midterm
Research Methods
Scientific method — steps used to design studies that allow researchers to objectively and consistently find answers to specific research questions
Theory — general set of ideas about the way the world works
Hypothesis — testable statement guided by theories that makes specific predictions
Choose a research method — determine way that hypothesis is tested
Collect data — take measurements of the outcomes of test
Analyze data — understand data and discover trends or relationships between variables
Report findings — publish articles in scholarly journals
Revise theory — incorporate new information into our understanding of our world
paradigm shift — e.g. earth orbit around sun
Anecdotal evidence is not enough to draw scientific conclusion
single experience might not represent later ones
personal experience not like others
result might not have been affected by hypothesis
Experiment — scientific tool to measure effect of one variable on another
Independent Variable — variable manipulated by scientist
Dependent Variable — variable being observed by scientist
Experimental Group — with manipulation of independent variable
Control Group — no independent variable
WIthin-Participants Design — manipulating independent variable within each participant to minimize effect of participant differences on the dependent measure
problems — time, cost, difficulty, improvement
Practice Effect — improvement in performance over the course of an experiment as a result of experience, separate from the effect of the independent variable
Between-Participants Design
Confounding Variable — variable associated with independent variable that obscures the effects of independent variable on the outcome, makes it difficult to draw findings
try to make participants as similar as possible
Sampling — selecting a subgroup representative of the underlying population to study
Sample needs to reflect population so experiment can be generalized
Random Sample — subset of people selected at random so it is most representative of the larger population, equal chance of everyone
Random Assignment — assign participants to experimental or control group at random to avoid biases
fairly compare the difference conditions of the experiment
Bias
Placebo Effect — exhibits a response to a treatment that is not due to its real therapeutic effects
Participant Bias — may bias their performance to align with results expected
Blinding — participants do not know whether they belong to the experimental or control group
Experimenter Bias — actions made by the experimenter, intentionally or not, that influence the outcome of the experiment
Double-Blind Studies — neither the experimenter nor the participants know which group the participant belongs to
Data — quantifiable values which measure the outcome of a test
Descriptive statistics — describes data in a way that summarizes at a glance the overall results of an experiment
Histogram — used to report number of times groups of values appear, information about data frequency
Frequency Distribution — type of graph illustrating distribution of how frequently values appear
Normal Distribution — smooth, symmetrical, bell-shaped curve containing a single peak
Measures of central tendencies
Mean — average value
Outliers — extreme points, distant from others
Mode — value that appears most frequently
Median — center value in a data set when arranged numerically
Measures of variability — show how “spread out” data is
Standard Deviation
results can just be due to chance
Inferential Statistics — allow us to use results from samples to make inferences about overall, underlying populations
T-Test — statistical test that considers each data point from both groups to calculate the probability that two samples were drawn from the same population
P-Value — a probability (0-1) indicating the likelihood of this difference being observed even if no “real” difference exists
probability should be less than 5%
Statistical Significance — when difference between 2 groups is due to some true difference between properties of 2 groups and not due to random variation
Type 1 Error — believing a difference when a difference does not exist (false alarm)
Type 2 Error — failing to see a difference when a difference does exist (miss)
Observational research
avoid unethical experimental manipulation
Correlation — measure of strength of relationship between two variables
Correlation Coefficient (r) — number between -1 and +1, indicating both the strength and direction of the correlation
Correlation does not equal causation
Causation — one variable caused an effect in another variable
graph used to display the relationship between two variables in data set
Inductive reasoning uses a specific observation to generalize
Classical Conditioning
Classical Conditioning (Pavlovian) — learning of a contingency between a particular signal and a later event that are paired in time/space
Contingency — when one event reliably predict another, an association may be formed between these two events
e.g. dogs salivated before food reached their mouth, promotes survival/efficient (prepare for digestion)
e.g. antelope fleeing to sounds, smells, and sights
one stimulus reliably and accurately predicts the occurrence of a second stimulus
Unconditioned Stimulus US — any stimulus or event that triggers a response naturally without prior learning
Unconditioned Response UR — response after US, natural
Conditioned Stimulus CS — paired with unconditioned stimulus to produce a learned contingency, was previously neutral
may take several trials before CS can trigger a CR alone, becomes a contingent relationship
Conditioned Response CR — occurs once the contingency between the CS and the US has been learned
e.g. dog salivating at sound of metronome
| | Unconditioned
• no prior learning required | Conditioned
• prior learning required |
| --- | --- | --- |
| Stimulus
• triggering event | US | CS |
| Response
• outcome | UR | CR |
relationship
Acquisition — process by which contingency between CS and US is learned
negatively accelerated increasing function, large amount of learning takes place in early trials
some can be acquired in a single trial
Extinction — loss of CR when CS no longer predicts the US over trials, weakens response, less reliable
Inhibition — creates a new inhibitory response, does not unlearn
Spontaneous Recovery — sudden recovery of a CR following a rest period after extinction, just by encountering the CS
The conditioned response occurs at a reduced strength when the conditioned stimulus is presented alone.
