Psych 258 - Midterm #1 Review

Cognition

Acquiring and processing information about the world in order to make behavioral decisions

• Involves different abilities:

  • Perception

  • Attention

  • Memory

  • Language

  • Decision making

• Primarily concerned with understanding the processes that produce complex behaviours, such as remembering, recognizing, or making a decision

• Estimated 86 billion neurons in the human brain

3 prong approach to studying cognition

1. Neuroscience: the study of the brain itself

2. Cognitive psychology: the study of human behaviour, using experiments, to understand how the mind works

3. Computational modelling: simulating the brain using computers

Mind body problem

The question or debate of how mental events (ex. thoughts, beliefs and sensations) are related to/caused by physical mechanisms taking place in the body (ex. cellular/molecular processes in the brain)

Dualism

Views the mind and body as consisting of fundamentally different kinds of substances/properties and are separate from one another

Monism

There is only one kind of basic substance in the world, of which our mind and body are both made

• Physicalism: the only kind of reality is physical 

• Idealism: the only kind of reality is mental; all reality is a mental construct; reality only exists in the mind (like The Matrix)

• Neutral monism: there is only one kind of substance that is neither just physical or mental, and the mind and body are composed of that same element

Structuralism

All about introspecting on one’s own conscious mental states in order to understand the mind; breaks down complex processes into simpler elements

• Says we should try to study the workings of the mind directly

• Wanted to discover basic principles of how elements interact and form the working mind

• Founded by Wilhelm Wundt in the late 19th century, brought to America by his student Edward Titchener

• Not seen as a scientifically valid method (no objectively measurable data, no replication, can only access conscious processes)

• Introspection: a technique employed by the structuralists to study the mind by training people to examine their own conscious experiences

• Cortical blindness: a condition in which an individual with damage to the visual cortex will report having no visual experience, despite having working eyes

• Blindsight: a phenomenon in which someone who reports blindness due to cortical damage still shows behaviour consisting with some perception

Behaviourism

Emphasized using observable stimuli and behaviours as the basis of scientific experimentation

• Deliberately went in the opposite direction as structuralism

• Founded by John Watson in the early 20th century

• Treats the brain as a black box, whose mechanisms cannot be investigated; we can only see the results of the processes that occur in the brain

• Stimulus: something that stimulates the senses of the experimental subject

• Response: the behaviour that the experimental subject engages in after a stimulus is presented

Fundamental flaw in behaviourist approach: It does not account for flexibility in cognition that allows for the generation of novel behaviors that have not been observed or performed

Challenges to behaviourism

• Noam Chomsky argued that behaviorism could never achieve its goals of explaining behavior through conditioning because people engage in novel behaviours that they have never had a chance to learn

• Edward Tolman argued for latent learning, which was a fatal flaw in the behaviorist approach since it cannot account for the flexibility of cognition to generate novel, intelligent behaviors that have not already been observed or performed

• Latent learning: learning in the absence of any reward or punishment conditioning, as in Tolman’s maze experiments

Rise of computers

• Function: mappings between one set of objects and another (inputs and outputs)

• Algorithm: a set of operations that produces the input/output mapping of a function

• Transistor: a device used in computers to control whether or not a current flowed through parts of the system

• Advent of computers happened in the early 50s

• Turing’s ideas strongly influenced the first designs of electrical computers that began in the early 1940s (start of the use of binary)

• Vacuum computers were used during WWII for ex. breaking codes used for secret enemy messages but were expensive, unreliable, and big

• Big leap in 1947 with the electrical transistor (bell labs)

• Cognitive revolution: a movement in the 1950s that proposed that the mind could be understood as a computational system

• Information processing: an approach to human cognition that views it as a type of computation with sensory information serving as an input which is processed by the brain to determine a behavioral output

• Cognition can be seen as a kind of algorithm made up of sequences of operations 

• Boxes in flowcharts don’t represent different brain areas, rather they refer to different computational steps or stages

Cognitive approach

We can measure observable behaviour in order to test theories of the underlying mental processes

• Cognitivism: an approach in psychology that uses behavior as a method for developing and testing theories of the underlying processing of the mind

• Reaction time: a measure of how long it takes an experimental subject to respond to a given task or query

