Figure 1

Data in various formats from four studies of intensity (or sensitivity) dependent sensory amplification. Fascinatingly, all four datasets turn out to obey the same law (Eq. 1, see Fig. 2). (a) Ratings of the brightness of five light intensities are higher when a sound comes from the direction of the light⁴. This is the single most compelling dataset on perceptual enhancement – note how the variable gap between the enhanced and unenhanced functions beautifully illustrates the Principle of Inverse Effectiveness (which is not always as clear-cut as found here). (b) Sub-threshold multisensory neurons in cat visual cortex (area PLLS) fire for visual stimuli, do not fire for audio, but have higher firing rates when both stimuli are present¹⁷. (Dashed line shows the unamplified baseline). (c) Subject ratings for loudness of seven audio signals are higher if the subject’s hand is also stimulated¹⁰. (d) Colored lights at short and long wavelengths look brighter³² (dotted function) than would be predicted based on their luminance³³ (dashed function) − a performance-based measure. This spectral broadening (enhancement) of chromatic brightness spectral sensitivity relative to luminance spectral sensitivity has been thought to be due to a neural weighted combination of hue and luminance responses, but an alternate explanation can be seen in Fig. 2.