PSYX2247 Mid semester exam open book notes (wk1-6) PDF

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PSYX2247 Week 1 NotesIntro & General Principles__ Our perceptual systems are very complex, however most of us take them for granted (consider individuals with disabilities).  Although complex, they are still fallible. We have disagreements about what was truly perceived.  Psychophysical resea...

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PSYX2247 Week 1 Notes Intro & General Principles __________________________________________________________________________________

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Our perceptual systems are very complex, however most of us take them for granted (consider individuals with disabilities). Although complex, they are still fallible. We have disagreements about what was truly perceived. Psychophysical research. Perceptions are meaningful experiences of objects and events. Qualia – simple sensations.  Qualia divide the sensory world into qualitatively different modes of sensation, known as sensory modalities. Vision, audition, somatosensation, olfaction, gustation, vestibular sense (balance), proprioception (bodily position), kinesthesis (motion), nociception (pain). The number of receptors differs between modalities. Cerebral cortex – the outer layer of the human brain. Thought to contain the neurons required for conscious perceptual experience.

Psychophysics 

Three key elements of perception: (1) sensory stimulation, (2) neural responses to stimulation, (3) perceptual experiences which correlate with neural responses.

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Psychophysical linking hypotheses are linking propositions positing a specific causal link between neural activity in the brain and perceptual experience. Ernst Weber and Gustav Fechner. “Just Noticeable Difference” (JND)  Weber. Fechner developed a set of experimental methods known as psychophysical methods, used for relating mental and physical events.

Sensory thresholds 

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Psychometric function is a graph-relating stimulus value (e.g., intensity) to the response rate of an experimental subject (e.g., proportion of “yes responses”).  Probabilistic nature of sensory thresholds. As the size of the increment increases, there is a gradual increase in probability that the participant will detect it.

Sensory magnitude   

Variation in intensity affects detectability, but also sensory magnitude.  E.g. the brightness of a light, the loudness of a sound etc. Magnitude estimation is a technique that allows the establishment of the precise relationship between physical stimulus magnitude and sensory magnitude. “Steven’s power law” is a non-linear relationship between stimulus intensity and perceived magnitude, in which equal ratios of intensity produce equal ratios of magnitude.

Sensory adaptation 

Continuous exposure to a sustained stimulus has 3 consequences for sensation: 1. Sensitivity changes so that a different level of stimulus intensity is required to induce a sensory response. 2. The apparent intensity of the stimulus changes. 3. The rate at which sensory magnitude increases with stimulus level usually steepens.

Cognitive neuroscience 

Studies the parts of the nervous system that are involved in cognition (including sensation and perception).

Lesions   

Help us study different functions of different parts of the brain, by seeing what a person/animal does without the part of the brain in question. Lesion studies have played an important part in establishing the localisation of function as a basic principle of cortical organisation. Localisation of function is the view that neurons underlying a specific sensory or cognitive function are located in a circumscribed brain area.

Clinical cases  

In humans, researchers mostly study individuals who have lost certain functions due to accidents involving brain injury. Tatsuji Inouye was an army physician that studied head injuries from bullet wounds, he was one of the first to devise that the visual field is mapped in an orderly way on the surface of the human occipital cortex.

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Early theories of perception were inspired largely by the anatomical features of sensory systems.  Electrical Field Theory of perception.

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Stephen Kuffler, 1950s, one of the first to use microelectrode recording – a technique in which electrical activity is recorded from single cells in a live animal using fine insulated wires. “Feature detectors” – are a view that individual neurons in the brain act as detectors for individual stimulus features.

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Neuroimaging 

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Computerised tomography (CAT) scans are a medical technique in which x-rays are passed through the body at different angles, and the resulting data are processed by a computer to create detailed images of bodily structures.  They can reveal areas of brain damage Magnetic resonance imaging (MRI) scanners magnetic properties of brain molecules. Direct brain stimulation  transcranial magnetic stimulation (TMS) involves directing a brief magnetic pulser to a subject’s head.

