1 Week1:Introduction Overview of Cognitive Psychology
• What is cognitive psychology? • Why do we study cognitive psychology? • History of cognitive psychology
Information-processing approach
• The human brain and neurons
Unit Overview • Goal: Develop a scientific understanding of how the human mind processes information • In essence, this is an introductory/intermediate level cognitive psychology unit
o We will build upon your first-year units (PYB100 and PYB102) o More emphasis on a data-driven, experiment-oriented aspect of cognitive
psychology
What is Cognitive Psychology? • The science of:
o how the mind is organized to produce intelligent thought o how the human mind is realized in the brain
• Why do we study cognitive psychology?
o Why not? (i.e., curiosity-driven intellectual inquiry) o “Real-world” purposes
Why Do We Study Cognitive Psychology?
• Understanding mechanisms governing human thought will be useful for studying:
o why certain thought malfunctions occur (clinical psychology) o how people behave with other individuals (social psychology) o how financial decisions are made (business and economics)
Why Do We Study Cognitive Psychology?
• Practical applications o For example:
• False memory and eyewitness testimony • Spatial cognition and the design of GPS systems
o Understanding brain disorders o e.g., research on navigation systems and Williams Syndrome
Williams Syndrome
• Patients with Williams Syndrome (WS) have difficulty in processing visuospatial information
• However, their spatial navigation is not entirely impaired o They can learn repeated routes better than age-matched healthy individuals
(Bostelmann et al., 2017) • How do we make sense of this? • Here comes cognitive psychology!
o Humans have two distinct navigation systems: response-based (don’t need to think about locations, just follow directions, WS can perform) and place-based (I am in F block and I want to go the O Block, WS does not have place-based)
o Brain structures that are critical for the response-based system are not affected in WS
o WS example of how cognitive science can give answers to real life problems
History of Cognitive Psychology Early philosophy: where does knowledge come from?
• Nativism: knowledge is innate o Plato, Descartes, Kant o We possess all the knowledge we need, learning is uncovering this
• Empiricism: knowledge is acquired through experience
o Aristotle, Bacon, Berkeley, Locke, Hume, Mill ** No need to remember the names of philosophers
** Need to know Nativism and Empiricism 1.
Early Psychology • Different ways of studying the human mind
o Structuralism: by analyzing the mind into components o Functionalism: by understanding what the mind does in response to stimuli
(environments) • Behaviorism: by studying input-output association
Structuralism Structuralism
• Analysis of the human mind into primitive componential elements o Basic idea: just like water can be broken down into component parts (i.e.,
hydrogen and oxygen), the mind can be broken down into elements (such as sensation and thought)
o Used chemistry as a model o This can be done by introspection – trained psychologist looking into their own
mind o Wundt and Titchener
• Changed the nature of psychology research— from philosophical to (more) scientific • Two problems: subjective and unreliable, no generalisable
Functionalism Functionalism
• The mind is defined solely by its function o how it responds to various stimuli (e.g., sensory inputs) o As long as the same functional role is played, it doesn’t matter what components
the mind is made of o This was also studied by introspection (but less intense and analytic than
structuralists’ method) o William James
• Provided many ideas that formed the foundation of contemporary psychological research • Weakness: little or no empirical support
Behaviorism
• Only the (directly) observable should be studied o Strictly about stimulus-response relations o Rigorous experimental approach o Watson, Skinner
• Played an important role in introducing experimental methods to psychological research,
data driven psychology • Kept the mind completely as a black box
Cognitive Revolution Cognitive Revolution • During World War II, research on human performance was intensively conducted
o What makes a better soldier? – Need to behave accordingly in extreme stressful situations
o This revealed a shortcoming of behaviorism—it was not so useful for solving practical issues – ignores what is going on inside the human mind (black box)
• Development in other scientific fields o Information theory o Linguistics o Computer science (especially artificial intelligence) o They provided psychologists with tools and models for the analysis of intelligent
behaviour
Information-Processing Approach
• Cognitive psychology = re-defining psychology as the science of human information processing
Opened black box to look at the processes that are occurring.