Stimulus Generalization — stimuli similar to the CS will elicit a CR
example
extinction — flattens the curve
Stimulus Discrimination — causes extinction of stimuli similar to CS
CS + — presence of biological stimulus
CS - — absence of biological stimulus
simultaneous CS+ and CS- presentation — intermediate response
Generalization Gradient — graph demonstrating the extent to which similar stimuli elicit the same CR as the CS, appears like a bell shaped curve, original CS elicits strongest and less similar stimuli elicit weaker responses
Taste Aversion — rapid form of acquisition, taste
Phobias — anxiety disorder, exhibits an exaggerated, intense, and persistent fear of certain situations, activities, things, or people, often disproportional to the danger that is posed, often the result of a specific traumatic experience involving the feared stimulus
Treating — implosive therapy, encourages individual to confront CS that causes them anxiety by repeatedly presenting or imagining it in the absence of the anxiety-causing US
Treating — systematic desensitization, individual is presented with gradual exposure to the feared CS without exposure to US
Compensatory conditioning — counteract expected changes to body
e.g. sweet taste → rise in blood sugar → release insulin
not always beneficial → e.g. coke zero, morphine addict experiencing withdrawal
facilitating homeostasis — When we learn what cues predict danger, our bodies can respond to the danger earlier by responding immediately to those cues, homeostasis is keeping the internal state of the body constant
Addiction — stimulus, often a drug (US), elicits a compensatory response (UR), after continued use the environment in which the drug is taken (CS) will trigger compensatory responses (CR) preparing body for drug effect
Drug Tolerance — with each successive use of drug, effectiveness decreases, especially when taken in the same environment because it triggers compensatory responses before the drug is taken, requires more drug to achieve same effects
Overdose — individual administers too much of a drug body cannot compensate for, often occurs when individual takes a drug they have previously taken in a new environment
Withdrawal — symptoms occurring after a discontinuation of a medication or drug, occur most often when in the environment in which they previously took drugs, are internal compensatory responses that would normally oppose the drug effect, brings body to levels away from homeostasis
Non-Associative Learning — info about one external stimulus
Habituation — decrease in behavioural responding to a repeated stimulus, e.g. clothes
Sensitization — increase in behavioural responding to a repeated stimulus, e.g. horror movie
Associative Learning — how 2+ info are related
Classical Conditioning
Operant Conditioning — learn that a behaviour leads to a particular outcome
Long-term potentiation (LTP) — strengthening of synaptic connections between neurons
According to the textbook, which of the following findings most accurately captures how Dr. Tolman thought about learning and performance in his paper, "Cognitive Maps in Rats and Men".
Learning may occur despite no signs of improvement in performance.
Instrumental Conditioning
Classical vs Instrumental
Classical Conditioning — involuntary, association between biological stimuli
Instrumental Conditioning — voluntary, behaviours and consequences
Instrumental Conditioning (Operant) — learning of a contingency between a behaviour and a consequence
Law of Effect by Thorndyke
behaviours with positive consequence — “stamped in” (more often)
behaviours with negative consequence — “stamped out” (less often)
e.g. cat pulling on rope behaviour
Reinforcer — any stimulus that is presented after a response that impacts the frequency the response is performed
4 CONSEQUENCES:
Presentation of reinforcer | Removal of reinforcer | |
|---|---|---|
Increase in behaviour 😜✅⬆ | Reward (🫳🍬) | Escape (🙅💩) |
Decrease in behaviour 😿❌⬇ | Punishment (🫳💩) | Omission (🙅🍬) |
describe how reinforcement can be used to influence behaviour
works best when the consequence immediately follows the response
Only omission and punishment trainings will "stamp out" behaviours. Variable ratios of greater magnitude are more resistant to extinction than fixed ratios of lesser magnitudes.