Some basic concepts   

Dendrites. Axons. Action potentials (nerve impulses).

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Terminal button. Neurotransmitters. Photoreceptors (electrical signals from light). Mechanoreceptors (e.g., Pacinian corpuscle). Transduction (environment into energy).

Hierarchical processing  

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Several structures in the brain receive nerve impulses created by transduction. In between transduction (start) and arrival at the cortex (finish), the signals from each sensory organ (e.g., ears, eyes, nose) move across a series of synapses at successively higher levels for neural processing (i.e., hierarchical). Thalamus. The Cortical receiving area is an area of the cortex where afferent (incoming) fibres from a sense organ terminate; aka the primary sensory cortex. Cortical association area receives information from neurons in a cortical receiving area; aka the secondary sensory cortex. Specific nerve energy is the idea that neural signals in the sense are differentiated by their pathways in the nervous system, rather than by differences in the nature of the signals themselves.

Neurons in the sensory systems generally only respond to a particular set of stimuli – known as neuron selectivity. For example, horizontal versus vertical lines. OR selectivity of sound frequencies. A cell may only respond to a stimulus presented in a specific spatial area. This is commonly referred to as the receptive field.

Univariance and population coding 

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Univariance is a universal problem in sensory coding. For instance, the response of many visual neurons depends on a whole constellation of stimulus parameters. Such as size, contrast, orientation, and motion direction. Univariance is a principle of neural coding inn which any one level of excitation in a neuron can be produced by different combinations of stimulus values. Population coding is a consequence of univariance. It is a general principle of sensory processing, according to which different values of a perceptual attribute are coded by different patterns of activity in a whole population of neurons.

Generally, cells that respond to similar stimuli are located near each other in the brain.

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An extreme example is a topographic map. Staining is a technique used for identifying substances in and around cells, using chemical stains that are selectively taken up by certain kinds of tissue. Cortical magnification is the exaggerated cortical representation of one part of a sensory dimension or surface compared to another.

The brain has a certain element of plasticity; however this is only possible for a limited time during development, known as the “critical period”. Neural adaptability is a universal feature of sensory systems. It is the ability of a sensory system to vary its response characteristics to match prevailing stimulation. Neural signals show certain degrees of variability even in the absence of adaptation or shortterm plasticity.  Responses to the repeated presentation of the same stimuli vary between each presentation, and this situation is referred to as “noise”.

Computational neuroscience  

Studies the computations performed by the nervous system. Computation, in this sense, refers to the manipulation of quantities or symbols according to a set of rules.

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Alan Turing (1912–1954), Claude Shannon (1916–2001), and David Marr (1945–1980). Shannon developed a mathematical theory that consisted of 3 parts: a signal source, a transmission line, and a receiver. Shannon identified key properties of any such system:  Channel capacity—the number of signals it can transmit simultaneously  Transmission rate—how quickly the signals travel along the channel  Signal redundancy—the amount of information carried in the signal  Noise—intrusion of information that is unrelated to the signal. Shannon used these properties to create his “Information Theory”. Marr argued that an adequate theory of any information processing system like the visual system had to consider three levels of analysis (Marr, 1982, p. 25):

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 Computational theory “What is the goal of the computation, why is it appropriate, and what is the logic of the strategy for carrying it out?”  Representation and algorithm “How can this computational theory be implemented? In particular, what is the representation of the input and output, and what is the algorithm for the transformation?”  Hardware implementation “How can the representation and algorithm be realized physically?”

Basic concepts in computational neuroscience    

Representation. Analog representation. Symbolic representation. Rate code.

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computational procedure used to transform one representation into another.

COMPUTATIONAL NEUROSCIENCE SUMMARY The foundations of computational neuroscience were laid by three mathematicians: • Alan Turing introduced the concept of universal computation • Claude Shannon developed Information Theory • David Marr introduced the three-level distinction between computational theory, representation, and hardware implementation. Basic concepts include: • Analog and symbolic representation • Computation.

