Perception Flashcards
Perception
Process of how your brain makes sense of the world. Uses information from all senses to do this.
Sensory Phenomena
Our senses are central to communication, threat detection, object/person recognition, navigation. Experiences or sensations that come from how the brain processes input from senses.
Sensory Perception
Process of receiving and interpreting information from the world through our senses. Involves sensation which feeds our perception.
Perceptual Phenomena
Interesting or unusual experiences that happen because of the way our brain interprets sensory information.
Top Down Perception
Begins with prior knowledge or expectations/experiences used to interpret sensory information. Uses predictions.
Bottom Up Perception
Starts with raw data rom senses and works up to an understanding. Builds meaning from scratch and does not take expectations or experiences into account. No influences.
Psychophysics
Way to measure perception. Relate a precisely defined physical stimulus with a precisely measured behavioural response.
Absolute Threshold
Smallest amount of stimulus energy necessary for an observer to detect a stimulus.
Method of Limits
Method of measuring thresholds. Zoom in on threshold level. Stimulus is increased and decreased step by step until it is sensed. Done multiple times.
Method of Adjustment
Twiddle a dial. Allows the person being tested to control the stimulus themselves. Repeated multiple times.
Staircase Methods
Increase or decrease stimlus based on a person’s response. If person detects the stimulus, it is made weaker (go down a stair). If person does not detect stimulus, it is made stronger (goes up a stair).
Method of Constant Stimuli
Presenting a random mic of stimulus intensities to see how often each one is noticed. Slow, but accurate.
Psychometric Function
A graph or curve that shows the relationship between the intensity of a stimulus and a person’s ability to detect or respond to the stimulus. Used in psychophysics to measure how sensitivity or perception changes with varying stimulus strength.
Difference Threshold- Just Noticeable Difference
The smallest difference between 2 stimuli that a person can detect.
Weber’s Law
How much a stimulus has to change before we notice a difference. The bigger the original stimulus, the bigger the change must be for us to notice it.
Weber’s Fraction
E.g. You can detect 2g weight difference when holding a 100g object. 2/100 = 0.02. This means that you need at least 2% weight change to notice a difference.
Magnitude Estimation
Method used to measure how strong a person thinks a stimulus is, like how bright or painful something is. Participants assign numbers to a stimulus which are proportional to its subjective magnitude. Standard stimulus is given a value, then other stimulus are shows. The person rates each one based on how strong it feels compared to the standard.
Fundamental Criteria (Popper, 1960)
Falsifiability theory/Criterion of Demarcation.
Scientific Theory must be falsifiable. If a theory cannot be tested or disproven, it is not scientific. Explanatory, falsifiable and parsimonious.
Levels of Explanation
Anatomical and physiological
Psychological and behavioural
Theoretical and philosophical
Perceptual Theory- Physiological Approach (indirect)
Barlow (1921-2020)
How biological structures allow us to sense and interpret the world. Originally single-unit electrophysiology coupled with psychophysics. More recently neuroimaging.
Ecological Approach (direct)
Gibson (1904-1979) How we perceive the environment based on direct interaction. Involves actively engaging with and responding to the environment. Naturalistic observations. Analysis of optic array. Extensive use of virtual environment.
Computational Approach
Marr (1945-1980)
Brain is like a computer.
Phenomenological Approach
Focuses on how things appear to us through our experiences, without trying to explain them based on underlying mechanisms or theories. About describing the world as it is experienced by the individual.
Perception for Action (Milner/Goodall)
Brain has 2 pathways for processing visual information. One for identifying objects (ventral stream) and one for guiding action (dorsal stream).
Bayesian Approaches (Mamassian/Ernst)
Brain combines old knowledge and new sensory input to make informed decisions about the environment. Process of probalistic reasoning.
Predictive Coding (Ernst/Muckli)
Brain is constantly making predictions about sensory input and adjusting those predictions based on new information.
Active Vision (Findlay/Gilchrist)
Eye movements are essential as they help us actively explore and gather information from the environment.
Optic Array
A Gibsonian Concept
Refers to all the structured light that reaches the eye from the environment. Light that reflects off surfaces, textures, objects, and carries information about the world.
No thinking or mental processing involved.
Gibson believed perception is direct.
We do not need to interpret or infer meaning from raw data.
Optic Array contains affordances- clues about the world and how to interact with different environments.
Visual Encoding
Converting visual information into a form that the brain can store and later retrieve.