  • The more cognitive processes involved in a task, the longer the response takes

Hypothesis vs phenomenon driven research

1. Researchers develop and test a hypothesis and assess whether their results support that hypothesis

2. An outcome or effect is found as a result of an experiment/study without being predicted as a hypothesis, so researchers conduct follow-up studies to try and replicate and/or extend upon the found effect

Experimental measures

• Experimental subject: a person on whom the experiment is being conducted

• Independent variable: the conditions that are being manipulated by the experimenter in order to determine their effects on the dependent variable

• Dependent variable: the properties that are being measured in an experiment

• Speed-accuracy tradeoff: when a participant in an experiment sacrifices accuracy in their responses for greater speed or vice-versa

Accounting for variability in behavioural measures

Noisy data can be due to participant mistakes, lack of attention, or other factors, all of which can “drown out the effects of the independent variable” and can lead to misleading results

• Trial: repetitions of an experimental condition, typically used in order to compensate for variability in performance across attempts; results are usually averaged

• Individual differences: variations in performance across different individuals in cognitive tasks

  • To account for this variability, have a large sample size to balance out differences, which will lead to more generalizable results

Complementary approaches to cp

1. Cognitive neuroscience: a scientific field that merges brain imaging with behavioural experimentation

   • Common now due to its non-invasive practices 

2. Behavioural neuroscience: a scientific field that assesses behaviour and neurological factors in animals as models of human function

   • Often implants microelectrodes in animals’ brains to record activity of individual brain cells while the animal is awake and behaving

   • Has some ethically questionable techniques that involve permanently damaging neural tissue, temporarily deactivating parts of the brain, or breeding genetic mutants that have some variation in their neurophysiology

   • Optogenetics: a technique used to control the activity of brain cells based on introducing light-sensitive proteins into the cells and activating them with light

   • Opsin: light-activated proteins, used in optogenetics to experimentally modify the activity of neurons

3. Computational neuroscience: a scientific field that uses computer models of the brain to model real brain function

Nervous system

Consists of the brain, neurons, nerves, and glial cells whose function is to allow different portions of the body to communicate with one another

• Neurons: specialized cells that can receive and transmit information

• Nerves: bundles of connective tissue that allow neurons to communicate with one another and other parts of the body

• Glial cells: cells within the nervous system that provide support to neurons

Autonomic ns

A portion of the peripheral nervous system that connects to most organs in the body and regulates certain unconscious bodily functions

• Ex. heart rate, respiration, digestion

Sympathetic vs parasympathetic ns

1. A subdivision of the autonomic nervous system that unconsciously regulates certain functions of the body to prepare for immediate action

   • Fight or flight: a sympathetic nervous system response that prepares the body with increased strength and stamina in response to a perceived threat

2. A subdivision of the autonomic nervous system that regulates certain bodily functions under conditions when immediate action is not needed; ramps up long-term survival processes

Parts of involuntary systems

• Brainstem: a stalk-like structure at the base of the brain that connects it to the spinal cord and regulates involuntary functions (ex. heart rate and breathing)

• Hypothalamus: a small but highly complex cluster of neurons that lies in the center of the brain that regulates multiple involuntary behavioural functions (ex. temperature, hunger, thirst, etc)

• Reflex action: the simplest form of autonomic behavioural responses in which the spinal cord generates the behavioural signal without the brain

Parts of voluntary systems

• Cerebrum: the largest portion of the human brain, sitting at the top of the brain and consisting of the cerebral cortex and related structures; controls and regulates voluntary behaviours; consists of:

• Cerebral cortex: a folded, layered structure that is the largest single structure and the most superficial portion of the human brain (evolutionarily newest part of human brain)

  • Gray matter: the topmost layer of the cortex, consisting of neuronal cell bodies

  • White matter: the layer of the cortex underneath the gray matter, consisting of axonal nerve tracts; connects neurons to each other

• Hippocampus: a complex structure which is involved in memory formation and is structurally an extension of the temporal lobe of the cortex and is involved in the formation of long-term memories

• Amygdala: involved in emotional processing

Encephalization quotient

A measure of actual brain size relative to the size that would be predicted based on body size alone; actual brain size relative to expected brain size based on size of the body