Decomposing Mental Processes • Formulate a theoretical model of how output is made from a given input
o Models usually consist of multiple processing stages • Measure the time taken for each processing stage – i.e. collect data • Analyze which variable affects which processing stage
Sternberg Paradigm
Sternberg Paradigm • Was this number in the list?
9
• Horizontal axis – number of stimulus • Vertical axis – time • 2 numbers – 460ms • 6 numbers – 610ms • time increases the more numbers there are. • The rate of increase is constant, add one digit e.g. 2 to 3, the reation time increases by
38ms, 5 to 6 – increase is again 38ms • Each of the comparisons take 38ms
Was this number in the list? 9 (harder to see)
Should take longer as initial perception takes longer. Reaction time increases but by the same amount across the list
Was this number in the list? 9 Change the response buttons – harder to press
Red line - Everything should get longer but increase should be the same across the board. If data matches the predictions – your model is supported
The Science of Cognition The Science of Cognition All are one thing , but your main focus may be:
• Cognitive psychology o the science of how the mind is organized to produce intelligent thought and how it
is realized in the brain • Neuroscience
o the study of the structure and function of the nervous system • Cognitive neuroscience
o attempts to gain insights into cognitive processes by studying the brain and behaviour
Cognitive psychology is the science of: a. how mental disorders such as schizophrenia and autism can be treated b. how the human mind processes information to produce intelligent thought and behavior c. how people behave differently when they are by themselves and when they are in a group d. how unconscious drive controls our thought and behavior
Answer: B
Testing for learning • In my lecture, I will give you exam-style questions from time to time and ask you to
actually work on them • Why do I do this? Because this should help you better learn lecture materials
o This is not to give you a sneak preview of possible exam questions o This is not just to “switch gears” either o Instead, this is based on the so-called testing effect
Testing effect
• A typical learning framework o Learning occurs while you are studying o Testing is only for assessing what you have learned
• The testing effect o Testing (i.e., retrieval of information from memory) is actually a powerful learning
tool o It works best when you can receive immediate feedback o For details, see Roediger and Butler (2011)
• Front – Anterior, rostral • Back – posterior, caudal • Top – superior, dorsal • Below – Inferior, ventral • Lateral – outer side • Medial – inner side of brain
• A cell in the brain that accumulates and transmits electrical activity • Plays essential roles in neural information processing • Neurons are connected with each other at synapses, forming a network
• Neurons most important cell in the brain – processes information • Gulia cells – supporting functions so that neurons can function better • Neuron forms networks, connects by synapses
How the Neuron Works
• For each neuron, how it works is quite simple— whether it fires or not • The rate of firing can vary
• Fires – generating a action potiental, crosses threshold, burst of electrical activity, no half-
way wither fires or does not fire. All or none. • Rapid firing – neuron is activated more strongly
How the Neurons Work
• What single neurons can represent is quite limited • It is thought that groups of neurons, not individual neurons, represent information in the
brain
o Thus, when we talk about the brain in this unit, we will be mostly talking about areas of the brain (groups of neurons), as opposed to single neurons that constitute the brain areas
Different Areas of the Brain
• The brain is not one uniform thing • Different areas of the brain have different functions
• No need to memorise the diagram • Brain is made of multiple areas which have multiple functions
2 Week2:Psychophysics • Thresholds
o What is the smallest change in a stimulus that can be detected? o What is the smallest/largest magnitude of stimuli for each sensory modality?
• Signal detection– How do we detect a signal out of noise?
Thresholds Thresholds
• Difference threshold o The smallest change in a stimulus that can be detected (a.k.a. JND–Just Noticeable
Difference)
• Absolute threshold o The minimum intensity of a stimulus that can be detected
• Weber’s law
• Weber found that the size of the JND is a function of the magnitude of a reference stimulus o For example, if a weight has to be 41 g before it can be discriminated from a 40 g
reference weight (JND = 1 g), then the JND would be 10 g for a 400 g reference weight
• 1/40 = 0.025 => Weber Fraction • JND changes according to the reference object
Weber’s law
• This constant ratio of JND and the intensity of a reference stimulus (i.e., DI / I) is called the Weber fraction for that stimulus dimension
Fechner’s law
Fechner’s law • Fechner built upon Weber’s findings
o Fechner’s idea: if a Weber fraction is constant for a given stimulus dimension, then the mind might use the Weber fraction as a unit for perceiving that stimulus dimension
• To measure something, you need a unit, the unit must be constant • k = measurement
Implications of Fechner’s law
• Fechner’s law relates internal experience (psyche) and physical environment (physics) o Psyche + physics → Psychophysics
• Fechner’s law is about the absolute, not relative, intensity of a stimulus o Turning the focus of research from difference thresholds to absolute thresholds
• Fechner’s law asserts that our psychological experience of the intensity of a stimulus tends to change less quickly than the actual change in stimulus intensity
How do we measure thresholds?
