The edge of awareness: Mask spatial density, but not color, determines optimal temporal frequency for continuous flash suppression

Abstract

The study of how visual processing functions in the absence of visual awareness has become a major research interest in the vision-science community. One of the main sources of evidence that stimuli that do not reach conscious awareness-and are thus "invisible"-are still processed to some degree by the visual system comes from studies using continuous flash suppression (CFS). Why and how CFS works may provide more general insight into how stimuli access awareness. As spatial and temporal properties of stimuli are major determinants of visual perception, we hypothesized that these properties of the CFS masks would be of significant importance to the achieved suppression depth. In previous studies however, the spatial and temporal properties of the masks themselves have received little study, and masking parameters vary widely across studies, making a metacomparison difficult. To investigate the factors that determine the effectiveness of CFS, we varied both the temporal frequency and the spatial density of Mondrian-style masks. We consistently found the longest suppression duration for a mask temporal frequency of around 6 Hz. In trials using masks with reduced spatial density, suppression was weaker and frequency tuning was less precise. In contrast, removing color reduced mask effectiveness but did not change the pattern of suppression strength as a function of frequency. Overall, this pattern of results stresses the importance of CFS mask parameters and is consistent with the idea that CFS works by disrupting the spatiotemporal mechanisms that underlie conscious access to visual input.

Limits on visual awareness of object targets in the context of other object category masks: Investigating bottlenecks in the continuous flash suppression paradigm with hand and tool stimuli

“…This has been shown to be the optimal temporal frequency for suppression in other CFS studies (Drewes et al, 2018;Zhu, Drewes, & Melcher, 2016), but is actually a slower rate than Cohen et al (2015), who used ~117 ms (8.5 Hz); nevertheless we found comparable breakthrough times (see Experiment 3). A trial started with the presentation of the black fixation dot for 250 ms which then turned red for 200 ms to alert participants that the trial was about to start.…”

“…A further image characteristic that could influence breakthrough times is the amount of edges (local clustering of contrast changes). In fact, it has previously been suggested that the amount of edges could determine CFS because increased spatial density of Mondrian masks result in longer breakthrough times (Drewes, Zhu, & Melcher, 2018). However, in this previous study, their manipulation of spatial density changed both edge content and global spatial frequency content, contrast and luminance.…”

“…The CFS paradigm involves fast presentations of large masks over a relatively long trial time. This would challenge processing capacity in early visual cortex, which could then result in large effects of edge content on reaction time measures (Drewes et al, 2018), especially when using stimuli with relative high or low edge-content such as hands and tools. This could, in turn, mask other potential effects due to the representational architecture.…”

Limits on visual awareness of object targets in the context of other object category masks: Investigating bottlenecks in the continuous flash suppression paradigm with hand and tool stimuli

“…A new mask image was shown every ;167 ms (6 Hz). This has been shown to be the optimal temporal frequency for suppression in other CFS studies (Drewes et al, 2018;Zhu, Drewes, & Melcher, 2016) but is actually a slower rate than Cohen et al (2015), who used ;117 ms (8.5 Hz); nevertheless, we found comparable breakthrough times (see Experiment 3). Before each trial, a black fixation dot was presented for 250 ms, which then turned red for 200 ms to alert participants that the trial was about to start.…”

“…A further category-specific image characteristic that could influence breakthrough times is the amount of edges (local clustering of contrast changes). In fact, it has previously been suggested that the amount of edges could determine CFS because increased spatial density of Mondrian masks result in longer breakthrough times (Drewes, Zhu, & Melcher, 2018). However, in this previous study, the manipulation of spatial density changed both edge content and global spatial frequency content, contrast, and luminance.…”