• Strongly correlated with intelligence

Contralateral

A spatial relationship between the brain and the body observed in vertebrates in which one side of the brain controls or receives input from the opposite side of the body; information received on one side of the body will be processed in the opposite side of the brain

Spatial relationships

Dorsal: up

Ventral: down

Frontal/anterior: front

Caudal/posterior: back

Anatomical divisions of the cortex

• Gyri: the “hill”-like projections of the folds of the cerebral cortex

• Sulci: the “valley”-like indentations of the folds of the cerebral cortex

  • Both of these serve to make it possible to increase the surface area of brain that can fit inside of the skull

• Lobe: the four anatomical divisions of the cortex that exist on each hemisphere

• Fissure: a deep sulcus fold in the cerebral cortex, separate 4 brain lobes

• Hemisphere: each of the two halves of the cerebrum, divided into left and right, and connected by the corpus callosum; each hemisphere shows different functional properties

• Corpus callosum: a band of fibers that connect to the right and left hemispheres of the cerebrum

Brain /4

• Occipital: visual processing

• Frontal: executive functioning (as we age, this area becomes more connected and important) and planning

• Temporal: meaning of sensory information and language and visual memory

• Parietal lobe: attention, somatosensory processing, and sensory integration

• Limbic: emotional processing

Functional localization

Specific parts of the brain do different specific jobs; controversial but there is some supporting evidence

• Difficult to establish the functions that various brain regions perform

Neuropsychology

The study of brain function and impairment due to brain pathology

• Aphasia: the loss of language comprehension or expression due to brain damage

• Broca’s/Expressive aphasia: a form of aphasia typically due to damage to the inferior frontal gyrus that leads to slow and laboured speech production

  • Slow and deliberate speech and writing

  • Problems with identifying words and forming sentences

• Wernicke’s/Receptive aphasia: form of aphasia typically due to damage to the superior temporal gyrus that leads to fluid/fluent but nonsensical speech production, people with this also have issues understanding language

  • Fluid speech that lacks meaning

  • Difficulty understanding language being spoken to them

• Speech therapy can help people overcome these incurable conditions, but it depends on how damaged their brain is 

• Language processing is doubly dissociated - one function can be maintained while the other is impaired

Split brain

Patients (typically epileptic) who have had their corpus callosum severed, disconnecting the two hemispheres of the cortex; typically recover and show mostly normal cognitive function

• Left hemisphere: language processing (stroke patients show coordination difficulties)

• Right hemisphere: spatial processing (stroke patients show language impairments)

Limitations to neuropsychology

• Scientists can’t proactively damage human brings

• Researchers are dependent on individual cases as they occur

• Brain damage is rarely isolated to one area

• Small sample sizes reduce generalizability of findings

• These limitations can be somewhat addressed using new technologies

Cognitive neuroscience

A subfield of neuroscience that measures and analyzes active brain processing in awake and (typically) healthy individual; uses technology and imaging machines to measure relevant metrics associated with cognitive activity

EEG

Electroencephalography

• Measures electrical activity due to neural or other processing at the surface of the scalp; able to measure very fast changes in brain activity

  • Can measure when brain activity happens with high precision

  • Cannot measure where brain activity happens with high precision

ERP

Event-related potential

• Rapid changes in electrical potential, as measured by EEG, due to the onset of a stimulus; charges are usually switching between positive and negative

fMRI

Functional magnetic resonance imaging

• A technique in cognitive neuroscience for measuring ratios of oxygenated blood flow in the brain in order to determine task-related neural activity; indirect measure of brain activity

  • Relies on the fact that neurons that engage in firing activity must replenish their resources and nutrients, which is accomplished through a process called the hemodynamic response: blood delivers oxygen more quickly to active neurons than to inactive neurons

  • Better spatial resolution than EEG

  • Downside: very large and expensive

  • Subtraction method: brain activity during an experimental task minus (-) activity during a control task

  • Block design: have participants complete several trials of a task and average responses together

MVPA

• Multi-variate pattern analysis

• A data-analysis that uses machine learning to decode what task or stimulus a participating in engaging, based on the distribution of activity across the brain

  • Need to decide which areas of the brain to look at, image that brain activity, and test whether a computer can identify the correct brain activation patterns

