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Chapter 5

Chapter 5 textbook notes

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Department
Psychology
Course Code
PSYA01H3
Professor
Steve Joordens

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Chapter 5: Sensation
- Our senses are the means by which we experience the world; everything we learn is detected by
sense organs and transmitted to our brains by sensory nerves
- Milner and Goodale: ^s]]}vÀ}}}À]]ov}Ç}v}o}(Zu}ÀuvZ
Zv]uoul]v}}µÀv}µ]vZÁ}o_
- Sense systems do that depending on (1) specific modality of the information (2) characteristics
of the information and the state of the brain at the time it receives it
- Visual system provides stability in the face of rapid shifts in its input.
- Sound is not so variable, and is more gradual. Our auditory sense has more time to process
signals
- When we feel an object, the experience is active, not passive
Sensory processing:
- Experience is studied by distinguishing between sensation (detection of simple properties of
stimuli, such as brightness, colour, warmth and sweetness) and perception (detection of objects
both animate and inanimate, their locations, movements and backrounds).
- Ex: seeing the colour red is a sensation, but seeing a red apple is a perception
Transduction:
- Sense organs detect stimuli, provided by light, taste, sound, odor or mechanical contact with
the environment. Information about these stimuli is transmitted to the brain through neural
impulses t action potentials carried by the axons in sensory nerves
- The task of these sense organs is to transmit signals to the brain of the events that have
happened in the environment. The task of the brain is to analyze this information and to
reconstruct what has occurred
- transduction ( leading across): process by which the sense organs convert energy from
environmental events (physical stimuli) into neural activity (changes in the activity of receptor
cells of sensory organs)
- in most senses, specialized neurons called receptor cells ( a neuron that directly responds to a
physical stimulus, such as light, vibrations, or smell) release chemical transmitter substances
that stimulate other neurons, thus altering the rate of firing their axons
- table 5.1 page 130 t types of transduction accomplished by our sense organs
Sensory coding
- we can tell apart 7.5 million different colours and recognize 10 000 odors
- A code is a system of symbols or signals representing information (ex: spoken English, written
&vZU((]o]PZY
- if we know the rules of a code, we can convert a message from one medium to another without
losing any information
- we do not know the precise rules by which the sensory systems transmit information to the
brain, but we know that they take two general forms: (1) Anatomical coding and (2) Temporal
coding
- Firing of a particular set of neurons tells where the body is being touched (anatomical coding),
and the rate at which these neurons fire (temporal coding) tells how intense the touch is.
www.notesolution.com
1) since the brain has no direct information about the physical energy impinging on a given
sense organ, it uses anatomical coding to interpret the location and type of sensory stimulus
according to which incoming nerve fibers are active. Ex: if you rub your eye, you will
mechanically stimulate the light-sensitive receptors located there. This stimulation produces
action potentials in the axons of the nerves that connect the eyes with the brain (the optic
nerves)
- Anatomical coding: a means by which the nervous system represents information; different
features are coded by the activity of different neurons
2) temporal coding is the coding of information in means of time. Simplest form is rate. Ex: light
touch to the skin can be encoded by a low rate of firing.
- Temporal coding: a means by which the nervous system represents information; different
features are coded by the pattern of activity of neurons.
- all sensory systems use rate of firing to encode the intensity of stimulation
Psychophysics
- a branch of psychology that measures the quantitative relation between physical stimuli and
perceptual experience ( sensations they produce)
- to study perceptual phenomena, scientists used two methods to measure peoples sensations:
(1) the just-noticeable difference and (2) procedures of signal detection theory
1) JND: the smallest difference between two similar stimuli that can be distinguished; also called
difference threshold
- in germany, Ernst Weber investigated the ability of humans to discriminate between various
stimuli. He measured the JND t the smallest change in the magnitude of a stimulus that a
person can detect, and discovered that the JND is directly related to the magnitude of the
stimulus.
- Different senses had different ratios (ex: ratio for detecting differences in the brightness of
white light is 1 in 60). These ratios are called Weber Fractions
- Gustav Fecher µt[}v}(Z:E}uµ}ov]}vX
- His contribution to psychology was to show how a logarithmic function could be derived from
t[]v]o
- íììÇ(&Zv[Á}lUS. S. Stevens suggested a power function to relate physical
intensity to the magnitude of sensation
2) signal detection theory: a mathematical theory of the detection of stimuli, which involves
discriminating a signal from the noise in which its embedded and which takes into account
]]v[Á]oo]vPv}}]vPZ]Pvo
- Psychological methods rely heavily on the concept of threshold (the point in which a stimulus,
}ZvP]vZÀoµ}(]uµUviµYXdZo]vÁv]À]vPv
not perceiving). The JND can also be called a difference threshold (the minimum detectable
