Why Mach bands are not seen at the edges of a step.

Unlabelled: Mach bands are seen at the two ends of a ramp in luminance from one uniform level to another. Narrow, sharp-edged stimuli centered on the ramp attenuate both Mach bands simultaneously.

Conclusion: Mach bands are not seen at the edges of an abrupt step change in luminance because the sharp edges actively suppress them.

Intermodulation components of the visual evoked potential: responses to lateral and superimposed stimuli.

Nonlinear interactions in the human visual system were studied using visual evoked potentials (VEPs). In one experiment (superimposed condition), all segments of a dartboard pattern were contrast reversed in time by a sum of two sinusoidal signals. In a second experiment (lateral condition), segments in some regions of the dartboard pattern were contrast reversed by a single sinusoid of one frequency, while segments in other (contiguous) regions of the pattern were contrast reversed by a single sinusoid of another frequency.

Attenuation of Mach bands by adjacent stimuli.

Pronounced bright and dark bands are seen at the bright and dark edges of half-shadows and similar distributions of illumination. These are the so-called Mach bands. A pair of vertical Mach bands was generated with a ramp pattern in the central strip of a horizontal tripartite oscilloscope display.