  • Involves training NNs on labelled stimuli so it can process brain data and identify which activity patterns match with which stimuli in human brains

fNIRS

• Functional near-infrared spectroscopy

• A tool of cognitive neuroscience which uses near-infrared light in order to measure oxygenated vs non-oxygenated hemoglobin, a component of blood to derive the hemodynamic response

TMS

• Transcranial magnetic stimulation

• A research technique that uses magnetic pulses to disrupt localized brain processing in order to observe effects on cognitive function

  • Goes further in determining causal effects of specific brain regions on behaviour

  • High spatial and temporal resolution

  • It can only disrupt regions close to the surface of the brain, and it cannot precisely pinpoint what effect it is having on the brain

  • Can determine if a part of the brain is causally involved in a specific function

Brain localization

Typical functional localization is not fixed

• Neuroplasticity: the ability of the brain to reorganize the spatial arrangement of its functions

  • Proves that the function of different parts of the cortex is not due to their inherent physical structure but based on the inputs to those regions

• A possible limitation of methods of cognitive neuroscience is that it largely depends on the assumption that the brain really is made up of distinct modules that carry out different functions

  • This assumption may be incorrect - scientists aren’t sure yet

• Similar cell organization in sensory and motor cortexes

Limitations of cognitive neuroscience approaches

• Techniques only tell us when and where brain activity occurs, not how (doesn’t give insight into how the neurons and circuits are carrying out functions)

• Depends on the assumption that the brain is made up of distinct molecules that carry out different functions (identifying cause and effect may not be feasible)

Neurons

Differ from other somatic cells because they are specially equipped with the means to receive and transmit information

• Neurons: cells specialized for processing and communication

• Dendrite: branch-like projections that protrude from the cell body of a neuron and contain receptor sites to which neurotransmitters can bind

• Axon: a projection of the neuronal cell body along which action potentials are propagated, terminating in the release of neurotransmitters; sends out the result of the neuron’s processing

• Myelin sheath: keep electrical signal insulated; makes it go faster

Other neuron terms

• Synapse: the site at which communication between two neurons occurs. It consists of an empty space between the axon terminal of a neuron that is sending information and receptors on the dendrites of the receiving neuron

• Neurotransmitters: chemical agents that serve as "messengers" between neurons

• Synaptic vesicles: storage sites within a neuron that hold neurotransmitters prior to their release

• Receptors: sites on the dendrite of a neuron to which neurotransmitters can bind

• Reuptake: a process in which neurotransmitters in the synaptic cleft are re-absorbed by a sending neuron

• Action potential: the all-or-none firing of a neuron that leads to the release of neurotransmitters (electrical signal)

Types of neurons

• Excitatory: when the firing of a neuron causes a receiving neuron to fire more frequently (become more active)

• Inhibitory: when the firing of a neuron causes a receiving neuron to fire less frequently (become less active)

  • Neurons are either one or the other

• Each neuron only releases a single type of neurotransmitter

• Some neurotransmitters can be excitatory in some areas of the body and inhibitory in others

• Electrical communication is much faster and more reliable than chemical communication

  Types of neurons:

1. Sensory/receptor neurons: neurons that receive their activation from physical stimulation of the body through the outside environment

• Transduction: the conversion of information from one form to another

2. Motor neurons: neurons whose output leads to activation (which comes from the CNS) of muscle fibers and allow us to move

• Release and termination of neurotransmitters cause fibres to contract and release

3. Association neurons: neurons that receive their inputs and send outputs to other neurons; receiving and sending information to and from neurons

Special neuron terms

• Neural convergence: when multiple neurons send signals to a single neuron

• The wider the stimulus, the more the neuron responds

• The brain can use layers of simple biological circuits, to produce increasingly complex and sophisticated computations

• Specificity encoding: a theory of neural coding in which a complex pattern or object is encoded by the response of a single neuron (AKA grandmother neuron)

• Distributed encoding: a theory of neural representation in which complex patterns or objects are represented by the distribution of activation across many neurons

  • Many neurons are active in response to a single stimulus such as an object or face; different objects are distinguished by the specific pattern of activation

• Sparse coding: a theory of neural coding in which a complex pattern or object is encoded by the distribution of responses across a small set of neurons; a small number of neurons are active for any given complex stimulus

ANNs

A type of machine-learning models based loosely on the brain consisting of layers of nodes connected by modifiable weights that determine their activations