difference between two stimuli). An absolute threshold is the minimum value of a stimulus that
can be detected --- that is, discriminated from no stimulus at all.
- By convention, the threshold is the point at which a participant detects the stimulus 50% of the
time
www.notesolution.com
- According to the signal detection theory, every stimulus event requires discrimination between
signal (stimulus) and noise (consisting of both background stimuli and random activity of the
nervous system)
- Figure 5.3 page 133
- Receiver operating characteristic curve (ROC curve): a graph of hits and false alarms of
]]vµv]((vu}]À]}vo}v]]}vV]v]}o[]o]Ç}
particular stimulus.
- Named for its original use in research at the Bell Labratories to measure the intelligibility of
speech transmitted through a telephone system
Vision
- Wavelength: the distance between adjacent waves of radiant energy; in vision, most closely
associated with the perceptual dimension of hue
- Wavelength of visible light ranges from 380 to 760 nanometers.
- Entire range of wavelengths is known as the electromagnetic spectrum
- The part we see as light is called the visible spectrum
- Figure 5.6 page 135
The Eye and its Functions
- Figure 5.7 page 135
- Cornea: the transparent tissue covering the front of the eye
- ScleraWZ}µPZ}µoÇ}(ZÇVZ^ÁZ]_}(ZÇ
- Iris: consists of two bands of muscles (controlled by the brain) that control the amount of light
admitted into the eye / the size of the pupil
- Aqueous humour: the watery fluid filled in the space space immediately behind the cornea
- lens: the transparent organ situated behind the iris of the eye; helps focus an image on the
retina. Contains no blood vessels and is functionally dead tissue
- cornea and lens help image to be focused on the inner surface of the back of the eye
- accommodation: changes in the thickness of the lense of the eye that focus images of near or
distant objects on the retina
- nearsightedW}oÁZ}[Ç}}o}vP~(}v}lVZÇv}vÀovo
correct the focus
- farsighted: people whos eyes are too short. They need a convex lens
- retina: the tissue at the back inside surface of the eye that contains the photoreceptors and
associated neurons, performs the sensory functions of the eye
- photoreceptors: specialized neurons that transducer light into neural activity in the retina
- information from the photoreceptors is transmitted to neurons that send axons toward one
point at the back of the eye t the optic disc. All axons leave the eye at this point and join the
optic nerve, which travels to the brain.
- Johannes Kepler is credited with the suggestion that the retina, not the lens, contained the
receptive tissue of the eye.
- Christoph Scheiner demonstrated in 1625 that the lens is simply a focusing devise. Recorded the
v]}v}(ZÇ(}uv}Æ[Ç
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Description
Chapter 5: Sensation - Our senses are the means by which we experience the world; everything we learn is detected by sense organs and transmitted to our brains by sensory nerves - Milner and Goodale: ^I]Z]}L}o}}]]ZoZLZ} }L}o}ZK}KLZZ ZL]KoKlZ]L}}Z]L} ]LZ}o_ - Sense systems do that depending on (1) specific modality of the information (2) characteristics of the information and the state of the brain at the time it receives it - Visual system provides stability in the face of rapid shifts in its input. - Sound is not so variable, and is more gradual. Our auditory sense has more time to process signals - When we feel an object, the experience is active, not passive Sensory processing: - Experience is studied by distinguishing between sensation (detection of simple properties of stimuli, such as brightness, colour, warmth and sweetness) and perception (detection of objects both animate and inanimate, their locations, movements and backrounds). - Ex: seeing the colour red is a sensation, but seeing a red apple is a perception Transduction: - Sense organs detect stimuli, provided by light, taste, sound, odor or mechanical contact with the environment. Information about these stimuli is transmitted to the brain through neural impulses J action potentials carried by the axons in sensory nerves - The task of these sense organs is to transmit signals to the brain of the events that have happened in the environment. The task of the brain is to analyze this information and to reconstruct what has occurred - transduction ( leading across): process by which the sense organs convert energy from environmental events (physical stimuli) into neural activity (changes in the activity of receptor cells of sensory organs) - in most senses, specialized neurons called receptor cells ( a neuron that directly responds to a physical stimulus, such as light, vibrations, or smell) release chemical transmitter substances that stimulate other neurons, thus altering the rate of firing their axons - table 5.1 page 130 J types of transduction accomplished by our sense organs Sensory coding - we can tell apart 7.5 million different colours and recognize 10 000 odors - A code is a system of symbols or signals representing information (ex: spoken English, written L Z7] o]2ZZ; - if we know the rules of a code, we can convert a message from one medium to another without losing any information - we do not know the precise rules by which the sensory systems transmit information to the brain, but we know that they take two general forms: (1) Anatomical coding and (2) Temporal coding - Firing of a particular set of neurons tells where the body is being touched (anatomical coding), and the rate at which these neurons fire (temporal coding) tells how intense the touch is. www.notesolution.com
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