An algorithm is a specific

PSYX2247 Week 2 Notes Sound, Ear & Brain; Auditory Perception __________________________________________________________________________________

Sound as a physical stimulus   

Sound consists of pressure waves carried by vibrating air molecules. Compressions: air pressure increased. Rarefactions: air pressure decreased.

Simple sounds   

E.g., air pressure produced by a gong is called a longitudinal wave.  Particles that cause it to vibrate back and forth in the same direction as the wave Repetitive variation in air pressure in the simplest sound wave can be described mathematically as a sine wave. Sound air pressure waves travel at a consistent speed of 335m/s.

Frequency 

Hertz (Hz).

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Variation in frequency relates perceptually as variation in perceived pitch. Low freq  bass High freq  treble

Amplitude   

Decibels (dB). Corresponds to the amount of pressure change created. dB SPL  decibels applied to sound pressure levels.

The dB SPL scale      

Measures sound pressure relative to a fixed reference pressure. Near minimum sound detectable by humans (1000Hz). The dB SPL scale is logarithmic.  E.g., each tenfold pressure change = a change in 20dB. Logarithmic scale is chosen, as it can compact a wide range of pressure levels into a single diagram of specific dB values, (approx. 0 – 140). Perceptually, SPL corresponds roughly with sound loudness. However, distinguishing the difference between “loudness” and “frequency and pitch” is complex.

Phase   

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Phase defines a specific point on a waveform. Measured in degrees. 1 entire cycle of a waveform = 360 degrees of a phase. When two waves interact, phase is important.  Similar phase valued wavelengths tend to simulate each other.  Opposite phase valued wavelengths (180 degrees apart) cancel each other out. Phase also describes relative timing of two waves to each other (i.e., one leading, one following). Waves with smaller phase values tend to lead waves with larger phase values.

Complex sounds  

Sounds are often not one single sine wave – they are comprised of many wavelengths. The different frequencies, amplitudes, and phases of these sine waves (in a single complex sound) make up the complex wavelength.  E.g., a single note on a guitar is comprised of many different sine waves.

Fundamental frequency and harmonics – guitar analogy (assume standard tuning). 

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The lowest frequency in a series (of waves?) is called the FUNDAMENTAL FREQUENCY. It is considered the FIRST HARMONIC in a series.  If you pluck a guitar string without fretting, this is an example of the fundamental frequency. If you put your finger 1 octave higher on the 12th fret, you get the FIRST OVERTONE, and the SECOND HARMONIC. https://www.youtube.com/watch?v=RwyHs7P8OhM&ab_channel=PhysicshelpCanada Harmonics are numbered according to their distance from the fundamental.  According to the example, this would mean frets are numbered according to their distance from the open string (which is the fundamental frequency). Many natural sounds contain a spectrum of notes and are therefore not periodic.

Fourier theory 

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Allows for a sound, either periodic, or nonperiodic, to be broken down into its respective composition of sine waves. Fourier analysis is the procedure that breaks down the complex signal into parts. After analysis, the Fourier spectrum is the collection of amplitude values at each frequency, drawn from the original signal. Fourier synthesis, therefore, is the construction of the original complex signal, by adding the Fourier spectrum back together.

Spectrograms    

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Fourier theory assumes the signal continues perpetually. However, a musical instrument note starts at a specific point in time and shifts through different harmonics at different times. Different instruments sound dissimilar on the same notes, as their initial attack is different. The spectrogram is essentially comprised of several Fourier spectra, taken for a signal over different time periods.

A frequency filter is any process that modifies frequency content of signals passing through it. For example, the human head is a filter that allows low frequencies to pass but blocks out higher frequencies; a low-pass filter. Transfer functions: A function that describes a linear filter’s frequency response, in terms of the degree of attenuation at each frequency. Filters must obey three rules to be considered linear: 1. Output of the filter never contains any frequency component that was not present in the input signal.

