Concepts

Difference threshold

The smallest reliably detectable change depends on what it is compared with.

Definition

A difference threshold, also called a just noticeable difference, is the change between stimuli detected at a specified performance criterion.

How to understand it

Unlike an absolute threshold, this measurement asks whether two intensities differ. The starting intensity matters. Weber’s law describes an approximate proportional relationship between a detectable increment and the original intensity across some conditions. It is a useful pattern for introductory reasoning, not a guarantee that one fixed ratio applies to every sense or the entire intensity range.

A careful comparison keeps the task clear: noticing that a stimulus exists and noticing that it has changed are different judgments. Repeated trials and a stated criterion are needed because performance varies. In a lesson, compare several starting levels rather than using one successful judgment as evidence for a universal rule about human sensitivity.

Evidence: (Spielman et al., 2020); (Noba: Sensation and Perception, n.d.)

Comparing fictional display settings

Teaching scenario

A class imagines two screens, one relatively dim and one bright. Each receives the same small increase in output, and students predict whether the increments will be equally noticeable. They design a repeated comparison task with several increment sizes. The lesson concerns the relation between increment and baseline; it provides no actual threshold values and makes no claim about a particular device or participant.

Constructed for learning. This scenario is not a report of an empirical finding or a diagnosis.

Common confusion: Absolute threshold

A difference threshold compares stimuli or changes; an absolute threshold concerns detecting a stimulus at all.

Compare absolute and difference thresholds

Evidence: (Spielman et al., 2020); (Noba: Sensation and Perception, n.d.)

Limits of the concept

  • Weber’s proportional rule is approximate and has limits across intensities and sensory tasks.
  • A numerical change in a device setting does not automatically equal a measured change in physical stimulation.

Evidence: (Spielman et al., 2020); (Noba: Sensation and Perception, n.d.)

Textbook connection

Direct coveragePsychology 2e: 5.1 Sensation versus Perception

Direct JND, baseline-intensity, and Weber’s-law coverage.

Supplementary concepts may extend beyond this section. The source notes below identify the evidence for those details.

Related concepts

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Sources and inspection notes

Checked October 21, 2026. An inspection date is not a source publication date. Definitions and scenarios on this page are original teaching explanations.

  1. Noba: Sensation and perception. (n.d.). https://nobaproject.com/modules/sensation-and-perceptionPsychophysics, probabilistic thresholds, and stimulus-driven versus knowledge-guided processing.

    Opened and inspected on 21 October 2026. Academic teaching synthesis; not a primary experiment.

  2. Spielman, R. M., Jenkins, W. J., & Lovett, M. D. (2020). Psychology 2e. OpenStax. https://openstax.org/books/psychology-2e/pages/5-1-sensation-versus-perceptionCourse textbook section

    Opened actual subsection on 21 October 2026; title and URL verified. Course textbook, not independent primary evidence.