• Activation level: the numerical value of a node in a neural network

• Activation function: a function that takes in the weighted sum of the previous layer's inputs and returns the activation level of the node

• Input layer: the first layer of an ANN; the activation level of each node in this layer is determined by values of the data itself

• Output layer: the final layer of an ANN that represents the networks decision about the input

• Hidden layers: the intermediate layers between input and output in an ANN. The units in the hidden layer encode patterns in the input layer or in previous hidden layers

• Training set: the dataset used to train a neural network

• Error/loss: the difference between the observed output and the correct output of an ANN, used as a measure of its performance and minimized during training

• Backpropagation: a technique for gradually changing the weights of a neural network in order to reduce the error

• Validation set: a dataset used to test the performance of an ANN after it has been trained to determine whether it can generalize to unseen examples

Generative models

• Discriminative: a class of ML models that is trained to determine which class or category a given input is derived from

• Generative models: a type of ML model that is trained to produce novel examples of a certain category of data

Sensation

Conversion of physical properties of the world or body into a neural code by the peripheral nervous system

• Takes place in sensory neurons

• Transduction: converting physical stimulation into neural code

Perception

Processing and interpretation of the sensory information into a form that is useful for behavioural decision

• Includes 5 senses

Exteroception vs interoception

1. The sensing and processing of information from the external environment by the five basic senses: vision, audition, touch, taste, and smell

2. The sensing and processing of information from inside the body

   • Proprioception: the perception of the location of the limbs in space

   • Nociception: the perception of pain due to internal bodily damage

   • Equilibrioception: the perception of bodily balance

   • Feeling full from eating

   • Feeling something in your throat

Sensory receptors

1. Chemoreceptors: sensory receptors with nerve endings specialized to respond to chemicals in the environment 

• Found in the nose, mouth, skin, and internal organs

2. Mechanoreceptors: sensory receptors specialized to respond to mechanical force

• Found in the skin, inner ear, and arteries

3. Thermoreceptors: sensory receptors specialized to respond to heat and cold

• Found in the skin and throughout several internal organs

4. Photoreceptors: sensory receptors specialized to respond to light; increased exposure leads to decreased neurotransmitter production

• Found in the eyes, more specifically in the retina

Sensory modalities

1. Transduction of physical energy into a neural code by the senses

2. Transmission to the brain through subcortical and then cortical structures

3. Processing in the cortex to generate behaviour

Pathway of light

• Light first passes through the cornea: a transparent, rubbery layer of tissue at the front of the eye that bends light in order to help it land on the correct part of the back of the eye

• Then, light passes through a small opening in the iris: circular ring of coloured muscle at the front of the eyeball that contracts or relaxes in order to determine pupil size

• Pupil: small opening in the iris, controls how much light is allowed to pass into the eye

  • The function of only letting in so much light is to ensure light from specific locations hits specific parts of the retina

Retina info

• Focus: a property of an image in which specific locations in the environment correspond to specific locations on the imaging device

• After it goes through the pupil, light travels to the retina: a structure in the back of the eye consisting of multiple layers of neurons, including photoreceptors in the final layer which transduce light

• Rods: outside of central vision, that responds to lower light but with reduced spatial acuity and no colour differentiation

• Cones: largely contained in the central fovea of the retina, that supports high spatial resolution and colour vision under higher lighting conditions; come in 3 different varieties that respond differently to different wavelengths of light; centre of the retina

• Fovea: depression in the retina that is densely packed with cone photoreceptors and is responsible for seeing detailed properties

Info compression of the retina

• This pre-processing is thought to compress/reduce the amount of information that the retina needs to send to the brain

  • Compression is necessary because visual information needs to be sent to the back of the eye through the optic nerve: a bundle of axons that transmit visual information from the retina to the brain

• Sensory system of the eye produces a 2-D array of measurements, and the brain constructs a 3-D image based off of that

• Visual information processing takes place across multiple brain structures

• 90% of visual information from the retina goes to the thalamus

• Thalamus: a subcortical region of the brain that serves as something of a way-station between sensory inputs and the cortex; sets circadian rhythms and controls basic eye movements

Primary visual cortex

First region of the cortex to receive visual input; neurons respond to fairly simple patterns mostly consisting of oriented edges of particular sizes