• It is not always easy to measure thresholds in part because we are so good as perceivers o For example, we can (Galanter, 1962):
Ø sight a candle flame from a distance of 48 km on a clear dark night Ø hear a mechanical watch ticking at a distance of 6 m in a noise-free
environment Ø taste a teaspoon of sugar dissolved in 7.6 liters of water Ø smell one drop of perfume diffused through three rooms Ø feel the wing of a fly dropped on our cheek from a height of 7 cm
How do we measure thresholds?
3 ways to measure thresholds: • Thus, procedures have been developed to measure thresholds as precisely as possible
o Method of constant stimuli o Method of limits o Staircase procedures
• Each method has its advantages and disadvantages •
Method of constant stimuli • Construct a set of stimuli with magnitudes ranging from above to below the presumed
threshold value • Present these stimuli a number of times in a random order • Participants respond whether or not they detect the stimulus on each trial (Yes/No) • Plot the proportion of detections occurring at each stimulus magnitude • The threshold is taken as the magnitude at which the stimulus is detected a criterion
proportion of the time (e.g., 50%)
• Threshold is point at which the detection rate is 50% - 50% of the time the stimulus is detected
Method of constant stimuli
• Advantages o Allows the shape of the psychometric function to be established (more trials –
more accurate) o Provides an accurate estimate of threshold
• Disadvantages
o Requires pre-testing to roughly estimate the threshold o Wastes a lot of trials which lie far from the threshold (making this method time-
consuming) o It is difficult to measure changes in threshold over brief time periods with this
method
Method of limits • This method measures the threshold without determining the shape of the psychometric
function • The method of limits uses ascending and descending series of trials
o Descending series • Present the stimulus at a suprathreshold level • Decrease stimulus intensity in small steps until participants can no longer detect the
stimulus o Ascending series
• Present stimulus at a subthreshold level Increase stimulus intensity in small steps until participants can detect the stimulus
• Start high continue incrementally down until stimulus is detected • Then change to low intensity and incrementally step up until stimulus has been detected.
Continue those steps. • Average of the response changes is the threshold
Method of limits
• Advantages o More efficient (i.e., quicker) than the method of constant stimuli o Still reasonably accurate in determining the threshold (not as accurate as method
of constant stimuli) • Disadvantages
o Many trials are still “wasted” as they are presented at intensities away from the threshold
o Participant may habituate (get used to giving a “yes” or “no” response) and thus overshoot the true threshold – this is why you have to alternate between ascending and descending, if you just went descending the average would be pushed downward, opposite effect if you just used ascending – thus alternating cancels the overshooting effect out.
o The overall shape of the psychometric function cannot be derived, ignores the extreme ends and makes measurement more efficient.
Staircase procedures
• Staircase procedures are designed to overcome these problems o They involve linked series of ascending and descending runs with each successive
run being based on the outcome of the preceding run o The stimulus is presented either above or below threshold and the intensity is
changed in small steps until a reversal (change in response) occurs o The direction of change is then reversed when another reversal in response occurs o The procedure is terminated after a criterion number of reversals
The threshold is taken as the average of these reversal intensities
Staircase procedures • Advantages
o Even more efficient than the method of limits o Can be modified in a number of different ways to overcome other limitations e.g.
