The neural basis for violations of Weber's law in self-motion perception

A prevailing view is that Weber's law constitutes a fundamental principle of perception. This widely accepted psychophysical law states that the minimal change in a given stimulus that can be perceived increases proportionally with amplitude and has been observed across systems and species in hundreds of studies. Im-portantly, however, Weber's law is actually an oversimplification. Notably, there exist violations of Weber's law that have been con-sistently observed across sensory modalities. Specifically, percep-tual performance is better than that predicted from Weber's law for the higher stimulus amplitudes commonly found in natural sensory stimuli. To date, the neural mechanisms mediating such violations of Weber's law in the form of improved perceptual per-formance remain unknown. Here, we recorded from vestibular thalamocortical neurons in rhesus monkeys during self-motion stimulation. Strikingly, we found that neural discrimination thresh-olds initially increased but saturated for higher stimulus amplitudes, thereby causing the improved neural discrimination performance required to explain perception. Theory predicts that stimulus-dependent neural variability and/or response nonlinearities will de-termine discrimination threshold values. Using computational meth-ods, we thus investigated the mechanisms mediating this improved performance. We found that the structure of neural variability, which initially increased but saturated for higher amplitudes, caused improved discrimination performance rather than response nonlin-earities. Taken together, our results reveal the neural basis for vio-lations of Weber's law and further provide insight as to how variability contributes to the adaptive encoding of natural stimuli with continually varying statistics.

Automated summary

Weber's law is considered a fundamental principle of perception, but it is an oversimplification with observed violations; perceptual performance exceeds predictions from Weber's law for higher stimulus amplitudes commonly found in natural sensory stimuli; the study reveals the neural basis for violations of Weber's law and how variability contributes to adaptive encoding of natural stimuli.