Sensation refers to our ability to detect or sense the physical qualities of our environment.

There are several types of thresholds including sensory, absolute, and difference. The sensory threshold is the weakest stimulus an organism can detect a sensation. The most important sensory threshold is the absolute threshold, which is the smallest detectable level of a stimulus. Every sense has an absolute threshold. The absolute threshold is defined as the lowest intensity at which a stimulus can be detected (recently, signal detection theory has offered a more nuanced definition of absolute threshold: the lowest intensity at which a stimulus will be specified a certain percentage of the time, often 50%).

The minimum amount of change in sensory stimulation needed to recognize that a change has occurred is known as the difference threshold or just-noticeable difference (JND). JND is the minimum amount by which stimulus intensity must be changed to produce a noticeable variation in sensory experience. For many sensory modalities, over a wide range of stimulus magnitudes sufficiently far from the upper and lower limits of perception, the JND is a fixed proportion of the reference sensory level, and so the ratio of the JND/reference is roughly constant (that is the JND is a constant proportion/percentage of the reference level).

Known as Weber’s Law, this states that the difference threshold is proportional to the magnitude of the stimulus, where ΔI is the difference in threshold and I represent the initial stimulus. Modern approaches to psychophysics (the branch of psychology that deals with the relationships between physical stimuli and mental phenomena), including signal detection theory, imply that the observed JND is not an absolute quantity, but will depend on situational and motivational as well as perceptual factors.

At its most basic, signal detection theory states that the detection of a stimulus depends on both the intensity of the stimulus and the physical/psychological state of the individual. Basically, we notice things based on how strong they are and on how much we’re paying attention.

Sensory adaptation happens when our senses no longer perceive a stimulus because of our sensory receptor ‘s continuous contact with it. If you’ve ever entered a room that has a terrible odor, but after a few minutes realized that you barely noticed it anymore, then you have experienced sensory adaptation. Like thresholds, adaptation can occur with any sense, whether it’s forgetting that the radio is on while you work or not noticing that the water in the pool is cold after you’ve been swimming for a while.

Sensory perception is complicated, and involves many different systems in the brain and body. Sensory interaction can even occur, in which one sensory modality affects another (for example, needing to turn down the music in the car so you can see the street signs better).

Practice Questions

 Khan Academy

Somatosensory effects of Temple Grandin’s squeeze box on hypersensitivity

 

MCAT Official Prep (AAMC)

Official Guide P/S Section Question 29

Section Bank P/S Section Question 81

Practice Exam 3 P/S Section Question 58

Key Points

• Sensory thresholds are the point at which a stimulus causes a sensation within an individual. Weber’s law relates related to the change in intensity of a stimulus to its ability to meet the threshold value.

• Sensory adaptation can occur when an organism is not perceiving stimuli that remain relatively constant over prolonged periods.

Key Terms

Sensory threshold: The point at which a stimulus causes a sensation within an individual; below the sensory threshold, there will be no sensation.

Absolute threshold: A thing or event that evokes a specific functional reaction in an organ or tissue.

Just-noticeable difference (JND): the amount something must be changed in order for a difference to be noticeable, detectable at least half the time.

Stimulus: Anything effectively impinging on any of the sensory apparatuses of a living organism, including physical phenomena both internal and external to the body.

Sensation: A mental process (such as seeing, hearing, or smelling) resulting from the immediate external stimulation of a sense organ often as distinguished from a conscious awareness of the sensory process.

Sensory adaptation: The process in which changes in the sensitivity of sensory receptors occur in relation to the stimulus.

Weber’s Law: The difference threshold is proportional to the magnitude of the stimulus.

Psychophysics: The branch of psychology that deals with the relationships between physical stimuli and mental phenomena.

Signal detection theory: The detection of a stimulus depends on both the intensity of the stimulus and the physical/psychological state of the individual.

Sensory interaction: a phenomenon in which one sensory modality (ie hearing) affects another (ie vision)