instead of one N response you require 2 (or more) N responses before the reversal, same for Y responses;
• Disadvantages o Estimation of the threshold tends to require more complex calculations (especially
when the procedure is modified), making it less intuitive
Staircase procedures • The standard procedure yields an estimate of the 50% threshold • By requiring two “yes” responses before the stimulus intensity is decreased, this procedure
can estimate the 70% threshold o That is, staircase procedures can be used to figure out the overall shape of the
psychometric function
Staircase procedures • The issue of habituation can be addressed by running multiple series of trials
simultaneously
Signal Detection Signal detection • We can never perceive stimuli under the perfect conditions
o There is always some noise, even when there are no stimuli in the environment • And we can never know whether we are perceiving the true stimuli (signal) or the noise
(we only know that our neurons are firing, we don’t know the cause) • As a result, often, what we do is to use a certain criterion with which we (unconsciously)
decide that we have perceived the signal
• Horizontal axis – level of activity in brain • Lower level – attribute to noise, higher activity – attribute to signal • Frequency of activity sensitivity level - Noise curve & Signal + Noise curve
• Decision criterion – you decide on level • If activity level is higher than the criterion level – interpret as Yes • If activity level is below the criterion level – interpret as No
Signal detection • On some signal trials the level of activity will be above the criterion, leading to a correct
“yes” response (hit) • On other signal trials the level of activity may be below the criterion, leading to an
incorrect “no” response (miss) • On some catch trials the level of activity maybe above the criterion, leading to an incorrect
“yes” response (false alarm) • On other catch trials the level of activity will be below the criterion, leading to a correct
“no” response (correct rejection)
Above – 2 correct responses – hit and correct rejection
Above – Incorrect results – false alarm and miss
Signal detection • The separation between the signal + noise and noise distributions tells us how sensitive an
observer is to that stimulus o This measure of sensitivity is called d-prime (d’). o The closer the distributions or the smaller the d’ the less sensitive o The further apart the distributions, the larger the d’, the more sensitive to the
stimulus, doing a better job distinguishing between signal and noise, less overlap, less miss & FA, more Hits
Signal detection How do we estimate d’?
• The proportion of hits (or misses) tells us the location of the criterion relative to the signal + noise distribution
• The proportion of false alarms (or correct rejections) tells us the location of the criterion relative to the noise distribution
• Convert these proportions to z-scores o These scores tell us the distance from the criterion to each distribution mean
• d’ is then the “sum” of these distances o d’ = Z(FA) − Z(HIT)
Distribution of Z scores
Signal detection • d’ is a measure of sensitivity which is independent of response bias • In other words, it is possible to get the same d’ from a range of different response patterns • Moving the criterion bar also changes the response patterns • We can see this effect in a receiver operating characteristic curve (ROC curve)
This curve shows the range of hit and false alarm rates that yield the same sensitivity (d’)
3 Week3:PerceptionandCognitionHearing #1 Auditory Physiology and the processing of Sound
• The nature of sound • Basic physiology
o Outer ear o Middle ear o Inner ear (cochlea) o Central auditory pathways
Theories of the encoding of sound frequencyThe Nature of Sound #1 • Sound is caused by changes in air pressure, air is pushed – moves air particles along,
push and pull, particles leave an area and move to the next space, then pushed again. • Sound is a wave of air. • These pressure waves are characterised by amplitude, frequency and phase
o Amplitude (decibels: dB) = loundness height of sound wave, strength, amplitude is physical dimension – i.e. how loud, loudness is the subjective perception
o Frequency (Hertz: Hz)= pitch; Speed, higher frequency = higher pitch
o Phase = position within a cycle degrees and angle of position in the wave 0-360°
• A pure tone (sine wave) is the simplest sound wave
4 The Nature of Sound #2 Loudness of some common sounds
dB = decibels = amplitude = loudness dB Source 180 Space shuttle launch (from 45m) 160 Loudest rock band 140 Pain threshold 120 Loud thunder 111 Loudest recorded shout 100 Heavy traffic noise 80 Vacuum cleaner 60 Normal conversation 40 Quiet office 20 Soft Whisper zero Absolute Threshold of hearing
• The Nature of Sound #3 Frequency:
Hz = Hertz = Frequency = Pitch
• Human hearing range: 20-20000 Hz • One cycle per second is a Hz • Most of our auditory experience involves a small fraction of this range
Eg typical vocal range: 80-1100 Hz
• World health org – study in unsafe levels of noise from earphones – 85dB for 8hours or 100dB for 15mins in damage.
