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Chapter 5

Psychology 1000 Chapter Notes - Chapter 5: Additive Color, Taste, Roygbiv


Department
Psychology
Course Code
PSYCH 1000
Professor
Prof
Chapter
5

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Chapter 5
Sensation and Perception
1
Chapter 5:
Sensation and Perception
- Synthesia is the experience of “mixing sense”
o Experience sounds as colours or tastes as touch sensations have
different shapes
- Sensory-Impaired people provide glimpses into different aspects of how we
“sense” and “understand” our world
- Whether the stimulus is light, sound waves a chemical molecule, or pressure
o Sensory receptors must translate information into the only language
your nervous system understands
Language of nerve impulses
Process of transduction
- Feature detectors
o Specialized neurons that break down and analyze the specific features
of the stimuli
- Then numerous stimulus “pieces” are reconstructed into a neural
representation that is then compared with previously stored information
- This matching of a new stimulus with our internal storehouse of knowledge
allows us to recognize the stimulus and give it meaning
- Then we consciously experience a perception
- We know what specific parts of the brain are specialized for different sensory
functions
o Some sort of cross wiring so that one activity in one part of the brain
evokes responses in another part of the brain
o Both normal perceptual processes and synaesthesia relate to one of
the big mysteries in cognitive neuroscience
Called the binding problem
- The stimulation we receive through our sense organs in immediately
organized and transformed into the experiences that we refer to as
perceptions
Sensation stimulus-detection process by which our sense organs respond to
and translate environmental stimuli into nerve impulses that are sent to the
brain
Perception making “sense” of what our senses tell us is the active process of
organizing this stimulus input and giving it meaning
Sensory Processes
- Brain cannot “understand” light waves, sound waves or the other forms of
energy that make up the language of the environment
- Contact with the outer world is possible only because certain neurons have
developed into specialized sensory receptors
o They transform these energy forms into the code language of nerve
impulses
- Many species have senses that humans lack together

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Chapter 5
Sensation and Perception
2
- Whatever the source of stimulation, its energy must be converted into nerve
impulses
o Only language the nervous system understands
Transduction process whereby the characteristics of a stimulus are
converted into nerve impulses
- More than five classical senses with which we’re familiar with
o Vision (sight)
o Audition (hearing)
o Touch
o Gustation (taste)
o Olfaction (smell)
- There are senses that provide information about balance and body position
- Sense of touch can be subdivided:
o Pressure
o Pain
o Temperature
- Immune system also has sensory functions that allow it to detect foreign
invaders and to receive stimulation from the brain
- We have specialized sensors that can detect many different kinds of stimuli
with considerable sensitivity
Psychophysics studies relations between the physical characteristics of
stimuli and sensory capabilities
o Concerned with two kinds of sensitivity
Limits of sensitivity
Differences between stimuli
Stimulus Detection: Absolute Threshold
Absolute Threshold lowest intensity at which a stimulus can be detected
correctly 50% of the time
- Lower the absolute threshold, greater the sensitivity
Signal Detection Theory
- A fixed absolute threshold is inaccurate
o No single point on the intensity scale that separates non-detection
from detection of a stimulus
Decision Criterion: a standard of how certain they must be that a stimulus is
present before they will say they detect it
Signal Detection Theory: concerned with the factors that influence sensory
judgements
The Difference Threshold
- The smallest difference between two stimuli that people can perceive 50% of
the time
o Also referred to as the just noticeable difference (jnd)
- Weber’s Law

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Chapter 5
Sensation and Perception
3
o The difference threshold (jnd) is directly proportional to the
magnitude of the stimulus with which the comparison is being made
o Can be expressed as Weber fraction
- Holds up reasonably well within the most frequently encountered range
- The smaller the fraction, the greater the sensitivity to differences
Sensory Adaptation
- Sensory systems are finely attuned to changes in stimulation
- Diminishing sensitivity to an unchanging stimulus is called sensory
adaptation
Adaptation: part of every day experience (sometimes called habitation)
- Sensory adaptation may reduce our overall sensitivity
o It’s adaptive
o Frees our senses from the constant and the mundane to pic up
informative changes in the environment
The Sensory Systems
Vision
- Normal stimulus for vision is electromagnetic energy, or light waves
o Measure in nanometres
- Our visual system is sensitive only to wavelengths extending from about 700
nanometers (red) down to about 400 nanometers (blue-violet)
- ROY-G-BIV
The Human Eye
- Light waves enter the eye through the cornea
o Transparent protective structure at the front of the eye
- Behind the cornea is the pupil
o Adjustable opening that can dilate or constrict to control the amount
of light that enters the eye
- Coloured iris that surrounds the pupil
- Low levels of illumination cause the pupil to dilate
o Bright light triggers constriction of the pupil
- Behind the pupil is the lens
o Elastic structure that becomes thinner to focus on distant objects and
thicket to focus on nearby objects
- The retina is light sensitive
o Multi-layered tissue at the rear of the fluid-filled eyeball
- Lens reverse the image from right to left and top to bottom when it’s
projected on the retina
o The brain reconstructs the visual input into the image that we
perceive
- Myopia is when the lens focuses the visual image in front of the retina
resulting in a blurred image for faraway objects
o Eyeball is longer than normal
o Nearsightedness
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