* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Perception
Neural engineering wikipedia , lookup
End-plate potential wikipedia , lookup
Signal transduction wikipedia , lookup
Holonomic brain theory wikipedia , lookup
Functional magnetic resonance imaging wikipedia , lookup
Neural oscillation wikipedia , lookup
Neuroethology wikipedia , lookup
Embodied cognitive science wikipedia , lookup
Activity-dependent plasticity wikipedia , lookup
Emotion perception wikipedia , lookup
Multielectrode array wikipedia , lookup
Endocannabinoid system wikipedia , lookup
Binding problem wikipedia , lookup
Mirror neuron wikipedia , lookup
Premovement neuronal activity wikipedia , lookup
Development of the nervous system wikipedia , lookup
Neuroanatomy wikipedia , lookup
Neural modeling fields wikipedia , lookup
Neuroesthetics wikipedia , lookup
Nonsynaptic plasticity wikipedia , lookup
Optogenetics wikipedia , lookup
Response priming wikipedia , lookup
Caridoid escape reaction wikipedia , lookup
Pre-Bötzinger complex wikipedia , lookup
Neurotransmitter wikipedia , lookup
Clinical neurochemistry wikipedia , lookup
Perception of infrasound wikipedia , lookup
C1 and P1 (neuroscience) wikipedia , lookup
Metastability in the brain wikipedia , lookup
Single-unit recording wikipedia , lookup
Channelrhodopsin wikipedia , lookup
Molecular neuroscience wikipedia , lookup
Evoked potential wikipedia , lookup
Neural correlates of consciousness wikipedia , lookup
Biological neuron model wikipedia , lookup
Neural coding wikipedia , lookup
Synaptic gating wikipedia , lookup
Nervous system network models wikipedia , lookup
Neuropsychopharmacology wikipedia , lookup
Time perception wikipedia , lookup
Feature detection (nervous system) wikipedia , lookup
Perception Chapter 1 Why study perception -philosophy, computer science, medicine -hearing problems, speech recognition, robots that can see The Perceptual Process -perception is the end result of complex behind the scenes processes Perceptual process: is a sequence of processes that work together to determine our experience of and reaction to stimuli in the environment. 7 Perception 8 Recognition 9 Action Experience and Action 6 Processing 5 Transmission 6 Transduction Electricity Stimulus 1 Environmental Stimulus 2 Attended Stimulus 3 Stimulus on the receptors Stimulus -exists both out there, in the environment and within the persons body Environmental Stimuli and Attended Stimuli Environmental: is all of the things in our environment that we can potentially perceive Ex. Trees, path, Attended stimulus: focusing on the stimuli and making it the center of attention. -the attended stimulus changes from moment to moment Ex. Moth Stimulus on the Receptors -the stimulus activates a receptor Ex. Image of the moth is formed in the retina -this image is a representation of the moth Electricity -everything we perceive is based on electrical signals in our nervous system Transduction -is the transformation of one form of energy into another form Ex. Pattern of light in the retina is transformed into electrical signals Transmission -electrical signals active other neurons and eventually are transmitted to the brain -if the signals don’t reach the brain there’s no perception Processing -As the signals are being transmitted they undergo neural processing interactions btw neurons *in the brain the original electrical representation of the stimulus that is created by the receptors is transformed by processing into a new representation, and it is usually very different from the original signal. Experience and Action -we are aware of this stage Perception -is conscious sensory experience *Two additional steps: recognition and action are important outcomes of the process Recognition -is our ability to place an object in a category Ex visual form agnosia- an inability to recognize objects -this proves that perception and recognition are different processes -Dr.P perceived parts of objects but couldn’t identify them because of a tumor Action -includes motor activities such as moving the head or eyes and locomotion through the environment - Milner & Goodale propose that the goal of visual processing was for survival *overall perceptional process dynamic and continually changing Knowledge -is any information that the perceiver brings to a situation - can affect numerous steps in the perceptual process -Rat-man demonstration shows how recently acquired knowledge influences perception Bottom-up processing: based on incoming data (Data-based processing) *bottom-up is essential because the perceptional process begins with stimulation of receptors Top-down processing: based on knowledge (knowledge-based) *thus bottom-up and top-down processing often work together to create perception *as stimuli get more complex the more top-down processing is involved Study of Perception Psychophysical approach to perception: Gustav Fechner coined the term psychophysicsuse of quantitative methods to measure relationships between stimuli and perception. Definition: Any measurements of the relationship between stimuli and perception Physiologal approach to perception: measuring the relationship between stimuli and physiological processes . (A) Stimulusperception: Two colored patches are judged to be different. (B) Stimulus-physiology: A colored light generates a Neural response in the cat’s cortex. (C) Physiology-perception: Brain activity is monitored as a person indicates what he is seeing. As we study perception we are also concerned with how knowledge, memories, and expectations influence perception Cognitive influences on perception: these factors are the starting point for top-down processing Measuring Perception 1. Describing -indication characteristics of a stimulus Phenomenological method: describing what he/she perceives is the first step of studying perception 2. Recognition -placing a stimulus in a specific category Method: stimulus is presented and the observer indicates what is Detection (3) -becoming aware of a barely detectable aspect of a stimulus Classic psychophysical method I. Limits II. Adjustment