• 50% of young people are exposed to unsafe levels through use of headphones, 40% at entertainment venues.
• Once damaged cannot reverse.
The Nature of Sound #4 • Complex sounds can be build up from series of sine waves of varying amplitude, frequency
and phase • We can decompose complex sounds into their sine wave components by a process called
Fourier analysis. • Can break down any complex sound. • As we will see, the auditory system essentially does the same thing.
Graphs 2-4 above represent sine waves.
The Nature of Sound #5 • The lowest frequency component of a complex sound is called the fundamental • Many complex sounds are made up of harmonics – integer multiples of the fundamental
o If the fundamental frequency is 440 Hz, then the 2nd harmonic will be 880 Hz, the 3rd harmonic will be 1320 Hz and so on.
• eg if you have 3 tones – 440, 880, 1320 (all harmonic) and you mix them, the result is a
sine tone. The tones are integer multiples – if you mix 440, 800, 1320 (440 and 1320 are harmonic, but 800 is not and integer multiple)
– sounds like there are 2 different tones on top of each other.
The Ear
• Outer ear • Middle ear • Inner ear –
The Outer Ear Pinna • Increases the sound amplitude – amplifies the sound (air pressure) • Helps determine the direction from which a sound is coming
External auditory canal • Provides protection of inner structures • Increases the sound amplitude – smaller than pinna, as sounds travels into external auditory
canal the sound is amplified (air pressure) Eardrum (tympanic membrane)
• First thing in the body to detect sound • Vibrates in response to sound waves • Moves bones in the middle ear
The Middle Ear
• The Ossicles transmit the vibration of the eardrum (with some amplification) into the
cochlea through lever actions • Ossicles are connected to the inner ear structurre and the cochlea • They also provide protection against high amplitude sounds
o Muscles attached to the ossicles restrict the bones’ movements • Smallest bones in the human body
(Know functions and how they work, no need to remember the names)
The Inner Ear #1
• The inner ear consists of:
o Semi-circular canals (important for our vestibular sense – ie sense of orientation) – not auditory structure
o Cochlea • The cochlea contains auditory sensory receptors
o Oval window Ø Membrane covering an opening in the cochlea, entry to cochlea Ø The staples is attached directly to the oval window (ie this is where the
vibrations get into the cochlea) Ø The oval window is much smaller than the eardrum – the size difference
helps further amplify the sound waves o The cochlea is filled with a watery liquid, which moves in response to the
vibrations coming from the middle ear.
The Inner Ear #2
• Three canals in the cochlea
o Vestibular canal o Tympanic canal o Cochlea duct
• These canals are separated by:
(** Don’t need to know exact names, just ‘membrane’) o Reissner’s membrane o Basilar membrane
Ø On which auditory receptor cells (hair cells) are located (in the cochlea duct)
Ø Hair cells convert vibrations into neural signals • These membranes vibrate in response to vibrations of the oval window
The Inner Ear #3 • When the basil membrane vibrates, hair cells are also set in motion • This converts the vibrations into neural signals
The Inner Ear #4
• Entire cell is vibrating, fibres connect the ‘hairs’, when vibrations push the hair to one side the fibres cause the caps to open and potassium flows into the hair cells. In flow of potassium ions activates hair cell causing the neuron to fire.
• Vibration of the hair is last point of physical air pressure movement, from now on it is the neural signal.
• Central Auditory Pathways #1 • Nerve fibres from each cochlea synapse in a number of sites on the way to the primary
auditory cortex o The cochlear nucleus o The superior olivary nucleus o The inferior colliculus o The medial geniculate nucleus
• The signal arriving at the cochlear nucleus splits and goes to each of the ears is present in both hemispheres, cochlear nucleus only receives signal from respective ear.
o Beyond this point, input from both ears is present in both hemispheres
The Auditory Cortex #1 • Granted that a number of structures exist before the primary auditory cortex, what tasks are done there?
