Abstract
A dim light looks brighter when accompanied by a spatiotemporally coincident sound. The apparent brightness enhancement is a power law of the unenhanced signal. There is a class of neurons - modulated unisensory neurons - in visual cortex that follow the same enhancement power law with a similar exponent, suggesting that cortical modulated unisensory neurons could be a neural correlate of suprathreshold audiovisual brightness enhancement (Billock & Havig, 2018). However, audiovisual detection thresholds follow a different rule, a modified Pythagorean sum called the Minkowski equation, with an exponent of about 1.82 (Schnupp et al., 2005). We analyzed 41 neurons in cat extrastriate visual cortex (area PLLS) that respond to both visual and auditory stimuli (bimodal neurons) and have enhanced responses to audiovisual combinations (Meredith et al., 2012).
We find that this class of cortical neurons combine audiovisual stimuli in the same way as Schnupp's psychophysical data, obeying the Minkowski sum with a very similar exponent of about 1.75. This suggests that cortical bimodal neurons could be a neural correlate of audiovisual threshold sensitivity.
The result is especially interesting because some within-vision cue combinations inherent in binocular vision and color vision also obey the Minkowski equation, suggesting that sensory combination mechanisms could be neurally generic and broadly applicable.
Partly supported by NSF #1456650 to V. Billock