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Chapter 5

Chapter 5 Notes

Course Code
Steve Joordens

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Experiments: purple
Topics: Green
Key terms: yellow
Sensation: detection of the elementary properties of a stimulus
such as brightness, colour, warmth, and sweetness
seeing red colour
Perception: detection of the more complex properties of a stimulus, including its location and nature; involves
detection of objects (both animate and inanimate), their locations, their movements, and their background
seeing red apple
Transduction: The conversion of physical stimuli into changes in the activity of receptor cells of sensory organs
process by which the sense organs convert energy from environmental events into neural activity
each sense organ responds to a particular form of energy given off by an environmental stimulus and translates that
energy into neural firing to which the brain can respond
Ex. photons of light striking receptor cone cells cause biochemical changes in a molecule that leads to an action
Receptor cell: a neuron that directly responds to a physical stimulus, such as light, vibrations, or aromatic
releases neurotransmitters that stimulate other neurons which alter the rate of firing of their axons
Sensory Coding
2 primary dimensions to all sensory coding: quatitative and qualitative
quantitative variation: related to amount of energy present in a sensory stimulus (high decibel/loudness sound
vs. A low decibel/loudness sound)
qualitative variation: related to the kind of energy presented in a sensory stimulus (high frequency/pitch sound
vs. Low frequency/pitch sound)
Anatomical coding: a means by which the nervous system represents info; diff. features are coded by the activity of
diff neurons
quality is determined by which specific receptors are activated and which arent (eg. Red cones, but not blue cones, in
vision=anatomical coding)
Ex. if you rub your eyes, you will mechanically stimulate the light sensitive receptors located there . As a result, the
brain acts as if the neural activity int he optic nerves was produced by light-so you see stars and flashes
Temporal coding: a means by which the nervous system represents info; diff. features are coded by the activity of
diff neurons

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quantity is determined by the rate of action potentials (more energy=more potentials=temporal coding)
Ex. a light touch to the skin can be encoded by a low rate of firing & a more forceful touch by a high rate
Psychophysics: A branch of psychology that measures the quantitative relation between physical stimuli and
perceptual experience
the relationship btwn an external stimulus and the perceptual experience that it evokes in the mind
Just noticeable difference (jnd): the smallest difference btwn two similar stimuli that can be distinguished; also
called difference threshold
smallest change in magnitude of a stimulus that a person can detect
jnd s by a fixed proportion as the stimulus intensity s, and vice versa
Ex. the difference btwn two dim lights is actually much smaller than the difference btwn two bright lights; however, the
perceived difference btwn within each type of light is the same
Therefore, the ratio for detecting differences in brightness of white light is approx. 1 in 60
Ratio for detecting weight difference is 1 in 40
Ernst Weber (1795-1878) studied the minimum difference required btwn 2 stimuli
Webers law: the jnd for a stimulus is a constant proportion of the magnitude of the standard stimulus
the amt of physical energy necessary to produce a jnd increases with the magnitude of the stimulus
The JND is a threshold is a difference threshold & reflects how big a difference has to be before it is detected
how intense does a stimulus have to be before the subject claims to see, hear, smell, taste, or feel it? These sorts of
thresholds have been used to assess the sensitivity of our sensory apparatus
Weber fraction: The ratio btwn a jnd difference and the magnitude of a stimulus; reasonably constant over the
middle range of most stimulus intensities
Threshold: the point at which a stimulus, or a change in the value of a stimulus, can just be detected
Difference threshold: an alternative name for jnd
Absolute threshold: the minimum value of a stimulus that can be detected
is the intensity level of a stimulus (e.g. light) that is detected 50% of the time by observers
differs btwn individual observers & species
Ex. absolute threshold for hearing 12,000 Hz (very high pitch) would be higher in an old man compared to a young
man, and higher in a young man compared to a cat
(Green & Swets, 1974) Signal detection theory: A mathematical theory of the detection of stimuli, which involves
discriminating a signal from the noise in which it is embedded and which takes into account participants
willingness to report detecting the signal
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