Acquisition
Autoshaping
rewards spontaneous behaviour related to target behaviour
Shaping by successive approximations
rewards successive steps toward a target behaviour
reinforced for improvement
Chaining — technique used to develop a sequence of behaviours
Each behaviour is reinforced with the opportunity to perform the next behaviour in a sequence
reinforced for correct order
e.g. alphabet
Discriminative Stimulus (SD/S+) — signals to respond, behaviour will lead to outcome
Sδ/S- — signals to not respond, relationship is not valid
Can be generalized — stimuli similar to SD can also lead to response
can alter the generalization gradient if S+ and S- are both present e.g. green light and red light
graph
SD sets the occasion for voluntary response, does not elicit a reflexive response itself, signals when the response reinforcer outcome relationship is valid
Continuous Reinforcement — each response leads to a reinforcer
Partial Reinforcement
Ratio — reinforce after a num of responses
Interval — reinforce after some time since the last response
Fixed — constant reward
Variable — random ratio/interval before reward
partial reinforcement is much more robust than continuous reinforcement
lower chance of extinction
can be maintained for a period without reinforcers
Fixed
Variable
Ratio
FR-#
• **Ratio Strain** — if too stingy • pattern — “**Pause and Run”** • e.g. paid based on # shirts | VR-# • pattern — **linear ◦** slope shows average number of responses before reinforcement • e.g. slot machine || Interval | FI-#
• pattern — Scalloped
• response goes up just before the reinforcer, then pauses
• e.g. weekly quizzes | VI-#
• pattern — linear
• e.g. pop quizzes |graph patterns
Behaviour modification
Primary Reinforcer — satisfies biological need
Secondary Reinforcer — established through classical conditioning
Problem Solving & Intelligence
intelligence — the cognitive ability of an individual to learn from experience, reason well, remember important information, and cope with the demands of daily living
problem solving
forms of reasoning
Deductive — ideas/general info → specific conclusion (broad to specific, down)
Inductive — specific fact → general idea (specific to broad, up)
e.g. scientific method: theory (deductive) hypothesis → facts → new theory (inductive)
Functional Fixedness — our difficulty seeing alternative uses for common objects
tests
Reliability — produces the same result if one person takes it multiple times
Validity — actually measures the trait it is supposed to be measuring
lots of history of intelligence testing/what is intelligence
e.g. iq, multiples types of intelligence, learning styles
Multiple Intelligences — theory arguing that there are separate and independent intelligences for different purposes, brilliant in one area while lacking in another, eight intelligences were verbal, mathematical, musical, spatial, kinesthetic, interpersonal, intrapersonal, and naturalistic
Stanford-Binet Intelligence Test — involved 30 short tasks related to everyday life using all types of reasoning
Weschler Scales — scales standardized to produce an intelligence quotient, consists of Weschler Adult Intelligence Scale (WAIS) and Weschler Intelligence Scale for Children (WISC), mean score is 100, scores around mean fall along a perfect normal distribution with a standard deviation of 15
factors affecting intelligence
nature vs nurture — genetic vs environment
twins
Flynn Effect — raw IQ scores have been on the rise since 1932 (mean score is still always 100)
may be due to quality of life, education, nutrition, etc.
