Natural scenes vary considerably—forests and canyons for instance do not share an obvious physical property that make them “natural”. However, across natural scenes a common distribution of amplitude variations exists across spatial and temporal scales called the 1/fα amplitude spectrum (α ≈ 0.6—1.6). This property is also considered to underlie the scale-invariant, fractal properties of natural scenes. Since the visual system has evolved in a natural environment, it is theorised to be optimally tuned to the statistical regularities present in nature. However, the neural response to natural spatial and temporal frequency distributions has not been explored in great detail. To address this, as part of my research I have investigated the pattern of responses in early visual cortex (V1 – V4) to random noise movies that varied in their spatial (α = 0.25, 1.25, 2.25) and temporal (α = 0.25, 0.75, 1.25, 1.75, 2.25) amplitude spectra. Participants were scanned using fMRI while viewing the stimuli, and maximal BOLD activity was observed for stimuli within the natural spatiotemporal range (α = 0.75 and 1.25). These results suggest that early visual cortex is optimally tuned to process stimuli with natural 1/fα frequency distributions in space and time, reinforcing the theory that the visual system has evolved to become tuned to the statistical properties present in our natural environment.
Speaker: Dr Zoey Isherwood is a Postdoctoral Scholar at the University of Nevada, Reno. Her research has so far focused the aesthetic appreciation and visual processing of natural statistical properties—specifically the 1/fα amplitude spectrum. She received her PhD at UNSW Sydney under the supervision of Prof. Branka Spehar and Dr. Mark Schira.