Psych 230 Exam 1Chapter 1 Definition of Sensation and Perception - Sensation: The ability to detect a stimulus and, perhaps, to turn that detection into a private experience - Perception: The act of giving meaning to a detected sensation Psychophysics - Psychophysics: The science of defining quantitative relationships between physical and psychological (subjective) events - Thresholds (JND)o Two-point threshold: The minimum distance at which two stimuli (e.g., two simultaneous touches) can be distinguished o Just noticeable difference (JND): The smallest detectable difference between two stimuli, or the minimum change in a stimulus that can be correctly judged as different from a reference stimulus. Also known as difference threshold- Absolute Threshold: Minimum amount of stimulation necessary for a person to detect a stimulus 50% of the time - Weber and Fechner laws o Weber’s Law As stimulus level increases or decreases, the magnitude of change must increase proportionately to remain noticeable - larger stimulus values have larger JNDs - smaller stimulus values have smaller JNDs  Weber fraction = JND / Initial Stimulus Intensityo Fechner’s law A principle describing the relationship between stimulus magnitude and resulting sensation magnitude such that the magnitude of subjective sensation increases proportionally to the logarithm of the stimulus intensity  S = k log RS = psychological sensationR = physical stimulus level Graph- Stevens’ power law o Magnitude estimates o S = alb o (S) is related to stimulus intensity (I) by an exponent (b) o Graph- Methods (constant stimuli; limits; adjustment; magnitude estimation; cross-modality matching) o Method of constant stimuli: Many stimuli, ranging from rarely to almost always perceivable, are presented one at a time o Method of limits: The magnitude of a single stimulus or the difference between two stimuli is varied incrementally until the participant responds differently  Crossover values vs intensity o Method of adjustment: Similar to the method of limits, but the participant controls the stimulus directly o Magnitude estimation: The participant assigns values according to perceived magnitudes of the stimuli o Cross-modality matching: The participant matches the intensity of a sensation in one sensory modality with the intensity of a sensation in another - Signal Detection Theory (Hit; Misses; False alarm; Correct rejection; Criterion; Sensitivity or d’). o Signal detection theory: A psychophysical theory that quantifies the response of an observer to the presentation of a signal in the presence of noiseo There are four possible stimulus/response situations in signal detection theory: 1. Hit: Stimulus is present and observer responds “Yes” 2. Miss: Stimulus is present and observer responds “No” 3. False alarm: Stimulus is not present and observer responds “Yes” 4. Correct rejection: Stimulus is not present and observer responds “No”o Makes a distinction between an observers’ ability to perceive a signal and their willingness to report it. These are two separate concepts: Criterion: An internal threshold that is set by the observer. If the internal response is above criterion, the observer gives one response. Below criterion, the observer gives another response.  Sensitivity: A value that defines the ease with which an observer can tell the difference between the presence and absence of a stimulus or the difference between stimulus 1 and stimulus 2 - Sensitivity defines the ease with which we are able to tell the difference between the presence and absence of a stimulus.  Criterion willingness to report a signal Sensitivity ability to perceive a signalSensory Neuroscience and the Biology of Perception- Doctrine of specific nerve energies: formulated by Johannes MCller (1801–1858) statingthat the nature of a sensation depends on which sensory fibers are stimulated, not on how the fibers are stimulated - Where is the information from our senses processed first in the cortex? o Olfaction, auditory cortex, visual cortex, and somatosensory cortex are the 4 different areas where info from four different senses first reach the cortexo Cranial nerves: Twelve pairs of nerves (one for each side of the body) that originate in the brain stem and reach sense organs and muscles through openings in the skull o Sensory information Olfactory (I) nerves Optic (II) nerves Auditory (VIII) nerveso Muscles that move the eyes Oculomotor (III) Trochlear (IV) nerves Abducens (VI) nerves - Structure and function of neurons Structure o Axon Terminal: Although almost all neurons have only a single axon, most axons branch out at their ends into a number of axon terminals. Each axon terminal synapses with one or more downstream neurons. Thus, every neuron can “talk to” a large number of subsequent neurons.o Axon: Almost all neurons have a single axon, which transmits neural information from the cell body, through the axon terminals, and finally across synapses to other neurons. Axons can be very long—up to several meters for neurons in giraffes’ necks.o Cell body: Like all cells, every neuron has a cell body, sometimes called the soma. The cell body contains the nucleus, which holds the cell’s chromosomes. In most neurons, the cell body serves as a kind of collection center for information coming in through the dendrites from upstream neurons. If the cell body is excited enough about the information it receives from thedendrites, it will pass a signal down the axon, through the axon terminals,and across synapses to downstream neurons.o Dendrites: receive information from upstream neurons and transmit it to the cellbody. A neuron may have tens, hundreds, or even thousands of dendrites, so each neuron “listens to” a large number of preceding neurons.o Synapse: junction between neurons that permits information transfero Neurotransmitter: a chemical substance used in neuronal communication at synapsesFunctiono Inside neuron negative -o Outside neuron positive +o Neurons fire in an all or none fashion for each spike, and the number of spikes per second indicates how excited the neuron is o Each action potential starts near the cell body of a neuron and propagates down the axon towards the axon terminal  Electrochemical process involving Na+ and K+ ions moving in and out of the neurono Entire populations of neurons work in concert to process information