Absolute Threshold and Related Terms

1
Absolute Threshold and Related Terms

• Difference Threshold, Sensory Adaptation,
  Transduction, and Webers Law

2
Sensation and Perception

• To represent the world, we must detect physical
  energy (a stimulus) from the environment and
  convert it into neural signals. This is a process
  called sensation.
• When we select, organize, and interpret our
  sensations, the process is called perception.

3
Absolute Threshold

• One formal definition is that absolute threshold
  is the smallest intensity of a stimulus that has
  to be present for the stimulus to be detected 50
  of the time.

4
Absolute Threshold Example

• Think of an electric burner on a stove. Imagine
  turning that burner on and then placing your hand
  directly on it.
• At first you won't feel much heat because is
  takes time for the burner to heat up. But at some
  point it will get hot enough for you to
  detectmeaning, there is some temperature that is
  just hot enough for you to notice it.
• This isn't the point at which you get burned, but
  the point at which it is just hot enough for you
  to detect the presence of the heat.

5
Difference Threshold

• The difference threshold, a.k.a. the just
  noticeable difference (jnd), is the minimum
  difference in stimulation needed so that a person
  can detect the difference between two stimuli.

6
Difference Threshold Example

• For example, let's say I asked you to put your
  hand out and in it I placed a pile of sand. Then,
  I add tiny amounts of sand to your hand and ask
  you to tell me when you notice any change in the
  overall weight.
• As soon as you can detect any change in the
  weight, that difference between the weight of the
  sand before I added that last bit of sand and the
  amount of sand after I added it, is the
  difference threshold.

7
Sensory Adaptation

• We get used to things. This goes for lots of
  things in life including smells, sounds, sights,
  games, people, situationsseems like after a
  while we get used to everything.
• One reason we get used to everything is because
  of sensory adaptation, which is reduced
  sensitivity to stimulation that results from
  repeated or prolonged presentations of that
  stimulation.

8
Sensory Adaptation Example

• For example, my car was in for service recently
  and the dealer gave me a rental to use while the
  car was being serviced. As soon as I got into the
  car I was overwhelmed by the smell of smoke (even
  though I asked for a non-smoking car). It stunk!
• But after driving the car for 30 minutes or so, I
  didn't really notice the smell. I got used to it
  because I was immersed in it. I experienced
  sensory adaptation.

9
Transduction

• Transduction Technically speaking, transduction
  is the process of converting one form of energy
  into another.
• As it relates to psychology, transduction refers
  to changing physical energy into electrical
  signals (neural impulses) that can make their way
  to the brain.

10
Transduction Example

• For example, your ears receive energy (sound
  waves) and transduce (or convert) this energy
  into neural messages that make their way to your
  brain and are processed as sounds.

11
Webers Law

• Psychophysics
• Weber-Fechner law  Originated by the German
  physiologist Ernst Heinrich Weber (17951878) in
  1834 and elaborated by his student Gustav Theodor
  Fechner.
• The law states that the change in a stimulus that
  will be just noticeable is a constant ratio of
  the original stimulus. It was later shown not to
  hold for extremes of stimulation.

12
Webers Law- Example

• Webers Law If we can distinguish a
  Just-Noticeable Difference in sound intensity
  between 100 hand bells and 110 hand bells, we may
  argue that we may be able to distinguish the
  difference between 10 and 11 hand bells, or
  between 300 and 330 hand bells a 10 difference
  in each case. So argued the German physiologist E
  H Weber.
• Our thresholds for detecting differences are a
  roughly constant proportion to the size of the
  original stimulus. (approx. 10)