standardstimulus

Standard stimulus refers to a fixed reference stimulus used in psychophysical experiments as a baseline for comparison. It provides a consistent anchor against which other stimuli are judged or measured, helping to quantify perceptual differences in intensity, duration, wavelength, or other physical properties.

In experimental practice, the standard stimulus is presented alongside test stimuli in various trial formats. Participants judge whether a test stimulus is stronger, weaker, longer, or more similar to the standard. This setup is common in methods such as the constant-stimuli procedure, where a predefined set of stimuli including the standard is presented in random order, and in magnitude estimation tasks, where the standard serves as a 100-percent reference point.

Examples span multiple sensory modalities. In audition, a standard tone of a specified frequency and level may be used to assess loudness discrimination. In vision, a standard light intensity or color can anchor judgments of brightness or hue. In somatosensation, a standard tactile pressure might ground venous discrimination tasks. The standard is often chosen to be representative and easily calibrable for the domain under study.

Data from standard-stimulus experiments are used to construct psychometric functions and to estimate thresholds such as the just noticeable difference (JND). Weber’s law commonly emerges in this context, relating the perceptual difference to the standard magnitude (delta I divided by I).

Careful control of the standard is important: it should be precisely calibrated, stable across trials, and not induce adaptation or fatigue. Variability in the standard can bias results, so researchers may randomize stimulus order and monitor drift over sessions.

See also: anchor stimulus, reference stimulus, psychophysics, JND, threshold.