An illustration of the remarkable sensitivity of human vision is that on a clear, dark night, the most sensitive receptor cells in the eye can perceive the flame of a candle from a distance of 30 miles.

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An absolute threshold is a measure of a sensory system's sensitivity, referring to the minimum amount of stimulus energy required to be detected about 50% of the time. It represents the lowest level of physical energy that sensory receptors can reliably register as a sensation.

Absolute Threshold

Spielman, R. M., Jenkins, W. J., & Lovett, M. D. (2020, April 22). Psychology (2nd ed.). OpenStax. https://openstax.org/books/psychology-2e/pages/1-introduction

OpenStax Psychology (2nd ed.) Textbook

Subliminal messages are stimuli presented below the absolute threshold for conscious awareness. Although these stimuli are potent enough to activate sensory receptors and trigger nerve impulses to the brain, they are not consciously perceived. While research in laboratory settings has shown that individuals can process and react to information outside of their awareness, these hidden messages have been found to have very little influence on behavior in real-world contexts.

Subliminal Messages

Example of Absolute Threshold in Vision

The absolute threshold for human hearing demonstrates high sensitivity; under ideal quiet conditions, the hair cells within the inner ear are capable of detecting the sound of a clock ticking from 20 feet away.

Example of Absolute Threshold in Audition

The difference threshold, also known as the just noticeable difference, refers to the minimum amount of difference in stimulus energy required for a sensory system to detect a change about 50% of the time. While an absolute threshold measures the initial detection of a stimulus, the difference threshold measures the ability to detect variations between stimuli.

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