Absolute Threshold is the lowest intensity at which a stimulus can be detected correctly
50% of the time. The lower the abs. threshold, the greater the sensitivity.
Signal Detection Theory
- concerned with the factors that influence sensory judgments.
Decision Criterion -> a standard of how certain one must be that a stimulus is present
before they will say they detect it.
Not everyone has the same decision criterion. Factors affecting it can be fatigue,
expectation, and potential significance.
In a signal detection experiment, participants are told they may or may not hear a warning
tone. This makes persons expect to hear a tone, and may therefore pay higher attention to
listening for it.
The Difference Threshold
Difference Threshold is defined as the smallest difference between two stimuli that
people can perceive 50% of the time (Sometimes called just noticeable difference or
For example, a slight difference in the taste of food can signal that it has gone bad. Wine
tasters and piano tuners earn their living by being able to make very slight
discriminations between stimuli.
Weber’s Law -> states that the jnd is directly proportional to the magnitude of the
stimulus with which the comparison is being made, and can be expressed as a Weber
Fraction. The jnd value for weights is a Weber fraction of 1/50.
e.g If you lift a weight of 500 grams, another comparison object must weigh 510 grams
for you to discriminate between them.
Sensory Adaptation* -> the diminishing sensitivity to an unchanging stimulus. For
example (1) the feel of your wristwatch on your wrist – the feeling becomes unnoticeable
after some time. (2) Diving into a cold pool – the water may feel cold at first but
eventually your body becomes used to the temperature.
This shows that adaptation occurs in response to unchanging stimuli.
*Adaptation is also referred to as habituation
The Sensory Systems
is electromagnetic energy which is measured in nanometers (nm). Humans visual
system is sensitive only to wavelengths extending from about 700nm down to 400