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University of Toronto Scarborough
Steve Joordens

CHAPTER 5: SENSATION SENSORY PROCESSING Sensation: detection of simple properties of stimuli such as brightness, colour, warmth, sweetness Perception: detection of objects, their locations, their movements and backgrounds Perceptions dependant on learning, sensations involve innate, no clear boundary between the two Sensory Mechanisms: visual, auditory, gustatory, olfactory, somatosensory Transduction Only sense receptors brain processes detect things like temperature, salt concentration of blood, and these receptors cant inform it about what is going on outside (outside info gathered by sense organs outside the brain) Detected stimuli by sense organs transmitted to brain through neural impulse, task of sense organs to transmit signals to brain that are coded to represent faithfully the events that have occurred in environment, brain analyzes and reconstructs Transduction: process by which sense organs convert energy from environmental events into neural activity In most senses specialized neurons, receptor cells, release chemical transmitter substances that stimulate other neurons altering rate of firing In somatosenses dendrites of neurons respond directly to physical stimuli without receptor cells Location, Environmental Stimuli, Energy Transduced: Eye, Light, Radiant||Ear, Sound, Mechanical||Vestibular System, Head Tilt/Rotation, Mechanical|| Tongue, Taste, Recognition of Molecular Shape||Nose, Odor, Recognition of Molecular Shape Skin, Internal Organs, Touch, Temperature, Vibration, Mechanical, Thermal, Mechanical Muscle, Pain, Stretch, Chemical, Mechanical Sensory Coding Anatomical Coding: means by which nervous system represents info; different features coded by activity of different neurons Used to interpret the location, and type of sensory stimulus according to which incoming nerve fibres are active Sensory coding for body surface is anatomical, primary somatosensory cortex contains a neural map of the skin (receptors in skin send info to different parts of primary somatosensory cortex) same with visual cortex and visual field Temporal Coding: means by which nervous system represents info; different features coded by activity of different neurons Coding of information in terms of time, simplest is rate; firing faster or slower because of intensity of stimulus can communicate quantitative info to brain Psychophysics Psychophysics: systematic study of relation between physical characteristics of stimuli and sensations they produce The Principle of Just Noticeable Difference (JND)-Weber-smallest change in magnitude of a stimulus that a person can detect JND directly related to magnitude of stimulus below are Weber Fractions Two weights feel the same unless they differed by a factor of 1 in 40(can barely tell a 40g rate from 41) Differ between two brightness is 1 in 60 Fechners largest contribution show how a logarithmic equation could be derived from Webers principle Gustav Fechner, German physiologist, used Webers JND to measure peoples sensations, assumed it was basic unit of sensory experience and measured magnitude of sensation in JNDs {two frosted glass, increase one light till noticeable, then match the other one (that is one JND) then do again which is two, and so on, graph is steep curve turning to a standstill each point more apart} Pain takes less energy at higher intensities to produce JND Stevens made power function to relate physical intensity to magnitude of sensation S=kIb (S is psychological magnitude, I is intensity of physical stimulus, k is mathematical constant) Value of b for saccharin is 0.8, salt 1.3 Signal Detection Theory mathematical theory of detection of stimuli which involves discriminating a signal from the noise in which it is embedded and takes into account participants willingness to report detecting the signal Psychophysical methods highly rely on threshold (the line between perceiving and not perceiving) JND = difference threshold Absolute Threshold: minimum value of a stimulus that can be detected, discriminated from no stimulus at all Threshold is not absolutely fixed value, thus it is the point where the person detects it 50% of the time Every stimulus event need distinction between signal(stimulus) and noise(background stimuli and random nervous system activity) Experiment-sitting in room when light flashes may hear tone, at first easy, then the tone gets so faint can barely hear Cant tell if can really hear it or if we are imagining Response bias: tendency to say yes or no when not sure whether we detect stimulus Hits: yes when it is present, Miss: no when it is present, False Alarm: Yes when not, Correct Negative: No when not Affect the response bias through payments, the curve goes from $1 fine for false alarm, 50C for hit $1 fine for false alarm, $1 for hit, fine for false alarm, $1 for hit, 50C fine for false alarm, $1 for hit-THIS is a receiver operating characteristic curve (ROC) named in Bell Laboratories to measure intelligibility of speech through phone Detectability measured by relative distances of the curves from 45 degree angle VISION Light Wavelength: the distance between the waves of radiant energy Gamma, X-rays, Ultraviolet, Visible Color, Infrared, Radar, TV/Radio, AC Circuits 380nm Violet, 760 Red
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