Inner ear
Contains the vestibular system and the cochlea.
Cochlea
A spiral structure in the inner ear where the basilar membrane, containing auditory sensory neurons, is located.
Basilar membrane of the cochlea
Contains specialized receptor cells for transducing vibrations transmitted into the inner ear into neural signals.
- Occurs when hairlike structures named auditory cilia bend in response to vibration.
- Resulting signal is carried along the auditory nerve to the brain.
Place theory
Theory of pitch perception proposing that different sound frequencies are processed at different parts of the basilar membrane. The further into the basilar membrane (into the “swirl”), the lower the frequency.
- Accounts for selective hearing loss: cilia loss can occur at specific locations along basilar membrane.
- Best explains perception of higher pitched sounds, but doesn’t explain perception of lower pitch sounds (which have longer wavelengths, and thus lower frequencies).
Frequency theory
Theory of pitch perception proposing that frequency of auditory neuron firing matches frequency of sound wave.
- For higher frequencies, groups of neurons alternate firing to match the frequency.
- Best explains perception of low-pitched sounds (celia can fire up to 1000 per second, but we can perceive up to 6000 Hz), does not account for difference in pitch and loudness perception.
Pitch perception
Combination of frequency of neural firing (frequency theory) and location of stimulation on basilar membrane (place theory).
Primary auditory cortex
Located in temporal lobe. Contains place-frequency maps. Frequencies represented tonotopically (similar frequencies represented next to each other). Plasticity may occur if an organism is trained to percieve a particular frequency as a cue, thus increasing the cortical neurons that respond to said frequency.
Sound localization
Brain compares information coming from each ear, along with visual cues, to determine relative timing & intensity. Makes it difficult to locate sound if it’s coming from above (like at the movies).
E.g., if sound is coming from left side:
- Relative timing: sound will enter left ear slightly before right ear.
- Intensity: Head creates “sound shadow”, reducing intensity of sound in right ear.
Tactile sense
Perception of touch.
Mechanoreceptors
Sensory receptors that respond to mechanical stimulation (pressure, touch, vibration, stretch). Different types that respond to different types of stimulation.
- Myelinated receptors that allow fine-grained discrimination (movement, texture, localization).
- Unmyelinated receptors that respond to low-pressure, low velocity tacticle stimulation. Such stimulation found in intimate, affiliative interactions.
Receptors in the skin
Allow us to detect temperature and different types of noxious stimulation that causes pain. Skin sensations are often result of activation of multiple receptor types. Ex: Cold + pressure = wetness. As with other senses, respond most strongly to changes in stimulation. Ex: Running cold hands under lukewarm water will produce sensation of heat
Somatosensory homunculus
Visual representation of how areas of the body are represented based on their sensitivity rather their size. Most “important” areas of the body get the most real estate.
Primary somatosensory cortex
The region of the brain where the processing of touch sensations occurs.
Association areas (secondary somatosensory cortex)
Enable recognition of objects & more complex sensations (e.g., sensation of motion on the skin). Damage to these areas can result in tactile agnosia = inability to recognize object by touch.
Interoception
Ability to perceive signals originating within the body (Ex: breathing, hunger, thirst). Crucial for being able to maintain steady internal state.
Insula
Plays key role in processing these signals, imbues them with emotional & motivational significance.
- Ex: May interpret signals of sympathetic nervous system activation as anxiety (misreading = generalized anxiety).
- The ”social touch” receptors project directly here; may explain why social touch is experienced as soothing. Ex: Baboons grooming one another, “everything is ok” touch.
- Also thought to play a role in the experience of the “self” (distinguish yourself from others).
Proprioception
Sensory experience of the body’s position in space. Relies on specialized receptors (proprioceptors) in muscles, tendons, & joints, which detect changes in muscle length, tension, & joint position through mechanical deformation.
Vestibular system
System in the inner ear that helps maintain balance by detecting head movements and motion.
- Detects position of head relative to ground, linear acceleration, rotational movements of the head
- Movement of fluid in semicircular canals of the inner ear triggers cilia cells. Information travels along auditory nerve to medulla & cerebellum, and, eventually, (via the thalamus) to somatosensory cortex and primary motor cortex.
Vestibular working with the visual system
Work together to maintain balance. Harder to maintain balance withour input from visual system (ex: spotting while turning).
Kinesthesis
The senses responsible for monitoring the position and the movement of the body, including proprioception and the vestibular system.
Vestibular-ocular reflex
Reflex that helps stabilize your gaze during head movements. Wihtout it, you would have “blurry” vision all the time.
- Signal travels from semicircular canals to the brainstem, which then coordinates eye muscles to move eyes in opposite direction of head movement.
- Mismatch between senses can lead to motion sickness. Theory = brain detects this as poison + triggers response.
Ex: Have your friend spin with their eyes closed, and open their eyes. See if they move in the direction opposite the way they were spinning.
Olfaction
Sense of smell. Important functions:
- Detection of hazards (e.g., smoke, spoiled food).
