Sensory substitution devices remap channels: Paul Bach-y-Rita’s 1969 system pressed camera images into the skin, and later systems like the vOICe encode images as sweeping soundscapes for blind users. With training, users stop hearing beeps and start perceiving space.
That shift is the interesting part. Practiced users report the experience becoming perceptual rather than translational, and imaging shows visual cortex responding to the substituted signal. It is the strongest evidence that the brain is organized around tasks more than input channels.
Audio-reactive visualizers are substitution run for pleasure rather than necessity: structure in sound rendered as structure in light.