Fluctuation scaling in the visual cortex at threshold.
Fluctuation scaling relates trial-to-trial variability to the average response by a power function in many physical processes. Here we address whether fluctuation scaling holds in sensory psychophysics and its functional role in visual processing. We report experimental evidence of fluctuation scaling in human color vision and form perception at threshold. Subjects detected thresholds in a psychophysical masking experiment that is considered a standard reference for studying suppression between neurons in the visual cortex. For all subjects, the analysis of threshold variability that results from the masking task indicates that fluctuation scaling is a global property that modulates detection thresholds with a scaling exponent that departs from 2, β=2.48±0.07. We also examine a generalized version of fluctuation scaling between the sample kurtosis K and the sample skewness S of threshold distributions. We find that K and S are related and follow a unique quadratic form K=(1.19±0.04)S^{2}+(2.68±0.06) that departs from the expected 4/3 power function regime. A random multiplicative process with weak additive noise is proposed based on a Langevin-type equation. The multiplicative process provides a unifying description of fluctuation scaling and the quadratic S-K relation and is related to on-off intermittency in sensory perception. Our findings provide an insight into how the human visual system interacts with the external environment. The theoretical methods open perspectives for investigating fluctuation scaling and intermittency effects in a wide variety of natural, economic, and cognitive phenomena.
Departamento de Óptica, Facultad de Ciencias, Universidad de Granada, Edificio Mecenas, 18071, Granada, Spain.
José M
JM
Medina
Departamento de Óptica, Facultad de Ciencias, Universidad de Granada, Edificio Mecenas, 18071, Granada, Spain.
José A
JA
Díaz
D055253:Color Vision / Q000502:physiology; D004777:Environment; D006801:Humans; D008959:Models, Neurological; D011601:Psychophysics; D014793:Visual Cortex / Q000502:physiology*; D014796:Visual Perception / Q000502:physiology*