Principle of Least Commitment
Encoding Principle- Marr and Barlow.
Keeping options open, being flexible. Do not throw any information away that you might need later on.
Principle of Least Redundancy
Encode information as efficiently as possible.
Principle of Graceful Degradation
If system breaks, it should still be usable/function at a reduced level.
Retina
Thin layer of tissue at the back of the eye, acts like a camera sensor.
Detects light and converts it into neural signals.
Receptive field
The region of the retina that when stimulated, influences the firing rate of the neuron (Goldstein).
Region in which neuron is activated by external stimuli like light, touch or sound.
Phototransduction
Photoreceptors (rods and cones) turn light into electricity.
Photons of light are absorbed by visual pigment molecules.
Subsequent chemical changes result in chemical change.
Rods and Cones
Rods and cones are in the retina. Types of photoreceptors.
Rods= low light and motion detection.
Cones = bright light and colour vision.
L, M and S Cones
Long, Medium and Short Cones.
Long= red
Medium= green
Short= Blue
They work together to form Trichromatic Theory which allows us to see a wide range of colours.
Spectral Sensitivity
Ability of a photoreceptor to respond to different wavelengths of light.
Helps us to see and distinguish colour.
Metamer
Colour sensation that appears identical to another colour, even though the physical light it produces may be different. Due to varying perception of cones.
Visual Electrophysiology
Study of electrical activity in the nervous system in response to visual stimuli. Involves measuring the electrical signals generated by their retina, optic nerve, and visual pathways in the brain.
Experiments usually carried out on animals.
Tiny electrode placed close to or sometimes inside a visual neuron.
Visual stimuli are presented to the animal (normally paralysed or anaesthesitised)
Electrical signals in neuron are recoded.
Bipolar cells
Transmit visual info from photoreceptor cells to ganglion cells.
Ganglion cells
send visual signals to brain via optic nerve.
Respond with a spike train (series of action potentials generated by a neuron). More stimulation leads to increased firing rate of spikes per second. Responds to contrast between centre and surround. Finds intensity edges i.e. the interesting bits of images.
Optic Nerve
Carries visual information from retina to the brain.
Centre/Surround Structure
Organisation of neurons where centre responds to light in one way and surround responds oppositely.
Structure of Visual System
Light
Eye
Retina
Optic Chiasm
Lateral Genicualte Nucleus
Striate Cortex
Extrastriate Cortex
Optic Chiasm
X Shape, optic nerves from each eye meet and partially cross. makes sure info is sent to the correct hemisphere.
Lateral Geniculate Nucleus
Sits in the thalamus. Organises and filters usual input.
Bilateral nucleus.
6 layers.
Retinotopic organisation.
Striate Cortex
Primary Visual Cortex/V1.
First area that consciously processes visual info. Sits at back of brain in occipital lobe.
Extrastriate cortex
Higher Level Processing.
Just outside V1 in occipital love extending to temporal and parietal lobes.
M, P & K Cells
Types of ganglion cells.
Helps to transmit visual signals from retina to LGN in thalamus.
Magnocellular cells.
Parvocellular cells.
Koniocellular cells.
M-motion, spatial location.
P- fine detail, colour.
K- colour, contrast.
Retinotopy
retina’s spatial arrangements are preserved in the brain where adjacent areas of retina correspond to adjacent regions of visual cortex. Crucial for accurate visual processing.
V2
Secondary visual cortex or area 18. Second major area in the visual processing hierarchy. Located next to V1. Bridge between low-level processing in V1 and more complex processing in V3, V4 and MT/V5.
V3
Helps with processing the shape and structure of moving objects. Input from V1 and V2. Detects dynamic form i.e. shape of things in motion. Less specialised than V4 or MT, but supports both ventral and dorsal stream functions.
V4
Colour & Shape.
Crucial for colour perception and detailed form recognition. Input from V2. Processes colour constancy. Helps recognise complex patterns, curved shapes, and object details.
V5/MT
Middle Temporal.
Motion detection- especially direction and speed.
Input from V1, V2, and V3.
Damage here can lead to motion blindness (akinetopsia).
IT (Inferotemporal Cortex)
Object Recognition.
High-level visual processing- identifies objects, faces, and categories. Input from V4 and rest. Stores and retrieves visual memories. Supports face recognition.
Part of the ventral stream- the what pathway.