• Animal studies have shown that many auditory tasks can be performed without the auditory cortex being present! (Auditory cortex is the last stop)
• These include the responding to: o The onset of sound o Changes in sound intensity o Changes in sound frequency
• The Auditory Cortex #2 • Similar studies reveal task which cannot be performed without the cortex. These include:
o Discriminating the pattern of several tones o Discriminating the duration of sounds o Localising sound in space
• Thus, it seems that the cortex deals with more complex auditory tasks while the lower
structures deal with simple aspects of sounds. • Speech perception requires structures beyond the primacy auditory cortex. •
Frequency Coding #1 • Sounds are made up of a mixture of sine wave components • The auditory system isolates and identifies the frequencies of the components (as though it
carries out Fourier analysis)
o Frequency Coding #2 • The basilar membrane is about 30mm long and varies in stiffness and width along its
length • Travelling waves move along the basil membrane and peak at different points depending
on the frequency of the sound
o Frequency Coding #3 • Thus, the location (on the basilar membrane) of a peak identifies the frequency of a sound.
• When people have damage to a specific part of the cochlea, they tend to suffer from frequency-specific hearing loss, one section of the frequency range – not all of hearing.
• Stimulating auditory nerves at different cochlear locations leads to perception of sounds in different pitch
o Actually, this is one way in which the cochlear implant works. o
•
Frequency Coding #4 • Hair cells are tuned to different ranges of frequency according to the location along the basilar membrane
• Louder sound? – peaks higher but at the same frequency
Frequency Coding #5 • The auditory neurons in the primary auditory cortex are arranged in an orderly manner according to sound frequency
• This organisation is seen repeatedly in the auditory pathways o That is, tonotopic maps are present in the auditory system
• Hearing #2 • Outline • Auditory perception
o Pitch (frequency) o Loudness (amplitude) o Space perception
• When auditory information and visual information are available simultaneously
• Pitch Perception • So far, we reviewed how sound frequency is encoded in each ear (monaural encoding)
• Does one ear do all the work for pitch perception? o
Pitch Perception • Perception of a missing fundamental o When higher-order harmonics are present in the absence of the fundamental (first
harmonic), the missing fundamental is “filled in” o What if some harmonics are heard through only one ear?
• Sound 1 – 200 is missing, 400 is lowest so it is the fundamental, 600 and 100 are not
integer multiple of the fundamental – so you should hear 3 sounds • Sound 2 – all are integer multiples of the fundamental 200 – 1 sound
o Pitch Perception • A missing fundamental is perceived even when harmonics are presented to different ears
• Both hearing situations are the same • Need information from both ears •
Pitch Perception • Binaural pitch encoding o Structures beyond the cochlear nucleus should be contributing to pitch perception.
• Loudness Perception • Human auditory range (in terms of loudness perception): approx. 0-120 dB
o 0 dB = absolute threshold of hearing o 120 dB = loud thunder => past this we hear but we can’t tell the difference o from 0-120 dB – the range of this intensity is roughly 1000000000000 to 1!
• Loudness Perception • Two basic mechanisms
o Overall firing rates of hair cells o Range of firing – as amplitude goes up, more hair cells (range gets larger) start
responding
• When amplitude goes up the range of the hair cells firing increases •
Loudness Perception • Factors that affect loudness perception o Sound duration (longer = louder) o Frequency
• Loudness Perception
• Reference sound at 1000Hz (pitch) versus amplitude (loudness) 20 dB. • New sound - adjust the loudness of the new sound so that new sound and reference sound,
sound as loud, adjust the loudness of the new sound • eg 20Hz new sound, amplitude has to go to 80 dB • eg 100Hz, 38dB • As sound frequency goes down, the sound is quieter, need to increase dB in lower
frequency sound to get the same level of loudness • Lower frequency sounds are quieter than higher frequency
•
Loudness Perception • Generally, high frequency sounds are perceived to be louder (up to about 5000Hz) o Around 3000-5000 Hz, sounds are perceived to be loudest o As the amplitude goes up, the effect of frequency becomes smaller
• E.g. reference sound at 1000hz, 20dB, new sound – change the Hz of the new sound it
sound as loud as the reference – 100 Hz, amplitude can be lower (but still higher than 20dB) 38dB as sound frequency goes down it sounds quieter, have to increase the loudness level
• Lower frequency sounds are quieter than higher frequency sounds • As frequency goes up the sound gets louder
Auditory Space Perception • In auditory space perception, you try to determine a sound’s:
o Horizontal direction (azimuth) - not bad o Vertical direction - ok with head movement o Distance - not good, especially in open space
• Overall, vision provides more precise information about an object’s location
o What are the advantages of auditory space perception? We can only see what is in front of us, but we can hear 360° around us
• Auditory Space Perception • Why can we auditorily localise sounds at all?
