Neural correlates of perceptual filling-in of an artificial scotoma in humans

Abstract

When a uniformly illuminated surface is placed eccentrically on a dynamic textured background, after a few seconds, it is perceived to disappear and be replaced by the background texture. Such texture filling-in is thought to occur in retinotopic visual cortex, but it has proven difficult to distinguish the contributions of invisible target and visible background to signals measured in these areas. Here, we used magnetoencephalography to measure time-dependent brain responses in human observers experiencing texture completion. We measured responses specifically associated with the filled-in target, by isolating neural population signals entrained at the frequency of flicker of the target. When perceptual completion occurred, and the target became invisible, there was significant reduction in the magnetoencephalography power at the target frequency over contralateral posterior sensors. However, even a subjectively invisible target nevertheless evoked frequency-specific signals compared with a notarget baseline. These data represent evidence for a persistent targetspecific representation even for stimuli rendered invisible because of perceptual filling-in. magnetoencephalography ͉ perception ͉ perceptual completion ͉ visual cortex

A new taxonomy for perceptual filling-in

“…Similarly, target-specific responses to a perceptually filled-in artificial scotoma are reduced compared to responses to the visible target (Weil et al, 2007). However, even when invisible, target-specific responses remain, compared with a no-target baseline, indicating continued representation of these target-specific responses and consistent with an active process of perceptual filling-in.…”

The SSVEP tracks attention, not consciousness, during perceptual filling-in

“…Importantly, we developed a novel method that allowed us to capture neural markers of attention and/or consciousness during PFI, that separately frequency-tagged targets and their visual surrounds. We achieved this by building upon previous work that has facilitated PFI by making the surrounding regions dynamic, such as when updated with visual noise ( Davidson et al, 2020 ; De Weerd et al, 1998 ; De Weerd et al, 1995 ; Ramachandran and Gregory, 1991 ; Spillmann and Kurtenbach, 1992 ; Weil et al, 2007 ; Weil et al, 2008 ). Our critical manipulations were to calibrate the dynamic noise texture to evoke an SSVEP and to extend this texture over our enlarged target regions.…”

Growing evidence for separate neural mechanisms for attention and consciousness

“…Davidson and colleagues (Matthew J Davidson, Mithen, Hogendoorn, van Boxtel, & Tsuchiya, 2020) adapted a display where SSVEP stimuli faded from view due to visual adaptation (see also (M. J. Davidson, Graafsma, Tsuchiya, & van Boxtel, 2020;Schieting & Spillmann, 1987;Weil, Kilner, Haynes, & Rees, 2007)). Intriguingly, this perceptual fading is known to be enhanced by attention, in that attending to flickering stimuli results in more rapid and more frequent disappearance (DeWeerd, Smith, & Greenberg, 2006;Lou, 1999).…”