MST (Medial Superior Temporal)
Complex motion processing like rotation and expansion. Input from MT/V5.
Processes optic flow.
Part of the dorsal stream- the where/how pathway.
Spatial Frequency
How much detail is in a visual image, based on how often patterns repeat over space.
How the visual system detects fine vs coarse details.
Low SF- big broad shapes and blobs
High SF- fine detail and sharp edges.
Binocular Disparity
Difference between the images seen by your left and right eyes. This difference is used by the brain to create a sense of depth- helps to see world in 3D.
Happens in V1, especially in V2 and V3.
Scene Perception
The process by which we visually interpret and understand the environment around us.
Object Perception
Ability to recognise, identify and make sense of objects in our environment. Occurs through interpreting sensory input.
Gestalt Rules
Explains how we naturally organise visual information into meaningful patterns and wholes. Often subconsciously.
The whole is greater than the sum of its parts.
How humans innately perceive patterns and structure in usual input.
Proximity- group elements that are close together in space.
Similarity- group elements that are similar together in terms of shape, colour, texture or size etc.
Continuity- We perceive smooth, continuous lines rather than disjointed, jagged ones.
Closure- We tend to fill missing parts of a shape to see a complete figure.
Common Fate- Elements that move together, we group together i.e. a flock of birds.
Figure Ground- we instinctively separate main objects from background.
Symmetry and Order- we prefer symmetrical objects and orderly objects.
Perceptual Segregation
Process of separating one object from another or from the background in a visual scene. Allows us to detect what and where things are, and distinguish figure from ground. Relies on clues.
Illusory Contours
Subjective Contours.
Perceived edges or shapes that aren’t actually present in the visual input. Brain creates them. Example: Kanizca Triangle. V1 and V2 do this and even when we are consciously aware, we still see it. Our brains prefer simplicity, order and closure.
Object Categorisation
Super ordinate: Animal
Basic: Dog
Subordinate: labrador
Viewpoint Invariance
Ability to recognise an object regardless of angle or perspective. Essential for object constancy and goal directed actions.
View Point Invariance Approaches
3D Model- Structural Description Models. Brain creates 3D representations. We store objects as geons and their relationships.
2D View Based Model- We store multiple 2D views and interpolate between them.
Scene Gist
General description of a scene. Available after only a fraction of a second.
Global Image Features (Torraba and Oliva)- Scene Gist
Degree of naturalness- natural or manmade?
Degree of openness- visible horizon?
Degree of roughness- many or few objects?
Degree of expansion- distance or not?
Colour
Indirect Perception
Inferences and hypotheses.
Affects judgements.
I.e. Superstitious Perception
Superstitious Perception
When people perceive meaning patterns or causality in random unrelated events. Seeing patterns where none exist.
Cognitive Toponymy
How humans perceive name and mentally organise geographical spaces. Focuses on mental representations of place names.
TE, TEO, IT
IT = Inferotemporal cortex. Temporal lobe. High level processing. Part of ventral stream- what pathway. Heterogenous.
TE = temporal cortex. Object recognition and categorisation.
TEO= temporal occipital cortex. Junction of occipital and temporal lobes. Higher processing of visual stimuli. Integrating more detailed visual features.
Physiology of Object and Scene Perception.
fMRI experiments in humans revealed even more structures in temporal cortex.
FFA
Fusiform Face Area
OFA
Occipital Face Area
PPA
Parahippocampal Place Area
EBA
Extrastriate Body Area
VWFA
Visual World Form Area
Diagnosticity
What are the essential visual features which distinguish an object from other objects.
Grandmother Neurons
Hypothetical, specialised neurons that would be responsible for recognising a very specific, complex stimulus.
Single neuron can be involved in representing the recognition of something as specific as grandmother’s face.
Jennifer Anniston Neuron
Neurons that respond specifically to individual faces or objects.
Affordance
Gibsonian concept- Ecological Theory of Perception
Objects properties suggest to the perceiver what can be possible with the object.
Divided Attention
Common in everyday life.
Paying attention to more than one thing at the same time.
Selective Attention
Focusing on specific objects and ignoring others.
Why do we need attention?
Too much information to process it all. We have finite capacity.
Exogenous Attention
Guided by the environment
Endogenous Attention
Guided by the attender- internally. usually a combination of both exogenous and endogenous.