o Nothing on the basilar membrane directly indicates sound locations. o Basilar membrane – primarily driven by sound frequency
• Auditory space perception is a binaural process
o Interautral time difference Ø Onset difference Ø Phase difference
o Interaural intensity difference
• Interaural Time Difference Onset Difference
• Unless a sound is directly in front or behind you, it reaches two ears at different times (onset difference)
• In the diagram, the sound will reach your left ear first as it is closer to the sound source i.e. time difference between the 2 ears – interaural time difference/onset difference
• Difference changes in a systematic way according to the location of the sound in relation to your head
• E.g. sound source directly in front of you – distance from both ears is equal, therefore no difference; see graph at 0
• Move sound source to the left (in picture) – create a time difference, maximise the time difference; graph – interaural time difference increases – time difference reaches the maximum.
• Can also go 360 - directly behind the head (180°) – time difference = 0 •
Interaural Time Difference • How does the brain detect these onset differences? o The onset difference can be detected by a simple “delay line” mechanism in the
brain
• Picture 1 – sound source directly in front – when sound enters both ears it has to travel the
same distance in the brain when they meet • Picture 2 – sound is located to the right – sound in the right ear is received earlier and then
output from the right ear has to travel a longer distance to meet with sound from the left ear.
• The brain has to monitor where in the brain the 2 signals will meet. If they meet in the middle – no interaural time difference.
• This mechanism works better when the is an actual start to the sound •
Interaural Time Difference • The same sound will most likely be in different phases when it reaches each of the two ears (phase difference)
o But the phase difference is less useful for localising high-frequency sounds
• Phase difference – for continuous noise (ie no starting point) • In diagram above – 1000Hz continuous tone, 1 cycle per millisecond, 1000 times per
sec, .25sec phase goes from 0-90° to reach the left ear – phase difference between the 2 ears, at 90° – source must be next to the left ear
• 1000Hz pure tone, phase difference is not 90° – sound source is not next to one of the ears • 2000Hz tone, .25sec - 180°, twice as fast as 1000Hz, • 3000Hz, .25sec - 270° • 4000Hz, .25sec - 0° (full 360° revolution of sound wave) – ambiguous – could indicate that
the sound in right in front or behind, when really sound source could be next to the ear. • Phase difference for high frequency continuous is less useful as there is no meaningful
interaural time difference. •
Interaural Intensity Difference • The same sound should a bit more intense at an ear that is closer to the sound source o The energy of a sound decreases as it travels farther o The head works as a barrier that reduces the intensity of the sound (sound shadow)
Ø This effect is more pronounced for high-frequency sounds
• Left ear is closer, sound should be more intense at the left ear – provides information to
detect where the sound is. • Intensity – sound loses energy as it travels, the closer ear should receive a bigger intensity
sound, Right ear – sound has to travel longer distance – more energy lost, reduces intensity of the sound.
• Head acts as physical barrier to the intensity of the sound. Left ear isnot blocked by the hear, right ear is locked by the head, takes longer for the sound to reach that ear, loses energy, hence intensity.
•
• Low frequency sound, 2 cycles from source to other side of persons hear. Within each
cycle 1 push, 1 pull. Total – wave would hit the head 4 times, energy is lost with each contact with the head.
• High frequency sound 5 cycles from source to hear, when frequency of sound is greater wave has to hit the head more frequently therefore more energy is lost, creating a bigger intensity difference between left and right ear.
Frequency effects of auditory space perception
• Interaural time difference (phase difference) is useful for localising low-frequency sounds. • Interaural intensity difference is useful for localising high-frequency sounds. • What about sounds in the middle range?
o Interestingly, neither cue works particularly well for pure tones around 1000-3000 Hz
o Typical vocal range is about 1100Hz, above that sounds not that important to us – less sensitive – hypothesis.