intelligence development
Schema — mental framework for interpreting the world around us
Assimilation — incorporating new information into existing schemas
Accommodation — modifying existing schemas to fit incompatible information
children are active learners — sees so many new things and uses accommodation to change schema
piaget’s stages of cognitive development
Sensorimotor (0-2) — can engage with world
struggles with Object Permanence — realization that objects continue to exist when no longer visible
Preoperational (2-7)
struggles with:
Egocentrism — can’t understand the world from a different perspectie than own
Seriation — logically ordering a series of objects
Reversible Relationships — e.g. brother/sister
Conservation — e.g. same amount of fluid poured in thinner, taller container
Concrete Operational (7-12) — schemas are based on own observations of the world
struggles with Abstract Thinking and Reasoning — hypotheses
Formal Operational (12+)
criticisms
Decalage — development of skills out of order
reliance on language abilities
biases and heuristics
Confirmation Bias — tendency to seek out information that supports our hypothesis
look for evidence that you are wrong
Heuristic — mental shortcut
Availability Heuristic — tendency to make decisions based on the information that is most quickly available to us
e.g. most lottery winners don’t win big but we assume so
Representative Heuristic — tendency to assume what we are seeing is representative of the larger category we have in our mind
e.g. steve has traits of a professor but has a much higher chance of being a farmer — more farmers in the world
e.g. gamblers — think that previous spins affect probability of next spin
Availability VS Representativeness
Bounded Rationality
System 1 Thinking — quick
System 2 Thinking — deep, slow
Anchoring — The bias to be affected by an initial anchor, even if the anchor is arbitrary
Framing — The bias to be systematically affected by the way in which information is presented
Language
1. Characteristics of Language
RAP
Regular — Language follows grammatical rules, combination of morphemes called syntax
Arbitrary — Lack of resemblance between words and their meaning (e.g., “dog”).
no indication of the meaning of a word given by its phonemes
Productive — We can combine words to create unlimited new sentences.
no limitation to the number of combinations of words that can exist
Sapir–Whorf hypothesis: Language influences how we think and perceive the world
However, language does not necessarily determine what we can think.
2. Structure of Language
Phoneme: Smallest unit of sound in speech (e.g., /d/, /o/, /g/ in “dog”).
Morpheme: Smallest unit of sound containing information (e.g., “cats” = “cat” + “s”).
Syntax: Rules that govern how words in a sentence are put together, grammar
Semantics: Meaning of words and sentences.
sentence can have correct syntax but meaningless semantics (e.g., “Colourless green ideas sleep furiously”).
3. Language Development
2 months / 8 weeks — cooing sounds, vowel sounds
4 months / 16 weeks — turns head towards voices
6 months — begins babbling, adds consonant sounds
drawn-out sounds made up of variety of vowels and consonants
may sound like a real sentence or question because of the use of inflection and rhythm in the production of the babble
combinations progress to become real words
8 months — complex, non-random babbling
2 years — uses 50-250 words, 2-word phrases, vocabulary and two-word phrases develop substantially
2.5 years — vocabulary > 850 words
1.5-6 years — language explosion, rapid growth in complexity and vocabulary, most children have mastered the major aspects of language
Order — Makes cooing sounds, turns head toward voices, imitates sounds, babbles
Speech segmentation — identifying individual words in continuous speech
Better infant speech segmentation is associated with larger expressive vocabularies at age two
Expressive vocabulary: Words a person can produce.
difficult when hearing an unfamiliar language
Very young infants smile and respond to other people's presence, which are deemed language-related skills
4. Universal Phoneme Sensitivity
Infants can initially distinguish speech sounds across different languages
including non-native languages
During the first year, they become increasingly sensitive to sounds in their native language.
Perceptual narrowing: Reduced sensitivity to speech contrasts that are not relevant to the language they hear.
Habituation: Reduced attention to a repeated stimulus.
Head-turn procedure: Researchers introduce a new sound after habituation; turning toward it suggests the infant detects the difference.
6-8 months — performs best
by 10-12 months — lost most of their universal phoneme sensitivity
5. Theories of Language Development
Social Learning Theory
Language is learned through:
Imitation: Copying others.
Reinforcement: Consequences encourage or discourage behaviours. (Instrumental Conditioning)
Evidence: Children learn by observing and interacting with others.
Limitation: Children produce novel sentences and grammatical errors they were never taught.
Genie: A child who experienced extreme language deprivation. Her case highlights the importance of early language exposure and social interaction.
Innate Mechanism Theory
Associated with Noam Chomsky.
Humans have an innate biological predisposition to acquire language.
Language Acquisition Device (LAD): Chomsky’s proposed innate mechanism for acquiring grammatical rules.
Children actively learn and apply grammatical patterns rather than simply copying speech.
Baby Nancy seems to prefer to listen to a stranger speak rather than listen to her mother playing piano.
Neural activation — prefer speech sounds over non-speech sounds
Supporting evidence: Children generate novel grammatical combinations; some deaf children spontaneously develop structured sign systems.
Common Language Errors
Overextension: Applying a word too broadly (calling every four-legged animal “doggie”).
Underextension: Applying a word too narrowly (calling only your own dog “doggie”).
