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Chapter notes

Course Code
Steve Joordens

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Roshan Singh
Mr. Joordens
Chapter 6 Notes
Differences between sources of information in the environment have important consequences for the way
sensory systems process that information. In other words, a difference in the world we see and the world
we hear. Visionary senses require one to pick up frames quicker than auditory senses require
distinguishing sound waves. Because they are all attuned to different aspects of our world, the senses
contribute to the richness of experience.
Audition (speech) is really important for social behaviour. Vision provides information about distant
events as well as the sense of smell. The other senses deal with events occurring immediately nearby such
as the taste of our favourite food and the touch of a loved one.
When we feel objects our experience is active instead of passive, as we try to feel the shape, texture and
other details of that object. Information from specialized organs in the inner ear and receptors in muscles
and joints is produced by our own movements. This information helps us to maintain our balance as we
engage in our everyday activities.
Experience is studied by distinguishing between sensation and perception.
SensationThe detection of the elementary properties of a stimulus.
Elementary properties are brightness, colour, warmth and sweetness.
PerceptionThe detection of the more complex properties of a stimulus (animate and inanimate),
including its location and nature; involves learning.
Psychologists used to believe that perceptions depended heavily on learning whereas pure sensations
involved inborn physiological mechanisms. But, neither behavioural nor physiological have been able to
establish a boundary between sensation and perception.
Our sensory mechanisms include:
Visual system
Auditory system
Gustatory system
Olfactory system
Somatosensory system
Traditionally we are known to have 5 senses, but in fact we have a few more. The somatosensory system
for example has separate components that can detect touch, warmth, coolness, vibration, physical damage,
head tilt, head movement, limb movement, and muscular contraction and so on. Calling these components
senses is based what we want to base our terminology on.

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Roshan Singh
Mr. Joordens
Chapter 6 Notes
The sense receptors the brain has detects temperature and salt concentration of the blood and is useless to
inform the brain about the outside world. Sense organs outside the brain are able to do the job as they
detect stimuli provided by light, sound, odour, taste or mechanical contact with the environment.
Information about these stimuli is transmitted to the brain through neural impulses. (action potentials
carried by axons in sensory nerves)
TransductionThe conversion of physical stimuli into changes in the activity of receptor cells of sensory
Each sense organ responds to a particular form of energy given off by the environment:
Light (radiant energy)Eye
Sound (mechanical energy)Ear
Tilt and rotation of head (mechanical energy)Vestibular system
Taste (Recognition of molecular shape)Tongue
Odour (Recognition of molecular shape)Nose
Touch, Temperate, Vibration (mechanical energy, thermal energy, mechanical energy)Skin,
internal organs
Pain, Stretch (Chemical reaction, mechanical energy) - Muscle
Receptor cellA neuron that directly responds to a physical stimulus, such as light, vibrations or
aromatic molecules.
Different stimuli cannot be translated into different types of action potentials. The information must be
somehow be coded in the activity of axons carrying information from the sense organs to the brain.
A code is a system of symbols or signals representing information. If we know the rules, we are able to
convert a message from one medium to another without losing any information. But, we do not know the
rules used by our sensory organs. The 2 general forms of coding used though are:
Anatomical codingA means by which the nervous system represents information; different
features are coded by the activity of different neurons. Example: Rubbing your eyes. It not only
distinguishes among the sense modalities but also among the stimuli of the same sense modality.
Temporal codingA means by which the nervous system represents information; different
features are coded by the pattern of activity of neurons. The simplest form of temporal code is
rate. Example: Light touching skin, the degree of touching determines the rate of firing.

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Roshan Singh
Mr. Joordens
Chapter 6 Notes
Therefore, the firing of a particular set of neurons (anatomical code) tells where the body is being
touched; the rate at which these neurons fire (temporal code) tells how intense that touch is.
PsychophysicsA branch of psychology that measures the quantitative relation between physical stimuli
and perceptual experience.
In order to study perceptual phenomena, scientists found 2 reliable ways of measuring peoples sensations:
Just-noticeable difference
Procedures of signal detection theory
Just-noticeable difference (jnd)The smallest difference between two similar stimuli that can be
distinguished. Also called difference threshold.
Ernst Weber investigated the ability of humans to discriminate between various stimuli during the 18th
century. He discovered a principle true for most sensory organs and i.e. jnd is directly related to the
magnitude of that stimulus. Example: A certain ratio required before we could determine the difference
between the 2 objects such as their weight. The ratio was 1 to 40 i.e. a person could barely differentiate
between 40 and 41 grams, 80 and 82, 400 and 410. But, psychologically they are all the same jnd.
Different senses have different ratios.
Weber fractionThe ratio between a just-noticeable difference and the magnitude of a stimulus;
reasonably constant over the middle range of most stimulus intensities.
Gustav Fechner also used Weber’s concepts by assuming that jnd was the basic unit of a sensory
experience. Fechner’s concept can be used through the light bulb example behind the 2 discs of frosted
glass. One is a sample and the other is a comparison. We start with comparison and then use that intensity
as the starting point and continue onwards until a difference is recognized in our sample and so on.
A graph would be measured like this: The values on the X-axis are measures of physical intensity i.e.
something measured with respect to the objective world. The values on the Y-axis are jnds. So, in a
general sense it is a mapping between the physical and psychological worlds.
The amount of physical energy necessary to produce a jnd increases with the magnitude of a stimulus.
Fechner’s graph was a representation of the logarithm function through Weber’s ratios.
For scenarios where it would take less energy to create a jnd at higher intensities is shaped as a tip of a
hockey stick with the points closer together at higher intensities.
After 100 years, Stevens produced a mathematical function for Fechner:
S = kI^b; where S is the psychological magnitude of the sensation and I is the intensity of the physical
stimulus. k stands for a mathematical constant that adjusts for the way physical intensity is measured. The
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