• Moving farther along, there are neurons that respond to complex shapes and then, even higher up, there are neurons that respond to features as specific as faces, objects, or places

• Some coding has revealed that simulated brains may be using some of the same principles as biological brains

• Idea of functional localization in visual processing says (although quite contentious and controversial) that some regions of the cortex respond specifically to particular classes of stimuli

• Most signals from ex. the left eye should go to the right hemisphere and vice versa

Visual processing disorders

• Agnosia: a disability in which an individual has difficulty recognizing or perceiving certain kinds of visual stimuli while maintaining the ability to process other kinds of stimuli

• Prosopagnosia: a visual deficit that leads to an inability or difficulty in recognizing faces

  • Does not suffer general visual/memory impairments

  • Can recognize objects and their functions

  • Can identify a face from other objects, but not identity

• Semantic agnosia: a visual deficit leading to the inability to recognize objects

  • Can identify faces and identities

  • Impaired ability to name tool/object use and functions

FFA and LOC

1. Fusiform face area: a region in the inferior temporal cortex that shows greatest activity when a subject is performing face-specific tasks

2. Lateral occipital cortex: a region in the occipital cortex that shows greatest activity when a subject is performing object-recognition tasks

Presence of such specialized brain activity suggests to some researchers that these parts of the brain are geared towards processing particular classes of objects

Streams of info

• After the visual input first reaches the visual cortex, the axons leading away diverge in two different directions, referred to as different streams of information

  • Dorsal stream: projects upward and terminates in the parietal lobe

    • Monkeys with damage to this area could do this matching task but had difficulty when they had to compare the location of the object across trials

    • More concerned with the “where” or action

  • Ventral stream: projects downward and terminates in the temporal lobe

    • Monkeys with damage to this area had difficulty doing a visual matching task when it involved determining whether some object was the same or different across trials

    • More concerned with the “what” aspects or perception

Parts of the ear

• Pinna: visible portion of the ear made up of folded cartilage; serves to gather and transmit sound into the ear canal

• Ear canal: a narrow tube following from the pinna that amplifies certain sound frequencies and transmits them to the eardrum

• Eardrum: a thin piece of tissue separating the ear canal from the inner ear that amplifies certain frequencies and passes them to a series of tiny bones called the ossicles

• Ossicles: a set of three tiny bones that amplifies certain frequencies and relays them to the cochlea, ensuring the appropriate frequencies and amplitudes

• Cochlea: a coiled, bony structure in the inner ear that is filled with fluid and contains the basilar membrane

• Basilar membrane: a strip of tissue inside the cochlea that contains the hair cells that transduce sound

  • Hair cells: a type of mechanacoreceptor in the basilar membrane that are stimulated by vibrations in the fluid in the cochlea, which they convert into a neural signal that is sent to the brain; organized in a coil shape

  • Tonotopic map: a spatial arrangement of neural structures (such as hair cells) in which locations are organized based on the frequency of sound they encode; as you go further along the coil the frequency gets lower

Primary auditory cortex

Region in the temporal lobe of the cortex that is the first to receive auditory information in the cortex

• Neurons here respond to specific auditory properties such as pitch and rhythm

• Also projects a dorsal (sound localization) and ventral (sound identification) stream

Sound waves

Oscillating movements in the air caused by vibrations of objects in the environment

• Properties of sound waves:

  • Frequency (wavelength): a measure of the lengths of a wave defined as the distance between the crests of sequential waves (shorter wavelength means higher frequency and vice versa)

  • Amplitude: the length from the trough of a wave to its crest (higher amplitude means more powerful vibration/louder and vice versa)

Basic taste receptors

1. Sweet

2. Salty

3. Bitter

4. Sour 

5. Savoury (umami)

Brain areas for taste and smell

• Primary gustatory cortex: the first region of the cortex to receive information from the gustatory system

• Lateral sulcus: a deep fissure that divides both the frontal and parietal lobes form the temporal lobe

• Olfactory epithelium: a strip of tissue in the nasal cavity that contains the chemical sensory receptors that support the sense of smell

• Sensory neurons transduce the chemical information and send it to the olfactory bulb (specialized brain structure at the bottom of the forebrain that receives the information from the olfactory epithelium)