- Enhances taste.
- Important for emotional & social experiences.
- Loss of smell and depression correlated (although causality not clear).
Epithelium
Mucous membrane in the nasal cavity that contains olfactory receptor neurons with their own cilia (olfactory cilia).
- Chemical odor molecules bind to cilia like in a lock-and-key system, which triggers action potentials through the bundle of receptor neuron axons which comprise the olfactory nerve.
Olfactory bulb
Structure just above the nasal cavity that receives input from olfactory sensory neurons. Involved in basic processing: i.e. can distinguish good and bad smells.
Glomeruli
Sperical clusters of neurons located in the olfactory bulb. Different parrerns of activation across glomeruli encode different odors.
Higher level olfactory processing (transduction pt.2)
- Information from olfactory bulb is sent directly to parts of the limbic system (amygdala and hippocampus), which accounts for strong odour-memory connections and the emotional motivational force of odours.
- Additional links to primary olfactory cortex in the temporal lobe and olfaction association cortex located in underside of frontal lobes. Allows us to identify and discriminate odours, integrate contextual information.
Smell as a component of flavour
An opening (nasal pharynx) connects back of mouth cavity with nasal cavity. Allows us to smell substances that have entered the mouth. Thus, food flavour consists of both the stimulation of the taste receptors in the mouth and smell receptors in the nose. Both inputs converge in orbitofrontal cortex (part of the olfaction association cortex).
Olfactory sensitivity differences
- Individual differences: genetic component, but also influenced by experience.
- Deterioration of smell sensitivity with age; may contribute to decrease in ability to taste food, as well as depressive symptoms.
- Women generally more sensitive to odours (evident during reproductive years, more pronounced during pregnancy). Important for mate selection, avoiding to poison the fetus.
Genetic component to interpersonal “chemistry”
Major Histocompatibility Complex (MHC) genes play significant role in immune system; help recognize and respond to pathogens. Selection of MHC-dissimilar mates may confer benefits for offspring (genetic variation).
Ex: Study asked women to rate odours of t-shirts previously worn by
group of men. Odours of men with dissimilar MHC antigens more attractive. Replications not consistent though.
Gustation
Sense of taste. Chemical molecules in food stimulate taste receptors contained inside taste buds on the tongue
- Receptors correspond to 1 of 5 taste molecules (sweet, salty, sour, bitter, savoury/umami).
- NOT organized into different regions on the tongue.
Primary gustatory cortex
Located in the insula. Sends connections to various cortical areas, including orbitofrontal cortex, where neural signals for taste and smell are combined (transduction).
- Damage in this area results in loss of conscious experience of taste.
- Artificial stimulation produces experiences of taste.
Importance of taste
Thought to have evolutionary functions:
- Promote increased nutrition.
- Prevent intake of poison or disease-causing substances.
However, human may learn to enjoy bitter foods that are safe for consumption.
Ex: Women have more sensitivity to bitter tastes, heightened sensitivity during pregnancy (avoid poisonning fetus).
Ex. 2: Heightened bitterness sensitivity in children (learn what to eat and not to eat).
Sensory interactions / integration
Various sensory systems are integrated to create a unified perceptual experience.
Ex:
- Visual signals and vestibular signals are integrated to inform balance.
- Olfactory signals interact with gustatory signals to perceive flavor.
- Visual signals inform auditory signals and affect what we perceive as speech sounds.
Visual dominance
When sight and sound are in conflict, sight usually wins.
- Ventroliquist effect = Sound localization is driven by visual stimulus.
- McGurk effect = Visual stimulus changes perception of sound (Ex: ba vs fa).
Ex: Rubber hand illusion = stroking fake hand while stroking real hand, brain “adopts” fake hand.
Additional examples of top-down processing:
- Hedonic quality of touch is moderated by contextual variables: Touch is more pleasant when paired with smiling (vs. frowning) face.
- Pleasantness of touch decreased when paired with disgusting odour.
- Taste is influenced by contextual variables:
The kinds of foods we grow up eating can shape likes and dislikes.
Wine tastes better if we think it’s more expensive.
Something palatable might taste aversive if we were expecting a different flavour.
Takeaway of perception
Our perceptions are not a direct read out of objective properties of objects out there in the world, but are brain’s construction of “what makes sense”.
- Not aware that this is happening—our perceptions feel ”real”.
- Highly adaptive, but can sometimes lead to illusions or misperceptions.
Visual association cortex
Combines incoming sensory inputs with prior knowledge & expectations. Damage = Inability to recognise faces. Those who suffer from this may only recognize incoherent shapes.
Reversible figures
Demonstrate how our overall perception of an object may differ from the elements from which its perception is derived.
Illusory contours
One example of how the whole can affect perception of parts. Visual stimuli with illusory contours activate edge-detector neurons in the primary visual cortex. Due to the fact that higher areas that receive input from primary visual area also feed back into these primary areas & affect neural activation there.
