Lightness and saturation changes are read as one strength dimension

What it is

Conditional integrality of lightness and chroma means that in some classification and judgment tasks, light–dark and vivid–gray variations in one color sample interfere, so observers cannot fully ignore one while reporting the other. Garner and Felfoldy's experiments found value and chroma integral on the same Munsell chip, but little interference when the dimensions occupied separate chips. The title therefore does not mean every lightness-plus-saturation display collapses to one readable value.

Why it happens

Variation on an irrelevant dimension can slow classification of the target dimension, while correlated variation can produce redundancy gain. Color-appearance dimensions also couple through luminance, reference white, and gamut, so computationally orthogonal coordinates need not be psychologically separable. If two independent variables control lightness and chroma, a change in one may mask, reinforce, or cancel the appearance of the other.

Studying it

Use a Garner speeded-classification design: classify one dimension while the other is constant, correlated, or varying irrelevantly, then swap the target dimension. Match baseline discriminability or apparent interference may merely reflect unequal steps. In visualization, also test separate lookup of each source variable and their joint query, manipulating whether both dimensions occupy one mark or spatially separated marks.

Where it stops holding

Integrality is conditional on stimulus, coordinate system, step size, and task rather than an absolute label for color attributes. Congruent lightness and chroma can reinforce order or salience when both encode one variable, but gamut clipping can reverse one path and create conflicting redundancy. Faceting marks can reduce direct interference while increasing visual travel.

Applying it

• Do not default to mapping two independent quantities to lightness and chroma of one mark. If the task requires it, test both separate lookup and joint judgment.
• Prefer more separable combinations such as position or shape with color, and explain the two mappings separately in the legend.
• For redundant lightness-plus-chroma encoding of one variable, verify monotonicity across the gamut. Interaction may isolate one variable and must work with keyboard and touch.
• Never leave two values encoded only as overall “strength.” Supply text, values, units, and noncolor cues so screen-reader users can retrieve each variable.

Related

• Same group: U1.06.1 Lightness carries order — the first-choice colour dimension for ordinal data · U1.06.2 The same lightness reads as different values on light and dark backgrounds · U1.06.3 Saturation supports fewer discriminable levels than lightness · U1.06.5 Saturation differences are nearly invisible on small marks
• Adjacent: U1.10.1 Encoding one variable on two channels improves judgment robustness · U1.10.3 Two different variables sharing one visual dimension interfere with each other
• Search terms: Garner interference · integral dimensions · lightness chroma