III. Constant Absolute threshold: the smallest amount of stimulus energy necessary to detect a stimulus. Method: Limitsexperimenter presents stimuli in ascending or descending order Find the Cross over point between yes and no Adjustmentobserver or experimenter adjust the stimulus intensity continuously until the observer can just barely detect the stimulus Constant stimuliexperimenter presents five to nine stimuli with different intensities in random order -threshold is defined as the intensity that results in detection of 50% of the trials *constant stimuli the most accurate b/c many observations and stimuli in random order, minimizes observer judgment and expectation *method of adjustment fastest Difference Threshold: the smallest difference between two stimuli that a person can detect Method: same methods except participants are asked whether they detect a difference btw two stimuli -the difference threshold is the difference btw the standard weights and comparison weights that the observer said “different” *the magnitude of the stimulus increases so does the size of the DL DL/S=K Weber’s Law S is the value of the standard stimulus K is Weber’s fraction Magnitude Estimation (4) -measuring above-threshold perceptions Method: Stevens -experimenter first presents a standard stimulus to the observer and assigns it a value (10) he/she presents lights of different intensities and the observer is asked to assign a number that is proportional to the brightness of a standard stimulus - can do without standard *doubling intensity does not necessarily double brightness Response compression: as intensity increased, the magnitude increases but not as rapidly as intensity. Ex. Brightness Response expansion: as intensity is increased, perceptual magnitude increases more than intensity. Ex. Electric shock -the intensity of a stimulus and our perception of its magnitude follow the same general equation for each sensepower functions P=KSn Steven’s power law P is perceived magnitude S is stimulus intensity -taking the log of the power functions results in straight lines -the slopes of the straight lines indicate n -response compression slope of less than 1 -response expansion slope of more than 1 Search -looking for a specific stimulus ex. Visual search -measuring reaction time important for mechanism of perception Other methods -same or different stimuli *different people may have a different response criterion -doesn’t matter if it’s the same person also not important if we are testing many people and averaging their response (Appendix) Signal detection theory: only one stimulus intensity is presented and sometimes no stimulus is presented. When the tone is presented: saying yeshit Saying nomiss When no tone is presented: saying yesfalse alarm Saying nocorrect rejection Chapter 2 Aristotle- heart was the seat of the mind and the soul Galen- health, thoughts and emotions determined by spirits flowing from the ventricles Descartes-flowing spirits, specified the pineal gland as the seat of the soul Thomas Willis- brain responsible for mental function, different functions in different regions, brain disorders due to chemistry Structure of the nervous system 1. Reticular Theorylarge network of fused nerve cells 2. Neuron theorydistinct elements or cells, the discovery of staining proved this theory Golgi developed staining by immersing a thin slice of brain tissue in a solution of silver nitrate created individual cells that were stained Mueller: doctrine of specific nerve energies which stated that our perception depend on nerve energies reaching the brain and that the specific quality we experience depends on which nerves are stimulated *nerves from each sense reach different areas of the brain Edgar Adrian: recorded electrical signals from a single neuron Basic Structure of the Brain -cerebral cortex: covers the surface of the brain and contains machinery for perceptions, language, memory, and thinking Modular organization- specific functions are served by specific areas of the cortex Ex. primary receiving areas: the first areas in the cerebral cortex to receive the signals initiated by a sense receptor Visionoccipital lobe Hearingtemporal lobe Skin senses (touch, temp, pain) parietal lobe All sense, perceptions that involve coordinationfrontal lobe Structure of neurons Cell body: mechanisms for survival Dendrite: receive signals from other neurons Axon or nerve fiber: filled with fluid that conducts electrical signals *variation in the structure Receptors: type of neuron specialized to respond to environmental stimuli a.) Light (vision) b.) pressure changes in air (hearing) c.) pressure changes in skin (touch) d.) chemicals in the air (smell) e.) chemicals in liquid form (taste) *all respond to the environment and generates an electrical signal Recording Electrical Signals Nerve: consists of the axons of many neurons Method: microelectrodes (small shafts of glass/metal) measure the difference in charge between two electrodes recording electrode: where the electrical signal will occur Reference electrode: not affected by the electrical signal -the differences btw electrodes is recorded on an oscilloscope Resting potential: -70mV Action potential: signal 40mV lasts 1ms Chemical Basis Action potential: sodium rushes in the neuron and potassium rushes out -the flow of ions in and out of the neuron is due to permeability Selective permeability: occurs when a membrane is highly permeable to one specific type of molecule but not to others -stimulation of the receptors triggers a process that makes the membrane selectively permeable to sodium, so sodium flows in -when the action potential reaches +40mV the membrane becomes selectively permeable to potassium so potassium flows out *sodium-potassium pump is necessary to maintain this gradient Action Potentials Properties: 1.) Propagated response: once the response is triggered it travels all the way down the axon without decreasing in size *important property of neurons because it enables them to transmit signals over long distances 2.)Action potential remains the same size no matter