Perception requires attention
Inattentional Blindness- when you do not see something in plain sight because your attention is occupied by another task or object. Invisible Gorilla experiment- Simon and Chabris. Our brains have limited attnetional resources.
Change blindness- we can fail to notices major changes in our environment. When the change coincides with a visual interruption or distraction. Door study- Simons and Leven, 1998. Our brains do not store all info we see.
Continuity Errors
Mistakes made during film making or story telling where details do not match up between shots or scenes. Unintended inconsistency.
Can be due to both: inattentional blindness and change blindness (error that happens following a cut in the action).
E.g. Lord of the Rings, Harry Potter
Spotlight of Attention
Attention is like a spotlight on a dark stage. Wherever the light shines, that is what you are most aware of. Focus. Peripheral awareness- you can vaguely sense things in the dark edges, but not clearly.
Attention as glue: The Binding Problem
Binding problem: question of how the brain combines separate features into a single, unified perception of an object.
Attention as the glue: Anne Treisman proposed this in her Feature Integration Theory. Attention acts like glue that binds separate features into a unified object representation.
Feature Integration Theory
Treisman
Suggests we process features of objects in 2 stages:
1. Pre-attentive stage- automatic and fast, happens without conscious effort
2. Focused attention stage- attention is need to glue or bind features together. Where you recognise what you are looking at.
Illusory Conjunctions
When attention is divided or overloaded, people may incorrectly combine features from different objects.
Data in Support of Feature Integration Theory
Experiments using short presentations of several objects with multiple features show that features are easily mismatched on recall.
Parallel Search
When your brain processes all items in a visual field silmultaneously to find a target. It is fast, automatic and does not require focused attention. Happens during the pre-attentive stage.
Conjunction Search
When you are looking for a target that is defined by a combination of two or more features, rather than a single unique feature. Requires focused attention.
EG. Find the red circle among:
Red squares
Blue circles
You can’t use color alone (other red shapes exist), and you can’t use shape alone (other circles exist).
You have to find the conjunction of “red” + “circle.”
Serial search
Visual search process where brain examines one item at a time, sequentially, to find a target. Slower than parallel search and is typically used when target shares multiple features with distractors. Happens during focused attention stage. One item at a time. Research time increases linearly as number of distractors increases.
Gamma Band Oscillations
Brain waves with a frequency between ~30 to 100 Hz. Often centred around 40Hz. Typically associated with active cognitive processing. Linked to attnetion.
How do we direct our attention to different parts of a scene?
Eye movements involved.
Dominant theory: Stimulus Salience- we direct our eyes to the most salient object in the scene; the thing that pops out.
Monotropism
Theory of autism which has emerged from experiences of autistic people.
People have a limited ability to divide attention between multiple tasks or stimuli. Instead they focus on one thing intensely, often with narrow focus.
An interest model
- Tendency for an autistic person’s interests to draw them in more strongly than a non-autistic person
- In a monotropic mind, fewer interests are aroused and attract more processing resources
- Harder to deal with things outside of these interests e.g. look at a face and listen to what a person is saying at the same time.
Attention as Enhancement
We respond faster to attended objects/locations. In some cases contrast is also enhanced. Attention enhances physiological responses. In parietal cortex firing rates of visual neurons increase if the object is attended.
Motion
Ability of the visual system to detect and interpret movement in the environment.
Motion of objects in the 3D world causes changes in the retinal image.
Motion Detection
Process of sensing and recognising movement in a visual scene.
Retina- detects changes in light as objects move.
Optic nerve- sends signals to the brain.
Visual cortex- specialised for processing motion signals.
Temporal comparison- brain compares images over time to detect change.
Delay and Compare
Model used to explain how humans and animals detect motion.
Measure image at one place and time and then later at another place and time.
Velocity = Distance/Time
If both signals align after the delay, the system infers motion in a specific direction.
Reichardt Detector
Based on the delay and compare principle.
Takes signals from 2 neighbouring light sensors. It delays one signal, then compares it to the other. If the object is moving in the right direction, the signals match up. If it moves in the wrong direction, they do not match and so no motion is detected.
Apparent Motion
When you see movement even though nothing is actually moving. Your brain creates the illusion of motion from static images shown in a sequence.
Phi Phenomenon
When two lights blink on and off in succession, and it looks like one light is moving between them.
There’s no actual movement, just blinking lights.
Beta Movement
Brain sees a series of still images and interprets it as continuous motion.
Is motion an illusion?
