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Non-monotonic noise tuning of the BOLD signal to natural images in monkey primary visual cortex | ||
Gregor Rainer | ||
Max Planck Institute for Biological Cybernetics | ||
The perceptual ability of humans and monkeys to identify natural images declines monotonically as noise is added to the Fourier phase spectrum of the images. Unlike behavioural performance, blood-oxygenation-level-dependent (BOLD) signal levels in the primary visual cortex (V1) of the anesthetized monkey were non-monotonic. The BOLD response had a V-shaped tuning function with local maxima for non-degraded natural images and pure noise patterns (random phase with natural amplitude spectrum), and a minimum for intermediate images with Fourier phase interpolated between natural and random phase. I will describe a simple model, which suggests that the V-shaped tuning function may be a result of a trade-off between the number of responsive V1 neurons and the strength of the response. In addition, BOLD activity in extrastriate cortex will be compared with single unit data recorded in awake monkeys using the same stimuli. Together, these studies aim to shed light on the representation of natural images in visual cortical areas and to advance our understanding of the relation between single unit activity and BOLD signal levels for complex natural inputs. | ||