Brain areas for touch

• Nerve endings project to the spine and then to the somatosensory cortex (region of the brain, located in the temporal lobe, that receives multiple sources of sensory information from across the body, including sensation of touch)

• Cortical homunculus: spatially organized map of the human body, contained within the somatosensory cortex, that processes touch information

Constructive vs direct

(Models of perception)

1. Model of perception in which the sensory information is used to generate a mental model of the environment that is assumed to have caused the sensory stimulus; Hermann von Helmholtz

   • Behavioural decisions are then based on the inferred model rather than the sensory stimulation itself

   • The fact that our two eyes take in different angles of an image shows that our brain takes an unstable, divided sensory input and turn it into a stable, unified model of the world

2. Theoretical approach to perception that holds that the sensory stimuli be used to guide behaviour in an action/perception loop, without the construction of a mental model; James Gibson

   • Perception is direct based on the relationship between the sensory stimulus and a person’s actions

   • There is a more one-to-one connection between external stimuli and perception

Ambiguity of sensory stimulus

• Our entire notion of the external world is a construct of the brain, based on available (highly ambiguous) sensory evidence

• Illusions serve to demonstrate that they are assumptions (brain usually assumes incorrectly, hence why illusions are illusions)

• We have to guess how light or dark an object is based on the amount of light coming from the object as well as other parts of the image

• The fact that perception requires guessing can also be seen in a class of stimuli called bi-stable (property of a stimulus that has alternating stable perceptual interpretations, ex. the cube with the red and green dots which changes the dot that you perceive to be closest to you)

Perception processing

• Bottom-up processing: perceptual processing that is applied generally to all stimuli and doesn’t depend on specific knowledge of the stimulus or its category

• Top-down processing: perceptual processing that leverages stimulus or category specific knowledge

• Phenomic restoration effect: involves the brain “filling in” missing sounds from a speech signal, based on expectations about which sounds belong to that portion of speech

Components of visual perception

1. Image segmentation: brain may want to know how to divide up the image into different objects and regions

2. Depth perception: while the image is 2-D, the brain wants to know where those objects are in 3-D 

3. Object recognition: brain wants to identify what the objects are

Visual grouping

• The perception of discrete visual elements as forming a larger pattern or whole

• Ex. important to recognize that a desk continues behind a chair even if the chair is obscuring the view of part of it

• Similarity: tendency to group together features of the image that have similar properties in some dimension (ex. colour or luminance)

• Proximity: tendency to group features of the image that are close together 

• Good continuation: tendency to see the image as ex. made up of two straight, overlapping lines rather than two separate V’s connected at their vertices

Depth perception

• Important to figure out both how far away an object is from you and to determine the shape of the object which is critical for recognition

• Because retinal images are 2D, the brain must infer the third dimension indirectly

• Many known cues of depth perception:

  • Objects blocking other objects

  • Binocular disparity: the fact that the image of the world falling on each of the two eyes is different; changes a function of how far away an object is in depth from the point you are fixating on 

    • Stereopsis: the use of binocular disparity (the fact that image falling in the two eyes is different) in perceiving depth

• Babies start to develop depth perception once they start crawling (indicating that it’s a learned skill)

Recognition

Matching an incoming stimulus to a stored representation in memory

• Template model: a simple model of recognition that depends on directly matching an incoming image to an image of an object or category in order to determine whether they reach some threshold of similarity

  • Subject to failure because every time that you view an object, the image it produces on your retina is different due to external factors such as changes in depth, lighting, and viewpoint

• Identification: a form of recognition that consists of determining whether a given image corresponds to a specific individual object or individual

• Classification: a form of recognition that consists of determining whether a given image corresponds to a class or category

• General recognition: the ability for a computer to classify a broad class of different objects

Inattentional blindness

The failure to perceive an object or event that occurs in plain sight; failure is not due to visual impairments

• Where you focus your attention determines what properties of a scene you are and are not able to report on

• Change-blindness: the inability to detect differences in two alternating flashed images

• People can sometimes miss changes even when they’re looking directly at a changing object

• Inattentional deafness: auditory information is not perceived when a different high-load task is being performed (high-load task usually has a visual component)

• Senses of hearing and vision share a limited neural resource