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Chapter 5

Psychology 1000 Chapter Notes - Chapter 5: Detection Theory, Absolute Threshold, Electromagnetic Spectrum


Department
Psychology
Course Code
PSYCH 1000
Professor
Dr.Mike
Chapter
5

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Chapter Five Notes
Sensation and Perception
p.170-211
Key term: Synesthesia
Mean quick literally “mixing of the senses”, colours or tastes as touch
sensations that have different shapes
Sensation
1. Stimulus is received by sensory receptors
2. Receptors translate stimulus properties into nerve impulse (transduction)
3. Feature detectors analyze stimulus features
4. Stimulus features are reconstructed into neural representation
5. Neural representation is compared with previously stored information in
brain
6. Matching process results in recognition of stimuli
Weather the stimulus is light, sound waves, a chemical molecule, or
pressure, you sensory receptors must translate this information into the only
language your sensory receptors understand, the language of nerve
impulses.
Perceptions and sensations are very hard to separate,
The stimulation that we receive through our sense organs is
instantaneously organized and transformed into the experience that we refer
to as perceptions
Sensation: Is the stimulus- detection process by which our sense organs
respond to and translate environmental stimuli into nerve impulses that are
sent to our brain
Perception: Making “sense” of what our sense tell us- is the active process of
organizing this stimulus input and giving it meaning
Sensory Process
You 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 only is possible because certain neurons have
developed into specialized sensory receptors that can transform these
energy forms into the code language of nerve impulses
5 Senses: vision, audition (hearing), touch, gustation (taste), and olfaction
(smell), but there are actually much more than these
We are designed to take away from the environment the information that
we need to survive

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Psychophysics: studies relations between the physical characteristics of
stimuli and sensory capabilities, considered with two types of sensitivity
1) absolute limits of sensitivity (Softest sound? weakest salt solution we can
detect)
2) Second has to do with difference between stimuli (how much difference in
tones must there people before we are able to tell that they are not identical
Stimulus detection: The absolute threshold
Absolute threshold: as the lowest intensity at which a stimulus can be
detected correctly 50 percent of the time, thus the lower the absolute
threshold the greater the sensitivity
Many of our senses are surprisingly sensitive
Table 5.1 on page 172, some approximate absolute thresholds for various
sense
Signal Detection theory
Psychologist concluded that the concept of a fixed absolute threshold is
inaccurate because there is no single point on the intensity scale that
separates non- detection from detection of a stimulus
Detection criterion: a standard of how certain they must be that a stimulus is
present before they will say that they detect it
Signal Detection Theory:is concerned with the factors that influence sensory
judgments
The matrix shows four possible outcomes for this theory (p.p 172)
Signal detection research shows us that perception is, in part a decision
Subliminal stimulus: Is one that is so weak or brief that, although it is
received by the senses, it cannot be perceived consciously- thus the stimulus
is well below the absolute threshold
It is argued that subliminal cues can bias what we perceive at a conscious
lever al may alter our conscious experience of those stimuli
The difference threshold
Is defined as the smallest difference between two stimuli that people can
perceive 50 percent of the time, it is sometimes called the just noticeable
difference (jnd)
Weber’s law: states that the difference in threshold is directly proportional to
the magnitude of the stimulus with which the comparison is being made, and
can be expressed in weber’s fraction. The smaller the fraction, the greater
sensitivity to differences.
Sensory Adaption
Sensory systems are finely tuned to changes in stimulation

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Sensory neurons are engineered to respond to a constant stimulus by
decreasing their activity, and the diminishing sensitivity to an unchanging
stimulus is called sensory adaptation
Adaptation occurs in every sensory modalities
Although sensory adaptation may reduce our overall sensitivity, it is
adaptive because it frees our senses from the constant and the mundane to
pick up information changes in the environment
The Sensory systems
Vision
The normal stimulus for vision is electromagnetic energy, or light waves,
which are measured in nanometers (nm).
Humans can only perceive tiny portions the electromagnetic spectrum
includes x-rays, television, and radio signal
Our vision is sensitive only to wavelengths extending about 700 nm (red)
down to 400 nm (blue- violet)
You can memorize the order of the spectrum from higher to lower
wavelengths with the name ROY G. BIV: red, orange, yellow, green, blue,
indigo, violet. It goes from highest Infrared to ultraviolet
The Human eye
Light waves enter the eye through the cornea (a transparent protective
structure at the front of the eye
Behind the cornea is the pupil (an adjustable opening that can dilate or
constrict to control the amount of light that enters the eye)
The iris surrounds the pupil and controls it’s size (muscles)
Lens, elastic structure that becomes thinner to focus on distant objects and
thick to focus nearby objects. The lens reverses the image from left to right
and up to down when projected in the retina, but the brain reconstructs this
image in the ay that we perceive it
Retina: multi layered tissue at the rear of the fluid filled eyeball
Our ability to see clear depends on the lens’s ability to focus the image
directly onto the retina
myopia (nearsightedness) : eyeball is longer than normal therefore can’t see
far away
Hyperopia (farsightedness): occurs when lens do not thicken enough
Eye glasses and contacts are designed to correct for the natural lens’s
inability to focus the visual image directly onto the retina
Photoreceptors: The rods and cones
The retina is a multi-layered screen that lines the back surface of the
eyeball and contains specialized sensory neurons, is actually an extension of
the brain
It contains two light sensitive receptor cells, called rods and cones (120
million rods and 6 million cones
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