When we see motion, it might not necessarily exist. Brain predicts motion.
Static Motion Illusion
Images that look like they are moving, even though they are completely still. Your brain thinks there is motion because of how the image is designed.
Why?
Delays in how brain processes light and dark areas.
Eye movements.
Contrasting colours and patterns.
The Correspondence Problem
The challenge of determining which elements in one sensory input correspond to elements in another.
E.g. Apparent motion- sequence of two dots, one appears on the left, then another appears on the right. Your brain sees them as one dot moving, even though there is not actual movement. The brain has to decide that dot A in corresponds to dot B.
Nearest Neighbouring Match
Heuristic in the brain that is used to solve the correspondence problem by assuming that elements close to each other across space or time likely correspond.
Common Fate
Gestalt Rule
Elements that move together or change in the same way over time are perceived as belonging together.
The Aperture Problem
The ambiguity that arises when a moving object is viewed through a small “window”.
Causes problems for determining direction of motion of a moving object.
Barberpole Illusion
Aperture Problem Example.
Motion illusion where a diagonal stripe moving inside a rectangular aperture appears to move vertically, even though its actual motion is diagonally upward or downward.
Optic Flow
Pattern of retinal motions that we see if we move towards or away from an object.
Gives us info about speed and direction of heading.
Corollary Discharge
Neural signal sent from motor system to sensory areas of brain, alerting them that a movement is about to happen. So, the brain can predict and adjust. Without this, eye movements would make the world look like it is constantly in motion. I.e. why we cannot tickle ourselves.
Area V5/MT
Middle temporal area
Motion processing hub of visual brain
In the extrastriate cortex.
Specifically direction and speed of moving objects.
Area MST
Medial Superior Temporal
Handles complex motion
Optic flow processing- when you move through space
Area FST
Fundus of the Superior Temporal Sulcus
In Extrastriate cortex
Combines motion and form- moving shapes and complex visual features
Biological Motion
Visual perception of movement patterns produced by living beings.
Self motion
Perception of our own movement through the environment, as opposed to the movement of external objects.
Motion Trajectory
The path that an object follows over time as it moves through space.
hMT+
Human middle temporal area
Motion detection and interpretation of visual movement.
V3
processing of complex visual stimuli. form, motion, depth.
Vestibular System
sense of balance and spatial orientation.
Helps us maintain posture, detect motion and keep body oriented.
disorders of vestibular system: vertigo, dizziness.
Point-Light Display
Used to study biological motion perception.
Involves a series of lights attached to key joints of human or animal. Move in ways that mimic natural body movement.
Wavelength
The distance between two peaks of a light wave. Determine the colour of light we see.
Shorter wavelengths (like violet and blue) are at the beginning of the visual spectrum. Longer wavelengths (like red) are at the end. Controls how we perceive different colours of light.
Shorter = cool colours
Longer = warm colours
Benham’s Disc
Optical illusion that creates the perception of colour where none actually exists. The disc only has black and white segments arranged in a specific pattern, but when you spin the disc quickly, your brain interprets rapidly changing patterns. Perceives a colour effect. Colours are not real.
How is the colour of objects determined?- Spectral Reflectance
How they interact with light.
Visible light ranges from 380 nm (violet) to 750 nm (red).
When light hits the object, the objects surface determines what happens to that light. Some wavelengths are absorbed by object and some are reflected back to our eyes. The colour we perceive is the result of the wavelengths that are reflected.
Diagnosticity of Colour
how colour can communicate or distinguish things, such as help us identify objects.
i.e. traffic lights- red, yellow and green colours are diagnostic of the status of traffic.
Memory Colours
Prior knowledge of an object’s characteristic colour affects its appearance.
Trichromacy
Young-Helmholtz Theory
How humans perceive colour through the activity of three types of cone cells in the retina.
S Cones- Short- blue
M Cones- Medium- green
L Cones- Long- red
Colour matching experiments- people can match any colour by mixing just three wavelengths of light (red, green, blue).
Physiological evidence.
Genetic studies- colour blindness often results from the loss or malfunction of one cone type.
Metamers can fool the trichromatic system.
Spectral Sensitivity
How responsive a photoreceptor is to different wavelengths of light across the visible spectrum. How sensitive something is to each colour of light.
Metamer
Physically different spectra
Perceptually equivalent colours
Activate cones by same amounts
Opponent Process Theory
Ewald Hering
We perceive colour through oppossing neural processes.
e.g. Red v Green, Blue v Yellow.
