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PSYCH 2E03 (32)
Chapter 2

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Gautam Ullal

Psych 2E03: Sensory Processes Chapter 2: Introduction to the Physiology of Perception The Brain: The Mind’s Computer - Early history of the physiological approach:  Brain is responsible for mental functioning, different functions were located in different regions, and disorders of the brain were disorders of chemistry.  Advances in technology, microscopes and staining, led to visualization of neurons  Electricity is transmitted down the nerve  Doctrine of specific nerve energies: our perception depends on nerve energies reaching the brain and the specific quality we experience depends on which nerves are stimulated  Electronic amplifiers to record nerve impulses - Basic structure of the brain:  Much of the research on the connection between the brain and perception has focused on activity in the cerebral cortex  Modular organization: specific functions are served by specific areas of the cortex  Primary receiving areas: first areas in the cerebral cortex to receive the signals initiated by each sense’s receptors – occipital lobe, temporal lobe, parietal lobe Neurons: Communication and Processing - Cell body: contains mechanisms to keep the cell alive - Dendrites: branch out from cell body to receive electrical signals from other neurons - Axon/nerve fiber: filled with fluid that conduct electrical signals - Receptors: neurons that are specialized to receive information from the environment - Recording electrical signals in neurons:  Neurons are bathed in liquid  Neurons are surrounded by a solution rich in ions  Solution outside the axon of a neuron is rich is positively charged Na+ ions; solution inside the axon is rich is positively charged K ions  Ions create electrical signals in the neuron when they flow across the cell membrane of the axon  Microelectrodes: small shafts of glass or metal with tips small enough to pick up the electrical signals from a single neuron  Difference in charge between the two electrodes is -70 millivolts, inside is 70mV more negative than the outside  Resting potential: -70mV, neuron’s charge when it is at rest  Charge inside the fiver increases from -70mV to 40mV then returns back to resting potential  Action potential/nerve impulse: rapid increase in positive charge  Na ions rush into the fiber at the beginning of the action potential  Inflow of Na is followed by an outflow of K bringing the charge back to its original level  Rapid changes in Na and K flow that create the action potential are caused by changes in the fiber’s permeability to Na and K  Propagated response: action potential travels down the axon without decreasing the amplitude enabling neurons to transmit signals over long distances - Basic properties of action potentials:  Action potential remains the same no matter how far it has traveled or how intense the stimulus is  Changing the stimulus intensity does not affect the size of the action potentials but does affect the rate of firing  Refractory period: interval between the time on nerve impulse occurs and the next one can be generated in the axon (500-800 impulses/s)  Spontaneous activity: firing in the absence of stimuli from the environment  Action potential’s function is to communicate information - Events at the synapse:  Action potentials trigger chemical process that bridges the gap between the sending neuron and the receiving neuron  When action potential reaches end of presynaptic neuron it releases neurotransmitters that are stored in synaptic vesicles in the presynaptic neuron  Neurotransmitters flow into synapse to receptor site on postsynaptic neuron that are sensitive to neurotransmitters  When neurotransmitters make contact with receptor site matching its shape, it activates the receptor site and triggers a voltage change in postsynaptic neuron  At the synapse, an electrical signal generates chemical process that triggers a change in voltage in postsynaptic neuron  Excitatory transmitters: cause inside of neuron to become more positive (depolarization)  Inhibitory transmitters: cause inside of neuron to become more negative (hyperpolarization)  Function of neurons is to transmit information and to process it, and both excitation and inhibition are necessary for this process Vision Begins in the Eye - Eye: consists of focusing mechanism in front, the lens and cornea, and the retina, which contains the receptors for vision, lining the back of the eye - Two kinds of visual receptors: rods and cones containing light sensitive chemicals, visual pigments, which react to light and trigger electrical signals - Optic nerve: conducts signals toward the brain - Light is the stimulus for vision:  Vision is based on visible light within the electromagnetic spectrum, a continuum of electromagnetic energy produced by electric charges that is radiated as waves  Wavelength: distance between peaks of electromagnetic waves  Visible light: energy within electromagnetic spectrum that humans can perceive  Light consists of small packets of energy, photons, with one photon being the smallest possible packet of light energy  Light is reflected from objects in its environment - Images are focused on the retina:  Light needs to be focused  Cornea: fixed focus  Lens: changes its shape to adjust the eye’s focus for stimuli located at different distances  Accommodation: increases focusing power by tightening muscles at the front of the eye increasing the curvature of the lens so that it gets thicker  Near point: distance at which your lens can no longer adjust to bring close objects into focus  Presbyopia: distance of near point increases with age Transforming Light Into Electricity - The rod and cone receptors:  One small area, the fovea, that contains only cones  Peripheral retina, includes all of the retina outside the fovea, contains both rods and cones  Although fovea is the only place where there are only cones, most of the
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