Role of Head Movements • Head movements are generally helpful for auditory localisation, ie finding a location of a
sound. • By changing the position of the ears, you can experience changes in interaural
time/intensity differences •
Horizontal vs vertical direction
• Humans perceive horizontal directions better than vertical directions though auditory cues o Pinnae are more effective in distinguishing front/back than above/below – because
of physical setup o Ear positions can be varied more freely along the horizontal dimension
Ø Two ears are located on the same horizontal plane Ø A greater range of head movement is possible along the horizontal
dimension than the vertical dimension o
Limits of auditory localisation • Most of the auditory localisation cues (interaural time difference and interaural intensity difference) both are dependant on the distance between a sound source and each ear – distance is longer creates greater distance and time difference
• As a result, it is difficult to distinguish locations of sound that are equidistant to an ear o Cone of confusion – some points around the circle of the cone same have distance
to the ear – no difference in interaural time and intensity – not distinguishable.
• Auditory distance perception • Two cues for auditory distance perception
o Loudness – if sound sounds louder it should be closer o The energy ratio of direct sound and reverberant (reflected) sound (not available in
open space), reflected sound has less energy • The utility(usefulness) of these cues is usually limited, however
o Loudness cues can tell us only about the relative distance, not a definite distance o Reverberation cues vary depending on various properties of the reflection surface
– difference surfaces reflect sound in different ways – usually you don’t know the properties of the surface, only in enclosed space,
•
Auditory distance perception As a result of the above limitations: • When we have auditory cues only, we underestimate the distance to a sound source • Our perception of auditory distance tends to be variable (imprecise) too •
• Distance perception by vision vs audition • Solid line – perfect performance, thicker line – actual performance • Visual perception - Up to 20m very accurate, error bars – shorter – very consistent
response pattern. • Auditory perception – (Thick line below thin line) underestimate physical distance to the
target, error bars – big – shows very inconsistent.
Visual Capture Interaction between vision and auditory information: • Vision Capture
When we can visually perceive where a sound “should be” coming from, it tends to overwrite our auditory localisation e.g. in lectures you think voice is coming from lectures mouth but in reality, voice was coming from speakers around the room
• When we have some visual information about how a stimulus “should” sound, it strongly affects how we actually hear the stimulus
Video • Separating the sounds we here from the sights we see.
McGurk Effect – auditory illusion, what you are seeing clashes with what you are hearing, mouth movement (visual) influence what we are hearing eg ‘bar’ but visually person is saying bar then far
Don’t think vision always dominates
• We give more weigh to information that (we think) is more informative o Vision: good source of special information o Audition: good source of temporal information
• Auditory information can influence our visual perception by providing conflicting temporal information
o Eg Sound induced flash illusion Video – when a single flash is accompanied with 2 beeps, the single flash is perceived as 2 flashes.
• Brain gives more weigh to information that is more informative
5 Week5:Vision • What is (visual) perception?
• Early visual information processing
o The nature of light o The anatomy of the eye Ø The retina
• Neural pathways to the brain • Visual areas in the cortex • Information coding in visual neurons
What is Perception?
• Dog in the picture, photo was processed to be black and white. • If after seeing the real picture, it is hard not to see the dog – but nothing has been changed.
The pattern represents a dog – vision perception of the image - making sense of the image. • Not just passively receiving info, giving meaning to the image – interpretation,
understanding the meaning. •
What is Perception? Awareness of the elements of environment through physical sensation (Merriam-Webster) – physical - colour, shape, location, texture etc. **Perception is not just receiving information through sensation; it involves interpretation and recognition of the information
Perception
• **Visual • Auditory • Tactile(haptic) • Olfactory • Gustatory • **Object • Space – locations within space • Time • Speech • Motion – object motion
** focus on in this unit visual perception of objects
Light Light • For an object to be visible it must either emit or reflect light • • What is light? • One way of understanding light is that it is a wave of electromagnetic radiation • - It is a wave, so one dimension of light is its wavelength. • • The human eye is only capable of detecting light within a narrow range of wavelengths