Overregularization: Applying a grammatical rule to an exception (“runned” instead of “ran”).
Key distinction: Social learning emphasizes experience and reinforcement; innate mechanism theory emphasizes biological preparedness. Both biological and environmental factors can contribute to language development.
6. Animal Communication
Honeybees: Waggle dance communicates food direction and distance.
Washoe: Chimpanzee that learned signs from American Sign Language. — not regular
Sarah: Chimpanzee that learned to use plastic symbols. — not productive
Kanzi: Bonobo that learned lexigrams through immersion and not conditioning. — arbitrary
Main takeaway: Animals can communicate meaningful information, but the animals studied demonstrated more limited grammatical flexibility and productivity than humans.
Lecture
Language is unique to humans. It is a complex system of communication allowing us share details andemotions with others
Changes over time — e.g. slang, some stay longer and some change
e.g. changing cultural values
Swearing — why do we swear? why do people get upset by certain words? why do we use certain words to make people upset?
Taboo words activate brain areas associated with negative emotion — right hemisphere
forces listener to think about an unpleasant or emotionally charged thought
Supernatural
damn, hell, for Pete’s sake — more potent in religious societies, awe and fear
Body effluvia and organs
shit, piss, asshole, snot, bloody — effluvia are major vectors of disease, disgust
Disease, death, and sickness
“a pox on you”, “a plague ‘o both your houses’ — dread
Sexuality
fuck, screw, dick — why negative? exploitation, illegitimacy, incest, jealousy, cuckoldry, desertion, abuse
Family/heritage
“Your mama’s so…”, “son of a” — general insults against family members, shame or hurt pride
Hate speech
racist, homophobic, sexist slurs — denounce someone as bad or “other” because they belong to a different group
why?
Euphemism — we have to talk about this for a while for a specific purpose, but let’s avoid thinking about how awful it is.
Dysphemism — i want you to think about just how awful this is.
e.g. shit vs feces, fuck vs copulate
Emphatic swearing
Cathartic swearing
Rage circuit theory — when mammals are injured or confined, emit sudden angry noise to startle attacker
Broca’s area — Production of language.
Dr. Laurel Trainor — the exaggerated changes in pitch helps infants discriminate between vowel sounds, aiding in the learning of vowel sound categories
Transparent orthographies — the more transparent orthographies a language contains, the fewer associations between letters and phonemes must be learned
Foreign Accent Syndrome — very rare cases following serious brain injury or stroke, some individuals sound as though they are speaking their native language with a novel, acquired foreign accent
Accent — manner of pronunciation unique to an individual, geographical location, or nation, occurs both between and within languages
Infant-Directed Speech — natural tendency for people to use higher pitched and exaggerated tones whenspeaking to infants, may help infants learn to segment speech
Categories & Concepts
1. Categorization
Categorization: Organizing incoming stimuli into categories to help us make sense of the world and take appropriate action.
We constantly categorize objects, people, situations, and experiences.
It often happens automatically, outside our conscious awareness.
Without categorization, every decision would become overwhelming.
2. Functions of Categorization
There are three main functions:
Classification: Groups dissimilar objects into the same category.
Example: A Chihuahua and a Golden Retriever are both classified as dogs.
Understanding: Identifies the intentions of a situation. — ability to evaluate a situation and act appropriately based on prior experiences.
Communication: Ability to describe complex ideas or objects using a single label
One category label can communicate a complex idea without explaining every detail.
The Illusion of the Expert
Definition: "The feeling that a task must be simple for everyone because it is simple for oneself."
Categorization can feel effortless, making us assume it is easy for everyone.
In reality, categorization is complex.
Simple, rather than complex categories, leave us susceptible to the Illusion of the Expert
3. Rules of Categorization
Researchers investigated whether categories could be defined using simple rules.
Some categories are easier to define than others.
Simple categories, rather than complex categories, leave us susceptible to the Illusion of the Expert.
Rules do not sufficiently explain categorization because many categories are difficult to define using specific rules.
4. Prototype Theory
Prototype: An internal representation of a category.
Prototype Theory: Objects are categorized by comparing them to an internal “best” or average representation of the category.
Prototypes are the average representation of all personal experiences.
A prototype does not have to be an actual object that exists.
New objects are compared to this average representation.
Example:
A robin is a typical bird for many people.