After light is detected by the three cone types, the output signals are combined and processed in the visual system into opponent channels. Explains why we cannot see a reddish green or a bluish yellow. Retinal ganglion cells start the opponent process. How we interpret and organise colour.
Blob
Found within V1
Primarily involved in colour processing.
Interblob
Found between the blobs
Process form and orientation, but not colour
Double Opponent Neurons
Respond only to colour contrast
Thought to be in V1
Controversial existence
Ocular Dominance
The tendency of neurons in the primary visual cortex to respond more strongly to input from one eye than the other.
Supports stereopsis- the ability to perceive 3D structure.
Colour Constancy
Our visual system’s ability to perceive the colour of an object as stable even when the lighting changes.
Without this, objects would appear to shift colour all the time as lighting changed.
Unique Hue
Perceived pure colour that doesn’t look like it contains any trace of another colour. It is just pure. 4 Unique Hues- Red, Green, Blue, Yellow
Science behind it: Opponent Process Theory. Our visual system processes colour in opponent pairs.
Spectral Power Distribution
Graph that shows the amount of light (power or intensity) emitted or reflected at each wavelength across the visible spectrum.
Chromatic Adaptation
Way to achieve colour constancy.
Ability of the visual system to adjust to changes in the colour of the light source so that the colour appears constant.
Silmultaneous contrast
nearby colours influence each other’s appearance.
Lightness Constancy
Perceived lightness stays relatively constant, even when the illumination changes.
Helps us distinguish shadows from material changes
Colour as Material Assumption
Our visual system tends to interpret colour as a property of a material surface. We assume colour belongs to an object rather than the illumination.
Proprioception
Sense of position of the limbs
Kinesthesis
Sense of movement of the muscles
Tactile Perception (Somaesthesis)
Sense of objects touching the skin
The Somatosensory System
Receptors
Spinal pathways
Brain regions
Receptors in the Somatosensory System
Sensory receptors- convert physical stimuli into neural signals that your brain can interpret
mechanoreceptors- detect mechanical deformation of the skin or deeper issues
thermoreceptors- temperature
nociceptors- pain
proprioceptors- body position and movement
Merkel Receptors- channel of the somatosensory system
respond to continuous pressure (sustained response)
involved in sensing fine details
Meissner Corpuscles- channel of somatosensory system
respond to application and removal of stimulus (transient response)
involved in handgrip control
Pacinian Corpuscles- channel of somatosensory system
respond to stimulus onset and offset (transient response)
detect vibration
also fine texture by moving fingers
Ruffini Endings- channel of somatosensory system
respond to continuous pressure (sustained response)
detect stretching of skin
Transient response
Typically short-lived before the receptor either adapts or stops firing
C-Tactile Mechanoreceptors
Specialised nerve fibres that respond to gentle, slow, touch. Allows us to perceive pleasant, comforting sensations.
Non-myelinated fibres, so slow conducting.
Signals sent to the insular cortex.
Free Nerve Endings
Unencapsulated nerve endings. Tend to be sensitive to a wide range of stimuli.
Tactile Receptive Field
Specific area of the skin where a sensory receptor (like mechanoreceptor) is sensitive to touch or pressure. Each sensory receptor has a receptive field.
Explored using two-point discrimination thresholds- large receptive fields, one neurone fires. Small receptive fields, two neruons fire.
Sensory Homunculus
The cortical area for different body parts is roughly equivalent to sensitivity.
Maps sensory information. Shows how different parts of body are represented in brain and how sensitive each area is to touch, pain, temperature and other sensations.
Somatosensory Cortex
located in the parietal lobe. Plays a crucial role in processing sensory information from the body.
Plasticity
Adult brain is very flexible and can modify itself to new situations.
Haptics Perception
How we use our somatosensory system to evaluate the world around us.
Active Touch
When we actively use our hands to explore objects in the world we are more efficient at gaining information than when the object is moved passively across our hand.
Exploratory Procedures
The way we explore objects with our hands is tailored to the amount of information that we hope to gain.
