Absolute Threshold and Related Terms Difference Threshold, Sensory Adaptation, Transduction, and Weber’s Law

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.

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.

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 detect…meaning, 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.

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.

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.

Sensory Adaptation We get used to things. This goes for lots of things in life including smells, sounds, sights, games, people, situations…seems 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.

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.

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.

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.

Weber’s Law Psychophysics Weber-Fechner law  Originated by the German physiologist Ernst Heinrich Weber (1795–1878) 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.

Weber’s Law- Example Weber’s 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%)