A penguin is less typical.
People verify "A robin is a bird" faster than "A penguin is a bird."
Why? A robin is more similar to the average representation of a bird.
Limitations of Prototype Theory
Prototype theory struggles to explain why internal representations change over time.
A single new experience should have little influence on the average representation.
However, research shows that even one recent experience can affect categorization.
5. Exemplar Theory
Exemplars: Individual examples that we compare to for categorizing novel stimuli.
Exemplar Theory: Objects are categorized by comparing them to all past examples of similar objects.
Instead of comparing an object to one average representation, we compare it to individual examples stored in memory.
If a new object sufficiently resembles a remembered example, we categorize it as belonging to that category.
Example:
You see a new dog.
You compare it to dogs you have encountered before.
If it resembles a previous example, you identify it as a dog.
Evidence for Exemplar Theory
Brooks, Norman, and Allen study:
Experienced dermatologists diagnosed skin disorders using slides.
Two weeks later, they diagnosed another set of slides.
Some disorders were repeated using different slides.
Dermatologists were 20% more accurate when they had previously encountered an example of that disorder.
Conclusion: A single recent example improved categorization, supporting Exemplar Theory.
6. Prototype Theory vs. Exemplar Theory
Prototype Theory | Exemplar Theory | |
|---|---|---|
Categorizes by comparing object to | internal average | past, similar objects. |
Uses an average representation. | Uses individual examples stored in memory. | |
Can explain why we respond faster to more representative objects | yes | yes |
Can exp;ain why a single encounter changes categorization patterns | no | yes |
May explain simple categorization better. | Currently provides a more compelling account of human categorization. |
Important for tests
Prototype = average representation
Exemplar = individual past examples
Both explain why we respond faster to familiar or representative category members.
Exemplar Theory explains why a single recent encounter can change categorization.
Prototype Theory may explain simple categorization better.
Both prototype theory and exemplar theory are experience dependent, and vary from person to person.
7. Development of Categorization in Children
Children as young as 3 years old can understand and generalize categories.
Three important abilities:
Generalize category information: A child learns something about one dog and applies that information to other dogs, even if they look different.
Understand hypothetical categorization: Children can understand that changing an object's appearance or function can affect how it is categorized.
Understand innate properties of categories: A raccoon painted to look like a skunk is still recognized as a raccoon.
8. Animal Categorization
Research demonstrates that baboons can learn to categorize objects.
Baboons were taught to classify objects as food or non-food.
They achieved approximately 90% accuracy.
They could also classify objects using abstract rules such as same and different.
They could apply these rules to novel objects.
Important: Animal categorization does not necessarily demonstrate language ability.
9. Categorization and Stereotyping
Stereotyping: Assuming that an entire social group of people share the same characteristics, traits, and behaviours.
Categorization allows us to make predictions about new members of a category.
However, applying assumptions to entire social groups can lead to stereotypes.
We may assume a new individual shares the characteristics associated with our mental representation of that group.
Science of Learning
cramming
takes more time
does not go into long-term memory
How to make learning efficient and long-lasting?
Where — Why you should be mindful of distractions in your environment and proactively suppress them
When — Why it’s more efficient to distribute your studying over time and across multiple sessions
How — Why practice testing and self-explanation are better than rereading, highlighting, or copying notes verbatim
Desirable Difficulties — Why strategies that initially slow down learning can actually be most efficient in the long run
where to study
task switching — decreases performance
pomodoro technique — on task 25 min, break 5-10 min, 3-4x, break 30 min
remove distractions
when to study
spacing effect — distributing studying across time is more efficient
retains information
save time
how to study
repeated exposure — rereading, highlighting, verbatim copying notes
tends not to work well
fools us
rapid short-term learning
intuitive and endorsed
effective of fluency
little output
retrieval practice — combination of output as well as input
practice testing
high output — retrieves from memory
self-explanation
actively engaged with learning material instead of a passive recipient of information
3x3 rule — successfully recall material 3 times in one initial study session, then recall the same material on 3 subsequent sessions with each session spaced roughly one week apart
interleaved practice
learn multiple lessons, mix up practice questions for multiple topics
desirable difficulties
good study methods will start slow but be better in the long-term
lecture
successive relearning — learn content to a specific criterion (practice retrieval plus study until correct), relearn the same material