Pain
Specialised nociceptors exist which are sensitive to stimuli which are potentially damaging to skin
Different types:
- Thermal
- Mechanical
- Chemical
- Silent (respond to inflammation)
Pain Phases and Dimensions
A-Delta fibre axons
- Myelinated, fast conducting
- initial, sharp pain
C-Fibre Axons
- Unmyelinated, slow conducting
- more prolonged, but less intense pain
Discriminative Dimension of Pain- what, where and how of pain experience. Locate and classify
Affective Dimension of Pain. Emotional and motivational aspects of pain.
Gate Theory
Classic modern theory of pain developed in the 1960s
Has components for both pain receptors and alternative mechanisms
How pain signals are modulated in the body before reaching the brain. The experience of pain is not solely the result of activation of pain receptors, but is also influenced by a complex interaction between sensory signals and neural pathways.
The gate is located in the dorsal horn of the spinal cord. Acts as a control system for how pain signals are transmitted to the brain.
Evidence for the role of the CNS in experiencing pain
Phantom Limbs
- Pain reported in amputated limbs
Endogenous brain chemicals modulate pain
Auditory Perception
Interpreting and understanding auditory stimuli. i.e. loudness, pitch, timbre.
Pitch
Perceived frequency of a sound. How we interpret the highness or lowness of a sound.
Derived from sound wave frequency
1 Hz= 1 oscilliation per second
Pitch is a metameric percept
The same sensation of pitch can be elicited by very different sounds
Timbre
Quality or colour of a sound that distinguishes it from other sounds, even if they share the same pitch and loudness. E.g. piano and violin sound different playing the same pitch because they have different timbres.
Derived from sound wave shape
Harmonics
Loudness
Derived from sound wave pressure level
Decibels: a physically measure of sound amplitude
Perceived loudness is measured by comparing two tones and deciding which one sounded louder
Perceived loudness also varies with sound frequency
Outer Ear
Pinna, Concha
First point of contact for sound waves from the environment. Collection and direction of sound waves towards the ear canal and inner ear structures.
Pinna- Has a distinct, curved shape that helps capture sound waves and funnel them into the ear canal. Curves and folds are called concha and helix. Helps in distinguishing sounds from different directions.
Pinna, Ear Canal, Tympanic Membrane
Ear Canal
Tubular passage that leads sound waves from the pinna to the eardrum. Approx. 2.5cm long. Funnels sound and protects eardrum.
Tympanic membrane
Eardrum
Thin, flexible membrane that vibrates when sound waves hit it. These vibrations are then transferred to the bones of the middle ear to be processed into nerve signals.
Middle Ear
Transmitting sound vibrations from outer ear to inner ear.
Amplifies and transforms sound waves.
Pressure boost up to 200x
Impedance Matching
The middle ear’s ability to efficiently transfer sound energy from the outer ear to the inner ear.
Without this, hearing would be drastically less sensitive.
Middle Ear 3 Ossicles
Tiny bones that work together to transmit and amplify sound vibrations from the eardrum (tympanic membrane) to the inner ear (cochlea). Smallest bones in the human body.
Malleus- attached to eardrum. Receives vibrations from tympanic membrane.
Incus- bridges the malleus and stapes by transmitting vibrations.
Stapes- sends vibrations to the inner ear.
Inner Ear
Contains the cochlea.
Pressure waves are transformed into neural signals.
Cochlea
Coiled structure
Fluid filled
Converts sound vibrations into neural signals
2.5 turns long, 3.5cm
Transduction
The Organ of Corti
The sensory organ (equivalent of retina in the eye)
Runs along the basiliar membrane
Contains hair cells with stereocilia: transducers that convert motion into neuronal signals
Start of the auditory nerve
Hair Cells
Inner- sensory receptors that send info to higher cerebral levels, 95% of fibers in auditory nerve
Outer- receive projections from upper cerebral levels, role in active filtering
Auditory Nerve
Transmits electrical impulses generated by hair cells in the cochlea to the auditory cortex in the brain.
Each nerve fires near peak displacement of the basiliar membrane.
Phase Locking
Neurons fire action potentials at specific phases in a sound wave cycle. Helps brain detect frequency of sounds by tracking time of waveforms, not just amplitude.
Basilar Membrane
Narrow and stiff at the base. Wide and flexible at the apex. Different parts of it are tuned to different frequencies. High frequencies occur at the base. Lower frequencies at the apex. Topographic organisation by frequency preserved up to the level of auditory cortex (tonotopy).
Pitch Perception
How we perceive frequency of sounds. Relies on 2 main models:
Place Model- pitch is determined by specific location along basilar membrane. Basilar membrane is tonotopically organised high frequencies activate base, low frequencies activate apex.