what the intensity of the stimulus is *increasing intensity changes the rate of firing (not the size of the action potentials) Limit to increasing late of firing is due to the refractory period (1ms) Refractory period- the interval between the time one nerve impulse occurs and the next one can be generated in the axon. Upper limit of rate firing= 500-800 impulses per second 3.) Spontaneous activity: neurons fire without stimuli and this establishes a baseline level of firing for the neuron *stimulation can be an increase or decrease from the baseline level of firing These changes in nerve firing can provide information about the intensity of a stimulus but it needs to be transmitted to other neurons, and the brain for it to be meaningful. Synapse Synapse: space between neurons -action potentials triggers the release of neurotransmitters from the synaptic vesicles -neurotransmitter flow from one neuron to another neuron’s receptor sites Lock and Key principle: receptor is only sensitive to certain neurotransmitters therefore the neurotransmitter must match in shape with the receptor as to trigger an action potential. Excitatory transmitterscause the inside of the neuron to become more positive (depolarization (process of a neuron becoming positive) is the excitatory response) *need enough excitatory neurotransmitters for action potential Inhibitory transmitterscause the inside of the neuron to become more negative (hyperpolarization (process of a neuron becoming positive) is the inhibitory response) *The response of a neuron is determined by the interplay of excitation and inhibition *inhibition is essential for the processing step Neural Processing Neural circuits: are groups of interconnected neurons Circuit with no convergence: the response of one neuron is not affected by surrounding neurons Convergence: the synapsing of more than one neuron onto a single neuron Circuit with convergence: The size of one neuron’s response increases when the stimulus size (the number of receptors) is increased Circuit with convergence and inhibition: the neuron responds best to a stimulus of a specific size Convergence and inhibition evidence has been obtained by measuring the property of neurons called the neuron’s receptive field. Receptive Fields Receptive field: is the area on the receptors that influences the firing rate of the neuron Method: -Measure a receptive field of a neuron by stimulating a cat’s retina with light and recording from a nerve fiver -cat is stationary and is looking at a screen -flash a small spot of light Excitatory area: areas where there’s an increase in neurons’ firing rate Inhibitory area: areas where there’s a decrease in neurons firing Since a receptive field is any area where stimulation influences firing both an excitatory and inhibitory area can make up a receptive field. Center-surround receptive fields: a center region that responds one way, and a surround region that responds the opposite way Ex. Excitatory-center-inhibitory-surround receptive field Ex. Inhibitory-center-excitatory-surround receptive field Since the center and surround respond to in opposite ways it causes an effect called center-surround antagonism (Neuron is a type of cell) Figure 3.21 Response of an excitatory-center-inhibitory-surround receptive field as stimulus size is increased. Color indicates the area stimulated with light. The response to the stimulus is indicated below each receptive Field. The largest response occurs when the entire excitatory area is illuminated, as in (b). Increasing stimulus size further causes a decrease in firing due to center-surround antagonism. Center-surround receptive fields also occur in the skin Sensory Code -receptive fields enable us to specify a neuron’s response For the best response from a receptive field you need both the optimal location and the size or shape of the stimulus. How does the firing of neurons represent various characteristics: specificity coding? Specificity Coding Specificity Coding: is the representation of particular objects in the environment by the firing of neurons that tuned to respond specifically to that object. -idea that a single neurons response to a specific responseKonorski and Lettvin Grandmother cell: according to Lettvin is a neuron that responds only to a specific stimulus Evidence: -little evidence -Quigora recorded from neurons that respond to very specific stimuli in patients with epilepsy -found that some neurons responded to a number of different views of just one person or building -neurons responded to different views of the stimulus, different modes of depiction, and even words signifying the stimulus -neurons respond to concepts -these neurons were in the hippocampus and the MTL (medial temporal lobe) areas associated with the storage of memories -However they are not grandmother cells because: if it was only one neuron responding to a stimulus it would extremely difficult to find neurons probably respond to different stimuli probably 50-150 different individuals or objects Distributed coding: the idea that a particular object is present not by the firing of a single neuron but by the firing of a group of neurons Distributed Coding -is the representation of a particular object by the pattern of firing of groups of neurons Advantage: it is doesn’t require a specialized neuron for every object Sparse Coding -Is the idea that a particular object is represented by the firing of a relatively small number of neurons -code for representing objects, tones, odours involve sparse coding Mind-Body Problem How do physical processes become transformed into the richness of perceptual experience? Neural correlate of consciousness (NCC): determining connections between stimuli and the firing of neurons, where consciousness can be roughly defined as our experiences Easy problem of consciousness: finding the NCC Hard problem of consciousness: How do physiological response become transformed into experience? I.e. how do sodium and potassium ions flowing across a membrane become the perception of a persons face? most researchers focus on NCC