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2. If the amplitude of the input to the filter is changed by a certain factor, then the output should change by the same factor. 3. If a number of sine wave inputs are applied to the filter simultaneously, then the resulting output should match the output that would be produced if the inputs had been applied separately, and their individual outputs summed. Linear filters are filters that modify amplitude of input frequency components but does not introduce components that were not present at input. Nonlinear filters are frequency filters that distort signals by adding new frequencies or by failing to respond at very low or high amplitudes.

Physiology of the auditory system 

Outer ear  middle ear  inner ear.

Outer ear   

Pinna (aka auricle). Concha. The outer ear is visible on the outside of the head, it acts as an amplifier as well as an acoustic filter.

Middle ear   

Comprised of three bones: the malleus incus and stapes. Malleus  incus  stapes (in order of connection). The stapes is connected to the cochlea, and this point of connection is also referred to as the oval window.

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Impedance is the degree of resistance offered by a medium to an oscillating signal (e.g., a sine wave). Impedance matching within the ear occurs when the middle ear matches up low acoustic impedance of the tympanic membrane with the high acoustic impedance of the oval window.

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The inner ear  

Incorporates both sense organs of hearing and balance. Cochlea is the sense organ for hearing.  Scala vestibuli  Scala tympani  Scala media  Cochlea partition

Uncoiled cochlea:

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Basilar membrane is housed by the cochlea partition, and it contains all the sensory hairs.

Mechanical properties of the cochlea   

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Vibration of the stapes disrupts cochlea fluid, and creates travelling waves along the basilar membrane, which sensory hairs pick up. Displacement is at its greatest on the “apical” end of the membrane, while the “basil” end is narrow and stiff. Frequency-to-place conversion is a method of encoding, where the place of maximum displacement on the basilar membrane codes the frequency of sound vibration. [1] One criterion for linearity is that amplitude of basilar membrane displacement should double when the amplitude of the input wave doubles. [2] Another criterion is that when two pure sinusoidal tones are presented together the membrane should vibrate in a way that reflects the sum of the two individual responses. Note that a pure sinusoidal tone is a sine wave of any frequency, phase and amplitude.

The Organ of Corti    

Formed by the basilar membrane. Separates the Scala vestibuli from the Scala tympani. Tectorial membrane lies on top of the basilar membrane. The hairs in the basilar membrane have 4 neat rows.  One of which lies on the inner side of the cochlear spiral (inner hair cells).  The other three rows lie on the outside of the spiral (outer hair cells).

Inner hair cells    

Cochlear hair cells are similar to the hair cells found within the vestibular organs. Cochlear hair cells produce graded receptor potentials in response to displacement of their stereocilia. The base of each inner hair cell makes contact with afferent fibres of the auditory nerve. Most of the sensory information about sound is conveyed through inner hair cells

Outer hair cells   

Are able to change their size, expanding and contracting along their length. They receive efferent stimulation from the cochlea nerve. They contain crucial proteins supporting the muscle-like contractions in response to stereocilia displacement.

Sound frequency coding in the auditory nerve    

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Intracellular resting potential for hair cells is -70 mV. Phase locking is the firing of hair cells in synchrony with variation of pressure in a sound wave. A fundamental function of the ear is to encode the frequency of sound waves that enter the ear. The mechanical and neural properties of the cochlea are suitable for using two different methods of encoding sound frequency of sound wave stimuli, known as place coding and rate coding. The place code theory is given that name because it identifies each pitch with a particular place along the basilar membrane. It assumes that any excitation of that particular place gives rise to a specific pitch. The rate coding model of neuronal firing communication states that as the intensity of a stimulus increases, the frequency or rate of action potentials, or "spike firing", increases. Rate coding is sometimes called frequency coding.

Intensity coding in the auditory nerve    

In each fibre, SPL must exceed a certain threshold value in order to register a change in fir...