Rate model-pitch is encoded in the timing of neural firing.
Function of Senses
Vision- electromagentic radiation
Hearing- mechanical vibrations
Touch- mechanical pertubations of the skin
Smell- chemical properties of gases
Taste- chemical properties of solids and liquids in contact with the tongue
Taste
Function-
sweet- high in calorific value
bitter- should be avoided (poisonous)
salty- important if dehydrated
Gustation- The basic tastes
Sweet
Sour
Salt
Bitter
Umami- meatiness, savouriness
The Tongue
Bitter near back
Sour
Intensive Area
Salty
Sweet closest to front
Taste Bud
Chemoreceptor cells
Supporting cells
Taste pores
Nerve fibres
Grouped in structures called papillae on the tongue
fungiform- tips and sides
foliate- sides
circumvallate- back
filiform papillae- no taste buds, for texture
Taste Receptors
specialised sensory cells that detect chemicals in mouth and send signals to brain that we interpret as taste.
found within tastebuds
Type 1- support cells, may detect salty taste
Type 2- detect sweet, umami, bitter
Type 3- detect sour and send signals via synapses
Replaced every ~10 days
Taste Receptors and Transduction
As soon as an appropriate tastant molecule attaches to the receptor , the cell depolarises and sends a signal down one of the gustatory nerves.
Typical Tastants
Sweet- Sugars: glucose, sucrose, fructorse
Sour- acids: citric, acetic (vinegar)
Salt- sodium chloride
Bitter- quinine (tonic water), caffeine
Umami- monosodium glutamate (soy sauce)
Taste Pathway
Signals from the taste cells travel along:
- the chorda tympani nerve, the glossopharyngeal nerve, the vagus nerve and the superficial petronasal nerve.
These make connections to the brain stem in the nucleus of the solitary tract.
From this to the thalamus and then to the insula and the frontal operculum cortex in the frontal lobe.
Fibres from the taste system also reach the orbitofrontal cortex, which also received olfactory signals.
Functions of Smell
Useful for detecting pheromones (chemo-signals used for communication between individuals of same species).
Helps us appreciate food
Danger detector- gas, smoke
Anosmia (total loss of smell) reduced quality of life
Achromatopsia
Complete Colour Blindness
Usually congenital
Caused by a defect in cone cells of the retina
Measuring Smell
Can measure detection thresholds for different odorant concentrations.
Recognition threshold normally requires about 3x the concentration compared to simple detection.
Interaction between odour labelling and identification: it is often easier to detect the presence of a smell when you can give it a name.
Problems with measuring smell
Controlling concentrations in stimulus presentations.
Can use an olfactometer to help control air flow and humidity
Two very similar molecules can smell completely different
Two very different molecules can smell the same
Olfactory System
Detects odour molecules in air, processes them, and sends signals to the brain.
Olfactory receptors- located in olfactory epithelium.
Olfactory bulb- odor molecules bind to receptors in nasal cavity and signals are sent to olfactory bulb. Acts as a processing centre.
Olfactory nerve- transmits signals from olfactory epithelium to the olfactory bulb.
Olfactory Mucosa
Specialised tissue located in the upper part of the nasal cavity. Detects odours. Initiates process of smelling.
Sensing smells
Odorants are inhaled and flow over olfactory mucosa. Odorent molecules stimulate the olfactory receptor neurons embedded in the mucosa which produce a neural signal. This signal is passed to the glomeruli in the olfactory bulb.
Encoding Smells
There are ~350 different classes of olfactory receptor neurons in humans. ORNs send output signals to glomeruli in olfactory bulb.
Olfactory Transduction
Process by which odour molecules are converted into electrical signals.
Flavour Perception
The “taste” of food is a societal obsession
What is typically called “taste” is actually “flavour”- combination of gustation and olfaction
Flavour perception deteriorates when nose is blocked.
Physiology of Flavour
Orbito-frontal cortex thought to be important
First place where taste and smell information combine
Bimodal neurones in OFC respond to taste and smell or taste and vision
Some evidence that activity in these neurons reflects the pleasantness of flavours
Synaesthesia
Stimulation of one sensory pathway leads to automatic, involuntary experiences in a second sensory pathway. Colours associated with numbesrs, sounds evoke colours (chromesthesia), words evoke tastes etc (lexical-gustatory synesthesia).
